Mitosis

The purpose of mitosis: Growth (2)

Enables unicellular zygotes to grow into multicellular organisms (same number of chromosomes as parent cell)

May occur across the whole body of the organism or be confined to certain regions, such as in the meristems (growing points) of plants

Purpose of mitosis: Repair (3)

Damaged tissues are repaired via mitosis, followed by cytokinesis

Continuous cell loss (e.g. skin, gut lining) requires constant cell replacement

Some animals show regeneration of body parts (e.g. zebrafish fins, axolotl limbs)

Purpose of mitosis: Asexual reproduction (4)

Involves one parent, producing genetically identical offspring

In unicellular organisms (e.g. Amoeba), mitosis results in reproduction

In multicellular organisms, offspring may detach from the parent after growth

Runners in strawberries and budding in Hydra and yeast

What are the 3 stages of the cell cycle? (3)

Interphase

Mitosis

Cytokinesis

Interphase: Growth 1 (4)

The cell increases in size and volume

Organelles (such as mitochondria and ribosomes) replicate

High rates of protein synthesis occur

Production of enzymes and proteins required for DNA replication

Interphase: Synthesis (4)

DNA replication takes place

Each single chromosome is copied (via semi-conservative replication) to form two identical sister chromatids joined at the centromere

The amount of DNA doubles, though chromosomes are not yet condensed or visible as distinct structures

They exist as a loose network called chromatin

Interphase: Growth 2 (4)

Further cell growth occurs

Energy stores (ATP) increase

Tubulin production and protein synthesis take place to form the spindle fibres

The cell conducts DNA error checking and repairs any damaged or mismatched base sequences before entering mitosis

What are the 4 stages of mitosis?

Prophase

Metophase

Anaphase

Telophase

What are chromatids?

One of the two identical halves of a replicated chromosome

What are centromeres?

The specialised, condensed region of a chromosome that holds sister chromatids together

What are spindle fibres? (2)

long protein structures made of microtubules

They equally divide genetic material during cell division

Prophase (5)

Chromosomes condense (visible when stained)

Each chromosome = 2 sister chromatids joined at a centromere

Centrosomes move to opposite poles

Spindle fibres (microtubules) form from centrosomes

Nuclear envelope breaks down

Metaphase (3)

Centrosomes are located at opposite poles of the cell

Spindle fibres are fully formed and are attached to the centromeres of the chromosomes

Chromosomes align on the metaphase plate (equator of the cell)

Anaphase (3)

Spindle fibres shorten, pulling chromatids apart

Centromeres divide, separating sister chromatids

Chromatids (now chromosomes) move to opposite poles

Telophase (3)

Chromosomes arrive at opposite poles and begin to decondense

Nuclear envelopes (nuclear membranes) begin to reform around each set of chromosomes

The spindle fibres break down

Cytokinesis

The cytoplasm divides to form 2 distinct daughter cells