Structure, function and growth of prokaryote and eukaryote cells (iii) Differentiation of cells into tissues and organs. (iv) Cell and tissue culture – Mammalian cell cultures – Bacterial and Fungal Cultures (v) Plant tissue culture

Development An organism starts life as a zygote (single fertilised cell). It undergoes three main stages to develop into an individual 1. Mitotic division to form a group of cells called the blastula. 2. Gastrulation Infolding of the cells to form a cup shape called a gastrula

Development cont… – The gastrula has three germ layers Endoderm – Develops into the alimentary canal Ectoderm – Develops into skin and nervous system Mesoderm – Develops into the muscles, skeleton, circulatory system, excretory system

Development cont… 3. Cell division and differentiation (specialisation) results in tissue and organ formation.

Differentiation Nearly all cells in an organism have the same DNA Differentiation depends on gene expression (the transcription of a gene into mRNA) i.e. which genes are ‘switched on’ and which genes are ‘switched off’.

Differentiation cont… During development the control of gene expression may be: Temporal (different genes expressed at different times in development) Spatial (cells in different places in the embryo expressing different genes) Example of differentiation to form an organism: Drosophila melanogaster

Control of Gene Expression in Bacteria Lac operon (aka Jacob-Monod hypothesis)

Stem Cells A stem cell is an undifferentiated cell which can undergo unlimited division to form other cells Source of stem cells – Adult e.g. bone marrow – Embryonic (from blastula stage ~ 150 cell stage) – Cancer cells – Umbilical Cord Blood Stem cells have the ability to differentiate, unlike specialised cells

Learning Activities Differentiation of Human Cells Read DART pg Scholar (Unit 1, no. 2) Web animations from Biozone website sbiology/stemcells.html sbiology/stemcells.html logy/lacoperon.html