Protein

6.1

Made of C,H,O,N sometimes S

N is amino

Central carbon

NH2 amino group

COOH acid group

Hydrogen Side chain

Chain of AAs = protein

Proteins are folded chains of amino acids (JOINED BY CONDENSATION)

Peptide Bonds form Between AAs

Structure: Primary, Secondary, Tertiary, Quaternary

P- Sequence of AAS

S- Twists and bends due to weak side chain attractions

T- Folds due to strong side chain interactions, bonds

Q- Two or more polypeptides in association

Denaturation: Altering the shape of a protein

Due to heat or acid

Cooking eggs, curdling milk to make cheese

Stomach acid will denature most proteins

Summary

  • Chemically speaking, proteins are more complex than carbohydrates or lipids; they are made of some 20 different amino acids, 9 of which the bod cannot make ( the essential amino acids)

  • Each amino acid contains an amino group, an acid group, a hydrogen atom, and a distinctive side group( R group) , all attached to a central carbon atom

  • Peptide bonds link amino acids together by way of a series of condensation reactions to create proteins

  • The distinctive sequence of amino acids in each protein determines its unique shape ad function

6.2

Protein digestion

Mouth, Stomach, Small intestine

Mouth:

  • Chewing and moistening only

Stomach:

  • HCI denatures proteins, unfolds them

  • Pepsinogen changed to active enzyme pepsin by acid

  • Pepsin Hydrolyzes polypeptides into shorter chains

Small Intestine

  • Pepsin deactivated by rising pH

  • Pancreatic proteases hydrolyze AA chains

  • Peptidases on intestinal cell surfaces hydrolyze to single AAs

Protein Absorption

Some AAs used by intestinal cells themselves for energy, parts

The rest goes into the bloodstream by villi capillaries

Whole proteins handled better then pre-digested AAs

Body will break down what it needs at the moment

Summary

  • Digestion of proteins is facilitated mostly by the stomach’s acid and enzymes, which first denature dietary proteins, then cleave them into smaller polypeptides and amino acids

  • Pancreatic and intestinal enzymes split the polypeptides further, to tripeptides and dipeptides, and then split most of these to single amino acids.

  • Then carriers in the membranes of intestinal cells transport the amino acids into the cells, where they are released into the bloodstream.

6.3

Protein synthesis:

  • DNA code is transcribed into MRNA within the nucleus (does not leave nucleus)

  • mRNA leaves nucleus to the cytoplasm and ribosomes

  • Ribosomes read the mRNA and tRNA bring amino acids accordingly (make polypeptides)

  • Condensation reaction occurs to add the AA to the growing polypeptide chain

  • Gene Expression

Cells control when and how much protein to make (CHANGES THE MAKEUP OF THE CELL AND BODY AT ANY GIVEN TIME)

Mutation- Any change in the DNA (if changes the amino acid sequence it could have serious consequences, sickle cell disease)

Makes protein non functional leading to disease

Role of Proteins

Structural:

  • COLLAGEN fibers, ligaments, Keratin skin cells

  • ENZYMES, protein catalysts (Anabolic or Catabolic)

  • HORMONES, protein messengers (insulin, glucagon, calcitonin)

Fluid balance regulators:

  • Hold fluid in vessels, without this fluid seeps into the tissues (edema)

BUFFERS of blood pH (<7.35 acidosis; >7.45 alkalosis)

Transporters:

  • Lipoproteins in blood

  • Across membranes as channels

Antibodies:

  • Specifically attack antigens for removal

  • Confer immunity to diseases

Clotting factors

  • Usually dissolved in blood plasma

  • Sticky when vessels tear

Precursors

NEUROTRANSMITTERS (serotonin)

VITAMINS (niacin)

Protein Metabolism

Protein turnover:

  • Constant breakdown of food to AAs (CATABOLISM)

  • Buildup of new proteins (ANABOLISM)

  • AAS in the bloodstream steady

Nitrogen balance

  • In from foods

  • Out in sweat, urines, feces

  • NITROGEN POSITIVE when needed to heal

  • NITROGEN NEGATIVE in starvation mode

Protein:

4kcal per gram for energy

Gluconeogenesis for glucose

Keto acids:

  • Deamination of AAs

  • Keto acids can enter many pathways, cholesterol production

  • Transamination of keto acids

  • both processes occur in the liver

Ammonia is toxic to the body

Liver makes urea with it (2NH3 + CO2 = CO (NH2)2)

Kidneys filter urea to the urine

HIGH PROTEINS CAN BE DEHYDRATING