Proteins & Amino Acids - Chapter 6 Flashcards
Structure of the Basic Protein
- Composed of carbon, hydrogen, oxygen and nitrogen
- Arranged in strands of amino acids (AAs)
Basic Protein Structure & Function
- All AAs have the same chemical backbone
- A single carbon atom, with an amine group and an acid group attached
- Each AA has a distinctive side chain which gives it its identity and chemical nature
- The side chains make the AA differ in size, shape and electrical charge (positive, negative or neutral)
Basic Protein Structure
& Function (20 AAs)
- 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 or fibrous structure
Sequence & Shape Determine Function
- DNA (genetic sequence) determines the AA sequence in proteins
- Specific structure/shape of proteins enables them to perform different tasks in the body
Function of Protein
- Working proteins: enzymes, antibodies, hormones, oxygen carriers, etc.
- Structural proteins: tendons, ligaments, fibres of muscles, found in our bones, teeth, hair and nails
Protein Synthesis Errors
- For each protein, there exists a standard AA sequence which is specified by heredity
- If a wrong AA is inserted = health consequence
- E.g., genetic diseases
- Sickle cell disease
- E.g., genetic diseases
Protein Digestion (Stomach)
Gastric acid (HCl) denatures protein, and pepsin (enzyme) cleaves some
peptide bonds
Protein Digestion (Small intestine lumen)
Pancreatic enzymes cleave polypeptides to di- and tri-peptides
Protein Digestion (Brush border membrane)
Enzymes cleave di- and tri-peptides to single AAs
Protein Absorption
- Intestinal cells absorb AAs and some di- and 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 to be taken up by body cells
- Body can reconnect AAs to make proteins
- Body can use AA for energy if necessary
All Different Functions of Proteins (Part 1)
- Growth and maintenance
- Structure, new tissue, repair (e.g., RBC lifespan is 90-120 days)
- Hormones and enzymes
- E.g., growth factors, insulin
- Immune function
- Antibodies
All Different Functions of Proteins (Part 2)
- Fluid and electrolyte balance
- Protein transport
- E.g., protein malnutrition and edema
- Acid-base balance
- E.g., protein buffers
- Blood Clotting
- Energy (Fig. 6-12)- Secondary function,
only if diet is deficient
in carbohydrate or total energy - No storage form of
AAs
- Secondary function,
Protein Utilization (Build Protein)
- AA used to build proteins
- Converted to other small nitrogen-containing compounds, e.g.,
vitamins (tryptophan → niacin) - Converted to other AAs
- After removal of amino group:
- Gluconeogenesis: carbon skeleton → glucose → blood
- Lipogenesis: carbon skeleton → fat (for fuel or storage)
Protein Utilization (Waste)
- 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)
Protein Utilization (Protein Synthesis)
- To prevent wasting and permit protein synthesis:
- Dietary protein must be adequate and supply all essential AA in proper amounts
- Need adequate energy from carbohydrate and fat
Recommendations
- Recommendations for intake:
- DRI: 0.8g/kg body weight
- Females: 46g/day
- Males: 56g/day
- DRI minimum amount: 10% total energy
◦ DRI maximum amount: 35% total energy
- DRI: 0.8g/kg body weight
Protein Quality &
Quantity
- Malnutrition:
- Digestive enzyme secretion slows as the digestive tract lining degenerates, impairing protein digestion and absorption
- Infection:
- Protein is required to enhance immune function
- Efficient use of protein:
- Must be accompanied by the full array of vitamins and minerals
Protein Quality &
Quantity (factors)
- Two 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
- High-quality proteins contain ample amounts
Protein Quality &
Quantity (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 (PDCAAS)
- Protein digestibility corrected amino acid score:
- Reflects protein digestibility
- Proportion of AAs provided
Measuring Protein
Quality (Scale 0-100)
- Egg white, ground beef, chicken products, fat-free milk, tuna = 100
- Soybean protein = 94
- Wheat protein = 25
- Combining complementary proteins can increase score
Nitrogen Balance
- Nitrogen intake compared to nitrogen excretion (through urine, feces,
skin, sweat, body fluids)- Depends on size and stage of growth:
- Equilibrium: normal healthy adult
- Positive: growing child, pregnant individual
- Negative: surgery patient, astronaut
