2. 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
3. Anaerobic Respiration
Comprises of these stages:
glycolysis:
glucose 2 pyruvate + NADH
fermentation:
pyruvate lactic acid
or
ethanol
cellular respiration:
4. Aerobic Respiration
Comprises of these stages:
Oxidative decarboxylation of pyruvate
Citric Acid cycle
Oxidative phosphorylation/ Electron Transport
Chain(ETC)
5. Brief overview of STARCHY
catabolism of FOOD
glucose to generate
α – AMYLASE ; MALTASES
energy
Glucose Glucose converted to glu-6-PO4
Start of cycle
Glycolysis in
Cycle : anaerobic cytosol
Aerobic condition;
2[Pyruvate+ATP+NADH] in mitochondria
Anaerobic condition Pyruvate enters as AcetylcoA
- Krebs Cycle
Lactic Acid fermentation in
muscle. - E transport chain
Only in yeast/bacteria
Anaerobic respiration or
Alcohol fermentation
6. 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
ST
E P1
p.495
7. 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
9. 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?
10.
11. Controlling glucose
metabolism
• found in Cori cycle
• shows the cycling of
glucose due to
gycolysis in muscle and
gluconeogenesis in
liver
• This two metabolic
pathways are not active
simultaneously. As energy store for
• when the cell needs next exercise
ATP, glycolisys is more
active
•When there is little
need for ATP,
gluconeogenesis is
more active
Fig. 18-12, p.502
12. Cori cycle requires the net
hydrolysis of two ATP and two
GTP.
glu cos e + 2 NAD + + 2 ADP + 2 Pi →
+
2 Pyruvate + 2 NADH + 4 H + 2 ATP + 2 H 2O
+
2 Pyruvate + 2 NADH + 4 H + 4 ATP + 2GTP + 6 H 2O →
Glu cos e + 2 NAD + + 4 ADP + 2GDP + 6 Pi
2 ATP + 2GTP + 4 H 2O →
2 ADP + 2GDP + 4 Pi
14. 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 anabolism
The other name of citric acid cycle: Krebs cycle and
tricarboxylic acid cycle (TCA)
Takes place in mitochondria
35. Overall production from glycolysis, oxidative
decarboxylation and TCA:
Oxidative Glycolysis TCA cycle
decarboxylation
- 2 ATP 2 ATP
2 NADH 2 NADH 6 NADH , 2 FADH2
2 CO2 2 Pyruvate 4 CO2
Electron transportation system
37. 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
40. 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:
hexokinase
glucose --------------> glucose 6-phosphate
•There are three enzyme-catalyzed reactions:
phosphoglucomutase
glucose 6-phosphate ---------------------> glucose 1-phosphate
glucose 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 α (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
α(1,6) linkage at least 4 glucose units away from nearest branch.
44. REGULATION OF GLYCOGEN METABOLISM
Mobilization and synthesis of glycogen under hormonal control.
Three hormones involved:
1) Insulin
•51 a.a. protein made by β 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 α 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.
45. 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.
FIGURE 18.6 The pathways of gluconeogenesis and glycolysis. Species in blue, green, and pink shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate).
FIGURE 18.9 Pyruvate carboxylase catalyzes a compartmentalized reaction. Pyruvate is converted to oxaloacetate in the mitochondria. Because oxaloacetate cannot be transported across the mitochondrial membrane, it must be reduced to malate, transported to the cytosol, and then oxidized back to oxaloacetate before gluconeogenesis can continue.
FIGURE 18.12 The Cori cycle. Lactate produced in muscles by glycolysis is transported by the blood to the liver. Gluconeogenesis in the liver converts the lactate back to glucose, which can be carried back to the muscles by the blood. Glucose can be stored as glycogen until it is degraded by glycogenolysis. (NTP stands for nucleoside triphosphate.)
Gerty and Carl Cori, codiscoverers of the Cori cycle.
