Mitosis and Meiosis

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Mitosis

Interphase: Before and after mitosis it inculdes

G1: normal cell function ~90% of a cells life

S: DNA and centrosome replicated

G2: Cell prepares to divide but the chromosomes aren't visable

Prophase:

Chromatin condenses and chromosomes become visable.

The nucleus disappears and he nuclear envelope breaks down.

Centrosomes migrate to opposite poles.

Spindle fibres form from microtubules to organise chromosomes.

Prometaphase:

Kinetochores assemble at centrosome and microtubules attach at kinetochores connecting the centromeres to the centrioles, Chromosomes begin moving.

Metaphase:

Chromosomes align along the middle of the cell

Spindle fibres co-ordinate movement this helps to ensure chromosomes separate properly so each nucleus has only one copy of each chromosome.

Anaphase

Sister chromatids separate at kinetochores and move to opposite poles they are pulled at the centrosome by motor proteins along microtubules

Telophase

Chromosomes arrive at opposite poles: daughter nuclei form and nucleoli from. Chromosomes are no longer visible.

Cytokinesis: DNA goes back to chromatin

Animal Cell: Belt of actin microfilaments form around equator of cell splitting the cell in two

Plant Cell: formation of new cell wall.

Cytoskelton

Provides:

Structural support that maintains shape of the cell and anchorage for organelles.

Motility for cell locomotion, cillia and flagella

Regulation that organises structures and activities of cells

Microtubules: responsible for movement in eukaryotic cells like cell division. It is made of tubulin found in all eukaryotic cells, at least 3 types are found alpha, beta or gamma. alpha and beta form heterodimers which are linked end to end to form protofilaments which associate to form a microtubule ~11-16 protofilaments. They are polar with addition and disassembly both occuring at the positive end.

Meiosis

Cell division to form gametes by meiosis 2 (same stages as mitosis: separation of 2 chromatids) and meiosis 1(separation of homologus chromosomes.

DNA is replicated and homologues align with each other at the equator

Meiosis 1: Homologues are separated but sister chromatids remain together.

Meiosis 2: separates sister chromatids

Chromosomal nondisjunctions: failure to separate homologus chromosomes or sister chromatids. Monosomic zygotes are lethal and most trisomic are aswell.

Chromosomal deletions delete part of the chromosome

Inversions: rotate a segement 180 degrees.