Cell Bio- Cell Cycle

Front 1

What is the cell cycle?

Back 1

A sequence of coordinated processes leading from one cell division to the next cell division.

Front 2

What is required for a division producing a more or less equal daughter cell?

Back 2

Doubling of the genetic material and other functional capacities of the cell during the cell cycle

Front 3

2 main phases of the cell cycle with subsequent sub- phases:

Back 3

1. Nuclear division & cell division (cytokinesis)
- Mitosis/ Meiosis

2. Interphase:
- G1 phase
- S phase
- G2 phase

Front 4

Characteristic morphological and physiological changes during cell cycle:

Back 4

Blebs and microvilli, rounding when entering mitosis, RNA synthesis and protein synthesis

Front 5

Duration of cell cycle of early embryonic cells:

Back 5

Shortened

Front 6

Cycles within the cell cycle:

Back 6

1. DNA synthesis cycle
2. Nuclear division cycle
3. Growth cycle
4. Cell division cycle

Front 7

Examples of independent functioning of the cycles:

Back 7

Egg cleavage, meiosis, endoreduplication

Front 8

Endoreduplication
a) What?
b) Function:

Back 8

a) Duplication of genome without mitosis

b) Usual in eukaryotes, results in increasing of nuclear DNA content permitting amplification of the genome of specialized cells

Front 9

DNA replication
a) In which phase?
b) Organization of DNA replication in eukaryotes:

Back 9

a) S phase

b) DNA replication of the chromosome is organized within replication units; replication fork and replication origin.

Front 10

DNA replication
a) Enzymes
b) Mechanism (5)

Back 10

a) DNA helicase: unwinding of double- stranded DNA, DNA polymerase: DNA replication per se, Primase: primer

b) 1. Leading strand: DNA polymerase- δ 3´-> 5´replication (continuos)
2. Lagging strand: DNA polymerase α replicates 5´-> 3´ (discontinuous, Okazaki fragments)
3. DNA polymerase β, DNA ligase: removal of primers
4. Topioisomerase ii: unwind DNA at the place where the replication fork meets
5. Telomerase: adds TTAGGG nucleotides in repeated sequences in the telomere region to prevent loss of coding sequences of DNA

Front 11

Are mitosis and cytokinesis usually joined processes?

Back 11

Yes

Front 12

How much do chromosomes condense during nuclear division:

Back 12

10 000x

Front 13

Mitotic phases and their characteristics: (5)

Back 13

1. Prophase: chromosone condensation (two sister chromatids)
2. Prometaphase: disintegration of nuclear envelope (nuclear lamina: lamins), microtubules of mitotic spindle attaches to the chromosomes (kinetochor)
3. Metaphase: chromosomes are in equatorial position
4. Anaphase: separation of sister chromatids---> loosened chromatids are pulled towards the poles of the mitotic spindle (anaphase A, anaphase B)
5. Telophase: reintegration of nuclear envelopes

Front 14

Anaphase A:

Back 14

Chromatids abruptly separate and move towards the spindle poles. This is achieved by shortening of spindle microtubules, with forces mainly being exerted at the kinotechores.

Front 15

Anaphase B:

Back 15

1. When the chromatids are fully separated. Involved polar microtubules elongating and sliding relative to each other to drive the spindle poles to the opposite sides of the cell.

2. 3 forces: kinesin a molecular motor protein that are attached to polar microtubules and push microtubules past each other.
- Dyenin pulls centromere towards the cell cortex.
- And lengtening the polar microtubules at the + end.

