Nutrient Metabolism: proteins Flashcards
What are Proteins?
• Proteins: large, complex molecules found in
cells of all living things
➢Synthesis controlled by genetic material (DNA)
➢Contain carbon, hydrogen, oxygen, nitrogen
➢Made from a combination of amino acids
• Most of the body’s protein is made of a combination of just 20 amino acids
• Proteins are long chains of amino acids
• Amino acids are connected by peptide bonds
➢di- tri-, oligo- (less than 10), poly- peptides
how many essential aa?
dont need to know which are essential or nonessential aa
• Nine essential amino acids
➢Cannot be produced in sufficient quantities to meet
physiological needs
➢Must be obtained from food
• 11 Nonessential amino acids
➢Can be synthesized in sufficient quantities
• Transamination
➢Transfer amine group from an essential amino acid
to a different acid group and R group
- eg. valine transfer amine group to a diff acid group and sife chain (make glycine)
➢Used to make nonessential amino acids
Conditionally essential amino acids
➢Nonessential amino acid becomes essential
➢Phenylketonuria (PKU): a condition where the body
cannot metabolize phenylalanine (essential) and it can build up to toxic levels if consumed in significant quantities in the diet
➢Our body produces tyrosine from phenylalanine
➢Tyrosine becomes a conditionally essential amino
acid that must be provided by the diet (cant make anymore
How are Proteins Made?
Protein turnover:
➢Existing proteins are degraded to provide the building blocks for new proteins
➢Amino acid pool includes amino acids from food and cellular breakdown
constant turnover, proteins degraded to aa
NT, enzymes, hormones can be made
excess makes carbs or fat to store later
energy is not preferred use but used when starving
get rid as free ammonia used to make urea
Dietary Protein
mTOR - mammalian target of rapamycin
major regulator of protein synthesis
• For protein synthesis, all essential amino acids must be available to the cell
• ~20 g is the maximal effective protein dose in healthy,
young individuals for muscle protein synthesis (even if you eat more than 20g, building muscle split to 3-4 meals/day)
• Branched chain-amino acids (BCAAs) may be able to
enhance muscle protein synthesis by activating mTOR
• Limiting amino acid ➢Essential amino acid that is missing or in the smallest supply (not avail) histidine essential for hemoglobin ➢Slows down or halts protein synthesis • Inadequate energy consumption ➢Limits protein synthesis
Dietary Protein
complete vs incompleteprotein
• Incomplete protein (low quality): insufficient
essential amino acids
➢Does not support growth and health
➢Many plant sources
• Complete protein (high quality): sufficient
amounts of all nine essential amino acids
➢Derived from animal and soy protein, quinoa
- animal based is more digestible and absorbale, 90% absorbed and soy other plant grains 50-70% only
Dietary Protein
mutual supplementaiton
complementary proteins
• Mutual supplementation: combine two or more incomplete protein sources to make a complete protein ➢Plant foods such as legumes, vegetables, cereals, and grain products ❑beans – low in methionine ❑rice – low in lysine eat all if you combind them together
• Complementary proteins: two or more foods
are combined to supply all nine essential
amino acids for a complete protein
doesn’t hae to be eaten at same time recommend 24 hour window
Metabolizing Protein for Energy
• The body preferentially uses fat and
carbohydrate as fuel sources
• Protein is saved for metabolic functions that
cannot be performed by other compounds
➢Protein: building and repair of body tissues
• Protein is used for fuel primarily when total
energy or carbohydrate intake is low
• Ammonia from amino acid deamination
➢Used as nitrogen source for synthesis of nonessential amino acids
➢High levels are toxic
➢Liver converts ammonia to less toxic urea
❑Eliminated by the kidneys in the urine
• After deamination, the carbon skeleton feeds into
energy production
The Importance of Proteins in the Diet
fxns
• Proteins serve numerous function in the body
➢Cell growth, repair, maintenance
➢Enzymes and hormones (insulin, glucagon)
➢Fluid and electrolyte balance (ATPase)
➢Acid−base balance (acidic blood bind neg side chains, basic blood binds pos side chains)
➢Immune system
➢Energy source (not preferred)
➢Nutrient transport and storage (proteins make lipoproteins to transport fats)
➢Neurotransmitter synthesis (NE, serotonin)
How Much Protein?
Nitrogen balance determines protein needs
➢Positive nitrogen balance
❑body is retaining or adding protein: growth,pregnancy
or recovery from illness or a protein deficiency
➢Negative nitrogen balance
❑body is losing protein: starvation of very-low-energy diets, severe illness, infections, high fever, burns
➢In nitrogen balance
RDA = 0.8 g per kg body weight per day
**➢80 kg (176 lb) = 80 * 0.8 g/kg = 64 g protein/day
• AMDR for energy from protein is 10−35% of
total energy intake
• Protein needs are higher during growth and
development (children, adolescents, and
pregnant/lactating women)
Adverse Effects of too Much Protein
• High protein intake considered greater than 2
g/kg body weight
➢may increase bone loss (only if somone doesnt have enough calc)
➢may increase kidney disease in people who may be
more susceptible to kidney disease (e.g. diabetics)
➢may be linked to increased risk for coronary heart
disease ( may be consuming too much red meats that have sat fat, BCAA can also lead to increased risk)
What About Vegetarian Diets?
Vegetarianism: restricting the diet to foods of
plant origin
• Can be low in some nutrients ➢Varied and adequate diet planning ➢Soy and complementary proteins ➢Vegetarian Food Guide Pyramid ➢Special attention to vitamins D, B12, and riboflavin (B2); minerals zinc and iron (Vegans)
recogized as nutrionally adequate
Potential Health Benefits Associated
with a Vegetarian Diet
- Reduced risk for obesity/type 2 diabetes
- Lower blood pressure
- Reduced risk for heart disease
- Fewer digestive problems
- Reduced risk for some cancers
less likely to smoke, more activitiy
confounding factors
