Enzymes 1 Flashcards
What are enzymes?
Are proteins that speed up (catalyse) specific chemical reactions
What are some general functions of enzymes?
Digestion Blood clotting Defence-immune system Movement Nerve conduction
What is function of nucleases?
Break down nucleic acid
What is function of proteases?
Hydrolyse peptide bond of other proteins
What is function of kinase?
Add phosphates to other substrates
Enzyme defects can cause inherited disease
Give examples of these diseases
Tays-Sachs disease=>amino acid deficiency. Are unable to cerebioside
Glycogen storage disease=> mutation of enzyme that mobilises glucose into blood
Phenylketonuria=> deficiency in liver enzymes enzyme. Phe can’t be broken down /converted into toxin in brain
Enzyme are drug targets
Give examples of such drugs
Antibiotics e.g. penicillin inhibits cell wall synthesis
Anti-inflammatory agents e.g. aspirin blocks enzyme that makes prostaglandin.
Anti cancer drugs e.g. methotrexate kills some types of cancer. Elle by shutting down dihydrofolate reductase
What are the key enzyme properties?
Increase reaction rate Show specificity Unchanged at end of reaction Don’t alter reaction at equilibrium Facilitate reaction by decreasing free energy of activation of reaction
What is an active site?
3D cavity or cleft that binds to substrate using electrostatic, hydrophobic, hydrogen bonding + VDW interactions
What is evidence that enzymes have active sites come from?
X-ray crystallography-> see where in enzyme substrate binds
Kinetics studies of enzyme activity
In what cells are Ras protein mutated?
In tumour cells
Effect is that it stops GTPase from working + Ras protein to stay switched in due to lack of hydrolysis of GTP. This means that Ras can communicate to all other proteins in cell + tell the cell to grow
How is RAS protein inactivated?
By hydrolysis of GTP
GTP-> GDP + Pi
What are E-S binding energy used for?
To bring molecules together in active site
To constrain substrate movement
Stabilise +ve and -ve charges in transition state
To strain particular bonds in substrate=>making breakage easier
Use co factors=> bring new chemistry. React chemically with substrate + change pathway by which reaction goes
What is lysozyme?
Enzyme that acts as a natural antibiotics egg white, saliva + tears
What is function of lysozyme?
It severs polysaccharide chains that form cell walls of bacteria
What is reaction catalysed by lysozyme?
Hydrolysis
Enzyme adds water molecule to single bond between 2 adjacent sugar groups in polysaccharide chain thereby causing bond to break
For colliding water molecule to break bond linking 2 sugars, polysaccharide molecule has to be distorted into a particular shape (transition state) in which atoms around bond have altered geometry + electron distribution
Why is hydrolysis slow?
Because in aqueous solutions at room temp, energy of such collisions almost never exceeds activation energy
What is Km?
Concentration of substrate when reaction reaches half of Vmax
What is Vmax?
Maximum rate when enzyme is saturated with substrate
Small Km means ……
Higher affinity as low concentration of substrate is required to reach half of Vmax
What happens to Km and Vmax in competitive inhibition?
Vmax is unaltered
Km is increased
What happens to Km and Vmax in non competitive inhibition?
Vmax is decreased
Km is unaltered
What is feedback inhibition and what happens?
In feedback inhibition, an enzyme acting early in reaction pathway is inhibited by late product of that pathway
Wherever large quantities of final product begins to accumulate, product binds to an earlier enzyme + slows down its catalytic action, limiting further entry of substrates into that reaction pathway More products, the more it inhibits
Feedback inhibition is ……… regulation.
Negative regulation
It prevents enzyme from acting
Enzymes can also be subject to ….. regulation
Positive regulation
In which enzyme’s activity is stimulated by a regulatory molecule rather than being suppressed.
It occurs when product in one branch of metabolic maze stimulates activity in another pathway
Describe the structure of allosteric enzymes?
Have 2 or more binding sites that influence each other
Multi subunit complexes
Regulatory sites + catalytic sites are on different subunit=> regulatory molecule often has a shape that is totally different from shape of enzyme’s preferred substrate
Regulation occurs via conformational changes
Exhibit non-Michaelis-menten kinetics
Involved in feedback inhibition of metabolic pathway
