5) The Mitotic Cell Cycle

Question 1

state 5 of the chromosome’s essential structures ?

Answer 1

• DNA
• Histone proteins
• sister chromatids
• centromere
• telomere

Question 2

what is the function of the centromere ?

Answer 2

holds the two chromatids together

Question 3

what is the function of telomere ?

Answer 3

(a region of repetitive DNA sequences at the end of a chromosome.)
- prevents genes from being lost during DNA replication.
- Telomeres protect the ends of chromosomes from becoming frayed or tangled.
- Each time a cell divides, the telomeres become slightly shorter.

Question 4

what is the function of histone proteins ?

Answer 4

• provides structural support to the chromosome.
• responsible for DNA packing (the DNA wraps around the histones. Histones are positively charged proteins and hence can easily bind to negatively charged DNA)
• during prophase, forms strands that fold/twist together to form chromatid.

Question 5

what are sister chromatids ?

Answer 5

identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere

Question 6

give basic overview of mitosis

Answer 6

• produces genetically identical daughter cells
• produces DIPLOID cells
• produces 2 cells

Question 7

state 4 main roles of mitosis

Answer 7

-Growth
● Replacing dead or damaged cells
● Repairing damaged tissue (via cell replacement)
● Asexual reproduction

Question 8

state the 3 stages of cell cycle (including the 3 stages for interphase + 4 stages for mitosis)

Answer 8

• interphase (G1, S, G2)
• mitosis (prophase, metaphase, anaphase, telophase)
• cytokinesis

Question 9

explain the G1stage of interphase

Answer 9

o G1 - the cell receives a signal committing the cell to replicate DNA,
- the cell grows and makes proteins & mRNA.
- produces cell organelles (mitochondria, er)

Question 10

what happens during cytokinesis ?

Answer 10

• the parent and replicated organelles move to opposite sides of the cell
• the cytoplasm divides thus producing two daughter cells.

Question 11

what are stem cells ?

Answer 11

cells produced by mitosis that are undifferentiated, (which can be made into specialised cells by differentiation)
- can divide unlimited number of times

Question 12

what causes cancer ?

Answer 12

• uncontrollable cell division
• formation of a mass of cells (tumour)

Question 13

explain prophase (Present)

Answer 13

• nucleolus disappears
• chromosomes condense
• centrioles move to opposite poles (where they form poles of spindle)

Question 14

explain metaphase (Middle)

Answer 14

• spindle fibres attached to the centromere.
• spindle line up at equator.
• each centrosome reaches a pole.
• nuclear membrane disappears.

Question 15

explain anaphase (Apart)

Answer 15

• microtubules pull on spindles
• centromeres make a V shape
• chromatids separated and move to opposite poles –> turn into chromosomes

Question 16

explain telophase (Two nuclei)

Answer 16

• spindle fibres disintegrate
• chromosomes uncoil/uncondense.
• nuclear envelope & nucleolus reforms

Question 17

explain the S stage of interphase

Answer 17

o Synthetic - DNA replication (2 copies of DNA made),
- chromosome no. also doubles, - histone synthesis, attach to DNA.
- each chromosome becomes 2 chromatids.

Question 18

explain the G2 stage of interphase

Answer 18

o G2 - cell replication for mitosis.
- cell growth
- protein & cell organelle synthesis.
- mitochondria and chloroplasts divide.
- spindle begins to form.

Question 19

explain the difference of cytokinesis in animals & plants

Answer 19

animals :
-cytoplasm separates by in-tucking of the cell surface membrane at equator of spindle.
- “pinches” cytoplasm in half

plants :
- golgi forms vesicles of new cell wall materials
- these collect along the line of the equator of the spindle
- vesicles merge (forming new cell surface membrane & cell walls)

Question 20

formula for mitotic index

Answer 20

number of cells in mitosis (chromosomes can be seen) / total number of cells

Question 21

what can mitotic index be used for ?

Answer 21

• diagnose cancer
• assess effectiveness of treatment (eg: radiation) before, or during period of time

Question 22

what is a cancer causing agent

Answer 22

carcinogen (in uv radiation, cigarette smoke, x rays)

Question 23

state the substances used to synthesise DNA during the S phase

Answer 23

• atp
• nucleotides
• DNA polymerase

Question 24

basics of cytokinesis in plant cells (3)

Answer 24

• cytoplasm divides
• cell plate forms across equator
• cell wall forms

Question 25

function of spindle fibre

Answer 25

• orientates chromosomes at equator
• movement of chromatids to opposite poles