topic 2A: cell division

Question 1

1. interphase

Answer 1

-the DNA REPLICATES semi conservatively (s phase)
-leading to 2 CHROMATIDS (identical copies) joined at a CENTROMETRE
-the number of ORGANELLES and volume of CYTOPLASM increases, protein synthesis at G1 and G2 phase

Question 2

2. mitosis

Answer 2

the NUCLEUS DIVIDES to produce 2 nuclei with IDENTICAL copies of DNA produced by the parent cell

Question 3

3. cytokinesis

Answer 3

-the CYTOPLASM and CELL MEMBRANE divides to form 2 new genetically identical daughter cells

Question 4

describe the behaviour of chromosomes during stage 1 PROPHASE of mitosis and the role of spindle fibres attached to centrometres in the separation of chromatids

Answer 4

STAGE 1
-chromosomes condense becoming shorter and thicker so visible and apear as 2 sister chromatids joined by a centromere
-the nuclear envelope breaks down
-the CENTRIOLES (tiny bundles of protein) move to opposite poles forming SPINDLE (protein fibres) NETWORK
-(spindle fibres start to ATTACH to chromosomes by their CENTROMERES)

Question 5

stage 2 METAPHASE

Answer 5

-Spindle fibres ATTACH to chromosomes by their CENTROMETRES
-Chromosomes align along EQUATOR

Question 6

stage 3 ANAPHASE

Answer 6

-spindle fibres shorten and contract
-CENTROMERE DIVIDES
-pulling chromatids (from each pair) to opposite POLES of cell

Question 7

stage 4 TELOPHASE

Answer 7

-chromosomes uncoil, becoming longer and thinner
-nuclear envelopes reforms, so there are now 2 nuclei
-spindle fibres and centrioles break down

Question 8

explain the importance of mitosis in the life of an organism

Answer 8

Parent cell divides to produce 2 genetically identical daughter cells for:

-GROWTH of multicellular organisms by increasing cell number
-REPLACING cells to repair damaged tissues
-ASEXUAL reproduction

Question 9

Describe how tumours and cancers form

Answer 9

-a mutation in the DNA / genes thats controlling mitosis can lead to uncontrolled cell division
-a tumour formed if this results in mass of abnormal cells, invades surrounding tissue
-MALIGNANT tumour: cancerous, can spread (metastasis)
-BENIGN tumour: non-cancerous

Question 10

Suggest how cancer treatments control rate of cell division

Answer 10

-some disrupt SPINDLE FIBRE ACTIVITY AND FORMATION:
-so chromosomes can’t attach to spindle by their CENTROMERE
-so chromatids can’t be SEPARATED to opposite poles (no ANAPHASE)
-so prevents / slows MITOSIS

-some prevent DNA REPLICATION during interphase:
-so can’t make 2 COPIES of each chromosome (CHROMATIDS)
-so prevents and slows MITOSIS

-these are MORE EFFECTIVE against cancer cells due to uncontrolled cell division, but also disrupts the cell cycle of rapidly dividing healthy cells

Question 11

Describe how prokaryotic cells replicate

Answer 11

binary fission in prokaryotic cells involve:
1. REPLICATION of circular DNA
2. REPLICATION of PLASMIDS
3. DIVISION of CYTOPLASM to produce 2 daughter cells, each with a SINGLE copy of circular DNA and a VARIABLE number of copies of plasmids

Question 12

Describe how viruses replicate

Answer 12

virus are NON LIVING and DO NOT UNDERGO CELL DIVISION:

1. ATTACHMENT PROTEINS attach to complementary RECEPTORS on host cell
2. Inject viral NUCLEIC ACID (DNA/RNA) into host cell
3. Infected HOST CELL REPLICATES virus particles:
   a. Nucleic acid replicated
   b. Cell produces viral protein / capsid / enzymes
   c. Virus assembled then released