Cell Division and Cell Cycle

Question 1

The stages through which all eukaryotic cells pass from one cell division to the next is known as the

Answer 1

Cell cycle

Question 2

What phase involves growing and actively metabolising?

Answer 2

Interphase

Question 3

What phase involves dividing?

Answer 3

M phase

Question 4

What is inactive DNA called?

Answer 4

Heterochromatin

Question 5

What is euchromatin?

Answer 5

Genes are expressible. Depends on cell type and metabolic requirements.

Question 6

What happens to chromatin strands in the very early stages of mitosis?

Answer 6

In the very early stages of mitosis, chromatin strands become more and more condensed and duplicate (‘pair of sister chromatids’)

Question 7

Describe the centromere

Answer 7

a fixed point along the chromosome
consists of heterochromatin DNA
pair of sister chromatids attach at centromere (so called “sister chromatid pair’)
Joined chromatids known as chromosomes
controls the movement of the chromosome

Question 8

When chromosomes duplicate, sister chromatids are initially linked to each other by protein complexes called…

Answer 8

Cohesins

Question 9

When do kinetochore form?

Answer 9

Late pro-metaphase

Question 10

What is a kinetochore?

Answer 10

It is a region with proteins attached to the centromere during cell division

Question 11

What do kinetochores do?

Answer 11

Control assembly and disassembly of the spindle fibre microtubules

Question 12

List a few functions of a telomere

Answer 12

Protect end of chromosome from deterioration or from fusion with neighbouring chromosomes
Maintain the structural integrity of the DNA
Ensures complete DNA replication with telomerase
Position chromosomes in the nucleus

Question 13

Interphase is divided into:

Answer 13

G1 phase, S phase, and G2 phase

Question 14

Briefly explain the G1 phase

Answer 14

Cell is metabolically active and continuously grows

Cell prepares to duplicate DNA
High levels of RNA transcription and protein synthesis
many of the proteins synthesized will be used for DNA synthesis and chromosome replication during S phase
Increasing number of organelles such as mitochondria

Continuation of cytokinesis (i.e. physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells)

Question 15

Briefly explain the S phase

Answer 15

DNA synthesis & replication
Continuation of RNA transcription and protein synthesis
Duplication of centrosome (cytoplasm around centrioles)

Question 16

Briefly explain the G2 phase

Answer 16

DNA has already replicated in preparation for division
Continuation of growth and metabolism
RNA transcription and protein synthesis in preparation for mitosis.

Question 17

How long does mitosis and cytokinesis last in a typical rapidly proliferating human cell?

Answer 17

Mitosis and cytokinesis last approx. 1 hour total.

Question 18

When does G0 phase take place?

Answer 18

Cells enter the G0 phase from a cell cycle checkpoint in the G1 phase.

Some cells temporarily or reversibly stop dividing… these cells exit G1(leaving the cell cycle) to enter Quiescence orG0
Remain metabolically active but… no longer proliferate unless stimulated by appropriate extracellular signals (growth factors)

Question 19

What is senescence and what does it result in for the cell?

Answer 19

Other cells permanently stop dividing due to age or accumulated DNA damage (‘senescence’) and undergo apoptosis (or ‘programmed cell death’).

Question 20

What leads to cell cycle arrest at the G1 checkpoint?

Answer 20

The presence of damaged DNA leads to cell cycle arrest at a checkpoint also in G1. Several checkpoints function to ensure that complete genomes are transmitted to daughter cells.

Question 21

What does the G1 checkpoint ensure?

Answer 21

Towards the end of G1 phase
* May stop the cell progressing to the S-phase
* Regulated by a protein called p53 which delays DNA synthesis until DNA damage is repaired causing withdrawal from the cycle, or causing cell death rather than becoming cancerous (implicated in cancer progression)

Question 22

What happens during the M phase?

