5. Nutrition and metabolism of proteins

Question 1

Protein roles in the body

Answer 1

100000 proteins 
contribute to:
-structure (skin, hair, bones..)
-enzymes 
-Immunity and defence
-Hormones
-storage and transport
-energy storage

Question 2

Amino acids structure and role

Answer 2

Are the building blocks for proteins, donors on nitrogen for (DNA and RNA) and methyl donors
amino group+side chain+carboxylic acid group+ alpha caron and hydorgen
amminoacids togheter with peptide bonds

Question 3

Classification of amino acids

Answer 3

Indispensable/essential: we can not synthesize them so we have to take them from diet (lisine, methionine)

• conditionally indispensable/essential: can be synthesize but materials are not fully available
• dispensable/non essential:can be synthetize with N and C sources.

Question 4

Essential amino acids examples:

Answer 4

valine- leucine- isoleucine- methionine- tryptophan-histidine

Question 5

conditionally essential amino acids:

Answer 5

glycine-arginine-glutamine- cystine-taurine

Question 6

dispensable amino acids:

Answer 6

glutamic acid-glutamine-alanine-serine-aspargine

Question 7

Protein and N

Answer 7

Protein are the main source of nitrogen in the body –> protein content is used for total N measurements

Protein intake is sufficient if: Nintake-Nexecrection=0

Question 8

What’s the requirement for protein intake?

Answer 8

10-20% of total energy intake

Question 9

Digestion of proteins

Answer 9

DIGESTION IN STOMACH BUT PRIMARY STRUCTURE DIGESTED IN THE SMALL INTESTINE
stomach: gastric HCl denatures proteins and activation of pepsinogen to pepsin
small intestine: trypsin- hydrolyses basic amino acids
chymotrypsin-hydrolyses or aromatic amino acids
other enxyme that digest other type of amino acids

Question 10

What’s the issue with plant protein digestibility?

Answer 10

they have lower digestibility cause they have proteases inhibitors
cooking and soaking always distroy these protease inhibitors

Question 11

Explain amino acid tranport

Answer 11

They require active transport inside cell against a concentration gradient

• the transporters recognise amino acids based on shape e chemical properties
• enegy dependent process

Question 12

What happens if small frgment of proteins are absorbed intact in people?

Answer 12

they lead to allergic reactions

Question 13

Explain the gluconeogenesis

Answer 13

convert amino acids into glucose for energy
tranamination of glutamate + oxalocetate to make alpha ketogluterate + aspartate

aphaketogluterate can be converted into energy in the TCA cycle

Not all the amino acids are glucogenic

Question 14

What happens if someone have too much proteins?

Answer 14

Excess of proteins is removed as urea via kidneys ( can lead to renal diseases)
Increased urinary calcium excrection (loss of bone mass, kidney stones)
Increase plasma homocysteine (risk factor for CVD)

Question 15

How N is expelled?

Answer 15

Urine (urea, creatinine, ammonia, uric acids, amino acids)

Faeces ( protein and amino acids)

Question 16

What happens if you have too little proteins?

Answer 16

Accelerated loss of muscle mass
Sarcopenia/muscle wasting-astrofia muscolare
In extreme cases: Kwashiorkor: liver demage, immune deficiency…

Question 17

What’s muscle wasting?

Answer 17

Loss of waight (5-10%) due to accelerated muscle proteolysis
anorexia and starvation lead to increased protein degradation
muscle wasting is increased in many diseases: diabetes, renal and livel failure,cancer

Question 18

What’s Sarcopenia?

Answer 18

Associated to aging 
Associated with: 
-decreased physical activity 
-reduced secretion of hormones
-increased insulin resistence
-increase protein intake but decrease appetite

Question 19

Insulin resistance and negative protein balance

Answer 19

Insulin can also regulate protein metabolism

Insulin resistance results in impaired muscle turnover

Question 20

relationship between exercise and protein metabolism

Answer 20

Exercise increase protein turnover (balance between intake and excretion)
improve insulin sensitivity
decrease urinary N execretion
difficult to increase muscle mass after 40
some evidence in which high intake of protein improve training and recovery

Leucine, isoleucine and valine stimulate insuline secretion which stimulate muscle synthesis

Question 21

Food allergy and proteins

Answer 21

All allergens are proteins
sensitization, cross reasctions

Remember that Alzheimer Huntington and Parkinson diseases start with accumulation of the wrong folded proteins