Cellular Metabolism 1 - Polysaccharides + Amino Acids Flashcards
+ Carbohydrates and amino acids
Catabolic Reactions?
Bond breaking
Anabolic Reactions?
Bond making (synthesising components)
3 Main Stages of Cellular Metabolism:
- Glycolysis - occurs in the cytosol, oxidation of glucose and reduction of NAD to generate ATP.
- TCA (TriCarboxylic Acid) cycle, occurs in the mitochondria.
- Oxidative Phosphorylation - occurs in the mitochondria, previously reduced co-factors from 1. and 2. are re-oxidised.
Which stage produces most ATP?
Oxidative Phosphorylation
What are the waste products from Cellular Metabolism?
H2O (from reduction of oxygen) and urea (from breakdown of amino acids)
∆G° for cellular oxidation of glucose = ?
-2872 kJ/ mol
∆G° for breaking of phosphoanhydride bond?
-31 kJ/ mol
How many molecules of ATP is generated for complete oxidation of glucose?
36-38
What does ∆G° have to be for the reaction to be feasible?
Negative
How is the Ea overcome in the reactions?
Enzymes and body temperature (heat)
Efficiency of this process?
41%
(-31 x 38) / -2872 = 0.41
What are the 6 types of reactions?
- Redox = electron transfer
- Ligation requiring ATP cleavage = covalent bond formation
- Isomerisation = rearrangement of atoms to form isomers
- Group Transfer = transfer functional group from one molecule to another
- Hydrolytic = Bond breaking by addition of H2O
- Addition or removal of functional groups = usually involves C=C double bond
Isomerase is responsible for…?
Isomerisation
Kinase is responsible for…?
Catalysing the transfer of phosphate groups from one molecule to another (group transfer)
Dehydrogenase is responsible for …?
Redox reactions
2 main stages of glycolysis?
- Form a high energy compound (invest ATP)
2. Split a high energy compound (generate ATP)
How many reactions in glycolysis?
10 small reactions (With small Eas)
Stage 1:
Equation
Type of Reaction
Glucose —-hexokinase—> glucose-6-phosphate + H+
Requires ATP, which adds a phosphate to the glucose (essentially irreversible commiting cell to glycolysis), forming ADP
Group transfer
Stage 2:
Equation
Type of Reaction
Glucose-6-phosphate —-phosphoglucose isomerase—> fructose-6-phosphate
Isomerisation
Stage 3:
Equation
Type of Reaction
fructose-6-phosphate —-phosphofructokinase—-> fructose-1,6-biphosphate
Requires ATP to form ADP
Group Transfer
Why are stages 2 and 3 important?
To try and make the molecule symmetrical
Stage 4:
Equation
Type of Reaction
fructose-1,6-biphosphate —-aldolase—-> glyceraldehyde-3-phosphate + dihydroxyacetone phosphate
2 high energy compounds produced
Hydrolytic
Stage 5:
Equation
Type of Reaction
dihydroxyacetone phosphate —-triose phosphate isomerase—-> glyceraldehyde 3-phosphate
End up with 2x glyceraldehyde 3-phosphate (one from stage 4)
Isomerisation
Stage 6:
Equation
Type of Reaction
This reaction occurs 2x:
glyceraldehyde 3-phosphate —-glyceraldehyde 3-phosphate dehydrogenase—-> 1,3-biphosphoglycerate
Requires NAD+ and Pi to form NADH (per reaction)
Redox and group transfer (dehydrogenation?)
Stage 7:
Equation
Type of Reaction
This reaction occurs 2x:
1,3-biphosphoglycerate —-phosphoglycerate kinase—-> 3-phosphoglycerate
Requires an ADP which accepts a Pi to form ATP (per reaction)
Group transfer
Stage 8:
Equation
Type of Reaction
This reaction occurs 2x:
3-phosphoglycerate —-phosphoglycerate mutase—-> 2-phosphoglycerate
Isomerisation
Stage 9:
Equation
Type of Reaction
This reaction occurs 2x:
2-phosphoglycerate —-enolase dehydration—-> phosphoenolpyruvate + H2O
Group removal
Stage 10:
Equation
Type of Reaction
This reaction occurs 2x:
phosphoenolpyruvate —-pyruvate kinase—-> pyruvate
Requires an ADP to form ATP (per reaction)
Group Transfer
Net result of glycolysis:
Uses 2ATP, produces 4ATP and 2NADH
Therefore 2ATP + 2NADH
What are the 3 fates of pyruvate?
- Alcohol Fermentation
- Lactate Production
- Acetyl CoA production
Why is pyruvate converted into another molecule (3 fates)?
NAD+ replenishment for the continuation of glycolysis
Alcohol Fermentation:
Equation
Type of Reaction
2 steps:
pyruvate —-pyruvate decarboxylase—-> acetaldehyde
Requires a H+ ion and releases a CO2 molecule
acetaldehyde —-alcohol dehydrogenase—-> ethanol
Requires NADH and H+ to form NAD+ and H2
Decarboxylation and dehydrogenation
Where does alcohol fermentation take place?
Anaerobic respiration in yeasts
Lactate Production:
Equation
Type of Reaction
pyruvate —-lactate dehydrogenase—-> lactate
Requires NADH and H+ to form NAD+ and H2
Redox
Where does lactate production take place, and why?
Anaerobic respiration in mammalians, because in order for glycolysis to continue, NAD+ must be replenished
What happens to the lactate afterwards?
Most of it is transported back to the liver, which has a large number of NAD+/NADH to covert the lactate back to pyruvate for other metabolic pathways
What can LDH (lactate dehydrogenase) and creatine kinase be used as a diagnostic tool for?
