The Cell Cycle

Question 1

what is the cell cycle

Answer 1

the cell cycle is a sequence of events where 2 cells are duplicated and divided

Question 2

What are the 2 main phases in the cell cycle

Answer 2

M phase and interphase

Question 3

What happens in the m-phase

Answer 3

nuclear division (mitosis)

cytoplasmic division

Question 4

what happens during interphase

Answer 4

This is defined as the period between cell division

G1 phase

S-phase is where DNA replication occurs

g2 phase

Question 5

What type of cells only divide when an appropriate stimulus is given

Answer 5

liver cells when they are damaged

Question 6

What type of cells divide on an ongoing basis

Answer 6

Hematopoietic and epithelial stem cells

Question 7

How do our cells make sure that each process in each stage has been carried out correctly

Answer 7

The cell-cycle has a control system that will delay later events until earlier events are complete

The 3 major checkpoints:

start point
G2/M checkpoint
metaphase-to-anaphase transition

Question 8

Start checkpoint

Answer 8

Right before transcription

Checks to see if the environment has the proper nutrients

Question 9

G2/M checkpoint

Answer 9

checks to see if all DNA is replicated and if DNA damage is repaired

Question 10

metaphase-to-anaphase transition

Answer 10

sees if all chromosomes are properly attached to the mitotic spindle

Question 11

Is there a specific mechanism that tells cells to proceed to the next stage

Answer 11

cell cycle is controlled my molecular switches

The switches are cyclin-dependent protein kinases (Cdks)

Question 12

Interphase

Answer 12

G1: where centrosome duplication is initiated
G2: centrosome duplication is completed
S-phase: chromosomes ae replicated (DNA replication)

Question 13

Prophase

Answer 13

1. replicated chromosomes condense
2. mitotic spindle assembly starts

Question 14

S-Phase

Answer 14

During chromosome replication, cohesins are deposited to hold the sister chromatids together

Question 15

What will happen at the end of G2? why does this need to happen?

Answer 15

replicated chromosomes will be dispersed, but tangled/
they need to be organized for mitosis

Question 16

Prophase

Answer 16

most cohesins will be removed
condensins will condense the DNA and the 2 sister chromatids will be organized and connected in the centromere by cohesins

Also the assembly of the mitotic spindle will begin and requires duplicated centrosomes

Question 17

What is centrosome structure

Answer 17

Contains a pair of centrioles that are organized at right angles

The centrosome is surf by pericentriolar material that the y-tubulin ring complex (y-TuRCs)

Question 18

Describe the mitotic spindle assembly

Answer 18

1. Assembly of microtubules that starts in Prophase
2. Microtubules dynamics (assembly and disassembly)

3.stabilize the inter pole microtubules (connected to DNA) through kinesins

4. Position astral microtubules (the ones facing outwards) through cytoplasmic dyneins

The completion of the mitotic spindle requires breakdown of nuclear envelop

Question 19

Where does nuclear envelope breakdown occur

Answer 19

It occurs between prophase and prometaphase

Question 20

What is nuclear envelope breakdown

Answer 20

This happens to at the beginning of mitosis so that the spindles can capture the condensed chromosomes

Question 21

Nuclear envelope breakdown

Answer 21

The phosphorylation of Latin’s and nuclear pore proteins triggers the disassembly of the nuclear envelope into small membrane vesicle

Question 22

Prometaphase

Answer 22

This occurs after the nuclear envelop breakdown

The chromosome are attached to the microtubules and chromosome movement begins

Question 23

Astral microtubules

Answer 23

Help position the mitotic spindle and cytoplasmic dyenin

Question 24

Inter pole microtubules

Answer 24

These are anti parallel microtubules that are cross-linked

Provide structural support for spindle poles

Question 25

Kinetochore microtubules

Answer 25

They attach and position specific chromosomes

Question 26

What is another name for metaphase-anaphase transition

Answer 26

Spindle assembly checkpoint

Anaphase will not begin until all chromosomes are attached to metaphase plate

Question 27

Anaphase

Answer 27

Separation of sister chromatids by separate cutting cohesin complex

Anaphase AM
Kinetochore microtubule shortened and sister chromatids are pulled apart

Anaphase B:
Spindle poles move outward

Question 28

Telophase

Answer 28

Chromosomes are now separated
The mitotic spindle disassembles
Nuclear envelop re-assembles
Chromosomes decondense

Question 29

How will the nuclear envelop reassemble after anaphase

Answer 29

Dephosphorylation of nuclear pores and Latin’s
It will re-assemble with nuclear laminate and pores

Question 30

cytokinesis in animal cells

Answer 30

Here the cytoplasm divided in 2 by a contractile ring of actin and myosin filaments

This contractile ring is at the cleavage furrow

This will mark the end of M phase

Question 31

When is the contractile ring formed

Answer 31

During anaphase actin and myosin filaments assemble

Question 32

What is the difference between cell division in plant cells

Answer 32

Mitosis is very similar in the two cells but in plant cells there is no centrosome

Cytokinesis will also be different because the membrane vesicles fuse together forming a new cell wall

Question 33

Cytokinesis in plant cells

Answer 33

Telophase: chromosomes separated. phragmoplasts start to form which will form cell plate

Cytokinesis: nuclear envelope re-assemble and chromosomes are decondensed. The cell plate will form and eventually mature into new cell wall