305 week 3 proteins

Protein digestibility score

Compares amino acid content with human requirements and digestibility.

Factors limiting digestion

Cell walls, enzyme inhibitors, and tannins reduce protein digestibility.

Daily protein requirement

Approximately 50 g/day or about 10% of a 2000 kcal diet.

Protein functions

Growth, tissue maintenance, immune function, transport, hormones, buffering, and energy.

Acute protein-energy malnutrition

Children are thin for their height.

Chronic protein-energy malnutrition

Children are short for their age.

High animal protein diet

Associated with increased risk of heart disease, some cancers, and calcium loss.

High-protein diet benefits

May assist weight control and support muscle repair in active athletes.

Kidney effect of high protein

High protein intake increases kidney workload.

Good protein sources

Beans, tofu, tempeh, quinoa, low-fat dairy, and soy products.

Complete amino acid intake

Eating a variety of protein sources provides all essential amino acids.

Protein structure basics

Each amino acid contains an amino group, carboxyl group, hydrogen, and side chain.

Amino group

Contains nitrogen (NH₂).

Additional elements in proteins

Some proteins also contain sulfur, phosphorus, or iron.

Essential amino acids

Cannot be synthesized and must come from food.

Nonessential amino acids

Can be synthesized by the body.

20 amino acids

Proteins are built from 20 different amino acids.

Nonpolar amino acids

Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Phenylalanine, Tryptophan, and Proline.

Polar amino acids

Serine, Threonine, Cysteine, Tyrosine, Asparagine, and Glutamine.

Acidic amino acids

Aspartic acid and Glutamic acid.

Basic amino acids

Lysine, Arginine, and Histidine.

Peptide bond

Covalent bond joining the carboxyl end of one amino acid to the amino end of another.

Hydrolysis

Breaks peptide bonds using water during digestion.

Dehydration synthesis

Forms peptide bonds by removing water during protein synthesis.

N-terminus

The amino end of a polypeptide.

C-terminus

The carboxyl end of a polypeptide.

Primary structure

The unique linear sequence of amino acids.

Secondary structure

Alpha helices and beta pleated sheets formed by backbone folding.

Tertiary structure

The three-dimensional shape produced by R-group interactions.

Forces stabilizing tertiary structure

Hydrogen bonds, ionic bonds, hydrophobic interactions, van der Waals forces, and disulfide bridges.

Quaternary structure

Association of two or more polypeptide chains.

Sickle cell anemia

Caused by a single amino acid substitution in hemoglobin.

Hemoglobin S

Hydrophobic interactions cause fibers to form, reducing oxygen transport.

Structural role

Proteins form bone, muscle, tendons, ligaments, scar tissue, hair, and nails.

GI cell renewal

Gastrointestinal cells are replaced approximately every 3 days.

Peptide hormones

Growth hormone, insulin, glucagon, calcitonin, parathyroid hormone, ADH, and thyroxine.

Protein hormone characteristics

Fast acting with relatively short half-lives.

Fluid balance

Plasma proteins create colloid osmotic pressure that draws water into blood.

Edema

Low plasma proteins reduce osmotic pressure, allowing fluid to accumulate in tissues.

Acid-base buffering

Proteins accept and release hydrogen ions to resist pH changes.

Transport proteins

Include channels, carriers, and active transporters.

Na⁺/K⁺ ATPase

ATP-powered protein pump that transports sodium and potassium.

Antibodies

Proteins that bind specific antigens such as bacteria, viruses, allergens, and toxins.

Protein as energy

Amino acids can be converted to ATP, glucose, or fat.

Deamination

Removes the amino group, producing ammonia.

Ammonia fate

The liver converts ammonia into urea.

Other amino acid products

Amino acids are precursors for norepinephrine, epinephrine, melanin, fibrin, and niacin.

Collagen

The most abundant protein in vertebrates, making up about 20% of human protein.

Collagen locations

Cartilage, tendons, bone, teeth, skin, and blood vessels.

Tropocollagen

The basic structural unit of collagen.

Collagen triple helix

Three left-handed helices form one right-handed triple helix.

Collagen Type I

Arteries, tendons, ligaments, skin, organs, and bone.

Collagen Type II

Cartilage.

Collagen Type III

Commonly found alongside Type I collagen.

Collagen Type IV

Basement membranes.

Collagen Type V

Cell surfaces, hair, and placenta.

Vitamin C function

Required for collagen cross-linking.

Vitamin C storage

Water-soluble vitamin stored for only about one month.

Scurvy

Vitamin C deficiency causing defective collagen synthesis.

Scurvy symptoms

Bleeding gums, loose teeth, petechiae, bruising, fatigue, dry skin, bone and muscle weakness, shortness of breath, and chest pain.

Severe scurvy

Hemolysis, internal hemorrhage, neuropathy, organ failure, coma, and death.

Elastin

Fibrous protein providing elasticity to skin, lungs, and blood vessels.

Elastin structure

Cross-linked tropoelastin with a random coil organization that is highly extensible.

Proteoglycans

Hydrophilic molecules that bind water and resist compression in cartilage and soft tissues.

Keratin

Strong fibrous protein forming hair and other tough structures with high stiffness and extensibility.