Cell Metabolism Flashcards
3 main stages of cellular metabolism
- Glycolysis
- TCA Cycle (tricarboxylic acid cycle)
- Oxidative phosphorylation
Definition of:
Glycolysis
Oxidation of glucose within the cystol of individual cells, generating ATP & NADH
substrate level phosphorylation of respiratory substrate glucose to synthesize pyruvate, ATP, NADH.
Definition of:
TCA cycle
Further oxidation of small molecules within the mitochondria of individual cells, generating ATP, NADH, FADH2 and waste products
Definition of:
Oxidative phosphorylation
Generation of ATP within the mitochondria by the reduction of O2 to H2O
(where the bulk of cellular ATP is generated)
Activation Energy barrier
large and needs to be overcome for the combustion of glucose & the free energy is released as heat
Glucose metabolism
Free energy liberated is invested in carries molecules such as ATP.
Relatively small activation energies overcome by enzymes & body temp
How many ATP molecules are made per glucose molecule?
38
6 types of reactions in metabolism
- Oxidation reduction
- Ligation requiring ATP cleavage
- Isomerization
- Group transfer
- Hydrolytic
- Addition or removal of functional groups
Definition of:
Oxidation-reduction
Electron transfer
Definition of:
Ligation requiring ATP cleavage
Formation of covalent bonds
i.e. carbon-carbon bonds
Definition of:
Isomerization
Rearrangement of atoms to form isomers
Definition of:
Group transfer
Transfer of a functional group from one molecule to another
Definition of:
Hydrolysis
Cleavage of bonds by the addition of water
Definition of:
Addition or removal of functional groups
Addition of functional groups to double bonds or their removal to form double bonds
Glycolysis end products
1 x 6 carbon molecule(Glucose) —(2 x ATP)—> 2 x 3 carbon molecules(Pyruvate)
(probably a throwback to the pathways used by prehistoric anaerobic bacteria)
2 main concepts of glycolysis
- Formation of a high energy compound
(involves the investment of E in the form of ATP) - Splitting of a high energy compound
(produces E in the form of ATP generation)
Glycolysis STEP 1
Glucose is phosphorylated into glucose-6-phosphate ( & H+)
enzyme: HEXOKINASE
- one ATP is turned into ADP
- irreversible
- traps glucose inside the cell bc of (-)ve charge
GROUP TRANSFER
Glycolysis STEP 2
Glucose-6-phosphate is turned into fructose-6-phosphate
enzyme: PHOSPHOGLUCOSE ISOMERASE
- aldose to ketose
- fructose can then be split into equal halves when cleaved later
ISOMERISATION
Which enzyme catalyses the phosphorylation of glucose into glucose-6-phosphate?
Hexokinase
Which enzyme catalyses the isomerization of glucose-6-phosphate into fructose-6-phosphate?
Phosphoglucose isomerase
Glycolysis STEP 3
Fructose-6-phosphate is phosphorylated by ATP into fructose-1,6-bisphosphate
enzyme: PHOSPHOFRUCTOKINASE
- regulation of enzyme -> entry of sugars into glycolysis pathway
GROUP TRANSFER
Which enzyme catalyses the phosphorylation of fructose-6-phosphate into fructose-1,6-bisphosphate?
phosphofructokinase
Glycolysis STEP 4
Fructose-1,6-bisphosphate is hydrolysed to glyceraldehyde-3-phosphate & dihydroxyacetone phosphate
enzyme: ALDOLASE
- 2 high energy compounds
HYDROLYTIC
Which enzyme catalyses the hydrolysis of fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate & dihydroxyacetone phosphate?
aldolase
Glycolysis STEP 5
Dihydroxyacetone phosphate is turned into glyceraldehyde-3-phosphate
enzyme: TRIOSE PHOSPHATE ISOMERASE (TPI)
- deficiency in TPI is the only glycolytic enzymopathy that is fatal- most sufferers die within 6 years
ISOMERISATION
Which enzyme catalyses the isomerisation of Dihydroxyacetone to glyceraldehyde-3-phosphate?
triose phosphate isomerase
Glycolysis STEP 6
2x glyceraldehyde-3-phosphate is dehydrogenated (oxidation) and phosphorylated into 1,3-bisphosphoglycerate
enzyme: GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE
- NAD+ –> NADH
-ATP –> ADP
REDOX & GROUP TRANSFER
Which enzyme catalyses the oxidation & phosphorylation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate?
glyceraldehyde-3-phosphate dehydrogenase
Glycolysis STEP 7
1,3-bisphosphoglycerate turned into 3-phosphoglycerate
enzyme: PHOSPHOGLYCERATE KINASE
- ADP –> ATP
GROUP TRANSFER
Which enzyme catalyses the conversion of 1,3-bisphosphoglycerate into 3-phosphoglycerate?
phosphoglycerate kinase
Glycolysis STEP 8
3-phosphpoglycerate is converted to 2-phosphoglycerate
enzyme: PHOSPHOGLYCERATE MUTASE
-shuffling of the phosphate group from the 3 to the 2 position (by removal and addition of phosphoryl groups)
ISOMERISATION
Which enzyme catalyses the isomerisation of 3-phosphpoglycerate to 2-phosphoglycerate?
