Biology Exam #2 - Ch. 5, 7, 8, 25
mRNA in gene expression
(Transcription) •Messenger RNA (mRNA) carries genetic information from DNA to ribosomes •mRNA is formed by the process of transcription. •First RNA polymerase binds to a promoter (in DNA). •The RNA polymerase adds complementary RNA nucleotides to DNA. •RNA polymerase stops at terminator •Processing of mRNA •Primary mRNA contains both introns and exons. •A guanine cap is added at one end. •A poly-A tail is added to other end. •The mature mRNA molecule is ready. (Translation) •each three-nucleotide unit of an mRNA molecule is called a codon.
Carbon Dioxide Fixation (Calvin Cycle)
-1st step -CO2 attached to a 5-carbon RuBP molecule -reaction occurs three times -result is 6 carbon molecule that splits in 2 3-carbon molecules -first 3-carbon is called 3PG -RuBP carboxylase is the enzyme that makes this happen -comparatively slow enzyme so there is a lot of it
Meiosis results in a change in chromosome number indicated by
2n to n
granum
A stack of thylakoids in a chloroplast
DNA does NOT have which of the following characteristics?
contains adenine, guanine, cytosine, and uracil
If the normal nucleotide sequence was TACGGCATG, what type of gene mutation is present if the resulting sequence becomes TAGGCATG?
deletion mutation
inner membrane and outer membrane
double membrane that surrounds the chloroplast
What lines up at the metaphase plate during metaphase II of meiosis and metaphase of mitosis?
each chromosome composed of two sister chromatids at both
The ______ contain(s) the information for the structure of the protein.
exons
stroma
fluid portion of the chloroplast; outside of the thylakoids
Which of the following statements is NOT true about oogenesis in humans?
four equal size daughter cells will form
Which of the following is a substrate of cellular respiration?
glucose
What phase(s) of cellular respiration produce(s) NADH?
glycolysis, preparatory reaction, and citric acid cycle
What lines up at the metaphase plate during both metaphase I of meiosis and metaphase of mitosis?
homologous chromosomes for meiosis, each chromosome is composed of two sister chromatids for mitosis
Why do organisms without oxygen need to convert pyruvate to lactate?
in order to regenerate NAD+
In the human female life cycle, meiosis begins
in the fetus
Metaphase I (Meiosis I)
tetrads (pair of homologous chromosomes) align at equatorial plane, each attaches to spindle fiber at kinetochore -independent assortment starts here
At the cellular level, photosynthesis occurs within
the chloroplast
In order to tell the source of particular atoms that take part in a metabolic pathway, sometimes radiolabeled molecules are used. These are molecules in which one atom or element has been replaced with its radioactive isotope. Which molecule would you need to radioactively label in order to produce radioactive oxygen during photosynthesis?
water
In the human life cycle, fertilization results in
zygote
G1 phase (cell cycle: interphase)
• growth and aquire material for DNA synthesis •Checkpoint - If DNA damaged then apoptosis •G0 occurs in some cells, such as nerve and muscle which do not go on to reproduce
Which of the following is not involved in the regulation of the cell cycle?
caspases
The production of ATP as a result of an electrochemical gradient is called
chemiosmosis
The substance that initially traps solar energy in photosynthesis is
chlorophyll
Reduction of Carbon Dioxide (Calvin Cycle)
-2nd step -Original carbon dioxide becomes CH20 -energy and electrons needed for this reaction are supplied by ATP and NADPH (from light reaction) -As 3PG become G3P, ADP + P and NADPH becomes NADP+
Regeneration of RuBP (Calvin Cycle)
-3rd step -takes 3 turns of the Calvin cycle to allow one G3P to exit -for every 3 turns of this, five G3P (3 carbon molecule used) -reforms 3 RuBP (5 carbon molecule) -5 x 3 (carbons in G3P) = 3 x 5 (carbons in RuBP)
Heterotrophs
-An organism that obtains organic food molecules by eating other organisms or their by-products. -similar to autotrophs in that they both use organic molecules produced by photosynthesis as a source of building block for growth and repair and as a source of chemical energy for cellular work
Describe the structure of the DNA molecule.
