F cell Enzymes Flashcards
What are enzymes?
Proteins that speed up (catalyse) specific chemical
reactions
What are some examples of enzyme functions?
- Digestion: carbohydrates, fats, proteins
- Blood clotting: fibrin clot catalysed by thrombin
- Defence-immune system-activation of complement
- Movement: muscle actomyosin is an ATPase
- Nerve conduction: membrane pumps for Na+, K+, Ca++
What is phenylketonuria?
Inherited enzyme disorder where you cannot convert Phe to Tyr.
What is glycogen storage disease?
cannot mobilise glucose
What is tay-sachs disease?
defect in processing a membrane
What the enzymes not alter?
Do not alter reaction equilibrium
What do enzymes facilitate?
Facilitate reaction by decreasing the free energy
of activation of the reaction
What do enzymes facilitate?
Facilitate reaction by decreasing the free energy
of activation of the reaction
What is an enzyme active site and how does it bind with specific substrates?
The active site is a 3-D cavity or cleft that binds substrate(s) with specificity through electrostatic, hydrophobic, hydrogen bonding and van der Waals interactions.
What are the evidence for active sites?
-X-ray crystallography
-Kinetic studies of enzyme activity
Lock and Key mechanism?
The active site was thought to have a fixed structure (the lock), which exactly matched the structure of a specific substrate (the key).
Induced fit mechanism?
This model suggests that an enzyme, when binding with its substrate, optimizes the interface through physical interactions to form the final complex structure.
What does lysozyme use to cleave its bacterial substrate?
Lysozyme uses strain to cleave its bacterial substrate
What does polysaccharide cleavage cause?
Polysaccharide cleavage causes bacterial rupture
and death
How do we obtain Vmax and Km values?
We use a double recipricol plot
-Measure V (rate of product formation) at various substrate
concentrations. Plot 1/V versus 1/[S]. Intercepts on the axes
provide values for Vmax and Km.
-X intercept=-1/km
-y intercept=1/vmax
What is a turnover number>
max no of substrate molecules handled per active
site per second. Carbonic anhydrase is a very efficient enzyme.
What happens to the Km and Vmax values in the presence of a competitive inhibitor?
In the presence of a competitive inhibitor: Km is increased (it takes more substrate
to achieve Vmax/2). However, Vmax is unaltered as the effects of the inhibitor can
be competed out at high substrate concentrations.
What is Km value?
Km value is that concentration of the substrate at which half of the active sites of the enzyme are occupied by the substrate
What is the Vmax value?
Vmax is the rate attained when the enzyme sites are saturated with substrate, i.e. when the substrate concentration is much higher than the KM
What happens to Km and Vmax value in the presence of a non-competitive inhibitor?
in the presence of a non-competitive
inhibitor, the substrate Km is unaltered; but the Vmax is reduced.
How is enzyme activity regulated in cells?
1.Control of gene expression
2.Compartmentation
3.Allosteric regulation
4.Covalent modification of enzyme
What does control of gene expresssion control in enzyme activity?
Control enzyme amount
What does compartmentation in enzyme activity regulation do?
Sequences in enzyme polypeptide chain target enzyme to ER, mitochondrion, nucleus etc
What happens in allosteric regulation for enzyme activity regulation?
a regulatory molecule (acting at a
pocket distinct from the active site) changes the enzyme
conformation to influence the active site and decrease (or in
some cases, increase) enzyme activity. Controls the flux
of material through a metabolic pathway.
What happens in covalent modification of enzyme in enzyme activity regulation?
Change enzyme shape and activity-e.g. phosphorylation
What regulates metabolic pathways?
Feedback inhibition regulates metabolic pathways
What are allosteric enzymes?
Multisibunit complexes
Where are the regulatory sites and catalytic sites located in allosteric enzymes?
Regulatory sites and catalytic sites on
different subunits
What does regulation of allosteric enzymes occur via?
Regulation occurs via conformational changes
What kinetics do allosteric enzymes exhibit and what graph does this give us in a V vs S plot?
Exhibit non-Michaelis-Menten kinetics:
V vs S plots are sigmoidal
What are allosteric enzymes involved in ?
Involved in feedback inhibition of metabolic pathways
What does bacterial DNA gyrase catalyse?
Gyrase catalyses ATP-dependent DNA supercoiling by a double- strand
DNA break.
What is novobiocin and what does it do and how?
-Antibiotic
-Inhibits gyrase
-Novobiocin (green) competitively
inhibits the binding of ATP (pink)
to gyrase
What does fluoroquinolones do?
Fluoroquinolones inhibit DNA resealing by gyrase/topo IV
