lecture 28 - glucose as a fuel molecule

Question 1

What is the name for the oxidation of glucose?

Answer 1

Glycolysis

Question 2

Where does glycolysis occur is eukaryotes?

Answer 2

In the cytoplasm of cells - not in the mitochondria

Question 3

What is the fuel of red blood cells, and why?

Answer 3

Glucose - energy can be extracted by glycolysis in the cytoplasm, as they do not have mitochondria for citric acid cycle and oxidative phosphorylation

Question 4

What is the preferred fuel for the brain?

Answer 4

Glucose

Question 5

What is a simple reason that the brain prefers glucose for fuel, as opposed to fats, etc.?

Answer 5

Glucose easily crosses the blood-brain barrier, but fats do not

Question 6

Do brain cells have mitochondria?

Answer 6

Yes - means they can extract maximum energy from glucose

Question 7

What is the preferred fuel molecule in the eye?

Answer 7

Glucose - glycolysis can proceed without oxygen or mitochondria, meaning that blood vessels and mitochondria do not affect refraction of light for vision

Question 8

What are the 2 types of muscle, in terms of function and fuel type used?

Answer 8

Red (type 1) and white (type 2) muscle

Question 9

What is the function of red muscle, and what is its preferred fuel type?

Answer 9

Endurance, uses fats for fuel

Question 10

What is the function of white muscle, and what is its preferred fuel type?

Answer 10

Sprinting, glucose as fuel

Question 11

What is the overall conversion in glycolysis?

Answer 11

Spitting of one molecule of glucose (6 Carbon) into 2 molecules of pyruvate (3 Carbon)

Question 12

In what form is energy conserved in glycolysis?

Answer 12

In ATP and NADH

Question 13

What are the 2 phases of glycolysis?

Answer 13

Energy investment phase, Energy payoff phase

Question 14

What occurs in the energy investment phase of glycolysis?

Answer 14

Activation of glucose - gets the molecule into a form so energy can be captured and required an an energy input of 2 ATP

Question 15

How much ATP is required per molecule of glucose in the energy investment phase of glycolysis?

Answer 15

2 ATP

Question 16

What occurs in the energy payoff phase of glycolysis?

Answer 16

‘Return on the investment’ of 2 ATP - making 2 net ATP.

Question 17

How many NADH are formed during glycolysis?

Answer 17

2 NADH + 2H+

Question 18

What is the byproduct of glycolysis?

Answer 18

2H2O in addition to the 2 pyruvate

Question 19

What is the net gain of ATP in glycolysis?

Answer 19

2 ATP per glucose molecule

Question 20

When does the physical splitting of a 6C to 3C molecule occur in glycolysis?

Answer 20

At the end of the investment phase - fructose 1,6-biphosphate is converted into two 3 carbon molecules by the aldolase enzyme

Question 21

What happens to the 3C molecules after they are split in glycolysis?

Answer 21

They are processed in the same way to form 2 identical pyruvate molecules

Question 22

Why does the conversion of Glucose-6-phosphate to Fructose-6-phosphate (second step in glycolysis) proceed despite having a positive delta G t standard conditions?

Answer 22

Cells are not in standard conditions of pH, etc. so the reaction is actually favourable

Question 23

What is the splitting reaction in glycolysis?

Answer 23

The aldolase enzyme is used to break 6 carbon FBP to 2 3 carbon sugars - DHAP and G-3-P

Question 24

How many phosphates do the 6 carbon sugars have before the splitting reaction in glycolysis?

Answer 24

2 phopshates each

Question 25

How many phosphates do the 3 carbon sugars have after the splitting reaction in glycolysis?

Answer 25

1 each

Question 26

What is the difference in energy source between substrate-level phosphorylation and oxidative phosphorylation?

Answer 26

In substrate-level phosphorylation, energy comes directly from substrate and there is a direct conversion of ADP to ATP. In oxidative phosphorylation, energy come indirectly from reduced on enzymes

Question 27

What is substrate level phosphorylation (SLP)?

Answer 27

The direct used of energy from a substrate molecule to drive the synthesis of ATP (or equivalent), in glycolysis thus involves the cleavage of a phosphate group from a glycerate molecule

Question 28

How is the addition of phosphate to 3 carbon molecule G-3-P in SLP powered?

Answer 28

The oxidation of G-3-P powers the addition without the need for ATP - NAD+ is reduced providing the oxidising power. This allows for an ATP profit later on when 1,3BPG is cleaved

Question 29

What is cleaved in the 1st substrate level phosphorylation?

Answer 29

Carbon 1 phosphate of 1,3-BPG, which is very reactive and releases energy for ADP phosphorylation when released.

Question 30

Why does arsenic inhibit glyocolysis?

Answer 30

Arsenate substitutes for phosphate, meaning that during cleavage the energy released is not captured as there is no appropriate enzyme so ATP cannot be synthesised.

Question 31

What occurs during the 2nd substrate level phosphorylation in glycolysis?

Answer 31

phosphate cleaved from PEP, releasing energy for the synthesis of ATP. The P is also transferred to ADP to make another ATP

Question 32

Is the delta G of glycolysis positive or negative?

Answer 32

Negative - pathway is energetically favourable

Question 33

What is pyruvate converted to in aerobic conditions?

Answer 33

acetyl-CoA

Question 34

Where does conversion of pyruvate to acetyl-CoA occur?

Answer 34

The mitochondrial matrix

Question 35

What type of reaction converts pyruvate to acetyl-CoA

Answer 35

Oxidative decarboxylation using pyruvate dehydrogenase enzyme

Question 36

What happens to pyruvate in anaerobic conditions?

Answer 36

Pyruvate is converted to lactate using lactate dehydrogenase, with energy captured in NADH in glycolysis lost to regenerate NADH to NAD+

Question 37

What is the purpose of lactate formation in anaerobic reactions of pyruvate?

Answer 37

NADH is oxidised to NAD+ which regenerates it for use in the G-3-P reaction of glycolysis, allowing glycolysis to continue generating ATP. This need arises due to low cellular concentration of NAD