bio exam 4
each individual chromosome at the beginning of mitosis is composed of
2 sister chromatids
what happens at the end of DNA replication?
2 strands of DNA are produced these 2 strands will then provide instructions for the 2 new daughter cells after cell division is completed.
Compare and contrast binary fission in prokaryotes and cell division in eukaryotes
Binary fission (prokaryotes) and mitosis (eukaryotes) both produce daughter cells that are genetically identical to the parental cell. Due to the relative simplicity of the prokaryotes, the cell division process, called binary fission, is a less complicated and much more rapid process than cell division in eukaryotes. The DNA of the nucleoid associated with proteins that aid in packaging the molecule into a compact size, there are no histone proteins and thus no nucleosomes in prokaryotes. The packing proteins of bacteria are, however, related to the cohesin and condensing proteins involved in the chromosome compaction of eukaryotes. Compared with eukaryotic cell division, bacterial cell division is simpler than eukaryotic cell division. Binary fission is a less complex process than mitosis.
compare and contrast DNA replication in eukaryotes and prokaryotes
Both prokaryotic and eukaryotic cells utilize a similar process that includes unwinding the DNA to expose the base sequence, assembly of complementary base nucleotides, bonding of the new assemblage to the parent strands, and rewinding each new DNA molecule. While there are many similarities, the replication of prokaryotes and eukaryotes involve differences. These differences in DNA replication reflect the contrast between prokaryotic and eukaryotic cells. Prokaryotic cells are quite simple in structure. They have no nucleus, no organelles and a small amount of DNA in the form of a single, circular chromosome. Eukaryotic cells on the other hand, have a nucleus, multiple organelles and more DNA arranged in multiple, linear chromosomes. eukaryotes- multiple origins of replication 14 DNA polymerase types telomerase present replicated slower prokaryotes- single origin of replication 5 DNA polymerase types telomerase not present replicated faster
of what biological molecules are chromosomes made?
DNA and protein
explain how enzymes proofread and repair errors in DNA
DNA polymerase proofreads every newly added base and corrects the bases. Mismatch repair enzymes recognize the wrong bases and leave them out, replacing them with the correct base.
the enzyme ____ builds a strand of DNA out of ____ using a ____
DNA polymerase; nucleotides; template strand
explain how the structure of DNA reveals the replication process
DNA replication. The double helix is unwound and each strand acts as a template for the next strand. Bases are matched to synthesize the new partner strands. DNA replication is the process of producing two identical replicas from one original DNA molecule. This biological process occurs in all living organisms and is the basis for biological inheritance. DNA is made up of two strands and each strand of the original DNA molecule serves as template for the production of the complementary strand, a process referred to as semiconservative replication. Cellular proofreading and error-checking mechanisms ensure near perfect fidelity for DNA replication.[1][2] In a cell, DNA replication begins at specific locations, or origins of replication, in the genome.[3] Unwinding of DNA at the origin and synthesis of new strands results in replication forks growing bidirectional from the origin. A number of proteins are associated with the replication fork which helps in terms of the initiation and continuation of DNA synthesis. Most prominently, DNA polymerase synthesizes the new DNA by adding complementary nucleotides to the template strand.
