28 Flashcards
What is glucose used as?
A fuel in all organisms (animals, fungi, plants, bacteria)
What is glucose oxidised in?
Glycolysis
Where does glycolysis happen
usually cytoplasmic in eukaryotes (other pathways mitochondrial)
Some cells in animals rlly on/ preferentially use…
Glucose
Glucose is essential as fuel for______ why?
red blood cells
Red blood cells do not have mitochondria, so do not have the other pathways
What is the preferred fuel in the brain but expand on ‘preferred’
- High energy requirement: human brain requires around 120 g of glucose per day
- Brain cells have mitochondria - can do other pathways
Why is glucose a preferred molecule?
ORIGNALLY: - Glucose easily crosses the blood-brain barrier, but fats do not (fats being the alternative source)
NOW: - A high level of fatty acid metabolism is dangerous - Relying on mitochondrial reactions and higher levels of oxygen risks anoxia (low oxygen) and higher production of damaging reactive oxygen species
Glucose is the favoured molecule in the _ _ _ WHY?
Eye
- blood vessels (bringing oxygen) and mitochodria would refract light in the optical path (lens, cornea) to retina
White muscles tend to use ______ red muscles tend to use_____
What is glycolysis
Splitting of glucose
- Conversion of one molecule of glucose (6 carbon) to two molecules of pyruvate (3 carbon)
- Pyruvate may be further metabolized aerobically or anaerobically
Where is energy conserved in glycolysis
Energy conserved in ATP and NADH
Two phases of glycolysis and the net
- Activation of glucose Getting the molecule into a form so energy can be captured Requires an energy input
- Return on the investment Making an ATP profit
(After glycolysis there is still carbon in pyruvate that can be extracted for energy)
What does the ‘energy investment’ phase entail? What does the ‘energy payoff’ phase entail?
- Splitting (6C to 3C) the
molecule occurs at the end of the investment phase - After a conversion, both 3C molecules are processed the same way
(On both sides ADP is getting phosphorlyated to ATP - both sides) - so for each split glucose these reactions are happening twice
The two molecules that split then what happens?
G3P continues on in glycolysis
DHAP cant go directly through and must be converted to G3P first
Key reactions for the activation of glucose
The splitting or aldolase reaction - what drives to relation of DHAP to G-3-P?
G-3-P is used in the energy payoff phase
- keeps concentration low
- drives reaction from DHAP to G-3-P
In terms of carbons and number of molecules and numbers of phosphates
The splitting or aldolase reaction
What enzyme allows the change from DHAP to G-3-P?
Triose phosphate isomerase (rearrangement)
How come DHAP and G-3-P aren’t actually at travelling in equal directions (equilibrium)
There isn’t 1 mol of each, G-3-P is used in the reaction pathway and therefore the reaction favours making more G-3-P from DHAP
(Always making both and only removing G-3-P)
Pathways for processing food molecules for ATP synthesis - Two key types of reactions:
- Those involving ADP and ATP ATP synthesis: ADP + Pi —> ATP
a. substrate-level phosphorylation- direct (A + ADP —> B + ATP) - energy comes from
substrate
b. oxidative phosphorylation - Indirect (reduced co-enzymes)
- direct (A + ADP —> B + ATP) - energy comes from
- Redox reactions Fuel molecules get oxidized
What is Substrate level phosphorylation (SLP)
The DIRECT use of energy from a substrate molecule to drive the synthesis of ATP (or equivalent)
How do you release the energy to drive a substrate-level phosphorylation what’s the problem with that?
One way to release the energy to drive a substrate-level phosphorylation is the cleavage of a high-energy phosphate ester bond on a substrate
But
But 1 ATP has been spent to add each phosphate on G-3-P….
….and we need a net gain of ATP in glycolysis
A key reaction for making an ATP profit: Oxidation of glyceraldehyde-3-phosphate - how does this work?
- NAD+ is reduced (provides oxidising power)
- phosphate from solution added to substrate
The addition of phosphate is powered by oxidation of G-3-P
The addition of phosphate does not require ATP
- glyceraldehyde-3-phosphate dehydrogenase uses the energy from the exisiting reaction to add the phosphate
(THIS IS HAPPENING TWICE FOR EACH GLUCOSE MOLECULE)
A key reaction for making an ATP profit: the 1 st substrate-level phosphorylation (SLP)
The #1 carbon phosphate of 1.3-BPG is very reactive
- phosphate is cleaved (phosphoglycerate kinase) releases energy (ΔG0´= -49.3 kJ/mol)
- energy used for substrate level phosphorylation
ADP + Pi —->ATP (ΔG0´= +30 kJ/mol)
Overall ΔG0´= -19.3 kJ/mol (coupled reaction)
P is also transferred to ADP to make ATP (not what makes it an SLP - its the energy that makes it a SLP)
How does arsenic poison glycolysis ?
- Arsenate (AsO4 -3) substitutes for phosphate (PO4-3)
- Unstable, arsenate hydrolyzed but energy not captured (as the enzyme is not used)
- ATP not synthesized by phosphoglycerate kinase
No net gain of ATP in glycolysis
How do we get form 3PG to PEP (what happens after first SLP)
Rearrangement: Getting the molecule into a form that enables the following reactions
A key reaction for making an ATP profit: the 2 nd substrate-level phosphorylation (SLP)
Phosphate cleaved: releases energy
ΔG0´= - 61.9 kJ/mol
Energy used for substrate- level phosphorylation
ADP + Pi —-> ATP
ΔG0´= +30 kJ/mol
Overall ΔG0´= -31.9 kJ/mol (coupled reaction)
P is also transferred to ADP to make ATP (not what makes it an SLP)
Overall reaction for glycolysis
Glucose + 2NAD + + 2ADP + 2Pi —-> 2 pyruvate + 2 NADH + 2ATP + 2H+
Glycolysis overall: ΔG0 ´= -73.3 kJ/mol
Pathway is energetically favourable
What happens to private under aerobic oxidation (O2 available)
Pyruvate is converted to acetyl-CoA to be further metabolized In the citric acid cycle
aerobic oxidation - standard thing that will happen -
Occurs in the mitochondrial matrix
Pyruvate dehydrogenase (enzyme)reaction
- Multienzyme complex with lots of cofactors/ coenzymes
Net reaction is an oxidative decarboxylation
- CO2 released (decarboxylation; 3C to 2C)
- pyruvate is oxidized, energy captured in NADH and used to
add Coenzyme A (CoA) to two-carbon chain
What does it mean Anaerobic glycolysis
Low oxygen
- red blood cells, muscles in anaerobic conditions
Anaerobic glycolysis of Pyruvate
When NADH is oxidised, the energy captured in the coenzyme NADH is lose
Lactate causes muscle fatigue
Why is pyruvate transformed into lactate in Anaerobic glycolysis
- low concentration of coenzymes in cells
- during aerobic oxidation coenzymes are oxidized (regenerated) in oxidative phosphorylation
- lactate dehydrogenase reaction oxidizes NAD
- allows for sufficient NAD+ for the glyceraldehyde-3- phosphate dehydrogenase reaction
- glycolysis can continue to generate ATP
