Cell Division

How do eukaryotic cells, prokaryotic and viruses replicate

Eukaryotic cells = enter cell cycle and divided by mitosis / meiosis

Prokaryotic cells = replicate by binary fission

Viruses = no cell division, non living

What are the thee key stages in the cell cycle?

Interphase = (G1, S, G2)

Nuclear division (mitosis or meiosis)

Cytokinesis

Describe the interphase stage in the cell cycle

G1: protein synthesis occurs to make proteins involved in synthesising organelles Organelles replicate. checkpoint at end of G, cell checked to see if it is correct size and no damaged DNA, if cell doesn’t pass these checks replication doesn’t occur

S: DNA is replicated

G2: cell grows, energy stores increase and newly replicated DNA checked for copying errors (DNA damage) at another checkpoint

If dna damaged, cell attempts to repair

LINGEST STAGE

what is mitosis?

Created two genetically identical diploid cells

Used for growth, tissue repair, asexual reproduction in plants, animal and fungi

4 stages:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Describe prophase

Chromosomes condense and become visible

animal cells - centrioles separate and move to opposite poles of cell

Centrioles create spindle fibres, released form both poles to create a spindle apparatus and make a spindle apparatus

Spindle apparatus attaches to centromere and chromatids on chromosome in later stages and chromatids on chromosome in later stages

Plants have spindle apparatus but lack centrioles

Descibe metaphase:

Chromosomes align along equator of cell

Spindle fibres released from centrioles and attach to centromere and chromatids

Spindle assembly checkpoint = ensures every chromosome has attached to a spindle fibre

Anaphase

Spindle fibre start to shorten and move towards centrioles and pull centromere and chromatids towards them (opposite poles)

Centromere divides into 2

Stage requires energy in form of ATP (provided by respiration in mitochondria)

Telophase

Chromosomes are now at each pole of the cell and become longer and thinner again

Spindle fibres disintegrate and nuclear membrane reforms

Cytokinesis

Cytoplasm splits into two genetically identical cells

Animals = cleavage furrow forms in middle of cell, cytoskeleton causes cell surface membrane to draw inwards until the cell split into two

Plant cell = cell surface membrane splits into two new cells due to fusing vesicle from Golgi apparatus

Cell wall forms new sections around the cell surface membrane to complete the division into two cells

How is mitosis observed?

Visible under light microscope in onion and garlic root tips

Thin slice of root tip placed on microscope and broken down with a needle

Stain added to make chromosomes visible and coverslip is pushed down to squash the tip of achieve a single layer of cells so light van pass through

Mitotic index

Number of cells in mitosis / total number of cells x 100

What is meiosis?

2 nuclear division , result in four

These plants have different nuclear divisions