L8 Flashcards
What are all proteins encoded by?
Genes
Name 6 functions proteins perform (receptors, hormones etc)
Structural proteins = Actin, Micro-tubules, intermediate filaments
Secereted proteins = Hormones
Membrane bound proteins = Receptors
Molecular motors = DNa helicase
Secreted structural proteins = cartialage
Intracellular proteins = cytosolic signalling molecules
How many genes encode proteins?
20,000
What are the difference between essential and non-essential amino acids?
Non-essential are made by the body from the essential AA or by breakdown of proteins.
Essential AA come from food in our diet..
What bonds are AA held together by and how are they formed?
AA held by peptide bonds, formed by condensation reaction to form a covalent bond.
How many AA do proteins contain?
Usually from 50-2000
Can be 30-10,000
Name 4 secondary structures of protein
a-helices
b-pleated sheets
Loops and turns
Random coils
What is the structure of an a-helix
Polypeptide backbone foldied into a spiral formed as H bonds form between carbonyl group and amine group 4aa along the chain
3.6 aa per turn
side chains face outwards
Where are a-helices abundant and why
Abundant in membrane proteins
Hydrophobic side chains interact w hydrophobic H-C tails of phospholipids
Hydrophilic backbone shielded from lipid environment and form H bonds
What is the b-sheet structure?
Flat structure(sheet)
Laterally packed strands
Each strand w 5-8AA
Shape due to H bonds between carbonyl group and amine group of neighbouring chain
Side chains extend above and below b-sheet
Describe the secondary structure “loops and turns”
3-5 AA long, form sharp bend redirecting polypeptide backbone
Hydrophilic residues found on surface of proteins
Describe the secondary structure “random coils”
Polypeptide chains w random configuration
How are tertiary structures formed? Name 3 tertiary structures
Secondary structure spontaneously fold into 3D conformations
Myoglobin
Tumour necrosis factor alpha
Barrels - 1st/last strand form H bonds forming a barrel
What is a coiled coil?
2 examples
2/3 a-helices wound around each other. Hydrophobic AA line up where helices meet.
Keratin
Collagen
What is a post translational modification (PTM)?
Covalent processing event from proteolytic cleavage(breaking of peptide bonds between AA) or addition of a modifying group
They modulate function of most eukaryote proteins by altering activity state, localization, turnover and interactions w other proteins.
When is protein denaturation permanent and when is it reversible?
Solvent denature proteins disrupting non-covalent interaction losing secondary and tertiary structures. But when solvent is removed the protein will renature
Heat can denature protein but it is irreversible denatured e.g. cooking an egg
What is assisted folding?
What are the two classes that assist in folding?
Molecular chaperones bind to partially folded polypeptide chains and assist in folding
Two classes are: Heat shock proteins
Chaperonins
What is protein charge dependent on>?
The AA side chains for example, carboxylic group :glutamic acid and aspartic acid will be negative
Whereas, N group: lysine, arginine, histidine will be positive
What is a protein domain?
Part of the protein tertiary structure that can exist independently of the rest of the protein chain. The domains can independently fold and be stable.
What is the signal sequence?
What happens if a protein does not have 1?
Protein leaves ribosome, part of AA sequence will contain the signal sequence to provide info of correct location of protein.
Proteins with none remain in the cytosol
What causes cystic fibrosis?
DNA mutation that alters protein shape.
The deletion causes mutant CTFR protein to become stuck in ER and abnormal chloride conductance occurs.
What causes Creutzfeldt-Jakob disease (CJD)?
Misfolding proteins.
Normal protein adopt misfolded prion
This binds to normal protein inducing conversion to abnormal conformation
Abnormal prions form tightly pakced b-sheets that are very stable
Misfolded prions build up in the brain forming amyloid plaques cause progressive slow death of nerves in the brain
