Proteins 2 Flashcards
Name 3 types of proteins which contain prosthetic groups?
Glycoproteins
Lipoproteins
Metalloproteins
What is a glycoprotein?
Compound composed of protein and carbohydrate
How are glycoproteins formed?
Post-translational modification (glycosylation) whereby a sugar molecule binds via an amino acid to the protein
What are examples of glycoproteins?
Immunoglobulins
Blood group determinants
Where does glycosylation occur?
ER and Golgi body
What does glycosylation play a role in?
- Protein stabilisation
- Affects solubility
- Protein orientation
- Signalling
- Cell recognition
How can glycoproteins be used in disease?
Provides a marker of long term diabetic control
How are glycoproteins used in diabetes?
- Non-enzymatic reaction forms glycated haemoglobin
- Condensation reaction between N-terminal valine and glucose forms aldimine
- Aldimine undergoes amadori rearrangement to from stable ketoamine
What are lipoproteins?
Proteins and lipids bonded together either covalently or non-covalently?
What is the function of lipoproteins?
To transport water-insoluble fats and cholesterol in the blood e.g. HDL, LDL
What are metalloproteins?
Protein molecules with a bound metal ion
What are the functions of metalloproteins?
Enzymes
Transport
Storage
Signalling
What functions can proteins have?
- Movement
- Enzymes
- Structural
- Protection
- Receptors
- Storage
- Hormones
- Transport
- Control of gene expression
What functions do globular proteins have?
Varied functions:
- Enzymes
- Hormones
- Transporters
- Stock of amino acids
- Structural function (actin and tubulin)
What functions do fibrous proteins have?
Structural function:
- Bone matrixes
- Muscle fibres
- Tendons
- Connective tissue
What functions do membranous proteins have?
Associated with cell/organelle membrane:
- Relay signals
- Membrane transporters
- Membrane enzymes
- Cell adhesion molecule
What is the binding ratio of haemoglobin to oxygen?
Haem group at the centre of each polypeptide chain binds one molecule of oxygen. One molecule of haemoglobin can bind four molecules of oxygen
Co-operativity
The increase in affinity of polypeptide chains when a substance binds to a sister polypeptide chain
What is the genetics behind sickle cell anaemia?
Single base change causes hydrophilic amino acid glutamic acid to be replace with hydrophobic valine
What are the properties of Hb S?
- Insoluble
- At low O2 levels it forms crystals and polymerises to form long chains, causing the RBC to change shape
What are the clinical features of Hb S?
- Sever haemolytic anaemia
- Hb S gives up oxygen in the tissues more easily than Hb A.
What is collagen?
- Fibrous protein that makes up 25% of the total protein in humans
- High tensile strength
What is collagen composed of?
Repeating unit Glycine-X-proline where X is alanine, hydroxyproline, lysine
What is the structure of collagen like?
- Polypeptide chain coils to form a helix
- 3 polypeptides then coil around each other
- They are held together by hydrogen bonds which can interact to form fibrils increasing the strength
What is vitamin C required for?
To convert proline to hydroxyproline and lysine to hydroxylysine.
What happens when someone is deficient in vitamin C?
Scurvy:
- Hydroxylysine and hydroxyproline are essential for stabilising the crosslinks between chains
- Weaker collagen is produced
Why does oesteogenesis imperfect occur?
- Glycine substituted for a larger amino acid
- Protein unable to form tight coil
- Reduced fibril interaction
- Loss of secondary, tertiary structure
- Weakened and brittle collagen produced
What is an LDL receptor?
A glycoprotein present on the surface of all cells which binds to apoB and causes the internalisation of LDL.
What are the classes of mutations relating to the LDL receptor?
- Class 1: no receptors produced
- Class 2: Receptors never reach cell surface
- Class 3: Receptors can’t bind LDL
- Class 4: Receptors don’t internalise on binding LDL
- Class 5: Receptors don’t release LDL
What is Familial Hypercholesterolemia?
An autosomal dominant disorder caused by mutations in LDL receptor
What does FH cause?
Elevate LDL concentrations in the blood which leads to cholesterol deposits in the skin, tendons and arteries and as a result early CV disease
