Proteins

Question 1

Amino acids

Answer 1

20 kinds, but only 9 are essential amino acids (EAA)
 Phenylalanine, valine, tryptophan, methionine, threonine, histidine, isoleucine, leucine, lysine
 EAA needs approx. 11% of total protein intake
 Typical diet supplies 50% as EAA
 Children have higher need for EAA, need high-quality protein in diet

Question 2

Each amino acid contains

Answer 2

carbon, hydrogen, and nitrogen

Question 3

“R” group

Answer 3

 Specialized side-group
 Examples:
Branch-chain amino acids (BCAA) have carbon and hydrogen “R” groups and can be used to make glucose if little or no CHO is consumed in the diet
 Leucine, isoleucine, valine
PKU (phenylketonuria) – disease caused by inability to convert “R” group of phenylalanine to form tyrosine

Question 4

Amino acids are connected via

Answer 4

peptide bonds
 Dipeptide
 Tripeptide  Polypeptide

Question 5

Denaturation

Answer 5

change in shape
 Heat, acid, alkali, agitation can denature
proteins and deactivate them  Cooking denatures protein
 Makes tough connective tissue softer, easier to chew, swallow, digest
 Kills bacteria
 Inactivates some biologically active proteins


Question 6

protein digestion starts…and ends…

Answer 6

Stomach – begins digestion of protein
 Acid denatures protein
 Pepsin breaks polypeptides into smaller peptides
 Small intestine - most protein digestion and absorption occurs here
 Pancreatic juice contains proteases which complete digestion of peptides
 Single amino acids and some di- and tripeptides are absorbed


Question 7

Protein turnover

Answer 7

constant synthesis and breakdown of protein
 Allows cells to adapt to changes in body circumstances
 Amino acids are easily recycled, so we do not need to eat as much protein
 If amino acid used for energy, made into glucose, or lost due to cell breakdown, waste product ammonia is produced
 Liver turns ammonia into urea which is filtered by kidneys for excretion

Question 8

protein functions in the body

Answer 8

Structure
 Collagen – structural protein
found in bones, skin
 Keratin – structural protein found in hair, nails
 Acid-base balance
 Some proteins act as buffers (resist pH change)
Oncotic pressure
 Presence of protein in small blood vessels attract water back into blood, partially counteracting blood pressure
 If low protein in diet, too much fluid accumulates in tissues = edema
 Hypertension, congestive heart failure, preeclampsia
Fig. 6.9


Question 9

What affect would a drop in pH (more acidic) have on body proteins?

Answer 9

they would become denatured, this is regulated from happening with the kidney.

Question 10

Why might an elderly adult with a poor appetite have edema in her feet and ankles?

Answer 10

insufficient protein intake leading to a problem in oncotic pressure, wherein protiens attract water to balance blood pressure. Too much water collects in the ankles causeing swelling.

Question 11

protein functions in the body (more)

Answer 11

Hormones
 Thyroid hormone, insulin, glucagon, growth hormone
 Enzymes
 Almost all are proteins or contain protein
 Immune system
 Antibodies are proteins
 Energy
 If low on CHO, liver and kidneys make glucose from
BCAA
 If starving, amino acids can be used for energy  muscle and organ wasting

Question 12

Why does a patient with a poor appetite have a higher risk for infection?

Answer 12

insufficient protein could be part of the problem as antibodies are made of protein.

Question 13

Why do enzymes and hormones from animal or plant foods not adversely affect our bodies?

Answer 13

This is kind of a loaded question. We know that stomach acid ‘kills’ the zillions of plant and animal based hormones, denatured proteins by acid. However we show that hormones are transfered through breastmilk, and that cooking food denatures enzymes in the foods that are needed to digest.

Question 14

High-quality/Complete

Answer 14

Source: animal protein

 Contains all 9 essential amino acids

Question 15

Lower-quality/Incomplete

Answer 15

 Source: plant protein
 Missing at least 1 essential
amino acid
 Limiting amino acid = essential amino acid missing from protein food or in body
 Complementary protein = plant protein that contains limiting amino acid of another plant protein


Question 16

Protein Needs

Answer 16

Need to balance protein lost from breakdown (can be determined by urea in urine)
 If growing, pregnant/lactating, or recovering from illness, need more protein
 RDA: 0.8 grams/kg
 8-10% of total kcal intake
 46-56 grams/day needed vs. 65-100 grams actual intake!

Question 17

Excess protein intake

Answer 17

amino acids stripped of nitrogen (converted to urea) and carbon skeleton stores as fat

Question 18

Protein-Energy Malnutrition

Answer 18

Marasmus – very inadequate protein and energy intake
 Means “to waste away”
 “Skin and bones” appearance
 Commonly seen in infants and young children not breastfed, weaned too early, or have water diluting formula
 Kwashiorkor – very inadequate protein, marginal or adequate caloric intake
 Marked edema, especially in belly
 “The evil spirit the first child gets when the next child is born”