Cell Metabolism 1 Flashcards
What are the 6 types of reactions in metabolism and explain them?
- Oxidation reduction: electron transfer (catalysed by dehydrogenase)
- Ligation requiring ATP cleavage: formation of covalent bond (i.e. carbon-carbon bonds)
- Isomerisation (catalysed by isomerases)
- Group transfer: transfer of functional group from one molecule to another (catalysed by enzymes including kinases)
- Hydrolytic: cleavage of bonds by the addition of water
- Addition (to double bounds) or removal (to form double bonds) of function groups
What is the first reaction in glycolysis?
glucose hexokinase
(ATP to ADP)
glucose 6 phosphate + H+
What is the second reaction in glycolysis?
glucose-6-phosphate
phosphoglucose isomerase
Fructose-6-phosphate
What is the third reaction in glycolysis?
fructose-6-phosphate
phosphofuctvokinase (ATP to ADP)
Fructose 1-6-bisphosphate
What is the fourth reaction in glycolysis?
fructose 1-6- bisphosphate
aldose glyceraldehyde 3-phopshate and dihydroxyacetone phosphate
What is the fifth reaction in glycolysis?
dihydroxyacetone phosphate triosephopshate isomerase (TP1)
glyceraldehyde 3-phosphate
What is the sixth reaction in glycolysis?
2 x glyceraldehyde 3-phosphate glyceraldehyde
3-phosphate dehydrogenase (NAD to NADH)
1-3-bisphosphoglycerate
What is the seventh reaction in glycolysis?
1-3-bisphosphoglycerate
Phosphoglyeracte kinase (ADP to ATP)
3-phosphoglycerate
What is the eighth reaction in glycolysis?
3 phosphoglycerate
Phosphoglycerate mutase
2 phosphoglycerate
What is the ninth reaction in glycolysis?
2-phosphoglycerare
Enolase
Phosphoenolpyruvate + H2O
What is the tenth reaction in glycolysis
phosphoenolpyruvate
pyruvate kinase (ADP to ATP)
pyruvate
What is the net result of glycolysis?
- Net gain of 2 ATP molecules
- Net gain of 2 NADH molecules (which can be used to generate ATP)
- 2 pyruvate molecules per mole of glucose
What are the three fates of pyruvate?
- Alcoholic fermentation
- Lactate production
- Acetyl CoA production
What are the stages in alcoholic fermentation?
pyruvate pyruvate decarboxylate (H+CO2) acetaldehyde alcohol dehydrogenase (NADH + H+ to NAD+) ethanol
What is the generation of lactate?
pyruvate lactate dehydrogenase (NADH H+ to NAD+) lactate
Why is the regeneration of NAD+ important?
- They allow NAD+ to be regenerated and thus glycolysis to continue, in conditions of oxygen deprivation
- I.e. conditions in which the rate of NADH formation by glycolysis is greater than its rate of oxidation by the respiratory chain
- NAD+ you recall is needed for the dehydrogenation of glyceraldehyde 3-phosphate which is the first step in generating ATP for the body
How does creatine phosphate act as a buffer?
-In muscle the amount of ATP needed during exercise is only enough to sustain contraction for around one second -A large reservoir of creatine phosphate is on hand to buffer demands for phosphate (25mM creatine phosphate c.f. 4mM ATP in resting muscle) creatine phosphate creatine kinase (ADP + H+ to ATP) creatine + ATP
What happens to pyruvate before it enter TCA cycle?
-Turns to Acetyl CoA pyruvate + HS-CoA Pyruvate dehydrogenase complex (NAD+ to NADH) Acetyl CoA + CO2
Describe the TCA Cycle
1.. Each turn of cycle process tow molecules of CO2 (waste) plus three molecules of NADH, one molecule of GTP and one molecule of FADH2 2. The Krebs cycle enzymes (with one notable exception) are soluble proteins located in the mitochondrial matrix space 3.. The bulk of ATP is generated when the reduced coenzymes are re-oxidised with the help of oxygen (oxidative phosphorylation) 4. This re-oxidation means that the TCA cycle only operates under aerobic conditions
How do Amino acids act in TCA cycle?
- Amino acid degradation is to remove the amino group (which is eventually excreted as urea) whilst the carbon skeleton is either funnelled into the production of glucose or fed into the Krebs cycle 2. Degradaition of all twenty amino acids gives rise to only seven molecules: pyruvate, acetyl CoA, acetoacetyl CoA, a-ketoglutarate, succinyl CoA, fumarate and oxaloacetate
What are three complexes in oxidative phosphorylation?
- NADH Dehydrogenase complex
- Cytochrome b-c1 complex
- Cytochrome oxidase complex
What are the two mobile carriers in oxidative phosphorylation?
Ubiquinone (co-enzyme Cytochrome C
What does glycolysis use?
2x ATP
What does glycolysis produce?
x4 ATP, x2 NADH, x2 Pyruvate
What sort of process is glycolysis?
