W5 : Proteins

Question 1

Even before digestion, protein undergoes changes when cooking. How does cooking change the conformation of protein and thus affect its bioavailability?

Answer 1

• Disruption of stability of tertiary/quaternary structure
• Protein uncoils and loose shape (denature)
• Improves accessibility to proteases during digestion, therefore increasing bioavailability

Question 2

Protein digestion

In the stomach, what does protein get digested into, and what enzyme(s) are involved?

Answer 2

Pepsinogen gets activated into pepsin, and pepsin cleaves proteins into smaller polypeptides and some free amino acids

Question 3

Protein digestion

In the small intestine, what is protein digested into and what enzymes are involved?

Answer 3

1. trypsinogen activated into trypsin (secreted by pancreas) by enteropeptidase – digests polypeptide (protein) into smaller peptides
2. intestinal tripeptidases – digest tripeptides into amino acids
3. intestinal dipeptidases – digest dipeptides into amino acids
4. intestinal aminopeptidases – removes amino acids one by one from the N-terminus of the peptide chain.

Question 4

protein absorption

How are proteins absorbed in the intestine?

Answer 4

Intestinal cells directly absorb the amino acidsinto blood stream (blood capillaries of villi), or absorb small peptides which then get broken down by intracellular peptidases

Question 5

Where are unabsorbed amino acids transported to?

Answer 5

Liver

Question 6

What is the equation for nitrogen balance?

Answer 6

Nitrogen balance = nitrogen intake - nitrogen excreted

Question 7

Under what situations will one have a

(i) positive nitrogen balance
(ii) equilibrium nitrogen balance
(iii) negative nitrogen balance

Answer 7

(i) when one retains more nitrogen than one excretes, for muscle building (e.g. body builders / pregnant women to have amino acids for baby)

(ii) Normal person

(iii) nitrogen retained < nitrogen excreted. When one is ill / when one is malnutritioned, body starts breaking down muscle protein / when one consumes low quality protein and does not have all the essential amino acids, body break down muscle

Question 8

What process do extra amino acids undergo?

Answer 8

Deamination

Question 9

What is deanimation and where does it occur?

Answer 9

Removal of nitrogen containing amino group from protein to produce ammonia + keto acid.

Occurs in liver

Question 10

Amino acids can undergo deamination to give keto acids and ammonia.

What other 4 purposes can keto acids have, other than being involved in synthesis of non-essential amino acids?

Answer 10

1. Production of ketones
2. Metabolised for energy
3. Production of glucose (carbon backbone) – gluconeogensis
4. Production of cholesterol

Question 11

Amino acids can also undergo transamination. What does transamination mean?

Answer 11

transferof an amino group to a keto acid to form new non-essential amino acids.

Question 12

In what 2 ways can non-essential amino acids be formed through transamination?

.

Answer 12

1. Keto acids from deamination + NH3 → amino acid
2. amino acid 1 + keto acid 2 → keto acid 1 + amino acid 2

(amino group from amino acid 1 transferred to keto acid 2)

Question 13

For excretion, ammonia is converted into ____ in the ____

Write the equation on how ____ is converted into ____.

Answer 13

urea, liver

2 ammonia + CO2 - H2O → urea

Question 14

After liver produces urea, how is it excreted?

Answer 14

Urea is transported into the bloodstream to the kidneys.

Kidneys undergo ultrafiltration to filter urea out of blood.

Question 15

When the liver is malfunctioning, there is high concentration of what substance in the bloodstream?

Answer 15

Ammonia (bc liver doesnt convert ammonia into urea effectively)

Question 16

Transamination requires which Vitamin as a coenzyme?

Answer 16

Vit B6

Question 17

What happens if the kidney is malfunctioning?

Answer 17

Low urea in urine

Indicates that:
- kidney is unable to excrete urea out effectively
- kidney can’t absorb and receive urea properly

Question 18

When will protein be broken down for energy?

