Proteins
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Draw the general structure of an amino acid, indicating the amino group, carboxyl group, R-group, and central carbon atom.
An amino acid consists of a central carbon atom bonded to an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom (-H), and a variable R-group. The R-group determines the specific properties of each amino acid.
Describe the formation of a peptide bond, including the molecules involved and the type of reaction.
A peptide bond is formed between two amino acids through a condensation reaction (removal of water). The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another, releasing H₂O and forming a C-N bond.
Explain the meaning of 'primary structure' in the context of proteins.
The primary structure of a protein refers to the specific sequence of amino acids in the polypeptide chain. This sequence is determined by the genetic code and dictates the subsequent folding and function of the protein.
Describe the roles of hydrogen bonds and hydrophobic interactions in stabilizing the tertiary structure of a protein.
Hydrogen bonds form between polar R-groups, stabilizing folds. Hydrophobic interactions cause nonpolar R-groups to cluster together in the protein's interior, minimizing contact with water and contributing to folding.
Distinguish between globular and fibrous proteins, with reference to their solubility and physiological roles.
Globular proteins are generally soluble due to hydrophilic amino acids on their exterior and perform metabolic functions (
Describe the quaternary structure of haemoglobin, including its constituent polypeptide chains and haem groups.
Haemoglobin has a quaternary structure consisting of four polypeptide chains: two alpha (α) chains and two beta (β) chains. Each chain is associated with a haem group containing an iron (Fe²⁺) ion.
Explain how the structure of haemoglobin relates to its function in oxygen transport, including the role of iron.
The iron (Fe²⁺) in each haem group reversibly binds to one oxygen molecule, allowing haemoglobin to carry four oxygen molecules. The quaternary structure allows for cooperative binding, where the binding of one O₂ increases the affinity for subsequent O₂ molecules.
Describe the structure of collagen, including the arrangement of collagen molecules to form collagen fibres.
Collagen consists of three polypeptide chains arranged in a triple helix. These triple helices align parallel to each other, forming collagen fibrils, which then assemble into strong collagen fibres, providing tensile strength.
Relate the structure of collagen molecules and collagen fibres to their function in providing tensile strength to tissues.
The triple helix structure of collagen molecules and the cross-linking between collagen fibrils provides high tensile strength, allowing collagen fibres to resist stretching and provide structural support to tissues like tendons and ligaments.
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