Cell Cycle, Mitosis, Meiosis

Question 1

How do cells become more specialized? What do genes and proteins have to do with this process?

Answer 1

• With every cell division, cells become more specialized. - Different genes in different cells get turned on and off. - This determines the set of proteins made and these proteins determine the functions of the cell and what it performs. Determines the type of cell.

Question 2

What is the overall overview of the cell cycle?

Answer 2

1. ) G1 Phase: Stockpile nucleotides, ATP, enzymes to replicate.
2. ) S Phase: Replicate DNA
3. ) G2 Phase: Synthesize microtubules and other proteins needed, stockpile ATP, and enzymes for mitosis/meiosis. 4.) Mitosis or Meiosis.

Question 3

What is the G0 phase? What happened here and why?

Answer 3

• In this phase, the cell stops replicating and dividing
• A cell enters G0 phase if it senses a lack of growth factors, nutrients, and other molecules needed for the cell cycle to continue.

Question 4

What steps is the Interphase made up of in the cell cycle?

Answer 4

• G0, G1, S, and G2 phases.

Question 5

What happens in the G1 phase of Interphase? Beginning and end.

Answer 5

• Retinoblastoma protein is phosphorylated to become active. This protein helps prevent the cell from growing until it is ready to do so.
• At the end of the G1 phase, the cell makes sure it has stockpiled the enzymes it needs to replicate DNA before going into S Phase.

Question 6

What happens at the beginning and end of the G2 phase?

Answer 6

• The cell must accumulate a certain level of the mitosis-promoting factor (MPF) in order to enter mitosis. This complex is activated by dephosphorylation.
• At the end of the G2 Phase, the cell checks for DNA damage; the presence of damage keeps the MPF from becoming activated and therefore preventing the cell from going into mitosis.
• The telomere lengths are checked by the cell. Telomere lengths shorten each cell cycle which indicates cell age.

Question 7

What could happen in metaphase of mitosis that could prevent the cell from continuing mitosis?

Answer 7

• During metaphase, the cell checks to see if all the chromosomes are aligned properly at the equatorial line and that all spindle fibers are connected to centromeres.
• If not, then MPF is not inactivated and the cell cannot continue mitosis.
• For mitosis to continue the MPF needs to be inactivated

Question 8

What happens if the cell cannot fix its problems during any time of the cell cycle? How does this occur?

Answer 8

• The cell commands apoptosis, or cell death if it cannot fix its problems.
• It does this by turning on genes which induce apoptosis.

Question 9

What is the first phase of apoptosis?

Answer 9

• The first phase of apoptosis is called membrane blebbing.
• Blebbing is a part of the cell/membrane that bulges and eventually pops the cell open.

Question 10

What are the 5 stages of Mitosis?

Answer 10

1. ) Prophase
2. ) Prometaphase
3. ) Metaphase
4. ) Anaphase
5. ) Telophase - Cytokinesis occurs in the telophase - cytoplasm, and organelles divide into the two daughter cells.

Question 11

What happens at the end of interphase?

Answer 11

• There are no discernible chromosomes left (chromosome is decondensed), spindle fiber apparatus not yet formed, the nuclear membrane is intact

Question 12

What happens in prophase of mitosis? Beginning and end? What is the end of prophase called?

Answer 12

Beginning:

• Chromatin and chromosomes begin to condense.
• Centromeres begin to move toward opposite poles.
• Since DNA was replicated in S phase, each chromosome has two sister chromatids. Which can be seen underneath a microscope in late prophase.

End: Called Prometaphase

• Chromosomes obviously condensed.
• Nuclear envelope disintegrates (disappeared) and centrosomes move towards the poles dividing the cell. Spindle fibers grow out of the centrosomes toward the centromeres and binds to the chromosomes.

Question 13

What happens during metaphase?

Answer 13

• Nuclear envelope disappeared.
• Spindle fibers attached to kinetochores of sister chromatids of each chromosome (occurred in prometaphase).
• Cell undergoes a spindle-assembly checkpoint to be sure every chromatid has been bound by a spindle fiber.
• Chromosomes aligned at the equator.

Question 14

What happens during anaphase of Mitosis?

Answer 14

• Nuclear envelope still disintegrated.
• Each spindle fiber is attached to kinetochores of chromatids.
• Sister chromatids are split apart, pulled towards opposite poles, into separate chromosomes.
• Centrosomes and spindle fibers still very visible.

