Proteins and Enzymes - Flashcards

Flashcards cover amino acids, peptide bonds, protein structure (primary to quaternary), myoglobin and hemoglobin, plasma proteins, immunoglobulins, coagulation, structural proteins, enzymes, kinetics, and clinical relevance.

What defines an amino acid and where is the alpha-carbon located?

An organic molecule with both an amino group (−NH2) and a carboxyl group (−COOH); the alpha-carbon is the central carbon to which all groups attach, including the varying R-group.

How many common amino acids exist and what determines their properties?

20 common amino acids; properties are determined by the R-group (side chain), which affects polarity, charge, hydrophobicity, and folding.

Name the four classifications of amino acids by R-group properties.

Nonpolar (hydrophobic); Polar uncharged (hydrophilic); Charged acidic; Charged basic.

What is a peptide bond and how is it formed?

A covalent bond between the carboxyl group of one amino acid and the amino group of another, formed by a dehydration synthesis (condensation) reaction with release of a water molecule.

What is a dipeptide versus a polypeptide?

Dipeptide = two amino acids linked; polypeptide = long chains of many amino acids.

Why is the peptide bond rigid and planar?

Because of partial double-bond character from resonance, the C-N bond cannot rotate freely, making the peptide bond planar and rigid.

What is the difference between peptides and proteins?

Peptides are short chains of amino acids; proteins are large macromolecules with one or more long polypeptide chains and a unique 3D structure that determines function.

What are the four levels of protein structure?

Primary, Secondary, Tertiary, and Quaternary.

Define primary protein structure and its significance.

The linear sequence of amino acids in a polypeptide; determined by DNA; dictates all higher levels of structure and function.

What stabilizes an alpha-helix and what is a typical example.

Stabilized by hydrogen bonds between backbone atoms; bonds form every 4th amino acid; keratin is a typical example in hair.

What is a beta-pleated sheet and how are its hydrogen bonds formed?

Polypeptide strands lie side-by-side in a pleated arrangement; hydrogen bonds form between adjacent strands, providing strength and flexibility (e.g., silk fibroin).

What stabilizes tertiary protein structure?

Interactions among R-groups: hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bonds; these define the molecule’s 3D shape and active sites.

Define quaternary protein structure and give an example.

Arrangement of multiple polypeptide subunits into a functional protein; example: hemoglobin with two alpha and two beta chains.

Describe myoglobin: structure, location, and function.

Single polypeptide chain with one heme; located mainly in muscle; stores oxygen and has high oxygen affinity, releasing O2 only at very low levels.

Describe hemoglobin: structure, location, and function.

Four polypeptide chains (2 alpha, 2 beta), each with a heme group; located in red blood cells; transports oxygen and exhibits cooperative binding affected by pH, CO2, and temperature.

What mutation causes sickle cell anemia and why is it significant?

A single amino acid substitution in the beta chain (glutamate to valine) alters folding, causes aggregation, and sickling of red blood cells, impairing oxygen delivery.

What are plasma proteins and their general roles?

Proteins dissolved in blood plasma synthesized mainly in the liver; roles include maintaining osmotic pressure, transporting substances, immune defense, and clotting.

What is albumin and its primary functions?

The most abundant plasma protein (~60% of plasma proteins); maintains oncotic (osmotic) pressure, transports fatty acids, bilirubin, steroids, drugs; contributes to buffering.

What are globulins and their classes?

Heterogeneous plasma proteins: alpha and beta globulins (transporters and enzyme inhibitors); gamma globulins (immunoglobulins/antibodies) for immune defense.

What are immunoglobulins and their role in immunity?

Glycoproteins produced by plasma cells; Y-shaped with antigen-binding sites; neutralize pathogens, promote opsonization, and activate the complement system; classes include IgG, IgM, IgA, IgD, IgE.

What are the key proteins involved in blood coagulation and their roles?

Fibrinogen (soluble) is converted to fibrin (insoluble) to form clots; prothrombin is converted to thrombin; a cascade of clotting factors drives hemostasis.

Name two structural proteins and their roles.

Collagen provides tensile strength in connective tissues (triple helix); keratin forms hair, nails, and protective layers (fibrous networks).

What is the definition and role of enzymes?

Biological catalysts that speed up biochemical reactions without being consumed; highly specific and lower activation energy; do not change the reaction equilibrium.

What is the enzyme active site and the ES complex?

Active site is a pocket formed by the enzyme where the substrate binds; the enzyme-substrate (ES) complex facilitates the reaction and is highly specific.

Differentiate the Lock-and-Key and Induced-Fit models of enzyme action.

Lock-and-key: active site is rigid and exactly fits the substrate; Induced-fit: active site is flexible and adjusts upon substrate binding to optimize interaction.

What are the main factors affecting enzyme activity related to temperature and pH?

Temperature: optimal around 37°C; below slows activity, above denatures; pH: each enzyme has an optimal pH, deviations alter charge and can denature it.

How does substrate concentration influence enzyme activity and Vmax?

At low substrate concentrations, activity increases with [S]; at high [S], enzymes become saturated and reach Vmax where adding more substrate has no effect.

What are the types of enzyme inhibitors and how do they act?

Reversible inhibitors (competitive, noncompetitive, uncompetitive) bind non-covalently; irreversible inhibitors bind covalently; competitive inhibitors block the active site, while noncompetitive/uncompetitive alter enzyme function elsewhere or after binding.

Give clinical examples of enzymes in diagnostics and therapy.

Cardiac enzymes (troponin, CK-MB) indicate heart damage; liver enzymes (ALT, AST) indicate liver injury; pancreatic enzymes (amylase, lipase) indicate pancreatitis; enzymes can be drug targets; PKU is a genetic enzyme disorder.

Summarize how protein structure relates to function in one line.

A protein’s 3D structure, from primary to quaternary, determines its specific function, whether catalytic, transport, structural, or defensive.

What key nursing-relevant concepts connect proteins to patient care?

Proteins support immunity, tissue integrity, fluid and electrolyte balance, and drug metabolism, making understanding their structure-function relationships essential for nursing care.