Gprotein linked Plasma membrane receptor Works with Gprotein

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 • • Structure Enzymes Antibodies Transport Movement Receptors Hormones

Proteins • Polypeptide chains of Amino Acids linked by “peptide bonds”.

Amino Acids • • • All have a Carbon with four attachments: -COOH (acid) -NH 2 (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. • • 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: • • 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: • p. H 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 1 st 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: • p. H 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.