Describe the events that occur in both stages of meiosis
Diploid Cell (2N): From a preceding mitotic division, the Oogonium (Spermatogonium) enters meiosis with DIPLOID (2N) chromosomes but TETRAPLOID (4N) DNA. Chromosomes then duplicate to produce SISTER CHROMATIDS (or HOMOLOGOUS DYADS). Prophase I: Dyad pairs align to create "TETRADS", non-sister chromatids connect and trade sections at a "CHIASMA", a process called "CROSSING OVER". Metaphase I: SPINDLE FIBERS attach to each dyad at the KINETOCHORE. Tension from spindle fibers aligns the tetrads at the cell equator. Anaphase I: Chiasmata break apart and sister chromatids begin migrating toward opposite poles. Telophase I: CLEAVAGE FURROW forms beginning the process of CYTOKINESIS (cell division). Resulting daughter cells are HAPLOID (1N). Prophase II: Spindle formation begins and centrosomes begin moving toward poles. Metaphase II: Tension from spindle fibers aligns chromosomes at the metaphase plate. Anaphase II: CHROMATIDS separate and begin moving to the poles. Telophase II: CLEAVAGE FURROW forms beginning CYTOKINESIS. Gamete (1N): NUCLEAR ENVELOPES form and chromosomes disperse as CHROMATIN. Meiosis has produced 4 DAUGHTER CELLS, each with 1N chromosomes and 1N DNA. Later, in fertilization, male and female 1N gametes will fuse to form a 2N ZYGOTE. meiosis I- first round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid meiosis II- second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells
the part of meiosis that is similar to mitosis is
In meiosis 2, which is quite similar to mitosis, the two diploid cells further divide into four haploid cells.
DIFFERENCE BETWEEN INTERPHASE AND INTERKINESIS IN MEIOSIS
Interphase: is the longest phase of cell cycle, overall takes 16 hours for a growing mammalian cell. It consists three stages: G1 (Gap-1) phase: It is presynthesis stage, in which cell prepares for DNA replication, which takes 5 hours. Due to which chromosomes are replicated. S (synthetic) phase: It is synthetic phase, in which DNA replication takes place. This phase over in 7 hours. G2 (Gap-2) phase: It is post synthetic stage, where cell gets ready for cell division or else we can say for Mitotic phase. This phase completes in 3 hours. Interkinesis is also known as interphase II that occurs during meiosis, between meiosis I and meiosis II. No DNA replication takes place during this phase, i.e. this phase lacks S-phase.
Explain the mechanisms within meiosis that generate genetic variation among the products of meiosis
Meiosis generates haploid gametes from diploid parental cells via 2cycles of division during the 1st division, genetic diversity is generated by 2 distinct processes: CROSSING-OVER and INDEPENDENT ASSORTMENT-post-meiosis, a 3rd level of genetic diversification is generated by RANDOM FERTILIZATION
In another type of repair mechanism, _________, enzymes replace incorrect bases by making a cut on both the 3' and 5' ends of the incorrect base (Figure 14.19). The segment of DNA is removed and replaced with the correctly paired nucleotides by the action of DNA pol. Once the bases are filled in, the remaining gap is sealed with a phosphodiester linkage catalyzed by DNA ligase. This repair mechanism is often employed when UV exposure causes the formation of pyrimidine dimers.
Nucleotide excision repair
explain how nucleotide subunits link to form a single DNA strand
Nucleotides join together through phosphodiester linkages between the 5' and 3' carbon atoms to form nucleic acids. The 3' -OH of the sugar group forms a bond with one of the negatively charged oxygens of the phosphate group attached to the 5' carbon of another sugar. When many of these nucleotide subunits combine, the result is the large single-stranded polynucleotide or nucleic acid, DNA () If you look closely, you can see that the two sides of the nucleic acid strand shown above are different, resulting in polarity. At one end of the large molecule, the carbon group is unbound and at the other end, the -OH is unbound. These different ends are called the 5'- and 3'-ends, respectively, shows a single strand of DNA.
explain how DNA synthesis occurs on both the leading and lagging strands in eukaryotes
Replication in eukaryotes starts at multiple origins of replication. The mechanism is quite similar to prokaryotes. A primer is required to initiate synthesis, which is then extended by DNA polymerase as it adds nucleotides one by one to the growing chain. The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short stretches called Okazaki fragments. The RNA primers are replaced with DNA nucleotides; the DNA remains one continuous strand by linking the DNA fragments with DNA ligase. The ends of the chromosomes pose a problem as polymerase is unable to extend them without a primer. Telomerase, an enzyme with an inbuilt RNA template, extends the ends by copying the RNA template and extending one end of the chromosome. DNA polymerase can then extend the DNA using the primer. In this way, the ends of the chromosomes are protected.
