Bio 111 lecture Exam 3
Mitosis Notes: 1) Prophase:
1) Prophase: The chromosomes begin to condense and become visible by light microscopy. The two sister chromatids appear to be attached at the centromere. The two centrosomes (which were duplicated during S-phase) begin to move to opposite ends of the cell. The centrosomes begin assemble of the microtubule containing structure, the mitotic spindle with dense asters forming at each centrosome. The cytoskeletal microtubules disassociate and the tubulin is added to the mitotic spindle. In animal cells but not plant cells, centrioles are located at the core of the centrosomes.
Mitosis Notes: Metaphase:
1. Chromosomes line up on equator 2. Each centromere attached to spindle fiber 3. Very end of metaphase - centromeres divide.
Mitosis Notes: 3) Metaphase:
3) Metaphase: The chromosomes are completely condensed. The chromosomes are paused and aligned at the metaphase plate, a plane half-way between the poles. A mitotic karyotype can be constructed from cells arrested at metaphase.
Mitosis Notes: 4) Anaphase:
4) Anaphase: Sister chromatids separate and begin to move to opposite poles. In anaphase A, the chromosomes are pulled by the centromeres towards the poles as the kinetochore microtubules shorten. In anaphase B, the poles push apart as the polar microtubules get longer. Anaphase A and B may occur in this order or at once, depending upon cell type.
Meiosis:
After all, the known DNA sequences of homologous chromosomes are essentially the same. The Chromosomal Theory of Inheritance (early 1900's) was based on five points: 1) Nuclei contain two sets of homologous chromosomes (1 maternal and 1 paternal). 2) Chromosome retain identity and are genetically continuous through the life cycle. 3) The two sets of homologous chromosomes are functionally equivalent. 4) Maternal and paternal homologous chromosomes synapse during meiosis then move to opposite poles. 5) Maternal and paternal homologous chromosomes segregate independently.
Meiosis:
Chromosome Number Different number for different species Full set = 2N=Diploid N = # pairs 1 pair from mother 1 pair from father. Humans = 23 pairs or 46 total. Sets of each pair are called - Homologous chromosomes.
Mitosis Notes: Daughter cells diploid (2n), not haploid (n) C. Importance of chromosome number and mitosis:
Daughter cells diploid (2n), not haploid (n) C. Importance of chromosome number and mitosis. Following cell division, each daughter cell must contain the same number of chromosomes as the parent cell 2. Since genes are located on the chromosomes, each new cell must contain the same number of genes as the parent cell.
Mitosis Notes: Telophase (reverse of prophase):
E. Telophase (reverse of prophase): 1. Nuclear envelops reforms (2) 2. Chromosomes lengthen and become indistinct (chromatin) 3. Nucleolus reappears.
GENETICS AND HEREDITY:
Exceptions to Mendel's Laws - Remember Mendel did not know about genes or chromosomes. The following are other ways that genes may express themselves. Incomplete Dominance - when offspring exhibit a phenotype intermediate to that of both parents. Codominance - 2 alleles affect the phenotype in separate distinguishable ways. Ex: MN blood factor. Multiple Alleles. More than two alleles exist for a given trait in a population of individuals. In the human ABO blood group, A and B are equally dominant and can occur together as codominants. The O blood group consists of two recessive genes that code for neither A nor B.
Meiosis:
Sexual reproduction allows the genetic information of two parents to recombine to form a new individual. One great advantage, from the population biology point-of-view, is that sexual reproduction produces a great deal of genetic variation through the shuffling of both beneficial and deleterious mutations. Sexual reproduction requires diploidy (the state of having two sets of chromosomes) with a set of chromosomes from each parent which allows greater genetic flexibility than haploidy does. Diploid cells may be either homozygous or heterozygous for any given gene. However, the gametes (sperm and ova) are specialized haploid cells produced by meiosis.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
The entire range of electromagnetic radiation is the electromagnetic spectrum. The most important segment for life is a narrow band between 380 to 750 nm, the band of visible light. While light travels as a wave, many of its properties are those of a discrete particle, the photon. Photons are not tangible objects, but they do have fixed quantities of energy.The amount of energy packaged in a photon is inversely related to its wavelength. Photons with shorter wavelengths pack more energy. While the sun radiates a full electromagnetic spectrum, the atmosphere selectively screens out most wavelengths, permitting only visible light to pass in significant quantities.
Meiosis:
The chiasmata can be formed anywhere along the chromosome but during diakinesis, the chiasmatic connections are translated to the chromosomes' ends. The homologous chromosomes are held together during synapsis by the synaptonemal complex. Metaphase I: Bivalent chromosomes attach to the spindle and align at the metaphase plate. The bivalents are randomly oriented with respect to the poles such that chromosomes (maternal or paternal or both) are evenly sorted. Only the chiasmata hold the paired homologues together. Anaphase I: Homologous chromosomes resolve the chiasmata and move (as a bivalent) to opposite ends of the cell.
Photosynthesis: Overview: The Process that feeds the biosphere
The chloroplasts of plants use a process called photosynthesis to capture light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules.
Here is a preview of the two stages of photosynthesis:
The fixed carbon is reduced with electrons provided by NADPH.ATP from the light reactions also powers parts of the Calvin cycle. Thus, it is the Calvin cycle that makes sugar, but only with the help of ATP and NADPH from the light reactions.The metabolic steps of the Calvin cycle are sometimes referred to as the light-independent reactions, because none of the steps requires light directly.Nevertheless, the Calvin cycle in most plants occurs during daylight, because that is when the light reactions can provide the NADPH and ATP the Calvin cycle requires. While the light reactions occur at the thylakoids, the Calvin cycle occurs in the stroma.
Mitosis Notes:
The mitotic spindle microtubules are dynamic structures that are continually growing and shrinking by the addition and loss of tubulin subunits. With the dissolution of the nuclear membrane, the plus ends of the mitotic spindle microtubules make contact with the kinetochores. The chromosomes are both pushed and pulled into alignment by the mitotic spindle microtubules. With anaphase, the centromeres split and the chromosomes separate and move towards opposite poles due to the action of motor proteins.
Mitosis Notes: 2) Prometaphase:
The nuclear membrane breakdown. Centrosomes stop as locations at opposite poles of the cell. As the nuclear membrane is no longer present, mitotic spindle microtubules make contact with the chromosomes with the CEN DNA sequences of the chromosomes centromere to form the kinetochore (a protein-DNA complex). Each chromosome develops two kinetochores, one for each sister chromatid. The kinetochores bind the free ends of the mitotic spindle microtubules to attach the chromosomes to the mitotic spindle. The chromosomes are forced toward the centre of the cell. The mitotic spindle microtubules can attach to the kinetochores (kinetochore microtubules), to microtubules from the other pole (polar microtubules) and to the proteins of the inner plasma membrane (aster microtubules).
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis:
The overall chemical change during photosynthesis is the reverse of cellular respiration. In its simplest possible form: CO2 + H2O + light energy --> [CH2O] + O2 [CH2O] represents the general formula for a sugar. One of the first clues to the mechanism of photosynthesis came from the discovery that the O2 given off by plants comes from H2O, not CO2.
Meiosis:
The process of creating a gamete (sex cell) is called MEIOSIS It is similar to mitosis, but will produce 4 daughter cells that are each haploid. Oogenesis - makes eggs (ovum) Spermatogenesis - makes sperm. PROPHASE I of MEIOSIS.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
The thylakoids convert light energy into the chemical energy of ATP and NADPH. Light is a form of electromagnetic radiation. Like other forms of electromagnetic energy, light travels in rhythmic waves. The distance between crests of electromagnetic waves is called the wavelength.Wavelengths of electromagnetic radiation range from less than a nanometer (gamma rays) to more than a kilometer (radio waves).
