lecture 28 - glucose as a fuel molecule Flashcards
What is the name for the oxidation of glucose?
Glycolysis
Where does glycolysis occur is eukaryotes?
In the cytoplasm of cells - not in the mitochondria
What is the fuel of red blood cells, and why?
Glucose - energy can be extracted by glycolysis in the cytoplasm, as they do not have mitochondria for citric acid cycle and oxidative phosphorylation
What is the preferred fuel for the brain?
Glucose
What is a simple reason that the brain prefers glucose for fuel, as opposed to fats, etc.?
Glucose easily crosses the blood-brain barrier, but fats do not
Do brain cells have mitochondria?
Yes - means they can extract maximum energy from glucose
What is the preferred fuel molecule in the eye?
Glucose - glycolysis can proceed without oxygen or mitochondria, meaning that blood vessels and mitochondria do not affect refraction of light for vision
What are the 2 types of muscle, in terms of function and fuel type used?
Red (type 1) and white (type 2) muscle
What is the function of red muscle, and what is its preferred fuel type?
Endurance, uses fats for fuel
What is the function of white muscle, and what is its preferred fuel type?
Sprinting, glucose as fuel
What is the overall conversion in glycolysis?
Spitting of one molecule of glucose (6 Carbon) into 2 molecules of pyruvate (3 Carbon)
In what form is energy conserved in glycolysis?
In ATP and NADH
What are the 2 phases of glycolysis?
Energy investment phase, Energy payoff phase
What occurs in the energy investment phase of glycolysis?
Activation of glucose - gets the molecule into a form so energy can be captured and required an an energy input of 2 ATP
How much ATP is required per molecule of glucose in the energy investment phase of glycolysis?
2 ATP
What occurs in the energy payoff phase of glycolysis?
‘Return on the investment’ of 2 ATP - making 2 net ATP.
How many NADH are formed during glycolysis?
2 NADH + 2H+
What is the byproduct of glycolysis?
2H2O in addition to the 2 pyruvate
What is the net gain of ATP in glycolysis?
2 ATP per glucose molecule
When does the physical splitting of a 6C to 3C molecule occur in glycolysis?
At the end of the investment phase - fructose 1,6-biphosphate is converted into two 3 carbon molecules by the aldolase enzyme
What happens to the 3C molecules after they are split in glycolysis?
They are processed in the same way to form 2 identical pyruvate molecules
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?
Cells are not in standard conditions of pH, etc. so the reaction is actually favourable
What is the splitting reaction in glycolysis?
The aldolase enzyme is used to break 6 carbon FBP to 2 3 carbon sugars - DHAP and G-3-P
How many phosphates do the 6 carbon sugars have before the splitting reaction in glycolysis?
2 phopshates each
How many phosphates do the 3 carbon sugars have after the splitting reaction in glycolysis?
1 each
What is the difference in energy source between substrate-level phosphorylation and oxidative phosphorylation?
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
What is substrate level phosphorylation (SLP)?
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
How is the addition of phosphate to 3 carbon molecule G-3-P in SLP powered?
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
What is cleaved in the 1st substrate level phosphorylation?
Carbon 1 phosphate of 1,3-BPG, which is very reactive and releases energy for ADP phosphorylation when released.
Why does arsenic inhibit glyocolysis?
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.
What occurs during the 2nd substrate level phosphorylation in glycolysis?
phosphate cleaved from PEP, releasing energy for the synthesis of ATP. The P is also transferred to ADP to make another ATP
Is the delta G of glycolysis positive or negative?
Negative - pathway is energetically favourable
What is pyruvate converted to in aerobic conditions?
acetyl-CoA
Where does conversion of pyruvate to acetyl-CoA occur?
The mitochondrial matrix
What type of reaction converts pyruvate to acetyl-CoA
Oxidative decarboxylation using pyruvate dehydrogenase enzyme
What happens to pyruvate in anaerobic conditions?
Pyruvate is converted to lactate using lactate dehydrogenase, with energy captured in NADH in glycolysis lost to regenerate NADH to NAD+
What is the purpose of lactate formation in anaerobic reactions of pyruvate?
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
