chapter 19 p3 Flashcards
Translational control:
These following mechanisms regulate the process of protein synthesis:
degradation of mRNA - the more resistant the molecule the longer it will last in the cytoplasm, that is, a greater quantity of protein synthesised.
binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins.
activation of initiation factors which aid the binding of mRNA to ribosomes (the eggs of many organisms produce large quantities of mRNA which is not required until after fertilisation, at which point initiation factors are activated).
Translational control:
Protein kinases
Protein kinases are enzymes that catalyse the addition of phosphate groups to proteins.
The addition of a phosphate group changes the tertiary structure and so the function of a protein.
Many enzymes are activated by phosphorylation.
Protein kinases are therefore important regulators of cell activity.
Protein kinases are themselves often activated by the secondary messenger cAMP.
Post-translational control involves modifications to the proteins that have been synthesised. This includes the following:
- addition of non-protein groups such as
carbohydrate chains, lipids, or phosphates - modifying amino acids and the formation of bonds such as disulfide bridges
- folding or shortening of proteins.
- modification by cAMP - for example, in the lac operon CAMP binds to the cAMP receptor protein increasing the rate of transcription of the structural genes.
Living organisms come in
all shapes and sizes from tulips to mosquitoes to humans. It is the same small group of genes, however, that control the growth and development of these vastly different living forms.
morphogenesis.
The regulation of the pattern of anatomical development
These genes were discovered by
scientists investigating strange mutations observed in fruit flies such as legs on the head in place of antennae or extra pairs of wings.
Fruit flies are small flies belonging to the genus Drosophila that feed and reproduce on rotting fruit.
They are small, easy to keep, and have a short life cycle so have always been a popular choice for use in genetic studies.
Homeobox genes are
a group of genes which all contain a homeobox.
The homeobox is a
section of DNA 180 base pairs long coding for a part of the protein 60 amino acids long that is highly conserved (very similar) in plants, animals, and fungi.
This part of the protein, a homeodomain, binds to DNA and switches other genes on or off, Therefore, homeobox genes are regulatory genes.
The common ancestor of the mouse and human is
thought to have lived about 60 million years ago.
Mutations have been accumulating ever since and evolution has led to two very different organisms.
Many of the homeobox genes present in the mouse and human, however, still have identical nucleotide sequences.
one of the homeobox genes.
Pax6
When mutated it causes a form of blindness (due to underdevelopment of the retina) in humans.
Mice and fruit flies also have this gene and disruption of the gene causes blindness in these organisms as well.
These findings suggest that Pax6 is a gene involved in the development of eyes in all three species.
Hox genes:
- (often used interchangeably with homeobox genes) are one group of homeobox genes that are only present in animals.
- They are responsible for the correct positioning of body parts.
- In animals the Hox genes are found in gene clusters - mammals have four clusters on different chromosomes.
- The order in which the genes appear along the chromosome is the order in which their effects are expressed in the organism.
- Human beings have 39 Hox genes in total that are all believed to have arisen from one ancient homeobox gene by duplication and accumulated mutations over time.
The layout of living organisms:
p1
Body plans are usually represented as cross-sections through the organism showing the fundamental arrangement of tissue layers.
Diploblastic animals have two primary tissue layers and triploblastic animals have three primary tissue layers.
A common feature of animals is that they are segmented, that is, the rings of a worm or the less obvious back bone of vertebrates.
The layout of living organisms:
p2
- These segments have multiplied over time and are specialised to perform different functions.
- Hox genes in the head control the development of mouthparts and Hox genes in the thorax control the development of wings, limbs, or ribs.
- The individual vertebrae and associated structures have all developed from segments in the embryo called somites.
- The somites are directed by Hox genes to develop in a particular way depending on their position in the sequence.
body layout diagram
The body shape of most animals shows symmetry.
Radial symmetry is seen in diploblastic animals like jellyfish. They have no left or right sides, only a top and a bottom.
Bilateral symmetry which is seen in most animals means the organisms have both left and right sides and a head and tail rather than just a top and bottom.
Asymmetry is seen in sponges which have no lines of symmetry.
Mitosis and apoptosis: p2
Cells undergoing apoptosis can also release chemical signals which stimulate mitosis and cell proliferation leading to the remodelling of tissues.
A sculptor working with clay will often add and remove clay during the reshaping process.
Hox genes regulate both mitosis and apoptosis.
process of apoptosis
