Flashcards in Protein Nutrition, Digestion, absorption Deck (32):
What determines the function of an amino acid
The variable 'R group'
What makes up an amino acid?
amino group, acid group, R group, H
Non-essential amino acids are?
we can make, either from essential aa or derive from other metabolic components
Essential aa are?
Required in our diet, we can't make ourselves
Roles of Proteins? (8)
- immune function
- Energy source
Conditionally Essential aa
When the thing that makes the aa has to be avoided, so nonessential aa become essential
Phenile pertenuria: have to avoid phenilalinine, can't make tyrosin
Bonds of proteins
peptide bonds (OH + H)
Polypeptides function due to?
Their sequencing of aa, determined by DNA/RNA
eg) haemoglobin (4pp bound)
if aa sequence altered, the protein can't function > Sickle cell anaemia
Main victims of Protein-energy malnutrition
what is the protein RDI? Total energy intake? Is this attainable?
12-25% of energy intake
This is very easy to achieve
Is taking protein supplements always necessary? What can this lead to
No. its very easy to achieve RDI, so you are getting excessive amounts of protein. Even when you are active, and your protein turnover is higher.
Potential links with CVD and renal stones?
High Quality Protein?
Provide enough of all the EAA
Meats do this
But vegans/vegetarians need to find other sources (supplements etc)
Difference in digestibility of proteins?
animal protein: 99%
plant protein: 70-90%
soy & legumes: 90%
Amino Acid composition means
Dietary protein must supply minimum
9EAA + N containing amino groups + energy
if there is not enough EAA synthesis limited
Recommended serving of protein?
1-2 per day of MIXED servings. By combing protein sources its easy to get EAA
Complementary proteins (provide SOME of the EAA)
Protein digestion in the mouth
mouth and salivary glands chew, crush and moisten protein-rich foods and mix them with saliva
Protein digestion in the stomach
Acid environment denatures proteins and actives pepsinogen > pepsin.
HCl: uncoats protein strands and activates stomach enzymes
Pepsin: cleaves proteins > smaller polypeptides and some free aa. Inhibits pepsinogen synthesis
Protein digestion in the SI
Degraded by a combo of pancreatic endopeptidases. (trypsin, chymotrypsin, elastase)
Polypeps >>>> smaller polypeptides and amino acids
Then pancreas enzymes (intestinal tri/di peptidases) of the surface of enterocytes hydrolyse these and they are absorbed
Peptides >>>> amino acids
What initiates protein digestion in the SI to occur. What happens next?
Trypsinogen >> Trypsin
by membrane -bound enteropeptidases
Trypsin (when high enough) has a negative feedback on trypsinogeen synthesis. It activates inactive enzymes such as chymotrypsinogen to their active form.
These active enzymes can now cleave off aa chains to make them absorbable.
Absorption of Proteins works by?
peptides/ aa absorbed through gut enterocytes, facilitated by either Na+ or H+ co-transporter.
A antiport in the BL membrane swaps Na+ for K+ and creates the necessary conc gradient
Larger peptides can be transcytosed and engulfed into membrane
venule > villi > portal vein > liver
Does digestion occur in the enterocytes?
Yes of di/tripeptides
Downside of using protein as energy?
Ammonia and urea.
These are toxic and need to be excreted
-Usually in nitrogen balance (protein/nitrogen intake = protein/nitrogen excretion)
-Nitrogen is taken into the body largely as aa.
-Majority excreted via urine as N products
-This is relatively stable over a wide range 50-300g
g Protein =
gN x 6.25
Negative Nitrogen balance? Factors that cause this?
Net loss of Nitrogen.
1) Decreased protein intake
2) starvation or decreased GI function
3) injury, trauma, burns (not enough protein> tissue damage leads to death)
4) illness or infection
5) some post-op conditions
6) many cancers
degradation > synthesis
Positive Nitrogen balance. Factors that produce this.
Net gain of Nitrogen (synthesis> degredation)
1) increased protein intake
4) recovery from illness/ trauma
Only for a short period, body quickly excretes
PEM stands for
occurs in developing countries, especially children
Why is malnutrition so dangerous in children
Leaves them vulnerable to infection >> low food makes infection worse >> hard to get them too eat when infection develops death
Two main forms of PEM
Marasmus (like anorexia nervosa)
-Severe deprivation or impaired absorption of protein, energy, vitamins, minerals.
- Leads to severe weight loss, muscle-wastage, no body-fat, growth
Why is it interesting that marasmus sufferers don't have oedema
If we got sick and decreased protein intact we would develop oedema, but this chronic malnutrition is different