Peptides and Proteins

Peptide

Unbranched chain of amino acids, classified by the number of amino acids present in the chain.

Peptide bond

Covalent bond between the carboxyl group of one amino acid and the amino group of another amino acid.

N-terminal end

The end of a peptide chain with a free amino group (H3N).

C-terminal end

The end of a peptide chain with a free carboxyl group (COO-).

Amino acid residue

Portion of the amino acid structure that remains after the release of H2O during peptide bond formation.

Primary Protein Structure

The order in which amino acids are linked together in proteins, determined by peptide bonds.

Secondary Structure of Proteins

Includes α-helix (coiled spring) and β-pleated sheet (extended protein segments held by H bonds).

Tertiary Structure of Proteins

Involves interactions like disulfide bonds, electrostatic interactions, hydrogen bonds, and hydrophobic interactions.

Quaternary Structure of Proteins

Organization among peptide subunits in multimeric proteins, with non-covalent interactions contributing to the structure.

Protein Denaturation

Partial or complete disorganization of the 3D structure of proteins, affecting secondary, tertiary, and quaternary structural interactions.

Enkephalins

pentapeptide neurotransmitters, bind at receptor sites of brain to reduce pain

Oxytocin

regulates uterine contractions and lactations

Vasopressin (ADH - Antidiuretic Hormone)

function in kidneys, decrease urine output, to decrease H2O eliminated during dehydration

Glutathione

tripeptide, regulator of redox reaction, protect cells from

peroxides and superoxides

Protein

peptide with at least 40 amino acid residues; protein and polypeptide used interchangeably.

Simple Protein -

only Amino Acid is present, may have sub unit as long as amino acid is present

Conjugated Protein

more than one peptide chain and contain non amino acid entities

The α-helix - protein chain

coiled spring; maintained by H bonds (intramolecular), Hydrogen bonds between every fourth amino acid

(β-pleated sheet)

two extended protein segments in same or different

molecules held together by H bonds

Disulfide Bonds

strongest bond for tertiary structure,-SH of two cysteine to form covalent bond ; intramolecular or intermolecular disulfide bond

Electrostatic Interaction (Salt Bridges)

acidic R group and basic R group: at different pH carry charges -COO- and NH3+, cation and anion

Hydrogen Bonds

occur in amino acids with polar R groups; weak, disrupted

by pH changes

Hydrophobic interactions

two nonpolar side chains, polar group outward

(toward solvent), nonpolar side chains inward and interact;

Protein Hydrolysis

When protein in solution of strong base and strong acid is heated, peptide bonds are hydrolyzed and free amino acids are produced

Complete protein hydrolysis

all peptide bonds are broken, Amino acids are the only products

Partial protein hydrolysis

some peptide bonds are broken , Amino acids and small peptides are produced

Fibrous protein

molecules w/ elongated shape & one dimension much longer -Linear and form aggregate to form macromolecular structure

α-Keratin

Fibrous protein, major constituent of hair, feathers, wool, fingernails and toenails, claws, scales, horns, turtle shells, quills, and hooves Coiling @ higher levels produce strength, intercoil disulfide bridge

Collagen

most abundant of all proteins in humans (30% of total body protein), is a major structural material in tendons, ligaments, blood vessels, and skin Rich proline content = triple helix conformation; form fibrils with cross linking on helices; stiffening of skin associated with aging

Globular protein

peptide chains folded into spherical or globule shapes Hydrophilic side chains on outside; hydrophobic in interior

plasma lipoprotein

involved in the transport system for lipids in the bloodstream

Chylomicrons

transport dietary triacylglycerols from the intestine to the liver and to adipose tissue.

Very-low-density lipoproteins (VLDL)

Transport triacylglycerols synthesized in the liver to adipose tissue

Low-density lipoproteins (LDL

transport cholesterol synthesized in the liver to cells throughout the body.

High-density lipoproteins (HDL)

collect excess cholesterol from body tissues and transport it back to the liver for degradation to bile acids.

Catalytic proteins

Role of biochemical catalysts = enzymes

Defense proteins

immunoglobulins or antibodies fxn in immune system

Transport proteins

Bind to small biomolecules and transport e.g. hemoglobin

Messenger proteins

transmit signals to coordinate biochemical processes between different cells, tissues, and organ ex. Hormones

Contractile proteins

Necessary for movement. Filament like proteins in muscles, flagella of sperm

Structural proteins

Stiffness and rigidity ex. Collagen & keratin

Transmembrane proteins

cell membrane and control movement

Storage proteins

Bind & store molecules for future use ex ferritin

Nutrient proteins

Important in early stages of life e.g. Casein in milk

Regulatory proteins

Site of binding for messenger proteins & enact function

Fluid-balance proteins

Maintain fluid balance between blood & tissue; e.g. albumin and globulin in capillary beds