Week 10 - mitosis and cell division

Question 1

Cell division - Binary fission

Answer 1

• carried out by prokaryotic cells

Question 2

Cell division - Mitosis

Answer 2

• carried out by most eukaryotic cells, resulting in the formation of identical daughter cells

Question 3

Cell division - Meiosis

Answer 3

• special type of division which produces non-identical daughter cells w/ half the DNA of parent cell

Question 4

Cell division - Bacterial

Answer 4

• no sexual life cycle, reproduction is simple
• single, circular bacterial chromosome is rep.
• replication begins @ origin of replication & proceeds bidirectionally to site of termination
• new chromosomes are partition to opposite ends of cells
• septum forms to divide the cell into 2 cells

Question 5

human genome

Answer 5

• CHROMOSOMES carry genes in linear order
• 23 chromosome pairs: 22 pairs of AUTOSOMES, 2 sex chromosomes
• SOMATIC CELLS have all 23 pairs of chromosomes

Question 6

Chromosomes - eukaryotic

Answer 6

Composed of chromatin

• a long thin mixture of DNA & protein
• chromatin can be folded & coiled to form chomosomes
• nucleosome = histone proteins + DNA

Question 7

Centromeres

Answer 7

• special region of the chromosome where the two copies of DNA become attached using cohesins
• location where the chromatids are attached to the mitotic spindle via KINETOCHORES

Question 8

Telomeres

Answer 8

• region of highly repetitive DNA sequence at the end of telomeres which ‘seals’ the end of chromosomes & prevents it being joined to other chromosomes

Question 9

Cell cycle

Answer 9

INTERPHASE

1. G1 (gap phase 1)
   - primary growth, phase, longest phase
2. S (synthesis)
   - replication DNA
3. G2 (gap phase 2)
   - growth & prep. organelles replicate microtubules organise DNA copies are checked
4. M (mitosis)
5. C (cytokenisis)
   - separation to form 2new cells

Question 10

Cell cycle - duration

Answer 10

• fruit fly embryo = 8min
• mature cells take longer
  → typical mammalian cell = 24hrs
  → liver cells take more than a year
• growth occurs during G1, G2, S phases
  → M phase takes 1hr
• most variation in length of G
  → resting phase G0 - cells spend more/less time here

Question 11

interphase

Answer 11

G1, S & G2 phases

G1: cells undergo major portion of growth

S: replicate DNA

G2: chromosomes coil more tightly using motor proteins; centrioles replicate; tubulin synthesis

Question 12

Kinetochore

Answer 12

• attachment site of microtubules

- consists of specialised proteins that bind tightly & specifically to the chromosome centromeres

Question 13

Microtubules

Answer 13

• microtubules are filamentous structures within cells
• aid movement, organisation of cellular structure & intracellular transport, cilia and flagella and CELL DIVISION
• made of protein called TUBULINS (alpha and beta)

Question 14

prophase

Answer 14

Individual condensed chromosomes first become visible w/ light microscope
- condensation continues throughout prophase

Spindle apparatus assembles

• 2 centrioles move to opposite poles forming spindle apparatus (no centrioles in plants)
• asters- radial array of microtubules in animals

nuclear envelope breaks down

Question 15

prometaphase

Answer 15

transition occurs after disassemble of nuclear envelope

microtubule attachment

• 2nd group grows poles & attaches to kinetochores
• each sister chromatid connected opposite poles

Chromosomes begin to move to centre of cell-congestion

• assembly & disassembly of microtubules
• motor proteins at kinetochores

Question 16

metaphase

Answer 16

Alignment of chromosomes along metaphase plate

• not an actual structire
• future axis of cell division
• chromosomes are attached to opposite poles & under tension

Question 17

anaphase

Answer 17

• begins when centromeres split
• key event: removal of cohesion proteins from al chromosomes
• sister chromatids pulled to opposite poles
• 2 forms of movement
  → anaphase A: kinetochores pulled towards poles
  → anaphase B: poles move apart

Question 18

telophase

Answer 18

• spindle apparatus disassembles
• nuclear envelopes forms around each set of sister chromatids → now called chromosomes
• chromosomes begin to uncoil
• nucleolus reappears in each new nucleus

Question 19

G0 & G2

Answer 19

• most cells of the human body are actually in G0 phase (non-dividing)
• some cells in humans may never divide while others can be “triggered” to go from G0 back to G1
• if a cell receives a ‘go’ signal to divide it will usually complete G1, S G2 & M phase

Question 20

Cytokenesis

Answer 20

• cleavageof the cell into equal halves
• animal cells: constriction of actin filaments produces a cleavage furrow
• plant cells: cell plate forms between nuclei
• fungi: nuclear membrane does not dissolve; mitosis occurs within the nucleus ; air of nucleous occurs w/ cytokenesis

Question 21

Cell cycle - checkpoints

Answer 21

1 G1/S checkpoint :

• decides to divide
• primary point for external sig. influence

2. G2/M checkpoint:
   - commited to mitosis
   - DNA replication complete
   - Assess success of DNA replication
3. Late metaphase (spindle) checkpoint
   - cells ensure that all chromosomes are attached to the spindle

Question 22

cancer

Answer 22

• unrestrained, uncontrol growth of cells failure of cell cycle control