ch03 cont
TRANSCRIPT
Carbohydrate metabolism
Break-down of glucose to generate energy
- Also known as Respiration. - Comprises of these different processes
depending on type of organism: I. Anaerobic Respiration II. Aerobic Respiration
Anaerobic Respiration
Comprises of these stages: glycolysis: glucose 2 pyruvate + NADH fermentation: pyruvate lactic acid or ethanol cellular respiration:
Aerobic Respiration
Comprises of these stages:Oxidative decarboxylation of pyruvate Citric Acid cycleOxidative phosphorylation/ Electron
Transport Chain(ETC)
STARCHY FOOD
α – AMYLASE ; MALTASES
Glycolysis in cytosol
Brief overview of catabolism of glucose to generate energy
Glucose converted to glu-6-PO4
Start of cycle
2[Pyruvate+ATP+NADH]
- Krebs Cycle
- E transport chain
Aerobic condition; in mitochondriaAnaerobic
condition
Lactic Acid fermentation in muscle.
Only in yeast/bacteria Anaerobic respiration or
Alcohol fermentation
Pyruvate enters as AcetylcoA
Glucose
Cycle : anaerobic
Gluconeogenesis
Conversion of pyruvate to glucose Biosynthesis and the degradation of many important
biomolecules follow different pathways There are three irreversible steps in glycolysis and the
differences bet. glycolysis and gluconeogenesis are found in these reactions
Different pathway, reactions and enzyme
p.495
STEP 1
is the biosynthesis of new glucose from non-CHO precursors.
this glucose is as a fuel source by the brain, testes, erythrocytes and kidney medulla
comprises of 9 steps and occurs in liver and kidney the process occurs when quantity of glycogen have been
depleted - Used to maintain blood glucose levels. Designed to make sure blood glucose levels are high
enough to meet the demands of brain and muscle (cannot do gluconeogenesis).
promotes by low blood glucose level and high ATP inhibits by low ATP occurs when [glu] is low or during periods of fasting/
starvation, or intense exercise pathway is highly endergonic *endergonic is energy consuming
STEP 2
The oxalocetate formed in the mitochondria have two fates:
- continue to form PEP- turned into malate by malate dehydrogenase and leave the mitochondria, have a reaction reverse by cytosolic malate dehydrogenase
Reason?
Fig. 18-12, p.502
Controlling glucose metabolism• found in Cori cycle• shows the cycling of glucose due to gycolysis in muscle and gluconeogenesis in liver
As energy store for next exercise
• This two metabolic pathways are not active simultaneously.• when the cell needs ATP, glycolisys is more active•When there is little need for ATP, gluconeogenesis is more active
Cori cycle requires the net hydrolysis of two ATP and two GTP.
OHATPHNADHPyruvate
PADPNADeglu i
222422
222cos
iPGDPADPNADeGlu
OHGTPATPHNADHPyruvate
6242cos
624422 2
iPGDPADP
OHGTPATP
422
422 2
Fig. 18-13, p.503
The Citric Acid cycle
Cycle where 30 to 32 molecules of ATP can be produced from glucose in complete aerobic oxidation
Amphibolic – play roles in both catabolism and anabolismThe other name of citric acid cycle: Krebs cycle and
tricarboxylic acid cycle (TCA)Takes place in mitochondria
Fig. 19-2, p.513
Fig. 19-3b, p.514
Steps 3,4,6 and 8 – oxidation reactions
5 enzymes make up the pyruvate dehydrogenase complex: pyruvate dehydrogenase (PDH) Dihydrolipoyl transacetylase Dihydrolipoyl dehydrogenase Pyruvate dehydrogenase kinase Pyruvate dehydrogenase phosphatase
Conversion of pyruvate to acetyl-CoA
p.518
Step 1 Formation of citrate
Table 19-1, p.518
Step 2 Isomerization
Fig. 19-6, p.519
cis-Aconitate as an intermediate in the conversion of citrate to isocitrate
Fig. 19-7, p.521
Step 3
Formation of α-ketoglutarate and CO2 – first oxidation
p.521
Step 4 Formation of succinyl-CoA and CO2 – 2nd oxidation
p.522
Step 5 Formation of succinate
p.523a
Step 6
Formation of fumarate – FAD-linked oxidation
p.524a
Step 7 Formation of L-malate
p.524b
Step 8 Regeneration of oxaloacetate – final oxidation step
Fig. 19-8, p.526
Krebs cycle produced:• 6 CO2
• 2 ATP• 6 NADH• 2 FADH2
Table 19-3, p.527
Fig. 19-10, p.530
Fig. 19-11, p.531
Fig. 19-12, p.533
Fig. 19-15, p.535
Overall production from glycolysis, oxidative decarboxylation and TCA:
Oxidative decarboxylatio
n
Glycolysis TCA cycle
- 2 ATP 2 ATP
2 NADH 2 NADH 6 NADH , 2 FADH2
2 CO2 2 Pyruvate 4 CO2
Electron transportation system
Fig. 18-CO, p.487
Glycogen stored in muscle and liver cells.
