PROTeenies Flashcards
3 primary functions of dietary proteins
- functional proteins in the body (enzymes, actin and myosin, collagen, fibrin, transport proteins, some hormones, antibodies, etc)
- essential amino acids for protein synthesis
- energy (10-15% of ATP)
RDA for dietary protein
- 8g/kg body weight/day
- increases during growth periods: infants, kids, teens, pregnancy, lactation, athletes. also for people suffering wasting from old age or end-stage cancer
protein AMDR
10-35% daily energy intake
how many proteinogenic amino acids are there in humans (the important ones)?
20
what is the chemical structure of an amino acid? (3 parts) which parts make up the carbon skeleton?
- an amino group (NH2)
- an acid group (COOH)
- a unique side chain
carbon skeleton: the acid group and side chain
how is protein quality determined?
determined by whether a given dietary protein provides all the essential amino acids in adequate amounts
how many essential amino acids are there?
9
what is a complete protein?
a protein that provides all 9 essential amino acids (can be combos of foods like rice and beans)
what are examples of complete plant proteins?
soy, quinoa, hemp seeds, buckwheat, chia seeds
what are incomplete proteins?
foods that lack one or more EAA (most plant proteins are incomplete)
what is primary protein structure?
amino acid chain
what is secondary protein structure?
folding of polypeptide chain into helices or sheets
what is tertiary protein structure?
three dimensional folding of the chain with side-chain interactions
what is quaternary protein structure?
protein consisting of more than one amino acid chain (functional protein)
what are the links between amino acids called?
peptide bonds
two amino acids linked together
dipeptide
three amino acids linked together
tripeptide
4 or more amino acids linked together (up to several thousand)
polypeptide
what happens to proteins in the mouth?
not much: just chewing them and moistening them
what happens to proteins in the stomach?
HCl denatures proteins (unravels them). HCl also activates the inactive proenzyme pepsinogen, to make pepsin. pepsin breaks up denatured proteins into smaller polypeptides and some amino acids. it also inhibits further pepsinogen synthesis.
what happens to proteins in the small intestine?
When polypeptides enter the small intestine, small intestine enterocytes release the hormone cholecystokinin (CKK). CKK in turn stimulates the release of inactive pancreatic proteases trypsinogen and chymotrypsinogen from the pancreas into the small intestine. then enterocytes release enteropeptidase in order to activate the proteases into trypsin and chymotrypsin. these proteases then break up polypeptides even more: into tripeptides, dipeptides and amino acids. these three kinds of peptides can then be absorbed into the enterocytes.
pepsinogen
the inactive form of pepsin. needs HCl in the stomach to be activated.
pepsin
the active form of pepsinogen. breaks down denatured proteins in the stomach into smaller polypeptides.
cholecystokinin
(CKK). a hormone released by small intestine enterocytes when proteins enter the small intestine.
-stimulates the release of pancreatic proteases (trypsinogen and chymotrypsinogen: inactive forms) into the small intestine
trypsinogen and chymotrypsinogen
- inactive proteases released into the small intestine by the pancreas. this release is stimulated by the presence of CKK, a hormone released by SI enterocytes in the presence of dietary polypeptides.
- the proenzyme enteropeptidase (“enterocyte peptide enzyme”) needs to be released from the enterocytes in order to convert them into their active forms, trypsin and chymotrypsin
trypsin and chymotrypsin
- active forms of pancreatic proteases trypsinogen and chymotrypsinogen
- need enteropeptidase, release by the enterocytes, to be activated
- inactive forms initially released by the pancreas in response to enterocyte hormone cholecystokinin (CKK)
enteropeptidase
(“enterocyte peptide enzyme”): the proenzyme released by the small intestine enterocytes that activate trypsinogen and chymotrypsinogen into their active forms, trypsin and chymotrypsin, so that they can break down polypeptides into tripeptides, dipeptides and amino acids to be absorbed into the enterocytes.
what happens to amino acids once they enter the enterocytes?
they leave the enterocytes and enter the bloodstream. they travel via the portal vein to the liver (just like carbs!).
what is the primary contributor of amino acids to the amino acid pool?
breakdown and turnover of old proteins in the body
amino acid pool
place in the liver where all amino acids go (dietary and old) to be turned into new proteins
what percentage of amino acids are released into the bloodstream by the liver?
only 30%
what does the liver do with amino acids? (4 options)
- synthesis of proteins or amino acid-derived compounds (ie carnitine)
- synthesis of non essential amino acids
- oxidized (used for immediate energy)
- converted to glucose or fatty acids
amination
using an ammonium ion (NH4+) to form an amino group, and attaching that to a carbon skeleton (side chain and acid group)
transamination
transferring an amino group from one amino acid to a different carbon skeleton to make a different amino acid
what happens when an amino acid is converted to glucose or triglycerides/what is it called?
gluconeogenesis and lipogenesis: amino acid group is removed (deamination) to get the carbon skeleton. the nitrogen is disposed of in urea. carbon skeleton is turned into pyruvate, and the pyruvate is turned into either glucose or TG.
deamination
removal of amino (nitrogen) group to get carbon skeleton for gluconeogenesis or lipogenesis. N is excreted.
urea cycle
takes place in the liver. used to excrete urea from N via urine or feces. increases with the increase of dietary protein.
cancer cachexia
complex metabolic syndrome characterized by involuntary muscle loss or “wasting”
- affects majority of end stage cancer patients
- leads to decreased survival rates and negatively affects cancer therapy (treatment is harder to tolerate)
treatment of cancer cachexia
increase protein RDA from 0.8g/kg/day to 1-1.5g
sarcopenia
characterized by progressive and generalized loss of skeletal muscle mass and strength (like cancer cachexia but not cancer related and slower).
-happens normally with age but sometimes unusually with bedrest or other conditions (punctuated decline)
treatment for sarcopenia
- physical exercise if possible–especially resistance
- diet and dietary supplements
- nutritional intervention (often the main one because old people have a hard time exercising)
- protein quality and adequate leucine specifically important
how to build muscle
- 1.6g/kg/day protein
- exercise and resistance training
- pace protein intake to every 3 hrs to avoid normal protein breakdown
- high branched chain amino acids like leucine (high in whey protein specifically)