- Depends on size and stage of growth:
Protein Energy
Malnutrition (Marasmus)
- <2 years age
- Total diet deficiency
- Slow, chronic
- Severe weight loss
- Muscle and fat loss
- <60% weight for age
- No edema
- No fatty liver
- Anxiety, apathy
- Appetite varies
- Hari, skin problems
Protein Energy
Malnutrition (Kwashiorkor)
- 1 – 3 years age
- Protein deficiency
- Rapid onset, acute
- Some weight loss
- Some muscle wasting
- 60-80% weight for age
- Edema
- Fatty liver
- Apathy, irritability
- Loss of appetite
- Hair, skin problems
Protein Energy
Malnutrition
- Worldwide:
- 33,000 children die every day, many are malnourished
- North America:
- PEM associated with chronic disease, poverty, eating disorders
What is Excess? (Protein Excess)
> 35% calories from protein
High intakes of animal protein (Protein Excess)
- Associated with obesity
- Increased intake of saturated fat
- Kidney and liver problems in animals
- More bone mineral loss with high intakes of purified protein
- More calcium lost in urine
- Evidence mixed for effect of meat protein on Ca
High intakes of protein (Protein Excess)
- 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 treatment for kidney problems = reduce protein intake
High protein diets for weight loss (Protein Excess)
- Protein used for energy and making glucose: must remove amino group and excrete it as urea via kidneys
- Low CHO: if <130 g CHO/d, then no glycogen stores and “ketotic”
- Body fat → ketone bodies for energy
- Blood glucose made from
- Dietary AAs (after meals)
- Muscle protein (when post-absorptive), and this results in muscle wasting
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 saturated fat: long term CVD risk?
- Diet high in dietary cholesterol
- Diet often low in some vitamins and minerals (e.g., calcium), and low in fibre
Controversy 6: Vegetarian Diets (Vegetarian)
- People choose vegetarian eating for many reasons:
- Healthy eating
- Culture
- Ethics
- Others?
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Vegetarian)
Plant-based foods, some or all animal foods eliminated
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Vegan)
Only food from plant sources (vegetables, grains, legumes, fruits, seeds, nuts,
etc.)
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Raw Vegan)
As above, but sprouted grains, and 75-100% of dietary intake is from uncooked food
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Lacto-ovo-vegetarian)
Eats dairy and eggs; no
flesh or seafood
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Lacto-vegetarian)
Eats dairy; no eggs, flesh, or
seafood
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Ovo-vegetarian)
Eats eggs; no milk products, flesh, or seafood
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Partial Vegetarian)
No red meat or limited
quantities
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Pesco-vegetarian/pescatarian)
No red meat or poultry
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Fruitarian)
Eats raw/dried fruit, seeds, nuts
Controversy 6: Vegetarian Diets (TERMS TO KNOW - Macrobiotic Diet)
Progressively eliminates
foods → brown rice, herbal tea, water → malnutrition and death
Controversy 6: Vegetarian Diets (Positive Health Aspects of Vegetarian Diets)
- Reduced risk of disease (obesity, heart disease, diabetes, hypertension, cancer)
- Diet is high in F&V, fibre, phytochemicals, some
vitamins/minerals (e.g., A, C, folate) - Lifestyle often excludes smoking and alcohol, and
emphasizes physical activity
- Diet is high in F&V, fibre, phytochemicals, some
- Lower fat diet and leaner body composition
- Maintain healthier body weight
- Better control of caloric intake due to fibre-rich bulky foods?
Controversy 6: Vegetarian Diets (Potential Pitfalls of Vegetarian Diets)
- May be harder to meet additional requirements for pregnancy, breastfeeding, illness, etc.
- Vitamin B12, vitamin D, Ca, Fe, Zn, and omega-3 fatty acid intakes may fall short,
especially for infants, children, adolescents, and older adults - Requires careful planning
Controversy 6: Vegetarian Diets (Summary)
- Whichever diet you choose, important that diet is well planned to include all necessary nutrients
- Aim for adequate, balanced, Calorie controlled, and varied
- Use moderation when choosing foods high in saturated fat, sugar, salt, or Calories
