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
• chromosomes condense and stain darker

Question 5

What happens during metaphase?

Answer 5

• centrioles begin to produce spindlefibres
• chromosomes 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)

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

Question 8

What is the formula for mitotic index?

Answer 8

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

Question 9

How does a tumour develop?

Answer 9

• initially an early tumour is formed through uncontrolled cell division
• the tumour enlarges from the edges (has no capsule so can uncontrollably grow) and begins to develop blood vessels and lymphatic vessels
• ?

Question 10

How do mutations affect the process of tumour growth?

Answer 10

• 2 genes called protoncogenes and tumour supressor genes
• if they are mutated the cell cycle cannot be controlled and this will lead to abnormal growth which causes tumours
• if both genes are mutated then the cancer will be more aggressive

Question 11

how do prokaryotic cells replicate?

Answer 11

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

Question 12

how do viruses replicate?

Answer 12

• 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