Proteins, Amino Acids Flashcards
(33 cards)
what type of isomers do protein have
L
BASIC unit of pro in
amino acids
does the body need pr
no but it needs its aa and nitrogen
•of the Over 300 AAs found in animal tissue how many are used for ptn synthesis
20 used for ptn synthesis (tRNA)
– all 20 AAs are essential (some have to be in the diet)
Common Post-Translational Amino Acids
- bone
OH-Lysine
• OH-Proline
Common Post-Translational Amino Acids
- muscle
• 3-Methyl histidine
– released during muscle breakdown via urine
INDISPENSABLE (ESSENTIAL) AMINO ACIDS
• IAA is one which cannot be made in the body or cannot be
made sufficiently to meet physiological needs, hence must
be supplied in the diet.
e.g., inability to make C-skeleton of AA de novo
• 10 AAs most commonly essential:
PHE HIS ILE LEU LYS MET TRP VAL THR (ARG ?)- not essential for human because made in the liver in the urea cycle
– Dependent on species and/or stage of growth:
GLY PRO ARG
• IAA as a misnomer: supply keto analogue (requires a
transaminase) or hydroxy analogue (requires a
dehydrogenase and a transaminase) and animal can
make the AA – used in renal failure patients
– exceptions THR, HIS and LYS
how can we mesure muscle breakdown
see it in urine because it will have no where else to go
if we eat a steak and it has 3- methyl histadine, what happens
cant break it down so it is seen in the urine
what do you do to see if the aa is necessary
take it out a diet until see protein imbalaance - dont know about arg because take a long time because we make some of it
ex histadine with babies is more rapidly turned over - 3 month study to see negative balance
whats wrong with aa supplements
have some with sulfur group, some with acid group- smell bad ex together aspertame- aspartic acid and phenylate- seperate really bad taste
when eating high protein diet
broken down and produces urea- and need the urea cycle to keep going- if not enough arg made then having some in the diet makes sense
DAA can be made in the body from
a) keto acid & transamination with another AA
e.g., ALA from pyruvate
b) another amino acid by conversion other than by
transamination
e.g., MET
→ CYS, PHE
→ TYR
Conditionally Indispensable Amino Acids
IAA and DAA inflexible classifications - too strict?
e.g., TYR essential in PKU, TAURINE [MET] essential in TPN
Amino Acid Tyrosine Cysteine Proline Arginine Glutamine Precursors Phenylalanine Methionine, Serine Glutamine Glutamine or Glutamate, Aspartate Glutamate, Ammonia
• Function is dependent upon
ptn
components, shape or conformation
• SIMPLE PROTEINS:
AAs only
• CONJUGATED PROTEINS:
AAs
combined with other non-ptn moiety [e.g.,
lipoprotein]- glycoprotein (cell signaling)
PRIMARY STRUCTURE
Sequence of strong covalently bonded AAs as dictated by the genetic code which determines the final form of ptn • The side chain of one amino acid differs from that of another amino acid making each amino acid different; however the polypeptide backbones do no differ between polypeptide chains
SECONDARY STRUCTURE:
Determined by attracting forces between nearby groups (R) in the peptide chain. Gives shape to the ptn. α-helix β-pleated sheet random coil
TERTIARY STRUCTURE:
The way a protein folds in a threedimensional space • Due to interactions occurring among R groups that are located at considerable distances from each other on the polypeptide chain e.g., cystine -S-S- • Produces binding and looping of the ptn molecule e.g., enzyme pocket - site of action
QUATERNARY STRUCTURE:
Aggregate of two or more polypeptide chains that form oligomers
held together by H bonds and electrostatic salt bridges (e.g.,
haemoglobin, regulatory enzymes).
ASSESSMENT OF PROTEIN QUALITY
D) Chemical Score (AA Score)
- non-biological method that requires knowledge of AA
composition of test ptn - compares AA composition of test ptn with ref ptn
e.g., egg, milk
IAA test ptn (mg/g ptn) ÷ IAA ref ptn (mg/g ptn) x 100
Criteria: IAA with lowest score = limiting AA
+ves: easily performed
-ves: knowledge of AA composition; no digestibility
ASSESSMENT OF PROTEIN QUALITY
E) Amino Acid Score (FAO/WHO reference pattern)
relates IAA content in food to IAA requirement for
given age group
IAA in food protein (mg/g ptn) ÷
same IAA reference pattern (mg/g ptn) x 100
- pattern of requirements for amino acids in the total
dietary protein is calculated by dividing each IAA
requirement by the recommended allowance of
reference protein for the given age group
ASSESSMENT OF PROTEIN QUALITY
F) Protein Digestibility-Corrected Amino Acid
Score (PDCAAS)
same as above except accounts for digestibility
- official FDA food labeling method
- except infant foods which use PER
IAA in food protein (mg/g ptn) x digestibility ÷
same IAA reference pattern (mg/g ptn) x 100
