Protein function
58 flashcards covering Protein function for the MCAT Biology & Biochemistry section.
Proteins are essential molecules in living organisms, made up of chains of amino acids that fold into specific shapes to carry out a wide range of functions. They act as enzymes to speed up chemical reactions, transport substances like oxygen in the blood, provide structural support in cells and tissues, and even serve as signaling molecules for communication between cells. Understanding protein function is key to grasping how biological systems work, from metabolism to immune responses, making it a foundational concept in biochemistry.
On the MCAT, protein function appears in biology and biochemistry questions that test your ability to identify roles, mechanisms, and interactions, often through multiple-choice scenarios involving enzyme activity, denaturation, or protein-ligand binding. Common traps include confusing protein structures with their functions or overlooking environmental factors like pH and temperature. Focus on mastering structure-function relationships, enzyme kinetics, and real-world applications to handle these questions effectively.
A concrete tip: Practice linking protein shapes to their specific jobs, like how hemoglobin's structure enables oxygen transport.
Terms (58)
- 01
Protein
A large biomolecule composed of one or more chains of amino acids linked by peptide bonds, performing a wide variety of functions in living organisms such as catalysis, transport, and structural support.
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Amino acid
The building blocks of proteins, each consisting of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain that determines its properties.
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Peptide bond
A covalent bond formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water and linking amino acids into a chain.
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Primary structure
The linear sequence of amino acids in a protein chain, determined by the gene encoding it and essential for the protein's overall function.
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Secondary structure
The local folding of a protein chain into regular patterns such as alpha helices or beta sheets, stabilized by hydrogen bonds between backbone atoms.
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Alpha helix
A common secondary structure in proteins where the polypeptide chain coils into a right-handed spiral, stabilized by hydrogen bonds parallel to the helix axis.
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Beta sheet
A secondary structure formed by beta strands connected by hydrogen bonds, creating a pleated sheet that can be parallel or antiparallel.
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Tertiary structure
The overall three-dimensional shape of a single protein chain, resulting from interactions between side chains such as hydrophobic effects and disulfide bonds.
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Quaternary structure
The arrangement of multiple protein subunits into a functional complex, as seen in hemoglobin, which consists of four globin chains.
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Denaturation
The process by which a protein loses its native three-dimensional structure due to factors like heat or pH changes, often leading to loss of function.
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Enzyme
A protein that acts as a biological catalyst, speeding up chemical reactions by lowering the activation energy without being consumed in the process.
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Substrate
The specific molecule upon which an enzyme acts, binding to the enzyme's active site to form an enzyme-substrate complex that facilitates the reaction.
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Active site
The specific region on an enzyme where the substrate binds and the catalytic reaction occurs, shaped to fit the substrate precisely.
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Lock and key model
A model of enzyme action where the enzyme's active site is a rigid structure that exactly matches the substrate, like a key fitting into a lock.
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Induced fit model
A model of enzyme-substrate interaction where the enzyme's active site changes shape slightly upon substrate binding, enhancing the fit and facilitating catalysis.
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Enzyme inhibition
The process by which a molecule reduces or stops an enzyme's activity, which can be competitive, noncompetitive, or uncompetitive, regulating metabolic pathways.
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Competitive inhibition
A type of enzyme inhibition where an inhibitor molecule competes with the substrate for binding to the active site, reducing the enzyme's effectiveness.
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Noncompetitive inhibition
Inhibition where the inhibitor binds to an enzyme at a site other than the active site, altering the enzyme's shape and reducing its activity regardless of substrate presence.
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Uncompetitive inhibition
Inhibition that occurs when an inhibitor binds only to the enzyme-substrate complex, decreasing both the apparent Km and Vmax of the enzyme.
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Allosteric site
A specific location on an enzyme or protein, distinct from the active site, where a molecule can bind and cause a conformational change that affects function.
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Michaelis-Menten equation
The mathematical equation V = Vmax [S] / (Km + [S]) that describes the rate of enzymatic reactions, where V is velocity, [S] is substrate concentration, Vmax is maximum velocity, and Km is the Michaelis constant.
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Km (Michaelis constant)
A measure of the substrate concentration at which an enzyme achieves half of its maximum velocity, indicating the enzyme's affinity for its substrate.
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Vmax
The maximum rate of an enzymatic reaction when the enzyme is fully saturated with substrate, reflecting the enzyme's turnover capacity.
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Lineweaver-Burk plot
A graphical representation of the Michaelis-Menten equation in double-reciprocal form, used to determine Km and Vmax by plotting 1/V against 1/[S].