Mitosis Notes Growth of cells:
There are three aspects of growth of cells which are Cell reproduction (cell division) animals get layer of cells, cell enlargement - plants get larger, Cell differentiation. Site of cell growth in plants - meristems
DNA, RNA, replication, translation, and transcription: Information in DNA sequence is the genome:
Genes are stretches of information in the sequence that encode for particular function (usually a particular protein, but sometimes also an RNA sequence) about 20,000 genes in humans typically 1000s of nucleotides long genes can be expressed (use to make proteins) or repressed (not used) regions of DNA are divided into coding and non-coding segments over 50% of human DNA is non-coding genes can be spliced together. genes are organized in the large-scale structure of the DNA in the nucleus In bacteria, genome usually circular.
Meiosis:
Genetics The Study of Inherited Characteristics Chromosome Holds the genetic information. Made of DNAGenes on chromosomes: Segments of DNA on a chromosome Code for a trait. Trait Characteristic Feature Variations in a population.
Concept: Alternative mechanisms of carbon fixation have evolved in hot, arid climates:
In effect, the mesophyll cells pump CO2 into the bundle-sheath cells, keeping CO2 levels high enough for rubisco to accept CO2 and not O2. C4 photosynthesis minimizes photorespiration and enhances sugar production. C4 plants thrive in hot regions with intense sunlight. A second strategy to minimize photorespiration is found in succulent plants, cacti, pineapples, and several other plant families. These plants are known as CAM plants for crassulacean acid metabolism.They open their stomata during the night and close them during the day. Temperatures are typically lower at night, and humidity is higher. During the night, these plants fix CO2 into a variety of organic acids in mesophyll cells. During the day, the light reactions supply ATP and NADPH to the Calvin cycle, and CO2 is released from the organic acids. Both C4 and CAM plants add CO2 into organic intermediates before it enters the Calvin cycle. In C4 plants, carbon fixation and the Calvin cycle are spatially separated. In CAM plants, carbon fixation and the Calvin cycle are temporally separated. Both eventually use the Calvin cycle to make sugar from carbon dioxide.
Mitosis Notes: III. Phases of mitosis:
Interphase: Not part of mitosis; a preparatory stage 2. Respiration, protein synthesis, growth occurs. Genetic material is duplicated (DNA replicates) itself. Cells usually small with no large vacuoles.
Photosynthesis: Overview: The Process that feeds the biosphere
Life on earth is solar powered.
Concept: Alternative mechanisms of carbon fixation have evolved in hot, arid climates:
Mesophyll cells are more loosely arranged cells located between the bundle sheath and the leaf surface.The Calvin cycle is confined to the chloroplasts of the bundle-sheath cells. However, the cycle is preceded by the incorporation of CO2 into organic molecules in the mesophyll. The key enzyme, phosphoenolpyruvate carboxylase, adds CO2 to phosphoenolpyruvate (PEP) to form oxaloacetate. PEP carboxylase has a very high affinity for CO2 and can fix CO2 efficiently when rubisco cannot (i.e., on hot, dry days when the stomata are closed). The mesophyll cells pump these four-carbon compounds into bundle-sheath cells.The bundle-sheath cells strip a carbon from the four-carbon compound as CO2, and return the three-carbon remainder to the mesophyll cells. The bundle-sheath cells then use rubisco to start the Calvin cycle with an abundant supply of CO2.
Meiosis: Metaphase:
Metaphase I Centromere of each chromosome becomes attached to spindle fibers. Spindle fibers pull tetrads into the middle (note they are lined up as tetrads)
Mitosis Notes: NUCLEAR AND CELL DIVISION:
NUCLEAR AND CELL DIVISION Nuclear division (mitosis) and cytoplasmic division (cytokinesis) occur during the M phase of the cell cycle. The process of mitosis (animal cell, plant cell) can subdivided into the following sub-phases: 1) prophase, 2) prometaphase, 3) metaphase, 4) anaphase and 5) telophase based upon the changing behavior and appearance of the chromosomes.
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis:
Powered by light, the green parts of plants produce organic compounds and O2 from CO2 and H2O. The equation describing the process of photosynthesis is: 6CO2 + 12H2O + light energy --> C6H12O6 + 6O2+ 6H2O C6H12O6 is glucose.
Mitosis Notes: Prophase:
Prophase : 1. Nuclear envelope disappears 2. Nucleolus disappears 3. Chromatin condenses (shortens and thickens) to become chromosomes 4. Later, spindle starts to form (spindle composed of microtubules - like muscles).
Meiosis:
Prophase I comprised of five stages; 1) leptotene, 2) zygotene, 3) pachytene, 4) diplotene and 5) diakinesis. (this was not covered in class) 1) Leptotene (Greek for "thin threads"): chromosomes begin to condense. 2) Zygotene (Greek for "paired threads"): chromosomes become closely paired. 3) Pachytene (Greek for "thick threads"): crossing over occurs. 4) Diplotene (Greek for "two threads"): homologous chromosomes begin to separate but remain attached by the chiasmata. 5) Diakinesis (Greek for "moving through"): chromosomes condense and separate until terminal chiasmata only connect the two chromosomes.
Meiosis:
Prophase II: DNA does not double - there is NO INTERPHASE Spindle forms in each of the two new cells and attaches to the chromosomes Metaphase II: Chromatids are pulled to the center of the cell and line up randomly at the equator (middle). Anaphase II: Centromeres spilt Sister chromatids separate and move toward opposite ends of the pole. Final Telophase II: Nucleus reforms. Spindle breaks down. Cytoplasm divides. 2nd division.
Meiosis: Sexual reproduction , Meiosis and genetic recombination:
Parents can produce many types of offspring Families will have resemblances, but no two are exactly alike. 2. Every cell has a nucleus Every nucleus has chromosomesThe number of chromosomes depends on the speciesEx. Humans have 46. 3. GENES are located on chromosomes genes control the TRAITS of the individual genotype determines phenotype. 4. Chromosomes come in matching sets -these are called homologous pairs Cells in your body have a complete set (all 46) - they are called DIPLOID Sex cells (sperm and eggs) only have half (23) - they are called HAPLOID. FIND THE HOMOLOG!
GENETICS AND HEREDITY:
Pleiotropic Effects - when an allele affects more than one trait. Ex: cystic fibrosis. Epistasis is an interaction between the products of two genes in which one of the genes modified the phenotypic expression produced by the other.
Concept: Alternative mechanisms of carbon fixation have evolved in hot, arid climates:
Today it does make a difference. Photorespiration can drain away as much as 50% of the carbon fixed by the Calvin cycle on a hot, dry day. Certain plant species have evolved alternate modes of carbon fixation to minimize photorespiration. C4 plants first fix CO2 in a four-carbon compound. Several thousand plants, including sugarcane and corn, use this pathway. A unique leaf anatomy is correlated with the mechanism of C4 photosynthesis. In C4 plants, there are two distinct types of photosynthetic cells: bundle-sheath cells and mesophyll cells. Bundle-sheath cells are arranged into tightly packed sheaths around the veins of the leaf.
Concept: Alternative mechanisms of carbon fixation have evolved in hot, arid climates:
Unlike photosynthesis, photorespiration does not produce organic molecules. In fact, photorespiration decreases photosynthetic output by siphoning organic material from the Calvin cycle. A hypothesis for the existence of photorespiration is that it is evolutionary baggage. When rubisco first evolved, the atmosphere had far less O2 and more CO2 than it does today. The inability of the active site of rubisco to exclude O2 would have made little difference.
