Protein Structure and Function - Done Flashcards
What is the function of myoglobin?
Oxygen and iron binding protein found in muscles
What is the function of calmodulin?
Calcium modulating protein - binds to other proteins to help them function
Where is porin found?
In the membrane of a cell - transmembrane protein
What is the importance of cytochrome C?
Important in the electron transport chain - oxidation and reduction reactions.
Inner membrane of mitochondria
What do lysozymes do?
Break down bacterial cell walls - glycoside hydrolase
What’s the function of alcohol dehydrogenase?
To remove hydrogen from alcohol, oxidising to aldehydes/ketones
(NAD+ goes to NADH)
What’s the function of collagen?
Main component of connective tissue - contains 2 uncommon amino acid derivatives which are at specific locations relative to glycine - modified post-translationally by different enzymes
Both enzymes require vitamin C as cofactor
In what form are amino acids?
L form
N —> C
Why is a trans arrangement of secondary amides favoured?
Trans form is more stable than Cis form.
Where does H-bonding occur in alpha helices?
At every Fourth amino acid - NH of one peptide bond is H-bonded to the C=O of another in the same chain
How many amino acids per helical turn in alpha helixes?
3.6 amino acids per turn
What do transmembrane proteins often contain?
An alpha helix - hydrophobic side chains interact w hydrophobic tails of phospholipids
Hydrophilic parts of backbone from internal H-bonds - allow polar molecule to pass through the membrane
What form of Beta sheet is stronger parallel or anti-parallel?
Antiparallel as amino acids residues are at right angles to each other - more stable bond formed
Parallel Beta sheets form weaker, longer H-bonds
What is a ‘domain’ in a protein?
A sub section of a tertiary structure that might have a distinct role of function - usually 100-250 amino acids long
What is the most stable conformation of any protein? How does this relate to ∆G?
With polar amino acids on the outer surface - so can interact with water - caused by repulsion of water against hydrophobic groups.
Protein is folded in such a way the free energy of the folded form is minimised (so ∆G is maximised)
What are incorrectly folded proteins called?
Aggregates - can cause serious damage as neurodegenerative diseases like Alzheimer’s
What are chaperone proteins?
Proteins that assist with the folding of other proteins along the most energetically favourable pathway.
What are prions and what’s the danger they pose?
Prions are proteins that have misfolded, considered infectious as prion protein can cause normal protein to misfold - can spread from cell to cell.
What subunits make up haemoglobin?
2 alpha-globin
2 beta-globin
All held together by non-covalent interactions
What is the significance of the ‘coiled-coil’?
2/3 Alpha helices wrap around each other - occurs when hydrophobic side chains are on one side, reducing H-bonding disruption in cytosol
Structural purpose - skin & muscle contraction
What’s the significance of collagen’s structure?
Triple helix containing glycine residues at every third amino acid, forcing glycine into the centre to give long overlapping arrays of strong fibrils.
How doe elastin differ from collagen?
Elastin is loose with unstructured polypeptides which are cross linked - allowing the protein to stretch and relax
What is retinal’s function and where does it bind?
Binds to Rhodopsin, a purple, light sensitive pigment made by rod cells. It binds to the protein via a covalent bond to a lysine side chain
Helps detect light as retinal changes shape by absorbing a photon.
What is the heme group in haemoglobin?
A cofactor - Fe binds to oxygen reversibly
What are antibodies classed as?
Immunoglobulin proteins
Where does antibody specificity lie in antibodies?
Specificity lies in the antigen binding site
How are antibodies held together?
With numerous disulphide bridges
What are antibodies made up of?
Antiparallel Beta - pleated sheets, aside from the hyper variable loops that bind to the antigen
What do lysozymes do and why does it occur?
They are natural antibiotics that sever polysaccharide chains in bacterial cell walls - burst. Can hold 6 linked sugars at a time.
It occurs because the free energy of the severed chain is lower than the intact chain - energetically favourable.
Where dose trypsin cleave?
At carboxyl terminal of lysine or arginine
Where does elastase cleave?
At carboxyl terminal of alanine, valine, serine, glycine, leucine & isoleucine.
Where does chymotrypsin cleave?
At carboxyl terminal of phenylalanine, tryptophan & tyrosine
Define feedback inhibition and state why it occurs
An enzyme acting early in a reaction pathway is inhibited by a late product of that pathway -
Occur when large quantities of final product accumulate, slowing catalytic action of the enzyme
What does aspartate transcarbamoylase catalyse?
Catalyses important reaction that starts synthesis of pyrimidine rings
How does cytosine triphosphate cause feedback inhibition?
When plentiful it binds to aspartate transcarbamoylase, turning it off