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Transport proteins
Proteins that facilitate the movement of molecules across cell membranes, such as channel proteins or carriers, essential for nutrient uptake and waste removal.
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Channel proteins
Proteins that form pores in cell membranes, allowing specific ions or molecules to pass through via passive diffusion based on concentration gradients.
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Carrier proteins
Membrane proteins that bind to specific molecules and undergo conformational changes to transport them across the membrane, often against gradients using energy.
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Hemoglobin
A globular protein in red blood cells that binds and transports oxygen from the lungs to tissues, also carrying carbon dioxide back to the lungs.
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Cooperative binding
A phenomenon in multi-subunit proteins like hemoglobin where the binding of one ligand molecule increases the affinity for subsequent ligands on other subunits.
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Bohr effect
The influence of pH and carbon dioxide on hemoglobin's oxygen affinity, where lower pH decreases affinity, facilitating oxygen release in active tissues.
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Structural proteins
Proteins that provide support and shape to cells and tissues, such as collagen in connective tissue or keratin in hair and nails.
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Collagen
A fibrous structural protein that forms the main component of connective tissues, providing strength and flexibility due to its triple-helix structure.
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Actin and myosin
Proteins involved in muscle contraction, where actin forms thin filaments and myosin forms thick filaments that slide past each other using ATP energy.
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Antibodies
Proteins produced by the immune system that bind specifically to antigens, marking them for destruction and helping neutralize pathogens.
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Immunoglobulins
A class of antibodies with a Y-shaped structure, consisting of two heavy and two light chains, that recognize and bind to specific foreign substances.
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Hormone receptors
Proteins on cell surfaces or inside cells that bind to specific hormones, triggering signal transduction pathways that regulate cellular activities.
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Signal transduction
The process by which a cell converts an extracellular signal into an intracellular response, often involving a cascade of protein interactions.
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G-protein coupled receptors
A large family of cell surface receptors that, upon ligand binding, activate G-proteins to initiate signaling pathways, regulating processes like vision and neurotransmission.
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Post-translational modification
Chemical changes to a protein after its synthesis, such as phosphorylation or glycosylation, that alter its function, stability, or localization.
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Phosphorylation
The addition of a phosphate group to a protein, often by kinases, which can activate or deactivate the protein's function in signaling pathways.
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Glycosylation
The attachment of carbohydrate groups to a protein, occurring in the endoplasmic reticulum and Golgi, which affects protein folding, stability, and cell recognition.
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Ubiquitination
The process of tagging a protein with ubiquitin molecules, marking it for degradation by the proteasome, thus regulating protein levels in the cell.
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Chaperone proteins
Proteins that assist in the proper folding of other proteins, preventing misfolding and aggregation, especially under stress conditions.
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Prion diseases
Disorders caused by misfolded prion proteins that induce normal proteins to misfold, leading to neurodegeneration as seen in mad cow disease.
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Protein folding
The process by which a polypeptide chain assumes its functional three-dimensional shape, guided by interactions and sometimes chaperones.
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Hydrophobic effect
The tendency of nonpolar amino acid side chains to cluster in the protein's interior, away from water, driving the formation of tertiary structure.
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Isoelectric point
The pH at which a protein has no net electrical charge, causing it to be least soluble and often used in protein purification techniques.
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Electrophoresis
A technique that separates proteins based on their size and charge by applying an electric field, commonly used in gels to analyze protein mixtures.
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SDS-PAGE
A type of electrophoresis that denatures proteins with SDS and separates them by size, allowing determination of molecular weight.
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Western blotting
A method to detect specific proteins in a sample by separating them via electrophoresis, transferring to a membrane, and using antibodies for identification.
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Protein purification
The process of isolating a specific protein from a complex mixture using techniques like chromatography to study its function.
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Affinity chromatography
A purification technique that uses a ligand specific to the target protein, binding it to a column and allowing separation from other molecules.
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Zymogen
An inactive precursor of an enzyme, such as pepsinogen, that is activated by cleavage, preventing unwanted activity until needed.
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Proteases
Enzymes that break down proteins by hydrolyzing peptide bonds, playing roles in digestion, protein turnover, and apoptosis.
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Apoptosis
Programmed cell death involving proteases like caspases that dismantle the cell in a controlled manner, essential for development and homeostasis.
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Motor proteins
Proteins that convert chemical energy into mechanical work, such as kinesin moving along microtubules to transport cargo in cells.
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Kinesin
A motor protein that walks along microtubules toward the plus end, using ATP to transport vesicles and organelles within the cell.
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Cytoskeletal proteins
Proteins like actin, tubulin, and intermediate filaments that form the cell's internal framework, providing structure and enabling movement.