1.6 : Cell Division

Question 1

what are the phases of cell division?

Answer 1

G1, S, G2 (interphase) Mitosis, Cytokinesis

Question 2

what occurs in G1?

Answer 2

the first phase of growth :

• cytoplasm is active
• new organelles are formed (synthesis of new organelles in cytoplasm)
• intense biochemical activity of growing cell
• accumulation of energy store before nuclear division occurs again.

Question 3

what occurs during the synthesis (S) phase?

Answer 3

synthesis of the DNA :
-chromosomes are replicated –> chromatids formed (two sister chromatids = replica of chromosome)
(chromatids remain attached until they divide again during mitosis).

Question 4

what occurs in G2?

Answer 4

second phase of growth :

• more growth of cell
• preparation for mitosis
• increase in amount of cytoplasm

Question 5

what phases are there in mitosis?

Answer 5

• prophase
• metaphase
• anaphase
• telophase

Question 6

how does cell division occur in bacteria?

Answer 6

-binary fission –> replication starts at specific gene (the one that translates into the replication-triggering enzyme.

Question 7

what occurs during the interphase? what type of chromosome is dispersed in this phase?

Answer 7

• Chromosomes are actively involved in protein synthesis –> copies of information of a particular gene / group of genes in the form of mRNA –> taken for use in the cytoplasm (ribosomes in cytosol) –> assemble proteins from amino acids –> these are combined in sequences dictated by the information from the gene –> assembled in the form of mRNA.
• compact chromosome - dispersed in interphase = chromatin (only visible during mitosis)

Question 8

what does the nucleolus contain?

Answer 8

contains proteins & mRNA = site of synthesis of ribosomes, which then are dispersed into sytoplasm.

Question 9

how is the cell cycle controlled? how?

Answer 9

• regulated by a molecular control system.
• the cell cycle contains many key checkpoints where signals operate –> these have to be overridden for the cell cycle to continue (key checkpoints at G1, G2, M)

Question 10

what occurs in the G2 checkpoint?

Answer 10

a ‘continue’ signal is received –> allowing the cell to go to M (mitosis) and C (cytokinins)

Question 11

what are the molecular control substances in the cytoplasm of cells?

Answer 11

Kinase and Cyclin.

Question 12

what are Kinases? why are they referred to as CDK?

Answer 12

• enzymes that activate or inactivate other proteins

- kinases are activated by specific cyclins = cyclin-dependent kinases (CDK)

Question 13

what occurs when the cyclin concentration in the cytoplasm increases?

Answer 13

(cyclin concentration changes constantly)

increases –> combine with CDK molecules –> forms a complex –> functions as a mitosis - promoting factor (MPF)

Question 14

what occurs when MPF accumulates?

Answer 14

MPF accumulates –> it triggers chromosome concentration & fragmentation of the nuclear membrane and spindles

Question 15

what occurs in mitosis?

Answer 15

• cell division occurs where the nucleus divides first.
• chromosomes (present in the form of chromatids) –> are separated (pulled apart by spindles) –> then they are accurately distributed between two daughter nuclei.

Question 16

what is metastasis? (cancer)

Answer 16

when the tumor cells break away from the primary tumour, and are carried to other parts of the body causing a secondary tumour to form.

Question 17

when does cancer arise?

Answer 17

cancer arises when the cell cycle operates without its normal control, causing repeated division of cells by mitosis.

Question 18

what is a mutation?

Answer 18

a change in the amount or chemical structure of DNA of a chromosome.

Question 19

what is the name for a ‘cancerous’ and ‘non-cancerous’ tumour?

Answer 19

• malignant (cancerous)

- benign (non cancerous)

Question 20

what is a benign tumour?

Answer 20

a tumour that absorbs nutrients, enlarges and may compress surrounding tissues but doesn’t spread from the site of initiation.

Question 21

what is a malignant tumour?

Answer 21

a tumour that consists of cells that secrete signals triggering the growth of blood and lymph vessels to serve the tumour cells at the expense of other tissues.

Question 22

what are causes of DNA damage?

Answer 22

• ionising radiations.
• non-ionising radiations.
• chemicals (tobacco smoke & asbestos)
• virus infection
• diet.

Question 23

what are proto-oncogenes?

Answer 23

genes that code for the proteins that stimulate the cell cycle.

Question 24

what are tumour-suppressing genes?

Answer 24

genes that code for proteins that stop a cell cycle if damaged DNa is copied.