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Food Chemistry - FDSC251 > U7 - a + b > Flashcards

U7 - a + b Flashcards

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1
Q

what type of amino acids link by a peptide bon

A

L

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2
Q

what is the N terminus

A

the beginning is signaled by the presence of a free amino group on the left hand side of the chain

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3
Q

what is the c terminus

A

the end of a chain is signaled by the presence of a free COOH group on the right hand side of the chain

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4
Q

what kind of bond is the peptide bond similar to and why

A

double bond. it’s essentially planar since the max rotation is 6 degrees

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5
Q

how are the carboxyl oxygen and amino hydrogen across a double bond situated

A

trans

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6
Q

what causes the primary structure to twist

A

L chiral form of amino acids and steric hindrance

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7
Q

what stabilizes the alpha helix

A

hydrogen bonding

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8
Q

what interact in an alpha helix

A

the carbonyl oxygen and the hydrogen on a nitrogen 4 amino acids down the chain

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9
Q

how many AA involved an 1 turn

A

3.6

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10
Q

what is the sequence that forms an alpha helix

A

-P-N-P-P-NN-P

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11
Q

what cant form an alpha helix

A

proline and hydroxyproline

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12
Q

what stabiizes the beta sheet

A

hydrogem bondin

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13
Q

how many AA involved in a beta sheet

A

5-15

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14
Q

what sequence forms a beta sheet

A

-N-P-N-P-N-P-N

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15
Q

what are the forms of the beta sheet and which is more stable

A

parallel and antiparallel *

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16
Q

what stabilizes the suprahelix

A

hydrogen bonds supplied by glycine

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17
Q

basic unit of suprahelix

A

tropocollagen

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18
Q

what is a suprahelix

A

3 identical macromolecules intertwined

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19
Q

what type of protein does a suprahelix form

A

structural collagen

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20
Q

why does the protein form a tertiary strucutre

A

to associate into its lowest free energy form

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21
Q

what kind of interactions are involved in the tertiary structure

A

hydrophobic interactions
electrostatic bonds between opposite charges
hydrogen bonding
covalent disulfide links

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22
Q

what is the quaternary structure and what 3 things can it form

A

2 or more tertiary globular proteins associating into dimers, tetramers, or octamers

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23
Q

what are the 2 most important simple proteins to food scientists

A

albumins and globulins

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24
Q

what are albumins soluble in

A

neutral distilled water

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25
Q

what are globulins soluble in

A

neutral, distilled salt solutions

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26
Q

examples of globulins

A

b-lactoglobulin, myosin and actin

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27
Q

what are glutelins soluble in

A

dilute acid or base

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28
Q

exmple of glutelin

A

gluten

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29
Q

what are prolamines soluble in

A

50-90% ethanol

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30
Q

example of prolamine

A

gliadin

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31
Q

what are scleroproteins solble in

A

nothing. not water ofr salts. makes it resistant to hydrolysis

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32
Q

examples of scleroproteins

A

keratin and collagen

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33
Q

what are histones soluble in

A

water

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34
Q

what do histones precipitate in

A

ammonia

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35
Q

what are conjugated proteins

A

proteins + prosthetic group

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36
Q

what are lipoprotein

A

protein + lipid

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37
Q

what function do lipoproteins serve

A

emulsifiers

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38
Q

examples of sources of lipoprotein

A

egg yolk, milk

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39
Q

what are glycoproteins

A

protein + carb

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40
Q

when do O links form

A

OH of serine or threonine and a sugar

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41
Q

when do N links form

A

amide of asparagine and a sugar

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42
Q

what are metalloproteins

A

protein + metal ion

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43
Q

what form do the metal ions usually take

A

loosely chelated

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44
Q

example of metalloprotein

A

Fe+ chelated to a porphyrin ring in myoglobin and hemoglobin

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45
Q

what are phosphoprotein

A

protein + inorganic phosphate

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46
Q

examples of phosphoprotein

A

casein and rennin

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47
Q

where does the phosphate link in phosphoproteins

A

OH of serine and threonine

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48
Q

True or false: albumins that are salted out of protein mixture solution retain their functional and physical properties