GENETICS AND HEREDITY: What is a gene:
a. A gene is a sequence of DNA bases responsible for the synthesis of a protein. b. Different expressions of a gene are called alleles c. A change in the DNA sequence is called a mutation.
GENETICS AND HEREDITY: III. Segregation:
a. The parental (P) generation was crossed to produce the first filial (F1) generation. 1) The F1 generation did not have any intermediate traits (i.e., either tall or short) . 2) The F1 generation was then crossed to produce the F2 generation. 3) The expressions present in the F1 generation occurred in the F2 generation at a ratio of 3:1. 4) Mendel concluded that discrete units, occurring in pairs and separating into different sex cells, must control these traits. 5) This is called Mendel's Principle of Segregation. 6) The expressions can be represented in a diagram called a Punnett Square/forked diagrams..
GENETICS AND HEREDITY: Mitochondrial Inheritance:
a. mtDNA is transmitted to offspring only from the mother because sperm cells lose theirmitochondria prior to the fertilization of the egg cell. b. mtDNA mutation rates have been used to construct evolutionary relationships between primate species and between living human populations. 1) Parent generation Mendell used were both pure breeding, with homozygous alleles ex. TT and tt - for tall and short genotypes and phenotypes 2) F1 generation (First Filial) all have heterozygous alleles ex. Tt - heterozygous tall genotypes and phenotypes 3) F2 generation (Second Filial) result in 3:1 ration of phenotypes ex. TT, Tt, Tt, tt - for three phenotypically tall and one short plant.
Meiosis:
homologous pairs form -chromosomes trade genes, Crossing-over increases the number of possible gene combinations. Steps of Meiosis.
DNA, RNA, replication, translation, and transcription:
1. Rough strain (nonpathogenic). When this strain is injected into a mouse, the mouse lives. 2. Smooth strain (pathogenic). When this strain is injected into a mouse, the mouse gets pneumonia and dies. 3. Heat-killed smooth strain. When heat-killed smooth cells are injected into a mouse, the mouse lives. 4. Rough strain & heat-killed smooth strain. When these two types of cells are injected into a mouse as a mixture, the mouse gets pneumonia and dies. Griffith concluded that the R-strain bacteria must have taken up what he called a "transforming principle" from the heat-killed S bacteria, which allowed them to "transform" into smooth-coated bacteria and become virulent.
Mitosis Notes: Anaphase:
1. Sister chromatids are pulled to opposite end of cell by contraction of spindle fibers 2. Each chromatid is now considered one chromosome
Mitosis Notes: 5) Telophase:
5) Telophase: The daughter chromosomes arrive at the pole and begin to revert to chromatin. The nucleoli develop, the spindle disassembles and the nuclear envelope reappears. Cytokinesis occurs. The assembly of the mitotic spindle microtubules and chromosome attachment is key to ability of the mitotic spindle to move the chromosomes during mitosis. The tubulin subunits have polarity and assembly of the mitotic spindle microtubules occurs with the minus (-) end located at the centrosome and the plus (+) end growing out.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
A photosystem is composed of a reaction center surrounded by a light-harvesting complex. Each light-harvesting complex consists of pigment molecules (which may include chlorophyll a, chlorophyll b, and carotenoid molecules) bound to particular proteins. Together, these light-harvesting complexes act like light-gathering "antenna complexes" for the reaction center. When any antenna molecule absorbs a photon, it is transmitted from molecule to molecule until it reaches a particular chlorophyll a molecule, the reaction center.At the reaction center is a primary electron acceptor, which accepts an excited electron from the reaction center chlorophyll a.The solar-powered transfer of an electron from a special chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions. Each photosystem—reaction-center chlorophyll and primary electron acceptor surrounded by an antenna complex—functions in the chloroplast as a light-harvesting unit.
GENETICS AND HEREDITY:
A scientist and monk by the name of Gregor Mendel (1822 or 23 - 1884) contributed significantly to the understanding of genetics in the 1800s by being the first to actually count numbers of offspring in crosses involving pea plants. He is often called the father of genetics. Son of a farm family - not wealthy Did very well in school but to get more education he became a monk and attended the University of Vienna. Over a period of 7 years he bred and counted about 28,000 pea plants.He chose the pea plant because others had bred many varieties of peas and there were known characters. Also, because the pea flower has both female and male parts in the same flower and usually self fertilizes. By removing the stamens. he could cross-fertilize them by hand. Fig 14.1 Mendel chose 7 characters that showed 2 traits for that character, like purple versus white flowers, rather than a blending of the colors. Table 14.1 Character - a heritable feature. Trait - a variant for a character. Mendel's Experimental Design - Mendel began his crosses with true-breeding varieties (homozygous) that contained only one type of gene for each character. At first, he only looked at one character at a time - a monohybrid cross.The first generation in a succession of crosses is the P or parental generation; their offspring are the F1 generation or first filial generation.
DNA, RNA, replication, translation, and transcription: Base-pairing and strand interactions:
A, G are too long (double ring purines). C,T are too short (single ring pyrimidines). need one long and one short nucleotide per pair. C-G have three hydrogen bonds (slightly stronger matching). A-T have two hydrogen bonds (slightly weaker matching). base stacking of aromatic rings allows sharing of pi electrons and adds stability to interior structure of DNA some hydrophobic driving force as well pair structure allows template for semi-conservative copying.
Mitosis Notes: Two parts to cell division:
A. Mitosis- division of nucleus (each daughter cell has complete set of blueprints) B. Cytokinesis - division of cytoplasm
Concept: Photosynthesis converts light energy to the chemical energy of food
All green parts of a plant have chloroplasts. However, the leaves are the major site of photosynthesis for most plants. There are about half a million chloroplasts per square millimeter of leaf surface.The color of a leaf comes from chlorophyll, the green pigment in the chloroplasts. Chlorophyll plays an important role in the absorption of light energy during photosynthesis. Chloroplasts are found mainly in mesophyll cells forming the tissues in the interior of the leaf. O2 exits and CO2 enters the leaf through microscopic pores called stomata in the leaf.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
An absorption spectrum plots a pigment's light absorption versus wavelength.The light reaction can perform work with those wavelengths of light that are absorbed. There are several pigments in the thylakoid that differ in their absorption spectra. Chlorophyll a, the dominant pigment, absorbs best in the red and violet-blue wavelengths and least in the green. Other pigments with different structures have different absorption spectra. Collectively, these photosynthetic pigments determine an overall action spectrum for photosynthesis.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
An action spectrum measures changes in some measure of photosynthetic activity (for example, O2 release) as the wavelength is varied. The action spectrum of photosynthesis was first demonstrated in 1883 in an elegant experiment performed by Thomas Engelmann. In this experiment, different segments of a filamentous alga were exposed to different wavelengths of light. Areas receiving wavelengths favorable to photosynthesis produced excess O2. Engelmann used the abundance of aerobic bacteria that clustered along the alga at different segments as a measure of O2 production.
Mitosis Notes: Animals:
Animals: Key thing to remember is the purpose of mitosis: the exact duplication of cellular "master plan" in nucleus. Constant number of chromosomes for each species. Humans = 46 2. A sunflower = 4 3. A fern = 1250 4. Most plants 20-40 chromosomes.
