Cell Division

Mitosis or MeiosisUsed for growth and repair of cells

2 new cells form

Each daughter cell is genetically identical to the parent cell

Involves 2 divisionsInvolves

1 division

Daughter cells contain half the number of chromosomes than parent cell

Sections of DNA get swapped

The job of cell division:•For multi-cellular organisms to grow•To replace worn out/damaged cells•Reproduction in every organism

There are 2 types: Mitosis and Meiosis

Mitosis is involved in:DEVELOPMENT – the formation of a multicellular organism from a single fertilised eggGROWTH – involves an increase in size through the division of cells by mitosisCELL REPLACEMENT – many cells within a multicellular organism are constantly dying and being replaced by mitosisASEXUAL REPRODUCTION – asexual reproduction in certain plants and lower eukaryotic animals, involves the process of mitosis

Budding in this species of Hydra is a formof asexual reproduction; new individualsare produced as outgrowths of the parent

by the process of mitosis

Mitosis

At GCSE:

1) Parent cell 2) Chromosomes make identical copies of themselves 3) They line up along the centre they move apart 4) Two daughter cells form with identical chromosomes to the parent cell

Meiosis

Chromosomes & their instructions

Daughter cells need a full set of all these instructions in order to make new cells

What are the main differences between the genetic material of eukaryotes and prokaryotes?

DNA and histones

So…Chromosomal DNA is folded and tightly bound to proteins called histones.

DNA+histones=chromatin

Each human chromosomes contains 1 very long DNA molecule which if unravelled would measure 4.8cm (& this is just ONE chromosomes) therefore there is a packaging problem!

Apart from sex chromosomes, both chromosomes in a pair contain the same genes. They are HOMOLOGOUS pairs of chromosomes.

Although they contain the same genes e.g. hair colour, they may be different versions of the same gene (alleles) e.g. blue/brown hair.

E.g. one chromosome may have one allele for blue eyes and the other chromosome may have the allele for brown eyes.

Humans= 23 pairs of chromosomes

MITOSISThe nucleus divides to form 2 identical daughter cells

Daughter cells are genetically identical to parent cell

Used for: growth, asexual reproduction (e.g. yeast), wound healing

DIPLOID parent cell with one pair of homologous chromosomes

2n

Chromosome from father

Chromosome from mother

Each chromosome duplicates (DNA synthesis) to form 2 pairs of chromatids held together by a centromere

Diploid daughter cells genetically identical to parent cell

Mitosis is a continuous process but for convenience of description is

divided into FOUR MAIN STAGES:

Prophase

Metaphase

Anaphase

Telophase

Please

Make

Another

Two

The following slides describe the process of mitosis in a hypothetical animal cell that

possesses two pairs of homologous chromosomes

Mitosis in brief:

4 phases: PMAT (In total IPMAT)

Prophase-replicated chromosomes supercoil (thicken & shorten)

Metaphase-Replicated chromosomes line up down the middle of the cell

Anaphase-The replicas of the chromosomes are pulled apart from each other towards opposite poles of the cell

Telophase-two new nuclei are formed

MITOSISYou need to know the different stages of mitosis in more detail.

Using the textbook p140-141 for further info

Make models of the different stages of mitosis with play doh

Annotate each stage with information explaining what is happening

The cell cycle• The cell cycle is an ordered set of events, culminating in cell

growth and division into two daughter cells

• It is the sequence of events that occurs between one cell division and the next.

G1 stage stands for "GAP 1“

S stage stands for "Synthesis“

G2 stage stands for "GAP 2“

M stage stands for "mitosis"

3 main stages:

1)Interphase

2) Mitosis

3) Cell division (cytokinesis)

Read p74-75 Kent Advanced Biology ‘The cell cycle’ and make brief notes of what happens in each of these 3 stages

Interphase:Cell grows, carries out functions, replicates DNAThe chromosome now consists of 2 sister chromatids joined at the centromere.Around 90% of the cell cycle

Mitosis:Nuclear division takes placeChromatids separate into the 2 new nuclei

Cytokinesis: (Cell division)The cytoplasm divides to form 2 new daughter cells

Interphase:(Before mitosis)DNA replication

3 stages of interphase (G1, S & G2)

What is the cell doing in G1, S and G2?

Read p28 and fill in chart

Stage What happens

G1

S

G2

Stage What happens

G1 Active stage, growing, proteins made, organelles replicate

S DNA replicates and 2 sister chromatids form from each chromosome

G2 Growth till mitosis: Mitochondria divide, chloroplasts divide in plants

Cytokinesis:Division of the cell

May occur during or after telophase

The whole cell splits to form 2 new cells each one containing a full set of chromosomes identical to the parent cell.

Each daughter cell is now capable of doing everything the parent cell can.

This cell is inInterphase

The chromosomesare not visible asthreads but appearas chromatin(granular material)in the nucleoplasm

During this stage the cell prepares for mitosis – DNA replicates and new

organelles are manufactured

The chromosomeshave spiralised andcondensed – they are shorter and thicker and visible as clear threads

The nucleolus hasshrunk in size

Spindle fibres are beginning to formclose to the nucleus and the nuclear

membrane disintegrates

This cell is inProphase

By late prophase thechromosomes can beseen to have replicated, with each chromosome now consisting of twochromatids

Each replicated chromosome lines up independently along the equator of the cell

Replicated chromosomes attach to the spindle fibres by their centromeres

This cell is inMetaphase

Spindle fibres have grown across the cell

The centromeresof each chromosomereplicate and thechromatids repelone another

The spindle fibres contract and pullthe separated chromatids to

opposite poles of the cell

This cell is inAnaphase

A single chromatidfrom each chromosome has reached the poles of the spindle – thechromatids are nowdescribed as chromosomes

The chromosomesbegin to uncoil and appear as chromatinonce again; a nuclearmembrane formsaround each set ofchromosomes

Cytokinesis (divisionof the cytoplasm)follows telophase

In animal cells thisinvolves constrictionof the cell membrane along its central axis, and division of the cellinto daughter cells

This cell is inTelophase

In the plant cell shown in the photograph, this involves the formation of a cell membrane in the middle of the cell followed by secretion of cell wall material on either side of this membrane

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