Anaerobic
What are the 3 fates of pyruvate?
- Alcoholic fermentation
- Lactate production -Both generate NAD+ to regenerate for glycolysis to continue
- Acetyl CoA production (create acetyl-CoA to enter TCA cycle)
What is Beri Beri?
-Deficiency of thiamine -Thiamine pyrophosphate is a cofactor of the Pyruvate Dehydrogenase complex. It readily loses the highlighted proton and the resulting carbanion attacks pyruvate.
What are symptoms of Beri Beri?
damage to the peripheral nervous system, weakness of the musculature and decreased cardiac output
What does each cycle of Krebs produce?
2x CO2 3x NADH 1x GTP 1x FADH2
How are amino acids removed?
-Amino group removed (excreted as urea) and carbon skeleton is either funnelled into the production of glucose or fed into the Krebs cycle.
What does the degradation of all 20 amino acids give rise to?
Pyruvate Acetyl CoA Acetoacetyl CoA a-ketoglutarate Succinyl CoA Fumarate Oxaloacetate
What is an example of amino acids in TCA cycle?
-Alanine (C3) undergoes transamination by the action of the enzyme alanine aminotransferase -Pyruvate can enter the TCA cycle -Glutamate is re-converted to a-ketoglutarate (NH4 side product to urea)
Why is NADH needed to enter the mitochondrial matrix?
To be used to regenerate NAD+
What are two shuttles to get NADH into mitochondrial matrix?
-The glycerol phosphate shuttle (skeletal muscle brain) -The malatate-aspartate shuttle (liver kidney and heart)
What is the glycol phosphate shuttle?
Electrons from NADH, rather than NADH itself are carried across mitochondrial membrane via a shuttle. 1. Cytosolic glycerol 3-phosphate (G3P) dehydrogenase transfers electrons from NADH to DHAP to generate glycerol 3-phosphate. 2. A membrane bound form of the same enzyme transfers the electrons to FAD. These then get passed to co-enzyme Q, part of the electron transport chain.
What happens in the malate aspartate shuttle?
-Transamination -AT-aspartate transaminase -MDH-malate dehydrogenase
What does oxidation of 1 x acetyl CoA molecule give?
3 x NADH + 1 x FADH2 + 1x GTP = 12 ATP
What happens in process of oxidative phosphorylation?
Re-oxidation of the reduced co-factors NADH and FADH2 by the process of oxidative phosphorylation yields the following:
Summarise respiration
-Glycolysis is a cytosolic process -2 x ATP = each mole of glucose -ATP is first invested to generate a high energy compound then split to generate ATP. -NAD+ is regenerated by the production of alcohol (yeasts) or lactate (mammals) -Acetyl CoA can be generated in the mitochondria Creatine phosphate buffers [ATP -For every Acetyl CoA molecule entering the TCA Cycle, GTP and several reduced co-factors are made (NADH, FADH2) -Amino acids can also enter the TCA cycle following transamination reactions -Electrons from NADH generated in glycolysis require two shuttles to enter the mitochondria -Both glycolysis and the TCA cycle generate useful synthetic building blocks
What does fatty acid metabolism produce?
Acetyl CoA
Where are fast derived from?
Diet De novo synthesis in liver Storage in adipose tissue
How are fats sorted?
-Fats are insoluble so require bile salts to be absorbed by the gut -Bile salts are created by the liver and stored in the gall bladder -Bile salts aid absorption of fat and fat-soluble vitamins (2, 7, 9, 10) -Lack of bile salts -> steatorrhoea (fatty, oily stools)
What is orlistat?
-Inhibits pancreatic and gastric lipases -Reduces fat absorption by 30% -Treats obesity for up to 2 years -SEs: abdominal pain, urgency to defecate, increased flatus, steatorrhoea
What do lipoproteins do?
-Lipoproteins transport lipids in the plasma -Categorised by density
What are chylomicrons?
-Fats (with bile salts) absorbed by enterocytes in brush border of small intestine -TGs incorporated into chylomicrons (CM) -> transported in lymphatics to thoracic duct -> left subclavian vein -They acquire apoproteins from HDL following release into the bloodstream -Lipoprotein lipase helps absorb the fats -> fatty acids then used for beta-oxidation
What is apoprotein formed by?
-Synthesized from cholesterol and phosphatidylcholine (lecithin) -Catalysed by Lecithin: Cholesterol Acyltransferase (LCAT)
What are HDLs?
-“good cholesterol” -> take cholesterol from peripheral tissues back to the liver for use or disposal (reverse cholesterol transport) -> lower total serum cholesterol.
What are LDL?
-“bad cholesterol” as prolonged elevation of LDL levels leads to atherosclerosis (hardening of the arteries)
What is beta oxidation?