-DNA is a polynucleotide strand with a backbone of alternating phosphate and sugar groups. -Two strands make up a double helix. -The strands are held together by hydrogen bonding. -Complimentary Base Pairing •Adenine (A) always pairs with Thymine (T) •Guanine (G) always pairs with Cytosine (C)
Frederick Griffith (1928)
-Discovered transformation during an experiment that involved injecting mice with smooth S cells, rough R cells, heat-killed S cells, and heat-killed S cells with living R cells. -concluded that some substance necessary for the bacteria to produce a capsule and be virulent must have passed from the dead S-strain bacteria to the living R-strain bacteria -the change in the phenotype of the R-strain must be due to a corresponding change in their genotype -The transforming substance was potentially the genetic material
Oswald Avery, Colin MacLeod, and Maclyn McCarty (1944)
-Expounded upon Frederick Griffith's Streptococcus pneumoniae experiment, removing all but one of the macromolecules in each determination. Found that DNA was molecule of heritability. -DNA from S strain bacteria causes R strain bacteria to be transformed so that they can produce a capsule and be virulent -The addition of DNase, an enzyme that digests DNA, prevents the transformation from occurring. This supports the hypothesis that DNA is the genetic material -The addition of enzymes that degrade proteins has no effect on the transforming substance, nor does RNase, an enzyme that digests RNA. This shows that neither protein nor RNA is the genetic material.
Explain how mitosis maintains the chromosome number from the mother cell to the daughter cells.
-Following DNA replication during interphase, each chromosome in the parental nucleus is duplicated and consists of two sister chromatids -during mitosis, the centromeres divide and the sister chromatids separate, becoming the daughter chromosomes that move into the daughter nuclei -therefore, daughter cells have the same number and kinds of chromosomes as the parental cell (the blue chromosomes are inherited from one parent and the red ones are inherited from the other)
Explain how the product of the Calvin cycle is used to form the other molecules found in plants.
-G3P is used for glucose, sucrose, starch, cellulose, fatty acid, and amino acid synthesis -combined with fructose to form sucrose which helps plants transport carbohydrates from one part of the plant to another -starting point for synthesis of starch and cellulose, starch is the storage form of glucose and cellulose is the structural component of cell walls -plant can use the hydrocarbon skeleton of G3P to form fatty acids and glycerol which are combined in plant oils and help the plant to produce protein
Distinguish between the aerobic and anaerobic phases of cellular respiration.
-Glycolysis is anaerobic because it takes place outside of the mitochondria and does not utilize oxygen -the prep reaction, citric acid cycle, and electron transport chain are all aerobic because they take place inside the mitochondria where oxygen acts as the final acceptor of electrons
Mitosis in Animal cells
-HAS centrioles and is circular NO cell plate -prophase, prometaphase, metaphase, anaphase, telophase
Explain the roll of electron carriers in cellular respiration.
-NAD+ is a coenzyme used in oxidation-reduction reactions in which it accepts two usually high-energy electrons plus a H+ ion and carries them to the ETC (NADH results) -FAD is another coenzyme used in oxidation-reduction sometimes instead of NAD+ also accepts two electrons and two H+ ions to become FADH2 -NAD+ and FAD pick up electrons at specific points in the cellular respiration pathways and then carry these high-energy electrons to an ETC in the mitochondria to drop them off -they're then free to go back and pick up more electrons
Describe how the proton gradient is created across the mitochondrial cristae.
-NADH passes electrons to the first electron acceptor -energy released is used to pump H+ ions into the intermembrane space of the mitochondria -protons accumulate in the intermembrane space (proton gradient)
Explain the role of photosynthesis for all organisms on earth.
