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Biochem - Year 1 Biomed > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What does catalysis acctually mean

A

Catalyse making and breaking covalent bonds between substrates at faster reaction rates

Reactions occur at a lower conditions eg ph or temp

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2
Q

How do you calculate keq equilibrium constant

A

K+1 (conc of 2 substrates)
/
K-1 (conc of products in reversible reaction)

Eg 100x100 units
/
2 x 2 units - the units left in reversible reaction

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3
Q

What is Keq correlated to

A

With energy released by the reaction

GIBBS FREE ENERGY - change from substrate to products

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4
Q

What does the Gibbs free energy value need to be for substrates to become products

A

-ve

Substrate must be at a higher energy level than end products

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5
Q

What is transition state

A

A form of substrate which is at high energy

If the transition state isn’t lowered eg by enzymes the reaction won’t reach equilibrium

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6
Q

Why don’t reactions happen spontaneously without enzymes

A

They need enzymes to lower activation energy to lower the transition state of the substrate

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7
Q

What does the ES complex reduce in order for reaction to reach equilibrium

A

Reduces transition state

This increases speed equilibrium is reached

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8
Q

Do active sites change after reaction?

A

No they are unaltered catalysts

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9
Q

There are 5 ways enzymes catalyse reactions - name them

A

1- proximity- substrates closer together

2- orientation- align correct bonds in substrates

3- strain - in induced fit the AS puts strain on bonds in substrate

4- acid base catalysis

5- covalent catalysis

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10
Q

How do enzymes use acid base catalysis to catalyse a reaction

A

Protons (H+) or hydroxyls (OH-) get donated
They are added into active site (introduced to charged side chains)

This overcomes the low concentration of reactive molecules

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11
Q

What is covalent cataclysms

A

When enzyme active sites temporarily bond covalently to substrates

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12
Q

There are 4 ways enzymes can be specific in their reactions - explain them

A

1- absolute - only work with 1 substrate

2- bond- the substrates need a specific bond eg oxygen bonds in esterase

3- group- only work on Eg hexose sugars

4- stereo - DISTINGUISH OPTIMAL ISOMERS eg L or D amino acids

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13
Q

There are 6 types of enzyme reaction, briefly explain them

A

1- oxidase/reductase - OIL RIG
2- transferase - transfer other groups to the substrates eg phosphates

3- lyases- rearrange bonds in substrates

4- hydrolases- insert H20 for hydrolysis eg of peptide bonds

5- isomerases - change the position of atoms

6- ligases/syntheses - synthesis of new molecules

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14
Q

What is the turnover number (Kcat)

A

Number of substrates converted by 1 enzyme in 1 second

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15
Q

Name an enzyme with very high Kcat

A

A and B amylase

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16
Q

Why do you always measure initial rate of reaction

A

Because the substrate conc is known

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17
Q

What increases rate of reaction

A

Increased substrate concentration- more ES complexes

18
Q

What does V proportional to S mean

A

Velocity /rate of reaction depends on substrate concentration

19
Q

What is it called when eventually all Es complexes are formed

A

Saturation of enzymes

20
Q

What is the Michaelis menton equation for velocity

A

V = Vmax x (s) / km + (s)

21
Q

What is v max

A

Maximum velocity shown when enzymes have reached saturation - infinite substrate concentration

22
Q

V max could never be found so who do scientists find it

A

Plot the graph and the concentrations they did get to and then use computer to predict v max

23
Q

Inhibitors can be irreversible and reversible, explain how some are irreversible

A

They bind to active site via covalent bonds

This prevents substrate binding

They bind to side chains such as cysteine or serine (reactive)

24
Q

What side chains do irreversible inhibitors bind to in active site via covalent bond

A

Reactive chains like serine or cysteine

25
Q

Explain how penecillin is an irreversible inhibitor

A

Penecillin binds to serine on glycopeptidetranspeptidase (PBP)

This inactivates the enzymes

Stops synthesis of cell walls in bacteria

26
Q

Penecillin is a B lactam antibiotic , what does this mean

A

B lactam is a complex of rings which will block the active site via covalent bonds

27
Q

How do bacteria become resistant to B lactam antibiotics

A

They have an enzyme called B lactamase which degraded the B lactam before it binds to PBP

28
Q

Why are competitive inhibitors most useful drugs

A

They bind to active site very tight so dosage can be lower

29
Q

How do competitive inhibitors change v max and Km

A

V max will be unchanged - the Es complex will still occur eventually

Km will be increased(more substrate concentration needed) for affinity

30
Q

How can you overcome a competitive inhibitor

A

By adding more substrate to outcompete

31
Q

Give an example of a competitive inhibitor

A

Methotrexate - anti cancer drug

Malonate- binds instead of succinate so no fumarate produced

32
Q

Explain the effect of non competitive inhibitors when bound to allosteric sites on vmax and km

A

V max will be decreased - they interfere will the ES complex and reaction reaching equilibrium

Km doesn’t change- the affinity to bind to substrate is the same because they bound to allosteric site

33
Q

Give example of a non competitive inhibitor

A

Deoxycycline used to treat gum disease

34
Q

What is an UNCOMPETITIVE inhibitor

A

Inhibitors which only bind to enzymes with multisubstrates

They bind INTO THE ES COMPLEX

35
Q

Explain the effect of uncompetitive inhibitors on km and vmax

A

Vmax is lowered as they prevent catalysis in the ES complex so lower reaction rate

Km is acctually lowered (higher affinity) because substrates bind to active site more efficiently (enzyme binds to allosteric site)

36
Q

When ph isn’t at optimum, what part of the active site is altered

A

The side chains which have charged molecules

Such as aspartate (0-) and lysine (NH3+)

37
Q

What is the optimum ph for enzymes

A

7.4

38
Q

There are enzymes with different optimum ph due to evolution. Give an example

A

Pepsin due to it being in stomach acid - 2 is optimum

39
Q

What happens in enzymes when they move out of optimum ph

A

If lower ph (acidic) they will remove COO- carboxylates and at high alkali conditions (OH-) they remove NH3+ side chains

40
Q

What happens at high and low ph to side chains

A

Protonation at low ph eg of histidine

At high ph carboxylate loses a proton and deprotonation occurs eg of glutamate and aspartate

Biochem - Year 1 Biomed (21 decks)

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