Protein

Describe the digestion of protein

Stomach: gastrin from gastric cells causes the release of gastric juices that contain hydrochloric acid (HCL) and pepsin. The gastric juices denature the quaternary, tertiary, and secondary structures of proteins while pepsin cleaves peptide bonds at the COOH end

Small intestine: regulatory hormones and peptides facilitate further digestion of proteins and polypeptides. Secretin and cholecystokinin stimulate the pancreas to produce digestive proenzymes and enteropeptidases. The end product of digestion are peptides and free amino acids

pepsinogen

inactive form of pepsin

proenzymes

inactive enzymes

Describe di and tri peptide absorption into the enterocyte

The enzyme Pept1, a symporter brings a peptide and H+ into the enterocyte along the concentration gradient. A separate antiporter allows H+ to leave the cell and Na+ to enter the enterocyte. Both of these transporters are passive, but this system requires the help of the N/K ATPase on the basolateral membrane to preserve the concentration gradient. Once inside the enterocyte, the peptides are broken down into singular amino acids

Describe amino acid absorption into the enterocyte

A sympoter transports sodium and an amino acid into the enterocyte while N/K ATPase transports the sodium back out of the enterocyte

Describe amino acid transport across the basolateral membrane

the amino acids are transported across the basolateral membrane through various transport systems-some are the same that carried amino acids into the enterocyte

How are the majority of amino acids absorbed?

As di and tri peptides

What type of amino acids are absorbed quicker?

Branch chain amino acids are absorbed faster

neutral AAs are absorbed faster than basic or acidic AAs

essential AAs are absorbed faster than nonessential AAs

Glutamate and Aspartate are very slowly absorbed as they are both acidic and non-essential

transanimation

transfer of an amino group from one amino acid to an alpha-keto amino acid

Which enzymes catalyze trans animation

aminotransferases

deanimation

removal of an amino group, no transfer

How is the amino group produced from deanimation excreted from the body?

it funnels through to urea cycle to be excreted as urea

How do proteins act as buffers?

Amino acids within proteins can take on H+ when the pH in the body is too low/acidic or give up an H+ when the pH is too high/basic

peptide hormones

insulin, glucagon, ghrelin, growth hormones, vasopressin

purpose of plasma proteins

in the blood, proteins attract and keep water inside blood vessels and contribute to osmotic pressure. When there is a deficiency in plasma proteins, water leaks of if the blood and into the interstitial space, causing edema (swelling). Ex: albumin

transferrins

carry iron in the blood

elastin

used to make connective tissue in the blood

keratin

used for hair and nails

acute phase proteins

stimulates the immune system and promotes wound healing, increase during sudden critical illness like infection or injury

RDA for protein

0.8g/kg

AMDR for protein

10-35% of energy intake (but calorie intake needs to be sufficient)

RDA for women in their 2nd and 3rd trimester

1.1g/kg

formula for nitrogen intake from diet

grams of protein x 0.16 (or /6.25)

kwashiorkor

caloric intake is adequate but protein is deficient

marasmus

chronic inadequate food intake

clinical signs of protein deficiency in children

stunted growth, thin and fragile hair, poor musculature, skin lesions, edema

sarcopenia

age related loss of muscle

What % of lean muscle mass do we loss each decade after 30%

3-8%, but we can reduce the decline with resistance exercises and 25-30g high quality protein 3x/day

Influences on muscle development

adequate dietary protein

gender, age

genetics

muscle use

benefits of protein in weight management

increased satiety/compliance with diet

reduced energy efficiency through thermogenesis

list the essential fatty acids

phenylalanine, valine, threonine, methionine, tryptophan, histidine, isoleucine, leucine, lysine