Cellular Metabolism Flashcards
What 6 types of metabolic reactions are present?
- Oxidation-reduction
- Ligand requiring ATP cleavage
- Isomerization
- Group transfer
- Hydrolytic
- Addition or removal of functional groups
What are oxidation-reduction reactions?
Electron transfer
What are ligation reactions?
Formation of covalent bonds
What are isomerization reactions?
Rearrangement of atoms to form isomers
What are group transfer reactions?
Transfer of a functional group from one molecule to another
What are hydrolytic reactions?
Cleavage of a bond by the addition of water
What are the reduction reactions?
Addition of electrons or the addition of hydrogen Removal of oxygen
What are oxidation reactions?
Addition of oxygen/removal of hydrogen
Name the hydrogen acceptors present within the electron transport chain:
Flavoprotein, coenzyme Q, cytochrome b,c,a
What is NAD?
Nicotinamide adenine dinucleotide. Coenzyme hydrogen acceptor. Oxidised form is denoted as NAD+
What is FAD?
Flavin adenine dinucleotide
What is the first step of glycolysis?
Glucose is phosphorylated into glucose-6-phosphate by hexokinase (Phosphoryl transfer)
Which enzyme catalyses the initial phosphorylation of glucose?
Hexokinase-4
What is step 2 of glycolysis?
Glucose-6-phosphate undergoes isomerization reactions into fructose-6-phosphate, under the action of phosphoglucoisomerase (Aldose to ketose)
What enzyme catalyses the isomerization of glucose-6-phosphate –> Fructose-6-phosphate?
Phosphoglucoisomerase
What is step 3 of glycolysis?
Fructose-6-phosphate is phosphorylated by ATP into fructose-1,6-bisphosphate by phosphofructokinase (group transfer)
How is fructose-6-phosphate phosphorylated into fructose-1,6-bisphosphate?
Phosphofructokinase
What is step 4 of glycolysis?
Fructose-1,6-bisphosphate is hydrolyzed into two molecules of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate (hydrolytic cleavage)
What molecules is fructose-1,6-bisphosphate hydrolysed into?
Glyceraldehyde-3-phosphate Dihydroxyacetone phosphate
What happens to dihydroxyacetone phosphate?
Undergoes isomerisation reaction into glyceraldehyde-3-phosphate via triosephosphate isomerase (TPI)
What is step 6 of glycolysis (Glyceraldehyde-3-phosphate –>)?
Dehydrogenated and phosphorylated by group transfer into 1,3-bisphosphoglycerate NAD+ is the hydrogen carrier,oxidises the molecule resulting in reduced NAD
How is reduced NAD formed through the conversion of glyceraldehyde-3-phosphate into 1,3bisphosphoglycerate?
Dehydrogenation of glyceraldehyde-3-phosphate reduces NAD into reduced NAD Oxidation-reduction reaction
What happens to 1,3-bisphosphoglycerate?
Under the action of phosphoglycerate kinase (group removal) into 3-phosphoglycerate (ADP is phosphorylated into ATP)
What enzyme catalyses the convention of 1,3bisphosphoglycerate into 3-phosphoglycerate?
Phosphoglycerate kinase
What is the destination of 3-phosphoglycerate?
3-Phosphoglycerate undergoes isomerization reaction into 2-phosphoglycerate by phosphoglycerate mutase
What enzyme isomerises 3-phosphoglycerate into 2-phosphoglycerate?
Phosphoglycerate mutase
What is the destination of 2-phosphoglycerate?
2-phosphoglycerate is converted into phosphoenolpyruvate by enolase (dehydration, water is removed)
What converts 2-phosphoglycerate into phosphoenolpyruvate?
Enolase
What type of reaction is the conversion of 2-phosphoglycerate into phosphoenolpyruvate?
Dehydration (water is removed)
What is the destination of phosphoenolpyruvate?
Phosphoenolpyruvate is converted into pyruvate by pyruvate kinase. ATP is formed
Where does glycolysis occur?
Cellular cytoplasm
What is glycolysis?
Substrate level phosphorylation of respiratory substrate glucose to synthesize pyruvate, ATP, and reduced NAD to generate ATP
Why is glucose phosphorylated?
Phosphorylation makes glucose more reactive, therefore unable to pass through cell membrane (negative charge)
How many gross ATP molecules is produced via glycolysis?
4
- (2 via 1,3bisphosphoglycerate –> 3-bisphosphoglycerate)
- 2 via phosphoenolpyruvate –> pyruvate
How many net ATP is produced?
2
What is the destination of the 2 NADH molecules under aerobic conditions?
