Protein structure
53 flashcards covering Protein structure for the MCAT Biology & Biochemistry section.
Protein structure refers to the intricate ways amino acids, the building blocks of proteins, arrange themselves to form functional molecules. At the most basic level, the primary structure is the linear sequence of amino acids linked by peptide bonds. This sequence then folds into secondary structures like alpha helices and beta sheets, driven by hydrogen bonding. Further, tertiary and quaternary structures create the overall three-dimensional shape through interactions such as hydrophobic effects and disulfide bridges, which are crucial for a protein's specific function in the body, such as enzyme activity or immune response.
On the MCAT, protein structure appears in biology and biochemistry questions that test your ability to identify levels of organization, explain how environmental factors like pH or temperature cause denaturation, and predict functional changes from structural alterations. Common traps include confusing secondary with tertiary structures or overlooking the role of cofactors; focus on mastering key interactions and real-world applications, like in diseases such as sickle cell anemia. Remember to practice sketching structures to solidify your understanding.
Terms (53)
- 01
Primary structure
The sequence of amino acids in a polypeptide chain, determined by the order of nucleotides in the gene, and held together by peptide bonds.
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Secondary structure
The local folding of a polypeptide chain into regular patterns such as alpha helices or beta sheets, stabilized primarily by hydrogen bonds between backbone atoms.
- 03
Alpha helix
A common secondary structure where the polypeptide chain coils into a right-handed spiral, with hydrogen bonds forming between every fourth amino acid.
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Beta sheet
A secondary structure consisting of beta strands connected by hydrogen bonds, forming a pleated sheet that can be parallel or antiparallel.
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Beta turn
A type of secondary structure that reverses the direction of the polypeptide chain, often stabilized by hydrogen bonds and proline residues.
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Tertiary structure
The overall three-dimensional shape of a single polypeptide chain, resulting from interactions between side chains, including hydrophobic effects and disulfide bonds.
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Quaternary structure
The arrangement of multiple polypeptide chains, or subunits, into a functional protein complex, stabilized by interactions between the chains.
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Amino acid
The building blocks of proteins, each consisting of a central alpha carbon attached to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain.
- 09
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 in a chain.
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Disulfide bond
A covalent bond between the sulfur atoms of two cysteine residues, which helps stabilize the tertiary and quaternary structures of proteins.
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Hydrophobic interactions
The tendency of nonpolar side chains to cluster together away from water, driving the folding of proteins into their functional shapes.
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Hydrogen bonding in proteins
Weak attractions between a hydrogen atom and an electronegative atom like oxygen or nitrogen, crucial for stabilizing secondary and tertiary structures.
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Van der Waals forces
Weak attractions between atoms or molecules due to temporary dipoles, contributing to the stability of protein tertiary structures.
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Ionic bonds in proteins
Electrostatic attractions between oppositely charged side chains, such as between acidic and basic amino acids, that help maintain tertiary structure.
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Hydrophilic side chains
Side chains of amino acids that are polar or charged, allowing them to interact with water and often located on the surface of proteins.
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Hydrophobic side chains
Nonpolar side chains of amino acids that avoid water and are typically buried in the interior of folded proteins.
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Denaturation
The process by which a protein loses its native structure due to disruption of stabilizing bonds, often caused by heat, pH changes, or chemicals, leading to loss of function.
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Renaturation
The refolding of a denatured protein into its original functional structure under appropriate conditions, demonstrating that primary structure determines the final shape.
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Chaperone proteins
Proteins that assist in the proper folding of other proteins, preventing misfolding and aggregation in the cell.
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Protein folding
The process by which a polypeptide chain achieves its functional three-dimensional structure, guided by thermodynamic stability and cellular factors.
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Protein motifs
Common patterns of secondary structures, such as the zinc finger, that recur in different proteins and often relate to specific functions.
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Protein domains
Distinct functional and structural units within a protein, often consisting of multiple motifs, that can evolve independently.