Mitosis Notes: DNA:
At a replicon, one strand of DNA is made in a continuous manner (the leading strand) and the other in a discontinuous manner (the lagging strand). DNA is made in only the 5-prime to 3-prime direction and the replication bubble opens the original double stranded DNA to expose both a 3-prime to 5-prime template (Leading strand template) and it complement. The lagging strand must be synthesized as a series of discontinuous segments of DNA. These small fragments are called Okazaki fragments and they are joined together by an enzyme known as DNA ligase. DNA synthesis is not perfect initially, so a proofreading mechanism is performed as part of the DNA polymerase enzyme itself. Since DNA polyerase requires a template and a free 3-prime hydroxyl group to add nucleotides on to, RNA primers are required to initiate DNA polymerization. An enzyme, primase which is part of a large complex of proteins called the primosome, synthesizes a small stretch of RNA (the primer) of 3-10 nucleotide in length, which will act as a starting site for the DNA polymerase.
Meiosis:
Autosomes & Sex Chromosomes Autosomes = #1-22 for all traits except sex. Sex chromosomes = Pair #23 XX (female) or XY (male)Why do cells divide by Meiosis? •To reduce chromosome number •In sex cells (haploid cells - sperm and egg) •In single celled organisms: Under changing conditions for Chromosome Variety Gonads make gametes! Testes make sperm - sperm development in boys begins at puberty and continues until death. Ovaries make eggs - egg development begins prior to birth. One egg is released every month during puberty. If the egg is unfertilized then menstruation occurs. Continues until menopause. Gamete development Immature egg or sperm cell = full set of chromosome (2N) Undergoes meiosis with 2 cell divisions. Develops into a mature egg or sperm (1N) The Cell Cycle of a Gamete Interphase Meiosis. Interphase •Full set of chromosomes (2N) •DNA has doubled (4N) Prophase I: DNA coils up and spindle form. DNA forms homologous chromosomes that line up with each other and form a 4-part structure called a tetrad. A tetrad consists of 2 homologous chromosomes each made up of 2 sister chromatids. Chromatids pair so tightly that non-sister chromatids can break off and exchange genetic info in a process called crossing-over.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
Because this energy difference varies among atoms and molecules, a particular compound absorbs only photons corresponding to specific wavelengths. Thus, each pigment has a unique absorption spectrum. Excited electrons are unstable. Generally, they drop to their ground state in a billionth of a second, releasing heat energy. Some pigments, including chlorophyll, can also release a photon of light in a process called fluorescence. If a solution of chlorophyll isolated from chloroplasts is illuminated, it will fluoresce and give off heat. Chlorophyll excited by absorption of light energy produces very different results in an intact chloroplast than it does in isolation. In the thylakoid membrane, chlorophyll is organized along with proteins and smaller organic molecules into photosystems.
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis:
Before the 1930s, the prevailing hypothesis was that photosynthesis split carbon dioxide and then added water to the carbon: Step 1: CO2 --> C + O2 Step 2: C + H2O --> CH2O C. B. van Niel challenged this hypothesis.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
Cyclic electron flow allows the chloroplast to generate enough surplus ATP to satisfy the higher demand for ATP in the Calvin cycle. Chloroplasts and mitochondria generate ATP by the same mechanism: chemiosmosis. In both organelles, an electron transport chain pumps protons across a membrane as electrons are passed along a series of increasingly electronegative carriers. This transforms redox energy to a proton-motive force in the form of an H+ gradient across the membrane. ATP synthase molecules harness the proton-motive force to generate ATP as H+ diffuses back across the membrane. Some of the electron carriers, including the cytochromes, are very similar in chloroplasts and mitochondria. The ATP synthase complexes of the two organelles are also very similar. There are differences between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts.
Mitosis Notes: Cytokinesis begins:
Cytokinesis begins A. Usually follows mitosis, Plants Cell plate forms in middle of cell from aggregating vesicles from Golgi ,- 2 plasma membranes, Later, cell wall material is laid down from Golgi.
Mitosis Notes:
Cytokinesis divides the cytoplasm after the chromosomes have been sorted to complete the process of cell division. Cytokinesis is not necessarily closely linked to nuclear division. There are numerous examples of the nuclear division without cytokinesis such as early Drosophila development involves several rounds of replication without cytokinesis (the cells form later). Cytokinesis in animal cells depends upon formation of the cleavage furrow. This is dependent upon the tightening of a contractile ring of actin microfilaments through the action of myosin (and ATP) to pinch the cell into two.
Mitosis Notes:
Cytokinesis in plant cells produce a cell plate between separated daughter nuclei. The cell plate is formed from materials (polysaccharides and glycoproteins) provides by vesicles derived from the Golgi apparatus.
DNA, RNA, replication, translation, and transcription: Overview Recall the central dogma of biology:
DNA (genetic information in genes) RNA (copies of genes)proteins (functional molecules) DNA structure One monomer unit = deoxyribonucleic acid composed of a base, a sugar (deoxyribose), and a phosphate directionality along the backbone 5' (phosphate) to 3' (OH) Double-strand pairing: complementary base-matching: A-T, C-G base-matching achieved by H-bonding and geometry (long vs short nucleotides) antiparallel (one strand 5'3', the other 3'5') Helical shape 10.4 nucleotides per turn.diameter = 2 nm. both major and minor grooves called B-DNA.
Mitosis Notes: DNA SYNTHESIS (Transcription):
DNA Replication is a semiconservative process that results in a double-stranded molecule that synthesizes to produce two new double stranded molecules such that each original single strand is paired with one newly made single strand. This was demonstrated by equilibrium density centrifugation. See DNA and transcription. The replication of DNA most often occurs in a bidirectional manner from an origin of replication from which two replication forks move in opposite direction. In prokaryotes = bidirectional DNA synthesis of the circular genome. In eukaryotes, DNA replication is initiated in multiple sites along a chromosomes called replicons. A number of proteins and protein complexes are involved in DNA synthesis.
Mitosis Notes:
DNA is manufactured during S phase. To prepare the cell for S phase (DNA synthesis), G1 phase occurs (the preparation of DNA synthesis machinery, production of histones). The cell prepares for mitosis in the G2 phase by producing the machinery required for cell division. The length of time spent in G1 is variable although growing mammalian cells often spend 8-10 hours in G1 phase, a cellular decision is made that cause cells to become arrested in G1 and thus enter the G0 state. G2 is usually shorter than G1 and is usually 4-6 hours.
Mitosis Notes: DNA:
DNA polymerases catalyze the synthesis of DNA by adding nucleotides, in a 5-prime to 3-prime direction, utilizing a single stranded region of DNA as a template. Four deoxynucleotide triphosphates (dATP, dCTP, dGTP,dTTP) only are incorporated into the growing chain by releasing the terminal two phosphate groups and covalently bonding the remaining phosphate to the 3-prime hydroxyl group of the previous nucleotide residue.
DNA, RNA, replication, translation, and transcription:
Each batch of phage was used to infect a different culture of bacteria. After infection had taken place, each culture was whirled in a blender, removing any remaining phage and phage parts from the outside of the bacterial cells. Finally, the cultures were centrifuged, or spun at high speeds, to separate the bacteria from the phage debris. Centrifugation causes heavier material, such as bacteria, to move to the bottom of the tube and form a lump called a pellet. Lighter material, such as the medium (broth) used to grow the cultures, along with phage and phage parts, remains near the top of the tube and forms a liquid layer called the supernatant. 1. One batch of phage was labeled with 35S, which is incorporated into the protein coat. Another batch was labeled with 32P, which is incorporated into the DNA. 2. Bacteria were infected with the phage. 3. The cultures were blended and centrifuged to separate the phage from the bacteria. 4. Radioactivity was measured in the pellet and liquid (supernatant) for each experiment. 32P was found in the pellet (inside the bacteria), while 35S was found in the supernatant (outside of the bacteria).
