Exam - Proteins Flashcards
what does protein provide
amino acids for protein synthesis
is protein an energy source
only when needed
what is protein a substrate for
glucose synthesis
what is the recommended protein intake
10-30%
what is the average protein consumption in North America
16% of daily calories
how many proteinorganic amino acids are there in humans
20 standard - 21 including selenocysteine
what is a proteinorganic amino acid
an animo acid that is incorporated into a protein during translation
what proteinorganic amino acids are part of the standard genetic code
all but selenocysteine
how many amino acids are considered essential for humans
9
what was the last amino acid to be added to the essential list
Histidine
where is protein mainly found in the body
blood (RBC)
connective tissue
eye lens
what percentage of protein is found in the RBC
35%
what percentage of protein is found in connective tissue
37%
what percentage of protein is found in the eye lens
34%
is percent protein content higher in animal derived foods or plants
animal derived foods
what is the only amino acid that does not exist as an enantiomer
glycine
what is the naturally occurring configuration of amino acids
L
how are amino acids connected
peptide bonds (covalent chemical bond) - condensation rxn
how do you break a peptide bond
add H20 (hydrolysis)
how many amino acids in dipeptides
2
how many amino acids in tripeptides
3
how many amino acids in oligopeptides
~50
how many amino acids in polypeptides
> 50
what is a biologically active protein made of
1 or more polypeptides
what is correct polypeptide folding assisted by
chaperone proteins
what is the primary structure of proteins determined by
the DNA sequence
what does the primary structure of a protein refer to
a polypeptide chain of amino acids
what is the secondary structure of proteins determined by
the hydrogen bonds that create a more stabile structure
what do the hydrogen bonds in proteins involve
only backbone atoms - no side chains
what are the 2 types of stabilized structures to exist
B-pleated sheets and a-helix
how does an a-helix occur
amino group makes a hydrogen bond with a carboxyl group 4 AAs down the chain
how does a B-pleated sheet occur
amino group makes a hydrogen bond with a carboxyl group in the folded back peptide chain
what does the tertiary structure of proteins correspond to
the arrangement of the secondary structure in 3D space
what does a tertiary structure consist of
one polypeptide chain with interactions between AA side chains
what does is a quaternary structure of protein
a combination of 2 or more tertiary structures that are required to make a functional protein
what does a quaternary structure form
multi-subunit complex
do all proteins have a quaternary structure
no
what is a native protein
a protein in its normal 3D conformation
what does a protein lose when it is denatured
its bioactivity
what does denaturing a protein affect
secondary, tertiary and quaternary structure
what are essential amino acids
not made by the body or cannot be made quickly enough to meet demands
what are conditionally essential amino acids
not normally required in the diet in a healthy individual - become essential under specific contexts
reasons for conditionally essential amino acids
genetic problem
development of disease
example of a genetic problem that would result in a conditionally essential amino acids
phenylketonuria
what is phenylketonuria
an inborn error of metabolism where a person is unable to breakdown Phe into Tyr - build up of Phe causes intellectual disability
what is the solution of phenylketonuria
limit Phe intake and supplement with Tyr
example of a disease that would result in a conditionally essential amino acid
liver disease (cirrhosis)
what does liver disease do
impairs Phe and Met catabolism - Tyr and Cys are synthesized from Phe and Met… impairment makes Tyr and Cys essential
what are non-essential amino acids
can be synthesized and are not essential to obtain from diet
for protein digestion - what occurs in the mouth
mechanical breakdown - no enzymatic digestion
for protein digestion what occurs in the stomach
enzymatic digestion:
HCl in gastric juice
pepsin (endopeptidase)
for protein digestion what is in the pancreas
pancreatic juice containing zymogens
what are zymogens
inactive digestive proenzymes
for protein digestion what occurs in the small intestine
zymogens are activated
enzymes break down peptides
absorption of AA
what are the 4 main components of protein digestion
mouth
stomach
pancreas
small intestine
what does the stomach produce
gastric juice
where is HCl secreted from
parietal cells
what is HCl release triggered by
gastrin
acetylcholine
histamine
what are the 2 functions of HCl
denatures protein (disrupts hydrogen and electrostatic bonds)
activates pepsin
what is pepsin secreted as
