KIN 280 A - Chapter 5: Protein Study Guide

Vocabulary flashcards covering the structural characteristics, synthesis, digestion, metabolic balance, dietary requirements, vegetarian classifications, and clinical implications of proteins from KIN 280 A Chapter 5.

Amino acids

The building blocks of proteins that contain carbon, hydrogen, oxygen, and nitrogen, each structured with a central carbon atom, an amine group, an acid group, a hydrogen atom, and a side chain ($20$ distinct amino acids are used to make proteins).

Side chain

The distinct chemical group attached to the central carbon of an amino acid that imparts unique properties to each of the $20$ different amino acids.

Essential amino acids

The $9$ amino acids that cannot be produced in sufficient quantities by the body and must be obtained from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Nonessential amino acids

The $11$ amino acids classified as synthesizable by the human body in sufficient quantities.

Transamination

The metabolic process of transferring an amino group from one amino acid to another compound, which the body uses to synthesize nonessential amino acids.

Peptide bond

The chemical bond that links amino acids together to assemble protein chains.

Transcription

The process by which DNA's genetic information is copied into messenger RNA (mRNA), which then carries the instructions from DNA to the ribosome.

Translation

The process occurring at the ribosome where mRNA instructions are read and transfer RNA (tRNA) delivers the corresponding amino acids to assemble them in the proper sequence.

Protein synthesis

The physiological process in which the body builds new proteins by joining amino acids into chains that fold into specific shapes determining their functions.

Protein degradation

The breakdown of existing bodily proteins into amino acids that can be recycled to manufacture new proteins.

Dipeptide

A peptide chain composed of exactly $2$ amino acids joined together.

Tripeptide

A peptide chain composed of exactly $3$ amino acids joined together.

Oligopeptide

A peptide chain consisting of $4\text{--}9$ amino acids joined together.

Polypeptide

A protein chain consisting of $10$ or more amino acids, according to the lecture slides.

Protein turnover

The continuous biological process of synthesizing new proteins while simultaneously breaking down existing proteins.

Amino acid pool

The supply of amino acids available in the body derived collectively from dietary food intake and the breakdown of existing body proteins.

Limiting amino acid

The essential amino acid that is missing or present in the smallest supply relative to the body's needs, thereby restricting or halting protein synthesis.

Hydrochloric acid ($\text{HCl}$)

A component of gastric juice that initiates protein digestion in the stomach by unfolding and denaturing protein structures.

Pepsinogen

The inactive gastric enzyme precursor secreted in the stomach that is activated into the protease pepsin.

Pepsin

An active gastric enzyme that breaks proteins down into shorter polypeptides and smaller pieces.

Gastrin

A hormone that regulates hydrochloric acid production and pepsin release in the stomach.

Trypsin

A pancreatic protease released into the small intestine that digests proteins and polypeptides into smaller peptides.

Chymotrypsin

A pancreatic digestive enzyme acting in the small intestine that breaks proteins into smaller peptides.

Carboxypeptidase

A pancreatic protease in the small intestine that cleaves individual amino acids from the ends of peptide chains.

Enterocytes

The absorptive epithelial cells lining the small intestine that absorb nutrients and contain intracellular digestive enzymes.

Enterocyte peptidases

Enzymes located within enterocytes that break dipeptides and tripeptides into individual, absorbable amino acids.

Hepatic portal vein

The major blood vessel that transports absorbed amino acids from the intestinal wall directly to the liver.

Antibodies

Immune system proteins that help defend the body against foreign pathogens, exemplifying the immune function of proteins.

Nitrogen balance

The clinical comparison between nitrogen consumed through dietary protein intake and nitrogen excreted from the body.

Positive nitrogen balance

A physiological state where nitrogen intake exceeds nitrogen excretion, occurring during growth, pregnancy, and recovery from illness or protein deficiency.

Negative nitrogen balance

A physiological state where nitrogen excretion exceeds nitrogen intake, occurring during starvation and low-energy-intake diets.

Nitrogen equilibrium

A state where dietary nitrogen intake equals nitrogen excretion, typically associated with maintaining body protein in a healthy adult.

Acceptable Macronutrient Distribution Range (AMDR) for protein

The recommended dietary intake range of $10\text{--}35\%$ of total daily calories allocated to protein ($4\,\text{calories per gram}$).

Recommended protein intake by body weight

The standard dietary guideline recommending $1.2\text{--}1.6\,\text{g}$ of protein per kilogram of body weight per day ($\text{g/kg/day}$) for adults, and approximately $1.2\text{--}2.0\,\text{g/kg/day}$ for active individuals.

Complete protein

A dietary protein source that contains adequate amounts of all $9$ essential amino acids.

Incomplete protein

A dietary protein source that is deficient or low in one or more of the $9$ essential amino acids.

Complementary proteins

Two or more incomplete protein sources that supply all $9$ essential amino acids when combined in the diet across the same day (e.g., beans with rice, peanut butter with whole-grain bread).

Plant-based complete proteins

Specific plant foods, namely soybeans and quinoa, that provide all $9$ essential amino acids in sufficient quantities.

Semi-vegetarian (flexitarian)

A dietary pattern based primarily on plant foods that occasionally incorporates meat or seafood.

Pescovegetarian

A vegetarian diet that includes plant foods and fish while excluding poultry and other meats.

Lacto-ovo vegetarian

A vegetarian diet that includes plant foods, dairy products, and eggs, but excludes meat, poultry, and fish.

Lacto-vegetarian

A vegetarian diet that includes plant foods and dairy products, but excludes eggs and all meats.

Ovo-vegetarian

A vegetarian diet that includes plant foods and eggs, but excludes dairy products and all meats.

Vegan

A strict vegetarian dietary pattern that exclusively includes plant foods and omits all animal products.

Cystic fibrosis (CF)

An inherited, single-gene disorder caused by a gene mutation resulting in a defective chloride transport protein, causing thick mucus that obstructs pancreatic enzymes and impairs respiratory and digestive function.