U6 Flashcards
proteins as structural components
skin, bones, tendons, muscles
catalytic agents
enzymes
regulating agents
hormones
immune agents
antigens and antibodeis
carriers
myoglobin and hemoglobin - O2 and CO2
nutritional role of proteins
provide AA and N
functions of protiens in food
water binding - texture emulsifiers gel forming coagulating dough forming palatability
what is palatablity
taste, texture, food quality
what protein in bread makes it palatable
gluten
what forms when milk coagulates. what products does this make
a curd. cheese, yogurt, sour cream
what forms when soy proteins coagulates. what product does this make
curd. tofu
what product is protein emulsification important for
sausages
endogenous enzymes
detrimental catalytic behavior in proteins - autolytic
exogenous enzymes
supplied by microbes in food
examples of beneficial catalytic behavior
proteases - tenderize meat
lipases - flavor development
amylases - form corn syrup.sugar products
example of a flavor potentiator
MSG - monosodium glutamate
examples of protein sources other than milk, eggs, and meat
rapeseed, beans, peas, leaves, microbes
what methods make meat analogs from soybean protein
texturization using extrusion
how many amino acids
20
what is the alpha carbon
connected to both NH2 and COOH groups
when is the AA protonated
low pH
when is the AA deprotonated
high pH
what is a zwitterion
COO- and NH3+. net charge zero
when does the zwitterion occur
isoelectric point
formula for isoelectric point
pI = (pk1 + pk2)/2
amino acids have attributes of a … (since the neutral form is still charged
salt
what properties do AA have that are similar to a salt
- crystalline strucutre
- wate soluble
- decompose at high temperatuers
- amphoteric - acid and bases
what occurs due to AA having 4 different substituents
optical isomerism and ability to rotate plant-polarized light. not superimposable
D or L?
both occur - racemic mixtures. but only L can form proteins
what is on the right for D and on the left for L
hyrgogen of alpha carbon
7 categories of amino acids
- aliphatic
- hydroxyl
- carboxyl
- base
- aromatic
- sulfur-containing
- imino
5 types of aliphatic AAs
glycine, alanine, valine, leucine, isoleucine
defining feature of aliphatic AA
hydrophobic
3 types of hydroxyl AA
serine, threonine, tryosine
defining feature of hydroxyl AA
presence of OH group
bonds that hydroxyl AAs make
h bonds
diester links
o-glycosidic links
2 types of carboxyl AA
aspartic acid and glutamic acid
defining feature of carboxyl AA
acidic. negative at pH7
isoelectric point is
bond that carboxyl AA can make
N-glycosidic link
what form do carboxyl AAs show in their natural form
amide - NH2. aspargie and glutamine
3 types of basic AA
histidine, lysine, arginine
defining feature of basic AA
basic - positive at pH7. isoelectric point is >ph7
what R group does histdine have
imidazole
what reaction does lysine do
maillard
what R group does arginine have
guanidine
3 types of aromatic AA
phenylalanine
tyrosine
tryptophan
which amino acid is in 2 groups
tyrosine
defining feature of aromatic AA
presence of aromatic group - absorbs UV light
what bonds can aromatic AA form
hydrophobic interactions
3 sulfur contianing AA
cysteine and methionine. cystine - which is the cysteine dimer
defining feature of sulfur AA
presence of a sulfur compound
what bonds can sulfur AA undego
disulfide crosslinks
what is a disulfide crosslink
RSSR - dimer of cysteine molecules, cystine, between peptides or within a peptide
2 types of imino aicds
proline and hydroxyproline
are iminoacids amino acids?
no - NH instead of NH2
what structure does proline interfere with and why
alpha helix because its incapable of forming hydrogen bonds
what increases as aliphatic AA chain lengthens
hydrophobicity
what is a diester link
one phosphate group linked to 2 hydroxyl AA via ester linkages
which is more acidic - aspartic or glutamic acid
aspartic
what does MSG stand for
monosodium glutamate
what reaction do carboxylic AA undergo
non-enzymatic browning - serve as reduction points for reducing sugars
what is more polar - amide or acid form of carboxyl AA
amide. makes it more watersoluble
is the sulfhydryl group acidic or basic
basic
what type of proteins contain iminoAA
structural
true or false - pH has no effect on charges of the side chains
false.
high ph - convert NH3 to NH2. supress + charge
low pH - convert COO to COOH. supress -
when is a protein least soluble
when it’s neutral at its isoelectric point
how many essential AA
9
what causes flavor from proteins
free AA and peptides
what do protein hydrolases do in food
make meaty/broth flavor
how do sulfur containing AA contribute to flavor
breaking down when heated releases H2S
what is responsible for bitter flavors
peptides
what is putrefaction
decay of proteins by enzymatic denaturation or decarboxylation by microbes. causes bad flavors and odors
True or false: cysteine is a peptide because it is formed of 2 AA
false
True or false: the isoelectric point of proteins is controlled by COOH and NH2 groups attached to the alpha carbon
false
A longer aliphatic chain in an AA will increase its…
hydrophobicity
Amino acids are optically active compounds because they have … alpha carbon atom
asymetric, chiral
The amphoteric properties of proteins help regulate the … of the human body
ph
The first carbon atom that attaches to a functional group is called…
alpha carbon
Coagulating milk casein is the main mechanism to produce
cheese
True or false: proline is considered an alpha amino acid
false
When the AA has its alpha amine group to the left, it rotates light
counterclockwise
AA can act as acids or bases, hence they are…
amphoteric
Disulfide crosslinks result from the presence of … in amino acids
sulfhydryl (methionine doesn’t form them)
The ability of AA to rotate plane-polarized light is…
optical isomerism
