Lecture 13: Protein nutrition, digestion and absorption Flashcards

1
Q

What is the role of proteins in the body?

A
Immune system
Hormones
Structural and mechanical
Transport
Fluid balance
Acid-base balance
Energy
Channels and pumps
Enzymes
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2
Q

Describe the constituents of a amino acid;

A

Side group (variable)
Acid group
Amino group

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3
Q

How many amino acids are there?

A

20 amino acids

9 of which are essential and must be obtained from foods i.e animal products, fish, soy products, quinoa

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4
Q

What sort of bonds to proteins have?

A

Peptide bonds

Di and tri-peptide

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5
Q

Whats important about protein folding?

A

Tertiary folding helps determine structure and function

Any variation in amino acids can change folding and thus function

i.e sickle cell anemia

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6
Q

Whats the RDI and AMDR of protein?

A

RDI; 0.84g/kg/day males and 0.75g/kg/day females

AMDR; 15-25% of energy intake

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7
Q

Whats the importance of protein quality?

A

Digestibility; Animal vs plant protein
Amino acid composition; limiting amino acid

That is if a food lacks one of the amino acids then this may limit how much of a protein can be made.

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8
Q

If someone is strict vegeterian or vegan, how can they ensure they get enough of the amino acids?

A

They can work out which foods are complementary for the amino acids and make sure they are getting all the essentials and not limiting

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9
Q

Prior to eating what can aide protein digestion?

A

Cooking

  • Unfolds, denatures proteins
  • Softens food
  • Easier to chew and swallow
  • Safer to eat
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10
Q

Describe steps 1-2 of protein digestion;

A

1) The mouth, Mechanical digestion, chewing and crushing

2) Saliva, lubricates foods

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11
Q

Describe how protein is digested in the stomach (step 3)

A

Acid activates pepsinogen to pepsin which breaks down large proteins into polypeptides and amino acids

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12
Q

Describe steps 4-5 of protein digestion

A

Polypeptides and amino acids enter the small intestine, the pancreas has released;

Trypsinogen
Chymotrpsinogen
Procarboxypepetidase

Enteropeptidase on the lumen surface of enterocytes activates trypsinogen-> trypsin (breaksdown peptide bonds, inhibits trypsinogen synthesis and converts;

Chymotrpsinogen -> chymotrypsin. (Breaks peptide bonds).

Procarboxypeptidase -> Carboxypeptidase. (Breaks apart peptide bonds at the carboyxl end)

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13
Q

Describe the further breakdown of polypeptides in the small intestine;

A

Luminal surface of enterocytes also contains enzymes;

  • Amino peptidase
  • Dipeptidase
  • Tripeptidase

These all release AA which are absorbed by the SI

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14
Q

How are AA transported across the apical surface of the enterocytes?

A

Primary active transport with Na+ (ATP)
Secondary active transport with Na+ (gradient, not ATP)
Di/tri-peptides with Na+ secondary active transport.

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15
Q

How do AA and di/tri-peptides enter circulation from enterocytes?

A

Di/Tri-peptides are broken down to AA

AA then undergo facilitated diffusion via various transporters

Na/K ATPase create the gradient.

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16
Q

What is the end product of AA metabolism?

A

Nitrogen/ammonia

17
Q

What can happens to the nitrogen pool?

A

Nitrogen Pool Supplies

Mainly;
NH3-> Urea cycle = Urea
Tissue protein

Some;
Pyruvate acid
Acetyl-CoA
Citric Acid Cycle

18
Q

What is nitrogen balance?

A

Rate of nitrogen in (Dietary AA) and loss of nitrogen (urea and some fecal)

Thus, energy needs must be met to prevent amino acids from being relocated to become an energy source

19
Q

What can urinary nitrogen be used for? and whats assessed

A

To assess the rate of nitrogen loss i.e tissue breakdown etc

Urinary nitrogen =

  • Urea
  • Creatanine
  • Uric acid

Indicates excess nitrogen (cus ammonia is toxic thus made into other forms)

20
Q

Whats the nitrogen intake equation?

A

N x 6.25 = G protein intake

21
Q

What is positive nitrogen balance?

A

Protein synthesis > Protein breakdown

  • Increased protein intake (short term)
  • Growth
  • Pregnancy
  • Recovery from illness or trauma
  • Gym
22
Q

What is negative nitrogen balance?

A

Protein synthesis < Protein breakdown

i.e
starvation
reduced GI function
stress
cancers
lactation
23
Q

What is nitrogen balance?

A

Protein synthesis = protein breakdown

healthy
protein needs being met

24
Q

What can cause protein energy malnutrition?

A
  • Infections i.e dysentary
  • Rehabilitation
  • Kwashiorkor (pot belly, ascites), Protein deficit but energy intake
  • Marasmus (Diet deficient in protein / starvation, no other foods)