Important in maintaining blood glucose levels.
Glycogen structure: α-1,4 glycosidic linkages with α-1,6 branches.
Branches give multiple free ends for quicker breakdown or for more places to add additional units.
Fig. 18-1, p.488
STEP 1
STEP 2
Glycogen phosphorylase
Phosphoglucomutase
Fig. 18-2, p.489
Glycogen Synthesis
•Not reverse of glycogen degradation because different enzymes are used.•About 2/3 of glucose ingested during a meal is converted to glycogen.•First step is the first step of glycolysis:
hexokinaseglucose --------------> glucose 6-phosphate
•There are three enzyme-catalyzed reactions:
phosphoglucomutaseglucose 6-phosphate ---------------------> glucose 1-
phosphateglucose 1-phosphate ---------------> UDP-glucose (activated
form of glucose)glycogen synthase
UDP-glucose ----------------------> glycogen
•Glycogen synthase cannot initiate glycogen synthesis; requires preexisting primer of glycogen consisting of 4-8 glucose residues with (1,4) linkage.•Protein called glycogenin serves as anchor; also adds 7-8 glucose residues.•Addition of branches by branching enzyme (amylo-(1,4 --> 1,6)-transglycosylase).•Takes terminal 7 glucose residues from nonreducing end and attaches it via (1,6) linkage at least 4 glucose units away from nearest branch.
p.490
Fig. 18-3, p.491
Fig. 18-4, p.492
REGULATION OF GLYCOGEN METABOLISM
Mobilization and synthesis of glycogen under hormonal control.
Three hormones involved:
1) Insulin•51 a.a. protein made by cells of pancreas.•Secreted when [glucose] high --> increases rate of glucose transport into muscle and fat via GLUT4 glucose transporters.•Stimulates glycogen synthesis in liver.
2) Glucagon•29 a.a. protein secreted by cells of pancreas.•Operational under low [glucose].•Restores blood sugar levels by stimulating glycogen degradation.
3) Epinephrine•Stimulates glycogen mobilization to glucose 1-phosphate --> glucose 6-phosphate.•Increases rate of glycolysis in muscle and the amount of glucose in bloodstream.
Regulation of glycogen phosphorylase and glycogen synthase
•Reciprocal regulation.•Glycogen synthase -P --> inactive form (b).•Glycogen phosphorylase-P ---> active (a).
•When blood glucose is low, protein kinase A activated through hormonal action of glucagon --> glycogen synthase inactivated and phosphorylase kinase activated --> activates glycogen phosphorylase --> glycogen degradation occurs.
•Phosphorylase kinase also activated by increased [Ca2+] during muscle contraction.•To reverse the same pathway involves protein phosphatases, which remove phosphate groups from proteins --> dephosphorylates phosphorylase kinase and glycogen phosphorylase (both inactivated), but dephosphorylation of glycogen synthase activates this enzyme.
•Protein phosphatase-1 activated by insulin --> dephosphorylates glycogen synthase --> glycogen synthesis occurs.
•In liver, glycogen phosphorylase a inhibits phosphatase-1 --> no glycogen synthesis can occur.
•Glucose binding to protein phosphatase-1 activated protein phosphatase-1 --> it dephosphorylates glycogen phosphorylase --> inactivated --> no glycogen degradation.
•Protein phosphatase-1 can also dephosphorylate glycogen synthase --> active.
p.493