Wardlaw's Perspectives in Nutrition Ch. 7

Structure of Protein

Carbon, hydrogen, water and nitrogen. Comprised of amino acids. Nitrogen/ amino group, Carboxyl/ acid group, Central carbon backbone, side group. R determines protein function and name.

Number of Amino acids: essential and nonessential

There are 20 amino acids. 9 are essential (indispensable), 11 are nonessential (dispensable).

Conditionally Essential Amino Acids

Caused by infancy, disease or trauma. When the body can not synthesize a normally nonessential amino acid (cannot convert Phenylalanine to Tyrosine; supplemental need for glutamine and arginine to heal)

Transamination

Transporting. The process through which nonessential amino acids are synthesized. The transfer of an amino group to a carbon skeleton to form a new amino acid.

Deamination

Deporting. When an amino acid looses an amino group without transferring it to a carbon skeleton. Once an amino acid breaks down to its amino-free carbon skeleton, the skeleton can be used for energy or synthesized into other compoounds. Excess nitrogen is sent to liver and excreted via urea cycle.

Essential Amino Acids

Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine

Nonessential Amino Acids

Alanine, Arginine, Asparagine, Aspartic Acid, Cysteine, Glutamic Acid, Glutamine, Glycine, Proline, Serine, Tyrosine

Peptide bonds

Chemical bonds formed between amino acids and protein. Through peptide bonding of amino acids, cells can synthesize dipeptides (joining of two amino acids), tripeptides (3 aa), oligopeptides (4-9aa), and polypeptides (10+)

Complete Proteins

Adequate amounts of all the essential amino acids. Animal proteins, except gelatin.

Incomplete Proteins

Inadequate amounts of 1 or more of the essential amino acids. May be present but in very low amounts. Plant proteins, except soy.

Complementary Proteins

Combining plant proteins to compensate for limiting amino acids. Different types of plants, grains, nuts, seeds, legumes and vegies.

Limiting Amino Acids

Grains: Lysine, Nuts and Seeds: Lysine, Legumes: Methionine and Tryptophan

Synthesis of Protein

Amino Acids are linked by peptide bonds to form protein, Synthesis is determined by gene expression. When you make the bond condensation occurs.

DNA Transcription Phase

DNA Code is transferred from the nucleus to the cystosol via messenger RNA (mRNA). DNA coded instructions determine the shape and function of the proteins

mRNA Translation Phase

tRNA goes and collects the amino acids and brings them to the ribosomes. ATP provides the energy needed to activate the tRNA in order to form each peptide bond. When the final one is connected the protein is released.

Protein Organization

Primary Structure: Cant mess with primary code or shape and ability to function will be wrong. Secondary Structure: Weaker bonds between nearby amino acids form spiral or pleat shape. Tertiary Structure: 3D folding determines shape. Quaternary Structure: multiple polypeptide strands come together.

Protein Chain organization

Order of aa determines shape and function. Shape determines its ability to sit in the receptor site. Cysteine and Methionine contain sulfur atoms that link to form sulfur bridges.

Sources of protein

Diet contains 65-100g. Breaking down and recycling body protein 250-300g. North American diet: 70% from meat, fish, milk, dairy, legumes and nuts. Worldwide: 30% comes from animal.

Sources of plant protein

Soy, edamame, Brown rice, pasta, legumes, cereal

Evaluation of Protein Quality

Amino Acid composition and Digestibility/ absorption. Animal sources more bioavailable. Concept only applies when intake is equal to or less than needed amount.

Excess Protein Intake

With excess intake, efficiency decreases and extra amounts are degraded. Extra nitrogen turns to fat, or becomes toxic and needs to be removed. Kidneys have to work really hard to get rid of excess nitrogen. It is dehydrating and acid pulls the calcium out of bones.

What happens with DNA Code errors

Ribosomes will not read the correct message. The polypeptide chain will be incorrect. Incorrect mRNA will be produced.

Anergy

Immune incompetence. There needs to be enough protein to make white blood cells and to fight bacteria.

Positive Nitrogen Balance

Growth, pregnancy, recovery after illness, athletic training, increased secretion of hormones such as insulin, growth hormone and testosterone. Must stay in positive nitrogen balance while growing.

Nitrogen Equilibrium

Healthy adult meeting protein and energy needs

Negative Nitrogen Balance

Inadequate intake of protein. Inadequate energy intake. fevers, infection, burns, bed rest, deficiency of amino acids, disease, increased secretion of hormones such as thyroid and cortisol.

Protein needs

AMDR: 10-35% of kcal

Adult RDA: 0.8g/kg of healthy body weight

Body in recovery: 0.8-2.0 g/kg body weight

Protein Digestion and Absorption

Cooking denatures protein. Stomach: HCL denatures protein. Pepsin begins enzymatic digestion. Small Intestine: Secretin and CCK released. Simulates release of pancreatic proteases (trypson, chymotrypsin, carboxypeptidases), Amino acids absorbed into the portal vein and sent to the liver.

Functions of Protein

Produce vital body structures. Maintain fluid balance, Contributes to the Acid Base balance. Forms hormones, enzymes and neurotransmitters.

More functions of proteins

Contributes to immune function. Transports nutrients. Forming glucose via glucogenesis. Provides 4kcal/g

Food Protein Allergies

Food proteins cause immune response reaction. IgE most commonly produced. Anaphylaxix- life threatening. 8 foods account for 90% of food allergies.

8 common food allergens

Peanuts, tree nuts, milk, eggs, fish, shellfish, soy, and wheat.

Vegetarian diets

Types: Vegan, lacto-vegetarians, lacto-ovo-vegetarians. Nutrient Concerns: B12, Calcium, iron, zinc, vitamin D, high quality protein, riboflavin.