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glucose oxidation Flashcards

1
Q

oxidation & reduction: how is energy conserved

A

ATP, NADH, FADH

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2
Q

oxidation & reduction: where is energy stored

A

the covalent bonds between each group which make up the tail of the molecule

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3
Q

oxidation & reduction: how is energy released

A

cleavage of bonds between the phosphate groups releases energy to drive reactions

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4
Q

how is NADH is reduced to NADH

A

NAD+ accepts a hydride (H-) = 2 electrons & one proton = NAD

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5
Q

how FAD is reduced to FADH2

A

FAD accepts 2 electrons & 1 proton

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6
Q

define redox coenzymes

A

accept electrons & carry them to the electron transport chain (NAD, FAD)

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7
Q

define oxidation

A

the burning of a sample

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8
Q

define oxidised using NAD as example

A

when electrons are transferred from carbs to NAD the carb has been oxidised

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9
Q

are carbs polar or non polar

A

polar due to high proportion of hydroxyl groups = highly water soluble

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10
Q

transport of glucose

A
  1. dietary carb are digested into glucose

2. glucose enters the bloodstream & enters cell via diffusion through glucose transporter protein GLUT

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11
Q

where are GLUTs

A

in all cells but different types

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12
Q

define GLUT

A

glucose transporter protein

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13
Q

where is GLUT 4 found

A

skeletal muscle and adipose tissue, and are insulin dependent.

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14
Q

define glycolysis pathway

A

central anaerobic pathway for glucose metabolism

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15
Q

where does glycolysis occur

A

in the cell cytosol

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16
Q

the two stages of glycolysis

A

energy consuming stage & an energy producing stage

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17
Q

steps in the energy-consuming phase (uses 2 ATP molecules)

A
  1. glucose enters cell
  2. enzyme hexokinase attaches a phosphate to convert glucose into glucose-6-phosphate = glucose goes from high to low concentration in cell
  3. glucose-6-phosphate is then rearranged, phosphorylated, and cleaved to produce two x 3 carbon molecules - glyceraldehyde-3-phosphate
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18
Q

what does converting glucose into glucose-6-phosphate do

A

addition of a phosphate group traps glucose in the cell & maintains a concentration gradient with higher glucose levels in the blood than inside the cell

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19
Q

steps in the energy-yielding phase

A
  1. glyceraldehyde-3-phosphate is oxidised
  2. de-phosphorylated
  3. rearranged to produce two molecules of pyruvate (3 carbon molecule)
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20
Q

summary of glycolysis & what it uses

A

one glucose molecule is broken into 2 pyruvate molecules

= uses 2 ATPs to drive initial reactions & created 4 ATPs & 2 NADH molecules

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21
Q

what is the net result of glycolysis

A

2 pyruvate, 2 ATP & 2 NADH

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22
Q

is glycolysis efficient for extracting energy

A

no its inefficient

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23
Q

what happens to the pyruvate after generated in aerobic conditions

A
  1. pyruvate is transported from the cytosol into the mitochondrial matrix
  2. converted into acetyl CoA by pyruvate dehydrogenase = oxidative decarboxylation reaction
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24
Q

what does the conversion into acetyl CoA release

A

releases dioxide & transfers two electrons that combine with NAD+ to form NADH = irreversible

25
Q

what inhibits pyruvate dehydrogenase

A

acetyl-CoA and NADH

26
Q

what activates pyruvate dehydrogenase

A

NAD+ and coenzyme A (CoA)

27
Q

what happens in the Krebs cycle aka citric acid cycle

A

Acetyl-CoA is processed through a series of reactions

28
Q

summary of Krebs cycle steps (8 steps)

A

begins = condensation of acetyl-CoA with oxaloacetate (OAA) to form citrate

ends = regeneration of oxaloacetate to start cycle again

29
Q

for every molecule of acetyl-CoA that enters the cycle –>

A

3 molecules of NADH, 1x FADH2 and 1 x GTP are produced

30
Q

what increases & inhibits activity in the krebs cycle

A

increase = oxaloacetate & NAD

inhibit = citrate & NADH

31
Q

what is the oxidative phosphorylation process

A

= where the energy derived from the metabolism of glucose in glycolysis & the krebs cycle is used to make ATP

32
Q

where in the mitochondria does the oxidative phosphorylation process occur

A

the inner mitochondrial membrane

33
Q

what components are needed to synthesise ATP in the mitochondria

A
  • electron transport chain (ECT) complexes I to IV

- enzyme complex ATP synthesis

34
Q

what does the ECT (electron transport train) consist of

A
  • four enzyme complexes & 2 coenzyme complexes (ubiquinone & cytochrome c)
35
Q

what does ECT act as & as a result what does it create

A

= act as electron carriers & proton pumps used to transfere H+ from the mitochondrial matrix into the space between the inner & outer mitochondrial membranes

= the sequential transfer of electrons has created an electrochemical gradient between the mitochondrial matrix and intermembrane space

36
Q

the steps in the electron transport chain ect

A
  1. Complex I: NADH Dehydrogenase
    - NADH donates pair of electrons to ubiquinone and protons are pumped across the membrane
  2. complex II: succinate dehydrogenase
    - FADH2 donates a pair of electrons to ubiquinone. no protons are pumped across the membrane
  3. Ubiquinone
    - Accepts one electron at a time from NADH and FADH2 and transfers these electrons to cytochrome c at complex III.
  4. Complex III: Cytochrome c reductase

cytochrome c accepts electrons from ubiquinone and pumps one proton per transfer of electron across the inner mitochondrial membrane.