Pass through the outer mitochondrial membrane into the electron transport chain
What is the destination of pyruvate under aerobic conditions?
Actively transported into the mitochondrial matrix, where it undergoes the link reaction
What is released from glucose phosphorylation into glucose-6-phosphate?
Proton
What ion is required to enable phosphorylation?
Magnesium ion
Why is magnesium required for the initial phosphorylation of glucose?
Positively charged ion shields negative ATP phosphate group.
What type of enzyme is phosphofructokinase?
Allosteric enzyme
Why is phosphofructokinase an allosteric enzyme?
The pace of glycolysis is dependent on enzyme activity, allosterically controlled by ATP. ATP is an inhibitor
What effect does ATP have on phosphofructokinase?
Inhibition
Why is the symmetrical configuration of hexose-bisphosphate useful?
High energy compound
What is mutase?
An enzyme that catalyzes the intramolecular shift of a chemical group (phosphoryl)
What are the advantages of enol phosphates? (Phosphoenolpyruvate)
Easier conversion to pyruvate due to higher group-transfer potential of the phosphoryl group in dehydration reactions.
What is the fate of pyruvate under anaerobic conditions?
Pyruvate is reduced to lactate by NADH to continue substrate-level phosphorylation via glycolysis. Lactate dehydrogenase (LDH) is used. Reoxidises NADH to continue glycolytic pathway. Occurs when oxygen is unavailable to be the final hydrogen acceptor during oxidative phosphorylation.
What enzyme is used for the reduction of pyruvate into lactate?
Pyruvate dehydrogenase
What is the benefit of pyruvate –> lactate conversion?
Reoxidises NADH to continue glycolytic ATP synthesis
What is the overall reaction for anaerobic respiration?
Glucose +2pi + 2ADP –> 2 Lactate + 2ATP + 2H2O
What is the fate of pyruvate under aerobic conditions?
Actively transported to mitochondrial matrix Link reaction Dehydrogenated and decarboxylated to an acetate Combines with Coenzyme-A (CoA) to form acetyl CoA
What enzymes convert pyruvate into acetyl-CoA?
Pyruvate dehydrogenase and pyruvate decarboxylase
What is the overall equation for the link reaction?
Pyruvate + NAD + CoA –> AcetylCoA + CO2 + NADH
What are the products of the link reaction per glucose molecule?
2 carbon dioxide 2 acetyl-CoA 2 NADH
What is the fate of pyruvate under anaerobic conditions in yeast?
Loses carbon dioxide –> Ethanal (Pyruvate decarboxylase) Ethanal is reduced by NADH to ethanol Alcoholic fermentation
What coenzyme assists with decarboxylation of pyruvate into ethanal?
Thiamine pyrophosphate
What is the neural response to lactate production?
Release of hydrogen ions enter into the blood, subsequently dropping blood pH Detected by chemoreceptors within the carotid sinus and aortic arch Triggers CNS to reduce muscle contraction, muscle have time to recover and return to aerobic respiration.
What happens to lactate in the blood plasma?
Transported to the liver, converted back to pyruvate
Where is lactate dehydrogenase predominantly located?
Heart, liver, kidneys, skeletal muscle, blood and lungs
What happens to LDH through cell necrosis?
Necrosis caused LDH release into circulation, hence influencing serum levels. Diagnostic of myocardial infarctions, liver disease, muscle injury, muscular dystrophy and pulmonary infarction
What is creatine phosphate?
Higher phosphoryl transfer potential than ATP. Thereby, ATP molecules having a relatively moderate intermediate position. Creatine phosphate reservoir within muscles, high potential phosphoryl groups, transferred to adp via creatine kinase
Which enzyme transfers the high potential phosphoryl group to ADP?
Creatine kinase
Which types of bonds exist in creatine phosphate?
Phosphoanhydride bonds
What is the equation of creatine phosphate?
Creatine phosphate + ADP + H= –> Creatine + ATP
What is Beri Beri?
Considered to be a thiamine deficient disease, damaged PNS Weakness of musculature
What is thiamine pyrophosphate?
Cofactor thiamine pyrophosphate to pyruvate dehydrogenase (PDH) Easily deprotonated into a carbanion that attacks pyruvate
How does thiamine pyrophosphate attack pyruvate easily?
Easily deprotonated into carbanion
What is the function of thiamine pyrophosphate?
Assists in the decarboxylation of pyruvate
What is the function of mitochondria?
Provides the site of aerobic respiration, releasing energy for the cell. The highly folded membrane provides proteins of the ETC for ATP synthesis by oxidative phosphorylation and Krebs cycle
What ribosomes does mitochondria possess?