phosphoglycerate mutase
Glycolysis STEP 9
2-phosphoglycerate is converted to phosphoenolpyruvate + H2O
enzyme: ENOLASE
-dehydration reaction (removes H and OH)
GROUP REMOVAL
Which enzyme catalyses the conversion of 2-phosphoglycerate into phosphoenolpyruvate?
enolase
Glycolysis STEP 10
Phosphoenolpyruvate is turned into pyruvate
enzyme: PYRUVATE KINASE
- ADP –> ATP
GROUP TRANSFER
Which enzyme catalyses the conversion of phosphoenolpyruvate into pyruvate?
pyruvate kinase
The net result of glycolysis?
- net gain of 2 ATP
2. 2 NADH
where does glycolysis take place?
Cellular cytoplasm
How many ATP molecules are produced during glycolysis?
4
2 via 1,3-bisphosphoglycerate
2 via phosphoenolpyruvate
Destination of NADH (aerobic conditions)
pass through outer mitochondrial membrane into the ETC
Destination of pyruvate? (aerobic conditions)
Actively transported into the mitochondrial matrix, where it undergoes the link reaction
What ion is required to enable phosphorylation?
Magnesium Ion
Why is mg required for the initial phosphorylation of glucose?
(+)vely charged ion shields negative ATP phosphate group
What type of enzyme is phosphofructokinase?
Allosteric enzyme
pace of glycolysis is dependent on enzyme activity, allosterically controlled by ATP
ATP is an inhibitor
Why is symmetrical configuration of hexose-bisphosphate useful?
High E compound
What is mutase?
An enzyme that catalyses the intramolecular shift of a chemical group (phosphoryl)
What are the advantages of enol phosphates? (phosphoenolpyruvate)
Dehydration elevates the group-transfer potential of the phosphoryl group. High phosphoryl transfer potential, thereby making it easier for the conversion into pyruvate & the generation of ATP
What is the fate of pyruvate under anaerobic conditions?
O2 cannot be the final e- acceptor
Pyruvate is reduced to lactate by NADH to continue substrate level phosphorylation via glycolysis
enzyme: LACTATE DEHYDROGENASE
- NADH –> NAD+ (reoxidation)
DEHYDROGENATION
Which enzyme catalyses the conversion of pyruvate to lactate?
lactate dehydrogenase
What is the benefit of pyruvate –> lactate conversion
Reoxidises NADH to continue glycolytic ATP synthesis
Lactate is transported to the liver, converted back to pyruvate
Overall reaction for anaerobic respiration
Glucose +2 Pi +2 ADP–> 2 Lactate + 2 ATP + 2 H20
Fate of pyruvate under aerobic conditions?
AT to mitochondrial matrix
Link Reaction
Dehydrogenated & decarboxylated to an acetate
Combines with Coenzyme-A (CoA) to form acetyl CoA
What is the fate of pyruvate?
(except anaerobic respiration)
yeast
- Pyruvate converted to acetaldehyde
enzyme: PYRUVATE DECARBOXYLASE
- H+ –> CO2
DECARBOXYLATION
- Acetaldehyde reduced to ethanol
enzyme: ALCOHOL DEHYDROGENASE
- NADH + H+ –> NAD+
REDUCTION
What is Creatine phosphate?
- acts as a source or buffer for ATP production
- doubles the time by which the cell is independent of respiration
- bonds: phosphoanhydride bonds
creatine phosphate reaction
Creatine phosphate is converted to creatine + ATP
enzyme: CREATINE KINASE
- ADP + H+ –> ATP
very thermodynamically favourable
Acetyl CoA generation
in the mitochondria
pyruvate + HS-CoA –> acetyl CoA + CO2
enzyme: PYRUVATE DEHYDROGENASE COMPLEX
- NAD+ –> NADH
- acetyl group is ligated to enzyme CoA & this carbonyl group here is lost as CO2
Structure of Acetyl CoA
thioester bond is a high-energy linkage– readily hydrolysed, enabling acetyl CoA to donate the acetate (2C) to other molecules
Pyruvate dehydrogenase complex consists of ..?
pyruvate dehydrogenase & pyruvate decarboxylase
Overall equation for the link reaction?
Pyruvate + NAD +CoA —> AcetylCoA + CO2 +NADH
Products of the Link reaction per glucose molecule
2 CO2
2 acetyl-CoA
2 NADH
What is Beri Beri?
Thiamine deficient disease, damaged PNS
Weakness of musculature
What is thiamine pyrophosphate?
Cofactor to the pyruvate dehydrogenase (PHD)
Easily deprotonated into a carbanion attacks pyruvate
What is the function of thiamine pyrophosphate?
Assists in the decarboxylation of pyruvate
Where does the Krebs cycle occur?
