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MEH > Carbohydrates III > Flashcards

Carbohydrates III Flashcards

1
Q

What is the entry stage point into stage 3

A

Acetyl CoA rather than pyruvate is the entry point into stage 3 (tricarboxylic acid (TCA) cycle)

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2
Q

What is the enzyme that regulates entry into the TCA cycle

A

Pyruvate dehydrogenase
is a key site of regulation of entry into the TCA cycle.

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3
Q

What does CoA stand for

A

Coenzyme A

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4
Q

What type of reaction are co-enzymes involved in

A

Catalytic Reaction

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5
Q

CoA (CoASH) what does the SH stand for

A

It stands for the Thioesters (with acyl groups) THE SULPHYDRYL GROUP

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6
Q

What groups are contained within an Actetly CoA

A

Contains a functional sulfhydryl group that reacts with carbonyl groups and forms acyl thioesters – such as acetyl CoA

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7
Q

What happens when you don’t have enough vitamins

A

Complex structures derived from vitamins cant be formed

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8
Q

Where is Pyruvate dehydrogenase (PDH) found

A

It is found in the Mitochondrial matrix

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9
Q

where does the pyruvate have to travel for the TCA cycle to occur

A

pyruvate transported from the cytoplasm across the mitochondrial membrane

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10
Q

What is PDH made from

A

PDH is a large multi-enzyme complex (5 enzymes)

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11
Q

What is the benefit of a large multi-enzyme complex

A

intermediates move from enzyme to enzyme without ever having to be released thus more effecient

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12
Q

Why do we need Vitamin B1

A

The different enzyme activities require various coenzymes (FAD, thiamine pyrophosphate and lipoic acid). B-vitamins provide these factors, so reaction is sensitive to Vitamin B1 deficiency.

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13
Q

Is the reaction CH3COCOOH + CoA + NAD+ –> CH3CO~CoA + CO2 + NADH + H+ a regulatory step and why ?

A

YES, Reaction is irreversible, so is a key regulatory step.

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14
Q

Pyruvate dehydrogenase (PDH) regulation?
What is it activated by -4
What is it Inhibited by - 4

A

activated by:
Pyruvate CoA
NAD+
ADP
Insulin
-This is called dephosphorylation

inhibited by:
acetyl-CoA
NADH
ATP
citrate
- This is called phosphorylation

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15
Q

What enzyme is used in phosphorylation

A

Kinase Enzyme

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15
Q

What enzyme is used in dephosphorylation

A

phosphatase Enzyme

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16
Q

What is another name for TCA cycle

A

KREBS CYCLE/ CITRIC ACID CYCLE

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17
Q

6 KEY points of info about Stage 3
(The Tricarboxylic Acid (TCA) cycle (Kreb’s cycle))

A
  • Mitochondrial
  • A single pathway –
  • Acetyl (CH3CO-) converted to 2CO2
  • Oxidative (requires NAD+, FAD)
  • Some energy produced GTP
  • (Also produces precursors for biosynthesis)
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18
Q

How many electrons are there within the chemical bonds of the Acetyl group

A

8

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19
Q

Where does the TCA cycle transfer the elections

A

NAD+ and FAD

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20
Q

why are there so many steps in the TCA cycle (2)

A

To conserve the energy present in the chemical bonds and use it efficiently for generating ATP.

Produces many intermediates which will be used in biosynthetic reactions.

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21
Q

What does glucose turn into - 2 steps

A

Glucose —-> 2 x acetyl groups into TCA —->
6 NADH 2 FADH2 2 GTP

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22
Q

What is GTP

A

Guanosine triphosphate - the energy currency that comes out of the TCA cycle

23
Q

What regulates the TCA cycle

A

Regulated by energy availability,
i.e.
ATP/ADP ratio
NADH/NAD+ ratio

24
Q

What is Isocitrate dehydrogenase?

