biochemistry of MSS prepared by Fikadu Seyoum Tola. This ppt essentially discuss about collegen biosnthesis, defect and muscle energy metabolism with its regulations.

1. Introduction to
• CARBOHYDRATE
• DIGESTION
• ABSORPTION

2. Brain storm
1. How glucose inters to the cell for metabolism
2. What is metabolism
3. What is metabolic pathway
4. What is glycolysis
5. What is the d/c b/n Anaerobic and Aerobic glycolysis
6. How many ATP produced by glycolysis
7. Which cell is completely depend on glycolysis to gain energy
8. Which organ use the most daily required glucose/energy?

3. Introduction to carbohydrate
CHO is chemically defined as aldehyde or ketone derivative of higher polyhydric
alcohol.
Carbohydrates are polyhydroxy containing molecules in its structure.
CHO is the most abundant organic molecules in the nature.
The name of carbohydrate came from hydrates of carbon.
The empiric formula for many simpler carbohydrates is (CH2O)n, where n >3.

4. Major function of carbohydrate
Major energy source of most organism
Storage form of energy in the body
Structural components of cell wall, exoskeleton and, cell membrane
Precursors of many others compounds in cell

5. Carbohydrate classification
1. Based on the number of sugar units
Monosaccharides= simple sugar that cannot hydrolyzed further. General formula : CnH2nOn
Disaccharides=Yields two molecules of the same or different molecules of monosaccharide on
hydrolysis. General formula : Cn(H2O)n-1
Oligosaccharides=Those sugars which yield 3 to 10 monosaccharide units on hydrolysis, e.g.
Maltotriose.
Polysaccharides=above ten monosaccharides.

6. Summary of CHO Digestion

7. CHO Absorption from GIT

8. CHO absorption
• All monosaccharides, are completely absorbed from the small intestine.
• Some disaccharides, which escape digestion, may enter the cells lining
intestinal lumen may be by pinocytosis; and are hydrolyzed within these
cells
• No carbohydrates higher than the monosaccharides can be absorbed
directly into the bloodstream in normal health.
• If they administered parenterally, they are eliminated as foreign bodies.

9. Mechanism of sugar absorption
1. Active transport Mechanisms:
Glucose and galactose are absorbed actively and it requires energy.
Sodium dependent sugar carrier-protein is called sodium-glucose co-transporter.
Sodium binding changes the conformation of the protein molecule, enabling the binding of
glucose to take place and thus the absorption to occur
2. Facilitated transport:
 Fructose and mannose is absorbed by facilitated transport
3. Simple passive diffusion:
 L-form of glucose and galactose, pentose sugars

10. Active transport
• It has two binding sites one for sodium and another for the glucose.
• It is sodium-dependent and energy-dependent.

11. Mechanism of Facilitated Transport

12. Facilitated Transport Vs Active Transport
Similarities
Both appear to involve carrier proteins.
Both show specificity.
Carrier’ is saturable so it has maximum
rate of transport.
Structurally similar competitive
inhibitors block transport.
Differences
Facilitated transport can act bi-
directionally,
 Active transport is unidirectional.
Active transport occur against chemical
gradient and hence requires energy.
Facilitated transport does not require
energy

13. Rate of monosaccharide absorption
• Cori studied the rate of absorption of different sugars from small intestine in rat
• The above study proves that glucose and galactose are absorbed very fast; fructose and
mannose intermediate rate and the pentoses are absorbed slowly

14. How Glucose inters to the cells

15. How glucose inters into the cell
• Since glucose is polar and hydrophilic molecule it cannot diffuse directly to the
cell
• There are a transport mechanism through which glucose get into the cells.
Transport mechanism
Na-independent facilitated diffusion Na-dependent glucose transport
They are designated GLUT-1 to GLUT-14 SGLT-1
No energy requiring, down conc. Energy is required
They are facilitated diffusion Move against conc.gradient