Identify variation among offspring as a potential evolutionary advantage to sexual reproduction
Sexual reproduction results in variation in the offspring. Asexual vs. sexual reproduction asexual- one parent, offspring genetically identical (ex: clone) sexual- two parents, offspring genetically different from both parents; genetic variation On the surface, creating offspring that are genetic clones of the parent appears to be a better system. If the parent organism is successfully occupying a habitat, offspring with the same traits would be similarly successful. There is also the obvious benefit to an organism that can produce offspring whenever circumstances are favorable by asexual budding, fragmentation, or asexual eggs. These methods of reproduction do not require another organism of the opposite sex. Indeed, some organisms that lead a solitary lifestyle have retained the ability to reproduce asexually. In addition, in asexual populations, every individual is capable of reproduction. In sexual populations, the males are not producing the offspring themselves, so in theory an asexual population could grow twice as fast There are several possible explanations, one of which is that the variation that sexual reproduction creates among offspring is very important to the survival and reproduction of the population. Thus, on average, a sexually reproducing population will leave more descendants than an otherwise similar asexually reproducing population. The only source of variation in asexual organisms is mutation. This is the ultimate source of variation in sexual organisms, but in addition, those different mutations are continually reshuffled from one generation to the next when different parents combine their unique genomes and the genes are mixed into different combinations by crossovers during prophase I and random assortment at metaphase I.
Understand how the cell cycle is controlled by mechanisms both internal and external to the cell
The cell division cycle is generally divided into four phases. In normal cells, progress from one phase to the next is always strictly controlled at so-called "checkpoints." Checkpoints can be considered safety measures for the cell, preventing the control system from dictating the start of another cell cycle event before the previous one has finished, or before any damage to the cell has been properly repaired. In addition to internal signals provided by the checkpoints, completion of the cell division cycle is also dependent upon external cues. When cell division is unregulated and independent of external cues, it has the potential of leading to one of the most devastating diseases that afflicts almost one in five people in first-world countries: cancer.
explain the process of DNA replication in prokaryotes
The first stage of DNA replication in prokaryotes is the uncoiling of the DNA double helix by the enzyme helicase. Helicase separates the DNA into two template strands. RNA primase then adds a short sequence of RNA to the template strands. This short sequence of RNA is a primer which allows DNA polymerase III to bind to the strands and start the replication process. Once this is done, DNA polymerase III adds nucleotides to each template strand in a 5'→3' direction. The nucleotides have 3 phosphate groups and are called deoxyribonucleoside triphosphates. Two of these phosphate groups break off during the replication process to release energy. Since the strands are anti-parallel (the two strands have their 5' end and 3' end in opposite sides) and replication can only occur in a 5'→3' direction, one of the strands will be replicated in the same direction as the replication fork and the other will be replicated in the opposite direction of the replication fork. This means that one of the strands is synthesised in a continuous manner (named the leading strand) while the other one is synthesised in fragments (named the lagging strand). The leading strand only needs one primer while the lagging strand needs quite a few as it is formed in fragments. These fragments are called Okazaki fragments. DNA polymerase I will remove the RNA primers and replace these with DNA. The enzyme DNA ligase then joins the Okazaki fragments together to form a continuous strand.
Explain how the three internal control checkpoints occur at the end of G1, at the G2/M transition, and during metaphase.