Answer 22

Chromatin fibres in the nucleus condense as the cell is about to divide

Form the chromatids and subsequent chromosomes visible with the light microscope

Each chromosome is seen to form a two-chromatid structure joined at the centromere

The process of condensation of the chromatin fibres involves extensive folding and looping

Question 23

What are the four phases in mitosis?

Answer 23

Prophase
Metaphase
- Prometaphase
- Metaphase
Anaphase
Telophase

Question 24

What happens in early prophase?

Answer 24

At onset of prophase the mitotic chromosomes appear

Each chromosome is seen to be divided into two sister chromatids

The sister chromatids are held together at the centromere

The centrioles duplicate and migrate with their centrosomes to the opposite poles of the cell

Question 25

What happens in late prophase?

Answer 25

The division of the chromosomes into chromatids is now clearly seen.

A cluster of microtubules called an aster extends from the centrioles and begins to form the mitotic spindle.

The nucleoli disappear

Question 26

This entire process happens when? The nuclear envelope breaks down releasing the chromosomes into the cytoplasm
Microtubules invade the nuclear space
The kinetochores form around the centromere of the chromosomes
Long protein filaments called kinetochore microtubules extended from poles on either end of the cell and search and attach to the kinetochores.
Polar microtubules from each aster overlap forming interconnections

Answer 26

Pro-metaphase

Question 27

Metaphase involves:

Answer 27

• The undivided centromere via its kinetochore is attached to a spindle fibre now called the kinetochore microtubule
• These microtubules pull sister chromatids back and forth until they align along the equator of the cell, called the equatorial plane or metaphase plate (equidistant from the centrioles) In the metaphase (or mitotic spindle) checkpoint, the cell ensures that it is ready to divide: Unattached kinetochores generate a signal to prevent premature progression to anaphase without all chromosomes being aligned
  This signal creates the mitotic spindle checkpoint

Question 28

Anaphase is when…

Answer 28

Each pair of chromosomes is separated into two identical, independent chromosomes.

Two events occur in order:
1. The proteins (cohesins) that bind sister chromatids together are cleaved, allowing chromatids to separate.
These sister chromatids are pulled apart by shortening kinetochore microtubules becoming sister chromosomes
Chromosomes are pulled toward the respective centrosomes to which they are attached.
2. The non-kinetochore microtubules elongate, pushing the centrosomes (and the set of chromosomes to which they are attached) apart to opposite ends of the cell.

Question 29

The separation of the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells is called

Answer 29

Telophase

Question 30

_______ breaks down except for some polar ________ which further elongate and persist

Answer 30

Mitotic spindle, microtubules

Question 31

Cytokinesis is the physical process of cell division, which ____________ of a parental cell into two daughter cells.

It performs an essential process to _________ in half and ensure that one nucleus ends up in each daughter cell.

Cytokinesis starts during the nuclear division phase called __________ and continues through __________.

Answer 31

divides the cytoplasm, separate the cell, anaphase, telophase

Question 32

A ring of actin microfilaments associated with the plasma membrane is called the

Answer 32

Contractile ring

Question 33

What does the contractile ring do?

Answer 33

Shrinks at the equator of the cell, pinching the plasma membrane inward (‘furrowing’) , and forming what is called a cleavage furrow.

Question 34

Cyclins are…

Answer 34

proteins that control the cell cycle at each checkpoint

Question 35

Cyclins activate…

Answer 35

Cyclin-Dependent Kinases (Cdks).

Question 36

What are CDKS?

Answer 36

Kinase are enzymes that catalyse the transfer of a phosphate from one phosphate donating molecule to another molecule) through interaction.

Question 37

In cancer cells, ______ are higher, and _________ protein is lower

Answer 37

cyclin levels, p53 tumor suppresor

Question 38

Meds to stop the cell cycle at certain checkpoints include:

Answer 38

Certain anti-cancer drugs stop the cell cycle at specific check points
Vinca alkyloids in mitosis
Cytarabine, methotrexate, fluorouracil in S-phase
Cisplatin preventing DNA replication