3.2 Protein

Animal proteins

• Complex carbs

  • No fiber/ starch

• Fats

  • High in saturated

  • High in cholesterol

• Micronutrients

  • Good source iron, zinc

  • Good source vitamin b12

Plant proteins

• Complex carbs

  • Good source fiber

• Fats

  • High in unsaturated

  • No cholesterol

• Micronutrients

  • Iron and zinc may be less absorbable

  • No b12

4 parts to amino acids

• Central carbon

• Acid group (COOH)

• Amino group (NH2)

• Side chain (also called R-group) – this gives the ammino acid specific properties

9 essential amino acids

The body cannot make and must come from the diet

11 nonessential amino acids

The body can make them from other amino acids

Conditionally essential amino acids

Nonessential amino acids may become essential in times of illness and stress

Amino acids link together to form

Peptides

Dipeptide

2 amino acids

Tripeptide

3 amino acids

Polypeptide chain

10+ amino acids joined together

Protein

Approx. 50+ amino acids joined together

Peptide bond

Amino group (NH3) of one amino acid binds with the acid group (COOH) of another

Lactoferrin

• 703 amino acids

• High concentrations in human milk

• Contain pocket for “hiding” iron so not available for bacteria

Collagen

Most abundant protein in our body (25%!). Gives strength & stretch to tendons & ligaments

Transporter protein

Helps transport substances across cell membranes

Denaturation

• Unfolding of a protein’s three-dimensional structure due to HEAT, ACID, AGITATION

  • After unfolding occurs, the protein no longer functions as it naturally did before

Digestion of proteins (mouth)

Mechanical digestion takes place through chewing to mix food with saliva

Digestion of proteins (pharynx & esophagus)

Pathway to transport food bolus to stomach via peristalsis

Digestion of proteins (stomach)

• Hydrochloric acid

• Pepsin

Hydrochloric acid

Denatures protein strands so enzymes can reach them, and activates pepsinogen into its active form, pepsin

Pepsin

Cleaves long polypeptide chains into smaller peptide fragments

Digestion of proteins (small intestine)

Pancreatic proteases and brush border enzymes break down the small peptides into single amino acids, dipeptides, and tripeptides ready for absorption

Digestion of proteins (large intestine)

Any remaining undigested protein matter is fermented by bacteria or pooped out

In the small intestine

• Amino acids, di- and tripeptides absorbed using transporter proteins

• Amino acids with similar functional groups use same transporters

• Inside cells, peptides are broken down into amino acids

• Amino acids enter blood and travel to liver via hepatic portal vein

• Little protein lost in feces

Many functions of proteins

• Structural

• Enzyme

• Immunity

• Fluid balance

• Movement

Protein turnover

Continually synthesis & degradation of protein that occurs in our body

Protein turnover rates vary by tissue

• Collagen & connective tissue: SLOW turnover

• Muscles: SLOW to MODERATE turnover

• Organs (e.g. intestine, liver): HIGH turnover

How is new protein synthesized?

• DNA contain the “recipe” to make proteins

• 1 gene code for 1 protein

Gene expression

• The process by which cells use genes to make proteins:

  • Transcription – DNA used to make mRNA

  • Translation – mRNA used to make protein

When sythesizing a protein

• If a nonessential amino acid is needed, body can make it

• If an essential amino acid is needed, body cannot make, and protein synthesis STOPS!

Limiting amino acids

The essential amino acid that is available in the lowest concentration relative to the body’s need

Inadequate intake of calories or carbs….

may lead to body proteins being broken down to make glucose

EXTRA protein intake CANNOT be stored

• It can be used immediately as an energy source

• It can be converted to glucose/fat and stored for future energy needs

Amino acids must first be…

Deminated

Deamination

Amino group is removed and converted to urea for excretion by the kidneys

After deamination

2 and 3+ carbon molecules can enter Cellular Respiration (at different places)

How to determine protein needs?

Nitrogen balance

Nitrogen balance

Protein synthesis = protein degradation

Measuring nitrogen balance

• Nitrogen In – from diet

• Nitrogen Out – lost in:

  • Sweat

  • Urine

  • Feces

Nitrogen balance is positive in

• Growing infants

• Children

• Adolescents

• Pregnant women

• People recovering from protein deficiency or illness

Nitrogen balance is negative in

• People who are starving

• Burn victims

• Severe injuries

• Infections

• Fever

Current protein recs

• AMDR: 10% - 35% of total calories

• RDA = 0.8 g/kg of healthy body weight

  • 70 kg (154 lb) adult = 56g of protein/day

  • Average consumption = 70g of protein/day

Protein on food labels

Minial info on food labels about protein amino acid make up (just toal protein)

Risks of low protein diets

• Kwashiorkor (adequacy)

• Sarcopenia (middle)

• Marasmus (inadequacy)

Risks of high protein

• Increased nitrogen products (uric acid) from animal-sourced proteins can lead to gout

• Increased water loss from kidney filtering urea can lead to dehydration and constipation

• High protein diet may increase calcium excretion which may increase risk of kidney stones