A

treu

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49
Q

An amino acid has to be … to form a peptide linkage

A

L-form

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50
Q

Alternating polar and nonpolar AA in a 1:1 ratio leads to the formation of…

A

beta sheet

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51
Q

True or false: quaternary structure is always observed in protein molecules

A

false

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52
Q

The bonding that is responsible for stabilizing the secondary structure is…

A

hydrogen

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53
Q

The process that leads to separation of different types of proteins according to their solubility in different salt solutions is…

A

salting out

54
Q

True or false: tertiary structure is stabilized by bonds other than hydrogen bonds

A

true

55
Q

The absence of an amino group in proline disrupts alpha helix formation because it can’t form…

A

hydrogen bonds

56
Q

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

A

b

57
Q

which is the most sensitive to its envitonment - protein, carbs, lipids

A

proteins

58
Q

what is denaturation

A

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

59
Q

what change in solubility occurs after denaturation

A

reduced

60
Q

what change in enzymatic occurs after denaturation

A

lost or decreased

61
Q

how does viscosity change after denaturation

A

increased and sometimes gelatinizes

62
Q

what change in crystallization occurs after denaturation

A

lost

63
Q

what change in reacted groups occurs after denaturation

A

they are now exposed and can polymerate or aggregate

64
Q

factors that cause denaturation

A

heat, pH, ionic strength chagne, chemical agents - hydrogen bond breakers, detergents organic solvents - surface forces,

65
Q

what happens when the protein is exposed to a higher level of heat

A

the kinetic energy increases, disturbing hydrogen bond

66
Q

what happens when the pH changes

A

affects the overall charge of the molecule and thus the electrostatic bonds in the tertiary

67
Q

what AAs are most vulnerable to changes in pH

A

Lys, Arg, Glu

68
Q

what happens when soluble proteins are exposed to pH near their isoelectric point

A

they precipitate

69
Q

how do hydrogen bond breakers function

A

they compete with peptides for hydrogen bonds

70
Q

examples of hydrogen bond breakers

A

urea, alcohol, acetone

71
Q

how do alcohol and acetone disrupt H bonds?

A

partial dehydration

72
Q

what is the degree in severity of alcohols breaking H bonds

A

not as severe as urea. the protein is precipitated from solution and minimally denatured

73
Q

functional importance of detergents

A

bridge hydrophobic and hydrophilic parts of a the protein, opening up the structure

74
Q

what structural property of detergents give them their functionality

A

they have both hydrophilic and hydrophobic parts

75
Q

example of a detergent

A

SDS - sodium dodecyl sulfate

76
Q

how do organic solvents denature proteins

A

they form a hydrophobic environment, thus causing the protein to turn inside out

77
Q

what effect can organic solvents have on protein function

A

can make them work in the opposite way - make lipase form triglycerides

78
Q

how do proteins reduce surface tension?

A

producing foams - air bubbles at the surface

79
Q

how do proteins orient themselves in these bubbles

A

hydrophobic facing the air and hydrophilic groups facing the water

80
Q

how do surface properties denature proteins

A

rearrangement due to IMFs in foam formation `

81
Q

what conditions are needed in the maillard reaction

A

protein-containing foods brown in heat + low-moisture conditions

82
Q

is the maillard reaction enzymatic or nonenzymatic

A

non-enzymatic

83
Q

what occurs in the molecular structure of the maillard reaction

A

an aldehyde group from a reducing sugar and a free Lys amino acid react, forming a glycosylamine

84
Q

what is amadori rearrangement

A

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

85
Q

what are melanoidins

A

brown pigment polymers of low-molecular weigh compounds. products of amadori rearrangement

86
Q

what value decreases in response to loss of Lys in non-enzymatic browning

A

protein efficiency ratio - PER

87
Q

what is PER

A

weight of protein gained / weight of protein consumed

88
Q

what type of amino acids undergo reactions with reducing sugars at high temps

A

AAs with a secondary amino group

89
Q

what condition is needed for cross-linking

A

high temperature

90
Q

what occurs during a cross-linking reaction

A

formation of an amide bond between COOH and NH2 groups of side chains

91
Q

why isnt the product of a cross-linking reaction a peptide bond

A

doesnt involve the alpha carbon

92
Q

is the product of cross-linking digestible?

