Differentiation
Cell & Molecular Biology
Genetic Control
• All cells in the body
have the same genetic
information
• Not all cells are
identical.
• Cellular differentiation
depends on changes in
gene expression
resulting in genes being
switched on or off
• Cell function and protein synthesis
– Proteins are synthesised according to DNA base
sequence.
– Cell function depends on a variety of proteins
– Some genes that code for essential proteins
(respiratory enzymes) are ‘switched on’ in all cells.
– Those that are specific to that particular cell
(haemoglobin in red blood cells) are switched on where
others that are unnecessary to that cell are ‘switched
off’ (genes for antibody production).
Advantage to Organism
• Protein synthesis requires a number of
resources.
• Genes that are not required remain switched
off and therefore save
–Energy and resources
–(ATP & amino acids)
Stem Cells & Differentiation
• Plants have
areas of
unspecialised
cells
(meristems)
that are capable
of dividing and
differentiating
into any other
cell type
(totipotent)
Stem Cells & Differentiation
All animals have a basic
body plan that begins the
division and differentiation
from zygote to fully
developed organism.
This development is
influenced by two factors;
1. A programme of genes
that specify the
pattern of the body,
2. Local cell interactions
that induce different
parts of the
programme
Stem Cells & Differentiation
Adult animals have
regions of stem cells
that can vary in potency.
eg
Multipotent stem cells
found in bone marrow
have limited abilty to
differentiate into blood
cells.
Control of Gene Expression
• Jacob-Monod hypothesis of gene expression
in prokaryotes (e.coli) simplifies the
mechanisms by which genes may be switched
on or off in the presence or absence of an
inducer
Then lac operon
• An operon is a region of DNA that contains an
operator gene that controls the expression of
the structural genes which make the proteins
or enzymes coded for.
The lac Operon
• Operon that controls lactose metabolism by the synthesis of
the enzyme -galactosidase.
• Regulator gene codes for repressor molecule
• Repressor molecule binds to operator
• Operator gene switched off by repressor molecule
• Operator switches off structural gene as transcription enzyme
cannot continue to structural gene
• Structural gene does not express -galactosidase
The lac Operon
• In the presence of lactose, the repressor molecule binds to
the lactose prevents binding to operator gene.
• Operator gene switched on
• Structural gene switched on
• Gene expression and synthesis of -galactosidase
Lactose is the inducer of gene expression