P1. Intro + amino acids Flashcards
5 biochemical/physiological roles of proteins
- play a role in structural components of skin, muscles, tendons and bones
- serve as catalytic agents for specific reactions (ie enzymes) without which life would not be possible
- serve as regulating agents or hormones
- act as antigens and serve as antibodies
- serve as carriers of O2 and CO2 (myoglobin and hemoglobin)
Proteins in diet provide (3)
- amino acids
- nitrogen
- energy (4cals/g)
which amino acids are essential? what does essential mean?
- essential = cannot be synthesized at all or fast enough to meet the body’s requirements
- histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, valine, lysine
do animal or plant proteins have all essential amino acids?
- animals do!
- plant proteins are generally deficient in one or more of the essential acids
food scientists look beyond nutritional aspects of food proteins to focus on their ____________
functionality
protein functionality refers exclusively to ?
- 5 examples
non nutritional functional properties of proteins in food systems
- water binding capacity
- emulsification capacity
- gel-forming ability
- coagulating properties
- dough-forming abilities
functional properties (increase/decrease) the value of proteins to manufacturers and consumers
increase!
protein functionality is important from a ____________ standpoint
palatibility
bread is much more palatable than whole kernels of wheat –> ability to leaven dough is due specifically to __________, a protein with peculiar _________ properties not found in other grains
- gluten
- elastic
water holding capacity of proteins is important for __________ or __________ of a number of food products
- texture
- juiciness
monosodium glutamate is a well-known _______ _________
protein hydrolysate
stability of proteins and the reactions they undergo during processing have to be considered –> __________ vs ______________
nutritional loss vs functionality loss
catalytic behavior in form of enzymes can be both ___A______ and _____B_______
- examples of B
A: beneficial
B: detrimental
- degradation of many food components either autolytically (endegenous enzymes) or as exocgenous enzymes supplied by microorganisms contaminating food
examples of uses of enzymes in food processing (4)
- proteases to tenderize meat
- lipase to speed up flavor development in cheese
- amylase to manufacture corn syrups/sugar (soft drinks)
- glucose oxidase to remove headspace oxygen from food packages
plant sources vs animal protein sources –> 3 benefits of plant + 2 benefits of 1 type of animal
- plant source: abundant, cheaper and more energy efficient to produce than animal or dairy source
- dairy sources: better cost and higher functionality than casein, egg albumin, soybean and other protein sources
meat analogs are made of ____ protein via ___________ using extrusion technology
- soy protein
- texturization
what makes use of pollock to make analogs of crab meat and scallops?
surimi
how many amino acids make up proteins?
generally 20
- but actually more than 20! (20 factorial) combinations and permutations
what is the secret to the success of living systems? (in regards to proteins)
their ability to build an almost infinite variety of protein structures, each with own unique chemical and physical properties
what is the general formula of an amino acid?
alpha carbon attached to COOH, NH2, H and functional group
what defines an amino acid?
the fact that an amino group (NH2) and a carboxylic acid (COOH) are attached on the same carbon (alpha carbon)
- presence of these 2 functional in such close proximity leads to some unusual properties
describe ion charges of amino acid (protonated/deprotonated?)at low pH, at neutral pH and at high pH
- low pH: NH3+ and COOH
- neutral pH: NH3+ and COO-
- high pH: NH2 and COO-
what is a zwitterion?
- what H moves where? why?
- when does it happen?
- NH3+ and COO- on the same amino acid
- the aa does not have they neutrally charged structure (NH2 and COOH) –> instead H from COOH moves to NH2
- at the amino acid’s isoelectric point
formula for isoelectric point
pI = (pk1 + pk2)/2
is the zwitterion considered charged? consquence?
yes! even with its neutral charge overall
- hence, amino acids have attributes of a salt (bc have positive and negative charges)
physical properties of aa (3)
- crystalline structure
- soluble in water
- decompose at relatively high temperatures
aa act as ______ and _______ and are said to be ___________
(IMPORTANT)
acids and bases
- amphoteric
for all aa, except ________, the alpha carbon is an _____________ carbon –> what does it mean?
- glycine
- asymmetric carbon
- 4 different substituents on the alpha carbon
alpha carbon is asymmetric –> what does that entail? (2)
- aa show optical isomerism (has a chiral carbon)
- can rotate plane-polarized light in opposite directions
optical isomers are _________ images of a compound, which are not __________
- mirror
- superimposable
what is the 3D structure of an amino acid (that makes it an optical isomer)?
tetrahedral
what is the reference compound to determine optical isomerism?
- where is the OH for D vs L
- glyceraldehyde
- COOH/large functional group on top, OH on the right = dextro (D)
- COOH on top, OH on the left = levo (L)
which group determines L or D on an amino acid?
NH3+ group!
(with COO- on top)
all proteins in body are only synthesized from __ amino acids
- why not the other version?
L!
- D form cannot be used by body for protein synthesis
synthetic production of aa generally leads to _________ ___________ of D and L isomers, of which only ____ have aa activity
- racemic mixture
- 1/2
7 categories of amino acids
- aliphatic side chains
- hydroxyl side chains
- carboxylic side chains
- basic side chains
- aromatic side chains
- sulfur containing aa
- imino acids
which 5 aa are aliphatic?
- glycine
- alanine
- valine
- isoleucine
- leucine
major feature of aliphatic side chains? (2)
- relatively unreactive
- increasing hydrophobicity as the chain lengthens
which 3 aa are hydroxyl aa?