A

isocitrate dehydrogenase (IDH) is an enzyme that is best known for its role in the Krebs cycle, catalyzing the oxidative decarboxylation of isocitrate

25
Q

What Upregulates and Downregulated Isocitrate dehydrogenase

A

Upregulated by a high level of ADP
Downregulated by High levels of NADH

26
Q

What does the TCA supply to the biosynthetic process - (4)

A
  1. Fatty Acids
  2. Amino Acids
  3. Heam
  4. Glucose
27
Q

Why does the TCA cycle not work without O2

A

Tightly coupled to electron transport chain – so does not function in absence of O2
(TCA cycle will come to a halt due to a lack of NAD+ and FAD.)

28
Q

Summary – Catabolism of glucose TCA cycle -4

A
  1. Broken all C - C bonds
  2. Oxidised all the C-atoms to CO2
  3. Broken all the C - H bonds
  4. Transferred all the H atoms (H+ + e-) to
    NAD+ → NADH+ H+
    FAD → FADH2
29
Q

What is the ∆Go for oxidation of glucose to CO2 and H2O

A
  • 2870 kJ.mole-1
30
Q

Where is the energy accounted for, or oxidation of glucose to CO2 and H2O

A
  1. ATP from Glycolysis  (4 ATP) 2 ATP net (= - 62 kJ.mole-1) TCAcycle2GTP = 2ATP (=-62kJ.mole-1)
    Total from substrate level phosphorylation = - 124 kJ.mole-1
  2. Still need to account for - 2746 kJ.mole-1
  3. Chemical bond energy of the e- in NADH and FAD2H
  4. ‘High energy’ electrons in NADH & FADH2 transferred to O2 with the release of large amounts of energy.
    This energy is used to drive ATP synthesis
31
Q

Key Points of stage 4 - Catabolism (4)

A

-Mitochondrial
-Electron transport and ATP synthesis
-NADH & FADH2 re-oxidised O2 utilised (reduced to H2O)
-Large amounts of energy (ATP) produced

32
Q

What is the use of reducing power in ATP synthesis?

A

Two processes
1. Electrons on NADH and FADH2 are transferred through a series of carrier molecules to oxygen (ELECTRON TRANSPORT)
Releases energy in steps
2. Free energy released is used to drive ATP synthesis (OXIDATIVE PHOSPHORYLATION)

33
Q

How does Mitochondrial electron transport work
(simplified)

A
  • Electrons are transferred through series of carrier molecules to O2, with release of energy.
  • [H+] gradient (an electrochemical gradient) is generated across the inner mitochondrial membrane = proton motive force (pmf)
  • ~30% of energy used to move H+ across inner membrane (a lot of the energy is released as heat.)
34
Q

What happens in the Proton translocating complexes

A

Energy from the electrons is used to translocate protons from the matrix into the intermembrane space.
This creates a Conc gradient of protons and generates an electrical gradient as you have a lot of positively charged molecules building up on one side of the membrane.

35
Q

What is the F1F0-ATPase or ATP synthase (synthetase)

A

It is present in the inner membrane of eukaryotic mitochondria and acts as the powerhouse of the cell by synthesizing ATP

36
Q

How does Proton translocating ATPase work

A
  • Return of protons (H+) is favoured energetically by the electrochemical potential (electrical and chemical gradient)
  • Protons (H+) can only return across membrane via the ATP synthase and this drives ATP synthesis
37
Q

Quick summary of Oxidative phosphorylation:

A
  • Occur in the mitochondria
  • Electrons are transferred from NADH and FAD2H to molecular oxygen
  • Energy released is used to generate a proton gradient (proton motive force (pmf))
  • Energy from the dissipation of the proton motive force is coupled to the synthesis of ATP from ADP
38
Q

When does NADH enter the Oxidative Phosphorylation pathway

A

At Complex 1 (Proton translocating complex 1)

39
Q

When does FADH2 enter the Oxidative Phosphorylation pathway

A

Complex 2

40
Q

What is the consequence of FADH2 entering later at complex 2 compared to NADH entering at Complex 1

A

Less proton transport via electrons of FADH2
You get less ATP synthesised

41
Q

What is the reason for NADH uses 3 PTCs and FADH2 using only 2?