DNA, RNA, replication, translation, and transcription: Higher-order DNA structure:
How do cells efficiently store very long chains of DNA? DNA wraps around protein "spools" to form nucleosomes.Nucleosomes are made of his tone proteins. Spools organize into chromatin fibers that pack in regular ways, on different length scale.
DNA, RNA, replication, translation, and transcription: The genome in eukaryotes is organized into chromosomes:
Human cells contain 46 chromosomes (22 each from mother and father)chromosomes are extended and replicated during interphase portion of the cell cycle extended allows for gene expression chromosomes are condensed, visible with light during cell division M phase) Special DNA sequences exist in each chromosome. replication origins - multiple locations where the replication machinery first binds to start replication. centromere - center "pinch point" of a chromosome that allows one copy of each to be pulled apart into two daughter cells during division. telomere - specialized sequences at the chromosomes end that facilitate replication there.
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis:
Hydrogen extracted from water is incorporated into sugar, and oxygen is released to the atmosphere (where it can be used in respiration). Photosynthesis is a redox reaction.It reverses the direction of electron flow in respiration. Water is split and electrons transferred with H+ from water to CO2, reducing it to sugar. Because the electrons increase in potential energy as they move from water to sugar, the process requires energy. The energy boost is provided by light.
Meiosis: Anaphase:
I Homologous chromosomes (each with 2 chromatids), separate and move toward opposite ends of the cell (note centromeres do not spilt)
Meiosis: Telophase:
I Spindle breaks down, Chromosomes uncoil , Cytoplasm divides, Result 2 new 2N cells , 1st cell division (2N).
DNA, RNA, replication, translation, and transcription: Frederick Griffith: Bacterial transformation:
In 1928, British bacteriologist Frederick Griffith conducted a series of experiments using Streptococcus pneumoniae bacteria and mice. Griffith wasn't trying to identify the genetic material, but rather, trying to develop a vaccine against pneumonia. In his experiments, Griffith used two related strains of bacteria, known as R and S. R strain. When grown in a petri dish, the R bacteria formed colonies, had well-defined edges and a rough appearance (hence the abbreviation "R") = nonvirulent, meaning that they did not cause sickness when injected into a mouse. S strain. S bacteria formed colonies that were rounded and smooth (hence the abbreviation "S"). The smooth appearance was due to a polysaccharide, or sugar-based, coat produced by the bacteria. This coat protected the S bacteria from the mouse immune system, making them virulent (capable of causing disease). Mice injected with live S bacteria developed pneumonia and died. As part of his experiments, Griffith tried injecting mice with heat-killed S bacteria (that is, S bacteria that had been heated to high temperatures, causing the cells to die). Unsurprisingly, the heat-killed S bacteria did not cause disease in mice. The experiments took an unexpected turn, however, when harmless R bacteria were combined with harmless heat-killed S bacteria and injected into a mouse. Not only did the mouse develop pnenumonia and die, but when Griffith took a blood sample from the dead mouse, he found that it contained living S bacteria!
DNA, RNA, replication, translation, and transcription: Avery, McCarty, and MacLeod: Identifying the transforming principle:
In 1944, three Canadian and American researchers, Oswald Avery, Maclyn McCarty, and Colin MacLeod, set out to identify Griffith's "transforming principle." To do so, they began with large cultures of heat-killed S cells and, through a long series of biochemical steps (determined by careful experimentation), progressively purified the transforming principle by washing away, separating out, or enzymatically destroying the other cellular components. Protein- and RNA-degrading enzymes had little effect on the transforming principle, but enzymes able to degrade DNA eliminated the transforming activity. These results all pointed to DNA as the likely transforming principle. However, Avery was cautious in interpreting his results. He realized that it was still possible that some contaminating substance present in small amounts, not DNA, was the actual transforming principle. Because of this possibility, debate over DNA's role continued until 1952, when Alfred Hershey and Martha Chase used a Δ approach to conclusively identify DNA as the genetic material.
Here is a review of the importance of photosynthesis:
In photosynthesis, the energy that enters the chloroplasts as sunlight becomes stored as chemical energy in organic compounds.Sugar made in the chloroplasts supplies the entire plant with chemical energy and carbon skeletons to synthesize all the major organic molecules of cells. About 50% of the organic material is consumed as fuel for cellular respiration in plant mitochondria. Carbohydrate in the form of the disaccharide sucrose travels via the veins to nonphotosynthetic cells.There, it provides fuel for respiration and the raw materials for anabolic pathways, including synthesis of proteins and lipids and formation of the extracellular polysaccharide cellulose. Cellulose, the main ingredient of cell walls, is the most abundant organic molecule in the plant, and probably on the surface of the planet. Plants also store excess sugar by synthesis of starch.Starch is stored in chloroplasts and in storage cells in roots, tubers, seeds, and fruits. Heterotrophs, including humans, may completely or partially consume plants for fuel and raw materials. On a global scale, photosynthesis is the most important process on Earth. It is responsible for the presence of oxygen in our atmosphere. Each year, photosynthesis synthesizes 160 billion metric tons of carbohydrate.
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis:
In the bacteria that he was studying, hydrogen sulfide (H2S), not water, is used in photosynthesis. These bacteria produce yellow globules of sulfur as a waste, rather than oxygen. Van Niel proposed this chemical equation for photosynthesis in sulfur bacteria: CO2 + 2H2S --> [CH2O] + H2O + 2S. He generalized this idea and applied it to plants, proposing this reaction for their photosynthesis: CO2 + 2H2O --> [CH2O] + H2O + O2
Here is a preview of the two stages of photosynthesis:
In the light reactions, light energy absorbed by chlorophyll in the thylakoids drives the transfer of electrons and hydrogen from water to NADP+ (nicotinamide adenine dinucleotide phosphate), forming NADPH. NADPH, an electron acceptor, provides reducing power via energized electrons to the Calvin cycle.
DNA, RNA, replication, translation, and transcription: The Hershey-Chase experiments:
In their now-legendary experiments, Hershey and Chase studied bacteriophage, or viruses that attack bacteria. The phages are composed of protein and DNA, with the outer structures made of protein and the inner core consisting of DNA. Hershey and Chase knew that the phages attached to the surface of a host bacterial cell and injected some substance (either DNA or protein) into the host. This substance gave "instructions" that caused the host bacterium to start making lots and lots of phages—in other words, it was the phage's genetic material. Before the experiment, Hershey thought that the genetic material would prove to be protein. To establish whether the phage injected DNA or protein into host bacteria, Hershey and Chase prepared two different batches of phage. In each batch, the phage were produced 6/12 in the presence of a specific radioactive element, which was incorporated into the macromolecules (DNA and protein) that made up the phage. One sample was produced in the presence of 35S, a radioactive isotope of sulfur. Sulfur is found in many proteins (disulfide bonds) and is absent from DNA, so only phage proteins were radioactively labeled by this treatment. The other sample was produced in the presence of 32P, a radioactive isotope of phosphorous. Phosphorous is found in DNA and not in proteins, so only phage DNA (and not phage proteins) was radioactively labeled by this treatment.
Meiosis:
MEIOSIS In the first part of meiosis (meiosis I) an unusual type of cell division produces two haploid cells that have chromosomes made up of two sister chromatids. The chromosomes pair up (a process called synapsis) to form a structure known as either a bivalent (two chromosomes) or a tetrad (four chromatids). Prophase I is the stage of meiosis where the homologous chromosomes pair and exchange DNA (genetic recombination).
