nutr 437 exam 4

functions of proteins

catalysts, messengers, structure, immunoprotectors, transporters, buffers, fluid balancers

hydrolases

cleave compounds

isomerases

transfer atoms in a molecule

ligases

join compounds

oxidoreductases

transfer electrons (in ETC)

transferases

move functional groups

hormones

synthesized and secreted by endocrine tissue and transported in blood to target tissue

types of protein hormones

tyrosine, tryptophan, insulin, glucagon

tyrosine is a precursor for

thyroid hormones, catecholamines (dopamine, epinephrine, norepinephrine)

tryptophan is a precursor for

melatonin and serotonin

contractile proteins

actin, myosin

fibrous proteins

collagen, elastin, keratin (linear shape, bone, teeth, hair, nail, skin)

globular proteins

myoglobin, enzymes (spherical, structural support)

immunoproteins

Y shaped, 4 polypeptide chains

bind to antigen to be recognized and destroyed

albumin

transports fatty acids, calcium, zinc, vitamin B6

transthyretin

transports vitamin A

transferrin

iron transport protein

ceruloplasmin

copper transport protein

lipoproteins

transport lipids in blood

buffers

regulate acid base balance

fluid balancer

contribute to osmotic pressure, protein draws water to blood

conjugated proteins

glycoproteins (in mucus), proteoglycans (in ECM, cartilage, skin)

primary protein structure

sequence of covalent bonds among amino acids in polypeptide chain (synthesized on ribosomes)

secondary protein structure

hydrogen bonding (weak), forms alpha helix, beta pleated sheet or random coil

tertiary protein structure

clustering of hydrophobic amino acids toward center of protein

ionic attraction of oppositely charged amino acids

strong covalent bonding between cysteine residues (disulfide bonds)

quaternary protein structure

interactions between 2 or more polypeptide chains, subunits held together by hydrogen bonds and electrostatic salt bridges, oligomers

oligomers

aggregated form (quaternary structure)

true or false: subunits in a protein can assume different spatial orientations relative to each other, changing properties and function

true

monomer

1 subunit

dimer

2 subunits (i.e. hemoglobin is an A, B dimer)

structure of amino acid

central carbon, amino group, carboxy group, and a side chain

what happens to amino acids in low pH

accept hydrogens

what happens to amino acids in high pH

donate hydrogens

amino acids with aliphatic/nonpolar side chains

glycine, alanine, valine, leucine, isoleucine

amino acids with hydroxylic groups (OH)

serine, threonine

amino acids with side chains containing sulfur

cysteine, methionine

amino acids with side chains containing acidic groups or their amides

acidic: aspartic acid, glutamic acid

amide: asparagine, glutamine

amino acids with side chains containing basic groups (additional amino groups)

arginine, lysine, histidine

amino acids with side chains containing aromatic ring

phenylalanine, tyrosine, tryptophan

imino acids

proline

amino acids formed posttransitionally

cystine (2 cysteine with disulfide bond)

hydroxyproline (extra OH)

hydroxylysine (extra OH)

3-methylhistidine (extra methyl)

zwitterions

have no net electrical charge

alanine, asparagine, cysteine, glutamine, glycine, isoleucine, leucine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine

negatively charged amino acids

aspartic acid, glutamic acid

positively charged amino acids

arginine, histidine, lysine

totally indispensable amino acids

lysine, threonine, histidine

9 nutritionally indispensable amino acids

phenylalanine, valine, threonine (PVT)

tryptophan, isoleucine, methionine (TIM)

histidine, leucine, lysine (HaLL)

polar AA

asp, cys, glutamine, ser, thr, arg, lys, his, glutamate, aspartate

conditionally essential AA

tyrosine, cysteine, proline, arginine, glutamine

exogenous sources of protein

animal products and plant products (grains, legumes, nuts, seeds, veg)

endogenous sources of protein

shed mucosal cells of intestinal epithelium, digestive enzymes and glycoproteins

contribute 70g/day

digestion in the stomach

HCl, pepsin

HCl function in digestion

breaks down 4, 3, 2, structure

initiates the conversion of pepsinogen to pepsin

pepsin function in digestion

hydrolyzes peptide bonds

produces large polypeptides, oligopeptides, free amino acids

small intestine in digestion

pancreatic enzymes, brush border peptidases, tripeptides absorbed

pancreatic enzymes function in digestion

trypsinogen becomes trypsin which triggers the conversion of chymotrypsinogen to chymotrypsin, procarboxypeptidases A and B to carboxypeptidases, proelastase to elastase, and collagenase

