Download f215 control of protein syntheses and apoptosis student version

F215 Module 1:
Control of Protein Synthesis,
Body Plans and Apoptosis
By Ms Cullen
Cyclic AMP (cAMP)
• cAMP in cells will activate some proteins by changing
their 3D structure.
• An example of this is glycogen in muscle cells.
• Glycogen is broken down by the enzyme glycogen
phosphorylase.
• It is synthesised by an enzyme called glycogen
synthase.
• If glycogen was being broken down and made at the
same time, it would be a waste of the cells energy.
cAMP
• To prevent this happening glycogen phosphorylase is
activated by cAMP and inhibited by ATP and glucose6-P (when these are present glycogen will not need
to be broken down to release more glucose for
respiration).
• The cAMP causes the enzyme to change shape,
revealing an active site to allow glycogen to be
broken down.
• ATP and G-6-P have the opposite effect, changing
shape to hide the active site.
Control of Protein Synthesis
• Each of our cells contains about 20,000 genes. Every
cell contains the same genes, but not all cells use all
these genes.
Examples: Only white blood cells will produce antibodies and
only certain skin cells will produce melanin.
• In a multicellular organism, each specialised cell will
only use particular genes.
• This also explains how a zygote can differentiate to
become specialised cells.
• In each cell type a particular set of genes are
‘switched on’ and others are ‘switched off’.
Control of Protein Synthesis
• Protein synthesis can be controlled at a
genetic level, by altering the rate at which
genes are transcripted.
• If transcription is increased then more mRNA
will be produced.
• This, in turn will be used to make more
proteins.
• In prokaryotes (eg bacteria) genetic control of
protein production often involves operons.
The lac operon
• Even in a single-celled organism such as Escherichia
Coli (E.coli), there are genes that are switched on
and others that are switched off.
• E.coli will adapt to their environment by producing
enzymes which will allow them to metabolise the
medium they are growing on.
• E.coli produce 2 enzymes to help with the digestion
and absorption of disaccharide lactose;
-galactosidase and lactose permease
• These enzymes will hydrolyse the disaccharide
lactose into glucose and galactose.
The lac operon
• However, if E.coli is grown on a medium with only glucose it
will not produce these 2 enzymes. The genes that control the
protein synthesis for these 2 enzymes will be ‘switched off’.
• If we then transfered the same E.coli bacterium to a medium
containing only disaccharide lactose, they would produce
both –galactosidase and lactose permease.
• The genes have been ‘switched on’. Lactose triggers this and is
known as the inducer.
• The section of DNA within the bacterium that controls this is
known as the lac operon.
• An operon is a length of DNA containing the base sequences
that code for proteins known as structural genes.
The E. coli lac operon and its regulator gene.
How the lac operon works by stopping RNA
polymerase binding to the promoter region when
lactose is absent from the growth medium
How the lac operon works when lactose is
present
http://vcell.ndsu.nodak.edu/animations/lacOperon/index.htm
Genes and body plans
• Some genes are responsible for the general structure of an
organism (eg body parts head, abdomen etc).
• Proteins will control this body plan and ensure that all the
parts grow in the correct place!
• Most of what we know about these genes has come about
from the study of the fruit fly drosophila.
• Proteins which control body plans are coded for by genes
known as homeotic genes. These homeotic genes have
sequences known as homeobox sequences.
• In drosophila there are 2 homeotic gene clusters; 1 controls
development of the head and anterior thorax; the other
controls development of the posterior thorax and the
abdomen.
Development in Drosophila
Controlled by homeobox genes
• Segments Md, Mx and Lb become head.
• Segments T1-3 become thorax.
• Segments A1-8 become abdomen.
Genes and body plans
• Homeobox genes – control the development of the
body plan of an organism, including the polarity
(head and tail ends) and positioning of the organs.
• All segmented animals from annelids (segmented
worms) to vertebrates have homeobox genes.
• Each homeobox gene contains 180 base pairs, which
are known as the homeobox.
• These produce polypeptides about 60 amino acids
long.
• Some of these polypeptides will initiate transcription,
and so regulate the expression of other genes.
Genes and body plans
• Homeobox genes are arranged in clusters
called Hox clusters. Nematodes have 1,
drosophila 2 and vertebrates 4.
• Homeobox genes work in a similar way in
most organisms, including plants and fungi.
Apoptosis - programmed cell death
• Sometimes it is necessary to get rid of cells as part of
development. For example, a tadpole eventually has
to lose it’s tail.
• In order of this to happen, tail cells will die and then
be consumed by phagocytes.
• Another example of this is the development of
fingers and toes. In an embryo the digits are
connected.
• They only separate when cells in the connecting
tissue undergo apoptosis.
• All cells contain genes that promote or inhibit
apoptosis.
embryonic hands
syndactyly hands
Series of events in apoptosis
Hayflick 1962
• Since the 1900’s normal body cells were
believed to be immortal.
• Leonard Hayflick came up with the idea that
normal body cells divide a limited amount of
times.
• He also proposed that cancer cells were
immortal.
• This provides the basis of most modern
research into cancer.