Download G-protein linked receptors

G-protein linked
• Plasma membrane receptor.
• Works with “G-protein”, an
intracellular protein with GDP or
GTP.
• Involved in yeast mating factors,
epinephrine (adrenaline), many
neurotransmitters, blood vessel
development.
G-protein
• GDP and GTP acts as a switch.
• If GDP - inactive
• If GTP - active
G-protein
• When active (GTP), the protein
binds to another protein (enzyme)
and alters its activation.
• Active state is only temporary.
G-protein linked receptors
• Very widespread and diverse in
functions.
• Ex - vision, smell,
G-protein linked receptors
• Many diseases work by affecting
g-protein linked receptors.
• Ex - whooping cough, botulism,
cholera, some cancers
G-protein linked receptors
• Up to 60% of all medicines exert
their effects through G-protein
linked receptors.
Signal-Transduction Pathways
• The further amplification and
movement of a signal in the
cytoplasm.
• Often has multiple steps using
relay proteins such as Protein
Kinases.
Protein Kinase
• General name for any enzyme
that transfers Pi from ATP to a
protein.
• About 1% of our genes are for
Protein Kinases.
Protein Phosphorylation
• The addition of Pi to a protein,
which activates the protein.
• Usually adds Pi to Serine or
Threonine.
Amplification
• Protein Kinases often work in a
cascade with each being able to
activate several molecules.
• Result - from one signal, many
molecules can be activated.
Proteins
• The molecular tools of the cell.
• Made of C,H,O,N, and
sometimes S.
Functions of Proteins
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Structure
Enzymes
Antibodies
Transport
Movement
Receptors
Hormones
Proteins
• Polypeptide chains of Amino Acids linked
by “peptide bonds”.
Amino Acids
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All have a Carbon with four attachments:
-COOH (acid)
-NH2 (amine)
-H
-R (some other side group)
Amino Acids
R groups
• 20 different kinds:
• Nonpolar - 9 AA
• Polar - 6 AA
• Electrically Charged
• Acidic - 2 AA
• Basic - 3 AA
Amino Acids
Levels Of Protein Structure
• Organizing the polypeptide
into its 3-D functional shape.
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Primary
Secondary
Tertiary
Quaternary
Primary
• Sequence of amino
acids in the
polypeptide chain.
• Many different
sequences are
possible with
20 AAs.
Secondary
• 3-D structure formed by
hydrogen bonding between
parts of the peptide
backbone.
• Two main secondary
structures:
a helix
β pleated sheets
Tertiary
• Bonding between the R groups.
• Examples:
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hydrophobic interactions
ionic bonding
Disulfide bridges (covalent bond)
Can also include H bonds
Quaternary
• When two or more
polypeptides unite to form a
functional protein.
• Example: hemoglobin
Is Protein Structure Important?
Denaturing Of A Protein
• Events that cause a protein to lose
structure (and function).
• Example:
• pH shifts
• high salt concentrations
• heat
Enzymes
• Biological catalysts made of protein.
• Cause the rate of a chemical reaction to
increase.
Chemical Reaction
AB + CD
AC + BD
AB and CD are “reactants”
AC and BD are “products”
Enzymes
• Lower the activation energy for a chemical
reaction to take place.
Enzyme Terms
• Substrate - the material and enzyme works
on.
• Enzyme names: Ex. Sucrase
- ase name of an enzyme
1st part tells what the substrate is. (Sucrose)
Enzyme Name
• Some older known enzymes don't fit this
naming pattern.
• Examples: pepsin, trypsin
Active Site
• The area of an enzyme that
binds to the substrate.
• Structure is designed to fit the
molecular shape of the
substrate.
• Therefore, each enzyme is
substrate specific.
Environment
• Factors that change protein structure will
affect an enzyme.
• Examples:
• pH shifts
• temperature
• salt concentrations
Enzyme Inhibitors
• Competitive - mimic the substrate and bind to
the active site.
• Noncompetitive - bind to some other part of
the enzyme.
Allosteric Regulation
• The control of an enzyme complex by the
binding of a regulatory molecule.
• Regulatory molecule may stimulate or inhibit
the enzyme complex.
Allosteric Regulation
Control of Metabolism
• Is necessary if life is to function.
• Controlled by switching enzyme
activity "off" or "on” or separating
the enzymes in time or space.