Download Proteins and Amino Acids: Function Follows Form

Proteins and Amino Acids:
Function Follows Form
BIOL 103, Chapter 7
Today’s Topics
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Why is Protein Important?
Amino Acids are building blocks of proteins
Functions of Body Proteins
Protein Digestion and Absorption
Proteins in the Body
Proteins in the Diet
The Pros and Cons of Vegetarian Eating
The Health Effects of Eating Too Little or Too
Much Protein
Why is Protein Important?
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A part of every cell
Needed in thousands of chemical reactions
Keep us “together” structurally
In short, proteins have many, many functions
from replacing skin cells, producing antibodies
to assisting in nutrient transport and muscle
contractions.
Food Sources of Proteins
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Beef
Chicken
Fish
Milk
Plant foods: beans, peas,
grains, nuts, seeds, and
vegetables (garlic, green
peas, mushrooms)
Amino Acids are Building Blocks of
Proteins
• Proteins are sequences of amino acids
• There are ______ amino acids:
1. Essential (9)
2. Non-essential (11)
3. Conditionally essential (6)
• Table 7.1 List of Amino Acids
Amino Acids Identified by Side Chains
Protein structure: unique 3D shapes
and functions
• Amino Acid Sequence
– Amino acids are linked by peptide bond:
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Dipeptide: 2 amino acids
Oligopeptide: 4-10 amino acids
Polypeptide: >10 amino acids
Protein: a chain with >50 amino acids
– Protein shape
• A _____________ of AA determines protein shape
• Shape of protein determines its _______________.
Protein Denaturalization: Destabilizing
a Protein’s Shape
• There are factors that can cause
a protein to unfold and lose
shape
1. Changes in Acidic or Alkalinity in
environment
2. High temperature/heat
3. Alcohol
4. Oxidation
• _______________ proteins lose
their ability to function properly.
Functions of Body Proteins
Protein Digestion
• Protein digestion
– Cells produce proteases (protein-digesting
enzymes) as proenzymes (inactive forms of
enzymes)
– In the stomach:
• Proteins are denatured by HCl
• Pepsin begins digestion: 10-20% of proteins
• Which one is a protease? A proenzyme?
Protein Digestion and Absorption
• In the small intestine:
– Proteases (from pancreas) break down remaining
proteins  small peptides
– Intestinal lining cells break down small peptides
 amino acids
– Amino acids are then absorbed into your intestinal
cells  travel via portal vein to liver  released to
general circulation
Summary of Protein Digestion and
Absorption
Undigested Proteins
• If not digested, continues down the GI tract 
feces
• Diseases of the intestinal tract cause problems
with digestion/absorption of proteins
1. Celiac disease: allergic to protein gluten
2. Cystic fibrosis: sticky mucus prevents digestive
enzymes (e.g. proteases) from reaching small
intestine  poor digestion  nutrients are not
absorbed  malnutrition
Proteins in the Body
• Protein Synthesis:
– Draws on AA pool as needed. If your body is
missing…
• Non-essential AA:
– Cell will make that AA
– Obtain it from liver
• Essential AA:
– Body make break down its own protein to supply the AA
Proteins in the Body
• Amino Acid Pool and Protein Turnover
– Cells in your body constantly build and breakdown
proteins  Protein turnover
• “protein recycling”
– When cells make proteins, they use amino acids
from amino acid pool: available amino acids in
body tissues and fluids that can be used to make
new proteins.
Proteins in the Body
• Synthesis of non-protein molecules
– Proteins are precursors of DNA, RNA, and
neurotransmitters
• Protein and Nitrogen Excretion
– Breakdown of amino acids by removing nitrogen
(amino) group/-NH2
– Amino groups converted to ____________
– Urea + water = _________  excretion (in kidney)
Function of Blood Amino Acid Pool
Nitrogen Balance
• We can evaluate our nitrogen balance to evaluate what is
happening in our body
– Nitrogen intake vs. nitrogen output
• Nitrogen equilibrium
– Nitrogen intake = nitrogen output
– Healthy adults
• Positive nitrogen balance
– Nitrogen intake > Nitrogen output
– Growth; recovery from illness
• Negative nitrogen balance
– Nitrogen intake < Nitrogen output
– Injury and illness
Proteins in the Diet
• Recommended protein intake
– Adult RDA = 0.8g/kg of body weight
– _________ have highest needs relative to body weight
• Why?