70S
What is the initial amino acid of mitochondrial transcripts?
Formylated methionine
Where does the Krebs cycle occur?
The mitochondrial fluid matrix
What is the role of the Krebs cycle?
Convert the acetate group to carbon dioxide and hydrogen. Complete oxidation of glucose
What is the initial step of the Krebs cycle?
Coenzyme A transfers the 2-carbon acetate to a 4 carbon compound (oxaloacetate) to form citrate
What is isocitrate decarboxylated to?
Citrate –> alpha-ketoglutarate
What is citrate converted into?
isocitrate
Describe the Krebs cycle pathway:
Citrate –> isocitrate –> alpha-ketoglutarate –> Succinyl-CoA –> Succinate –>Fumarate –> Malate –> oxaloacetate
How many molecules of carbon dioxide is released by one turn of the krebs cycle?
2 molecules of carbon dioxide
What are the products of the Krebs cycle?
2CO2, 3 NADH, 1FADH2, 1 ATP + 1GTP
How many molecules of water required for one turn?
2 water molecules
What molecule supplies phosphate groups to phosphorylate ADP to ATP?
Creatine phosphate
Whats is a transamination reaction?
Process by which amino acids are removed and transferred to acceptor keto acids
Which molecules arise from transamination of amino acids?
Pyruvate, acetyl-CoA, aceteoacetyl-CoA, alpha-ketoglutarate Succinyl CoA Fumarate Oxaloacetate
Which 3 amino acids are susceptible for phosphorylation
Serine, threonine, tyrosine (OH) group
What is formed from an alanine + ketoacid?
Pyruvate and glutamate via aminotransferase
Why is the glycerol phosphate shuttle used?
This is because the inner mitochondrial membrane is relatively impermeable to NADH and NAD+ (Glycolytic derived) Electrons are transferred to glycerol-3-phosphate into the mitochondrial membrane
What molecules does NADH transfer electrons to?
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 catalyzes the transfer of electrons?
Cytosolic glycerol-3-phosphate dehydrogenase
What is the destination of glycerol-3-phosphate within the inner mitochondrial membrane?
The electron 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
How does FADH2 transfer electrons?
Ubiquinone (COQ) & complex II reduced in the intermitochondrial membrane, transfers electrons to coenzyme Q
Where does the malate-aspartate shuttle occur?
Within 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?
Traverses into the inner mitochondrial membrane, and is reoxidised by NAD+ , forming NADH and Oxaloacetate
How is the formed oxaloacetate be transported across the inner mitochondrial membrane to cytosol?
Oxaloacetate transaminated into aspartate and alpha ketoglutarate via glutamate
What is the reaction of oxaloacetate and glutamate?
Oxaloacetate + glutamate –> Asparate + alpha-ketoglutarate
What enzyme catalyses the transamination of oxaloacetate?
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 and oxaloacetate
What is oxidative phosphorylation?
Subsequent oxidation-reduction reactions in which electrons are transferred from reduced NAD/FAD by a series of electron carriers to the final hydrogen acceptor, oxygen; generating ATP through chemiosmosis.
What is cytochrome oxidase?
Enzyme that recieves electrons from cytochromes and is reduced.
What is the final hydrogen acceptor in the ETC?
oxygen
How are NADH oxidised?
Formation of hydride ion; electron pair donation Hydride ion dissociates into proton and 2 electrons
Which complexes within the ETC pump hydrogen ions into the intermembrane space?
Complex 1, 3, and 4 are associated with proton pumps which actively pump hydrogen ions to establish an electrochemical hydrogen ion gradient
Which complex do hydrogen ions pass through into the mitochondrial matrix?
Complex 5, associated with ATPase
Which enzyme resides within complex II?
Complex II contains succinate dehydrogenase
What is the role of succinate dehydrogenase?
Catalyses the oxidation of succinate to fumarate. Transfers electrons to FAD –> FADH2
How is FADH2 reoxidised back into fad?
Electrons are transferred from FADH2 to iron sulfide proteins in complex II. The electrons are passed to Coenzyme Q and are passed to complex III
What is the maximum number of ATP molecules produced by oxidative phosphorylation?
38
Why is the number of ATP molecules produced less than the theoretical maximum?
- ATP used to actively transport pyruvate into the mitchondrion
- ATP used to shuttle electrons from reduced glycolytic NAD
- Energy needed to transport ADP from cytoplasm to mitochondria
- Protons leak across the outermitochondrial membrane, reduces number of protons left to generate proton motive force
What is another name for Coenzyme Q?
