Mitosis and replication

Question 1

What must happen before a cell can divide?

Answer 1

• organelles must replicate
• DNA must replicate
• cell must grow

Question 2

Why is it important that mitosis produces genetically identical copies of a parent cell?

Answer 2

• growth of new cells
• repair of damaged tissues
• asexual reproduction

Question 3

What are the stages of the cell cycle?

Answer 3

Interphase: - G1 (cell growth, organelle synthesis and replication)
- Synthesis - DNA replication
- G2 - (growth and protein synthesis for replication)

Prophase

Metaphase

Anaphase

Telophase

Cell division (cytokinesis)

Question 4

What happens during prophase?

Answer 4

• nuclear membrane and nucleolus disappears
• chromatin condenses into chromosomes - condense and stain darker

Question 5

What happens during metaphase?

Answer 5

• centrioles begin to produce spindlefibres which attach to the centromere of chromatids
• chromatids arrange in the middle of the cell on the equator, held by centromeres

Question 6

What happens during anaphase?

Answer 6

• spindlefibres attached to centromeres begin to contract and shorten
• as the spindlefibres shorten, the chromatids are separated and pulled to opposite sides of the cell (different poles)
• requires energy from ATP provided by mitochondrial respiration

Question 7

What happens during telophase?

Answer 7

• spindlefibres disintegrate
• chromosomes disperse and become long and thin and the nuclear membrane reforms
• cell plate forms and membrane begins to cleave, cytoplasm splits in 2

Question 8

What is the formula for mitotic index?

Answer 8

number of cells with visible chromosomes divided by total number of cells observed x100

Question 9

how do prokaryotic cells replicate?

Answer 9

BINARY FISSION
- replication of plasmids, circular DNA and ribosomes
- replicated molecules attach to the membrane and the membrane grows which pulls molecules apart
- start of cell division - cell begins to cleave
- the cell splits into 2 separate daughter cells

Question 10

how do viruses replicate?

Answer 10

• the virus attaches to a target cell eg. epithilial cells
• the cell engulfs the virus by endocytosis
• viral contents are released, viral RNA enters the nucleus where it is replicated by the viral RNA polymerase
• viral mRNA is used to make viral proteins
• new viral particles are made and released into the extracellular fluid. The cell, which is not killed in the process, continues to make new viruses

Question 11

Why does the membrane act as a bilayer?

Answer 11

• hydrophilic heads are attracted to water and the hydrophobic heads are repelled by water

Question 12

Why is cholesterol important within the membrane?

Answer 12

• restricts lateral movement of molecules in the membrane
• this makes the membrane less fluid at higher temperatures which prevents water and dissolved ions from leaking out of the cell

Question 13

Why are viruses described as acellular and non-living?

Answer 13

• don’t contain any defining features like cytoplasm, cell surface membranes or organelles
• cannot replicate on their own - need a host cell to replicate
• no metabolic pathways

Question 14

What is the structure of a virus?

Answer 14

• genetic material (DNA or RNA)
  -protein capsid surrounds genetic material
• attachment proteins
• some have a lipid envelope