Glucose is a very adaptable metabolite that is able to meet both the material and energy requirements of the cell. Unlike fats which mostly only meet energy requirements.
Reasons why the whole 2834 kJ/mol (from the complete oxidation of glucose) is not released as heat
Biological systems cannot utilise heat as a source of energy
No single reaction of metabolism requires this amount of energy to be released in one step
Always need to overcome the activation energy
Enzymes are capable of effecting only small changes when they catalyse biological reactions, releasing the energy in steps.
During the catabolism of glucose the molecule is broken down in small steps and the energy is released in usable amounts (~ -30 kJ/mol) in the form of chemical energy, with ATP being the energy carrier.
Ten steps to glycolysis
1. Glucose
2. 2 Pyruvate
3. 2 ATP
4. 2 NADH + 2H+
5. Energy investment
6. Energy payoff
Glycolysis occurs in the cytosol
Coenzymes in glucose catabolism
ATP/ADP deliver/receive phosphates
NADH/NAD+ involved in oxidation/reduction reactions
ATP is also involved in transferring energy between reactions.
Aldehyde
Carboxylate
A ketone with 2 methyls = acetone
General Enzyme Naming Convention
Enzymes named after their substrate plus the enzymatic activity
Kinases phosphorylate substrates
Phosphatases dephosphorylate substrates
Not all enzymes follow this convention because of how their functions were originally discovered
Knowing the substrates and the steps involved, allows you to also name the enzymes.
Glycolysis - STEP 1
1. ATP
2. ADP
3. Hexokinase
4. Mg2+
5. GLUCOSE
6. GLUCOSE-6-PHOSPHATE (G6P)
Glucose-6-phosphate (G6P)
Aldehyde at top
6 carbon compound
Hydroxyl groups on the same side except for third carbon from top
Glucose by itself cannot cross a membrane. Uses transport proteins e.g., GLUT2 to move from a high to a low concentration. This process does not require energy.
Phosphorylation prevents the glucose from Returning. Remember G -> G6P is irreversible, powered by the energy from ATP hydrolysis using this enzyme hexokinase. Can be reversed but using a different enzyme.
Glycolysis - STEP 2
1. GLUCOSE-6-PHOSPHATE (G6P)
2. FRUCTOSE-6-PHOSPHATE (F6P)
3. Phosphoglucose isomerase
Glycolysis - STEP 3
1. FRUCTOSE-6-PHOSPHATE (F6P)
2. FRUCTOSE-1,6-BISPHOSPHATE (F1,6P)
3. ATP
4. ADP
5. Phosphofructokinase
Fructose-1,6-bisphosphate (F1,6P)
Bisphosphate means two phosphate groups added to different places
Glycolysis - STEP 4
1. FRUCTOSE-1,6-BISPHOSPHATE (F1,6P)
2. Dihydroxyacetone phosphate (DHAP)
3. Glyceraldehyde-3-phosphate (GAP)
4. Aldolase
This reaction is readily reversible and is catalysed by aldolase. The enzyme derives its name from the reverse reaction, an aldol condensation (reaction between an aldehyde and a alcohol).
Glycolysis - STEP 5
1. DHAP
2. GAP
3. Triose phosphate isomerase
Glycolysis - STEP 6
1. Glyceraldehyde-3-phosphate (GAP)
2. 1,3-bisphosphoglycerate
3. NAD+
4. NADH + H+
5. GAP dehydrogenase
Dehydrogenase means it is an oxidation step in which an aldehyde is converted to a carboxylic acid.
An usual phosphorylation step as the Pi comes from solution and NOT from ATP. What is driving this reaction is the oxidation step which is exergonic.
Glycolysis - STEP 7
1. 1,3-bisphosphoglycerate
2. 3-phosphoglycerate
3. ADP
4. ATP
5. Phosphoglycerate kinase
1,3-bisphosphoglycerate
A carboxylic acid linked to a phosphate = phospho-anhydride
An acid from the phosphate and an acid from the carboxylic acid results in a greater negative deltaG. Phosphoester bond as a result of the reaction between an acid and an alcohol. This has a negative deltaG.
Glycolysis - STEP 8
1. 3-phosphoglycerate
2. 2-phosphoglycerate
3. Phosphoglycerate mutase
The phosphoester is not sufficiently exergonic to produce ATP from ADP but this rearrangement allows, in the next step, for such a compound to be formed.
Glycolysis - STEP 9
1. 2-phosphoglycerate
2. Phosphoenol-pyruvate
3. Enolase
Phosphoenol-pyruvate
Enol is an alkene with a hydroxyl group
Donation of the phosphate group allows the enol to convert into the mores stable ketone (pyruvate).
Glycolysis - STEP 10
1. Phosphoenol-pyruvate
2. Pyruvate
3. ADP
4. ATP
5. Pyruvate kinase
Glycolysis
Three irreversible steps
The hexose sugar is first phosphorylated at both ends before splitting
Conversation to GAP, followed by oxidation and phosphorylation with Pi results in the triose phosphorylated at both ends
The four phosphates are used to generate 4 ATP
2 ATPs used to prime glycolysis.
4 ATPs produced from the glycolytic pathway as a result of substrate level phosphorylation 2x(step 7 & 10).
2 NADHs generated (equivalent to 3 ATPs per NADH through oxidation via the electron transport chain).
8 ATPs net gained from the conversion of glucose to pyruvate and the re-oxidation of the 2 NADHs produced.
Acetone
A ketone with 2 methyls
Glycolysis occurs in plants, animal cells, fungi and microbes.