Course review
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Learning objective
• Amino acids have an alpha carbon bonded to an amine, carboxyl, hydrogen, and R-group • The R-group varies between amino acids and determines chemical properties • Proteins contain C, H, O, N, and usually S
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Learning objective
• Condensation joins the carboxyl group of one amino acid to the amine group of another • A peptide bond forms and water is released • Chains have an N-terminus and C-terminus and are assembled at ribosomes
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Learning objective
• Essential amino acids cannot be synthesized and must be obtained from dietary protein • Non-essential amino acids can be made by transamination, mainly in the liver • Deficiency of essential amino acids limits protein synthesis and can cause malnutrition
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Learning objective
• Twenty coded amino acids can form vast numbers of sequences • Protein diversity depends on amino acid type, number, and order • Genes encode polypeptide sequences; the proteome is the full protein set expressed
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Learning objective
• Protein shape determines function, especially enzyme active sites • High temperature or unsuitable pH disrupts weak bonds and denatures proteins • Denaturation may be reversible in small proteins but often becomes irreversible
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Learning objective
• R-groups may be acidic, basic, polar hydrophilic, or non-polar hydrophobic • R-group chemistry determines solubility, interactions, folding, and function • Hydrophobic R-groups are often buried away from water in soluble proteins
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Learning objective
• Primary structure is the ordered amino acid sequence joined by peptide bonds • The sequence is controlled by DNA via mRNA • A single amino acid change can alter conformation and protein properties
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Learning objective
• Secondary structure forms when local regions coil or pleat • Alpha helices and beta-sheets are stabilized by regular hydrogen bonding • These structures can combine into domains such as coiled coils or beta sandwiches
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Learning objective
• Tertiary structure is the unique 3D folding of one polypeptide • R-group interactions stabilize the shape • Hydrogen bonds, ionic bonds, disulfide covalent bonds, and hydrophobic interactions are key
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Learning objective
• Soluble globular proteins often fold with hydrophobic residues in the core • Polar and charged residues are commonly exposed to water • Integral membrane proteins have hydrophobic regions facing lipid tails and hydrophilic exposed regions
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Learning objective
• Quaternary structure joins two or more polypeptide chains into one functional protein • Haemoglobin is conjugated: four globin chains plus haem groups with iron • Insulin and collagen are non-conjugated examples stabilized by disulfide bonds or triple helices
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Learning objective
• Globular proteins are compact, often soluble, and suited to transport, signalling, or catalysis • Insulin is a small globular hormone stabilized by disulfide bridges • Fibrous proteins such as collagen are long, insoluble, and provide tensile strength
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