Question 15

How do sister chromatids pull apart from one another? What enzymes are involved? What keeps sister chromatids together? During what stage(s) does this occur in?

Answer 15

• Sister chromatids cannot be separated until Cohesin is degraded by Separase.
• Cohesion keeps the sister chromatids intact at the centromere while the enzyme Separase degrades Cohesion down.
• This occurs during the end of metaphase and beginning of anaphase.

Question 16

What does Dynein do?

Answer 16

• Dynein is a motor proteins which pull sister chromatids apart.
• Dynein sits on two spindle fibers (made of microtubules) and pulls on two spindle fibers that are connected to chromosomes
• Move from the + end towards the negative end.

Question 17

What happens during early and end of Telophase?

Answer 17

Early:

• Nuclear envelope still not yet reformed.
• Chromatin is still somewhat condensed.
• Cells only beginning to cleave apart, new cell membrane not yet visible.

End:

• Sister chromatids (now chromosomes) have completely moved towards opposite end and no more movement is necessary.
• Chromatin decondenses, nuclear envelope forms, and spindle fibers begin to degenerate to some degree.
• New cell membrane material is synthesized so the two daughter cells are now separate functional cells.

Question 18

S Phase: What is are sister chromatids? Do chromosomes equal centromeres? How many DNA molecules?

Answer 18

• Sister chromatids are a single chromosome but there are two DNA molecules (One sister chromatid each).
• Chromosomes equal centromeres.

Question 19

In each cell cycle phase (G1, S, G2, M) how many chromosomes are there and how many DNA molecules are there? Start with 4 chromosomes.

Answer 19

1. ) G1 = 4 chromosomes and 4 DNA molecules.
2. ) S = 4 chromosomes and 8 DNA molecules.
3. ) G2 = 4 chromosomes and 8 DNA molecules.
4. ) Mitosis:

• Prophase and Prometaphase = 4 chromosomes and 8 DNA molecules.
• Metaphase = 4 chromosomes and 8 DNA molecules.
• Anaphase = 8 Chromosomes and 8 DNA molecules.
• Telophase = 4 chromosomes and 4 DNA molecules in each daughter cell.

Question 20

What type of cells undergo only meiosis and not mitosis? How many and what types of cells result after meiosis and mitosis?

Answer 20

• Spermatagonia and oogonia only undergo meiosis.
• 4 haploid daughter cells occur after meiosis (one set of chromosomes per cell)
• 2 diploid daughter cells occur after mitosis (two sets of chromosomes).

Question 21

When does recombination occur, between what types of chromosomes, and what are the results?

Answer 21

• Recombination occurs between homologous chromosomes during meiosis.
• Results in the child inheriting some chromosomes that contain a combination of gene alleles that come down from the grandfather and grandmother.

Question 22

What are the stages of prophase I and Prometaphase I in meiosis?

Answer 22

1. ) Leptotene: Chromatin condenses.
2. ) Zygotene: Chromatin condenses, homologous chromosomes pair up and engage in synapsis (aligning very close to each other) to produce bivalents (two chromosomes) aka tetrads (4 chromatids).
3. ) Pachytene: Chromatid condenses, and synaptonemal complex develops between homologous chromosomes (the homologous chromosomes come in contact with each other at one or more places in each p and q arm).
   - This step is when crossing over occurs: Non-sister homologous chromatids ( one from each pair of homologous chromosomes physically crossover at points of contact and exchange material (homologous recombination occurs).
4. ) Diplotene (crossover is over): The two chromosomes in each bivalent begin to separate, but remain joined to chiasma (places where crossing over took place).
5. ) Diakinesis: Chromatin condenses further, the two chromosomes in bivalent move farther apart, the two chromosomes now remain joined only at the ends.
   - Prometaphase I includes 3., 4., and 5.

Question 23

What is the overview of early and late Prophase I/Prometaphase I?

Answer 23

• Same as in mitosis.

Early:

• Chromosomes begin to condense and centrosomes begin to move toward opposite poles.

End:

• Chromosomes visible condensed, centrosomes have migrated to their opposite poles, nuclear membrane disappeared, and spindle fibers are reaching in to bind to chromosomes.