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Prosthetic groups
Non-peptide molecules tightly bound to proteins, such as heme in hemoglobin, that are essential for the protein's function.
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Heme group
An iron-containing prosthetic group in proteins like hemoglobin and myoglobin, which binds oxygen and gives these proteins their red color.
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Collagen
A fibrous protein with a triple helix structure, rich in glycine and proline, that provides strength and support in connective tissues.
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Hemoglobin
A globular protein with quaternary structure, consisting of four subunits, that transports oxygen in the blood by binding it to heme groups.
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Myoglobin
A monomeric globular protein that stores oxygen in muscle tissues, with a tertiary structure stabilized by a heme group.
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Allosteric regulation
The modulation of a protein's activity by the binding of a molecule at a site other than the active site, often causing a conformational change.
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Cooperative binding
A phenomenon in multi-subunit proteins like hemoglobin, where the binding of one ligand affects the affinity for subsequent ligands.
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Post-translational modification
Chemical changes to a protein after synthesis, such as phosphorylation, that alter its function, stability, or localization.
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Phosphorylation
The addition of a phosphate group to a protein, often on serine, threonine, or tyrosine residues, which can activate or deactivate the protein.
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Glycosylation
The attachment of carbohydrate groups to a protein, typically on asparagine, serine, or threonine, influencing protein folding and cell recognition.
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N-terminal
The end of a polypeptide chain with a free amino group, which is usually the starting point of protein synthesis.
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C-terminal
The end of a polypeptide chain with a free carboxyl group, marking the conclusion of the amino acid sequence.
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Zwitterion
The form of an amino acid with both a positive and negative charge, occurring at neutral pH, which affects its solubility and behavior.
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Isoelectric point
The pH at which an amino acid or protein has no net charge, causing it to be least soluble and influencing its electrophoretic mobility.
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pKa of amino acids
The pH at which the side chain of an amino acid is half protonated, determining its charge state and role in protein structure.
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Fibrous proteins
Proteins with elongated structures, like collagen, that provide mechanical support and are often insoluble in water.
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Globular proteins
Proteins with a compact, spherical shape, such as enzymes, that are typically soluble and perform dynamic functions.
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Conjugated proteins
Proteins that include non-amino acid components, like glycoproteins or lipoproteins, essential for their biological roles.
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Denaturing agents
Substances like heat, acids, or urea that disrupt protein structure by breaking hydrogen bonds and other interactions.
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Ramachandran plot
A graph that shows the possible phi and psi angles of amino acids in a protein, helping to visualize allowed conformations in secondary structure.
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X-ray crystallography
A technique used to determine the three-dimensional structure of proteins by analyzing the diffraction patterns of X-rays passed through crystals.
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NMR spectroscopy
A method that uses nuclear magnetic resonance to elucidate the structure and dynamics of proteins in solution.
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Acidic amino acids
Amino acids like aspartic acid and glutamic acid that have negatively charged side chains at physiological pH, influencing protein interactions.
- 46
Basic amino acids
Amino acids such as lysine, arginine, and histidine that have positively charged side chains, playing roles in enzyme active sites.
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Polar amino acids
Amino acids with side chains that can form hydrogen bonds, like serine and threonine, often found on protein surfaces.
- 48
Nonpolar amino acids
Amino acids with hydrophobic side chains, such as alanine and valine, that contribute to the protein's core stability.
- 49
Protein electrophoresis
A technique that separates proteins based on their charge and size in an electric field, used to analyze protein mixtures.
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SDS-PAGE
Sodium dodecyl sulfate polyacrylamide gel electrophoresis, a method that denatures proteins and separates them by molecular weight.
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Isoelectric focusing
An electrophoresis technique that separates proteins based on their isoelectric points in a pH gradient.
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Prion diseases
Disorders caused by misfolded proteins that induce normal proteins to adopt the same abnormal shape, leading to neurodegeneration.
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Ubiquitination
The attachment of ubiquitin molecules to a protein, marking it for degradation by the proteasome and regulating protein levels.