Reproduction: The Cell Cycle and Mitosis (HY)

Question 1

In animals, what is the difference in number of chromosomes between autosomal cells and germ cells?

Answer 1

autosomal cells are diploid (2 copies of each chromosome)

germ cells are haploid (1 copy of each chromosome)

Question 2

How many chromosomes do human autosomal and germ cells have?

Answer 2

autosomal cells (diploid): 46 (23 chromosomes from each parent)
germ cells (haploid): 23

Question 3

why are chromosomes not visible by light microscopy during interphase?

Answer 3

DNA is in a less condensed form - chromatin - during interphase

Question 4

What are the four stages of the cell cycle? What are the first three stages called when grouped together?

Answer 4

G1 - presynthetic gap 
S - synthesis of DNA 
G2 - postsynthetic gap 
M - mitosis
G1+S+G2 = interphase

Question 5

What is the G0 phase?

Answer 5

cells that are not preparing to replicate are within the G0 phase. this is an offshoot of the G1 phase.

Question 6

What occurs during the G1 phase?

Answer 6

1. create organelles for energy and protein production 2. grow size

Question 7

what is the name for G1/S checkpoint? what feature does it check for?

Answer 7

restriction point

checks if DNA is in proper condition for synthesis

Question 8

What occurs during the S phase?

Answer 8

1. synthesis of DNA to produce sister chromatids connected at a centromere

Question 9

Does ploidy of a cell change in S phase? What’s the ratio of DNA content in G2 phase to G1 phase?

Answer 9

No, ploidy does not change in S phase.

ratio of DNA in G2:G1 - 2:1

Question 10

What are features does the cell check for in the G2/M checkpoint?

Answer 10

checks for adequate size and proper replication of organelles and DNA

Question 11

What are the four stages of mitosis and what occurs right after mitosis?

Answer 11

1. prophase
2. metaphase
3. anaphase
4. telophase
   cytokinesis

Question 12

what is the main protein involves in the G1/S and G2/M cell cycle checkpoints?

Answer 12

p53 (tumor suppressor gene)

Question 13

what is the difference between oncogenes and tumor suppressor genes? (how do they function differently when they are mutated)

Answer 13

oncogenes - when mutated, they actively promote cell division
tumor suppressor genes - when mutated, they no longer can regulate/pause cell cycle

Question 14

what are the two molecules that are responsible for directing the cell through the cell cycle?

Answer 14

cyclins

cyclin-dependent kinases (CDKs) that phosphorylate transcription factors

Question 15

what are the two microtubule organizing centers of the cell?

Answer 15

1. basal body of flagellum/cilium

2. centrosome

Question 16

What happens during prophase?

Answer 16

1. chromatin condenses to chromosomes
2. centriole pair separates, move to opposite sides of cell, and form spindle fibers and asters
3. nuclear membrane dissolves
4. nucleolus disappears
5. (prometaphase) spindle fibers attach to kinetochores at centromeres

Question 17

what are asters?

Answer 17

microtubule structure that anchors centrioles to cell membrane

Question 18

what happens during metaphase?

Answer 18

1. chromosomes line up at metaphase plate (equatorial plate)

Question 19

what happens during anaphase?

Answer 19

1. centromers split and sister chromatids are pulled apart

Question 20

what happens during telphase?

Answer 20

reverse of prophase

1. spindle fibers disappear
2. nuclear envelopes reform
3. nucleoli reforms
4. chromosomes decondense to chromatin

Question 21

what happens during cytokinesis?

Answer 21

separation of cytoplasm and organelles

Question 22

In human, how many homologous pairs of chromosomes, chromosomes, and chromatids are present before and after S phase of the cell cycle?

Answer 22

before S phase: 23 pairs of homologous chromosomes, 46 chromosomes, 46 chromatids
after S phase: 23 pairs of homologous chromosomes, 46 chromosomes, 92 chromatids `