Lecture 8

Question 1

What is the cell cycle?

Answer 1

the life cycle of a cell, the period between

successive divisions of a cell.

Question 2

What is binary fission? (prokaryotes)

Answer 2

the normal life cycle of a bacterial cell
which involves:
Replication phase (R-phase = C-period);
Division phase (D-phase = D-period);
Interval phase (I-phase = B-period).

Question 3

Which cells lack the ability to divide?

Answer 3

Highly specialized cells e.g. RBC, neurones.

Question 4

What can liver cells, lymphocytes induce?

Answer 4

cell division by specific

stimulus.

Question 5

Hemapoetic stem cells, epithelia cells e.g. have?

Answer 5

Relatively high

level of mitotic activity.

Question 6

Interphase consists of (3)?

Answer 6

G1, S and G2 phases.

Question 7

What is G1 phase?

Answer 7

The gap phase
after the cell division.

The first phase in the interphase.

Growth and biosynthesis
activity phase.

The duration
of the G1 phase is highly
variable, also among different
cells of the same species.

Check points before entering S phase.

Question 8

What is S phase?

Answer 8

The DNA synthesis phase.
Starts with replication of DNA and finishes then the amount of DNA in the cell is doubled. Duplication of centrioles takes place.

Question 9

What is G2 phase?

Answer 9

The gap phase after synthesis of DNA and before the cell division. The cell conducts a series of checks before entering the M phase.

Question 10

What is M phase?

Answer 10

When cell actually divides.

Question 11

What is G0 phase?

Answer 11

The «resting phase».
Some G0 cells can return to the cell cycle
and resume replicating.
Cells that can return are called quiescent (dormant).
Senescent (aging) cell cannot resume.

Question 12

The key cell cycle regulation proteins?

Answer 12

Cyclin-dependent kinases (CDKs), which associate with one of different cyclins across the cell cycle to ensure accurate cell cycle progression.

Question 13

Does cell-dependent kinases have kinase activity?

Answer 13

No, unless they are associated with a cyclin.

Question 14

Concentration of cyclins in the cell fluctuates, Cyclin-dependent kinases concentration is?

Answer 14

Stable.

Question 15

Which are the three main Cyclin-dependent kinases complexes?

Answer 15

G1 cyclin-CDK;
S-phase cyclin-CDK;
Mitotic cyclin-CDK (also known as maturation
promoting factor).

Question 16

G1 cyclin-CDK includes CDK4 and CDK6 (Cyclin D’s). Which are their functions?

Answer 16

Reacts to exogenous signals like growth
factors and mitogen signals. Regulate the
phosphorylation state of the retinoblastoma
tumour suppressor (pRB) in G1, thereby
allowing the expression of genes required
for DNA synthesis.

Question 17

G1 cyclin-CDK includes also CDK2 (Cyclin E). Function?

Answer 17

Important for transition from G1 to S-phase.

Question 18

S-phase cyclin-CDK includes CDK2 and CDK1 (Cyclin A). Functions?

Answer 18

Promotes DNA synthesis. Targets are helicases and polymerases.

Question 19

Mitotic cyclin-CDK includes CDK1 (Cyclin B). Functions?

Answer 19

Important for transition from G2 to M-phase, activates APC/C complex. Regulate G2/M checkpoint.

Question 20

What are cell cycle checkpoints?

Answer 20

Surveillance mechanisms that monitor the order, integrity, and fidelity of the major events of the cell cycle.

Question 21

What are the major events of the cell cycle that has to be monitored?

Answer 21

growth to the appropriate cell size;
the replication;
integrity of the chromosomes;
accurate segregation at mitosis.

If the presence of a defect is detected, the arrest of cell
cycle progression takes place.

Question 22

G1/restriction checkpoint checks for?

Answer 22

Cell size, nutrients, growth factors, DNA

damage (environmental factors). Primary decision point.

Question 23

If damage is found in G1/restriction check?

Answer 23

G1 arrest and/or cell enters G0 phase

non-dividing state

Question 24

The S-phase checkpoint is?

Answer 24

A surveillance mechanism, that responds to DNA damage (spontaneous mutations).

The stabilization of DNA replication forks, which is critical for cell survival and genome stability.