-Photosynthesis converts solar energy into the chemical energy of a carbohydrate which allows photosynthetic organisms to synthesize over 150 billion metric tons of carbohydrates to fuel both themselves and consumers -the products of photosynthesis are also used up by cellular respiration in mitochondria and vice versa
Calvin cycle reactions
-Portion of photosynthesis that takes place in the stroma of chloroplasts and can occur in the dark; it uses the products of the light reactions to reduce CO2 to a carbohydrate. -light-independent -CO2 ----> CH20
Summarize the sequence of events that occurs during gene expression.
-When genes are expressed, the genetic information (base sequence) on DNA is first copied to a molecule of mRNA (transcription). -The mRNA molecules then leave the cell nucleus and enter the cytoplasm (in eukaryotes), where they participate in protein synthesis by specifying the particular amino acids that make up individual proteins (translation).
Describe the characteristics of cancer cells.
-are genetically unstable -do not correctly regulate the cell cycle -escape the signals for cell death -can survive and proliferate elsewhere in the body
Glycolysis
-breakdown of glucose into 2 pyruvate molecules -takes place in cytoplasm outside of mitochondria -no oxygen -transforms one 6-carbon molecule in two 3-carbon molecules pyruvate outside mitochondria
Describe why cancer is a failure of genetic control.
-cancer cells continue to cycle through the cell cycle -normal controls of the do not operate to stop the cycle and allow cells to differentiate -because of this, cancer cells tend to be nonspecialized -both the rate of cell division and the number of cells increase
Point mutations
-change in a single DNA nucleotide -Substitution: •May change a specific amino acid •May have no effect - silent mutation •May produce an abnormal protein •Sickle cell due to abnormal globin protein
Name the pigments required to absorb light energy for photosynthesis.
-chlorophylls a and b and the carotenoids -each absorb specific wavelengths -green light reflects and only minimally absorbed -leaves appear green
Citric Acid Cycle
-cyclical metabolic pathway of oxidation reactions that give off CO2 and produce one ATP -occurs in the matrix of the mitochondria -at the start, C2 acetyl group carried by CoA joins with a C4 molecule and C6 citrate molecule results -CoA is recycled to prep reaction -each 2 carbon acetyl group is oxidized to 2 CO2 molecules -reactions produce 3 NADH and 1 FADH2 -1 ATP is produced by substrate-level synthesis -altogether, the cycle accounts for two immediate ATP molecules per glucose molecule because it turns twice
Internal controls of cell cycle
-cyclin as an internal timekeeper -checkpoints within the cell: G1, S, G2 -p53 protein
Telophase I (Meiosis I)
-daughter cells have one chromosome from each homologous pair -the nuclear envelope and nucleoli reappear -may or may not be accompanied by cytokinesis
Cytokinesis
-division of the cytoplasm begins in anaphase and continues in telophase but does not reach completion until just before the next interphase -by that time, the new forming cells have received a share of the cytoplasmic organelles that duplicated during the previous interphase
Proto-oncogenes
-encode proteins that promote the cell cycle and prevent apoptosis -often likened to a gas pedal in a car because they cause cells to continue through the cell cycle
tumor suppressor genes
-encode proteins that slow the cell cycle -They are likened to the brakes of a car because they inhibit cells from progressing through the cell cycle -they promote apoptosis
exons
-expressed sequence of DNA; codes for a protein -information needed to produce the functional product, such as protein, is contained within these DNA sequences.
Write the overall equation of cellular respiration.
-glucose + oxygen ---> carbon dioxide + water -C6H12O6 + 602 ---> C02 + H20 -ADP+P ---> 36-38 ATP
External controls of cell cycle
-growth factors outside of the cell help carry it through certain checkpoints
Glycolysis inputs and outputs
-inputs: 6 carbon glucose, 2 NAD+, 2 ATP, 4 ADP + 4 P -outputs: 2 3-carbon pyruvate, 2 NADH, 2 ADP, 4 ATP total -2 ATP net gain
Distinguish between internal and external controls of the cell cycle.
