2. Cell Cycle

Question 1

Diploid vs haploid

Answer 1

Two copies of each chromosome vs containing only one copy of each chromosome

Question 2

Stages of interphase

Answer 2

G1, S, G2

Question 3

What happens at G0 stage?

Answer 3

quiescence: Cell lives nml life, in stable state, performs reg cellular processes. Not part of interphase or cell cycle. Typically for non dividing cells (ex: neurons)

Question 4

What happens at G1 stage?

Answer 4

Cells make organelles for energy and protein production like mito, ER, ribosomes; most cells = in this phase. Prepares for DNA replication too

Question 5

How to transition from G1 stage to S stage?

Answer 5

Restriction point aka G1 checkpoint - checks for DNA damage, cell size, nutrients, growth factors. Are we ready to do S phase?

Question 6

What happens at S stage?

Answer 6

Cell replicates chromosomes/chromatids into sister chromatids held by centromere

Question 7

What happens at G2 stage?

Answer 7

Cell makes sure DNA is correctly replicated and there are enough organelles to make daughter cells; prepares for mitosis

Question 8

What happens at M stage?

Answer 8

Mitosis

Question 9

What happens at prophase?

Answer 9

Chromatin condense to chromosomes, centrioles move to opposite sides of cell and form spindle fibers; nuclear membrane dissolves

Question 10

What happens at metaphase?

Answer 10

Chromosomes = attached to spindle fibers at kinetochores —> line up at metaphase/equatorial plate; involves kinesin

Question 11

What happens at anaphase?

Answer 11

Centromeres split –> sister chromatids separate via 2 spindle fibers; involves kinesin.

Question 12

What happens at telophase?

Answer 12

Spindle fibers disappear, nuclear envelopes reform, chrms relax (basically reverse prophase). Cleavage furrow initiates cytokinesis

Question 13

What happens at cytokinesis?

Answer 13

Separation of cytoplasm and organelles. Initiated by cleavage furrow; occurs in telophase

Question 14

Does meiosis occur in all cells?

Answer 14

No, only in gametocytes/germ cells

Question 15

Other names for meiosis I and II

Answer 15

reductional division and equational division

Question 16

Difference between meiosis I and II

Answer 16

Meiosis I separates homologous chrms to make haploid daughter cells; Meiosis II separates chrms similar to mitosis

Question 17

What happens in prophase I?

Answer 17

Same as prophase + homologous chrms intertwine at held by synaptonemal complex => synapsis –> each synaptic pair contains 4 chromatids => tetrad; crossing over at chiasmata occurs

Question 18

What happens at metaphase I?

Answer 18

Homologous pairs/tetrads line up at equatorial plate

Question 19

What happens at anaphase I?

Answer 19

Homologous chrms separate (segregation) to opposite sides of cell via single spindle fiber (as opposed to 2 spindle fibers in mitosis) => disjunction

Question 20

What happens at telophase I?

Answer 20

Nuclear membrane reforms, two sister chromatids still intact by centromere; interkinesis - chrms slightly uncoil

Question 21

What happens at prophase II, metaphase II, anaphase II, and telophase II?

Answer 21

Same as mitosis

Question 22

Purpose of G2 checkpoint?

Answer 22

Aka DNA damage checkpoint. Make sure DNA isn’t damaged and if DNA = replicated correctly; p53 = present. Are we ready to do M phase?

Question 23

centrosome vs centrioles vs asters

Answer 23

creates mitotic spindles and microtubules, they’re the main microtubules organizing centers and they anchor microtubules at one end and make sure they don’t depolymerize, assembly site for kinetochores; consists of 2 centrioles vs 2 centrioles w/in a centrosome, make spindle fibers vs star shaped centrioles + their associated microtubules

Question 24

How many times do somatic cells typically divide?

Answer 24

Enough till telomeres become too short to protect the DNA

Question 25

Which protein controls progression of a cell thru cell cycle?

Answer 25

Cyclin and cyclin dependent kinases

Question 26

What’s the mitotic spindle checkpoint?

Answer 26

Aka M checkpoint. In b/w metaphase and anaphase. Checks for chromosome attachment to spindle fibers at metaphase plate; are we ready to do anaphase?

Question 27

p53 vs TP53

Answer 27

Protein that suppresses propagation of cells with damaged DNA; promotes apoptosis, cell cycle arrest, and DNA repair pathways; present in G2/DNA damage checkpoint vs mutated form of p53, causes cancer

Question 28

What happens if cells can’t pass checkpoints?

Answer 28

If damaged DNA is the problem —> fix it np. Otherwise it can lead to apop, cancer - permanent activation of cell cycle, or senescence - permanent arrest of cell cycle (ie. Irreversible)