FHMP 008 Amino acids, protein structure and function Flashcards
what is the structure of an amino acid?
Amino group (N-terminus = left), Carboxyl group (right side), Side chain (R-group), H atom and central C atom
What is the R group?
- it is the variable group (has 20 variations)
- each amino acid has a different R group
what is the peptide bond and how is it formed?
- Amino acids are polymerised by Condensation to form Peptide Bond
- forms between the N- terminus (NH3) and the C- terminus (COO) and produces water
How are R groups classified
- 20 R groups in total
- 9 = hydrophobic ( mostly C-H)
- 11 = hydrophilic
- 6 hydrophilic are neutral ( all have O, OH or NH groups that form bonds with H2O) (mostly in active sites)
- 2 hydrophilic are acidic ( have COO- group)( in active sites and salt bridges)
- 3 hydrophilic are basic ( have N-H ) (some act as buffers)
What are the 4 levels of protein structure?
primary, secondary, tertiary, quaternary
What is the primary structure of a protein?
sequence of amino acids in a polypeptide chain
What is the secondary structure of a protein?
- 3D arrangement of a polypeptide chain
- alpha helix or beta-pleated sheet
- hydrogen bonding
describe the bonding in alpha helix structure
- helical arrangement, main protein chain repeats itself about every 4th turn
- R groups stick outwards
- carboxyl and amine groups hydrogen-bonded
- all H bonds are parallel to the helical axis
describe the bonding in beta pleated sheet
- main chain is extended: the R groups alternate up and down
- all carboxyl and amine main chain groups are hydrogen bonded
- all H bonds are perpendicular to main chain
- parallel sheets = N-terminus are at same end
- antiparallel sheets = N -terminus are at opposite ends
What is the tertiary structure of a protein?
- 3D folding of a polypeptide chain due to interactions between side chains of amino acids that lie in different regions of the primary sequence
- hydrogen bonding, salt bridges/ionic bond between opposite charges, hydrophobic/hydrophilic interactions and disulphide bridges
What is the quaternary structure of a protein?
3D arrangment due to interactions between different polypeptide chains in proteins composed of more than one polypeptide (subunit interaction)
what are the 3 types of protein?
fibrous, globular, hybrid
What are fibrous proteins?
- strong/insoluble/inflexible material e.g. collagen and keratin
- structural support e.g. tendons, bones, muscle, ligament, hair, skin…
- long strong fibers
- insoluble in water
- quaternary structure is held by covalent bridges
- more stable (less effected by environment)
give 3 examples of fibrous proteins
keratin, elastin, collagen
describe collagen
Fibrous protein.
3 polypeptides wound in rope-like structure (triple helix), very strong.
Every third amino acid in glycine (small).
tropocollagen assembles together to make collagen fibre
cross linking to increase strength
- skin, tendons, cartilage, bones, connective tissue
describe elastin
Fibrous protein in elastic fibres.
Quaternary.
Made of small, soluble tropoelastin molecules linked together via interactions between hydrophobic areas.
Alternate hydrophobic and lysine-rich areas.
Cross-linking covalent bonds between lysine.
- arteries, lungs, bladder, ligament
Describe keratin
Fibrous protein.
Large proportion of cysteine (containing sulfur).
Many strong disulfide bridges between alpha helices
- hair, nails, outer skin
What are globular proteins?
- water soluble proteins with a specific 3D shape e.g. enzymes, hormones, antibodies, haemoglobin
- spherical compact shape
- quaternary structure is held together by non-covalent forces
- used a lot in metabolism
- less stable (more effected by environment)
give 4 main types of globular proteins
- enzymes = catalase, trypsin
- transporters = haemoglobin, transferrin
- protection = antibodies (immunoglobulins)
- hormones = insulin
- DNA binding
- storage
- cell signalling
Describe haemoglobin structure
- 4 polypeptide chains held together by disulfide bonds, globular protein
- conjugated protein - contains a haem group ( iron ion ) to bind to O2
- 2 alpha, 2 beta chains
- binds to and carries/transports oxygen around the body
describe immunoglobulin structure
- antibodies, bind to antigens on pathogen and kills the pathogen
- 2 light chains, 2 heavy chains, Fab and Fc region
- Beta sheet structure ( 2 sheets)
- Y shaped
- hydrogen bonding, disulfide bridhes
what are hybrid proteins?
- proteins with both fibrous and globular proteins
give 3 examples of hybrid proteins
actin, myosin, fibrinogen