The mitochondrial fluid matrix
Role of the role of the krebs cycle?
convert the acetate group to CO2 & H
complete oxidation of glucose
Krebs Cycle STEP 1
ocxaloacetate–>
Coenzyme A transfers the 2-carbon acetate to a 4 carbon compound (OXALOACETATE) to form citrate
Krebs Cycle STEP 2
citrate–>
citrate –> isocitrate(6C)
Krebs Cycle STEP 3
isocitrate–>
citrate –> alpha-ketoglutarate (5C)
- NAD+ –> NADH
waste: CO2
Krebs Cycle STEP 4
a-ketoglutarate–>
a-ketoglutarate–> succinyl-CoA (4C)
- NAD+ –> NADH
waste: CO2
Krebs Cycle STEP 5
succinyl-CoA–>
Succinyl-CoA –> succinate (4C)
GTP released
Krebs Cycle STEP 6
succinate–>
succinate–> fumerate(4C)
-FAD –> FADH2
Krebs Cycle STEP 7
fumerate–>
fumerate –> malate (4C)
Krebs Cycle STEP 8
malate–>
malate –> oxaloacetate (4C)
-NAD+ –> NADH
Describe the krebs cycle pathway:
citrate –> isocitrate –> alpha-ketoglutarate –> succinyl-CoA –> succinate –> fumarate –> malate –> oxaloacetate
How many molecules of CO2 is released by one turn of the Krebs Cycle?
2 molecules
What are the products of the krebs cycle?
2 CO2 3 NADH 1 FADH2 1 ATP 1 GTP
How many molecules of H2O required for one turn?
2
What is a transamination reaction?
process by which amino acids are removed & transferred to acceptor keto acids
Which molecules arise from the transamination of a.a.?(7)
Pyruvate acetyl-CoA acetoacetyl-CoA alpha-ketoglutarate succinyl CoA fumarate oxaloacetate
Tricarboxylic acid cycle (TCA) waste products?
amino group is removed(excreted as urea)
carbon skeleton is funnelled into the production of glucose or Krebs Cycle
Which 3 a.a. are susceptible for phosphorylation?
Serine
threonine
tyrosin (OH) group
What is formed from an alanine + ketoacid?
Pyruvate & glutamate
enzyme: TRANSAMINASE
- switching amino group from one molecule to another
GROUP TRANSFER
Why is the glycerol phosphate shuttle used?
This is bc the inner mitochondrial membrane is relatively impermeable to NADH and NAD+ (Glycolytic derived)
Electrons are transferred to glycerol-3-phosphate into the mitochondrial membrane
enzyme: CYTOPLASMIC GLYCEROL-3-PHOSPHATE DEHYDROGENASE
What molecules does NADH transfer electrons to?
in glycerol phosphate shuttle
Dihydroxyacetone phosphate
Where is glycerol-3-phosphate located?
outer mitochondrial membrane
What happens to dihydroxyacetone phosphate upon electron donation?
Forms glycerol-3-phosphate
Which enzyme catalyses the transfer of e-?
Cytosolic glycerol-3-phosphate dehydrogenase
What is the destination of glycerol-3-phosphate within the inner mitochondrial membrane?
The e- pair is donated from glycerol-3-phosphate to FAD prophetic group of the mitochondrial glycerol dehydrogenase to produce dihydroxyacetone phosphate
How is dihydroxyacetone phosphate reformed?
Oxidation of glycerol-3-phosphate diffuses back into the cytosol to continue the shuttling process
What is subsequently formed via the glycerol phosphate shuttle?
FADH2
Where does the malate-aspartate shuttle occur?
within the heart and liver cells
What molecules does NADH transfer electrons to in the malate-aspartate shuttle?
oxaloacetate
What molecule is oxaloacetate converted into upon reduction via NADH ( malate-aspartate shuttle)?
Malate (Malate dehydrogenase catalyzes redox)
What enzyme catalyzes the reduction of oxaloacetate in the malate-aspartate shuttle?
Malate dehydrogenase
What is the destination of malate?
Transverses into the inner mitochondrial membrane, and is reoxidised by NAD+ forming NADH & oxaloacetate
How is the formed oxaloacetate be transported across the inner mitochondrial membrane to cytosol?
oxaloacetate transaminated into aspartate and alpha ketoglutarate via glutamate
Reaction of oxaloacetate & glutamate?
oxaloacetate + glutamate –> aspartate + alpha-ketoglutarate
enzyme: ASPARTATE-TRANSAMINASE
What is the fate of aspartate in the malate-aspartate shuttle?
Passes through the inner mitochondrial membrane into the cytosol, reacts with ketoacid to form glutamate & oxaloacetate
How many ATP molecules are produced by the reoxidation of one NADH?
3
How many ATP molecules are produced by the reoxidation of one FADH2?
2
Total ATP produced from the krebs Cycle?
3 x 3 + 1 x 2 + 1 = 12 ATP
What does a kinase enzyme catalyse?
Transfer a phosphate group to a substrate
What is substrate level phosphorylation?
Direct transfer of a high-energy phosphate group to ADP
What is lactate dehydrogenase? (LDH)
released when cells die into the circulation, hence serum levels of LDH, in diagnostic of tissue damage in situations such as a stroke & MI