pepsinogen
what is pepsinogen
an inactive zymogen
when is pepsinogen/pepsin active
in an acidic pH
when is pepsinogen/pepsin inactive
at a neutral pH
what causes a conformational change in pepsinogen
HCl - allows it to autoactivate itself
what does pepsin do
cleaves peptide bonds within polypeptide chain (endopeptidase)
what does pepsin mostly generate
oligopeptides and some free AAs
where are most amino acids absorbed
upper small intestine
what are the 2 ways amino acids are absorbed
facilitated diffusion
active transport
what percentage of amino acids are absorbed through active transport
> 60%
what does active transport entail
sodium-dependent transporters
do essential AAs absorb faster or slower than non-essential AAs
faster
is there any advantage in taking supplements in terms of absorption
no - the free amino acids don’t have an advantage over amino acids in food
qualities of facilitated diffusion
does not require sodium or ATO
does not concentrate against the gradient
qualities of active transport
sodium dependent
requires ATP
concentrates against gradient
what is PEPT1
peptide transporter 1 (active transport)
2 fates of amino acids used in small intestine
either transported out of intestinal cell or used directly within enterocyte
what are amino acids used directly in enterocyte used for
energy
synthesis of new protein
what percentage of essential amino acids are estimated to be used in the small intestine
30-40%
example of an amino acid that is highly used in intestinal enterocytes
glutamine
what does glutamine do in intestinal enterocytes
- generates energy for the cell
- stimulate cell proliferation
- increase synthesis of heat shock proteins
- drive mucus production to help prevent bacterial translocation
which organ is effective at taking up amino acids from circulation
the liver
what percentage of amino acids does the liver use
20%
what does the liver use amino acids for
making new proteins/enzymes
making peptide hormones
example of proteins made in liver
albumin and other transport proteins
what does the liver do with the remaining 80% of amino acids
catabolizes them
where does the liver send NH3
the urea cycle
where does the liver send carbon skeleton
the Krebs cycle
gluconeogenesis
lipogenesis
are BCAAs taken up by the liver
no
what are BCAAs used for
they are anabolic signals for tissues like muscle
what are the 4 aspects to consider when determining protein quality
- AA composition
- Digestibility
- Presence of toxic factors
- Species consuming the protein
when is an a protein considered high quality in aa composition
any protein that provides all essential AA
when is a protein considered high quality with digestibility
when they are more digestible
when is a protein considered high quality with toxic factors
the lesser the amount of toxic factors, the higher the quality
why is there protein quality differences for different species
differing protein needs (i.e ruminants don’t have any essential amino acids, so they can utilize lesser quality proteins compared to humans)
pros of using Protein Efficiency Ratio to assess protein quality
simple
cheap
sensitive to AA balance, digestibility and toxic factors
cons of using Protein Efficiency Ratio to assess protein quality
rats are not humans
growth, not maintenance
do not know why a protein has poor quality
pros of using chemical score to assess protein quality
simple and cheap
identifies limiting AA in food
used to optimize feeds by mixing different sources of proteins
cons of using chemical score to assess protein quality
does not account for digestibility or toxins
assumes whole egg is an ideal protein
what does measuring nitrogen balance do
determines protein quanitity
when is nitrogen balance > 0
during growth, pregnancy, and times of tissue repair
when is nitrogen balance <0
when you do not have enough protein
who is usually seen with a nitrogen balance < 0
serious tissue injuries
wasting diseases (sarcopenia)
long term fasting
what is the nitrogen balance for most adults
NB = 0
when are protein requirements higher
infancy
childhood
teenagers
pregnancy
lactation
2 types of abnormal protein intake
excessive intake
deficient intake
when might someone have excessive protein intake
- high protein diet
- protein supplementation
when might someone have deficient intake
- deficient in both protein quantity and energy (overall malnutrition)
- deficient in only protein quantity
what are high protein diets typically low in
carbs
2 common high protein diets
Atkins Diet
South Beach diet
what is the most criticized high protein diet
Atkins Diet
ratio of carbs, fats, and proteins in the Atkins Diet
C:F:P = 3:64:33
why is the Atkins Diet Criticized
no attention to the type of carbs or fats consumed
what is the ratio carbs, fats and proteins in the South Beach diet
C:F:P = 30:40:30