The integrity of the DNA is assessed at the G1 checkpoint. Proper chromosome duplication is assessed at the G2 checkpoint. Attachment of each kinetochore to a spindle fiber is assessed at the M checkpoint.
cytokinesis
a contractile ring of protein filaments is characteristic of which phase of cell division? a contractile ring of protein fibers creates the cleavage furrow that divides the cytoplasm into 2 cells.
karyotype
a picture of a full set of chromosomes
list and briefly describe the 3 processes that lead to variation in offspring with the same parents
a. crossover occurs in prophase I between non-sister homologous chromosomes. Segments of DNA are exchanged between maternally derived and paternally derived chromosomes, and new gene combinations are formed. b. random alignment during metaphase I leads to gametes that have a mixture of maternal and paternal chromosomes c. fertilization is random, in that any two gametes can fuse.
state the base-pairing rules for DNA and describe how complementary bases bind to each other
adenine-thymine or adenine-uracil in RNA(2 hydrogen bonds) cytocine-guanine (3 hydrogen bonds)
stage of mitosis involves a separation of sister chromatids?
anaphase
diploid dominant
animals such as humans
a circular chromosome is typically found in
bacteria (prokaryotes)
bacteria divide by
binary fission binary fission is the method used by bacteria (prokaryotes) to divide
alternation of generations
both haploid and diploid, although the haploid stage may be completely retained by the diploid stage. Plants haploid organism (gametophyte) gamete production (N) diploid organism (sporophyte) meiosis (2N)
Describe how cancer is caused by uncontrolled cell growth
cancer cells don't follow normal cell cycle regulation and don't follow normal checkpoints. "immortal". cancer cells divide uncontrolled. cell growth occurs when otherwise shouldn't. Cancer comprises many different diseases caused by a common mechanism: uncontrolled cell growth. Despite the redundancy and overlapping levels of cell cycle control, errors do occur. One of the critical processes monitored by the cell cycle checkpoint surveillance mechanism is the proper replication of DNA during the S phase. Even when all of the cell cycle controls are fully functional, a small percentage of replication errors (mutations) will be passed on to the daughter cells. If changes to the DNA nucleotide sequence occur within a coding portion of a gene and are not corrected, a gene mutation results. All cancers start when a gene mutation gives rise to a faulty protein that plays a key role in cell reproduction. Proto-oncogenes- maintain cell cycle and checkpoints, oncogenes=faster cell cycle Tumor-suppressing genes- prevent uncontrolled division, mutations lead to division of damaged cells Uncontrolled growth of the mutated cells outpaces the growth of normal cells in the area, and a tumor ("-oma") can result. Malignant tumor- cancer spreads, other areas affected; metastasis Benign tumor- cancer localized
Describe how chromatin is packaged in the nucleus.
chromatin- DNA and proteins (histones) loose in cell at rest condenses into chromosomes at start of cell division 30-nm fiber (chromatin); formed by nucleosomes coiling around each other, interacting at histone tails nucleosome- subunit of chromatin composed of a short length of DNA wrapped around a core of histone proteins (helix coiled around 8 histones) histones- one of several similar, highly conserved, low molecular weight, basic proteins found in the chromatin of all eukaryotic cells; associates with DNA to form nucleosomes (small proteins, amino "tails" extends out
metaphase
chromosomes line up in the middle of the cell during which stage of mitosis?
Distinguish between chromosomes, genes, and traits
chromosomes- made of DNA and protein (chromatin); occur when cell division starts genes- the functional units of chromosomes, determine specific characteristics by coding for specific proteins(physical and functional unit of heredity) traits- are the variations of those characteristics.
DNA repair enzymes
continually monitor DNA Nucleotide excision repair (Figure 14.19) - nuclease cuts out mistake, DNA polymerase adds correction, DNA ligase binds Figure 14.19 Nucleotide excision repairs thymine dimers. When exposed to UV, thymines lying adjacent to each other can form thymine dimers. In normal cells, they are excised and replaced.
in plants, the formation of the cell plate occurs during
cytokinesis
autosome
determine everything but sex in an individual any chromosome except a sex chromosome
Describe the three different life-cycle types among sexual multicellular organisms and their commonalities
diploid-dominant- such as with most animals including humans(vertebrates, phanerogams) (zygote) haploid-dominant- such as with all fungi and some algae(protists, fungi) (gametes) alternation of generations- in which the 2 stages are apparent to different degrees depending on the group, as with plants and some algae(mosses, liverworts, ferns) (diploid organism= sporophyte, 2n, meiosis) (haploid organism= gametophyte, n, gamete production) commonalities: fertilisation meiosis (n)
chromatin
disorganized strands of darkly staining material in the nucleus of a cell are called
Explain how the cytoplasmic content is divided during cytokinesis.