A
  • Electrons in NADH have more energy than in FADH2,
  • so NADH uses 3 PTCs, and FADH2 uses only 2.
42
Q

How much ATP is generated from
NADH
FADH2

A
  • Oxidation of 2 moles of NADH  synthesis of 5 moles of ATP (P/O = 2.5)
  • Oxidation of 2 moles of FADH2  synthesis of 3 moles of ATP (P/O = 1.5)
43
Q

what happens when there is a greater p.m.f. (proton motive force (pmf))

A

more ATP synthesized

44
Q

How is the ATP: ADP ratio regulating Oxidative Phophorylation

A
  • When [ATP] is high, i.e. [ADP] is low, then there is no substrate for ATP synthase (synthetase)
  • So inward flow of H+ stops
  • Concentration of H+ in the intermitochondrial space
    increases
  • Prevents further H+ translocation - stops electron
    transport
45
Q

What happens to oxidative phosphorylation when ADP is low

A
  • Normally oxidative phosphorylation and electron transport are tightly coupled
  • Both regulated by mitochondrial [ATP]
  • High ATP = Low ADP
  • When [ADP] is low, = no substrate for ATP synthase (synthetase)
  • So inward flow of H+ stops
  • Concentration of H+ in the intermitochondrial space increases – stops H+ pumping and electron transport
46
Q

How does Inhibition of oxidative phosphorylation occur (electrons)
give examples

A

Inhibitors block electron transport,
-e.g. cyanide (CN-) prevents acceptance of electrons by O2
-e.g Carbon monoxide prevents protons from biding to the proton translocating complex

47
Q

What do Uncouplers do in Oxidative Phosphorylation

A
  • Uncouplers increase the permeability of the mitochondrial inner membrane to protons
  • dissipate the proton gradient, thereby reducing the proton motive force
  • No drive for ATP synthesis
48
Q

What do OXPHOS diseases do

A

Genetic defects in proteins encoded by mtDNA (some subunits of the PTCs and ATP synthase)
Reduction in electron transport and ATP synthesis

49
Q

What is the efficiency of coupling of oxidative phosphorylation

A

∆Go for NADH/O = - 220 kJ.mole-1
2.5 ATP = + 78 kJ.mole-1
(142 kJ.mole-1 lost)

∆Go for FADH2/O = - 152 kJ.mole-1
1.5 ATP = + 47 kJ.mole-1
(105 kJ.mole-1 lost)

50
Q

What happens to the rest of the energy in oxidative phosphorylation?

A
  • What happens to the rest of the energy?
  • Lost as HEAT
  • Efficiency depends on the tightness of the coupling
  • Brown adipose tissue - degree of coupling controlled by fatty acids (uncouplers) - allows extra heat generation
51
Q

Where is brown tissue found

A

1.Newborn infants
to maintain heat, particularly around vital organs

2.Hibernating animals
to generate heat to maintain body temperature

52
Q

What is thermogenin (UCP1)

A

naturally-occurring uncoupling protein.

53
Q

What happens when it is cold

A

In response to cold, noradrenaline (norepinephrine) activates :
1. Lipase which releases fatty acids from Triacylglycerol
2. Fatty acid oxidation  NADH/FADH2  electron transport
3. Fatty acids activate UCP1
4. UCP1 transports H+ back into mitochondria
So, Electron Transport uncoupled from ATP Synthesis. Energy of
p.m.f. is then released as extra heat.

54
Q

Difference between
OXIDATIVE PHOSPHORYLATION and SUBSTRATE LEVEL PHOSPHORYLATION

A

OXIDATIVE PHOSPHORYLATION
-Requires membrane-associated complexes (inner mitochondrial membrane)
-Energy coupling occurs indirectly through the generation & subsequent utilisation of a proton gradient (pmf)
-Cannot occur in the absence of O2
-Major process for ATP synthesis in cells requiring large amounts of energy

SUBSTRATE LEVEL PHOSPHORYLATION
-Requires soluble enzymes (cytoplasmic & mitochondrial matrix)
-Energy coupling occurs directly through the formation of high-energy of hydrolysis bonds (phosphoryl-group transfer)
-Can occur to a limited extent in the absence of O2
-Minor process for ATP synthesis in cells requiring large amounts of energy

55
Q

What is the net yield of ATP from glucose?

A

Glycolysis - 7
PDH - 5
TCA - 20
TOTAL = 32 ATP

MEH (13 decks)

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