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
Mitochondria transfer chemical energy from food molecules to ATP; chloroplasts transform light energy into the chemical energy of ATP. The spatial organization of chemiosmosis also differs in the two organelles. The inner membrane of the mitochondrion pumps protons from the mitochondrial matrix out to the intermembrane space. The thylakoid membrane of the chloroplast pumps protons from the stroma into the thylakoid space inside the thylakoid. The thylakoid membrane makes ATP as the hydrogen ions diffuse down their concentration gradient from the thylakoid space back to the stroma through ATP synthase complexes, whose catalytic knobs are on the stroma side of the membrane. The proton gradient, or pH gradient, across the thylakoid membrane is substantial When chloroplasts are illuminated, the pH in the thylakoid space drops to about 5 and the pH in the stroma increases to about 8, a thousandfold different in H+ concentration. The light-reaction "machinery" produces ATP and NADPH on the stroma side of the thylakoid. Noncyclic electron flow pushes electrons from water, where they have low potential energy, to NADPH, where they have high potential energy. This process also produces ATP and oxygen as a by-product.
Meiosis:
Mitosis leads to cell proliferation and is essential for asexual reproduction including 1) mitotic division of unicellular organisms, 2) budding of offspring from the parent's body and 3) regeneration from pieces of a parent organism. Asexual reproduction produces new individuals that are genetically identical to the parent.
GENETICS AND HEREDITY:
Offspring of two members of the F1 generation comprise the F2 generation. Mendel repeatedly came up with the same results when examining seven pairs of contrasting traits. Mendel called the trait expressed in the F1 plants the dominant trait and the trait not expressed was recessive.When the F1 plants were allowed to self-fertilize, Mendel found 3:1 dominant to recessive phenotype in the F2 generation. When F2 plants were allowed to self-fertilize, Mendel found a 1:2:1 ratio of true-breeding dominant to not true-breeding dominant to true-breeding recessive. Today we use these terms: Each individual has two genes (Mendel's "factors") for each trait. When both genes are the same, the individual is said to be homozygous for that trait. If the two genes are different, the individual is heterozygous for that trait. Alternate types of genes for each trait are alleles. Fig. 14.3 Phenotype refers to the outward expression of the genes. The actual genetic makeup of an individual is the genotype.
Concept: Alternative mechanisms of carbon fixation have evolved in hot, arid climates:
One of the major problems facing terrestrial plants is dehydration. At times, solutions to this problem require tradeoffs with other metabolic processes, especially photosynthesis. The stomata are not only the major route for gas exchange (CO2 in and O2 out), but also for the evaporative loss of water. On hot, dry days, plants close their stomata to conserve water. This causes problems for photosynthesis.In most plants (C3 plants), initial fixation of CO2 occurs via rubisco, forming a three-carbon compound, 3-phosphoglycerate. C3 plants include rice, wheat, and soybeans.
Here is a preview of the two stages of photosynthesis:
Photosynthesis is two processes, each with multiple stages. The light reactions (photo) convert solar energy to chemical energy. The Calvin cycle (synthesis) uses energy from the light reactions to incorporate CO2 from the atmosphere into sugar.
Meiosis: GENETIC RECOMBINATION:
Random assortment of the different alleles of genes on different chromosomes depends upon the segregation and independent assortment of the chromosomes during meiosis I. Crossing-over of the chromosomes during meiosis I leads to genetic recombination of different alleles of genes on the SAME chromosome. When genes are located near each other on a chromosome, they act as if they are linked and parental allele combinations are more often than not inherited together by the grandchildren. Genetic variability is produced by genetic recombination through the process of crossing over when the chromosomes pair during meiotic prophase. Parental homologous chromosomes exchange segments during crossing over to produce recombinant chromosomes. Genetic mapping based upon the measurement of recombination frequencies is used to map gene locations.
Meiosis:
Telophase I: Chromosomes arrive at the poles and nuclear envelopes form and cytokinesis occurs. Meiosis II: The second part of meiosis (meiosis II) is very similar to mitotic division except that DNA synthesis does not occur between the two stages. Sperm and ova are produced by two main processes 1) meiosis and 2) specialized cell differentiation. Gametogenesis differs greatly between spermatogenesis and oogenesis. Spermatogenesis converts the spermatocyte into four spermatids. During oogenesis, asymmetric cell division produces one large cell and three small ones that degenerate into three polar bodies. Meiosis produces genetic diversity by recombining the diploid cell's genetic complement to generate a haploid gamete. This diversity depends upon the segregation and assortment of combination of alleles. Importantly, diploid organisms can bear recessive alleles of genes that are can be completely masked by the other (usually wild type) allele. In the mid-1800's, Gregor Mendel formulated his "Laws of Inheritance" from his famous pea experiments. Mendel's "Law of Segregation" ensures that alleles of each gene separate from each other during gamete formation. Mendel's (more controversial) "Law of Independent Assortment" suggests that alleles of each gene separate independently of the other genes. Chromosomal behavior provides strong support for the laws of segregation and independent assortment.
Concept:The Calvin cycle uses ATP and NADPH to convert CO2 to sugar:
The Calvin cycle has three phases. Phase 1: Carbon fixation In the carbon fixation phase, each CO2 molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP). This is catalyzed by RuBP carboxylase or rubisco.Rubisco is the most abundant protein in chloroplasts and probably the most abundant protein on Earth. The six-carbon intermediate is unstable and splits in half to form two molecules of 3-phosphoglycerate for each CO2.
Concept:The Calvin cycle uses ATP and NADPH to convert CO2 to sugar:
The Calvin cycle has three phases. Phase 2: Reduction During reduction, each 3-phosphoglycerate receives another phosphate group from ATP to form 1,3-bisphosphoglycerate. A pair of electrons from NADPH reduces each 1,3-bisphosphoglycerate to G3P.The electrons reduce a carboxyl group to the aldehyde group of G3P, which stores more potential energy. If our goal was the net production of one G3P, we would start with 3CO2 (3C) and three RuBP (15C). After fixation and reduction, we would have six molecules of G3P (18C). One of these six G3P (3C) is a net gain of carbohydrate. This molecule can exit the cycle and be used by the plant cell.
Concept:The Calvin cycle uses ATP and NADPH to convert CO2 to sugar:
The Calvin cycle has three phases. Phase 3: Regeneration The other five G3P (15C) remain in the cycle to regenerate three RuBP. In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle to regenerate three molecules of RuBP. For the net synthesis of one G3P molecule, the Calvin cycle consumes nine ATP and six NADPH. The light reactions regenerate ATP and NADPH.The G3P from the Calvin cycle is the starting material for metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates.
Concept:The Calvin cycle uses ATP and NADPH to convert CO2 to sugar:
The Calvin cycle regenerates its starting material after molecules enter and leave the cycle. The Calvin cycle is anabolic, using energy to build sugar from smaller molecules. Carbon enters the cycle as CO2 and leaves as sugar. The cycle spends the energy of ATP and the reducing power of electrons carried by NADPH to make sugar. The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphate (G3P). Each turn of the Calvin cycle fixes one carbon. For the net synthesis of one G3P molecule, the cycle must take place three times, fixing three molecules of CO2. To make one glucose molecule requires six cycles and the fixation of six CO2 molecules.
Mitosis Notes:
The Cell Cycle: DNA replication and mitosis Cell cycle begins with the formation of two cells from the division of a parent cell ends when the daughter cell does so as well. Observable under the microscope, M phase consists of two events, mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm). As replication of the DNA occurs during S-phase, when condensation of the chromatin occurs two copies of each chromosome remain attached at the centromere to form sister chromatids.After the nuclear envelope fragments, the microtubules of the mitotic spindle separate the sister chromatids and move them to opposite ends of the cell. Cytokinesis and reformation of the nuclear membranes occur to complete the cell division. Most of the time, cells are in interphase, where growth occurs and cellular components are made.