Answer 18

During starvation : When one is not receiving enough nutrients / calories from fats and carbs

• because protein is NOT the main source of energy, usually carbs and fats will be broken down first

Question 19

What happens when protein in the body is broken down for energy?

Answer 19

It leads to wasting of lean body tissue → muscle loss (which also leads to weight loss)

Question 20

Is weight gain due to only when protein intake exceeds needs?

Answer 20

No, weight gain occurs when both energy (calories) and protein intake exceeds needs.

Question 21

Protein quality is determined by which 2 factors?

Answer 21

1. Digestibility
2. Amino acid composition (contains essential amino acids)

Question 22

What happens if a person is missing 1 essential amino acid?

Answer 22

all protein production in the body shuts down

Question 23

What are essential amino acids needed for?

Answer 23

Protein tissue formation (thus building muscles)

Question 24

What are complete proteins and what products are usually complete proteins?

Answer 24

Complete proteins are proteins that contain all essential amino acids in amounts needed to support growth and tissue maintenance

• animal products (meat, milk, eggs)

Question 25

What are incomplete proteins and what kinds of products are usually incomplete proteins?

Answer 25

Proteins that are deficient in 1 or more essential amino acids (not about sufficient amount)

• plant proteins
  
  • “Complementary” plant sources can be combined to form “complete” source of protein

Question 26

Since soybeans are a plant protein, it is an incomplete protein. True or False?

Answer 26

False, soybeans are considered a complete protein for adults

Question 27

In comparison to plant protein, animal proteins are likely to be ____ in ____ content

Answer 27

higher, fat (esp saturated)

• both plant and animal sources contain polyunsaturated fats (plant sources: oils and seeds)

Question 28

In what 2 ways can protein deficiency occur?

Answer 28

1. Protein deficiency can occur by itself : not consuming enough from protein food group
2. Protein deficiency can occur together with a lack in calories and nutrients such as iron/zinc/vitamin B12, niacin –> not eating enough in general

Question 29

During starvation, body protein is used as energy source. What are the 4 main consequences of this?

Answer 29

1. Reduce strength (muscle lost)
2. Lowered immunity (less antibodies [they are proteins] produced)
3. Abnormal organ function
4. Death

Question 30

Protein defiency in children

What is the main cause of Marasmus and what is it characterised by?

Answer 30

Marasmus : lack of protein due to lack in calories (not enough food in general)

Characterised by wasting (vvv skinny)

Question 31

Protein defiency in children

What is the main cause of Kwashiorkor and what is it characterised by?

Answer 31

Kwashiorkor: sufficient calories but insufficient protein –> may consume a lot of carbs etc but not enough protein

Characterised by swelling of the stomach

Question 32

45% of total calories from protein is a suitable level of proteins to be consuming. True or False?

Answer 32

False, recommended levels is 10-35% of total calories

Question 33

What kinds of symptoms can excess proteins cause? [3]

Answer 33

1. nausea
2. weakness
3. diarrhea

Question 35

What is the link between protein foods and cancer?

Answer 35

Consuming too much protein-rich foods can cause cancer

(especially diet high in red meats, where there is also high levels of saturated fat)

Question 36

Excess protein consumption also worsens the condition of people with ____ disease.

Answer 36

Kidney

Question 37

People usually take protein supplementation to increase their protein intake. What may be 2 problems associated with such supplements?

Answer 37

1. No safe level of amino acid supplementation – there is no universally agreed upper limit for amino acid supplementation
   - thus, may be harmful if one overconsumes supplements

2) Purity, dose and safety not guaranteed

Question 38

How is muscle size and strength built?

Answer 38

Consuming enough protein-containing foods and
resistance training

Question 39

What is the RDA of protein for adults per day?

Answer 39

0.8g per kg of body weight per day

Question 40

Which 2 groups of adults require additional protein in their diet?

Answer 40

1. Elderly – to reduce effects of muscle loss and retain strength
2. Pregnant women – protein to maintain maternal tissues / essential amino acids for fetal development / expansion of blood volume