-Fatty acid metabolism Beta-oxidation produces >50% the body’s energy -Predominates in times of fasting (uses fat stores) The “Runner’s Wall” is supposed to be the body switching from metabolising carbohydrate to metabolising fatty acids from fat in beta oxidation… -Fatty acids are converted ultimately into Acetyl CoA in the mitochondria which then goes on to produce ATP
What happens in beta oxidation?
- Fatty acids -> Acyl CoA 2. ATP->AMP; breaks x2 bonds 3. Acyl is carried across the membrane in acyl carnitine -> acyl bonds back to CoA 4. Primary Carnitine Deficiency (Autosomal Recessive) reduced uptake
What is the beta oxidation cycle?
-Cycle of oxidation, hydration, oxidation and thiolysis reactions (β-oxidation) -Palmitoyl CoA = 16C
What is the net result of each cycle of beta oxidation?
1x Acetyl CoA 1x Acyl CoA (2 carbons shorter)… 1x FADH2, 1x NADH
How many times does the beta oxidation cycle repeat?
-Cycle repeats (7 times) until a final 4-carbon Acyl CoA is metabolised into 2 final Acetyl CoA molecules -palmitoyl CoA + 7 FAD + 7 NAD+ + 7 H2O + 7 CoA 8 acetyl CoA + 7 FADH2 + 7 NADH
When does beta oxidation happen?
- Acetyl CoA from beta-oxidation enters TCA cycle when carbohydrate metabolism = fat metabolism 2. Oxaloacetate needed for Acetyl CoA entry to TCA cycle 3.When fat metabolism predominates (during fasting), acetyl CoA forms ketone bodies (don’t enter TCA cycle
What are ketone bodies?
Acetoacetate D-3-hydroxybutyrate Acetone
What is lipogenesis? What are the two enzymes involved?
-Instead of breakdown of fatty acids to generate energy… Creation of fats! [I.E. lipo (fat) genesis (creation)] -Two enzymes: 1. Acetyl CoA Carboxylase 2. Fatty Acid Synthase
What are differences between fatty acid oxidation and lipogenesis?
-Carriers: CoA vs ACP -Reducing Power: FAD/NAD+ vs NADPH -Locations: Mitochondrial Matrix vs Cytoplasm -In contrast to β–oxidation, Fatty acid biosynthesis involves just two enzymes: 1. Acetyl CoA Carboxylase and Fatty acid synthase. 2. Fatty acids are formed sequentially by decarboxylative condensation reactions involving the molecules acetyl-CoA and malonyl-CoA. 3, Following each round of elongation, the fatty acid undergoes reduction and dehydration by the sequential action of a ketoreductase (KR), dehydratase (DH), and enol reductase (ER) activity. 4.. The growing fatty acyl group is linked to an acyl carrier protein (ACP)
Where does lipogenesis occur?
liver, adipose, lactating breast tissue may also occur in cancer cells (target fatty acid synthase to remove energy source starve cancer)
What is elongation?
Elongation of the acyl group to make fatty acids longer than 16 carbons occurs separately from palmitate synthesis in the mitochondria and endoplasmic reticulum (ER)
Where does desaturation occur?
Desaturation of fatty acids requires the action of fatty acyl-CoA desaturases The enzyme that creates oleic acid and palmitoleic acid from stearate and palmitate, respectively, is called a ∆-9 desaturase, as it generates a double bond nine carbons from the terminal carboxyl group.
What are different types of acyl CoA dehydrogenase?
Acyl CoA dehydrogenase types – reduce different size Acyl CoA’s -Short-chain acyl-Co enzyme A dehydrogenase (<6C) -Medium-chain acyl-Co enzyme A dehydrogenase (C6-C12) -Long-chain 3-hydroxyacyl-Co enzyme A dehydrogenase (C13-C21) -Very long-chain acyl-Co enzyme A dehydrogenase (>C22)
What is MCADD?
-Beta-oxidation metabolic disorder) -MCADD - deficiency of medium type… (autosomal recessive) Can contribute to SIDS -Never go without food for longer than 10–12 hours (a typical overnight fast) -Adhere to a high carbohydrate diet -Patients with other illness resulting in appetite loss or severe vomiting need IV glucose to make sure that the body is not dependent on fatty acids for energy
Summarise lipids and fatty acid synthesis
- Lipids are derived from three sources
- Lipids are transported by lipoproteins of varying density
- Hydrophilic outer shell, hydrophobic core
- HDL and LDL are major lipoproteins
- Fatty acid synthesis (lipogenesis) uses distinct locations and mechanisms
- The process is usually restricted to liver, adipose and breast tissue and breast
- Disorders of β-oxidation can be life threatening if unmanaged.
- Lipids are conjugated to co-enzyme A and need carnitine to enter mitochondria
- They undergo a cycle of oxidation, hydration, oxidation and thiolysis reactions (β-oxidation)
- Each round shortens the acyl CoA by two carbons, generating one molecule of acetyl CoA, NADH and FADH2
- Fatty acid metabolism generates more ATP/mole than glucose metabolism
