B1.2 Proteins Flashcards
B1.2.1 Generalized structure of an amino acid
Central carbon atom = alpha carbon
Amine group (-NH2)
Carboxyl group (–COOH)
Hydrogen atom
R-group, range of possibilities
AA are amphiprotic bc is COOH acidic and NH2 basic.
B1.2.2 Condensation reactions forming dipeptides and longer chains of AA
AA are linked in a condensation reaction with C-N peptide bonds. These are formed between the amine group of one AA and the carboxyl group of another. It is catalysed in cells by ribosomes.
B1.2.5 Effect of pH and temperature on protein structure - Denaturation
Tertiary structure is stabilized by R-group interactions, and disruption causes a conformational change.
Soluble proteins often become insoluble, forming a precipitate, as h-phobic R-groups are exposed to water.
B1.2.5 Effect of pH and temperature on protein structure - Heat
Heat causes vibrations within the molecule that can break intermolecular bonds or interactions.
Proteins vary in their heat tolerance.
B1.2.5 Effect of pH and temperature on protein structure - pH
Positive and negative charges on R-groups are changed, breaking ionic bonds within the protein or causing new ionic bonds to form.
B1.2.6 Chemical diversity in the R-groups
as a basis for diversity in protein form and function - POLAR
Electrons are unequally shared (δ+,δ−), = polar. Presence of electroneg. atoms means h-bonding or dipole-dipole interactions occur.
Are hydrophilic. Partial charges allow them to interact w/ water molecules in h-bonding.
B1.2.6 Chemical diversity in the R-groups
as a basis for diversity in protein form and function - NON-POLAR
Made mostly of hydrocarbon/non-polar structures. Lack of electroneg. atoms means electrons are evenly distributed = no dipoles. Interacts through London forces. Hydrophobic, side chains can’t h-bond.
B1.2.6 Chemical diversity in the R-groups
as a basis for diversity in protein form and function - CHARGED
Ionizable side chains can donate or accept protons. Electrons are redistributed in response to gain (pos. charge) or loss (neg. charge), creating a net charge.
Charges allow interactions w/ water in ion-dipole and h-bonding interactions, making them hydrophilic.
B.1.2.7 Impact of primary structure on the conformation of proteins
The linear sequence of AA which form a PP chain. Bonds around the alpha carbon can rotate, allowing PP to fold into various three-dimensional shapes.
B1.2.8 Pleating and coiling of secondary structure of proteins
The shape of a folding protein due to h-bonding between its amine and carboxylic acid groups.
B1.2.8 Pleating and coiling of secondary structure of proteins: α-helix
The polypeptide is wound into a helical shape, with hydrogen bonds between adjacent turns of the helix.
B1.2.8 Pleating and coiling of secondary structure of proteins: β-pleated sheet
Two or more polypeptide sections run oppositely in parallel, forming a pleated sheet with hydrogen bonds between them due to tetrahedral bond angles.
B1.2.9 T tertiary structure dependance on bonds/interactions: ionic bonds
Between charged R-groups.
Amine groups turn positive (NH2 + H+ -> NH3) by accepting proton.
Carboxyl groups turn positive (COOH -> COO- + H+) by donating proton.
B1.2.9 T tertiary structure dependance on bonds/interactions: h-bonds
Between polar R-groups. H atom links two electroneg. atoms.
B1.2.9 T tertiary structure dependance on bonds/interactions: disulfide bonds
Covalent bonds between two sulphurs in a pair of cysteines.
B1.2.9 T tertiary structure dependance on bonds/interactions: London forces
A temporary attractive force which arises when electrons in adjacent atoms create temporary dipoles. Mostly occurs in non-polar groups.
B1.2.10 Effect of polar and non-polar AA on tertiary structure of proteins
Globular proteins must be water-soluble to function in cytoplasm/extracellular fluid. Hydrophilic AA are on the surface and hydrophobic AA are in the centre, maximizing h-bonding with water.
B1.2.11 Quaternary structure of non-conjugated and conjugated proteins
The three-dimensional arrangement of multiple polypeptides, linked by interactions similar to those in tertiary structure.
Non-conjugated proteins = only PP subunits. Conjugated proteins = include non-PP subunits, enhancing chemical and functional diversity.
B1.2.11 Conjugated proteins examples
Haemoglobin’s polypeptide chains each have a haem group that binds oxygen, enabling oxygen transport.
Enzymes can also have non-PP components to enhance catalytic activity.
B1.2.12 Relationship of form and function in globular proteins
Rounded shape, formed by the folding up of polypeptides, stabilized by R-group bonds. The conformation of a globular protein is critical to its function. E.g. deciding active site of enzymes.
B1.2.12 Relationship of form and function in fibrous proteins
Elongated and don’t contain the typical folding of the tertiary structure. Don’t form secondary s., quaternary s. is pp chains linked into fibres/filaments by H-bonds.
