Cell Reproduction

Method of cell division

nucleus divides into daughter nuclei each containing the same number of chromosones

Normally cells divide to replace dead or missing cells

cells lining the gut divide about twice a day

nerve cells dont divide

In an embryo, cell division occurs every 30 mins

reproductive cells undergo Meiosis

four dissimilar cells are formed

each cell contains only half of the parental chromosonal number

Strand of DNA and proteins in the nucleus of eukaryotic cells that carries the genes

made of Chromatin DNA complexed with protein

Organised into nucleosomes

Chromatin has the ability to condense into tightly packed structure - heterochromatin

Only visible by light microscope

Heterochromatin - chromatin organisation, lines the nuclear membrane at the pores

Euchromatin - threadlike, delicate, abundant in active transcribed cells, regions of DNA to be transcribed or duplicated, must be coiled before genetic code can be read.

All the human body's nucleated cells contain 46 chromosomes (23 pairs)

Contain all the information that governs all cellular activitys

DNA molecules - form of genes

DNA molecule regulate specific functions

blueprint determines synthesis of an RNA molecule or polypeptide

Not visible in non dividing cells

Stages are G1, S (synthesis DNA replication) , G2, M (mitosis)

two cell division events need to be controlled

entry into S phase - replication

entry into M phase - Mitosis

when to initiate replication

when to initiate chromosonal condensation

the accumulation of a specific cellular mass

Some cells need to reach a specific growth rate for mitosis to begin

Time between Mphases controlled by timer genes

M phase requires completion of S phase

insure full DNA complements - completion of chromosonal replication factor

Reproduction Stages - INTERPHASE (before mitosis) , PROPHASE, MATAPHASE, ANAPHASE, TELOPHASE ----- CYTOKINESIS

Not part of Mitosis

Longest Phase

Where the cell grows

DNA duplicated, prepared for division

G1 phase - normal metabolic cellular

S phase - DNA duplicates

G2 phase - structures for mitosis are formed

Chromatin condenses into chromosomes

Sister chromatids joined by centromere

Nuclear envelope starts to break up

Nucleolus disapeers

chromosomes line up at equator by spindle fibres from opposite ends of the cell

Kinectochore= proteinaceous region that forms at both sides of centromere, binds to microtubules to pulls sister chromatids apart

Anaphase - Two sister chromatids break apart and are now seperate chromosomes that move to opposite spindle pores

Telophase

Chromosomes decondense

New patches of membrane fuse to form new nuclear envelope around them

Daughter cells are pulled apart

Contraction of microfilaments

Control of Mitosis 

Cell divides too often - cancer

Not often enough - death

Controls - growth factors, growth suppressors P53

unique type of cell division

only produces gametes

number of chromosomes halved

requires two divisions with no S phase

gene recombination so its genetically unique