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MBChB Year 1 Principles Biochemistry > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

What is V max?

A

The maximum velocity of a reaction (when all the enzyme has been used)

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2
Q

What is Km?

A

The concentration of substrate which is where Vmax is at 50%

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3
Q

In the reaction E + S = ES what are the two rate constants?

A

Forwards is K1 (enzyme association) and backwards is K-1 (enzyme dissociation)

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4
Q

In the reaction ES = E + P what represents the forward equation?

A

K2 - rate constant of enzyme conversion of substrate to product

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5
Q

What is the Michaelis Constant (Km)?

A

Km = (K-1 + K2)/K1

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6
Q

What is the Michaelis-Menten model?

A

[ES] = K1[E][S]/(K-1+K2)

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7
Q

How are Vmax and Km measured?

A

Measure initial reaction velocity (V0) at a known substrate concentration and repeat at increasing substrate concentration

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8
Q

How do you plot Vmax and Km on a graph?

A

Initial reaction rates (V0) are plotted as a function of substrate concentration. At infinite substrate concentration the initial reaction rate approaches a maximal rate Vmax. Take half of Vmax = Km

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9
Q

What are Vmax and Km as straight line components?

A

Vmax is the Y axis interception and Km is the x axis interception

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10
Q

How does level of Km affect substrate concentration?

A

Low Km means only a little substrate required and a high Km means a lot of substrate for half-maximal velocity

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11
Q

How do red blood cells and liver&pancreas both catalyse glucose conversion with different Km?

A

RBC: Hexokinase Km is 0.05mM glucose which maintains energy production by glycolysis even if glucose levels drastically fall
L&P: Glucokinase Km is 5mM glucose which enables glucose sensing and homeostasis. It’s abundance in the liver is regulated by insulin and excess blood glucose is metabolised

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12
Q

What is MODY?

A

Maturity Onset Diabetes of the Young - loss of glucokinase activity = loss of insulin-mediated glucose homeostasis

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13
Q

What is the transcription factor in oxygen regulation pf gene expression?

A

Hypoxia inducible factor

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14
Q

What is the mechanism in oxygen regulation of gene expression?

A

Oxygen sensors (prolyl hydroxylases) –> transcription factor (hypoxia inducible factor) –> genes for surviving hypoxia (RBC synthesis, blood vessel growth and anaerobic survival pathways)

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15
Q

Do proline hydroxylases have a high or low Km?

A

High which enables oxygen sensitive oxygen sensing over physiological ranges of PO2

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16
Q

What are the problems with Monge’s disease?

A

Excessively high haemocrit, loss of arterial O2 saturation and loss of O2 regulation of Epo production

17
Q

What is Von Hippel Lindau Syndrome?

A

Loss of propyl hydroxyls activity which causes excessive blood vessel growth (angiogenesis) leading to haemangiomas in the brain and subcutaneous haemangiomas in the track spinal chord

18
Q

What is competitive inhibition?

A

A reversible inhibition in which the inhibitor binds to the active (catalytic) site and blocks substrate access - Orthosteric

19
Q

What is reversible non-competitive inhibition?

A

The inhibitor binds to a site other than the catalytic centre causing a conformational change which stops the enzyme from binding - Allosteric

20
Q

What is irreversible non-competitive inhibition?

A

Usually involves the formation or breakage of covalent bonds in the enzyme complex

21
Q

What affect does competitive inhibition have on Vmax and Km?

A

Vmax doesn’t change but Km varies

22
Q

What is the substrate for alcohol dehydrogenase (ADH)?

A

Methanol

23
Q

What does methanol poisoning cause?

A

Severe tissue damage and blindness by conversion to formaldehyde. (also drives metabolic acidosis)

24
Q

Is the ADH Km higher for ethanol or methanol?

A

Ethanol (by 20x)

25
Q

How do you treat methanol poisoning?

A

Treat patient with 40% ethanol in combination with dialysis and ventilation

26
Q

How does non-competitive inhibition affect Km and Vmax?

A

Vmas varies but Km does not change

27
Q

What is feedback inhibition?

A

Inhibition of rate limiting enzymes by end products (common form of allosteric control)

28
Q

Why is feedback inhibition important?

A

Avoids the build up of intermediates in the pathway which can be highly reactive and therefore biochemically dangerous

29
Q

Increasing substrate concentration with allosteric enzyme produces what kind of curve?

A

Sigmoidal (not hyperbola like with Michaelis-Menten)

30
Q

What is allosteric enzyme’s co-operative behaviour?

A

Allosteric factors modulate enzyme kinetic behaviour

31
Q

What can control allosteric enzymes?

A

Allosteric inhibitors and allosteric activators

32
Q

What is a major example of allosteric regulation?

A

The binding of oxygen to haemoglobin as it shows positive co-operativity and has multiple controllers (protons, CO2, 2,3 biphosphateglycerate)

MBChB Year 1 Principles Biochemistry (4 decks)

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