GENETICS AND HEREDITY:
The Testcross - When Mendel did not know the genotype of an individual expressing a dominant trait, he did a test cross by crossing the individual with a homozygous recessive for the trait. Fig. 14.6. Mendel's Laws (using today's terminology) Mendel's First Law: Law of Segregation, says that only one of a pair of alleles is passed to a gamete Mendel's Second Law: Law of Independent Assortment was determined when he worked with two traits at a time in dihybrid crosses. This law states that genes located on different chromosomes are inherited independently. Crossing two individuals that are heterozygous for both characters yields a phenotypic ratio of 9:3:3:1. If the genes are located on the same chromosome, they would be linked. Rules of probability, Rules of multiplication, Rules of addition Probability and genetics.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
The action spectrum of photosynthesis does not match exactly the absorption spectrum of any one photosynthetic pigment, including chlorophyll a. Only chlorophyll a participates directly in the light reaction, but accessory photosynthetic pigments absorb light and transfer energy to chlorophyll a. Chlorophyll b, with a slightly different structure than chlorophyll a, has a slightly different absorption spectrum and funnels the energy from these wavelengths to chlorophyll a. Carotenoids can funnel the energy from other wavelengths to chlorophyll a and also participate in photo protection against excessive light. These compounds absorb and dissipate excessive light energy that would otherwise damage chlorophyll. They also interact with oxygen to form reactive oxidative molecules that could damage the cell. When a molecule absorbs a photon, one of that molecule's electrons is elevated to an orbital with more potential energy. The electron moves from its ground state to an excited state.The only photons that a molecule can absorb are those whose energy matches exactly the energy difference between the ground state and excited state of this electron.
Mitosis Notes: Regulation of the Cell Cycle:
The length of the cell cycle varies depending upon the type of cell and is extremely important in many aspects of biology, especially development. The timing differences are primarily in the G1 phase, which may become very long (as in G0 phase). Variation in the length of the cell cycle depends upon cell cycle checkpoints which control the cells progression. These controls make certain that the cells machinery is operating properly with the correct timing. In addition, the cell cycle control mechanisms must make certain that each phase of the cycle is completed properly such that the next steps are prepared for. The control system must be able to respond to certain conditions that may affect the cell cycle. The cell cycle checkpoints determine if a cell is ready to progress to the next stage. Late in the G1 phase, the G1 checkpoint determines if the cell will enter the following S phase. In animals, the G1 checkpoint or restriction point, is largely controlled by growth factors. The G2 checkpoint determines if the cell will enter the M phase and requires the proper completion of DNA synthesis. The third cell cycle checkpoint is the spindle assembly checkpoint which occurs between metaphase and anaphase and requires the proper attachment of all the chromosomes to the spindle apparatus.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
The light reactions use the solar power of photons absorbed by both photosystem I and photosystem II to provide chemical energy in the form of ATP and reducing power in the form of the electrons carried by NADPH. Under certain conditions, photoexcited electrons from photosystem I, but not photosystem II, can take an alternative pathway, cyclic electron flow. Excited electrons cycle from their reaction center to a primary acceptor, along an electron transport chain, and return to the oxidized P700 chlorophyll. As electrons flow along the electron transport chain, they generate ATP by cyclic photophosphorylation. There is no production of NADPH and no release of oxygen. What is the function of cyclic electron flow? Noncyclic electron flow produces ATP and NADPH in roughly equal quantities. However, the Calvin cycle consumes more ATP than NADPH.
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
There are two types of photosystems in the thylakoid membrane. Photosystem I (PS I) has a reaction center chlorophyll a that has an absorption peak at 700 nm. Photosystem II (PS II) has a reaction center chlorophyll a that has an absorption peak at 680 nm. The differences between these reaction centers (and their absorption spectra) lie not in the chlorophyll molecules, but in the proteins associated with each reaction center. These two photosystems work together to use light energy to generate ATP and NADPH. During the light reactions, there are two possible routes for electron flow: cyclic and noncyclic. Noncyclic electron flow, the predominant route, produces both ATP and NADPH. 1. Photosystem II absorbs a photon of light. One of the electrons of P680 is excited to a higher energy state. 2. This electron is captured by the primary electron acceptor, leaving the reaction center oxidized. 3. An enzyme extracts electrons from water and supplies them to the oxidized reaction center. This reaction splits water into two hydrogen ions and an oxygen atom that combines with another oxygen atom to form O2. 4. Photoexcited electrons pass along an electron transport chain before ending up at an oxidized photosystem I reaction center. 5. As these electrons "fall" to a lower energy level, their energy is harnessed to produce ATP. 6. Meanwhile, light energy has excited an electron of PS I's P700 reaction center. The photoexcited electron was captured by PS I's primary electron acceptor, creating an electron "hole" in P700. This hole is filled by an electron that reaches the bottom of the electron transport chain from PS II. 7. Photoexcited electrons are passed from PS I's primary electron acceptor down a second electron transport chain through the protein ferredoxin (Fd). 8. The enzyme NADP+ reductase transfers electrons from Fd to NADP+. Two electrons are required for NADP+'s reduction to NADPH. NADPH will carry the reducing power of these high-energy electrons to the Calvin cycle.
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis:
Thus, van Niel hypothesized that plants split water as a source of electrons from hydrogen atoms, releasing oxygen as a byproduct. Other scientists confirmed van Niel's hypothesis twenty years later. They used 18O, a heavy isotope, as a tracer. They could label either C18O2 or H218O. They found that the 18O label only appeared in the oxygen produced in photosynthesis when water was the source of the tracer.
Mitosis Notes: DNA:
To make the DNA single stranded in the first place to allow DNA synthesis, the DNA must be unwound. As DNA synthesis requires a RNA primer that will eventually be digested away, standard DNA replication would result in linear chromosmes that would shrink with every round of replication. This is resolved in bacteria by the circular genome which does not have an end. In linear chromosomes, a specialized structure the telomere solves the end of DNA replication problem.
Concept: Photosynthesis converts light energy to the chemical energy of food
Veins deliver water from the roots and carry off sugar from mesophyll cells to nonphotosynthetic areas of the plant. A typical mesophyll cell has 30-40 chloroplasts, each about 2-4 microns by 4-7 microns long. Each chloroplast has two membranes around a central aqueous space, the stroma. In the stroma is an elaborate system of interconnected membranous sacs, the thylakoids. The interior of the thylakoids forms another compartment, the thylakoid space. Thylakoids may be stacked into columns called grana. Chlorophyll is located in the thylakoids. Photosynthetic prokaryotes lack chloroplasts. Their photosynthetic membranes arise from infolded regions of the plasma membranes, folded in a manner similar to the thylakoid membranes of chloroplasts
Concept: The light reactions convert solar energy to the chemical energy of ATP and NADPH:
Visible light is the radiation that drives photosynthesis. When light meets matter, it may be reflected, transmitted, or absorbed. Different pigments absorb photons of different wavelengths, and the wavelengths that are absorbed disappear. A leaf looks green because chlorophyll, the dominant pigment, absorbs red and blue light, while transmitting and reflecting green light.A spectrophotometer measures the ability of a pigment to absorb various wavelengths of light. It beams narrow wavelengths of light through a solution containing the pigment and measures the fraction of light transmitted at each wavelength.
