Chapter 2 - Cell Cycle, Mitosis/Meiosis Flashcards
Which phases of the cell cycle are part of interphase?
G1, S, and G2?
The cell spends 90% of its time in what phase?
Interphase
What is the purpose of the G0 phase (which is not part of the cell cycle)?
This is known as the quiescence phase where cells withdraw from the cell cycle and are not involved in division. The cells here simply live and carry out their functions without worrying about dividing.
What occurs during the G1 phase?
This is the longest phase, cells are growing/increasing their size and they are producing/dulicating more organelles.
What occurs during the S-phase?
This face is characterized by replication of DNA, that is the sister chromatids get duplicated. Now each chromosome has two sister chromatids instead of one bound by a centromere.
What occurs during the G2 phase?
The cell grows more, prepares for mitosis by making microtubules and going through more cell cycle checkpoints to ensure that the correct amount of DNA and organelles are present.
What are the main cell cycle checkpoints?
G1/S, Intra-S, G2/M, and Spindle Assembly Checkpoint
What is the G1/S checkpoint?
P53 the main protein in charge of this checkpoint, checks for DNA damage and if the cell has enough nutrients
What is the intra-S checkpoint?
It is a checkpoint during DNA replication that checks if the DNA is replicated correctly and there is no damage.
What is the G2/M checkpoint?
Makes sure that the cell has reached an adequate size and the organelles have been properly replicated.
What is the spindle assembly checkpoint?
This checkpoint occurs during metaphase of mitosis/meiosis and ensures that the kinetochore has attached properly to the microtubule
What are the proteins responsible for moving the cell along the different phases of the cycle?
The proteins responsible are known as cyclin dependent kinases which are always present in our cells and cyclins which are only present at certain times of the cell cycle, picking and dropping off. In the presence of cyclins, CDKs are activated which allow driving the cell cycle forward.
What is mitosis?
It is the process by which two identical daughter cells are created from a single cell. Occurs in somatic cells only. Creation of 2 diploid cells.
What happens during prophase?
- Condensation of chromosomes
- Centrioles move towards opposite sides of the pole
- Nuclear membrane dissolves and nucleoi disappear.
- Kinetochores assemble on the centromeres in the chromosome.
- Centrioles begin to form the mitotic spindle
What are kinetochores?
They are a special proteinaceous structure that builds on the centromere part of the chromosome. It is composed of over 45 proteins that make up an inner and outer plate. The kinetochore is the site to where the microtubules attach.
What are centromeres?
They are part of the actual chromosome, made of heterochromatin and repetitive DNA sequences. The centromere is where the kinetochore builds on.
What happens during metaphase?
This is characterized by the alignment of chromosomes at the metaphase plate. The chromosomes have to be attached to microtubules from both poles. There is a spindle checkpoint during metaphase which makes sure that the chromosomes are separated properly.
What happens during anaphase?
The centromeres split, allowing the sister chromatids to separate.
What happens during telophase?
The spindle apparatus disappears, a nuclear membrane reforms around each set of chromosomes, and the nucleoli reappear. The chromosomes uncoil, resuming an uncondensed form.
What happens during cytokinesis?
The cleavage furrow forms by a band of actin filaments that keeps constricting. Eventually the cell divides into two, leaving each cell with a complete set of chromosomes and organelles.
What is meiosis?
What is the process of forming germ cells, resulting in 4 non-identical gametes.
What makes up the mitotic spindle?
The mitotic spindle contains astral microtubules emanating outward to attach to the cell membrane and polar & chromosomal microtubules emanating towards the middle of the cell. The chromosomal microtubules attach to the chromosomes.
What is crossing over and when does it occur?
Crossing over is the exchange of chromosomal segments between nonsister chromatids, which allow for a genetic variation in offspring. It occurs when a chromatid breaks at a point of contact called the chiasma and exchanges equivalent pieces of DNA with a non-sister chromatid.
It occurs during prophase I of meiosis.
What happens during prophase I?
The normal things that happen, which is chromatin condensing, spindle, apparatus, formation, nucleoli, and nuclear membrane disappear. The major difference between meiosis and mitosis is what happens next, which is homologous chromosomes coming together and intertwining in a process called synapsis.
What is gene linkage?
It is the tendency for genes to be inherited together. Genes that are closer together are more likely to be linked and inherited.
Genes that are further away from each other physically, are more likely to undergo ______.