endopeptidases

trypsin, chymotrypsin

exopeptidases

carboxypeptidases

function of brush border peptidases

break down peptides and includes aminopeptidases, dipeptdylaminopeptidases, and tripeptidases

pepsinogen site of activity

stomach

pepsinogen substrate

most AA (aromatic, dicarboxylic, leu, met)

pepsinogen end product

peptides

trypsinogen site of activity

intestine

trypsinogen substrate

basic AA

trypsinogen end product

smaller peptides, some free AA

chymotryspinogen site of activity

intestine

chymotrypsinogen substrate

aromatic AA, met, asn, his

chymotrypsinogen end product

smaller peptides, some free AA

procarboxypeptidases site of activity

intestine

true or false: amino acids need carriers to be absorbed into enterocytes

true

most rapidly absorbed AA

met, leu, ile, val

why are AA supplements not superior to food

may create imbalance and there can be a competition of absorption especially if the AA consumed use the same carriers

true or false: the AA transport systems labelled with an uppercase letter are sodium dependent, with the exception of L, PAT, and IMINO

true

what happens to AA transporters that require sodium

sodium increases the affinity for the AA and it triggers a conformational change resulting in the delivery of sodium and AA into cytosol

which is faster: peptide transport or AA transporter

peptide

peptide transporter that transports di and tripeptides

PEPT1

what influences affinity of peptide transporter

stereoisomerism, side chain length, number of AA

true or false: peptide transport is the primary system for protein absorption

true

steps in peptide transport

peptides are transported into cell with H

H is pumped back into intestinal lumen in exchange for sodium

Na/K ATPase pumps sodium out of the cell for potassium

some AA are not transported out of enterocytes and into circulation, instead they are used for:

energy, synthesis, metabolized into other AA, urea cycle

what happens to glutamine in enterocyte

used for energy, synthesis of heat shock protein, generation of ammonia, added to enteral or parenteral nutrition products

what happens to aspartate in enterocyte

turns in oxaloacetate and into glutamate or alanine

intestinal glutamine metabolism

primary energy source for enterocytes, stimulates cell proliferation the prevent atrophy of gut mucosa, use up to 10 g/day

intestinal glutamate metabolism

forms alanine, used in proline synthesis, forms ornithine with aspartate

intestinal aspartate metabolism

occurs within enterocyte, very little found in portal blood

intestinal arginine metabolism

40% oxidized to citrulline and urea, citrulline taken up by kidney for arginine synthesis and liver for the urea cycle, can be conditionally essential

intestinal methionine and cysteine metabolism

52% methionine metabolized, cysteine from diet or methionine metabolism used to make glutathione, taurine, or pyruvate and sulfite

ways AA are absorbed into extraintestinal tissues

enter portal vein to liver, transport to hepatocytes (transporters and hormones), transport to other cells, gama glutamyl cycle

where does the gama glutamyl cycle happen

renal tubular cells, RBC, neurons

steps of amino acid metabolism

dietary proteins digested, release AA in blood, enter cells, deamination occurs, carbon skeleton is used

uses of carbon skeleton

energy (directly or converted to fat), glucose if needed, ketone bodies if needed, cholesterol (leucine)

glucogenic compounds

oxaloacetate, pyruvate, fumarate, succinyl coA, alpha ketoglutarate

AA precursor of pyruvate

alanine, glycine, serine, cysteine, tryptophan, threonine

AA precursors of oxaloacetate

aspartate, asparagine

AA precursors of fumarate

phenylalanine (tyrosine, aspartate)

AA precursors of succinyl coA

isoleucine (valine, methionine, threonine)

AA precursors of alpha ketoglutarate

arginine, histidine, proline, glutamate, glutamine

ketogenic compounds

acetyl coA, acetoacetate

AA precursors of acetyl coA

isoleucine, leucine, lysine, threonine, tryptophan

AA precursors of acetoacetate

phenylalanine, tyrosine, leucine

types of plasma proteins

albumin, transthyretin, retinol binding, blood clotting, immunoproteins, transport, acute phase proteins, stress (heat) shock