Lecture 10

Question 1

Why are some amino acids conditionally essential?

Answer 1

Some amino acids are conditionally essential under special circumstances. This is because non-essential amino acids are synthesized from other molecules.

Question 2

What properties determine the tertiary structure of proteins?

Answer 2

hydrophilic and hydrophobic interactions.

Question 3

What level of structure is denatured when proteins are denatured?

Answer 3

Denatured proteins result from deformed secondary, tertiary, and quaternary structure.

Question 4

What is an example of reversible denaturing of a protein?

Answer 4

If denaturing is caused by broken disulfide bonds the bonds can reform.

Question 5

What are changes that can be seen in denatured proteins?

Answer 5

Decreased solubility (forms precipitate)

Altered water binding activity

Loss of biological activity

Increase susceptibility to proteolytic attack

Increased viscosity

Inability to crystalize.

Question 6

What are the types of casein protein?

Answer 6

alpha, beta, gamma, and kappa casein.

Question 7

How are casein molecules arranged in milk?

Answer 7

micelles contain lots of casein molecules (10^4-5) and milk contains 10^15 micelles/L of milk.

Question 8

How are micelles held together?

Answer 8

Casein micelles contain a surface “hairy” layer of . Micelles are held together by electrostatic forces.

Question 9

What is the function of the “hairy” hydrophilic region of casein?

Answer 9

hydrophilic region makes the micelle soluble.

Question 10

How does casein assist calcium absorption?

Answer 10

calcium attaches to casein and this allows calcium to be absorbed in the body.

Question 11

How is yoghurt made from yoghurt milk?

Answer 11

1) yoghurt milk is heated at 85-90 degrees.
2) Cooled to 43 degrees to add cultures.
3) Bacteria are added to ferment to 4.6 pH.

Question 12

Why is yoghurt milk initially heated?

Answer 12

This denatures whey protein and increases water binding.

Question 13

Why are bacteria added to preheated yoghurt milk when producing yoghurt?

Answer 13

Precipitation of colloidal calcium phosphate.

Dissociation of caseins from micelles.

Precipitation of proteins as pH is reduced.

Question 14

How does hydrochloric acid assist digestion of protein?

Answer 14

Hydrochloric acid denatures proteins.

HCL activates pepsinogen and forms pepsin which can break some peptide bonds.

Question 15

How does the mouth assist protein digestion?

Answer 15

Saliva and mouth mechanical digestion can deform some proteins.

Question 16

How is pepsin production regulated?

Answer 16

Pepsin downregulates pepsin production in a negative feedback loop.

Question 17

How are proteins absorbed at the intestine?

Answer 17

Enzymes on surface of small intestine break down the di and tripeptides formed from free enzymes and as a result allow individual absorption of amino acids.

*These enzymes are known as brush border enzymes and include Glucoamylase, sucrase, land lactase.

Question 18

What happens to unused amino acids in the blood?

Answer 18

Unused amino acids are transported to liver for metabolism.

Question 19

What is a potential side effect of consuming predigested amino acids (BCAAs for example)?

Answer 19

Taking predigested amino acids could cause remodelling of the gut to uptake those certain amino acids and decrease absorption of other amino acids. (This is rare)

Question 20

What are the benefits of cooking foods with protein?

Answer 20

Cooking protein increases digestibility by denaturing proteins prior to consumption.