Protein (Pt1)
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51 terms
Terms | Definitions |
|---|---|
 What are the 3 basic structural components of amino acids? | -An amino group (-NH2) -A carboxyl group (-COOH) -A side chain (R) |
| Primary structure of amino acids: | sequence of amino acids in a polypeptide chain; linked with strong covalent peptide bonds |
| The specific sequence of amino acids... | -differentiates proteins -dictates secondary & tertiary structures -determines ultimate function |
| Secondary structure of proteins: | weak repeating linkages between nearby amino acids (ie H-bonds); promotes strength and rigidity, necessary in structural proteins |
| Types of secondary structure: | - alpha-helix: coiling of polypeptide chain forming a cylindrical shape - beta-pleated sheet: accordion-like - random coil: less stable due to amino acid side chain interference |
| Tertiary structure: | results from folding of a protein back upon itself, allowing interactions/bonds between R-groups on amino acids that are distant in the primary chain |
| Types of interactions in tertiary structure: | -hydrogen bonds -hydrophobic amino acids cluster in center -electrostatic attraction of oppositely charged aas -disulfide bridges (strong covalent bonds) between cysteine residues |
| Disulfide bond | (aka disulfide bridge) is a covalent bond formed thru oxidation of 2 thiol or sulfhydryl groups (R-SH); is one of the mechanisms by which tertiary structure is maintained (ex. cystine-cystine) |
| Protein classifications based on tertiary structure: | -Globular proteins -Fibrous proteins -membrane proteins |
| Globular proteins | generally soluble; includes most enzymes |
| Fibrous proteins | generally structural (ex collagen, keratin, elastin |
| Membrane proteins | generally receptors or channels that facilitate or control transport of molecules through membranes |
| Quarternary structure | results from association of several "subunit" polypeptide chains, linked by hydrogen or electrostatic bonding to form an oligomer |
| Conformational change in quarternary structure | conformational change in one subunit may affect structure and function of other subunits (ex hemoglobin) |
| Native conformation | is the conformation in which a molecule is biologically active |
| Chaperones | proteins that assist the non-covalent folding or unfolding and the assembly or disassembly of other macromeloecular structures, but do not occur in these structures when the structures are performing their normal biological functions |
| Folding of proteins | occurs during synthesis, aided by chaperones |
| Can denatured proteins regain native conformation? | No. Denatured proteins do not spontaneously regain native conformation. |
| Amino Acid Polarity: | tendency to interact with water; non-polar amino acids are hydrophobic |
| AA Electrical charge: | based on ionization at physiological pH |
| Zwitterions: | have no charge in R group, so amino (+) and carboxy (-) group charges cancel each other and result in no net charge. |
| AA classification by | -polarity -electric charge -structure (of side chain) |
| Side chains that are electrically charged or contain hydroxyl groups are __________ and interact with water, so tend to orient ____________ part of the protein. | polar tend to project on the surface of proteins |
| Side chains with phenyl rings are _________, hydrophobic, and often orient ___________ of protein structures. | nonpolar orient toward the inside of protein structures |
| Acidic side chains ___________ hydrogens. | release hydrogens |
| Basic side chains __________ hydrogens. | accept hydrogens |
| AA can act as a buffering system in blood by | AA in proteins accept hydrogens when pH is too low, and donate hydrogens when the pH is too high. |
| Aliphatic AA side chains | contain hydrogen or hydrogen and carbon in straight chain or branched configuration (non-cyclic/non-aromatic) |
| Sulfur containing AA are polar or nonpolar; hydro- phobic or philic? | non-polar hydrophobic |
| Post-translationally & biosynthetically formed sulfur containing aa | slide 28 |
| Essential (indispensable) amino acids: | AA's that cannot by synthesized in the body and must be present in the diet. |
| Totally indispensable amino acids: | cannot be synthesized sufficiently from their alph-keto acids |
| What are the totally indispensable aa's? | Threonine, Histidine, Lysine |
| Conditionally indispensable aa's | physiological circumstances can prevent synthesis of an amino acid from its precursor (ie; compromised liver function, inborn errors of metabolism) |
| Exogenous protein sources: | ingested dietary protein from animal and plant foods |
| Endogenous protein | -desquamated mucosal cells (50g pro/d) -digestive enzymes and glycoproteins (17 g pro/d) |
| Digestion of protein involves denaturation of ______, ______ & _____ by gastric acid, allowing ..... | denaturation of the quanternary, tertiary and secondary structures by gastric acid, allowing enzyme access for hydrolysis of the peptide bonds in the primary structure. |
| Enzymatic "hydrolysis" of peptide bonds begins with _______ in the ______, and involves the addition of ____ molecule of _____. | pepsin in stomach involves the addition of 1 molecule of water |
| Enzymes involved in digestion of protein in the stomach: | -HCl -Pepsin (Pepsinogen) [ Pepsinogen --HCl--> Pepsin ] |
| Enzymes involved in digestion of protein in the sm intestine: | Pancreatic -Trypsin (trypsinogen) -Chymotrypsin (chymotrypsinogen) -Carboxypeptidase A & B (procarboxypeptidase A/B) -Elastase (proelastase) -Collagenase |
| Enzymes involved in digestion of protein in brush border: | amino, di and tri -peptidases |
| Intestinal absorption of amino acids is a ________ mechanism - only ____% of amino acids are absorbed as free amino acids. | secondary mechanism 33% |
| There are specific and overlapping transporters for various AA's; most transporters are ________ dependent. | Na+ dependent |
| Essential and branched chain AA's are absorbed __________ than non-essential and smaller AA's | absorbed faster |
| Supplemental amino acids may _______ for absorption, resulting in ________. | compete imbalance |
| Nitrogen retention is ________ from amino acid supplements than from food sources. | lesser. nitrogen retention is greater for protein from food sources. |
| What is the primary form of amino acid absorption? | Absortion of Peptides is the primary mechanism for aa absorption |
| _____% of amino acids are absorbed as peptides. | 67% |
| Di and tri -peptides are absorbed ________ than amino acids. | absorbed faster |
| Specific transporters for peptides are: | - H+ co-transport - H+/Na+ exchange at brush border - Na+/K+ exchange at basolateral membrane |
| Absorbed amino acids in the enterocyte are retained for synthesis of: | -Apoproteins -Digestive enzymes (brush border) -Hormones -Nitrogen-containing compounds -Other amino acids |
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