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis:
Water appears on both sides of the equation because 12 molecules of water are consumed, and 6 molecules are newly formed during photosynthesis. We can simplify the equation by showing only the net consumption of water: 6CO2 + 6H2O + light energy --> C6H12O6 + 6O2
Here is a preview of the two stages of photosynthesis:
Water is split in the process, and O2 is released as a by-product. The light reaction also generates ATP using chemiosmosis, in a process called photophosphorylation. Thus light energy is initially converted to chemical energy in the form of two compounds: NADPH and ATP. The Calvin cycle is named for Melvin Calvin who, with his colleagues, worked out many of its steps in the 1940s. The cycle begins with the incorporation of CO2 into organic molecules, a process known as carbon fixation.
Meiosis:
When GAMETES combine, the ZYGOTE (offspring) gets half from mom (23) and half from dad (23) ZYGOTES are diploid (46)
DNA, RNA, replication, translation, and transcription:
When Hershey and Chase measured radioactivity in the pellet and supernatant from both of their experiments, they found that a large amount of 32 P, appeared in the pellet, 7/12 whereas almost all of the 35S appeared in the supernatant. Based on this and similar experiments, Hershey and Chase concluded that DNA, not protein, was injected into host cells and made up the genetic material of the phage.
Meiosis:
When sperm and egg meet, their chromosomes much match for the zygote to develop properly.
Concept: Alternative mechanisms of carbon fixation have evolved in hot, arid climates:
When their stomata partially close on a hot, dry day, CO2 levels drop as CO2 is consumed in the Calvin cycle. At the same time, O2 levels rise as the light reaction converts light to chemical energy. While rubisco normally accepts CO2, when the O2:CO2 ratio increases (on a hot, dry day with closed stomata), rubisco can add O2 to RuBP. When rubisco adds O2 to RuBP, RuBP splits into a three-carbon piece and a two-carbon piece in a process called photorespiration.The two-carbon fragment is exported from the chloroplast and degraded to CO2 by mitochondria and peroxisomes. Unlike normal respiration, this process produces no ATP. In fact, photorespiration consumes ATP.
GENETICS AND HEREDITY: Review: Chromosomes:
a. Chromosomes are the structures that develop during cell division as DNA forms into tight coils. b. Humans have 46 chromosomes (gorillas and chimps have 48). c. Chromosomes generally occur in pairs. d. There are two basic types of chromosomes, autosomes and sex chromosomes. 1) Sex chromosomes are designated X and Y, with females resulting from an XX pairing, and males from an XY paring. 2) The X chromosome also functions as an autosome, but the Y appears to have no function other than the determination of sex (this may be incorrect). 3) Any abnormal pairing of autosomes usually results in death soon after conception, while abnormal pairing of sex chromosomes usually results in sterility or other non-fatal consequences.
GENETICS AND HEREDITY: Misconceptions Regarding Dominance and Recessiveness:
a. Dominance and recessiveness are not all or nothing situations. b. Some characters can be co-dominant, like blood type, which includes A, B, O, and AB. c. Dominant alleles are not stronger or better than recessive alleles. d. Dominant alleles are not even necessarily more common than recessive alleles.
GENETICS AND HEREDITY: The Biological Basis of Life: Genetics:
a. Genetics is the study of how traits are transmitted from one generation to another. b. It is crucial to our understanding of disease processes, as well as our understanding of the process of evolution.
GENETICS AND HEREDITY: Genetic Principles Discovered by Mendel
a. Gregor Mendel (1822-1884) developed his theory of heredity while working with garden peas. b. Purebred strains were crossed to produce hybrids, and Mendel calculated the frequencies of traits in each generation, with the results being the empirical basis for his theory.
GENETICS AND HEREDITY: Independent Assortment:
a. Mendel also made crosses with two traits simultaneously, such as plant height and seed color. b. The results indicated that the proportion of F2 traits did not affect each other. c. Mendel called this relationship the Principle of Independent Assortment. 1) The loci coding for height and seed color happened to be on different chromosomes that are sorted independently from each other during meiosis and are therefore not linked traits. d. The genes that code for different traits assort independently of each other during gamete formation. e. This occurs when genetic loci controlling two characters are located on separate chromosomes. f. If loci are on the same chromosome, they are linked traits and are not independently assorted.
GENETICS AND HEREDITY: Dominance and Recessiveness:
a. Mendel used these terms to describe the fact that one (recessive) trait in the F1 generation was masked by the expression of the other (dominant) trait. b. Variations of genes at a locus are termed alleles. c. Various traits such as plant height, stem length, etc. are controlled by two alleles at one locus. 1) When two copies of the same allele occur at one locus, the individual is homozygous. 2) When two different alleles are paired at the same locus, the individual is heterozygous. d. The actual genetic makeup is called the genotype. e. The observed manifestation of the genotype is called the phenotype. f. The Punnett Square can be used to predict the proportions of F2 genotypes and phenotypes.
GENETICS AND HEREDITY: Mendelian Inheritance in Humans:
a. Mendelian traits are also called discrete traits or traits of simple inheritance. b. There are over 9,600 discrete traits in humans. 1) Most are biochemical in nature and the result of harmful alleles. c. The ABO blood groups are inherited in a Mendelian fashion, and others include Sickle-Cell Anemia, Tay-Sacks Disease, and Albinism. d. Sex-linked traits are controlled by loci on sex chromosomes.
GENETICS AND HEREDITY: Review: Cell Division:
a. Mitosis - cell division in somatic cells and unicellular life forms. 1) Results in identical diploid daughter cells. b. Meiosis - or reduction division, is cell division that results in gametes. 1) Results in haploid daughter cells (i.e., in humans, cells with 23 chromosomes).
GENETICS AND HEREDITY: III. Mutations - When a Gene Changes:
a. Mutations can occur in somatic and gamete cells 1) If they occur in somatic cells, they affect the individual 2) If they occur in gametes, they are passed on to offspring and have Evolutionary consequences.
GENETICS AND HEREDITY: New Frontiers:
a. PCR (polymer chase reaction) is a process which allows the rapid synthesis of large amounts of DNA from small samples 1) Useful in genetic typing for medical and criminal cases. b. Recombinant DNA technology is used to insert genes from one species into another. 2) Useful in the production of medicines, such as insulin. c. Genetically altered products such as plants that resist frost, and animals that grow larger and resist disease offer great promise, but also safety and ethical issues. d. Cloning - There are two types of cloning, reproductive and therapeutic. 1) Reproductive cloning involves the replacement of an egg cells nucleus with those from an adult donor, which is then induced to grow and develop, resulting in a genetically identical offspring. i. The first animal ever cloned was an African toad, cloned in 1969. ii. The first mammal cloned was a mouse, cloned in 1981. iii. Dolly the Sheep was the first higher life form cloned, in 1997. 2) Therapeutic cloning involves the manipulation of stem cells, which are then Induced into developing into specific tissues, such as liver, heart, or nerve tissues. i. This offers great promise in disease control, and the possibility to replace almost any diseased organ, but also has a controversial side. ii. This is controversial because, at present, the best source of stem cells is from embryonic tissue, which can be cloned, or taken from fetuses (aborted or donated) e. The Human Genome Project, started in 1990, with the goal of sequencing all 30,000 human genes, and completed in 2002. 1) Still working on discovering the identity and functions of the proteins produced by these genes.
GENETICS AND HEREDITY: Heredity Introduction:
a. The Genetic principles described by Mendel in the 1870s form the basis of modern genetics. b. Although farmers and herders recognized for thousands of years that they could manipulate the frequency and expression of traits in plants and animals, no one before Mendel could explain how these traits were modified through selective breeding. c. The predominant erroneous belief was that physical traits were the result of the blending of traits from both parents. Even Darwin, unaware of Mendel's work, believed this. d. Mendel proved that many physical traits were inherited through the discrete transmission of information, from one parent or the other, not the result of blending.
