Proteins Flashcards
What is released when a peptide bond is formed?
Water
What is the primary structure of a protein
The sequence of amino acids
What is the secondary structure of a protein?
The spatial arrangement of amino acid residues that are near each other in the linear sequence
What are the two structural forms of the secondary structure?
Alpha helix, beta sheets
What stabilises the alpha helix structure?
H bonds between the NH groups and the CO groups in the next turn of the helix
What stabilises the beta sheets?
H bonds between the amide groups of the linear polypeptide chains
What is the tertiary structure?
The spatial arrangements of amino acids residues that are far apart in the linear sequence
What is the tertiary structure held together by?
Van der waals forces Ionic interactions Hydrogen bonds Disulphide bridges Hydrophobic interactions
Where do ionic interactions take place?
Between two oppositely charged R groups
What environment is needed for intra polypeptide hydrophobic interactions to occur?
An environment within proteins from which water is excluded
Where do disulphide bridges occur?
They are strong covalent bonds that occur between two cysteine residues
They are common in extra-cellular proteins
They can occur between as well as within a polypeptide
What is the quaternary structure?
The spatial arrangement of individual polypeptide chains in a multi-subunit protein
What structure remains in tact after denaturation?
The primary structure
What are common causes of denaturation?
Acids Heat Solvents (ethanol) Cross linking reagents (formaldehyde) Chaotropic agents (urea) Disulphide bond reducers (2 mercaptoehanol)
What is the effect of denaturation?
Decrease in solubility
Altered water binding capacity
Loss of biological activity
Improved digestibility
What is glycosylation?
Post translational modification whereby a sugar molecule binds via an amino acid to the protein
Give an example of a glycoprotein
Immunoglobulins
Where does glycosylation occur?
In the ER and the golgi apparatus
What is the roles of glycosylation?
Protein stabilisation Affects solubility Protein orientation Signalling Cell recognition
What is the function of lipoproteins?
Transport of water, insoluble fats and cholesterol in the blood
What are metalloproteins?
Protein molecule with a bound metal ion
What are the functions of metalloproteins?
Enzymes
Storage
Signalling
Transport
Why does haemoglobin have four subunits?
The binding of O2 to one sub unit alters its shape
This in turn causes a change in shape of the other sub-units so that they bind O2 more easily
Co-operative binding
How does sickle cell anaemia arise?
Substitution of one amino acid, hydrophilic Glutamic acid is replaced with hydrophobic amino acid Valine
What are the clinical features of sickle cell anaemia?
Severe haemolytic anaemia
Oxygen is given up more easily in the tissues
What is the structure of collagen?
Polypeptides coil to form a helix
Held together by hydrogen bonds
Interactions form fibrils which increases strength
What is the effect of scurvy?
Vitamin C deficiency, there is less hydroxyproline and hydroxylysine which are essential in stabilising cross links between chains of collagen, so collagen produced is weaker
What is the effect of osteogenesis imperfecta?
Protein cannot form into a tight coil due to amino acid substitution
There is less interaction between fibrils
Loss of secondary and tertiary structure
Weakened and brittle collagen is produced
What are the possible mutations of the LDL receptor?
No receptors produced Receptors never reach cell surface Receptors can't bind LDL Receptors don't internalise on binding LDL Receptors don't release LDL
What disease can result as an effect of LDL mutation?
Familial hypercholesterolemia, resulting in early cardiovascular disease