- serine
- threonine
- tyrosine
major features of hydroxyl side chains? (2)
- OH = reactive moiety = serve as hydrogen bonding site
- ability to form ester linkage with phosphate group
__________ linkages, where one _________ group is linked to ____ hydroxyl aa via _______ linkages can play an important role in the ______ structure of a protein and make it less susceptible to _______________
- diester linkages
- 1 phosphate groups
- linkes to 2 hydroxyl aa
- via ester linkages
- the 3D structure
- LESS susceptible to denaturation
which proteins have a lot of diester linkages, making them very stable to ________
- milk proteins! like casein
- stable to heat
carbohydrates are often attached to the OH group of __________ or ________ by an ___________ linkage
- serine
- threonine
- O-glycosidic linkage
what are the 2 carboxylic amino acids (+ 2)?
- aspartic acid
- glutamic acid
- asparagine
- glutamine
the __ carboxylic group of aspartic acid is ___% ionized at pH 3.8 while the ___ carboxyl of glutamic acid is ___% ionized at pH ____ (higher or lower than aspartic?)
- gamma
- 50%
- delta
- 50%
- pH 4.2
the pkas of glutamic acid are higher or lower than aspartic acid for respective groups?
higher!
proteins that contain significant amounts of aspartic and glutamic acid tend to have (high/low?) isoelectric points
low
the __________ salt of glutamic acid (name?) is renowned for its flavor enhancing/flavor-potentiating properties
- monosodium salt
- monosodium glutamate
aspartic acid and glutamic acid are also found in nature as their corresponding ________: (2)
- corresponding amides
- asparagine and glutamine
the amides are more/less polar than acid forms and hence make proteins more ________________
- more
- water-soluble
glutamic acid, glutamine, asparagine, aspartic acid –> what is the order of increasing hydrophobicity? relative to glycine
- glutamine (-400)
- asparagine (-40)
- aspartic acid (2250)
- glutamic acid (2300)
carboxylic group:
sugars and carbohydrate are often attached to the _________ group of __________ by a _________________ linkage
- amide group
- asparagine
- N-glycosidic linkage
asparagine and glutamine are readily hydrolyzed to their corresponding acids under which 2 conditions?
- heat
- acidic conditions
chemical reaction equation of hydrolysis of asparagine?
asparagine + H2O –> aspartic acid + NH4+
3 basic amino acids?
- lysine
- histidine
- arginine
lysine has _(#)__ amino groups, with the ____ amino group being one of the most reactive groups: 50% ionized (NH3+) at pH ______
- 2
- epsilon
- 10.5
lysine readily undergoes rapid reaction with ___________ ___________ (name of reaction?), which reduces/increases the availability of this __________ aa.
- reducing sugars
- Maillard reaction
- reduces
- essential
arginine has a very basic ________ group, with a pK of ______
guanidino group
- 12.5
proteins that have significant amounts of lysine and arginine tend to have high/low isoelectric points
high
R group of histidine?
- strongly or weakly basic?
imidazole group
- weakly basic: 50% ionized at pH 6
the overall charge of protein is determined by charges on the ________ and ________ amino acids side chains. especially bc ?
- acidic and basic
- amino and carboxylic groups on alpha carbon are tied up in the peptide bonds
pH strongly affects charges on side chains:
- need a very high/low pH to suppress positive charges on the acidic/basic side chains (convert ______ to ______)
- need a very high/low pH to suppress negative charges on the acidic/basic side chains (convert _______ to ________)
- high pH
- basic side chains
- NH3+ to NH2
- low pH
- acidic
- COO- to COOH
when the overall charge of the protein averages out to neutral, the protein is said to be at its _________ ________, usually a point of highest/lowest solubility
- isoelectric point
- lower solubility
3 aromatic aa
- phenylalanine
- tyrosine
- tryptophan
aromatic aa have an ________ _____ in their structure and are responsible for the ______________ absorbance of most proteins at _____ nm
- aromatic ring
- ultraviolet (UV)
- 280
aromatic aa are all quite (hydrophilic/hydrophobic) and play an important role in (3 words) through ___________ interactions
- hydrophobic
- stabilizing protein conformation
- hydrophobic
tryptophan is considered to be somewhat _______ and is capable of ionizing beyond pH _____.
- basic
- 10
tyrosine is reactive owing to its _____ group, capable of forming ______ linkages with __________ and is often used to conjugate with (2)
- OH
- ester
- phosphates
- sugars and polysaccharides
3 sulfur containing amino acids
- cysteine
- dimer cystine
- methionine
cysteine is very reactive and can undergo ________/_________ reactions to form the dimer _______, which can in turn be reduced to ___________
- oxidation/reduction
- cystine
- cysteine
if a dimer forms btw 2 ________ residues in 2 separate protein strands or within a single strand, it forms a _______ crosslink (__-___-____-____)
cysteine
- disulfide
- R-S-S-R
the sulfhydryl group (-___) of cysteine is acid/basic and is 50% ionized at pH ______.
- SH
- basic
- 8.2
by definition, (2) are not true aa because they don’t contain ?
- proline and hydroxyproline
- contain true amino (NH2) group, but an imino (NH) group instead
Which 2 aa are imino acids?
proline and hydroxyproline
proline and hydroxyproline are unique bc they interrupt what?
natural tendancy to form an alpha helix
proline and hydroxyproline are found extensively in structural proteins such as ________
collagen
