2.2 all cells arise from other cells

What are the 3 stages in the cell cycle

1. Interphase

2. Mitosis

3. Cytokinesis

What occurs in interphase

• S-phase - DNA replicates semi conservatively, leading to 2 chromatids joined at a centromere

• G1/G2 - number of organelles and volume of cytoplasm increases, protein synthesis

What occurs in mitosis

• nucleus divides

• To produce 2 nuclei with identical copies of DNA produced by parent cell

What are the 4 stages of mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

What occurs in prophase

• chromosomes condense, becoming shorter/ thicker (so visible)

• Nuclear envelope breaks down

• Centrioles move to opposite poles forming spindle network

What occurs in the metaphase

• spindle fibres attach to chromosomes by their centromeres

• Chromosomes align along equator

What occurs in anaphase

• spindle fibres shorten/ contract

• Centromere divides

• Pulling chromatids (from each pair) to opposite poles of the cell

What occurs in telophase

• chromosomes uncoil, becoming longer/ thinner

• Nuclear envelope reforms into 2 nuclei

• Spindle fibres/ centrioles break down

What stage of photosynthesis is the picture

Prophase

What stage of the cell cycle is the picture

Interphase

What stage of photosynthesis is the picture

Metaphase

What stage of photosynthesis is the picture

Anaphase

What stage of photosynthesis is the picture

Telophase

What stage of the cell cycle is the picture

Cytokinesis

Why do some eukaryotic cells not undergo the cell cycle

• within multicellular organisms, not all cells retain the ability to divide (e.g neurons)

• Only cells that retain this ability go through a cell cycle

Explain the importance of mitosis in the life of an organism

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

How are tumours and cancers formed

• mutations in DNA/ genes controlling mitosis can lead to uncontrolled cell division

• Tumour formed if this results in mass of abnormal cells

What are malignant and benign tumours

Malignant = cancerous, can spread (metastasis)

Benign = non-cancerous

How cancer treatments control rate of cell division — some disruptions spindle fibre activity/ formation

• chromosomes can’t attach to spindle by their centromere

• So chromatids can’t be separated to opposite poles (no anaphase)

• So prevents/ slows mitosis

How cancer treatments control rate of cell division — some prevent DNA replication during interphase

• so can’t make 2 copies of each chromosome (chromatids)

• So prevents/ slows mitosis

How do prokaryotic cells replicate

By binary fission

1. Replication of circular DNA

2. Replication of plasmids

3. Division of cytoplasm to produce 2 daughter cells (single copy of circular DNA, variable number of copies of plasmids)

Why do viruses not undergo cell division

Because they are non living

Describe how viruses replicate

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:

• nucleic acid replicated

• Cell produce viral protein/capsid/enyzyme

• Virus assembled then released