Ubiquinone
What is the role of coenzyme Q?
Associated with Complex II; transfers electrons from complex 1 –> 3, and 2 –> 3 NADH dehyrogenase complex –> cytochrome bc1
Describe the order of electron transfer from NADH?
NADH dehydrogenase complex in 1 (Flavoprotein) –> Coenzyme Q –> Cytochrome bc1 –> Cytochrome C –> Cytochrome A (Complex IV) –> oxygen
How many ATP molecules are formed per reduced FAD molecule?
2 ATP molecules
What is the term used to describe the enzymes invovled in the ETC?
Oxidoreductases
What is the chemiosmotic theory?
Hydrogen ions are actively pumped from the matrix through the inner mitochondrial membrane to the intermembrane space. Concentration of protons increase, difference in pH, electrical potential difference occurs. Acidic conditions Proton motive force causes hydrogen ions to diffuse along the electrochemical and concentration gradient through stalked particles into the matrix. Energy released from hydrogen ion influx, drives the rotation of ATPase enzymes, stimulating the catalysis of ADP and inorganic phosphate ions into ATP
What does negative standard redox potentials imply?
Greater reducing power, tendency to donate electrons
What does positive standard redox potentials imply?
Position of equilibrium favours positive direction, thus stronger oxidising agent
How are the electron carries arranged within the ETC?
In order of increasing oxidising power; energetically favourable
What is the purpose of teflon in a clark electrode?
Form oxygen-permeable membrane lining the base of the chamber
What material comprises the cathode (-) in the Clark electrode?
Platinum
What material comprises the anode (+) in the Clark electrode?
Silver
What potential difference is applied across the Clark electrode?
+60V
What occurs at the platinum electrode?
Oxygen diffuses through the Teflon membrane and is reduced to water.
What occurs at the Silver electrode?
Silver atoms oxidized to Ag+, four electrons are released
What is the role of the silver electrode?
The released electrons are required for the reduction of oxygen into water, thus the concentration of oxygen is directly proportional to the current;
What is the relationship between current and oxygen?
Direct proportionality Greater the concentration of oxygen, the greater the flow of electrons
What two components comprise ATP synthase?
Membrane bound part (F0) and a part that projects into the matrix space (F1)
What protein subunits comprise F0?
a,b,c
What protein subunits comprise f1?
alpha, gamma, beta
Which subunit initially rotates in ATP-synthase, drived by hydrogen ion diffusion?
C subunits rotate, releasing energy that enable conformation change
Which f1 subunit is connected to c subunit and is subsequently rotated?
Gamma
How does ATP synthase allow the production of ATP?
- F0 rotates, converting the mechanical energy into kinetic energy
- This allows the transportation of H+ from the intermembranal space to the matrix
- Which synthesises ATP
What type of energy drives ATP synthesis?
Torsional energy
What are the mechanisms of actions of cyanide and azide?
Bind with high affinity to the ferric form of cytochrome oxidase (Complex IV), blocking final transfer of electrons to oxygen, inhibiting aerobic respiration
What is the mechanism of action of Arsenic?
Inhibits action of pyruvate dehydrogenase, thus pyruvate cannot be converted into Acetyl-CoA
What type of inhibitor is malonate?
Competitive inhibitor
What is the mechanism of action of malonate?
Resembles succinate, acts as a competitive inhibitor of succinate dehyrogenase. Thus slows down the flow of electrons from succinate to ubiquinone by inhibiting the oxidation of succinate to fumarate
What is End-product inhibition?
End product binds to early enzymes, rendering it inactive via non-competitive inhibition. Controls rate of reaction
What is the mechanism of action of oligomycin?
Antibiotic produced by streptomyces, inhibits oxidative phosphorylation by binding to the stalk of ATP synthase, blocks flow of protons into matrix. Accumulation of protons within the intermembrane space.
Why does the inhibition of ATP synthase by oligomycin present pathology?
Saturation of intermembrane space with protons means that protons cannot be actively pumped, inhibits ETC electron flow
What is the mechanism of action of DNP?
Shuttles protons across the inner mitochondrial membrane uncouples from oxidative phosphorylation from ATP synthesis. Increases metabolic rate and body temperature
What kind of molecule is DNP?
Proton ionophore
What does DNP cause?
Non-shivering thermogenesis
Why does non-shivering thermogensis occur?
Uncoupling of oxidative phosphorylation, UCP-1 (thermogenin), channel activated in response to drop in core body temperature, allows protons to bypass ATP synthase, releasing heat from dissipation of the proton gradient
