Proteins I Flashcards
______ flavors can arise in proteinaceous systems due to low molecular weight ________________
Bitter
hydrophobic peptides
Aromatic amino acids are largely (hydrophilic/hydrophobic)
hydrophobic
What does the following sequence favour?
-P-N-P-P-N-N-P-
a-helix formation
Proline and hydroxyproline are found extensively in __________ proteins
structural
________ can serve as an attack point for reducing sugars
Amides
The hydrophobicity of ________ AA increases as their chain lengthens
aliphatic
The amino acids linked by peptide bonds represent the _______ level of structure of proteins
primary
_______ is 50% ionized at pH 10.5
Lysine
Glycine, Alanine, Valine, Leucine, and Isoleucine are _______ AA.
aliphatic
______________ AA are readily hydrolyzed to their corresponding acids under conditions of heat and/or acidic conditions
Carboxylic
OH-group on hydroxyl AA serve as a _________ bonding site and is a generally reactive moiety.
hydrogen
____________ AA are found extensively in structural proteins
Imino acids
The D configuration has an OH group on the _______
right
Gamma-COOH group of ___________ are 50% ionized at pH 4.2
glutamic acids
Quaternary structures do not have ___________, unlike tertiary structure
NO covalent bonds (disulfide crosslinks)
What are nonpolar AA?
Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Phenylalanine or Tryptophan
Serine, Threonine, and Tyrosine are __________ AA.
hydroxyl
A protein’s lowest point of solubility is at its ____________
isoelectric point
___ separate macromolecules, of which __ are identical, are intertwined to form a suprahelix
3 2
_______ aromatic AA is reactive due to its OH group; forms _____ linkages with phosphate
Tyrosine ester
At low pH, the amino acid is _______
protonated (NH3+)
The ____________ AA provide flavor due to their breakdown when being cooked, mainly due to the release of ______
sulfur-containing H2S
_______ speed up the flavor development in cheese
Lipases
The R group in Histidine is the _________ group
imidazole
What determines whether a helical structure forms?
AA composition
The ability to leaven dough is specifically due to __________
Gluten
The peptide bond is an ______ bond
amide
Surimi makes use of __________ to make analogs of crab meat and scallops
pollock
Monosodium glutamate is the _____________ salt of glutamic acid
monosodium
The _______ amino group is the most reactive amino group in Lysine.
epsilon
Synthetic production of amino acids generally leads to _________ mixtures of D and L isomers
racemic
In carboxylic AA, at pH 7 and above, most of the free carboxyl groups would be _________ charged.
negatively
Why aren’t proline and hydroxyproline considered to be amino acids?
- They do not contain a true amino group (NH2) - Instead they contain an imino group (NH)
________ readily undergoes rapid reaction with reducing sugars (Maillard reaction), which reduces the availability of this essential amino acid
Lysine
What structure does the following sequence favour?
-N-P-N-P-N-P-N-
B-sheet formation
Due to the ____________ form of AA and __________, protein polymers tend to twist upon itself
L-chiral steric hindrance
What are exogenous enzymes supplied by?
Microorgniams contaminating food
Amino acids can act as acids or bases and are said to be __________
amphoteric
The ___ structure wants to reduce its free energy
3rd
__________ are mirror images of a compound, which are not superimposable. ________ are an example
Enantiomers Amino acids
For all amino acids (except _______), the alpha-carbon is an asymmetric carbon
Glycine
The __________ group of cysteine is very basic, and ionized at pH 8.2
sulfhydral (-SH)
Meat contains an appreciable amount of ___________, which provide flavor as well as being a source of ____________ products
free amino acids Maillard reaction
_______ is considered to be somewhat basic, and is capable of ionizing beyond pH 10
Tryptophan
_______ are used to tenderize meat.
Proteases
Proteins that have a significant amount of _______ and _______ tend to have high isoelectric points
lysines arginines
All proteins are synthesized from __ amino acids
L
Proteins are composed of ___ amino acids
20
_________ AA are relatively unreactive
aliphatic
The L configuration has an OH group on the _______
left
Disrupted _______ is extensively used in the food industry as a gelling agent
collagen
When an asymmetric carbon is present, molecules can rotate ___________ light in _______ directions
plane-polarized opposite
The suprahelix is held together by _______ bonds supplied by ________
hydrogen glycine
Lysine contains ___ amino groups
2
Lysine, Histidine, and Arginine are _______ AA.
basic
The side chains of the amides of _____________ and _____________ play a role in non-enzymatic browning reactions
aspartic acid glutamic acid
_____________ are used to make meaty flavours
Protein hydrolysates
A very low pH is needed to suppress the _____ charges on the _____ side chains (i.e. to convert _____ to ____)
negative acidic COO- to COOH
_____________ and _____________ do not contribute to a-helix formation
Proline hydroxyproline
A very high pH is needed to suppress the _____ charges on the _____ side chains (i.e. to convert _____ to ____)
positive basic NH3+ to NH2
_______ is used to remove headspace oxygen from food packages
Glucose oxidase
The _______________ of proteins is important in stabilizing protein conformation through ________________
charge distribution electrostatic force
The _____ are more polar than the acid forms, and hence make proteins (more/less) water-soluble
amides more
The breakdown products of proteins , ________ and _______, are major contributors to flavor
amino acids peptides
__________ is a breakdown product of proteins that contributes to flavor in Chinese cuisine
MSG
__ amino acids cannot be used by the body for protein synthesis
D
Amino acids decompose at relatively ___ temperatures due to their attributes as a _____
high salt
In a diester linkage, one ________ group is linked to two ________ AA via ester linkages
phosphate hydroxyl
Sugars and carbohydrate are often attached to the amide group of asparagine by an ___-glycosidic linkage
N
What is autolytically?
