3.2.2 all cells arise from other cells

Cell cycle, binary fission, cancer, virus replication

how is eukaryotic dna found in the nucleus

how is eukaryotic dna found in the nucleus

Tightly wrapped around a histone protein forming chromatin

How does a non-dividing cell appear

Chromatin is dispersed so nucleus is a dark blob

How does a dividing cell appear when in mitosis

Chromatin coils up condensing to form short, thick chromatids

→ can be seen by microscope

What are the three stages of the cell cycle

1. Interphase

2. Mitosis

3. Cytokinesis

What is mitosis

Eukaryotic cell divides to produce two identical daughter cells

What are the phases of mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

What happens in interphase

Cell carries out usual functions/metabolic processes

What happens in prophase

• chromosome condense to become shorter and thicker and so become visible

• Nucleolus disappears and nuclear membrane breaks down (so genetic material free in cell)

• Spindle fibres develop from the centrioles and span pole to pole

What happens in metaphase

• Sister chromatids held by centromere

• Chromosomes line up on equator, attached by spindle fibres

What happens in anaphase

• Spindle fibres pull individual sister chromatids apart

What happens in telophase

• Chromosomes unravel and become indistinct

• Nuclear membrane reforms around each group of chromosomes

What happens in cytokineses

Cytoplasm divides leaving two identical daughter cells

How do prokaryotic cells divide

Binary fission

Describe the process of binary fission

1. Circular DNA molecule (and plasmids) replicate

2. Both copies attach to cell membrane; bacteria increases in size

3. Cell membrane begins to grow and pinch inwards, dividing cytoplasm

4. Cell wall forms, creating two identical daughter cells

Describe the process of a virus replicating

1. Virus attaches to host using attachment proteins

2. Injects its nucleus acid into host cell

3. Injected nucleus acid provides the ‘instructions’ for hist cell to start producing the viral nuclei acid

4. Other viral components are synthesised (e.g. proteins and enzymes)

5. Mature viruses are assembled

6. Host cell ruptured, releasing the newly produced mature viruses

What is metastasis

Malignant cells invading other regions of the body to form secondary cancers

What can anti cancer drugs do

Kill cancer cells OR slow the rate of cell division (disrupt the cell cycle)

How does chemotherapy disrupt the cell cycle

• Prevent DNA replicating

• Inhibit metaphase by interfering with spindle formation

→ chromosomes can’t line up and sister chromatids can’t be separated