Unit 2 - Cell Cycle Flashcards Preview

Molecular Medicine > Unit 2 - Cell Cycle > Flashcards

Flashcards in Unit 2 - Cell Cycle Deck (89)
Loading flashcards...
1

key tasks for proliferating cells

  • replicate entire genome (ONCE) - fertilised egg → entire organism, cellular regeneration, in response to injury
  • separate duplicated chromosomes equally into daughter cells (UNLIKE stem and germ cells)
  • co-ordinate cell growth and proliferation by ensuring cells have enough energy and metabolites before entering into the processes

2

key events of the cell cycle

3

Gap phase G1

cell growth and regulatory events (checkpoints)

4

synthesis phase (S)

DNA replication occurs

5

gap phase 2 G2

cell growth and regulatory events (checkpoints)

6

M phase - mitosis

chromosomes are segregated and cells divide

7

when may cells exit cycle into G0

if terminally differentiated, senescent or if inhibitory signals are received

8

cell cycle timing

varies between cells depending on function and origin

Our genetic material is very large and will take a while to duplicate accurately, and segregate it between daughter cells

enzymes are conserved

 

9

DNA polymerases

highly conserved enzymes

require a 3'-OH group for activity and so require a primer

needed to extend DNA strands in a 5' → 3' direction

replicative polymerases = Pol δ and Pol ε

10

DNA replication overview

DNA is unwound and RNA primer molecules bound are synthesised by primase

primers are then extended by replicative polymerases (δ or ε) in a 5' → 3' direction

⇒ lagging strand is discontinuously synthesised

also leads to 'end replication problem' which is solved by telomerase

11

primase function

extend chains of DNA against the template provided by the pre-existing chromosome

12

Okazaki fragments

discontinuous segments being synthesised from RNA primer

13

telomerase function

allow intact replication of RNA ends

arises from the need of our polymerases to have our primer structure

14

steps in DNA synthesis - lagging strand

  1. helicase unwinds DNA, RPA loads - Pol α-primase synthesises a short primer
  2. Pol α displaced and Pol δ/Pol ε loaded
  3. Pol δ/Pol ε extend the primer
  4. downstream primer is removed (nuclease)
  5. Okazaki fragments are ligated

SIMILAR PROCESS OCCURS ON LEADING STRAND, ensuring both strands of DNA molecule are going to be duplicated completely

15

Pol α-primase function

  • Synthesise a short RNA primer against the template provided by the original DNA strand
  • Allow replicate of polymerases (Pol delta or epsilon) to extend in 5' to 3' direction from the 3'-OH in a process that will give rise to the new DNA strand
  • Primer is then removed by nuclease activty
  • Individual extended primers, now the actual DNA sequences, are ligated together again to give a continuous new DNA strand that will base pair with the original DNA strand and will be complementary to it due to extend of polymerase

16

M phase overview

chromosomes condense and attach to microtubules from mitotic spindle

all chromosomes must be attached before sister chromatids can separate

each daughter cell receives 1 set of chromosomes

chromosome segregation is irreversible so this process is highly-regulated

17

what happens when all chromatids have attached to the poles of mitotic spindle

the sister chromatids - duplicated pairs of chromosomes - will separate from one another

(held together after replication but prior to separation during mitosis)

18

6 phases of mitosis

prophase

prometaphase

metaphase

anaphase

telophase

cytokinesis

19

prophase

chromosomes begin to condense

requires condensin and DNA topoisomerase II

the (duplicated) centrosomes separate

histones undergo mitosis-specific modifications

Lose their diffused localised volume and begin to adopt a more tightly packed conformation that is mechanically necessary for them to migrate to opposite poles later in mitosis

intact nuclear envelope

20

what makes up chromatin

histones

21

prometaphase

microtubules from opposite spindle poles (centrosomes) bind chromosomes at kinetochores (waist) to initiate bipolar orientation

nuclear envelope breakdown occurs - can now spread out into the cell

 

22

metaphase

all chromosomes have made bipolar attachemnts to spindle poles

chromosomes align at metaphase plate

23

what is the key tightly-regulated step in mitosis

between metaphase and anaphase

24

anaphase

chromatids separate and move toward the opposite spindle poles - poles separate

nuclear envelope reassembly commences - reassembles around the chromosomes as they move apart

25

telophase

nuclear envelope reassembles around sister chromatids

poleward movement of chromosomes continues

cleavage plane is specified (Plane along which the cytoplasm will eventually separate)

26

cytokinesis

separation of daughter cells

formation of the cleavage furrow by a contractile ring of actin filaments (between the 2 masses of chromosomes)

chromosomes decondense and nuclear structures reform

27

vertebrate centromeres

the primary constriction in higher eukaryote chromosomes

heterochromatin region

centromeric heterochromatin carries the kinetochore

megabase arrays of highly repetitive satellite DNA

chromosomes contain varying amounts of satellite DNA of varying sequence

principal component of human CEN sequences is α-satellite DNA - monomer structure = 171 bp - arranged into complex repeats (2-32 monomers/repeat)

28

principal component of human CEN sequence

 α-satellite DNA

29

key function of centromeric DNA sequence

it carries proteinic structure known as kinetochore

microtubules attach to kinetochore

30

vertebrate kinetochore

complex proteinaceous structure that controls chromosome-microtubule attachment and mitotic spindle assembly

trilaminar structure

kinetochore assembly on centromeric chromatin = temporally-regulated process involving several pathways

controls attachment of kinetochore to the microtubules

inner plate connects to chromosomes