Mitosis/Meiosis/The Cell Cycle

Question 1

Stages of mitosis

Answer 1

IPMAT

Prophase
chromosomes condense, spindle forms, organelles and nuclear envelope disintegrate

Metaphase
chromosomes attach to the spindle and line up on the metaphase plate

Anaphase
centromeres split, chromosomes separate and move to poles

Telophase
chromosomes cluster at poles, organelle and nuclear envelopes reform

Cytokinesis
cytoplasm furrows and the cell divides

Question 2

Meiosis I

Answer 2

reduction division 46 -> 23 homologous chromosomes are separated

Prophase I: LZPDD

leptotene - 2 sister chromatin threads condense, nuclear volume increases

zygotene - synapsis forms (pairing of chromosomes)

pachytene - dyad forms and crossing over occurs

diplotene - longest stage; nuclear membrane disappears, homologous chromosomes separate, formation of synaptonaemal complex (which helps with chromosome pairing and recombination)

diakinesis - division. the 4 parts of the tetrads are visible

(tetrad: foursome formed by 2 homologous chromosomes that have replicated)

Question 3

Meiosis II

Answer 3

equatorial division 23-> 23

sister chromatids are separated producing 4 haploid gametes

Question 4

Variation during meiosis

Answer 4

Crossing over
Independent assortment
Errors in replication

Question 5

Crossing over

Answer 5

exchange of genetic material by a recombinase enzyme

introduces genetic variation

Question 6

Independent assortment

Answer 6

during anaphase I the centromeres DO NOT duplicate and divide
only 1 member of each pair of chromosomes goes into daughter cell
maternal and paternal chromosomes are randomly sorted (independent segregation)

Question 7

Consequences of variation during meiosis

Answer 7

• changes in protein structure and function
• natural variation e.g. eye colour
• inherited/genetic disease e.g. Down’s = trisomy 21
  edwards syndrome = trisomy 18
  patau syndrome = trisomy 13

Question 8

The cell cycle

Answer 8

Interphase
G1
S
G2

Question 9

The cell cycle

Answer 9

Interphase
G1
S
G2
M
G0

Question 10

G1

Answer 10

synthesis of rna and proteins

checkpoint: nutrients, growth factors?

Question 11

S

Answer 11

dna replication

Question 12

G2

Answer 12

dna repair and preparation for mitosis
checkpoint: dna replicated, damage? cell size?

M checkpoint: chromosomes on spindle?

Question 13

Cell cycle checkpoints

Answer 13

the cell cycle is controlled by cdks

progression to the next stage is triggered by phosphorylation and cyclins

G1: cyclin E/cdk2
S: cyclin A/cdk2
G2: cyclin B: cdk1
M: cyclin D/cdk2

Question 14

cdks are inhibited by

Answer 14

p16 and p21

p16 inhibits G1/s
p21 checks cell morphology and dna

cdk mutations cause uncontrolled cell division = cancer

Question 15

DNA replication components

Answer 15

• dna helicase - unwinds dna
• binding proteins - stabilise unwound dna
• dna polymerase - synthesises the leading strand
• rna primase - adds rna primer to okasaki fragments
• dna ligase - joins the okasaki fragments

Question 16

Apoptosis

Answer 16

programmed cell death
normal process
atp dependent
small 200bp dna fragments

Question 17

Necrosis

Answer 17

uncontrolled/necrotic cell death
external factors
no atp
random degradation
inflammatory