-internal controls help control the timing of events occurring within the cell -external controls, such as growth factors from the outside of the cell, tell the cell whether or not to divide
Transposons (causes of gene mutations)
-jumping genes -Specific DNA sequences that move within and between chromosomes
Electron Transport Chain
-located in the cristae of mitochondria -electrons passed to a series of electron carrier (some carriers are cytochromes or iron-containing proteins) -high energy electrons enter the system and low-energy electrons leave the system (energy source) -2 electrons per NADH and FADH2 enter this and drop off electrons -energy is captured and stored as H+ ion -Oxygen combines with H+ ion to make H2O -NAD+ and FAD are recycled to pick up more electrons -NADH passes electrons to the first electron acceptor -energy released is used to pump H+ ions into the intermembrane space of the mitochondria -protons accumulate in the intermembrane space (proton gradient) -net gain of 32-34 ATP
Describe the purpose of meiosis.
-occurs in any life cycle that involves sexual reproduction -reduces the chromosome in such a way that the daughter nuclei receive only one of each kind of chromosome -it reduces the chromosome number from diploid (2n) to haploid (n) -ensures that as a result of sexual reproduction, the next generation will of individuals will have the diploid number of chromosomes and a combo of different traits different from either parent
Describe how oncogenes and mutated tumor suppressor genes work.
-oncogenes are mutated proto-oncogenes that become cancer-causing genes because they continuously activate the Ras protein to send the signal for the cell to divide even when there is no growth factor present -when tumor suppressor genes mutate, their products no longer inhibit the cell cycle. ex: p53 can't inhibit the cell cycle in order repair damaged DNA
Describe the similarities and differences between cellular respiration and photosynthesis.
-photosynthesis is the formation of glucose while cellular respiration is the breaking down of glucose -organelle for cellular respiration is mitochondria while the organelle for photosynthesis is the chloroplast -both are metabolic pathways within cells, and therefore consist of a series of reactions that the overall equation doesn't indicate -both use an ETC located in membranes and produce ATP by chemiosmosis -Both use electron carriers: photosynthesis uses NADP+ and cellular respiration uses NAD+ -Photsynthesis turns 3PG into G3P and cellular respiration turns G3P into 3PG -Plant cells run both processes -Photosynthesis produces oxygen, while cellular respiration uses oxygen.
Autotrophs
-photosynthetic organisms that produce their own food -producers that have the ability to synthesize carbohydrates, feed not only themselves but also consumers, which must take in preformed organic molecules
prepatory reaction
-pyruvate is oxidized to acetyl CoA and carbon dioxide is removed -Because glycolysis ends with 2 molecules of pyruvate, the prep reaction occurs twice per glucose molecule -oxidation reaction in which hydrogen atoms are removed from pyruvate by NAD+ and NADH results -gains two high energy electrons
Light reactions
-reactions of photosynthesis that use energy from light to produce ATP and NADPH -light-dependent -H20 ----> O2 -noncyclic electron pathway
Describe the human life cycle in terms of haploid and diploid cells.
-requires both meiosis and mitosis -a haploid sperm (n) and a haploid egg (n) join at fertilization, and the resulting zygote has the full, or diploid (2n), number of chromosomes.
Mitosis in Plant cells
-same phases as in animal cells -have centrosome and spindle but no centrioles or asters -a particular plant tissue, meristematic tissue, retains the ability to divide throughout the life of a plant
thylakoid space
-space inside thylakoid membrane -site of proton gradient built up in photosynthesis
Elongation (Step 2 of Translation)
-the process by which the polypeptide increases in length. -This occurs one amino acid at a time. -requires energy 1. A tRNA with attached peptide is at the P site, and a tRNA carrying the next amino acid is arriving at the A site. 2. Once the next tRNA is in place at the A site, the peptide chain will be transferred to this tRNA. 3. Translocation-mRNA shifts one codon, and the peptide-bearing tRNA is now at the ribosome P site. 4. "Spent" tRNA exits. New codon is at the A site and ready for next complementary tRNA.