Using endogenous enzymes
Soy sauce is a _____________ produced by the fermentation of soybeans
protein hydrolysate
The quaternary structure of proteins represents ___ or more tertiary globular proteins associating as a group to form _______, ______, or________
2 dimers, tetramers, or octamers
When _________________ AA are incorporated into a protein side chain, they interrupt the natural tendency to form an _______ since they cannot form intramolecular ________ bonds
imino a-helix hydrogen
________ is weakly basic; ionized at pH 6
Histidine
_______ is a protein with elastic properties not found in other grains
Gluten
The peptide bond has a ____________ character
partial double bond
_________ AA play an important role in stabilizing protein conformation through hydrophobic interactions
Aromatic
What is attached to the alpha carbon in an amino acid?
- NH2 - COOH - R-group
Amino acids have a crystalline structure, and are soluble in water since they have the attributes of a _______
salt
The a-helix is stabilized by _______ bonding due to the repetitive proximity of the peptide ___________ (electron-rich) and the _________ from the nitrogen ___ residues away
hydrogen carbonyl oxygen hydrogen 4
Proline and hydroxyproline are _______ acids
imino
________ are usually 5-15 AA in length
B-strands
_____ has been linked to Chinese Restaurant Syndrome
MSG
Carbohydrates are often attached to the OH group of _________ or _________ by an __-glycosidic bond
serine threonine O
When the overall charge on the protein averages out to neutral, the protein is said to be at its ____________
isoelectric point
The suprahelix is found in _________
collagen
_________ AA are very reactive and play an important role in protein structure
Carboxylic
At its isoelectric point, the amino acid is a ___________
zwitterion
_______ proteins can form a curd
Milk and soybean
________ contains a very basic guanidino group, which has a pKa of 12.5
Arginine
The structure of an enantiomer is _______
tetrahedral
Phenylalanine, Tyrosine, and Tryptophan are _______ AA.
aromatic
In a peptide bond, the ________ is linked to the __________
a-amino group a-carboxyl group
Does glutamic acid or glutamine dissolve better in water?
Glutamine
Collagen is a major structural animal protein composed of large amounts of _______ and _______
glycine proline
The polypeptide chain starts at the __-terminus with the ____ group, and ends at the ___-terminus with the ____ group
N amino C carboxyl
The C-CO-NH-C unit is planar with the ___________ and ___________ of the peptide bond always trans to each other
carboxyl oxygen amino hydrogen
Aspartic and glutamic acids are found in nature as their corresponding _______: ____________ and ____________
amides asparagine glutamine
Proteins that contain significant amounts of aspartic and glutamic acid tend to have _____ isoelectric points.
low
Rotation of the _________ is restricted to 6o
peptide bond
As the pH of an amino acid is increased, ___ protons are stripped away
Two
________ is very reactive and can undergo oxidation/reduction reactions to form the _____ cystine
Cysteine
dimer
The major feature of ________ AA is their ability to form an ester linkage with a phosphate group
hydroxyl
________ linkages play an important role in the 3D structure of a protein, and make it less susceptible to denaturation
Diester
__________ is a synonym for optical isomer
Enantiomers
AA are generally considered to be precursors of _____________ odors and flavors in meat and fish
putrefactive
Putrefactive odors and flavors are due to compounds produced by the _____________________________ by _________
enzymatic deamination or decarboxylation of free AA microbial enzymes
Meat analogs from soy protein via ___________ using __________ technology
texturization extrusion
B-carboxyl group of __________ are 50% ionized at pH 3.8
aspartic acids
What is the issue with racemic mixtures?
Only half have AA activity
Cysteine, Cystine, and Methionine are _______ AA.
sulfur-containing
If a _____ forms between ___ cysteine residues, it forms a _______________
dimer 2 disulfide crosslink
__ AA are considered essential
9
Each turn of the a-helix involves ___ AA residues
3.6
_______ are used to manufacture corn syrups/sugars
Amylases
What are the 5 types of interactions/bonds found in the tertiary structure of proteins?
- Hydrophobic interactions - Electrostatic interactions - Hydrogen bonding - Disulfide crosslinks - Van der Waals interactions
_______ amino acids are responsible for UV absorbance of most proteins at 280
Aromatic
The basic subunit for the suprahelix is ___________
tropocollagen
