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Membranes > Metabolic Regulation and Control > Flashcards

Metabolic Regulation and Control Flashcards

1
Q

What happens if there is too little glucose in blood supply?

A

brain problems (<5mM)

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2
Q

What happens if there is too much glucose in blood supply?

A

osmotic water loss and damaged blood vessels

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3
Q

What hormone is released to buffer against a high conc of glucose in the blood?

A

Beta sells release insulin

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4
Q

What hormone is released to buffer against a low conc of glucose in the blood?

A

Alpha sells release glucagon

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5
Q

What happens after the release of insulin?

A
  • increase rate of glucose transported into cell
  • increased rate of glucose utilisation and ATP generation
  • inc conversion of glucose to glycogen
  • inc protein synthesis
  • inc fat synthesis
    blood glucose conc decline and homeostasis is restored
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6
Q

What happens after the release of glucagon?

A
  • increased breakdown of glycogen to glucose
  • increased breakdown of fats to fatty acids
  • inc synthesis and release of glucose
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7
Q

What is the flow of metabolism determined by?

A

The amount and activity of enzymes

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8
Q

What is homeostasis?

A

The maintenance of an internal environment

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9
Q

What happens during a steady state rate?

A
  • maintaining of homeostasis
  • rate of synthesis of a metabolite equals its rate of conversion to product
  • all enzymes in a pathway operate at the same net rate
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10
Q

What is the net flow of the typical metabolic pathway?

A
  • reactions will all operate near equilibrium
    (A->BCDE)
  • Any small change in conc of metabolite which affects the net rate
  • e.g. if increase of [B], rates of reaction will change so that it will make more of C to lower the [B] to make it back to the equilibrium
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11
Q

What is the Keq and Mass Action Ratio of the typical metabolic pathway?

A

Keq and MAR are close (0-100)

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12
Q

What is a FAR-from equilibrium reaction?

A
  • an irreversible reaction
  • ΔG &laquo_space;0
  • e.g. PFK1
  • slow rate
  • changes in [substrates] have little effect on the reaction
  • only changes in enzyme activity (allosteric interactions) can significantly alter the rate
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13
Q

What is the Keq and Mass Action Ratio of a FAR-from equilibrium reaction?

A

MAR «< Keq

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14
Q

Give an example of an enzyme with a FAR-from equilibrium reaction.

A

PFK-1

  • F6P + ATP -> F1,6BP + ADP
  • 3rd step of glycolysis
  • insufficient activity, too few molecules of PFK1 present and activity limited by effectors
  • rate of reaction is too slow to allow reaction to approach equilibrium
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15
Q

Which type of equilibrium is the control point?

A

The FAR-from equilibrium reaction is the control point

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16
Q

Why is the rate determining step hypothesis proved to be wrong?

A
  • because the net rate is the same
  • found contradictory results during genetic engineering experimental findings
  • too simplistic a view
17
Q

What is the rate determining step hypothesis?

A

The RDS enzyme was expected to:

  • occur at the beginning of a pathway or at branch points
  • have low activity overall
  • catalyse a non-equilibrium reaction
  • be allosteric (subject to feedback inhibition, covalent modification)
18
Q

What is metabolic regulation?

A
  • processes that maintain homeostasis at molecular level

- hold the concentration of a metabolite at a steady level over time

19
Q

State an example of regulation vs control of glycogen synthesis from blood glucose.

A

Regulation:
- insulin activation of Glycogen synthase by phosphorylation cascade prevents major changes in G6P levels
Control:
- insulin increases in uptake of glucose into cells (GLUT4) and synthesis of Hexokinase to increase flux towards glycogen

20
Q

How was the testing of the single RDS (Rate determining step) hypothesis conducted?

A
  • genetic engineering experiment
  • increase the amount of the RDS enzyme to see if the flux would increase proportionately
  • saw that hexokinase increased glycolytic rate much more than PFK-1 did (rat liver)
  • in yeast, increasing PFK1 by 5 produced <10% increase in flux through glycolysis
21
Q

What did the engineering experiment to test the RDS hypothesis show?

A
  • in most pathways, the control of flux is distributed over several enzymes
  • PFK1 regulation is not to control glycolytic flux but to produce metabolic homeostasis
22
Q

What is the most effective way to increase metabolic flux?

A

The Metabolic Control Analysis predicts that you can do this by raising the concentration of all enzymes in a pathway

23
Q

What is a substrate cycle?

A

2 or more enzymes catalyse opposing reactions

  • one usually requiring ATP
  • they may amplify metabolic signals (with modest changes in rate of enzymes) and stimulate flux through a pathway
24
Q

State an example of reciprocal regulation of glycolysis and gluconeogenesis by substrate cycle of PFK1 and FBP.

A
  • Both enzyme have allosteric controls that ensure both reactions do not occur fully simultaneously (e.g, inc in AMP and decrease in Citrate promotes PFK1 whereas does opposite to FBP)
  • some glycolysis can happen during gluconeogenesis
  • important in Bumble bees to maintain temperature to inc glycolysis (generating heat) during gluconeogenesis
25
Q

What sort of kinetics is seen in an allosteric enzyme?

A

Sigmodial kinetics

- forms S shaped curve graphs

26
Q

How can the MM equation be shown in sigmodial kinetics? What is K0.5 and n?

A

V=( Vmax.[S]^n )/ (K0.5)^n + [S]^n
K0.5 = binding constant, [S] at half Vmax
n = Hill coefficient

27
Q

What does the hill coefficient show?

A

how good the interactions are between subunits of an allosteric protein or enzyme

  • > 1 then there is cooperation present (allosteric)
    e. g. Haemoglobin, Glycogen phosphorylase b
28
Q

Define allosteric activator

A
  • preferentially stabilises enzyme in high affinity R-state
  • binding increases affinity
  • oxygen and hemoglobin
29
Q

Define allosteric inhibitor

A
  • binding decreases the affinity for the substrate
  • preferentially stabilises enzyme in low affinity T-state
  • 2,3-BPG binding to hemoglobin decreases affinity for O2
30
Q

Define homotropic allostery

A

The effector is the substrate itself

31
Q

Define heterotropic allostery

A

The effector is another molecule or metabolite

32
Q

What are the two main models for explaining allosteric effects?

A

Concerted/ symmetry model and the Sequential model

33
Q

What is the concerted/ symmetry model of explaining allosteric effects?

A
  • protein must be oligomeric
  • proteins exist in 2 conformational states in rapid equilibrium, a low affinity T state (Tense) or a high affinity R state (relaxed)
  • substrate binding shifts the conformation of ALL subunits from T to R states
  • allosteric inhibitor favours T state, allosteric activator favours R state
34
Q

What is the sequential model of explaining allosteric effects?

A
  • R and T states
  • binding of substrate to one T state subunit causes it to convert to R-state
  • this interacts with adjacent T-state subunits so that the next substrate can bind more readily
  • hybrid T-R-state enzyme

Membranes (19 decks)

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