All cells arise from other cells (3.2.2)

do all cells within multicellular organisms have the ability to divide?

No

what are the stages of the cell cycle?

• Interphase

• Prophase

• Metaphase

• Anaphase

• Telophase

• Cytokinesis

What is the interphase?

Takes up most of the cell cycle

Synthesis and growth stages:

• normal functions and divide preparation

• Cells DNA is unravelled and replicated to double its genetic content

• Organelles replicated

what is the prophase?

• chromosomes condense, getting shorter and fatter, becoming visible.

• Centrioles separate and move to opposite side of poles, responsible for creating spindle fibres. Collectively called the spindle apparatus.

what stage of mitosis is this?

prophase - chromosomes become visible

what is the metaphase?

• chromosomes are seen to be made of two chromatids

• Chromosomes align along the equator of the cell

• spindle fibres released from poles now attach to centromere and chromatid

what is this stage of mitosis called?

metaphase

what is the anaphase?

• spindle fibres start to retract - pull the centromere and chromatids to opposite poles.

• causes centromere to divide into two - individual chromatids pulled to each opposite pole. ( now referred to as chromosomes )

• Requires ATP

what is this stage of mitosis?

anaphase

what is the telophase?

• chromosomes at each pole become longer and thinner. Leaving only wider spread chromatin.

• spindle fibres disintegrate, nucleus starts to reform.

what stage is this of mitosis?

telophase

what is cytokinesis?

• Cytoplasm splits in two to create the two new genetically identical cells.

what is the equation for the mitotic index?

MI = number of cells with condensed chromosomes/ total number of cells x 100

How are tumours made?

Mitosis is controlled by genes. If there’s a mutation in a gene that controls cell division, cells can grow out of control.

Cells keep on dividing to make more and more - forming a tumour.

What is the difference between benign and malignant tumours?

Benign

• Slower growing, don’t spread. NOT harmful

Malignant:

• cancerous, fast and uncontrolled division. Metastasise (spread to other tissue) and form secondary cancers.

What are some treatments for cancer?

Some treatments target cell cycle and are designed to control the rate of cell division.

Disrupt certain stages of the cell cycle - preventing cell division stopping growth of cancerous tumours.

What stages of the cell cycle do some cancer treatments target?

• S phase ( DNA replication) . Some drugs and radiation damage DNA - preventing replication.

• Metaphase - some drugs interfere with the formation of spindle fibres

How do prokaryotic cells replicate?

Binary Fission

• Circular DNA and plasmids replicate

• Identical DNA molecules are moved to opposite ends of cell and splits in two

• Plasmids often don’t spread equally between 2 cells - so daughter cells are different. Each have one copy of circular DNA.

• Cell membrane starts to divide - new cell wall forms between 2 DNA molecules

How do viruses replicate?

As they are non-living they don’t undergo cell division

• viruses use their attachment proteins to bind to complementary receptor proteins on surface of host cells

• They inject their nucleic acid ( DNA/RNA) into host cell

• Injected cell replicates the viral particles