U7 - a + b Flashcards
what type of amino acids link by a peptide bon
L
what is the N terminus
the beginning is signaled by the presence of a free amino group on the left hand side of the chain
what is the c terminus
the end of a chain is signaled by the presence of a free COOH group on the right hand side of the chain
what kind of bond is the peptide bond similar to and why
double bond. it’s essentially planar since the max rotation is 6 degrees
how are the carboxyl oxygen and amino hydrogen across a double bond situated
trans
what causes the primary structure to twist
L chiral form of amino acids and steric hindrance
what stabilizes the alpha helix
hydrogen bonding
what interact in an alpha helix
the carbonyl oxygen and the hydrogen on a nitrogen 4 amino acids down the chain
how many AA involved an 1 turn
3.6
what is the sequence that forms an alpha helix
-P-N-P-P-NN-P
what cant form an alpha helix
proline and hydroxyproline
what stabiizes the beta sheet
hydrogem bondin
how many AA involved in a beta sheet
5-15
what sequence forms a beta sheet
-N-P-N-P-N-P-N
what are the forms of the beta sheet and which is more stable
parallel and antiparallel *
what stabilizes the suprahelix
hydrogen bonds supplied by glycine
basic unit of suprahelix
tropocollagen
what is a suprahelix
3 identical macromolecules intertwined
what type of protein does a suprahelix form
structural collagen
why does the protein form a tertiary strucutre
to associate into its lowest free energy form
what kind of interactions are involved in the tertiary structure
hydrophobic interactions
electrostatic bonds between opposite charges
hydrogen bonding
covalent disulfide links
what is the quaternary structure and what 3 things can it form
2 or more tertiary globular proteins associating into dimers, tetramers, or octamers
what are the 2 most important simple proteins to food scientists
albumins and globulins
what are albumins soluble in
neutral distilled water
what are globulins soluble in
neutral, distilled salt solutions
examples of globulins
b-lactoglobulin, myosin and actin
what are glutelins soluble in
dilute acid or base
exmple of glutelin
gluten
what are prolamines soluble in
50-90% ethanol
example of prolamine
gliadin
what are scleroproteins solble in
nothing. not water ofr salts. makes it resistant to hydrolysis
examples of scleroproteins
keratin and collagen
what are histones soluble in
water
what do histones precipitate in
ammonia
what are conjugated proteins
proteins + prosthetic group
what are lipoprotein
protein + lipid
what function do lipoproteins serve
emulsifiers
examples of sources of lipoprotein
egg yolk, milk
what are glycoproteins
protein + carb
when do O links form
OH of serine or threonine and a sugar
when do N links form
amide of asparagine and a sugar
what are metalloproteins
protein + metal ion
what form do the metal ions usually take
loosely chelated
example of metalloprotein
Fe+ chelated to a porphyrin ring in myoglobin and hemoglobin
what are phosphoprotein
protein + inorganic phosphate
examples of phosphoprotein
casein and rennin
where does the phosphate link in phosphoproteins
OH of serine and threonine
True or false: albumins that are salted out of protein mixture solution retain their functional and physical properties
treu
An amino acid has to be … to form a peptide linkage
L-form
Alternating polar and nonpolar AA in a 1:1 ratio leads to the formation of…
beta sheet
True or false: quaternary structure is always observed in protein molecules
false
The bonding that is responsible for stabilizing the secondary structure is…
hydrogen
The process that leads to separation of different types of proteins according to their solubility in different salt solutions is…
salting out
True or false: tertiary structure is stabilized by bonds other than hydrogen bonds
true
The absence of an amino group in proline disrupts alpha helix formation because it can’t form…
hydrogen bonds
An electrostatic attraction between 2 polar groups that occurs when a hydrogen atom covalently bonds to a highly electronegative atom such as nitrogen or oxygen is called
a. Electrostatic bonding
b. Hydrogen bonding
c. Covalent bonding
b
which is the most sensitive to its envitonment - protein, carbs, lipids
proteins
what is denaturation
unfolding of tertiary and unraveling of secondary due to disruption of the weak interactions - not a breaking of the peptide bonds in the primary structure
what change in solubility occurs after denaturation
reduced
what change in enzymatic occurs after denaturation
lost or decreased
how does viscosity change after denaturation
increased and sometimes gelatinizes
what change in crystallization occurs after denaturation
lost
what change in reacted groups occurs after denaturation
they are now exposed and can polymerate or aggregate
factors that cause denaturation
heat, pH, ionic strength chagne, chemical agents - hydrogen bond breakers, detergents organic solvents - surface forces,
what happens when the protein is exposed to a higher level of heat
the kinetic energy increases, disturbing hydrogen bond
what happens when the pH changes
affects the overall charge of the molecule and thus the electrostatic bonds in the tertiary
what AAs are most vulnerable to changes in pH
Lys, Arg, Glu
what happens when soluble proteins are exposed to pH near their isoelectric point
they precipitate
how do hydrogen bond breakers function
they compete with peptides for hydrogen bonds
examples of hydrogen bond breakers
urea, alcohol, acetone
how do alcohol and acetone disrupt H bonds?
