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Biological Chemistry > Lecture 9 DA > Flashcards

Lecture 9 DA Flashcards

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1
Q

Why does metabolism have so many steps?

A

Energy changes involved need to be kept small, manageable, and controlled.

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2
Q

What is a benefit of metabolism having so many steps?

A

Chemically resistant bonds can be manoeuvred.

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3
Q

What is catabolism? What form of gibbs free energy does it have? Is it oxidation or reduction?

A

Catabolism releases energy, and is exergonic or oxidative. Has negative gibbs free energy.

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4
Q

What is anabolism? What form of gibbs free energy does it have? Is it oxidation or reduction?

A

Anabolism requires energy, and is endergonic or reductive. Has positive gibbs free energy.

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5
Q

Are cells isothermal?

A

Yes.

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6
Q

What is gibbs free energy?

A

Energy derived from oxidation of dietary fuels.

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7
Q

What becomes of gibbs free energy?

A

Transduced into useful work (anabolism) or stored as ATP.

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8
Q

Can absolute free energy (G) be measured?

A

No, but the difference of substrates vs products can be known - ΔG.

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9
Q

What is ΔG°?

A

Standard free energy change when pH=0, at [1M] and 25°C.

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10
Q

What is ΔG°’?

A

Standard biologcal free energy change, pH=7, at [1M], and 25°C.

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11
Q

What is ΔG?

A

Change in free energy, the actual change in the cell.

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12
Q

What does it mean when a reaction has negative free energy, in terms of products and reactants?

A

Products contain less free energy than the reactants.

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13
Q

Are reactions with negative gibbs free energy sponatneous or not? Why?

A

Yes, because the products have less energy, and are more stable than the reactants.

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14
Q

What does it mean when a reaction has positive free energy, in terms of products and reactants?

A

Products have more energy than the reactants.

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15
Q

Are reactions with positive gibbs free energy sponatneous or not? Why?

A

No, because the products have more energy, and energy input is needed.

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16
Q

Why is reaction coupling so important?

A

If reactions are coupled properly, it can be such that an endergonic reaction is driven by the gibbs free energy of an exergonic one.

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17
Q

Give an example of reaction coupling.

A

A -> B, ΔG°’ = 20kj/mol
X -> Y, ΔG°’ = -33kj/mol
Therefore, A + X -> B + Y
ΔG°’ = 20 + -33, so -13kj/mol when coupled, and is spontaneous.

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18
Q

What is needed for reaction coupling?

A

Enzymes are needed.

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19
Q

What is the most commonly used reaction for coupling?

A

ATP -> ADP

20
Q

What forms of NTPs are used for protein, lipid, and glycogen synthesis respectively? How is this useful?

A

GTP - protein
CTP - lipid
UTP - glycogen
This allows for compartmentalisation.

21
Q

In ATP (and other NTPs), is the bond energy between the phosphates high? Why are they called a high energy bond?

A

High energy bond for the phosphate bonds is a misnomer, the bonds themselves are not high energy, but have a high free energy. They are in fact, very weak, given all the negative elctrostatic stresses.

22
Q

Why do phosphate bonds in ATP (and other NTPs) have so much free energy?

A

The negative charges between the phosphates contribute to a high tension, is unstable and strained, wanting to break apart, given its a weak bond. Hence the high free energy.

23
Q

Why is ATP so popular as an energy donor?

A

It is stable (despite the high phosphate tension) and enzymes recognise the adenosine for handling.

24
Q

How much ATP is needed per day by the body? How much is there found at any given time? What is the reason for this disparity?

A

ATP needed - 45kg
ATP found - 1g
Constant resynthesis of ADP to ATP required to meet demand.

25
Q

Give an example of coupling using glutamine to glutamate.

A

Glutamine synthase required.
Starts by first phosphorylating the glutamine using ATP. The phosphate is replaced by an amine group, resulting in glutamate.
Enzyme integrates energy from ATP -> ADP to substitute the phosphate group with an amine, finishing the reaction.

26
Q

What does pure ATP hydrolysis release (aside from ADP and Pi)? Are there any exceptions?

A

Heat only. Exceptions when bound non-covalently to a protein. Hydolysis allows protein to switch between two conformations (myosin heads).

27
Q

What kind of reaction is ATP synthesis?

A

Strongly endergonic ~30kj/mol.

28
Q

What is substrate level phosphorylation? How much ATP is produced this way?

A

When ATP synthesis is coupled to a metabolic exergonic reation. Largely anaerobic. 5-10% of cellular energy produced this way.

29
Q

Where does a cell obtain most of its ATP synthesis?

A

Oxidative phosphorylation.

30
Q

Do other forms of energy currencies exist aside from ATP?

A

Yes, there are many for different situations. They just arent as universal.

31
Q

How does substrate level phosphorylation work?

A

Works by making intermediates that have a higher free energy for phosphate hydrolysis than ATP, and use that energy to make ATP from ADP.

32
Q

What cofactor is necessary for ATP synthesis?

A

NADH.

33
Q

What are NAD+, NADH and NADPH used for?

A

NADH - ATP synthesis
NAD+ - catabolic reactions
NADPH - reductive biosynthesis (anabolism/photosynthesis)

34
Q

What is NAD?

A

Specialised e- carrier, and a cofactor of some enzymes.

35
Q

What does NADP accept?

A

Hydride ion, H-

36
Q

What does NADP act as?

A

Water soluble carrier of electrons, from one metabolite to another.

37
Q

What is FMN composed of? What about FAD? What are they both known as?

A

FMN has a base, ribitol and phosphate.
FAD has an extra ribose adenine on the end.
They are flavoproteins.

38
Q

What is the function of a flavoprotein?

A

Can accept 2 electrons and 2 protons, acting asa temporary store of electrons.

39
Q

Is FAD reduced or oxidised? what about FADH2?

A

FAD is oxidised, FADH2 is reduced.

40
Q

What are the major redox coenzymes involved in energy transduction from food to ATP synthesis?

A

NAD+, FAD, FMN.

41
Q

How many electrons/protons do NAD+, FAD, and FMN carry?

A

NAD+ takes one hydride ion, H- (2 electrons, 1 proton), the other proton is released to solution.
FMN and FAD take 2 electrons and 2 protons.

42
Q

What is a source of molecular hydrogen?

A

Reduced NASH.

43
Q

What is the ATP produced per mol of NADH oxidised? How much does the body make, and why?

A

7.3mol of ATP per mol of NADH oxidised. Body makes closer to 2.5mol.
Actual in vivo rate doesn’t match up with standardised calculations.

44
Q

What state are most glycolytic intermediates in? Why?

A

Phosphorylated. It isnt recognised by receptors in this form, and are trapped in. Allows easier identification by enzymes as well.

45
Q

How are irreversible reactions used?

A

They can be used to regulate the pathway.

46
Q

Why are the start or end of a pathway not used for pathway control using irreversible reactions?

A

Are too drastic, better at more than one point throughout the pathway, as intermediates act as precursors.

47
Q

What can glycolysis intermediates be used for aside from glycolysis?

A

Biosynthesis.

Biological Chemistry (15 decks)

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