Crossing over relative to each other.
How does crossing over create genetic diversity?
It allows each daughter cell to have a unique pool of alleles from a random mix of maternal and paternal origin.
What happens during metaphase I?
Homologous pairs aline at the metaphase plate and each chromosome attaches to 1 separate spindle fiber by its kinetochore. This is different from metaphase in mitosis because each chromosome is connected by two spindle fibers on opposite poles.
What happens during anaphase I?
Disjunction/segregation occurs meaning that homologous pairs separate and are pulled to opposite poles of the cell. This event is random because the paternal and maternal chromosomes separate randomly and can end up in either daughter cell.
What occurs during telophase I?
A nuclear membrane forms around each nucleus, nucleoli reappear in the spindle apparatus disappears. The cell prepares to divide.
Crossing over explains which one of Mendels laws?
Mendels second law of independent assortment, which states that the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes.
Segregation during anaphase I explains which one of Mendels laws?
Mendels first law of segregation states that the two alleles of a gene locus segregate from each other and each gamete has an equal probability of obtaining either allele that is either the paternal copy or the maternal copy of the chromosome.
At what phase does nondisjunction occur?
Anaphase I and/or Anaphase II
What is non-disjunction?
It is when the chromosomes or chromatids fail to separate properly.
If nondisjunction occurs during meiosis I, what will the gametes look like?
If the homologous chromosomes don’t separate, two of the daughter cells will have an extra chromosome each and two of the daughter cells will be missing a chromosome (have none).
If nondisjunction occurs during meiosis II, what will the gametes look like?
If the sister chromatids failed to separate in only one daughter cell during meiosis II, then one gamete will have an extra chromosome and the other gamete will be missing a chromosome. The two other gametes from the daughter cell which didn’t have nondisjunction occur will be normal.
What is a diploid cell?
A cell that has two complete sets of chromosomes, one from each parent.
What is a haploid cell?
A cell that has one set of chromosomes.
If a daughter cell has an extra chromosome, what is this condition called?
Trisomy
If a daughter cell is missing a chromosome, what is this condition called?
Monosomy
What are homologous chromosomes?
They are two related but non-identical chromosomes. One chromosome from the mom and the other chromosome from dad.
What kinds of cells in the body are most likely to be in the G0 phase of the cell cycle?
Fully differentiated, neurons, cardiac cells, multi-nucleated skeletal muscle cells
How many chromosomes are in a haploid cell?
23
How many chromosomes are in a diploid cell?
46
What is an inversion mutation?
A chromosomal mutation where a segment of the chromosome breaks off and then flips backwards, and reattaches to the same spot of the chromosome.
What is a translocation mutation?
A chromosomal mutation that involves two chromosomes which aren’t homologous. Part of one chromosome is transferred to another nonhomologous chromosome
What is the difference between a mutagen and a carcinogen?
A mutagen is a chemical or physical substance/event that causes genetic mutations.
Carcinogens are substance that cause cancer, some carcinogens are mutagens, but not all.
What is the function of the synaptonemal complex? When does it form?
It is a protein structure which connects homologous chromosomes together and aids in synapsis and recombination. It forms during prophase I of meiosis.
What is the difference between a single crossover and a double crossover?
Single crossover - nonsister chromatids only cross over at one point
Double crossover - nonsister chromatids cross over at 2 points
Differentiate between aneuploidy and polyploidy
Aneuploidy - the addition or loss of one or more chromosomes (trisomy, monosomy)
Polyploidy - the addition of an extra set of chromosomes for each chromosome #
Example of polyploidy
Baby has 3n chromosomes, with a total # of 69 chromosomes
Mismatch repair (MMR)
DNA mismatch repair is a conserved pathway occurring in both prokaryotes & eukaryotes mostly during & right after the S phase (but also other parts of cell cycle).
DNA proofreading; how is it different from MMR?
DNA proofreading is carried out during the process of DNA replication by DNA polymerase III. MMR occurs right after replication.
It uses 3’ to 5’ exonuclease activity to remove the wrong base.
What is the most serious type of DNA damage?
How does the cell fix this?
Double stranded break.
Non-homologous end-joining - chromosome is glued back together, but results in a small mutation at the site
Homologous recombination - the broken chromosome pairs up w/ its homologous chromosome & uses it as a template to replace the damaged region; cleaner repair