Front 16

Meiosis
a) What?
b) Why is genetic recombination realized?
c) Main parts of meiotic cell cycle:

Back 16

a) Transfer from diploid generation to haploid generation (in animals production of haploid gametes)
b) Because of crossing over
c) Meiosis I, meiosis II

Front 17

Cytokinesis
a) Starts:
b) What:

Back 17

a) Mostly during mitotic anaphase
b) Enables approximately equal division of other cellular components (cytoplasm and organelles). New cellular boundary is formed at the equator of the mitotic spindle

Front 18

Cytokinesis Mechanism
a) Animal cells:
b) Cells of higher plants:
c) Algae and fungi:

Back 18

a) Process of cleaving (furrowing) by the contractile ring (non- muscle myosin II and actin filaments)

b) New cell boundary is formed from a cell plate from vesicles of ER (phragmoplast)

c) Invagination of plasma membrane

Front 19

Doubling of functional capacities of the cell
a) Two ways
b) e.g
c) Organelles duplicated:

Back 19

a) Precise duplication of nuclear DNA vs. doubling of other cytoplasmic components (including organells)

b) 1. Synthesis of proteins and RNA
2. Duplication of organelles

c) 1. Ribosomes
2. Simple membrane organelles: ER, Golgi
3. Complex "cell like" organelles: mitochondria and chloroplast

Front 20

Resting cells (G0):

Back 20

Non dividing cells which are NOT in the cell cycle

Front 21

G0 phase
a) Transition into G0 phase (Two ways:)
b) Physiological characteristics if G0 phase

Back 21

a) 1. Permanent transition to G0 phase is connected with the transition to terminal differentiation stages.
2. The transition between cell cycle (G1) and G0 phase in both directions is connected with changes in cell physiology and it requires a certain time period

b) Changes of the Myc protein level

Front 22

Mechanism of cell cycle control
a) Activation
b) Progression

Back 22

a) G0--> G1. Activation is started by the expression of primary response genes and after the expression of secondary gene cascade

b) Progression: G1--> S-->G2--> M--->....
G1 block, G2 block

Front 23

Mechanism of activation
1. Expression of primary response genes (early response genes)
a) How:
b) Important primary response genes:
c) Function of primary response genes:

2. Expression of secondary genes
a) What?
b) Which?

Back 23

1. a) Not mediated. It is a direct response to stimulatory signal (expression/ synthesis of a protein mediator is not required)
b) c-fos, c- jun, c- myc
c) Primary response genes code transcription factors which regulate expression of secondary genes. These transcription factors also regulate expression of primary response genes---> enhancement of the signal

2. a) Secondary genes represent effector genes of the cell cycle. Their expression has a character of cascade.
b) Genes coding CDK, genes coding cyclins, c-myb and p53 gene

Front 24

Rb protein function in activation:

Back 24

Positive feedback loop---> enhancement of the signal stimulating activation

Front 25

1. c- myc:
2. c-fos & c- jun:

Back 25

1. Crucial gene of activation
2. Fos protein & Jun protein are transcription factors (they form heterodimer)

Front 26

Mechanism of progression
a) Important enzymes/ proteins:
b) Requirements:
c) Mechanism:

Back 26

a) Cyclin dependent kinase (CDK) (serine- threonine kinase) and cyclin

b) Binding of protein cyclin is necessary for CDK activation--> CDK- cyclin complex. CDK is the CATALYTIC subunit and cyclin is the REGULATORY subunit. Cell cycle is regulated by a system of several CDKs and relevant cyclins

c) Linear growth of cyclin level---> activation of CDK---> induction of relevant cell cycle process (transition to S phase, transition to mitosis)---> degradation of cyclin---> inactivation of CDK....

Front 27

Complex cyclin E/ CDK2:

Back 27

Regulation of transition into S phase

Front 28

Complex cyclin B/CDK1:

Back 28

Regulation of transition to mitosis

Front 29

CDK inhibitors:

Back 29

Tools of progression that inhibit the CDK-cyclin complex by binding to it. (e.g: p21)

Front 30

DNA damage effect on progression:

Back 30

DNA damage--->protein p53 activation---> induction of protein p21 expression---> inhibition of cyclin E/CDK2---> block transition into S phase. p53 enables to block potentially very dangerous replication of damaged DNA

Front 31

M phase starts with:

Back 31

Duplication of centromers

Front 32

Are chromosome translocation pathological?

Back 32

Yes except from in crossing over in prophase I of meiosis