division of the cytoplasm following mitosis that forms 2 daughter cells. Division is not complete until the cell components have been apportioned and completely separated into the 2 daughter cells. eukaryotes- cell wall, cell plate, Golgi vesicles prokaryotes- actin ring, cleavage furrow and contractile rings
during the life of a cell, the process cytokinesis refers to
division of the cytoplasm of one cell into 2 cells cytokinesis occurs at the end of mitosis, or cell division. the cell would have twice as many chromosomes.
describe the structure of DNA and how the 2 strands of DNA are oriented with respect to each other
double helix, antiparallel, hydrogen bonded nitrogenous bases hold the strands together (adenine-thymine, guanine-cytocine)
interphase (s)
during the s phase, you would expect to find the amount of DNA increasing from the minimum the amount of DNA ranged from 5 to 10 picograms.
state the role of telomerase in DNA replication
enzyme contains a catalytic part and a built-in RNA template. it attaches to the end of the chromosome, and complementary bases to the RNA template are added on the 3' end of the DNA strand. Once the 3' end of the lagging strand template is sufficiently elongated, DNA polymerase can add the nucleotides complementary to the ends of the chromosomes. Thus, the ends of the chromosomes are replicated.
Describe the structure of prokaryotic and eukaryotic genomes
eukaryote- the genome consists of several double-stranded linear DNA molecules. Each species has a characteristic number of chromosomes in the nuclei of its cells. prokaryote- the genome is composed of a single, double-stranded DNA molecule in the form of a loop or circle. The region in the cell containing the genetic material is called a nucleoid.
discuss the similarities and differences between eukaryotic and prokaryotic DNA
eukaryotic DNA- nucleus, membrane bound, 1+ linear chromosome, "supercoiled" prokaryotic DNA- nucleoid, not bound by a membrane, one singular chromosome
haploid dominant
fungi
Describe the three stages of interphase
g1- the cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus s- (synthesis of DNA) DNA replication can proceed through the mechanisms that result in the formation of identical pairs of DNA molecules-sister chromatids-that are firmly attached to the centromeric region. The centrosome is duplicated. The two centrosomes will give rise to the mitotic spindle, the apparatus that orchestrates the movement of chromosomes during mitosis. in animal cells, in the center centrosomes are associated with a pair of rod-like objects which are at right angles to each other, centrioles. Centrioles help organize cell division. Centrioles are not present in the centrosomes of other eukaryotic species, such as plants and most fungi. g2- the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation. Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase. There may be additional cell growth. Final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis.
