HNSC UNIT 6

Proteins

Protein Structure

• composed of carbon, hydrogen, oxygen, and nitrogen

• Arranged in strands of amino acids (building blocks of proteins)

Amino Acid Chemical Backbone

• a single carbon atom, with an anime group and an acid group attached

• Each AA has a distinctive side chain which goes it its identity and chemical nature

• The side chains make the AA differ in size, shape, and electrical charge (+,-, or neutral)

20 Amino Acids:

• 8 indispensable/essential, some may become conditionally essential (e.g. histidine)

• Joined together by peptide bonds to form proteins

  • 2 AA = dipeptide

  • 3 AA = tripeptide

  • >3 AA = polypeptide

Building Protein

• AAs chemically attracted to or repelled from each other

  • Creates a coil shape

• Spots along the coil attracted/repelled

  • Globular structure of fibrous structure

Function of Proteins

• working proteins

• Structural proteins

Working Proteins

• enzymes, antibodies, hormones, oxygen carriers, etc.

Structural Proteins

• tendons, ligaments, fibres of muscles, found in our bones, teeth hair and nails

Sequence and Shape Determine Function

• DNA determines the AA sequence in proteins

• Specific structure/shape enables them to perform different tasks in the body

Protein Synthesis Errors

• for each protein, exists a standard AA sequence which is specified by heredity

• If a wrong AA is inserted → health consequence

  • Genetic diseases

Protein Digestion

• stomach

• Small intestine lumen

• Brush border membrane

Protein Digestion - Stomach

• starts here

• Gastric acid (HCL) denatures protein, and pepsin (enzyme) cleaves some peptide bonds

Protein Digestion - SI lumen

• pancreatic enzymes cleave polypeptides to di and tri peptides

• Cleaving makes it more usable

Protein Digestion - Brush Border Membrane

• enzymes cleave di and tri peptides to single AAs

Protein Absorption 

• intestinal cells absorb AAs and some di/tri peptides and release them into the bloodstream 

• absorbing larger peptides may contribute to food allergies (immune response)

• carried to liver - used or released back into blood 

• body can reconnect AAs to make proteins and use AA for energy is necessary 

Functions of Proteins 

• growth and maintenance 

  • structure, new tissue, repair 

• hormones and enzymes 

  • growth factors, insulin 

• immune function

  • antibodies

• acid-base balance 

  • protein buffers 

• blood clotting 

Protein Utilization

• AA used to build proteins 

• converted to other small N containing compounds

• converted to other AAs 

AAs Are Wasted When:

• energy is lacking

• protein is overabundant 

• an AA is oversupplied (e.g. supplement)

• diet has too few essential AA (i.e. low protein quality) 

To Prevent Wasting and Permit Protein Synthesis:

• dietary protein must be adequate and supply all essential AA is proper amounts 

• need adequate energy from carb and fat

Protein in Food

• protein found in all food groups

Protein DRI’s

• DRI: 0.8g/body weight 

  • females 46g/day

  • males 56g/day

• DRI min: 10% total energy 

• DRI max: 35% total energy 

Protein Quantity

• malnutrition, infections, state of health can increase need for protein

  • malnutrition: digestive enzyme secretion slows as the digestive tract lining degenerates, impairing protein digestion and absorption 

  • infection: protein is requires to enhance immune function

  • efficient use of protein: must be accompanied by the full array of vitamins and minerals 

2 Factors Influence Protein Quality

• digestibility (improved by moist heat)

  • animal protein: >90% absorbed

  • plant protein: 70-90% absorbed

• amino acid composition

  • high quality proteins contain ample amounts of all essential AAs

Complementary Proteins

• 2 or more proteins whose AA structures supply the essential AAs missing from the other

• need complementary proteins in same day

Measuring Protein Quality

• protein digestibility-corrected amino acid score (PDCAAS):

  • reflects protein digestibility

  • proportion of AAs provided

• scale of 0-100

  • egg white, ground beef, chicken, fat free milk = 100

  • soybean protein = 94

  • wheat protein = 25

  • combining can increase score

Nitrogen Balance

• N intake compared to N excretion (through urine, feces, skin, body fluids)

• depends on size and stage of growth:

  • equilibrium: normal healthy adult

  • positive: growing child, pregnancy

  • negative: surgery patient, astronaut

Protein Energy Malnutrition - Marasmus

• <2 years age - no fatty liver

• total diet deficiency - anxiety

• slow, chronic, severe weight loss - appetite varies

• <60% weight for age - hair, skin problems

• no edema

Protein Energy Malnutrition - Kwashiorkor

• 1-3 years age - fatty liver

• protein deficiency - irritability

• rapid onset, acute - loss of appetite

• some weight loss - skin and hair problems

• muscle wasting (some)

• 60-80% weight for age

• edema

Protein Excess - Animal Protein Intake

• >35%

• associated with obesity

• increased intake of saturated fat

• kidney and liver problems in animals

• more bone mineral loss

• more calcium lost in urine

Protein Excess - High Intakes of Protein

• worsen existing kidney disease in humans

• increase work of the kidney to excrete nitrogen wastes: amine group of AAs is excreted as ammonia or urea

• effective kidney treatment = reduce protein intake

Protein Excess - For Weight Loss

• protein used for energy and making glucose: must remove amino group and excrete it as urea via kidneys

• low CHO: if <130g CHO/day, then no glycogen stores and (ketonic)

High Protein Diets

• initial rapid weight loss due to more water loss from body; loss of body fat and muscle mass in long term

• diet high in dietary cholesterol

• diet often low in some vitamins and minerals and low in fibre

Vegetarian

• plant-based foods, some or all animals eliminated

Vegan

• only food from plant sources

Raw Vegan

• only food from plant sources but sprouted grains and 75-100% of intake is from uncooked food

Lacto-Ovo-Vegetarian

• eats eggs and dairy; no flesh or seafood

Lacto-Vegetarian

• eats dairy; no eggs, flesh, or seafood

Ovo-Vegetarian

• eats eggs; no dairy products, flesh, seafood

Pesco-Vegetarian

• no red meat or poultry

Partial Vegetarian

• no red meat, or limited quantities

Fruitarian

• eats raw/dried fruits, seeds, nuts

Macrobiotic diet

• progressively eliminates foods → brown rice, herbal tea → malnutrition and death