Protein Structure Flashcards
How many dif amino acids
20
What are essential amino acids
Ones that animals have to obtain through their diet
General structure of amino acid
Central C atom bonded to an amine group(-NH2), carboxylic acid group (-COOH), a hydrogen and a side chain (-R)
Primary structure of a protein
Two AAs join in condensation reaction to form a dipeptide with a peptide bond(C double bonded to O and single bonded to N with single bond to H) formed between the two subunits, repeated to form polypeptide chain.
What determines the specific order of AAs in polypeptide
DNA sequence in genes
Secondary structure
Specific 3D shape protein takes due to hydrogen bonding between AAs. Alpha helices form due to coiling forming a spiral shape. Beta pleated sheets form due to folding, forming almost flat but kinked sheet of AAs. Many proteins have a mix.
How do hydrogen bonds form
Between oxygen atom in C=O group which has negative charge and hydrogen atom in N-H group which has positive charge. These attract to form H bond-causes polypeptide chain to twist and fold into shapes.
Tertiary structure
Bonds form between atoms on side chains forming specific 3D shape of protein which is essential for its function. Forms ionic, disulfide(two cysteine) bridges, hydrophobic and hydrophilic reactions and hydrogen bonds. Where single chain proteins stop.
Quaternary structure
More than one polypeptide chain bonded together, must have at least 2 sub units
Conjugated protein
Contain non-protein molecules forming part of the structure of the protein(these parts called prosthetic groups)
Condensation reaction
Carboxylic group of one AA+amine group of other=peptide bond+water molecule
Haemoglobin structure
Globular protein, quaternary structure with four polypeptide chains(each containing a heme group-prosthetic). Two alpha and two beta chains.
Globular proteins and example
Polypeptide chain folded into compact spherical shape. Coiled up so hydrophilic parts of chain on outside(for metabolic reactions) and hydrophobic parts on inside= soluble so can transport in fluids. Eg haemoglobin
Fibrous protein and example
Long insoluble polypeptide chains tightly coiled around each other so rope shape, chains cross linked for extra strength - so have structural role. Eg collagen (triple helix with strong cross links) found in connective tissue.
What makes fibrous proteins so strong
Strong crosslinks between polypeptide chains, staggered chains so no weak spots, large proportion of hydrophobic R groups means insoluble, H bonds between chains in collagen.
