WH+lecture+5-protein - Protein Structure and Digestion What...

Protein
Structure and Digestion

What is Protein?

One or more folded strands of amino
acids

Made of C,H,O and Nitrogen

Supplies 4 kcal/g

Found in animal and plant foods

In the body- has structural and
regulatory functions

Sources of Protein

One ounce of meat= 7 g

One cup of milk= 8 g

½ cup beans= 6-10 g

Vegetables/grains= 2-3 g per serving

Fruits= 1 g per serving

Amino Acids

Building blocks of protein

Folded chains

Each protein molecule contains a
specific number and sequence of
amino acids

20 types- 9 are essential

Nonessential can be made by a
process called transamination

20 Amino Acids

Structure of Amino Acids
Alanine

Conditionally Essential

6 nonessential amino acids are made
from essential amino acids

Tyrosine/ phenylalanine

Cysteine/ methionine

Arginine

Glutamine

Glycine

Proline

Protein Structure

Amino acids are linked by peptide
bonds

Dipeptide

Tripeptide

Polypeptide

Protein- one or more polypeptide
chains folded into a 3-D shape

Protein Structure
Sequence
determined by DNA

Denaturation

Changes in protein structure due to
heat or acid

Raw egg vs. cooked egg

Acidic marinade can cook raw fish

Raw meat vs. cooked meat

Protein Digestion

Begins in Stomach

HCL acid
•
Denatures proteins
•
Activates pepsin

Small intestine

Trypsin and chymotrypsin

Brush border enzymes

Amino acids, di and tripeptides enter mucosal cell

Inside mucosal cell- further breakdown

Absorption of Amino
Acids

Amino acids cross mucosal cells by Active
Transport – several different transport
systems (some are shared)

Too much of one amino acid may impair
absorption of other amino acids

Arginine shares same transport system as
lysine-
if you take arginine in pill
form what will happen to lysine??

What happens if a protein is
not completely digested?

Allergic reaction- body thinks the
whole protein is a foreign substance

Immune system reacts

Happens in infants or those with GI
disease

Benefit to infants

Protein Metabolism

Absorbed amino acids are sent to the
liver

Can be used to make blood or liver
proteins

Can be used for energy

Can be released to other tissues

Can be used to make nonprotein
molecules

Amino Acid Pool

Refers to available amino acids in
body tissues and fluids

Comes from diet and body stores

300 g of protein synthesized a day
(only 100g coming from the diet)

Protein and energy intake adequate

Energy deficient, protein excessive

Protein Synthesis-
process of
reading genetic information

Amino acid pool is used to make body
proteins

Instructions on how to make each
protein comes from our genes (DNA)

Reading the instructions- Process of
Transcription and Translation

Proteins are made in the ribosomes

Gene expression- using genetic
information to make proteins