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The sum of chemical reactions in cells
- Energy (ATP) yielding.
- Conversion of fuels to end products.
- Energy (ATP) requiring
- Biosynthetic processes
- forming ATP by direct phosphorylation of ADP.
- Transfer of phsphoryl group from "high energy" to ADP.
- Does not require O2
- important for ATP in tissues short of 02, for example, exercising muscle.
- Requires O2
- For synthesis of ATP
- Oxidation of 2 nucleotides by electron transport chain
- 1. NADH
- 2. FADH2: flavin adenine dinucleotide
- "Emergency" energy-producing pathway when oxygen is the limiting factor
- important in RBC: they lack mitochondria, so they only use glycolysis.
- Exercising: When oxidative metabolism can't keep up with increased demand.
- The brain: Glucose is it's main fuel (120g/day)
- Pyruvate is the end product in mitochondria cells and from oxygen supply
- occurs in the cytosol
- Common step in BOTH Respiration and Fermentation
- uses 2ATP in energy investment phase & produces 4ATP in payoff phase.
- pyruvic is last step, if too much then turns acidic
- regulated by phosphofructokinase
- The oxidation of glucose to pyruvate
- oxygen is required to reoxidize NADH that formed during glyceraldehyde
- oxidative decarboxylation of pyruvate to acetyl CoA, a fuel of TCA(citric acid) cycle
- Glucose+2ADP+2NAD+ -> 2Pyruvate+2ATP+2NADH+2H
- (energy generated: 4atp + 5atp by oxidation of 2nadh) - Energy Invested: 2atp = 7ATP
- Electrons from NADH are transferred to electron transport chain(ETC) via 2 shuttle systems & NAD is returned to cytosol
- Net gain of 2atp & 2nadh/glucose
- Glycerol phosphate shuttle: 2nadh to 4 atp
- Malate asparate shuttle: 2nadh to 6ATP
- oxidation of glucose to lactate
- Pyrvate reduced to lactate as NADH is oxidized to NAD+
- Occurs without oxygen
- Allow ATP production in tissue lacking mitochondria ex; in RBC's and cells deprived of O2
- Glucose+2ATP --> 2Lactate -> 2ATP
- or glucose+2atp->2pyruvate+4atp+2nadh
- requires initial input of ATP
- Occurs in Cytoplasm
- provides substrate with 1st step in respiration
- Energy Invested: 2ATP - energy generated: 4ATP = 2ATP total
- reduction of pyruvate to lactate by lactate dehydrogenase NAD
- Net gain of 2atp & no NADH/glucose
- Lactate converts back to pyruvate in liver & excreted in the urine.
- RBC has no mitochondria so only anaerobic resp.
G Protein coupled receptor (GPCR)
Binding site for ligand (a hormone or neurotransmitter)
G Protein coupled receptor (GPCR)
Interacts with G-proteins
Slide 12: GTP-dependent regulatory proteins
- The G proteins (A,B,Y) sub-units bind to GTP and GDP to form a link between Receptor and Adenylyl Cyclase
- Inactive form: A is bound to to GDP
- Active form: A is bound to GTP and dissociates from B and Y sub-units.
- active state is short-lived because A has inherent GTPase activity, resulting in hydrolysis
- cAMP: 2nd messenger system
- CyclicAMP activates protein kinase A by binding to 2 regulatory subunits, causing release of active catalytic subunits
- Active subunits transfer phosphate from ATP to protein substrates
- Phphorylated proteins act directly on cell's ion channels, and in enzymes they become activated or inhibited
- Protein Kinase A can also phosporylate proteins that bind to DNA, causing changes in gene expression
Dephosphorylation of proteins
phosphate added to proteins by protein kinases are removed by protein phosphatases
Hydrolysis of cAMP
- cAMP -> 5AMP by cAMP phosphodiesterase
- 5amp is not intracellular signaling molecule
- Phosphodiesterase: Inhibited by methylxanthine derivatives such as theophylline in caffein
2 transport mechanisms for glucose to go into cells
- 1. NA+ independent, facilitated diffusion
- 2. Na+ Monosaccharide COtransporter system
- glucose transports from extracellular fluid
- In tissues such as muscle and fat, the hormone Insulin is required to transport
Ch.8 slide14, Control of Glucose: high glucose
Pancreas B cells are in effect, insulin takes glucose into target tissue.
Ch.8 slide14, Control of Glucose:Low glucose
Pancreas A cells are in effect, Glucagon is used in the target tissue.
COtransports 1 glucose or galactose, and 2 sodium ions
Transports glucose and galactose, not fructose.
Transports glucose, glactose, and fructose.
- transports glucose and galactose, not fructose.
- For Neurons
Transports fructose, but not glucose or galactose.
- Nicotinamide Adenine Dinucleotide
- oxidizing agent
- accepts 2 H to reduce to NADH+H+
- One H is in medium as proton H+.
- The other as hydride ion, H- attaches to the top of nico. ring.
1st step of glycolysis
- Phosphorylation of Glucose to Glucose-6-phosphate
- Irreversible & traps glucose inside cell
- 2 enzymes involved: Hexokinase, Glucokinase.
- present In all tissues
- active in low (Km) glucose conc.; High affinity for glucose. high substrate affinity.
- low (Vmax); doesn't phosphorylate more sugars (large amount of glucose) than the cell can use
- active in low glucose concentrations
- Can't phosphorylate large amount of glucose
- Inhibited by G-6-P
- Not induced by insulin
- Substrate specificity: Glucose, fructose, galactose.