Alfred Hershley and Martha Chase (early 1950s)
-used a virus called a T phage, composed of radioactively labeled DNA and capsid coat proteins, to infect Escherichia coli bacteria. -discovered that the radioactive tracers for DNA, but not protein, ended up inside the bacterial cells, causing them to become transformed -As only the genetic material could have caused this transformation, Hershey and Chase determined that DNA must be the genetic material.
Summarize the events that occur during the process of DNA replication.
1.Strands start hydrogen bonded. 2.DNA helicase unwinds and "unzips" the double-stranded DNA. 3.New strands built complementary base pairing of nucleotides by DNA polymerase. 4. DNA ligase seals any breaks in the sugar-phosphate backbone. 5. The two double helix molecules are identical to each other and to the original DNA molecule.
Explain how ATP can continue to be produced in the absence of oxygen.
ATP continues to be produced in the absence of oxygen through fermentation.
Describe the advantages and disadvantages of fermentation
Advantages: -recycles NADH -NAD+ is a coenzyme -quick burst of energy -used when you have low oxygen levels Disadvantages: -ethanol and lactate can be poisonous to cells -provides much less ATP than aerobic respiration
Which of the following is NOT a frameshift mutation of the nucleotide sequence CATUAUCCC?
CATUAUCGC CTUAUCCC CCATUAUCCC ATUAUCCC Answer: CATUAUCGC
The Calvin cycle reactions are dependent upon a supply of
CO2, NADPH, and ATP
G1 checkpoint
Cell cycle main checkpoint. If DNA is damaged, apoptosis will occur. Otherwise, the cell is committed to divide when growth signals are present and nutrients are available.
Compare the overall chemical equations for photosynthesis and cellular respiration.
Cellular respiration -C6H12O6 + 602 ---> C02 + H20 Photosynthesis -C02 + H20 ----> C6H12O6 + 602 essentially they each provide the inputs of their processes to one another
Metaphase
Centromeres of duplicated chromosomes are aligned at the metaphase plate (center fully-formed spindle). Kinetochore spindle fibers attached to the sister chromatids come from opposite spindle poles. -Spindle fully formed -Each chromosome has two kinetochores, one for each sister chromatid -Each attached to spindle microtubules from opposite poles of cell
Early Prophase
Centrosomes have duplicated. Chromatin is condensing into chromosomes, and the nuclear envelope is fragmenting.
Where is NAD+ converted to NADH?
Cytoplasm and Matrix of the Mitochondrion
During the process of transcription, the information in
DNA is converted into RNA information.
The enzyme that reads the template strand and makes a complementary strand of DNA is
DNA polymerase
telophase
Daughter cells are forming as nuclear envelope and nucleoli reappear. Chromosomes will become indistinct chromatin -roughly the opposite of prophase -Spindles reduce in size -Nuclear envelope reforms -Chromosomes uncoil and lengthen
Explain the energy-investment phase and energy harvesting phases of glycolysis.
Energy investment steps: -2 molecules of ATP used Energy Harvesting steps: -NADH synthesis -chemical changes lead to substrate level phosphorylation, formation of 4 ATP -phosphate passed directly to ATP from enzyme
Upon examination, a cell is found to have twice as much DNA as the normal diploid state but is no longer in the process of replicating the DNA. All of the DNA is found within a single nucleus. Which stage of the cell cycle is this cell in?
G2 phase
One of the products of the Calvin cycle is
G3P
Prepatory Reaction inputs and outputs
Inputs: 2 NAD+, 2 pyruvate, and 2 CoA Outputs: 2 NADH, 2 acetyl CoA, and 2 CO2
Citric Acid Cycle inputs and outputs
Inputs: 2 acetyl groups, 6 NAD+, 2 FAD, 2 ADP + 2P Outputs: 4 CO2, 6 NADH, 2 FADH2, 2 ATP -2 ATP net gain
What role does NAD+ play in cellular respiration?
