Cell division - mitosis

Question 1

Chromosome structure

Answer 1

DNA forms a complex with RNA/proteins to form chromatin

chromatin packed into beads called nucleosomes consisting of two loops of the DNA helix wrapped around 8 histones

supercoiling and condensation of chromatin forms chromosomes

Question 2

What is chromatin?

Answer 2

A complex of DNA, histones and nonhistone proteins from which chromosomes are made

Question 3

Is chromatin basophilic or acidophilic? In other words how will it stain?

Answer 3

basophilic

Question 4

What are the 2 types of chromatin?

Answer 4

Heterochromatin

Euchromatin

Question 5

What is heterochromatin?

Answer 5

a highly condensed form of interphase chromatin which is transcriptionally inactive

Stains very intensely!

Question 6

What is euchromatin?

Answer 6

the least condensed extended state of chromatin

known as active chromatin - transcriptionally active

Stains very lightly!

Question 7

In order for a eukaryotic cell to divide into two, the two into four, etc. two processes must alternate…

What are these two processes?

Answer 7

doubling: doubling of DNA in S phase of the cell cycle
halving: of that genome during mitosis (M phase)

Question 8

What happens during M phase of mitosis?

Answer 8

Mitosis

and division of parent cell into daughter cells

Question 9

What is the G₀ phase ?

Answer 9

Term applied to cells which divide infrequently or not at all

It is the period when cells carry out their differentiated function

Question 10

What happens during G1 phase of the cell cycle?

Answer 10

also called the gap phase, it’s the interval between completion of mitosis and the beginning of S phase

Question 11

What occurs during S phase

Answer 11

Replication of DNA/RNA/proteins

duplicated chromosomes called sister chromatids

Question 12

What happens during G2 phase of the cell cycle?

Answer 12

It’s the interval between the end of S phase and the beginning of mitosis

protein synthesis occurs

Question 13

What are the G1, S and G2 phases (together) termed?

Answer 13

interphase

Question 14

What is the purpose of interphase (G1, S and G2)?

Answer 14

to allow the cell additional time to grow and duplicate its chromosomes

Question 15

What are the 6 stages of Mitosis?

Answer 15

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Cytokinesis

Question 16

Summarize the events of Prophase

Answer 16

1st Stage of Mitosis

Chromatin condense to form visible chromosomes

chromosomes not yet attached to the mitotic spindle

chromosomes consist of 2 sister chromatids joined at centromere

centrioles duplicate and move to opp poles acts as microtubule organising centres

microtubules form the spindle apparatus between the centrioles

Question 17

Summarize the events of Prometaphase

Answer 17

Starts with the disassembly of the nuclear envelope

nucleoli regress

chromosomes move to equator

Microtubules from the mitotic spindle bind to specialized protein complexes (kinetochores) on each pair of sister chromatids

Question 18

Summarize the events of Metaphase

Answer 18

The chromosomes align along the equatorial plate of the spindle

spindle consists of microtubules running from pole to pole

Question 19

Summarize the events of Anaphase

Answer 19

connections between sister chromatids are cut by proteolytic mechanisms

Daughter chromosomes moved to opposite poles of the spindle by action of the microtubules

Question 20

Summarize the events of Telophase

Answer 20

the condensed chromosomes decondense into their interphase state

nucleoli reappear

Nuclear envelope re-assembles around each group of chromosomes to form two daughter nuclei

spindle disappears

Question 21

Summarize the events of cytokinesis

Answer 21

Process by which the cytoplasm is cleaved in two

Begins in anaphase

involves a transient structure made of actin filaments (contractile ring)

contractile ring attaches to the membrane-associated proteins on the cytoplasmic face of the membrane

Question 22

Describe the main cell cycle regulators

Answer 22

Early Response Transcription Factors like c-fos and c-jun promote cell division

Cyclins (G1, S-phase, and M-phase cyclins) - promote the events that happen in each phase, conce rise and fall as each phase occurs

Cyclin-dependant kinases - CDKs (G1 CDKs, S-phase CDKs, M-phase CDKs) - levels remain fairly stable

Question 23

What can happen if cells progress to the next phase of the cell cycle before the previous phase is properly completed?

Answer 23

Catastrophic genetic damagge can occur

Question 24

What is the purpose of a cell cycle checkpoint?

Answer 24

Control mechanisms at such checkpoints make sure the cell progresses through the cell cycle - completing each step in order (otherwise castastrophic genetic damage can occur)

Question 25

What do mitogens do in the cell cycle?

Answer 25

They stimulate cells to enter G1

Question 26

What was the term “tumor” formerly used to denote?

Answer 26

any localized swelling in the body caused by inflammation or abnormal cell proliferation

Now we use it as a synonym for neoplasm

Question 27

What are neoplasms?

Answer 27

abnormal mass of tissue formed by uncoordinated cell proliferations

Can be benign or malignant depending on their growth rate and invasiveness

Question 28

How is the cell cycle regulated

how can rate of mitosis be increased/decreased ?

Answer 28

Repressor genes reduce mitosis

some hormones and growth factors trigger cell division

usually rate of cell production = rate of cell death

most cancers caused by mutation of repressor genes

Question 29

How do CDKs work?

Answer 29

CDKs become activated upon binding with cyclin

activated CDKs cause phosphorylation to activate or inactivate target proteins

these proteins allow the cells entry into the next phase of the cell cycle

Question 30

what are the centrosomes ?

Answer 30

structures the microtubules attach to, forming the spindle

organelle located near the nucleus in the cytoplasm that divides to form two centrioles that migrate to opposite poles of the cell during mitosis