- Role: provides cells with Glu. 6 Phos. needed for energy
- In liver and pancreatic B cells
- (high Km): Active in high glucose concentrations. low substrate affinity.
- (High Vmax): Phosphorylates large amount of glucose
- Induced by insulin
- Not inhibited by Glucose-6-Phos. but promotes clearance of glucose by liver in FED (Feeding) state
- Substrate Specificity: Glucose only
- Role: allows for intracellular glucose to convert to glycogen or triacylglycerols.
- indirectly inhibited by fruct6phos
- indirectly stimulated by glucose
- functions as a glucose sensor in maintenance of blood glucose homeostasis.
- Diabetes type 2 (maturity onset) decrease the activity of glucokinase
Isomerization of glucose 6 phosphate
- Isomerization of glu6phos to Fructose 6-phosphate
- catalyzed by phosphoglucose isomerase
- reversible reaction
- Not rate-limiting or regulated step
- important control point
- committed step of glycolysis.
regulation of energy in PFK-1
- Inhibited allosterically by high levels of ATP, and high levels of citrate (indicates cell is making ATP).
- Activated allosterically by high conc. of of AMP, with which energy stores are depleted, and fruc. 2,6 Biphosphate formed by PFK2.
- 1 ATP is utilized
Most potent activator of PFK-1
- Fructose 2,6-bisphosphate
- Activates enzyme even when ATP levels are high.
- Formed by phosphofructokinase-2 (PFK-1)
- Kinase activity: produces fructose 2,6biphosphate
- Phosphatase activity: dephosphorylates fructose 2,6 bisphosphate to to fructose 6-phosphate.
- In liver-kinase domain is active if dephosphorylated, inactive if phosphorylated.
Phosphorylation of glucose to glucose-6-phosphate
- 1st regulated step in glycolysis
- Irreversible: traps glucose inside the cell
- 1. ATP utilized
- 2. enzymes involved (hexokinase & glucokinase)
- induction of insulin (increased) and lack of inhibition of G6P promote clearance of glucose by liver.
- Decreased levels of glucagon and elevated levels of of insulin following a carb-rich meal.
- Increase fructose 2,6-bisphosphate
- intracellular signal, glucose is abundant.
Starvation (fasting state)
- elevated levels of glucagon, low levels of insulin occur during fasting.
- decrease in intracellular conc. of fruc 2,6 bisphos.
- decrease in glycolysis
- inrease in gluconeogenesis
- Glycerol 3-P is converted to DHAP(used in gluconeogenesis)
pg.100 High Insulin/glucagon ratio causes *
- decreased cAMP
- reduced active protein kinase A
decreased protein kinase A favors *
Dephosphorylation of pfk-2/FBP-2
Dephosphorylated pfk2 is active when *
FBP-2 is inactive; favors fructose 2,6-bisphosphate.
Elevated fructose 2,6-bisphosphate activates *
PFK-1; which leads to increased glycolysis.
Reversible reaction ?
conversion of G6P to Fructose-6-phosphate
Irreversible reaction ?
conversion of F-6-P to 1,6 bisphosphate by PFK1
Rate limiting step of glycolysis
Fructose 2,6 biophosphate controlled by
Reversible conversion of F-1,6 bisphosphate to ?
3 Carbon by aldolase A. triophosphate isomerase
slide 31: triophosphate isomerase reversibly converts ?
glyceraldehyde 3 phosphate to dihydroacetone phosphate (DHAP)
DHAP reversibly converts ?
glycerol 3 phosphate by glycerol 3 phatsphate dehydrogenase (needs NADH as cofactor)
Slide 33: Reversible glyceraldehyde 3P to 1,3BPG by glyc. 3P dehydrogenase using
NAD(must be replenished for glycolysis to continue)
Regulation & irreversible rxn involves
conversion of PEP to pyruvate by kinase
Anaerobic Respiration/metabolic acidosis/anaerobic glycolysis
- reversible conversion of pyruvate to lactate by lactate dehydrogenase using NADH cofactor
- in shock, extreme exercise cyanide poison, CO poisoning
- In alcoholics do to inc. NADH
over production or under utilization of lactic acid leads to lactic acidosis
Genetic defects/toxins that inhibit glycolysis
- Recessive inherited pyruvate kinase defeciency: have up to 25% normal PK
- Fluoride ions inhibit enolase
- arsenate works as an uncoupling agent to substrate by binding to P-glycerate kinase & glyc-hyde3P Dehydrnase.
pathway proceeding without ATP synthesis. Resulting in 0 ATP yield.
regulated rxns are also irreversible rxns
8.2 rxn catalyzed by PFK1
is the rate limiting rxn of glycolytic pathway
8.3 contracting skeletal muscle shows
incr. conversion pyruvate to lactate.
8.4. pt has weakness, fatigue, sob, vertigo. hemoglobin <7(normal 13.5), isolated RBC's, low lactate production. what anemia is this?
(this is defect in glycolysis)
ethanol synthesis ?
- in yeast and bacteria (inestinal flora)
- thiamine pyrophosphate dependent pathway
Pyruvate dehydrogenase complex ?
- inhibited by acetyl CoA
- source of Acetyl coA for TCA and faty acid synthesis
Pyruvate carboxylase ?
- activated by Acetyl CoA
- replenishes intermediates of TCA
- provide substrate for gluconeogen.
nutrients like Carbs, fats, proteins through catabolism gives you
energy poor productus CO2, H20, NH3
Precursor molecules like AA's sugars, fatty acids, nitrogenous bases through Anabolism give you
complex molecules like proteins, polysaccarieds, lipids, nucleic acids.
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