– Physical stress ______________ your body’s needs for
proteins
– Infection, burns, fevers, surgery, intensive weight
training
• Consumption in the US
– Generally within or higher than recommended range
Problem Set 7, Question 1:
• How is it that our bodies are able to synthesize
so many proteins in our body when our
dietary protein requirement is relatively low?
Protein Quality
• Protein Quality
– Complete proteins: supply all essential amino
acids
• “high-quality proteins”
• Examples: animal proteins, soy proteins
– Incomplete proteins: low in one or more essential
amino acids
• “low quality proteins”
• Examples: most plant proteins
Protein Quality
• Incomplete and Complementary Proteins
– Except soy, proteins in other plant foods is
incomplete (lacks 1 or more essential AA).
– Two incomplete complementary proteins =
complete protein
• Examples: rice and beans, peanut butter and bread,
pea soup with crackers, corn and tortilla.
Evaluating Protein Quality
• A high-quality protein:
1. Provides all the essential amino acids at amounts the
body needs
2. Provides enough other amino acids to serve as
nitrogen sources for making non-essential amino
acids
3. Easy to digest
4. Protein digestibility-corrected amino acid score
(PDCAAS): measure of protein quality that takes
account the AA composition of the food and the
digestibility of the protein.
Proteins and Amino Acids as Additives
and Supplements
• Protein and AA additives
– Contribute to structure,
texture, taste of foods
• Protein and AA
supplements
– Used for a variety of
reasons: dieters, athletes,
certain diseases.
– Risks are unknown
Vegetarian vs. Vegan
Vegetarian
• “Diet”
• Don’t Eat: Meat, seafood
• Types:
– Ovo-vegetarian: eats eggs
– Lacto-vegetarian: eats dairy
products
• Products: Don’t mind using
animal-derived products.
Vegan
• “Diet + Lifestyle”
• Don’t Eat: Meat, eggs, milk,
honey, or any food derived
from animals.
• Products: Avoids using
animal-derived products
including clothing,
cosmetics, household,
foods.
Pros and Cons of Vegetarian Eating
Problem Set 7, Question 4
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Health Benefits
Less fat, saturated fat,
cholesterol
More magnesium, folate
More antioxidants
More fiber and
phytochemicals
Reduces risk for heart
disease, hypertension, and
cancer.
Health Risks
• Vegans may be low in:
calcium, iron, zinc, vitamin
D, ____________________
• Higher intake of
______________________
• More restrictive food
choices = less nutrients
The Pros and Cons of Vegetarian Eating
• Diet recommendations (pg. 258):
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Choose a variety of foods
Choose whole, unrefined foods
Choose a variety of fruits and vegetables
Choose lower-fat dairy products and eggs in
moderation
5. Consume a regular source of vitamins B12 and D
• Fortified foods or supplements
The Health Effects of Too Little Protein
• Dietary protein = essential amino acids
• Protein deficiency: occurs when energy and/or
protein intake is inadequate
• Protein-energy malnutrition (PEM)
– Kwashiorkor: severe ______________ deficiency
• Symptoms: edema, poor growth, bloated belly
• Affects those between age of 18-24 months old
• Associated with extreme poverty
The Health Effects of Too Little Protein
• PEM, cont.
– Marasmus: severe ________________ deficiency
• Chronic PEM; “withering”
• Affects Infants and 6-18 months old children
• Usually the children are short and thin for their age
• How to treat?
– Nutritional rehabilitation
• Gradual and careful refeeding
• Must start with fluid and electrolyte balance, then
introduce nutrients
Protein-Energy Malnutrition
The Health Effects of Too Much Protein
Problem Set 7, Q5
• Name two health effects related to consuming
a very high protein diet.