A checkpoint is a cascade of signalling events that puts replication on hold until a problem is resolved.

Question 25

G2-phase checkpoint?

Answer 25

DNA damage checkpoint serves to prevent the cell from entering cell division (M-phase) with genomic DNA damage. In response to extensive DNA damage, p53 activates gene expression for specific proteins to induce apoptosis.

Question 26

M-phase checkpoint?

Answer 26

Check for the mitotic spindle assembly. Prevents separation of the duplicated chromosomes until each chromosome is properly attached to the spindle apparatus. Arrest anaphase in the case of mistake.

Question 27

What is P53 protein?

Answer 27

Nuclear DNA-binding phosphoprotein, transcription factor.

Question 28

What is P53 protein able to do and when it is activated?

Answer 28

Is able to bind specific DNA sequences. | Is activated by increasing the protein's half-life and the rate of translational initiation of its mRNA.

Question 29

Cell aging: cellular senescence is?

Answer 29

Irreversible arrest of cell proliferation. The senescence arrest is considered irreversible. Two main pathways are involved - p53/p21 and p16/pRB.

Question 30

What is apoptosis?

Answer 30

Form of cell death, also known as programmed cell death is a normal phenomenon, occurring frequently in a multicellular organism.

Question 31

Apoptosis takes place in?

Answer 31

Embryonic development, Adult human body – cells with genomic damage, senescent cells, cells which are not required anymore. Human diseases – overactive initiation of apoptosis (type 1 diabetes).

Question 32

What are caspases?

Answer 32

A family of proteases which are responsible for triggering apoptotic changes in the cell. The protease cascade is irreversible - once a cell reaches a critical point along the path to destruction, it cannot turn back

Question 33

Apoptosis can be initiated by two different pathways:

Answer 33

Extrinsic pathway – extracellular messenger protein called tumor necrosis factor (TNF). Intrinsic pathway – activation is regulated by Bcl-2 proteins.

Question 34

After the cell death pathway is activated what happens to the cell?

Answer 34

``` The cell shrinks and condenses. The cytoskeleton collapses. The nuclear envelope disassembles. The nuclear DNA breaks up into fragments. The cell surface is altered. ```

Question 35

DNA repair process exists in?

Answer 35

Both in prokaryotes and eukaryotes

Question 36

Control of DNA repair is closely tied to?

Answer 36

regulation of the cell cycle.

Question 37

What is mismatch repair (MMR)?

Answer 37

Repair DNA REPLICATION ERRORS – remove base mismatches and small insertion/deletion loops. The mismatch repair mechanism is strand-specific.

Question 38

What is Nucleotide excision repair (NER)?

Answer 38

Repairs DNA damages inducted by ENVIRONMENTAL FACTORS – radiation, mutagens (including chemical). Important mechanism in excision of UV light inducted DNA damage.

Question 39

What is Base excision repair (BER)?

Answer 39

Removes damaged BASES in DNA sequence. Responsible for removing small, non-helix-distorting errors.

Question 40

BER (base excision repair) is initiated by?

Answer 40

DNA glycosylase that recognizes and removes the damaged base. Two pathways exists: short (removes one base lesions) long (removes 2-10 base lesions)

Question 41

Homologous recombination repair (HR) | and Non-homologous end joining (NHEJ) can repair?

Answer 41

Both can repair DOUBLE-STRAND BREAKS (DSB). Homologous recombination repair (HR) uses a homologous DNA TEMPLATE and is highly accurate. Non-homologous end joining (NHEJ) fixes the broken ends without using a template and is often accompanied by loss of some nucleotides. NHEJ being more active in G1 and HR dominating during S and G2 phases.

Question 42

Which two repair pathways exists for NER (nucleotide excision repair)?

Answer 42

Two repair sub-pathways exists - one for transcriptional active DNA (TC-NER) and one for global genomic (GG-NER).

Question 43

How does the progression of the cell cycle prior restriction checkpoint differ from cell cycle progression after the restriction checkpoint?

Answer 43

After the restriction checkpoint the progression of the cell cycle is no longer depending on growth factors!

Question 44

The binary fission begins after initiation of?

Answer 44

Mass is reached and DNA replication is initiated.