1.6 Cell Cycles

Question 1

What must a cell do before it can divide?

Answer 1

• make new organelles
• copy DNA in DNA replication
• synthesise new proteins
• cell growth

Question 2

What is a chromosome?

Answer 2

• a long, thin structure of DNA and protein in the nucleus of eukaryotic cells carrying genes

Question 3

When can you see chromosomes?

Answer 3

• only become visible under a microscope when chromatin condenses prior to division
• sister chromatids attached by the centromere

Question 4

What is the role of the telomere?

Answer 4

• act as a cap/buffer and prevents DNA degeneration

Question 5

What are characteristics of supercoiled chromosomes?

Answer 5

• can’t perform usual functions
• easily segregated
• can be easily stained
• increase in size from 30nm to 500nm

Question 6

What are the 3 stages of interphase?

Answer 6

G1: cell growth and proteins produced
S: synthesis and replication of sister chromatids
G2: more growth and new organelles made

Question 7

Stages of mitosis

Answer 7

IPMAT + cytokinesis

Question 8

Explain prophase

Answer 8

• chromosomes in replicated form - 2 sister chromatids joined by centromere and condensed giving a thicker, shorter appearance
• nuclear envelope and nucleolus break down
• centrosomes move to opposite poles of cell and a spindle starts to from
  —> spindle fibres made from protein microtubule, tubulin

Question 9

Explain metaphase

Answer 9

• centrosomes reach a pole
• chromosomes line up on the equator of the cell and attach to spindle fibres by their centromeres

Question 10

Explain anaphase

Answer 10

• centromeres joining sister chromatids split as motor proteins walk along the spindle, causing chromosomes to be pulled apart as chromatids
• taken to opposite poles of the cell centromere first

Question 11

Explain telophase

Answer 11

• separated chromosomes reach the opposite poles of the cell
• nuclear envelope forms around the 2 sets of duplicated chromosomes
• 2 identical nuclei form, and once cytokinesis occurs, 2 identical daughter cells are made

Question 12

What is cytokinesis?

Answer 12

Division of the cytoplasm following divisin

Question 13

How does cytokinesis occur in animal and plants?

Answer 13

Animal: constriction of the parent cell around the equator from the outside inward - cleavage furrows
Plant: droplets of cell wall material (cellulose deposit) form a cell plate across the equator of a parent cell from the centre outward

Question 14

Significance of mitosis

Answer 14

Generic stability: 2 GI cells that are exact replicas of parents
Growth + repair: produce new cells, grow repair and replace, in adult mammals tissues (ie skin) are replaced daily
Asexual reproduction: unicellular organisms produce identical offspring - clones.

Question 15

Explain the significance of mitosis in terms of damage and disease

Answer 15

• uncontrolled CD leads to tumours and therefore cancer ie tumour suppressor and proto-oncogenes
• cell cycle length is controlled by genes, so when they’re damaged the cell cycle is unregulated
• timely replacement of cells + tissue

Question 16

Role of tumour suppressor and proto-oncogene genes

Answer 16

• tumour suppressor: slow and regulate CD, if mutate then don’t regulate so lead to tumour
• proto-oncogene: encourage cell growth and repair, mutate means don’t regulate so tumour forms

Question 17

Drugs that treat cancer

Answer 17

Cisplatin: prevents DNA replication to halt tumour growth
Vinca alkaloids: inhibit metaphase by interfering with spindle formation

Question 18

Ploidy level

Answer 18

The number of complete sets of chromosomes in an organism
- humans are diploid
- 1 = haploid

Question 19

Explain meiosis 1

Answer 19

• PROPHASE 1: dna condenses and becomes visible, chromosomes arranged in homologous pairs (bivalent). Crossing over of non-sister chromatids may occur (wrap @ chiasmata and lead to genetic variation). Centrioles migrate to poles and spindle is formed as the nucleolus and nuclear envelope break down
• METAPHASE 1: bivalents line up along equator with spindle fibres attached to centromere. Position each other independently- independent assortment (GV)
• ANAPHASE 1: homologous pairs separated as microtubules pull chromosomes to opposite ends of spindle centromere first. Centromeres do not divide.
• TELOPHASE 1: chromosomes arrive at poles. Spindle fibres break down and nuclear envelopes form around 2 groups, and nucleolus reforms. (Some plant cells go to meiosis 2 without reformation)

Question 20

Explain meiosis 2

Answer 20

• PROPHASE 2: centrioles separate and organise new spindle and right angle to old. Nuclear envelope and nucleolus break down.
• METAPHASE 2: chromosomes line up at equator which chromosomes attach to spindle fibre by centromere. Independent assortment occurs again
• ANAPHASE 2: centromeres divide and individual chromatids pulled to opposite poles centromere first, creating 4 groups of chromosomes with half the number of chromosomes of the parent cell
• TELOPHASE: nuclear membrane and nucleolus reforms around each group of chromosomes. Cytokinesis occurs. 4 gametes are made

Question 21

Cells produced by meiosis are … and mitosis are …

Answer 21

• haploid
• diploid

Question 22

What is the significance of producing haploid eggs?

Answer 22

Genetic variation via fertilisation of a zygote and restore diploid number

Question 23

Explain diff between cells produced in mitosis and cells in meiosis

Answer 23

• 2 v 4
• diploid v haploid
• GI v GD

Question 24

Importance of meiosis

Answer 24

• genetic variation due to genetically different cells
• restore diploid state as meiosis produce haploid