It is a coenzyme and electron carrier
The individual(s) credited with the discovery of the structure of DNA is (are)
James Watson and Francis Crick
Describe the important events of meiosis that cause the halving of the chromosome number in daughter cells.
Meiosis I •Homologues line up side by side at the equator (synapsis). •When homologous pairs separate, each daughter cell receives one member of the pair. •The cells are now haploid. Meiosis II and Fertilization •Sister chromatids migrate to opposite poles to become individual chromosomes. •Each of the four daughter cells produced has the haploid chromosome number.
G2 checkpoint
Mitosis checkpoint. Mitosis will occur if DNA has replicated properly. Apoptosis will occur if the DNA is damaged and cannot be repaired
Explain the role of mitosis in the cell cycle.
Mitosis is the process responsible for regeneration and repair. Mitosis helps in cell growth and development. Cells can grow old and wear off or they can get bruised and injured but eventually, they repair and regenerate.
Identify the electron donation and final acceptor molecules of the electron transport chain.
NAD+ and FAD are both carriers that donate electrons to the final acceptor, Oxygen, as it combines with hydrogen ions and forms water
Which molecules donate electrons to the electron transport chain of respiration?
NADH and FAD
Anaphase II (Meiosis II)
Sister chromatids separate and become daughter chromosomes that migrate toward the poles.
introns
Noncoding segments of nucleic acid that lie between coding sequences (exons).
Prophase
Nucleolus has disappeared, and duplicated chromosomes are visible. Centrosomes begin moving apart, and spindle is in process of forming. -DNA condenses into chromosomes -Mitotic spindle begins to form -Spindle fibers made of Tubulin -Part of the cytoskeleton -Organized and produced by centrosomes
Which of the following statements is TRUE concerning sunlight radiation used for photosynthesis?
Only the red, blue, and violet wavelengths of visible light are used for photosynthesis.
What is the final electron acceptor at the end of the electron transport chain in photosynthesis?
Oxygen
Interkinesis
Period of time between meiosis I and meiosis II during which no DNA replication takes place.
Synapsis occurs during what stage of meiosis?
Prophase I
What is the name of the enzyme that fixes carbon dioxide during photosynthesis?
RuBP carboxylase
Which of the following is the correct sequence for the cell cycle?
S-G2-M-G1 -The order of the cell cycle is G1, S, G2, and M. Since it is a cycle, you can start at any point, but the order of the stages will be the same.
Anaphase
Sister chromatids part and become daughter chromosomes that move toward the spindle poles. In this way, each pole receives the same number and kinds of chromosomes as the parent cell -Spindles shorten
M checkpoint
Spindle assembly checkpoint. Mitosis will not continue if chromosomes are not properly aligned.
Identify the electron donor and electron acceptors in the light reactions.
The electron donor is water (H20) and the electron acceptors are NADP+ which is then reduced to NADPH after accepting two electrons and an H+
Prometaphase
The kinetochore of each chromatid is attached to a kinetochore spindle fiber. Polar spindle fibers stretch from each spindle pole and overlap. -Nuclear envelope breaks down -Tips of spindle microtubules attach to kinetochores on chromosomes -Kinetochores - groups of motor proteins that can pull the chromosome along a spindle fiber -Chromosomes pushlNuclear envelope breaks down -Tips of spindle microtubules attach to kinetochores on chromosomes
ATP and ADP have a strong negative charge. How could that get into and out of the mitochondrion?
Through a membrane transport protein.
thylakoid membrane
The photosynthetic membrane within a chloroplast that contains light gathering pigment molecules and electron transport chains.
Describe the structure of the thylakoid and how this contributes to photosynthesis.
The thylakoid contains chlorophyll and other pigments that have the ability to absorb solar energy which drives photosynthesis -the thylakoid space is where H+ ions are pumped into to form a gradient
Describe why the H+ proton gradient across the thylakoid membrane is referred to as a storage of energy.