partial dehydration
what is the degree in severity of alcohols breaking H bonds
not as severe as urea. the protein is precipitated from solution and minimally denatured
functional importance of detergents
bridge hydrophobic and hydrophilic parts of a the protein, opening up the structure
what structural property of detergents give them their functionality
they have both hydrophilic and hydrophobic parts
example of a detergent
SDS - sodium dodecyl sulfate
how do organic solvents denature proteins
they form a hydrophobic environment, thus causing the protein to turn inside out
what effect can organic solvents have on protein function
can make them work in the opposite way - make lipase form triglycerides
how do proteins reduce surface tension?
producing foams - air bubbles at the surface
how do proteins orient themselves in these bubbles
hydrophobic facing the air and hydrophilic groups facing the water
how do surface properties denature proteins
rearrangement due to IMFs in foam formation `
what conditions are needed in the maillard reaction
protein-containing foods brown in heat + low-moisture conditions
is the maillard reaction enzymatic or nonenzymatic
non-enzymatic
what occurs in the molecular structure of the maillard reaction
an aldehyde group from a reducing sugar and a free Lys amino acid react, forming a glycosylamine
what is amadori rearrangement
after glycosylamine productionloss of water within the sugar portion of a molecule, causing scission and breaking up in to low-molecular-weight compounds that polymerize into brown pigments called melanoidins
what are melanoidins
brown pigment polymers of low-molecular weigh compounds. products of amadori rearrangement
what value decreases in response to loss of Lys in non-enzymatic browning
protein efficiency ratio - PER
what is PER
weight of protein gained / weight of protein consumed
what type of amino acids undergo reactions with reducing sugars at high temps
AAs with a secondary amino group
what condition is needed for cross-linking
high temperature
what occurs during a cross-linking reaction
formation of an amide bond between COOH and NH2 groups of side chains
why isnt the product of a cross-linking reaction a peptide bond
doesnt involve the alpha carbon
is the product of cross-linking digestible?
no; it’s not a peptide bond so proteolytic enzymes cant act on it
how are proteins treated to extract protein isolates
with alkali and heat
can new amino acids be formed if treated with heat and base?
yes - but only if free amino acids are available
what is lysinoalanine
an amino acid formed when proteins are treated with base and heat - poorly absorbed in the body
when does racemization between L and D amino acids occur
strong alkaline environmental conditions
what does proteolysis result in
loss of function and reduction in molecular weight. can cause bitter hydroophobic peptides
how does chymosin effect cheese making
cleaves he bond between 105phe and 106met in k-casein
what is putrefaction
degradation of free AA produced by proteolytic enzymes secreted by microorganisms
what are the 2 types of microbial enzymes involved in putrefaction
deaminases and decarboxylases
what is the function of deaminases and decarboxylases
remove amino acids and carboxyl groups from free AAs, producing volatiles
when is decarboxylase most active
low, acidic pH
when is deaminase active
high, basic pH
effect of putrefaction
lower molecular weight and more volatile products
what inhibits decarboxylation
DFMO
what supplies the enzymes for putrefaction
microbes
why are fish more susceptible to putrefaction
they undergo normal putrefaction + form products similar to those formed in putrefaction
what is the putrefactive- like reaction in fish
conversion of TMAO to TMA by trumethylamine-N-oxide reductase
is TMAO an amino acid>
no, but it has the same sensory putrefactiv properties
what is water binding capacity dependent on?
- presence of ions
- presence of hydrogen binding sites
- presence of polysaccharide prosthetic groups
- amino acid composition
how does water interact with the protein
it forms a hydration shell around polar groups
what is moisture sorption isotherm
it illustrates the equilibrium moisture associated with a material as a funciton of humidity - at constant temp1
what are the 3 regions in the moisture sorption isotherm
- bound water - H bonded or hydrated with ionic species
- water associated with bound water, but more mobile
- free water - mobile water
what are the 3 types of dehydration
- freeze drying
- spray drying
- drum drying
why does freezing cause denaturation in tissue systems
change in ionic strength and pH –> removal of water
why is freeze drying prefered
it maintains functionality, nutritive quality, and enzyme activity
why can denaturation occur in spray drying
higher temperatures are used and shear at the nozzle
when can denaturation and browning occur for drum dring
if sugars are present
Denaturation doesn’t effect the … structure of protein molecules
primary
True or false: melting cheese in grilled cheese sandwich is an example of milk casein denaturation
false
True or false: non enzymatic browning enhances the sensory characteristics and nutritive value of a food product
false
With the absence of carbohydrates and under high temperature conditions … reaction happens between protein molecules
crosslinking
Proteins with significant amounts of carboxyl functional groups on their side chain are sensitive to pH changes due to the … on that functional group
charge
In addition to surface charge, the … is essential for suspending protein molecules in their colloids
hydration shell
True or false: the hydration shell is crucial for the stability of protein colloidal suspension in water
true
True or false: Proteolysis is always considered undesirable in food
false
True or false: cheese making is a result of enzymatic proteolysis
true
The golden crispy fried chicken crust is a result of … reaction
maillard
Alcohol denature proteins due to…
partial dehydration
The change in pH denatures protein due to the change of … of side chain functional groups
charge
Frying an egg, which his a form of protein denaturation that takes place
a. Chemical composition
b. Physical properties
c. Both
d. Neither
b
