Protiens Flashcards
What elements do proteins contain ?
C, H, O, N, (sometimes) S
What are the monomers that make up proteins ?
Amino acids
What is the structure of an AA?
Consists of 1 central C atom bonded to a H atom, a Carboxylic group (-COOH), and amino group (-NH2) and a specific side chain/ R-group
What do R-groups determine ?
Property of AA
What are the four types of AA
Neutral and non-polar
Neutral and polar
Acidic and polar
Basic and polar
Which R groups are hydrophilic and which are hydrophobic ?
Polar forms H bond with water - hydrophilic
Non-polar cannot form H bonds - hydrophobic
How to categories the R groups into the four categories
Neutral and non-polar : no charge, no S,O,N
Neutral and polar : no charge, contains S O N
Acidic and polar : negative charge
Basic and polar : positive charge
What are the properties of AA?
Colourless
Crystalline solids
Generally soluble in water but insoluble in inorganic solvents
Dissolves in water to form ions : -NH2 to -NH3+ and -COOH to -COO-
Amphoteric : exhibits both acid and basic properties
Zwitterions formed when both amino and carboxyl group fully ionised
What are zwitterions ?
Molecules that bear charged groups of opposite polarities
What is the isoelectricc point ?
pH at which AA exists mainly in its zwitteroin form
What is electrophoresis ?
Separation technique based on the movement of charged ions under the influence of an electrical field
What type of AA move towards which end in electrophoresis ?
AA with net positive charge move towards the negative electrode (cathode)
AA with net negative charge move towards the positive electrode (anode)
What bond is formed between AAs?
Peptide bond (-CONH-)
What is the direction of a polypeptide ?
1st AA : amino end ( N terminus)
Last AA : carboxyl end ( C terminus)
What are the four levels of organisation ?
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
What does primary structure refer to ?
Type, number and sequence of AAs linked by peptide bonds
Why is primary structure important ?
Determines properties and 3D shape of polypeptide
Determine biological function of polypeptide
What does secondary structure refer to ?
Localised folds and coils that occur in the polypeptide chain
How are the folds and coils in secondary structure formed ?
Formed as a result of interchain H bond at reglar intervals along polypeptide backbone between AA lying close to each other
Is R group interaction involved in secondary structures ?
No
What are the two types of secondary structures ?
Alpha-helix (a-helix)
Beta-pleated sheet (ß-pleated sheet)
How is a-helix formed ?
The oxygen of the carbonyl group of residue n forms H bond with the H of the amino group of residue (n+4)
What is the structure of a-helix ?
The helix backbone winds around long axis resulting in right-hand coil with H bonds all aligned parallel to axis while the R groups project outward
Inter-chain H bonds stabilise the a-helix
How many AA (avg) are there per complete turn in the a-helix ?
3.6