Strokes, heart attacks, muscle injuries
Why can LDH and creatine kinase be used as a diagnostic tool?
Normally, these are present within cells. When a cell dies or is damaged, they are released into the circulation, so serum levels of LDH are elevated
AcetylCoA production (Link Reaction)
Equation
Type of Reaction
Pyruvate + HS-CoA —-pyruvate dehydrogenase complex—-> AcetylCoA + CO2
Requires NAD+ and releases NADH
Decarboxylation and redox?
Where does the Link Reaction occur?
In the mitochondria
Why can Acetyl CoA readily donate acetate to other molecules?
The thioester bond is a high energy linkage that can be readily hydrolysed
PDH complex stands for?
Pyruvate dehydrogenase
PDH is made up of?
3 enzymes and 5 co-factor enzymes, including thiamine pyrophosphate (a co-factor)
Lipoamide Reductase Transacetylase (Lipoamide)
Dihydrolipoyl Dehydrogenase (FAD)
Pyruvate Decarboxylase (Thiamine Pyrophosphate)
Other co-factors: NAD+ and CoA
Why is thiamine pyrophosphate useful in the PDH complex?
It readily loses a proton, and the resulting carbanion attacks pyruvate
Where is thiamine derived from?
Vitamin B1
What does deficiency of Vitamin B1/ thiamine cause?
Symptoms and which organ is more vulnerable?
Beri-beri, symptoms include damage to PNS (peripheral nervous system), weakness of musculature, and decreased cardiac output.
The brain - relies on glucose metabolism
Creatine Phosphate as a Buffer:
Equation
creatine phosphate —-creatine kinase—-> creatine + ATP
Requires ADP + H+ to form the ATP
Why is creatine phosphate useful in muscles?
Buffers demands for phosphates, i.e is readily able to supply phosphates to ADP to form ATP for muscle contraction (substrate level phosphorylation)
Where does the Krebs/TCA cycle take place?
Mitochondrial Matrix
First step of TCA?
2C molecule from Acetyl CoA joins with oxaloacetate (4C molecule) to form citrate (6C molecule)
What processes does the citrate undergo?
2 decarboxylations, several redox reactions to generate several reduced co-factors
Net products of TCA per glucose
10 NADH, 2 FADH2, 2GTP (so each Acetyl CoA generates 5NADH, 1 FADH2, 1 GTP)
How many ATPs do the 10 NADH and 2 FADH2 make respectively after reoxidation in the ETC?
30 ATP + 4 ATP
So overall, including glycolysis, how many ATPs used and generated?
2 ATP used and (4 + 30 + 4) 38 ATP generated, and 2 GTP generated
The 2 methods to transport electrons from NADH in the cytoplasm (glycolysis) into the mitochondrial matrix:
- Glycerol-phosphate Shuttle - skeletal muscle, brain
2. Malate-Aspartate Shuttle - heart, kidney, liver
Glycerol Phosphate Shuttle:
Glycerol 3- phosphate dehydrogenase has 2 forms, one found in the cytosol, one found in the mitochondria.
The cytosolic glycerol 3-phosphate dehydrogenase transfers electrons from the NADH in the cytosol, to a molecule from stage 5 glycolysis, dihydroxyacetone phosphate (DHAP) to form glycerol 3-phosphate (G3P). The G3P then goes through the mitochondrial glycerol 3-phosphate dehydrogenase, which transfers electrons to FAD. They then get passed to co-enzyme Q, which is a part of the ETC.
Transamination
An amine group is exchanged for a keto group
Malate-Aspartate Shuttle:
The electrons from NADH are transferred to malate in the cytosol, which is able to travel into the mitochondria, and donate the electrons to NAD+ inside the mitochondria.
In the cytosol: Aspartate —-aspartate transaminase—-> oxaloacetate
Transamination
Oxaloacetate —-malate dehydrogenase—-> malate
Requires NADH which forms NAD+
Redox
The Malate is able to go into the mitochondria and the reverse reactions occur:
In the mitochondria: malate —-malate dehydrogenase—-> oxaloacetate
Requires NAD+ to form NADH
Redox
oxaloacetate —-aspartate trasminase—-> aspartate
The aspartate is able to the leave the mitochondria and enter the cytosol.
Generic mechanism for amino acids to enter glycolysis / TCA:
Amino Acid Degradation
Deamination of the amino acid (removal of amine group) to leave behind the carbon skeleton. This is then funneled into the production of glucose or fed into the Krebs Cycle
How many molecules does the degradation of all 20 amino acids result in?
7
Pyruvate, acetyl CoA, acetoacetyl CoA, a-ketoglutarate, succinyl CoA, fumarate and oxaloacetate
Protein metabolism involves which main type of reaction?
Transamination - amine group from amino acid tranferred to keto acid, to form a new pair of amino and keto acids.
Group Transfer
How is Alanine metabolised?
Alanine + a-ketoglutarate —-Alanine Aminotransferase(ALT)—-> pyruvate and glutamate
Pyruvate enters the TCA and the glutamate is converted to a-ketoglutarate by glutamate dehydrogenase, which removes the NH4+ group (that is eventually converted to urea).
What does increased ALT levels in the blood indicate?
Problems with the liver
Which 3 enzymes, if mutated, cause decreased TCA activity?
Isocitrate hydrogenase, succinate dehydrogenase, fumerase
Why does decreased TCA activity increase chances of cancer?
Cancer cells respire anaerobically to get ATP
What is the Warburg effect?
Mutations in those 3 enzymes can result in anaerobic respiration, despite high oxygen settings
Using this knowledge (cancer cells respire anaerobically), what is a potential method to treat cancer cells?
Force them to undergo oxidative phosphorylation (aerobic respiration) for their supply of ATP, which may perhaps turn them non-malignant
