cell cycle

Question 1

name the different stafes of the cell cycle

Answer 1

1. interphase:
   G1 = cell increases in size
   S = DNA replicated semi conservatively
   G2 = cell ready for division, new organelles synthesised
2. nuclear vision: mitosis or meiosis
3. cell division/ cytokinesis: division of cytoplasm

Question 2

define a gene

Answer 2

section of DNA that codes for a specific polypeptide

Question 3

what is a chromosome?

Answer 3

independent DNA molecule (chromatid) supercoiled into a condensed form
- when duplicated, are attached at the centromere; producing identical sister chromatids

Question 4

homologous chromosomes

Answer 4

same genes
same loci
dofferent alleles of the gene (one maternal, one paternal)

Question 5

diploid

Answer 5

somatic (body) cels in homologous pairs
2n = 46
two copies of each chromosome

Question 6

haploid cells

Answer 6

one copy of each chromosome
gametes

Question 7

what is mitosis used for?

Answer 7

• repairs damaged tissues
• increasing cell numbers/growth of organism
• replacement of worn out cells
• produces genetically identical daughter cells

Question 8

describe the features of prophase

Answer 8

• nuclear membrane begins to breakdown
• centrioles move to opposite poles of the cell
• chromatins supercoils and condense in chromosomes

Question 9

describe the features of metaphase

Answer 9

• spindle fibres form
• spindle fibres attach to the centromere of chromosomes
• chromosomes align in the equator

Question 10

describe the features of anaphase

Answer 10

• spindle fibres shorten and contract
• centromere splits
• sister chromatids are separated to opposite ends of the pole

Question 11

describe the features of telophase

Answer 11

• nuclear membrane reforms
• chromosomes unwind

Question 12

describe the appearance and behaviour of chromosomes during mitosis

Answer 12

• during prophase, chromosomes supercoil and condense to become visible
• chromosomes appear as 2 identical sister chromatids joined by centromere
• metaphase, chromosomes align in the middle/equator of the cell
• chromosomes attach to spindle fibres
• by centromeres
• anaphase, centromere splits
• sister chromatids are pulled to oppsoite poles of cell, making a V-shape
• during telophase, chromatids uncoil and become thinner

Question 13

tumour suppressor genes

Answer 13

code for proteins that slow down cell cycle

Question 14

proto-onco genes

Answer 14

code for proteins that speed up cell cycle

Question 15

One method of treating cancer (AO2)

Answer 15

• drugs that inhibit cell division
• stop DNA replication/spindle formation/cytokinesis

Question 16

BINARY FISSION

Answer 16

• NOT mitosis
• replication of circular DNA
• replication of plasmids
• cytokinesis (division of cytoplasm) to produce 2 daughter cells

Question 17

mitotic index

Answer 17

number of cells with visible chromosomes divided by total number of cells
greater value = faster rate of CD

Question 18

where does mitosis occur in plants?

Answer 18

meristem

Question 19

why must a plant sample be soaked in HCl

Answer 19

breaks cellulose cell wall so stain can enter
OR
tissue squashed to one cell thick so light can pass through

Question 20

calculating length of time each stage of mitosis occurs

Answer 20

total numver of visible chromosomes divied by total number of cells
multiplied by time of one cycle (minutes)

Question 21

serial dilution

Answer 21

M1V1 = M2V2
M1 = DESIRED CONC
V1 = DESIRED VOL
M2 = ORIGINAL CONC
V2 = UNKNOWN VOL

Question 22

meiosis

Answer 22

• produces haploid gametes
• four genetically different daughter cells produced
  in first division, homologous chromosomes pair up and are separated
  in second division, chromatids are separated

Question 23

describe and explain what the student should have done when counting cells to make sure the mitotic index he obtained for the root tip was accurate

Answer 23

• repeat count to ensure figures are correct
  OR
• examine many cells to ensure representative sample

Question 24

meiosis results in cells with haploid number of chromosomes and show genetic variation. Explain how.

Answer 24

• homologous chromosomes pair up
• chromosomes are arranged in any order
• independent segregation
• crossing over
• equal sections of genes are swapped between chromosomes
• produces a new combination of alleles
• chromatids separated at meiosis

Question 25

describe the process of crossing over and explain how it increases genetic diversity

Answer 25

• homologous chromosomes form a bivalent pair
• chiasmata form
• equal lengths of the allele are exchanged
• produces new combination of alleles

Question 26

give 2 diferences between mitosis and meiosis

Answer 26

mitosis vs meiosis
- one division vs 2 divisions
- daughter cells genetically identical vs different
- 2 cells produced vs 4 cells produced
- diploid to diploid/haploid to haploid vs diploid to haploid
- separation of homologous chromosomes only in meiosis
- crossing over only in meiosis
- independent segregation only in meiosis

Question 27

calculaing the number of different chromosome combinations with meiosis wthout crossing over

Answer 27

2n
n = number of chromosomes
eg: if n=2 then 4
n=3 then 8