what is the emphasis on for carb intake in the South Beach diet
low glycemic index foods
are all high protein diets created equal
no - big differences in macronutrient content and types consumed
who should avoid high protein diets
people with kidney disease
what do most protein supplements deliver high levels of
BCAAs - rapidly absorbed and delivered to muscle
when does anabolic muscle response to a protein meal start to diminish
after 40 years of age - improve with protein supplements
what is marasmus
protein/calorie malnutrition - low intake of a balanced diet
what happens with marasmus
because everything is in balance - body starts to starve
how is marasmus characterized
complete loss of body fat and muscle, peeling skin, uneven pigmentation
what is kwashiorkor
protein deficiency - sufficient calories but deficient in proteins
what is the protein percentage in kwashiorkor
1-2%
what are kwashiorkor patients characterized by
enlarged abdomen
burns on skin
diarrhea
why do kwashiorkor patients have an enlarged abdomen
decreased plasma proteins causes osmotic imbalance in gut (edema) - osmotic fluid leaks leading to gut swelling
why do kwashiorkor patients have enlarged liver
inability to export fat from liver - cannot make VLDL
what is there a constant turnover between
protein synthesis and breakdown
what is the body very efficient at during protein breakdown
recycling amino acids - most reused to make a new protein (only a little bit is catabolized)
overall gist of urea cycle
NH4+ is toxic - needs to be converted to urea (safe molecule)
1st main difference between fed and fasted states
fasted - formation of both glutamine and alanine
fed - primarily involves glutamine
2nd main difference between fed and fasted states
fed state involves both liver and kidneys
fasted state involves just kidney
3rd main difference between fed and fasted states
fed - involves excretion of amino group as urea
fasted - involves excretion of amino group as ammonium directly
what does catabolizing an a-ketoacid (carbon skeleton) lead to
production of bicarbonate (HCO3-)
what is bicarbonate
weak base that reacts with an H+ (no pH change)
what does the fed state encourage
alkalosis (increase pH)
response to high protein diets intake (fed state)
- liver converts amino group to urea in a process that consumes HCO3-
- catabolism of sulfur containing amino acid produces a bit pf sulphuric acid to neutralize pH
what happens during a long term fast/starvation
minor amounts of protein are catabolized to release glycogenic acids for gluconeogenesis
during long term fast/starvation, what does the breakdown of TAG lead to
production of acidic ketone bodies
what does long term fasting encourage
slight acidosis - pH drops to ~7.0 (nutritional ketosis)
what does liver do to products of TAG breakdown (not water soluble)
converts long hydrocarbons into small soluble ketone bodies
how can the brain use ketone bodies
use for energy during starvation
4 important amino acids in nitrogen metabolism
glutamate
aspartate
alanine
glutamine
what are the 4 reactions that move nitrogen from catabolized protein between organs for excretion
transamination
oxidative deamination
glutamine production/glutamate regeneration
urea cycle
what are the types of reactions in transamination
bi-directionaly reactions
where is transamination active
all tissues
why is glutamate the main amino acid to undergo oxidative deamination
it is the main product of transamination
how is free NH4+ handled in extrahepatic tissue
used for synthesis of glutamine
how is free NH4+ handled in liver
for urea synthesis
how is free NH4+ handled in kidneys
excreted directly as is into urine
what is the primary inter-organ nitrogen carrier
glutamine
what percentage of glutamine in the body does muscle produce
90%
where does glutamine primarily travel to in the fed state
liver
where does glutamine primarily travel to in the fasted state
kidney
what is the most abundant amino acid in blood
glutamine
overall difference between glutamine synthesis and glutamate regeneration
same reaction - opposite
different enzymes are required
when is glutamate regeneration active in the liver
fed state
when is glutamate regeneration active in kidney
during fasting
what does the urea cycle do
toxic NH4+ is converted to less toxic urea in liver
urea transported to kidney for excretion
when is 80-90% of urinary N in the form of NH4+
fasted state
when is 80-90% of urinary N in the form of urea
fed state
what is deamination
remove of amino group from AA
what is the a-ketoacid
the remaining carbon skeleton after deamination
what is transamination
transfer of an amino group from an amino acid to an a-ketoacid
what function groups does an a-ketoacid contain
ketone and carboxylic acid
ketogenic
degraded AA that can be converted into Acetyl CoA
glucogenic
degraded AA that can be converted into glucose
