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MGD > Session 2 > Flashcards

Session 2 Flashcards

1
Q

How is the Fe atom bound to haemoglobin or myoglobin?

A

Via the proximal histidine residue on the other side of the haem group to the oxygen binding site.

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2
Q

What happens to deoxymyoglobin when oxygen binds to it?

A

The Fe is pulled slightly into the plane of the ring structure, causes a small change in overall protein conformation.

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3
Q

What relationship does oxygen show when binding to myoglobin?

A

A hyperbolic relationship, very low partial pressures of oxygen give 50% saturation in myoglobin.

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4
Q

What relationship does oxygen binding to haemoglobin show and why?

A

Sigmoidal relationship, oxygen binding promotes the R state of Hb so as more oxygen binds, more oxygen is likely to bind so a Sigmoidal relationship is shown.

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5
Q

What is the low oxygen affinity state of Hb called?

A

Tensile (T) state.

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6
Q

What is the high affinity state of Hb called?

A

Relaxed (R) state.

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7
Q

How is oxygen binding to Hb regulated?

A

Using 2,3-BPG, it acts as an inhibitor by reducing the affinity of O2 to Hb (promotes the T state), only 1 BPG molecule can bind per Hb tetramer

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8
Q

When does [2,3-BPG] increase and why?

A

Increases at high altitudes.

Promotes oxygen release in the tissues at high altitudes because [oxygen] is lower.

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9
Q

What is the Bohr effect?

A

Haemoglobin’s oxygen binding affinity is inversely related to both acidity and concentration of carbon dioxide.

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10
Q

How does carbon monoxide affect haemoglobin?

A

It combines with ferromyoglobin and ferrohaemoglobin to block oxygen transport, binds 250x more strongly than oxygen and also increases the affinity of other unaffected subunits to oxygen.

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11
Q

At what concentration does carbon monoxide become fatal?

A

50%

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12
Q

How are the glob in chains in adult, foetal and adult2 haemoglobin arranged?

A

HbA: 2 alpha and 2 beta chains
HbF: 2 alpha and 2 gamma chains
HbA2: 2 alpha and 2 delta chains

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13
Q

Why is HbF useful?

A

Has a higher binding affinity for oxygen than HbA (dissociation curve moves to the left) so oxygen can be transferred from the mothers blood supply to the foetus.

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14
Q

What mutation causes sickle cell anaemia?

A

A to T; Glutamine to Valine in the beta glob in chains.

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15
Q

What causes cell sickling in sickle cell anaemia?

A

Mutation to Valine causes a hydrophobic pocket to form, allows deoxygenated HbS to polymerise and become sickle shaped.

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16
Q

What properties do sickle cells have?

A

More prone to lyse

More rigid

17
Q

What are beta-thalassaemias and when do symptoms appear?

A

Decreased or absent production of beta-glob in chains so alpha-chains can’t form stable tetramers.
Symptoms appear after birth as beta-chains aren’t present in HbF.

18
Q

What are alpha-thalassaemias and when do symptoms appear?

A

Decreased or absent alpha-globin production, there are several different severities due to multiple copies of alpha-chains present. Beta-chains can form stable tetramers with increased oxygen affinity.
Symptoms appear before birth because alpha chains are present in HbF

19
Q

What is the transition state of a chemical reaction?

A

The high energy intermediate that lies between the substrate and product states.

20
Q

What is the activation energy of a reaction?

A

The minimum energy substrates must have to allow the reaction to progress.

21
Q

How can the rate of a reaction be increased?

A

Increase temperature: more molecules have activation energy.
Increase substrate conc: increases chances of molecular collisions.
Enzymes: lowers activation energy to facilitate formation of the transition state.

22
Q

What properties do enzymes possess?

A 
Highly specific
Unchanged after a reaction
Don't affect reaction equilibrium
Increase rate of reaction
Most are proteins and may require cofactors
23
Q

What is the active site of an enzyme?

A

The site where substrates bind and the chemical reaction occurs (usually a cleft or crevice).

24
Q

What forms the active site of an enzyme?

A

Amino acids from different parts of the primary sequence.

25
Q

What is the lock and key hypothesis of enzyme activity?

A

The active site is complimentary in shape to that of the substrate.

26
Q

What is the induced fit hypothesis of enzyme activity?

A

Binding of a substrate induces changes in conformation of the enzyme: a complimentarily shaped active site only forms after binding of the substrate.

27
Q

How are substrates bound to enzymes?

A

By multiple weak bonds: all types of non-covalent bonds are used but covalent bonds are usually too strong and would make binding too tight.

28
Q

What is V0 of a reaction?

A

The initial rate of reaction.

29
Q

What is the Michaelis-Menten model for enzyme catalysis?

A

Proposes that a specific complex between the enzyme and substrate is a necessary intermediate in catalysis:
V0={Vmax*[S]}/{Km+[S]}
Vmax is in mol/min and assumes an infinite amount of substrate.
Km is the Michaelis constant and is in M, it is the substrate conc that gives half the maximum velocity.
It predicts a rectangular hyperbola.
Not all enzymes obey the model; some regulated ones don’t.

30
Q

What does a low Km value signify?

A

A high affinity for a substrate.

31
Q

What does a high Km value signify?

A

A low affinity for a substrate.

32
Q

What is a Lineweaver-Burk plot?

A 
Graph depicting s rearrangement of the Michaelis-Menten equation.
X-intercept is -1/Km
Y-intercept is 1/Vmax
Gradient is Km/Vmax
X axis shows 1/V
Y axis shows 1/[S]
33
Q

What is the mechanism on irreversible inhibitors?

A

Bind very tightly to enzymes (usually using covalent bonds) to slow or prevent enzyme reaction occurring.

34
Q

What is the mechanism of reversible inhibitors?

A

Non-covalent binding so can freely dissociate from enzyme.
Competitive inhibitors bind at the active site and affect Km not Vmax
Non-competitive inhibitors bind at a site other than the active site and affect Vmax not Km

35
Q

What happens to a Lineweaver-Burk plot when a competitive inhibitor is used?

A

Km increases but Vmax stays the same.

X-intercept increases and gradient of line increases.

36
Q

What happens to a Lineweaver-Burk plot when a non-competitive inhibitor is added?

A

Vmax decreases but Km stays the same.

Y-intercept increases and gradient of line increases.

37
Q

How many oxygen groups can bind to haem in

myoglobin or haemoglobin?

A

1

MGD (10 decks)

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