FIGURE 18.13 Control of liver pyruvate kinase by phosphorylation. When blood glucose is low, phosphorylation of pyruvate kinase is favored. The phosphorylated form is less active, thereby slowing glycolysis and allowing pyruvate to produce glucose by gluconeogenesis.
FIGURE 19.1 The central relationship of the citric acid cycle to catabolism. Amino acids, fatty acids, and glucose can all produce acetyl-CoA in stage 1 of catabolism. In stage 2, acetyl-CoA enters the citric acid cycle. Stages 1 and 2 produce reduced electron carriers (shown here as e-). In stage 3, the electrons enter the electron transport chain, which then produces ATP.
FIGURE 19.2 The structure of a mitochondrion. (a) Colored scanning electron microscope image showing the internal structure of a mitochondrion (green, magnified 19,200 x). (b) Interpretive drawing of the scanned image. (c) Perspective drawing of a mitochondrion. (For an electron micrograph of mitochondrial structure, see Figure 1.13.)
FIGURE 19.3 An overview of the citric acid cycle. Note the names of the enzymes. The loss of CO2 is indicated, as is the phosphorylation of GDP to GTP. The production of NADH and FADH2 is also indicated.
FIGURE 19.3 An overview of the citric acid cycle. Note the names of the enzymes. The loss of CO2 is indicated, as is the phosphorylation of GDP to GTP. The production of NADH and FADH2 is also indicated.
FIGURE 19.6 Three-point attachment to the enzyme aconitase makes the two -CH2-COO - ends of citrate stereochemically nonequivalent.
FIGURE 19.7 The isocitrate dehydrogenase reaction.
FIGURE 19.8 Control points in the conversion of pyruvate to acetyl-CoA and in the citric acid cycle.
FIGURE 19.10 A summary of catabolism, showing the central role of the citric acid cycle. Note that the end products of the catabolism of carbohydrates, lipids, and amino acids all appear. (PEP is phosphoenolpyruvate; -KG is ketoglutarate; TA is transamination; is a multistep pathway.)
FIGURE 19.11 How mammals keep an adequate supply of metabolic intermediates. An anabolic reaction uses a citric acid cycle intermediate ( - ketoglutarate is transaminated to glutamate in our example), competing with the rest of the cycle. The concentration of acetyl-CoA rises and signals the allosteric activation of pyruvate carboxylase to produce more oxaloacetate. * Anaplerotic reaction. **Part of glyoxylate pathway.
FIGURE 19.12 Transfer of the starting materials of gluconeogenesis from the mitochondrion to the cytosol. Note that phosphoenolpyruvate (PEP) can be transferred from the mitochondrion to the cytosol, as can malate. Oxaloacetate is not transported across the mitochondrial membrane. (1 is PEP carboxykinase in mitochondria; 2 is PEP carboxykinase in cytosol; other symbols are as in Figure 19.10.)
FIGURE 19.15 A summary of anabolism, showing the central role of the citric acid cycle. Note that there are pathways for the biosynthesis of carbohydrates, lipids, and amino acids. OAA is oxaloacetate, and ALA is -aminolevulinic acid. Symbols are as in Figure 19.10.)
Control of carbohydrate metabolism is important in physical activity of all sorts.
FIGURE 18.1 The highly branched structure of glycogen makes it possible for several glucose residues to be released at once to meet energy needs. This would not be possible with a linear polymer. The red dots indicate the terminal glucose residues that are released from glycogen. The more branch points there are, the more of these terminal residues that are available at one time.
FIGURE 18.2 The mode of action of the debranching enzyme in glycogen breakdown. The enzyme transfers three (1 4)-linked glucose residues from a limit branch to the end of another branch. The same enzyme also catalyzes the hydrolysis of the (1 6)-linked residue at the branch point.
FIGURE 18.3 The reaction catalyzed by glycogen synthase. A glucose residue is transferred from UDPG to the growing end of a glycogen chain in an (1 4) linkage.
FIGURE 18.4 The mode of action of the branching enzyme in glycogen synthesis. A segment seven residues long is transferred from a growing branch to a new branch point, where an (1 6) linkage is formed.