This is a storage of energy because the H+ ions are released from the stroma into the thylakoid space to form the gradient by passing through ATP synthase complexes where ATP production also occurs
Which of the following proteins would you expect to be a coded for by a proto-oncogene
a growth factor receptor
During what stage do homologous chromosomes separate from each other?
anaphase I
The part of a transfer RNA molecule that binds to the codon is the
anticodon
Write the overall chemical equation for photosynthesis
carbon dioxide + water ----> glucose + oxygen
What are the two sets of reactions for photosynthesis?
light reactions, Calvin cycle reactions
The metabolic events that move electrons from water to NADP+ are referred to as what?
noncyclic electron pathway
Mutations in DNA
occur at random sites
What are the products of photosynthesis?
oxygen and carbohydrate
During what stage of mitosis does the nuclear envelope disappear and the chromosomes become distinct?
prophase
Which sequence of stages in mitosis is correct?
prophase, metaphase, anaphase, telophase
Because one original strand of the double-stranded helix is found in each daughter molecule, the replication process is called
semi-conservative
Metaphase II (Meiosis II)
sister chromatids line up at the metaphase plate
Which does NOT describe a function of the DNA polymerase molecule?
synthesize the proper nucleotide to match with the base read on the old strand
The nuclear membrane reappears in mitosis during
telophase
Explain what is meant by the term homologous chromosomes.
the same size chromosomes (long or short) but are indicated by different colors--the blue chromosomes are inherited from one parent, and the red are inherited from the other
The light reactions could be viewed as analogous to a hydro-electric dam. In that case, the wall of the dam that holds back the water would be analogous to...
the thylakoid membrane
If a cell stops at the G1 checkpoint, this is most likely due to what problem?
there is DNA damage
Imagine starting in the innermost space of the chloroplast and moving outward until leaving the chloroplast and entering the cytoplasm. What is the starting points an proper order of things you would move through?
thylakoid space - thylakoid membrane - stroma - inner membrane - outer membrane
Which is the process that synthesizes mRNA?
transcription
Which is the process by which a protein is constructed in the cytoplasm of eukaryotic cells?
translation
Oogenesis
•Begins in the fetus •Primary oocytes are arrested in prophase I •Resumes at puberty •One primary oocyte continues meiosis each menstrual cycle. •Primary oocyte (2n) divides in meiosis I to produce one secondary oocyte (1n) and one polar body (1n). •Division is unequal •Secondary oocyte receives most cytoplasm and half the chromosomes •If the secondary oocyte is fertilized, meiosis II will proceed. •Another unequal division will occur, with the egg receiving most of the cytoplasm. •A second polar body is also formed. •If the secondary oocyte is not fertilized, it disintegrates -this is SO long, sorry
Prophase II (Meiosis II)
•Cells have one chromosome from each homologous pair. •Each duplicated chromatid attaches to the spindle.
Cytokinesis in animal cells
•Cleavage furrow forms between daughter nuclei •Contractile ring contracts, deepening the furrow •Process continues until separation is complete
Describe the molecules necessary to Translation.
•Creation of proteins from RNA sequence •Translation requires several enzymes and different types of RNA molecules. •mRNA: sequence of bases in DNA is transcribed into mRNA, which ultimately codes for a particular sequence of amino acids to form a polypeptide •tRNA - transfer RNA: transports amino acids to ribosomes. •rRNA - Ribosomal RNA:
Errors in gene replication (causes of gene mutations)
•DNA replication errors are a rare mutation source. •DNA polymerase Proofreads to catches errors.
Describe the reasons for and process of apoptosis.
•Decreases number of cells •Occurs during development to remove unwanted tissue •Caterpillar to butterfly in chrysalis -programmed cell death -important to prevent cancer as the cells keep proliferating -occurs when if DNA of a cell is damaged in the G2 phase •Typical series of events brings about cell destruction through enzymes and internal or external signals •Fragments engulfed by white blood cells after the cell loses contact with neighbors and the nucleus fragments and plasma membrane forms blisters
Mutagens (causes of gene mutations)
•Environmental influences can cause mutations. •Radiation, X-rays, UV radiation, certain chemicals •DNA repair enzymes constantly monitor and repair.
