PHSC1212 Biochemistry - Lecture 5 Amino Acids pt 2

Peptide and disulfide

two covalent bond formations that are important for protein structure

Peptide bond

bond that holds amino acids together in a polypeptide chain, found in proteins

Covalent bond

What type of bond is a peptide bond?

Amino group of one amino acid and carboxyl group of another

What does a peptide bond happen between?

Water molecule

Peptide bond formation results in the loss of what?

Amino acid residues

left from loss of a water molecule due to peptide formation

Rotation around peptide bond

restricted by partial double bond character (resonance hybrids)

Double bond character

What restricts rotation around the peptide bond?

Limited rotational ability

characteristic of peptides due to resonance hybrids that is important for proteins folding into proper structure

Dipeptide

peptide with two amino acids

Tripeptide

peptide with three amino acids

Amino end to carboxyl end

How are peptide chains named?

Disulfide bond

bond formed between two cysteines via oxidation of sulfur atoms

Oxidation of sulfur atoms

How does the disulfide bond occur?

Cysteines

What is a disulfide bond formed between?

Cytosol

Where will most proteins not have disulfide bonds?

Reducing environment

What makes the cytosol an environment not conducive to disulfide bonds?

Outside the cell

Where will proteins with disulfide bonds usually be found?

Glutathione (GSH)

tripeptide with reactive thiol group; serves as an intracellular antioxidant; has cysteine residue

Intracellular antioxidant

What does glutathione serve as, which is the reason disulfide bonds aren't found in proteins inside the cell?

Cysteine residue

What gives glutathione the reactive thiol group?

Cysteine, glycine, glutamate

three amino acids of Glutathione

Vasopressin

nine amino acid peptide; important regulator of fluid retention by the kidneys

Kidney fluid retention regulation

What is vasopressin important for?

Atrial Natriuretic Peptide

28 amino acid peptide; has an opposite effect to that of vasopressin

Increase sodium and water excretion

What does atrial natriuretic peptide do?

Oxytocin

nine amino acid peptide; functions during lactation, overlapping physiological activity with vasopressin since very similar but different charges

During lactation

When does oxytocin function?

Disulfide bonds

Both oxytocin and vasopressin have what?

Charges

What do oxytocin and vasopressin differ in?

Antidiuretic hormone (ADH)

another name for Vasopressin

Components of proteins

primary amino acid function

Chemical messengers, precursors for other compounds, metabolic intermediates, modification sites of proteins

other biological roles of amino acids

Chemical messengers

molecules that carry information between cells

Glycine and glutamate

important amino acid neurotransmitters, can function by themselves without being built into a protein

Neurotransmitters

released from one nerve cell and influence the function of a second cell (usually another nerve cell or a muscle cell)

Neurotransmitters that can function without being built into a protein

important feature of glycine and glutamate

Thyroxine, gamma-amino butyric acid, serotonin and melatonin, catecholamines

other chemical messengers that are derivatives of amino acids

Thyroxine

a thyroid hormone produced by thyroid gland and tyrosine derivative

gamma-amino butyric acid (GABA)

glutamate derivative (carboxyl group missing)

Serotonin and melatonin

tryptophan derivatives

Catecholamines

tyrosine-derived neurotransmitters

Dopamine, epinephrine, and norepinephrine

examples of catecholamines

GABA, serotonin, and melatonin

neurotransmitters that are derivatives of amino acids

Nitrogenous bases

a component of nucleotides like DNA and RNA

Glycine, aspartate, and glutamine

precursors for synthesis of nitrogenous bases

Heme

prosthetic group found in hemoglobin, myoglobin, cytochromes, etc.

Heme synthesis

process that uses glycine to synthesize another compound

Purines and pyrimidines

nitrogenous bases used to build nucleotides like DNA and RNA

Standard and non-standard amino acids

serve as metabolic intermediates

Urea cycle

the primary mechanism in the body for disposing of nitrogenous waste with amino acid metabolic intermediates

gamma-carboxyglutamic acid

found in prothrombin, involved in blood clotting (made by adding a carboxylic acid functional group to glutamate)

4-hydroxyproline

component of collagen with proline residues

5-hydroxylysine

component of collagen with lysine residues

After polypeptide has been synthesized

When do modifications occur?

Phosphorylation

adding a phosphate group to an amino acid of a protein

Kinases and phosphatases

enzymes involved in phosphorylation

Kinases

enzymes that add phosphate

Phosphatases

enzymes that remove phosphate

Serine, threonine, tyrosine

amino acids commonly phosphorylated at the hydroxyl to regulate the activity of proteins

Hydroxyl

What group on serine, threonine, and tyrosine makes them good for phosphorylation?

Regulate protein activity

What can phosphorylation be used for?