A

no; it’s not a peptide bond so proteolytic enzymes cant act on it

93
Q

how are proteins treated to extract protein isolates

A

with alkali and heat

94
Q

can new amino acids be formed if treated with heat and base?

A

yes - but only if free amino acids are available

95
Q

what is lysinoalanine

A

an amino acid formed when proteins are treated with base and heat - poorly absorbed in the body

96
Q

when does racemization between L and D amino acids occur

A

strong alkaline environmental conditions

97
Q

what does proteolysis result in

A

loss of function and reduction in molecular weight. can cause bitter hydroophobic peptides

98
Q

how does chymosin effect cheese making

A

cleaves he bond between 105phe and 106met in k-casein

99
Q

what is putrefaction

A

degradation of free AA produced by proteolytic enzymes secreted by microorganisms

100
Q

what are the 2 types of microbial enzymes involved in putrefaction

A

deaminases and decarboxylases

101
Q

what is the function of deaminases and decarboxylases

A

remove amino acids and carboxyl groups from free AAs, producing volatiles

102
Q

when is decarboxylase most active

A

low, acidic pH

103
Q

when is deaminase active

A

high, basic pH

104
Q

effect of putrefaction

A

lower molecular weight and more volatile products

105
Q

what inhibits decarboxylation

A

DFMO

106
Q

what supplies the enzymes for putrefaction

A

microbes

107
Q

why are fish more susceptible to putrefaction

A

they undergo normal putrefaction + form products similar to those formed in putrefaction

108
Q

what is the putrefactive- like reaction in fish

A

conversion of TMAO to TMA by trumethylamine-N-oxide reductase

109
Q

is TMAO an amino acid>

A

no, but it has the same sensory putrefactiv properties

110
Q

what is water binding capacity dependent on?

A
  1. presence of ions
  2. presence of hydrogen binding sites
  3. presence of polysaccharide prosthetic groups
  4. amino acid composition
111
Q

how does water interact with the protein

A

it forms a hydration shell around polar groups

112
Q

what is moisture sorption isotherm

A

it illustrates the equilibrium moisture associated with a material as a funciton of humidity - at constant temp1

113
Q

what are the 3 regions in the moisture sorption isotherm

A
  1. bound water - H bonded or hydrated with ionic species
  2. water associated with bound water, but more mobile
  3. free water - mobile water
114
Q

what are the 3 types of dehydration

A
  1. freeze drying
  2. spray drying
  3. drum drying
115
Q

why does freezing cause denaturation in tissue systems

A

change in ionic strength and pH –> removal of water

116
Q

why is freeze drying prefered

A

it maintains functionality, nutritive quality, and enzyme activity

117
Q

why can denaturation occur in spray drying

A

higher temperatures are used and shear at the nozzle

118
Q

when can denaturation and browning occur for drum dring

A

if sugars are present

119
Q

Denaturation doesn’t effect the … structure of protein molecules

A

primary

120
Q

True or false: melting cheese in grilled cheese sandwich is an example of milk casein denaturation

A

false

121
Q

True or false: non enzymatic browning enhances the sensory characteristics and nutritive value of a food product

A

false

122
Q

With the absence of carbohydrates and under high temperature conditions … reaction happens between protein molecules

A

crosslinking

123
Q

Proteins with significant amounts of carboxyl functional groups on their side chain are sensitive to pH changes due to the … on that functional group

A

charge

124
Q

In addition to surface charge, the … is essential for suspending protein molecules in their colloids

A

hydration shell

125
Q

True or false: the hydration shell is crucial for the stability of protein colloidal suspension in water

A

true

126
Q

True or false: Proteolysis is always considered undesirable in food

A

false

127
Q

True or false: cheese making is a result of enzymatic proteolysis

A

true

128
Q

The golden crispy fried chicken crust is a result of … reaction

A

maillard

129
Q

Alcohol denature proteins due to…

A

partial dehydration

130
Q

The change in pH denatures protein due to the change of … of side chain functional groups

A

charge

131
Q

Frying an egg, which his a form of protein denaturation that takes place

a. Chemical composition
b. Physical properties
c. Both
d. Neither

A

b

Food Chemistry - FDSC251 (10 decks)

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