MBC - Cell metabolism I&II Flashcards
What do enzymes that end with KINASE do?
Carry out group transfer/ phosphorylation reaction
What are two main concepts of Glycolysis ?
Formation and Splitting of ATP
What are the 6 types of reactions that define metabolism?
Redox Ligation with ATP cleavage Isomerization Group transfer Hydrolytic Addition/removal of functional groups
How many ATP per molecule of glucose is synthesised in complete oxidation?
36-38
How does glucose metabolism happen? (Cellular oxidation for glucose)
Small activation energy overcome by enzymes and body temp - process is broken down to several discrete steps
How does glucose combustion happen?
Large activation energy as heat given to glucose - produce CO2 and water
What is oxidative phosphorylation?
Mitochondrial process that reduces oxygen to produce ATP
What is glycolysis?
Anaerobic cytoplasmic process that oxidises glucose to produce ATP, NADH and pyruvate
What is the TCA cycle?
Mitochondrial process that oxidises small molecules to generate ATP, NADH, FADH2 - Tricarboxylic Acids (Kreb’s) Cycle
What are the 3 main stages of cellular metabolism?
- Glycolysis
- TCA cycle
- Oxidative phosphorylation
Catabolic pathways
Metabolic pathways that release energy by breaking down complex molecules into simpler compounds
Anabolic pathways
Metabolic pathways that consume energy to build complicated molecules from simpler ones
Glucose to glucose-6-phosphate + H+
Hexokinase transfer phosphate group, ATP hydrolysed to ADP
Why is step one (G to G6P) of glycolysis irreversible?
Glucose charged, cannot leave by transporters
Step 2: Glucose 6-phosphate to fructose 6-phosphate
Phosphoglucose isomerase (isomerization - rearrange compound)
Step 3: Fructose 6-phosphate ——–> ?
Fructose-1,6-bisphosphate by phosphofructokinase
Why isomerise G6P to F6P?
Create symmetry when cleaved
Step 4: Fructose 1,6-BP to G3P and DHAP
Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate (high energy compounds) by Aldolase in hydrolytic reaction
Why regulate phosphofructokinase?
To control entry of sugars into glycolysis pathway by negative feedback
Dihydroxyacetone phosphate (DHAP) to G3P
Triose phosphate isomerase (TPI)
Why deficiency in TPI is fatal? (Glycolytic enzymopathy)
Shortage of RBC (Haemolytic anaemia)
Where does the second half - the splitting for ATP begin?
after glyceraldehyde-3- phosphate (G3P) is produced
(2) Step 6: what are used in the redox and group transfer of G3P to 1,3-bisphosphoglycerate? (3)
Glyceraldehyde-3-phosphate dehydrogenase and cofactor NAD + Pi
(2) Step 7: What happens from 1,3-bisphosphoglycerate to 3-phosphoglycerate?
Phosphoglycerate kinase phosphorylyse ADP to ATP (phosphate) group transfer
(2) Step 8: 3-phosphoglycerate to 2-phosphoglycerate
Phosphoglycerate mutase isomerization
(2) Step 9: 2-phosphoglycerate to phosphoenolpyruvate + H2O
Enolase (group removal/Dehydration)
(2) Step 10: Phosphoenolpyruvate ———–> ?
Pyruvate by pyruvate kinase
Net ATP after Glycolysis
Loss 2 ATP to gain 4 ATP = 2 ATP (+2NADH)
What are the 3 fates of pyruvate?
Ethanol (Alcoholic fermentation)
Lactate
Acetyl-CoA
How does alcoholic fermentation happen?
Pyruvate decarboxylase removes carboxyl group, alcohol dehydrogenase reduces acetaldehyde to ethanol
How to generate lactate from pyruvate?
Pyruvate reduced by lactate dehydrogenase
What purpose do alcoholic fermentation and lactate production serve?
Allow cofactor NADH is oxidised to NAD+ (use in glycolysis when oxygen deprived)
What does creatine kinase do?
Catalyses the breakdown of creative phosphate into creatine and ATP by phosphorylation of ADP
What acts as a buffer for phosphate demands?
Creatine phosphate
How long does creatine phosphate extend when cell is independent of respiration?