describe the key experiments that helped identify that DNA is the genetic material
hershey-chase experiment (fig. 14.4) finally established DNA as genetic material 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. the bacterial pellet was cultured. Bacteria infected with phage containing 32p-labeled DNA produced 32p-labeled phage. Bacteria infected with 35s-labeled phage produced unlabeled phage. In Hershey and Chase's experiments, bacteria were infected with phage radiolabeled with either 35S, which labels protein, or 32P, which labels DNA. Only 32P entered the bacterial cells, indicating that DNA is the genetic material
Describe cellular events during meiosis
interphase (s phase) - chromosomes are duplicated during interphase. The resulting sister chromatids are held together at the centromere. The centrosomes are also duplicated. meiosis I: prophase I- chromosomes condense, and the nuclear envelope fragments. Homologous chromosomes bind firmly together along their length, forming a tetrad. Chiasmata form between non-sister chromatids. Crossing over occurs at the chiasmata. Spindle fibers emerge from the centrosomes. prometaphase I- homologous chromosomes are attached to spindle microtubules at the fused kinetochore shared by the sister chromatids. Chromosomes continue to condense, and the nuclear envelope completely disappears. metaphase I- homologous chromosomes randomly assemble at the metaphase plate, where they have been maneuvered into place by the microtubules. anaphase I- spindle microtubules pull the homologous chromosomes apart. The sister chromatids are still attached at the centromere. telophase I and Cytokinesis- sister chromatids arrive at the poles of the cell and begin to decondense. A nuclear envelope forms around each nucleus and the cytoplasm is divided by a cleavage furrow. The result is two haploid cells. Each cell contains one duplicated copy of each homologous chromosome pair. meiosis II: prophase II- sister chromatids condense. A new spindle begins to form. The nuclear envelope starts to fragment. prometaphase II- the nuclear envelope disappears, and the spindle fibers engage the individual kinetochores on the sister chromatids. metaphase II- sister chromatids line up at the metaphase plate. anaphase II- sister chromatids are pulled apart by the shortening of the kinetochore microtubules. Non-kinetochore microtubules lengthen the cell. telophase II and Cytokinesis- chromosomes arrive at the poles of the cell and decondense. Nuclear envelopes surround the four nuclei. Cleavage furrows divide the two cells into four haploid cells.
if you were to remove the centrosomes from a cell, what do you think that would do to mitosis?
it would prevent chromosomes from segregating properly.
Compare and contrast mitosis and meiosis
meiosis and mitosis are both preceded by one round of DNA replication. DNA synthesis occurs in S phase of interphase, synapsis of homologous chromosomes, crossover, homologous chromosomes line up at metaphase plate, sister chromatids line up at metaphase plate, outcome number and genetic decomposition of daughter cells meiosis- synapsis of homologous chromosomes: during prophase I crossover: during prophase I homologous chromosomes line up at metaphase plate: during metaphase I sister chromatids line up at metaphase plate: during metaphase II number and genetic composition of daughter cells: four haploid cells at the end of meiosis II mitosis- synapsis of homologous chromosomes: does not occur in mitosis crossover: does not occur in mitosis homologous chromosomes line up at metaphase plate: does not occur in mitosis sister chromatids line up at metaphase plate: during metaphase number and genetic composition of daughter cells: two diploid cells at the end of mitosis However, meiosis includes two nuclear divisions. The four daughter cells resulting from meiosis are haploid and genetically distinct. The daughter cells resulting from mitosis are diploid and identical to the parent.
mitosis cytokinesis cell cylce
mitosis precedes cytokinesis
monomer/ polymer of DNA
monomer= nucleotides, bases polymer= nucleic acids
discuss the different types of mutations in DNA
mutation- variations in the nucleotide sequence of a genome induced mutations- result from an exposure to chemicals, UV rays, x-rays, or some other environmental agent. spontaneous mutations- occur without any exposure to any environmental agent; they are a result of natural reactions taking place within the body silent mutations- not expressed point mutations- affect a single base pair transition substitution- refers to a purine or pyrimidine being replaced by a base of the same kind transversion substitution- refers to a purine being replaced by a pyrimidine, or vice-versa
expect to occur during telophase of mitosis?
nuclear membrane beings to re-form.
during the replication of a DNA molecule, which elements of DNA join to turn a single strand into a double strand?
nucleotide bases nucleotide bases join to complete the double strand of DNA
DNA synthesis prokaryotes vs eukaryotes (table 14.2)
prokaryotes= single origin of replication replication faster (1000/sec) DNA pol = 5 Lack telomerase eukaryotes= many origins of replication replication slower (50-100/sec) DNA pol = 14 Telomerase present
compared with eukaryotic cell division, bacterial cell division is
prokaryotic cell division is simpler than eukaryotic cell division binary fission is a less complex process than mitosis.
initial phase of mitosis
prophase chromosomes become visible during the 1st phase of mitosis.
