Protein Nutrition, Digestion, absorption

Question 1

What determines the function of an amino acid

Answer 1

The variable ‘R group’

Question 2

What makes up an amino acid?

Answer 2

amino group, acid group, R group, H

Question 3

Non-essential amino acids are?

Answer 3

we can make, either from essential aa or derive from other metabolic components

Question 4

Essential aa are?

Answer 4

Required in our diet, we can’t make ourselves

Question 5

Roles of Proteins? (8)

Answer 5

• building material
• hormones
• enzymes (digestive)
• immune function
• fluid balance
• Transporters
• AB
• Energy source

Question 6

Conditionally Essential aa

Answer 6

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

Question 7

Bonds of proteins

Answer 7

peptide bonds (OH + H)

Question 8

Polypeptides function due to?

Answer 8

Their sequencing of aa, determined by DNA/RNA

eg) haemoglobin (4pp bound)
if aa sequence altered, the protein can’t function > Sickle cell anaemia

Question 9

Main victims of Protein-energy malnutrition

Answer 9

Children

Question 10

what is the protein RDI? Total energy intake? Is this attainable?

Answer 10

M: 0.84g/kg/day
F: 0.75g/kg/day

12-25% of energy intake

This is very easy to achieve

Question 11

Is taking protein supplements always necessary? What can this lead to

Answer 11

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?

Question 12

High Quality Protein?

Answer 12

Provide enough of all the EAA
Meats do this
But vegans/vegetarians need to find other sources (supplements etc)

Question 13

Difference in digestibility of proteins?

Answer 13

animal protein: 99%
plant protein: 70-90%
soy & legumes: 90%

Question 14

Amino Acid composition means

Answer 14

Dietary protein must supply minimum
9EAA + N containing amino groups + energy

if there is not enough EAA synthesis limited

Question 15

Recommended serving of protein?

Answer 15

1-2 per day of MIXED servings. By combing protein sources its easy to get EAA

Complementary proteins (provide SOME of the EAA)

Question 16

Protein digestion in the mouth

Answer 16

mouth and salivary glands chew, crush and moisten protein-rich foods and mix them with saliva

Question 17

Protein digestion in the stomach

Answer 17

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

Question 18

Protein digestion in the SI

Answer 18

Degraded by a combo of pancreatic endopeptidases. (trypsin, chymotrypsin, elastase)
Polypeps &raquo_space;» smaller polypeptides and amino acids

Then pancreas enzymes (intestinal tri/di peptidases) of the surface of enterocytes hydrolyse these and they are absorbed

Peptides&raquo_space;» amino acids

Question 19

What initiates protein digestion in the SI to occur. What happens next?

Answer 19

Trypsinogen&raquo_space; 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.

Question 20

Absorption of Proteins works by?

Answer 20

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

Question 21

Does digestion occur in the enterocytes?

Answer 21

Yes of di/tripeptides

Question 22

Downside of using protein as energy?

Answer 22

Ammonia and urea.

These are toxic and need to be excreted

Question 23

Nitrogen balance?

Answer 23

• 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

Question 24

g Protein =

Answer 24

gN x 6.25

Question 25

Negative Nitrogen balance? Factors that cause this?

Answer 25

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
7) lactation

Question 26

Positive Nitrogen balance. Factors that produce this.

Answer 26

Net gain of Nitrogen (synthesis> degredation)

1) increased protein intake
2) growth
3) pregnancy
4) recovery from illness/ trauma

Only for a short period, body quickly excretes

Question 27

PEM stands for

Answer 27

Protein-Energy Malnutrition

occurs in developing countries, especially children

Question 28

Why is malnutrition so dangerous in children

Answer 28

Leaves them vulnerable to infection&raquo_space; low food makes infection worse&raquo_space; hard to get them too eat when infection develops death

Question 29

Two main forms of PEM

Answer 29

1) Marasmus

2) Kwashiorkor

Question 30

Marasmus (like anorexia nervosa)

Answer 30

• Severe deprivation or impaired absorption of protein, energy, vitamins, minerals.
• Slowly develops
• Leads to severe weight loss, muscle-wastage, no body-fat, growth

Question 31

Why is it interesting that marasmus sufferers don’t have oedema

Answer 31

If we got sick and decreased protein intact we would develop oedema, but this chronic malnutrition is different

Question 32

Kwashiokor

Answer 32

infants and young children, more acute/rapid onset

• due to protein shortage or infection
• Some weight loss, some muscle wastage, some body fat
• 60-80% growth for age
• edma (fat tummy) , fatty lliver
• Anxiety, apathy, sadness
• Appetite loss
• hair dry, brittle, skin gets lesions