  1. Complex IV: Cytochrome c oxidase

molecular oxygen accepts electrons from cytochrome c, and pumps a proton across the inner mitochondrial membrane. The reduced oxygen and H+ ions from the mitochondrial matrix combine to form new water molecules. This is the basis for why we need to breathe in oxygen.

37
Q

what is the importance of oxygen in the ECT

A

Without oxygen acting as the final electron acceptor, electron flow through the ETC will cease, metabolism will cease, and the cell will eventually die.

38
Q

what does ATP synthase do

A

a complex that synthesises ATP

  • an F-type transmembrane pump which functions a bit like turbine
39
Q

how is the ATP synthase turbine powered

A

by the energy generated from the flow of H+ ions down the electrochemical gradient as they across the inner membrane and enter the mitochondrial matrix

40
Q

what enables the ATP synthase to make ATP

A

The flow of H+ ions through complex cause the shaft to rotate which enables ATP synthase to catalyse the phosphorylation of ADP to ATP (oxidative phosphorylation)

41
Q

how does ADP work as a regulator of oxidative phosphorylation

A
  1. addition of ADP into the mitochondria stimulates ATP synthase activity
  2. This lowers the proton gradient, as protons are used to power ATP synthesis.
  3. the reduction in the proton gradient causes an increase in respiration as the ETC works to re-establish the proton gradient, and maintain ATP synthesis
  4. When the concentration of ADP is depleted, ATP synthase activity terminates and oxygen uptakes decreases.
42
Q

how is ADP supplied to the mitochondrial intermembrane space

A
  1. ADP is transported in via the ATP/ ADP antiporter which exchanges mitochondrial ATP formed through oxidative phosphorylation, with ADP in the cytosol.
  2. The ATP/ADP antiporter allows one molecule of ADP to enter the matrix only if one molecule of ATP exits simultaneously.
  3. Phosphate is transported from the cytosol into the mitochondria via the HPO42−/OH− antiporter, which mediates the import of one phosphate coupled to the export of one OH−.
43
Q

what is the first line of defence against declining blood glucose concentration

A

glycogen stores

44
Q

what is glycogenesis

A

the formation of glycogen

45
Q

what is glycogenolysis

A

breakdown of glycogen

46
Q

where does Glycogenesis and Glycogenolysis occur

A

liver and muscle tissues

47
Q

glycogen synthesis steps

A
  1. glucose-6-phosphate which is isomerised to glucose-1- phosphate.
  2. Glucose-1-phosphate is then activated to the sugar nucleotide, uridine diphosphate (UDP)-glucose,
  3. before being linked to the growing glycogen chain by the enzyme glycogen synthase.
48
Q

what happens between meals when blood glucose levels begin to fall

A

liver glycogen in degraded to maintain blood glucose levels - we carry enough glycogen to maintain levels for 12-16hours

49
Q

the process of glucose breaking down

A
  1. glycogen debranching enzyme removes glucose from glycogen
  2. glycogen phosphorylase converts it to glucose-1-phosphate which is converted to glucose-6-phosphate.
  3. Finally, glucose-6-phosphatase removes the phosphate group to produce glucose, which is then released into our circulation
50
Q

degradation of glycogen in muscles

A

degraded to glucose-6-phosphate for glycolysis and energy production during prolonged exercise in much the same way.

  • However, muscle glycogen cannot be used to maintain blood glucose levels, as muscle tissues do not express glucose 6 phosphatase
51
Q

what is gluconeogenesis

A

when we fast for longer than 10 hours shift from glycogenolysis to the de novo synthesis of glucose via gluconeogenesis

= essential for maintaining blood glucose levels during prolonged fasting or starvation, when glycogen stores are depleted

52
Q

major substrates in gluconeogenesis (opposite of glycolysis)

A

being lactate, amino acid carbon skeletons, and glycerol from the breakdown of triglycerides

53
Q

what is the energy required to “power” gluconeogenesis

A

provided from the oxidation of fatty acids released from triglycerides

54
Q

pyruvate during anaerobic conditions

A

the Krebs cycle and ETC cannot proceed and pyruvate and NADH cannot be oxidised

  1. pyruvate is converted to lactate by lactate dehydrogenase = this reaction oxidises NADH to NAD+ to regenerate the pool of NAD+ that is needed to allow glycolysis to continue.
  2. lactate produced by muscle tissue diffuses into the bloodstream
    & is transported to the liver where it is converted back into pyruvate and used as a substrate in gluconeogenesis.
  3. The newly synthesised glucose is then released from the liver and taken up by other tissues, where it is oxidised to make ATP. This loop is known as the Cori Cycle.
55
Q

what is the cori cycle

A

= when oxygen is limited, pyruvate is converted to lactate to replenish the NAD+ supply for glycolysis to continue. Lactate is taken up by the liver and used as a substrate for gluconeogenesis.

56
Q

steps in glycolysis

A
  1. glucose uses ATP to create G3P
  2. this creates 2NADH and then 4ATP
  3. creating pyruvate x2 (goes into mitochondria)
  4. creates NADH
  5. then the pyruvate becomes Acetyl CoA in mitochondria
57
Q

Which complex in the electron transport chain is also an enzyme in the Krebs Cycle?

A

II

58
Q

what is diverted from glycolysis to be stored as glycogen

A

glucose 6 phosphate

59
Q

What enzyme regulates the conversion of glycogen into a form that can be utilised by muscles?

A

glycogen phosphorylase

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