Discuss the events during each stage of karyokinesis (mitosis).
prophase, prometaphase, metaphase, anaphase, and telophase=that result in the division of the cell nucleus. 1. Prophase- chromosomes condense, mitotic spindle begins to form 2. Prometaphase- nuclear membrane breaks down & mitotic spindle fibers attach to kinetochores 3. Metaphase- chromosomes are aligned at the metaphase plate 4. Anaphase- sister chromatids are separated from each other 5. Telophase- chromosomes arrive at opposite poles, de-condense, and are surrounded by a new nuclear envelope
chromatin is produced by DNA molecules wrapping around ____ molecules
protein DNA wraps around protein molecules to make chromatin. These protein molecules are known as histones, and they are some of the most highly conserved proteins in biology
Mitosis (cell division)
provides for the multiplication of cells needed for growth, development, and repair of injuries
what phase of mitotic interphase is missing from meiotic interkinesis?
s phase
how is DNA replicated? (Figure 14.12)
semiconservative hypothesis= each new DNA molecule = 1 new strand, 1 old strand
prokaryotic and eukaryotic replication
similarities: both are bi-directional processes DNA polymerases work 5' to 3' Leading and lagging strands Primers are required Primase (RNA polymerase (5' to 3') makes primers DNA helicase (untwists DNA) Single stranded binding protein (coats DNA to prevent strands re-annealing DNA ligase (seals breaks in the DNA backbone between 3' OH and 5' PO4 requires energy source) Topoisomerases (type I and II) (relieves stress of supercoiling (Type I) and introduces negative supercoiling (Type II) Initiator proteins (bin at the origin of replication) differences: origin of replication: prokaryotes= single, eukaryotes= multiple DNA polymerase types: prokaryotes= 5, eukaryotes= 14 Telomerase: prokaryotes= not present, eukaryotes= present RNA primer removal: prokaryotes= DNA pol I, eukaryotes= RNase H Replicated: prokaryotes= replicated faster, eukaryotes= replicated slower Strand elongation: prokaryotes= DNA pol III, eukaryotes= Pol δ: is the main polymerase on the lagging strand in eukaryotes, it is highly processive and has 3'->5' exonuclease activity & Pol ε: is the primary leading strand DNA polymerase in eukaryotes, and is also highly processive and has 3'->5' exonuclease activity (problems faced by eukaryotes that are not faced by prokaryotes) linear chromosomes with ends Much more genetic material; the typical animal cell has 50 times more DNA than the average bacterium (prokaryotes) Much more packaging; the nucleosomes (DNA wound around histones) and all the scaffolds and higher order packing.
prophase
spindle fibers first appear during which stage of mitosis?; spindle fibers begin forming the mitotic spindle during which phase of mitosis does the chromatin begin to condense to form the chromosomes?; chromatin begins to condense during prophase centrosomes separate and move to opposite poles of the cell; this occurs as the mitotic spindle is being formed
chargaff's rule
studied nitrogenous base composition of DNA regularity of ratios: adenine-thymine, cytosine-guanine, pyrimidine-purines
Explain the synapsis of homologous chromosomes
synapsis- formation of a close association between homologous chromosomes during prophase I In synapsis, the genes on the chromatids of the homologous chromosomes are aligned precisely with each other. The chromosomes are bound tightly together and in perfect alignment by a protein lattice called a synaptonemal complex and by cohesin proteins at the centromere.
before cell division
the blueprint (DNA) is copied, but during cell division, the parts (organelles) of the cell are divided between the two daughter cells
what kind of information is carried in the genome of DNA in a cell?
the sequence of amino acids in a protein
what happens to the cells chromosomes after cell division is complete?
they return a relatively formless state when not engaged in mitosis, chromosomes are stretched out as chromatin
why are checkpoints needed in mitosis?
to regulate cell division
homologous chromosomes
you inherit one-half of each chromosome pair from one of your parents. These chromosomes are referred to as