Double the time, allow longer muscle contraction
Where and how is acetyl CoA generated from pyruvate? (Link reaction)
Mitochondrial process where pyruvate dehydrogenase complex PDH (series of enzymes) and cofactors HS-CoA and NAD+ –> NADH (carbonyl group lost [decarboxylation], rest [dehydrogenated] ligated to enzyme CoA)
What is Acetyl CoA?
Molecule with thioester bond readily hydrolysed to donate acetate (2C) to Krebs cycle
What results from poor PDH function?
PDH catalyses reaction of pyruvate forming acetyl CoA
Beri-Beri, damage to PNS
What and how many molecules are produced in one turn of Krebs cycle?
3 NADH, 1 GTP, 1 FADH2, 2CO2
Where is the TCA cycle located?
mitochondria matrix
Why does the TCA cycle only operate in aerobic conditions?
Need sufficient oxygen for oxidative phosphorylation to re-oxidise the reduced cofactors to generate bulk of ATP
What are the two forms amino acids enter the TCA cycle?
Glucogenic and Ketogenic
What do glucogenic amino acids form in the TCA cycle?
Glucose
What is the general strategy of amino acid degradation?
Remove amino group (excreted as urea)
Carbon skeleton into production of glucose or Krebs cycle to produce ATP
How many molecules/skeletons of the degradation of 20 amino acid give rise to?
7 *constituents of TCA cycle
What does transamination reaction do?
Get Keto acid to enter TCA with enzyme transaminas
How does transamination work?
Switch amino groups of the amino acid (1) and Keto acid (1) to form Keto acid (2) and amino acid (2)
How does NADH produced in glycolysis enter mitochondria from cytosol?
By 2 shuttles:
The Glycerol-phosphate shuttle
The Malate-aspartate shuttle
Where are the glycerol-phosphate shuttles?
Skeletal muscle, brain
Where are the Malate-aspartate shuttle?
Liver, kidney, heart
How does the glycerol-phosphate shuttle work?
- Cytoplasmic G3P dehydrogenase transfer e- from NADH to DHAP to generate G3P
- Membrane-bound G3P dehydrogenase transfer e- to FAD
- FAD –> Co-enzyme Q (ETC)
How does the Malate-aspartate shuttle work?
Malate and Aspartate go in and leave mitochondria by antiporters
Inside: Malate oxidised to oxaloacetate (keto1) [NAD+ capture e- –> NADH] & transamined to aspartate (amino2)
Outside: Aspartate (amino1) transamined to oxaloacetate (keto2) then reduced [capture e-] to form malate [generate NAD+]
As malate enters, a-keto glutamate (keto1) leaves to reduce aspartate(amino1) to oxaloacetate (keto2)
As Aspartate leaves, glutamate (amino1) enters to oxidise oxaloacetate (keto1) to aspartate (amino2)
How many ATP molecules are formed by re-oxidation of NADH and FADH2 respectively?
3 and 2
What would happen if there were mutation in TCA enzyme genes?
Decrease TCA activity
Enhance aerobic glycolysis
What is produced in TCA cycle?
GTP/ATP and reduced cofactors (NADH, FADH2)
What are redox reactions?
Electron transfer by dehydrogenases
What are isomerization reactions?
Rearrangements of atoms to form isomers by isomerases
What are ligation reactions?
Formation of covalent bond (require ATP cleavage)
What are group transfer reactions?
Transfer of functional group from one molecule to another by kinases
What are hydrolytic reactions?
Cleavage of bonds by addition of water
What are addition/removal of functional reactions?
Addition of group to remove double bond
Removal of group to form double bond
What are the amino acids that can be phosphorylated?
Serine, Threonine, tyrosine (contain OH- group)
How is LDH a diagnostic tool?
Elevated levels of LDH could diagnose stroke & myocardial infarction
What are the 5 main classes of lipids?
- Free fatty acids
- Triacyglycerols
- Phospholopieds
- Glycolipids
- Steroids
How is fatty acid stored?
As triacyglycerols (3 fatty acid + 1 Glycerol) in the cytoplasm. The ester linkage help neutralise carboxylic acid groups to keep pH in range
What are the ways in which Acetyl CoA is produced?
