2LP. Transmission of genetic information from cell to cell in an organism

Question 1

Main features and concept of multicellular cell cycle (phases)

Answer 1

(G0)
G1: cell grows and cytoplasmic organelles are replicated
S: duplication of intact DNA and centrosome
G2: cell forms the materials that make up the spindle.
M: duplicated DNA and centrosome is halved

Question 2

Cell cycle checkpoints

Answer 2

1) Restriction point (end of G1)
- Growth factors
- Nutrients
- Cell size
- DNA damage

2) G2-M transition
- Cell size
- DNA damage
- DNA replication

3) Metaphase-anaphase transition
- Chromosome attachment to spindle

Question 3

M-phase: activation and activity of MPF

Answer 3

MPF: maturation promoting factor

• Cyclin-Cdk complex
• MPF promotes the entrance into mitosis (the M phase) from the G2 phase by phosphorylating multiple proteins needed during mitosis
• MPF is activated at the end of G2 by a phosphatase

Question 4

Events of mitotic phases

Answer 4

See notes

Question 5

Functional parts of chromosomes: telomere

Answer 5

A region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes

Question 6

Functional parts of chromosomes: centromere

Answer 6

A specialized structure on the chromosome, appearing during cell division as the constricted central region where the two chromatids are held together and form an X shape.

Question 7

Functional parts of chromosomes: kinetochore

Answer 7

The place on either side of the centromere to which the spindle fibers are attached during cell division.

Question 8

Functional parts of chromosomes: sister chromatids

Answer 8

The two sister chromatids in a chromosome each consist of 1 DNA molecule (?) and their DNA content is identical
Sister chromatids synthesized in S phase and hang together until anaphase

Question 9

Functional parts of chromosomes: additional protein complex (cohesin and condensin and their role)

Answer 9

Cohesin:
- Protein complex that regulates the separation of sister chromatids during cell division, either mitosis or meiosis. Cohesins hold sister chromatids together after DNA replication until anaphase when removal of cohesin leads to separation of sister chromatids

Condensin:
Large protein complexes that play a central role in chromosome assembly and segregation during mitosis and meiosis

Question 10

Structure and role of centrosome

Answer 10

MTOC: microtubule organizing center
Structure:
- 1 mother centriole (w/appendages) + 1 daughter centriole
- PCM: pericentriolar matrix
- γTuRC: γ tubulin ring found in PCM
- Microtubules attached to γTuRCs

Question 11

The centrosome cycle

Answer 11

Wiki:

1) Centriole synthesis
2) Centrosome Duplication (S)
3) Centrosome Maturation (G2)
4) Centrosome Separation (G2)
5) Centrosome Disorientation
6) Centrosome Reduction

Question 12

Structure of mitotic spindle

Answer 12

Astral MT
- any microtubule originating from the centrosome which does not connect to a kinetochore.

Kinetochor MT:
- attach to the kinetochor of chromosomes

Polar MT: Any of the spindle microtubules that come from each pole and OVERLAP at the spindle midzone

Question 13

Activity of APC

Answer 13

APC is mainly required to induce progression and exit from mitosis by inducing proteolysis of different cell cycle regulators

Question 14

Cytokinesis

Answer 14

Wiki: The process can be divided to the following distinct steps: anaphase spindle reorganization, division plane specification, actin-myosin ring assembly and contraction, and abscission

Question 15

Changes of DNA amount and chromosome number during cell cycle

Answer 15

See notes

Question 16

Types and causes of atypical mitosis

Answer 16

1) Endomitosis
- Nuclear envelope remains intact
- Polythene chromosomes or polyploid cell
2) No cytokinesis
- Multinucleated cell
3) Multipolar division
- Atypical duplication and division of centrosome
- Abnormal chromosome number
4) Bridge formation
- A chromatid is pulled from two poles
- Structural chromosomal aberration (breakage)
5) Non-disjunction
- Lack of kinetochor microtubule attachment
- Abnormal chromosome number

Question 17

Consequences of atypical mitosis

Answer 17

• Tumors (e.g Crocker’s tumor)

Question 18

Methods used to study cell cycle (practice presentation!)

Answer 18

Light microscopy studies
- Mitotic index
- Study of division markers (IHC)
- Detection of S phase
- Fucci (fluorescent, ubiquitination-based cell cycle indicator, Cdt1: repl. inhib. (see in G1), Geminin: Cdt1 inhib (see in S,G2, M))
Flow cytometry
- Shows cell cycle and ploidy

Question 19

Specific division markers

Answer 19

Ki67 Ag
- Cell proliferation (not expressed in G0 phase)

PCNA
- Proliferating cell nuclear antigen (expressed in S phase)

H3P
- Needed for chromosome condensation

Question 20

Detection of S phase

Answer 20

3H-thymidine (autoradiography)

BrDU thymidine analog (IHC)