proteins Flashcards
what are amino acids and what is their general structure
basic monomer units that combine to form di/polypeptides polymers
central carbon atom with amino group (-NH2) hydrogen (-H) carboxyl group (-COOH) R (side) group, each amino acid has a different R group
how do peptide bonds form
condensation reaction between carboxyl group and H from amino group forming a peptide bond (-CONH-), can be hydrolysed to form amino acids
what is the primary structure of a protein
many acid monomers joining together by condensation polymerisation - resulting chain is called a polypeptide. the sequence of AAs forms primary structure, determined by codon sequence on mRNA/DNA
how does the sequence of amino acids determine a proteins determine its ultimate shape and function
structure is determined by position of AAs. sequence of AAs determines primary structure, H bonds between AAs cause chain to twist into secondary structure, tertiary structure formed by interactions of R groups (disulphide bridges, ionic bonds, H bonds, hydrophobic/hydrophilic interactions), quaternary structure formed by interactions of >1 polypeptide chains, may have prosthetic groups. the shape determines its ultimate function
what is the secondary structure of a protein
the Hδ+ on the -NH has a slightly positive charge and the Oδ- on the -C=O group has a slightly negative charge on the linked amino acids. these two groups readily form weak H bonds. this causes the polypeptide chain to twist into a 3D shape eg a-helix and B-pleated sheet
what is the difference between an a-helix and B-pleated sheet
a-helix is a tightly coiled polypeptide strand. all N-H bonds on the same side of chain. H bonds parallel to helical axis. B-pleated sheet is composed of two or more polypeptide chains in a zig-zag shape which form H bonds between them which hold the shape together. N-H and C=O alternate from one side to the other
how to test for proteins
biuret test confirms presence of peptide bonds add at room temp. swirl to mix
positive - blue to lilac
how many amino acids are there and how do they differ from one another
20, differ by their R group
what is the tertiary structure of a protein
3D structure formed by further folding of the polypeptide. held together by disulphide bridges, ionic bonds and H bonds
describe each type of bond in the tertiary structure
disulphide bridges - strong covalent S-S bonds between molecules of the amino acid ‘cysteine’
ionic bonds - relatively strong bonds forming between charged R groups (pH changes cause these bonds to break)
H bonds - numerous and easily broken
what is the quaternary structure
functional proteins that may consist of more than one polypeptide (eg haemoglobin). precise 3D structure held together by the same bonds as tertiary. may involve addition of prosthetic groups eg metal ions or phosphate groups
define the structure and function of globular proteins
spherical and compact
hydrophilic R groups face outwards, hydrophobic R groups face inwards - usually water soluble
involved in metabolic processes eg enzymes and haemoglobin
describe the structure and function of fibrous proteins
can form long chains or fibres
insoluble in water
useful for structure and support eg collagen in skin