Glycolysis from glucose and Beta-oxidation from fatty acids
Where is Acetyl CoA production located?
Where ATP is synthesised, in the mitochondria
Where are fat derived from? (3)
- Diet
- De novo synthesis (liver) - Lipogenesis
- Storage in adipose (only in starvation) - broken down for metabolisation
Where are bile salts from?
Generated by the liver, stored in gall bladder
How does bile salt emulsify fat?
- Lipophobic outer section dissolves triacylglycerol
- Lipophilic (hydrophobic) interior contacting triacyglycerol break it down w/ enzyme pancreatic lipase into fatty acid
What happens in a lack of bile salts?
Fat passing through undigested/unabsorbed - cause Steatorrhea (fatty stool)
What inhibits fat absorption? (Treatment for obesity)
Orlistat - inhibits pancreatic lipases
- induce fat to go through undigested
What are the different types of lipoprotein?
Chylomicrons VLDL (very low density) IDL (intermediate) LDL (low) HDL (high)
What are chylomicrons for?
Dietary fat transport
Since lipids are highly hydrophobic, what are they transported in the plasma by?
Lipoproteins
What are HDLs for?
Reverse cholesterol transport (take cholesterol from peripheral tissue back to liver)
What are the characteristics of lipoproteins?
Monolayer of phospholipids
What are chylomicrons made of?
Apoprotein, phospholipid, triglyceride
What is the process of digestion of fat to tissue?
- Fat from diet absorbed by enterocytes
- Re-synthesise triglycerides and incorporate into chylomicron
- Chylomicron transported via lymphatics out into bloodstream (picking up apoprotein from HDL)
- Tissue use content of chylomicron
What happens when digesting chylomicrons?
Lipoprotein lipase located in capillary endothelial cell lining tissues (adipose, heart, skeletal muscle) recognise the apoprotein and induce degradation & digestion of triacylglyceride to from fatty acid and glycerol
Where is fatty acid and glycerol used?
Fatty acid - B-oxidation
Glycerol - return to liver for gluconeogenesis
What happens to the chylomicron remain?
- Picked up apoprotein from HDL in order to be recognised and uptake by liver
- Used to synthesis other molecules
What is the general anatomy of a lipoprotein?
- Phospholipid monolayer containing cholesterol & apoproteins
- Core of cholesterol esters and triacylglycerols
How are cholesterol esters synthesised?
In plasma, reaction from cholesterol and acyl chain of lecithin (catalysed by LCAT)
- transfer of acyl group onto cholesterol molecule
Why ester cholesterol molecules?
Increase hydrophobic so pack more tightly in lipoprotein core
Describe life cycle of VLDL, IDL, LDL, HDL
- VLDL produced from liver, apoprotein recognised by lipase
- Breakdown triacylglyceride into FFA & cholesterol (taken up by tissue) & glycerol
- Depleted VLDL transfers apoprotein to HDL –> turns into IDL
- HDL transfers cholesterol esters to IDL –> turns into LDL
- LDL either - content used for production of acetyl CoA,
then uptake by liver OR uptake by macrophages (PROBLEM: atherosclerosis)
What does prolonged elevation of LDL levels lead to?
Atherosclerosis
What is the difference between HDL and LDL?
- HDL lowers total serum cholesterol
- LDL transports cholesterol synthesised in liver to peripheral tissues
How does fatty acid generate acetyl CoA?
- Fatty acid converted to acyl CoA species
- Carnitine shuttle acyl CoA into matrix by translocase
- B-oxidation cycle to generate acetyl CoA
Where and how does fatty acid convert to acyl CoA species?
Outside mitochondria
Fatty acid + ATP + HS-CoA —> Acyl CoA + AMP + PPi
(hydrolyse phosphoanhydride bond to give 2Pi)
ATP–>AMP [2 high energy bond used]
How does the carnitine shuttle work?
- Couple acyl CoA to carnitine to form Acyl carnitine
- Translocase imports acyl carnitine and exports carnitine
- Enzyme catalyses reverse - CoA displaces carnitine to form acyl CoA in mitochondria
What is primary carnitine deficiency?
An autosomal recessive disorder, mutation in gene encoding carnitine tranporter
Reduced ability to uptake carnitine
[No FA –> no ATP –> no energy]
What happens in the B-oxidation cycle?