Describe the important events of meiosis that cause the genetic diversity of gamete cells.
•Genetic variation occurs in two ways: •First, crossing between nonsister chromatids in prophase I •Second, the independent assortment of chromosomes during anaphase I •Fertilization between gametes
Prophase I (Meiosis I)
•Homologous chromosomes come together as pairs by synapsis. •Each pair, with four chromatids, is called a tetrad. •Nonsister chromatids exchange genetic material by crossing over.
Anaphase I (Meiosis I)
•Homologous pairs separate and move toward opposite poles of the cell. •Independent assortment occurs when these homologues separate from each other during anaphase I.
Initiation (Step 1 of Translation)
•Initiation factors assemble ribosome components. •Small ribosomal subunit, mRNA, initiator tRNA, and the large ribosomal subunit •The initiator tRNA attaches to the start codon (AUG). •The ribosome has three binding sites for tRNA. •P (peptide) site, A (amino acid) site, and E (exit) site
Compare and contrast the processes of meiosis and mitosis.
•Meiosis occurs only at certain times •After the reproductive organs mature to produce gametes •Mitosis takes place almost continuously in all tissues as part of growth and repair. -Look at figure 5.16
Explain why DNA replication is called semiconservative.
•New DNA consists of one new chain of nucleotides and one from the parent DNA molecule. •Daughter DNA molecules identical to the parent molecule.
Cytokinesis in plant cells
•New cell wall created •A flattened, small disk appears between daughter cells. •A cell plate forms. •Vesicles release molecules to build new cell walls. •Vesicle membranes complete plasma membranes
Termination (Step 3 of Translation)
•New protein, rRNA, tRNA, and mRNA separate. •Occurs at a stop codon. •Last tRNA and polypeptide dissociate from one another. •The ribosome dissociates into two subunits.
Spermatogenesis
•Occurs in testes •Begins at puberty, continues throughout life •Primary spermatocytes (2n) divide in meiosis I to form two secondary spermatocytes (1n). •Secondary spermatocytes divide in meiosis II to produce four spermatids. •Spermatids then mature to sperm (spermatozoa).
Frameshift mutations
•One or more nucleotides are either inserted into or deleted from DNA. •The result can be a completely new sequence of codons and a nonfunctional protein. -the more dangerous mutation
rRNA in gene expression
•Ribosomes composed of many proteins and this -produced in a nucleolus within the nucleus •joins with proteins manufactured in and imported from the cytoplasm to form two ribosomal subunits - small and large •Subunits join just before translation is to occur •Has binding site for mRNA and three tRNAs
Telophase II (Meiosis II)
•The spindle disappears. •The nuclear envelope re-forms. •Cytokinesis occurs.
Describe the effect that gene mutations can have on cells.
•a permanent change in the sequence of bases in DNA. •Effect can range from none to complete inactivity of the protein.
S phase (cell cycle: interphase)
•each chromosome consists of one DNA molecule, called the chromatid •After DNA replication, each chromosome consists of two sister chromatids
Viruses (causes of gene mutations)
•insert their DNA into host Chromosomes •HPV - leads to cervical cancer
G2 phase (cell cycle: interphase)
•the cell synthesizes proteins for cell division •Checkpoint - If DNA damaged then apoptosis occurs
Miotic phase (Cell cycle)
•the division of the nucleus •The sister chromatids separate into daughter chromosomes. •Distributed to two daughter nuclei •Cytokinesis, the division of the cytoplasm, follows mitosis.
tRNA in gene expression
•transports amino acids to ribosomes. •Boot-like shape •Amino acid binds to one end, the opposite end has an anticodon •Complementary to a specific codon of mRNA •Order of mRNA codons determines the order in which tRNA brings in amino acids