Acyl CoA undergoes oxidation, hydration, oxidation & thiolysis reactions. Result in a molecule of acetyl CoA and 2C shorter acyl CoA than original.
What happens to the Acetyl CoA generated by B-oxidation?
- Enters TCA cycle when B-oxidation & carbohydrate metabolism are balanced (since oxaloacetate is needed for entry)
- Forms ketone bodies (acetoacetate, D-3-hydroxybutyrate, acetone) when fat breakdown dominates during fasting
How many acetyl CoA, FADH2 and NADH are formed during the B-oxidation?
n+1 : n : n
What is important to remember when calculating no. of ATP molecules produced in fatty acid metabolism?
Used 2 ATP equivalent in step 1 - Fatty acid –> Acyl CoA
Fatty acid metabolism vs glucose metabolism
FA met. generates significantly more ATP/substrate than glucose met.
What are the two enzymes in FA biosynthesis?
Acetyl CoA Carboxylase
Fatty acid synthase
How is fatty acid synthesised from acetyl-CoA & malonyl-CoA?
Elongation by 2C undergoing condensation, reduction, dehydration and reduction
How is B-oxidation different to FA biosynthesis?
Carrier: Coenzyme A (Beta) vs Acyl Carrier Protein (synth)
Oxidising/reducing power: FAD/NAD+ (Beta) vs NADPH (synth)
Location: Mitochondrial matrix (Beta) vs Cytoplasm (synth)
Where does elongation of acyl group to make FA longer than 16 C occur?
Occurs separately from palmitate synthesis in the mitochondria and ER
What enzyme is needed for fatty acid desaturation?
Fatty acyl-CoA desaturases
What is the ratio of molecules generated in the synthesis of FA? (Acyl group, CO2, H2O. CoA-SH, NADP+)
1 : n : n-1 : n+1 : 2n
Acyl group:CO2:H2O:CoA-SH:NADP+
n=malonyl CoA (C3)
What is the enzyme that creates oleic acid and palmitoleic acid from sterate and palmitate?
Delta-9 desaturase
How does delta-9 desaturase create oleic acid and palmitoleic acid from sterate and palmitate?
By generating a double bond 9 carbons from the terminal carboxyl group
What body tissue is de novo FA biosynthesis restricted to in adults?
Liver
Adipose tissue
Lactating breast
How to we target FA synthetase (FASN) in cancer?
Use of cerulenin (antifungal antibiotic) to inhibit FASN to reduce tumour growth
What do Acyl-CoA-dehydrogenases do?
They catayse the initial step in each cycle of fatty acid Beta-oxidation within mitochondria matrix
Why are there many types of Acyl-CoA-dehydrogenases?
As Acyl CoA chain gets shorter, we need different enzymes to carry out catalysis
What are the different types of Acyl-CoA-dehydrogenase?
Short-chain (<6)
Medium-chain (6-12)
Long-chain 3-hydroxy (13-21)
Very long chain (>22)
What is the disorder of B-oxidation?
MCADD - Medium chain acyl CoA dehydrogenase deficiency
What is MCADD?
An autosomal recessive disorder of B-oxidation that can be fatal (can cause Sudden Infant Death Syndrome SIDS)
- not good at breaking down fatty acid to generate energy
- Patients should never go without food for more than 10-12 hours - need CARBohydrate diet
What treatment should be given to MCADD patients who have appetite loss or severe vomiting?
i.v. glucose to make sure the body is not dependent on fatty acids for energy
Why are B-oxidation and FA synthesis in different places?
Makes no sense to synthesise something in a location where it could also be readily broken down
What is so special about ketone body D-3-hydroxybutylate?
It has no keto group, it is simply an acid
What happens in the case of an ODD chain FA B-oxidation?
Produce Propionyl-CoA (3C) and acetyl CoA (in final cycle oxidation)
What does propionyl CoA (3C) do as a building block?
It undergoes a series of reaction to become succinyl CoA and enters TCA cycle
What is non-esterified FA transported by in the plasma?
Albumin - a gobular plasma protein
What are MCADD patients advised to do?
Go for high carbs diet
Avoid fasting