16. Glucose transporter specialization function
• In facilitated diffusion, glucose movement follows a concentration gradient (from a high glucose
concentration to a lower one.
• However, GLUT-2, which is found in the liver and kidney, can transport glucose into these cells
when blood glucose levels are high,
• It also transport glucose from the cells to the blood when blood glucose levels are low

17. Glucose transporters
Adopted from text book of medical biochemistry, 8th edition

18. Fates of Glucose in the cell
What are the four(4) major fate of glucose?
1.To synthesize large polymers like glycogen, starch, cellulose
2.Metabolized to three carbon pyruvate and other intermediate through
glycolysis
3.To oxidized via PPP to yield ribose-5-phosphate and NADPH
4.To yield extracellular matrix and cell wall synthesis

19. Glycolysis

20. Introduction to glucose metabolism
• Glucose is the preferred source of energy for most of the body tissues.
• When the glucose metabolism is deranged, life threatening conditions may occur.
• Normal fasting plasma glucose level is 70 to 110mg/dL.
• After a heavy carbohydrate meal, it might reach up to 150 mg/dL
• Brain use approximately 120g/day glucose

21. What is metabolism
• The sum of all chemical transformation that occur inside the cell is called metabolism
• Metabolism can be catabolism or anabolism
• A series of reaction catalyzed by multienzyme sequence in which the product of one reaction
become the substrate for the next reaction is called metabolic pathway

22. Glycolysis
The word glycolysis derived from Greek word (glykys, “sweet” or “sugar,” and lysis,
“splitting”).
Glycolysis is the metabolic pathway through which glucose molecule is degraded in
series of enzyme-catalyzed reaction to yield 2 molecules of three carbon cpd called
pyruvate.
Glucose is not only an excellent source of fuel, but also provide intermediate metabolites
Amino acid
 Fatty acid
 Nucleic acid, and
 Coenzymes

23. Phases of glycolysis
• Glycolysis has 10 sequential enzymatic reaction that can be described by two major phases
1.Preparatory phase(energy investment)= 2ATP is consumed, phosphorylated intermediates are
produced.

24. Phase of glycolysis
2.payoff phase (energy generation)= net 2ATP produced, 2pyruvate,2NADH

25. Steps of glycolysis
Step-1 phosphorylation of glucose
Phosphorylated sugar molecules do not readily penetrate cell membranes, why?
1. Because there are no specific transmembrane carriers for these compounds,
2. They are too polar to diffuse through the cell membrane
Therefore, phosphorylation is the effective process to traps the sugar as cytosolic
glucose-6-phosphate

26. Step-2 Isomerization of glucose 6-phosphate
• Catalyzed by posho-hexose isomerase.
• The reaction is readily
oreversible and is
onot a rate-limiting or
onot committed step.

27. Step-3 Phosphorylation of fructose 6-phosphate
The 2nd phosphorylation reaction catalyzed by phosphofructokinase-1(PFK-1)
oIs the control point
oRate-limiting and
ocommitted step of glycolysis
oPFK-1 is allosterically regulated enz.
PFK-2 produce F2,6-bisphosphate from F-6-P
F 2,6-bp is activator of PFK-1 and inhibitor of phosphatase

28. Step-4 splitting of F 1,6 bisphosphate
• The reaction is catalyzed by Aldolase enzyme.
• Yield two different triose phosphates, glyceraldehyde 3-phosphate(aldose), and
dihydroxyacetone phosphate(a ketose)
• The reaction is reversible

29. Step-5 interconversion of triose
• Dihydroxyacetone phosphate must be isomerized to glyceraldehyde 3-phosphate
• This isomerization results in the net production of 2 molecules of glyceraldehyde
3-phosphate

30. Step-6 Oxidation of glyceraldehyde 3-phosphate
This is the 1st oxidative-reduction reaction in glycolysis
The aldehyde group of glyceraldehyde 3-phosphate is oxidized to 1,3-bisphosphoglycerate by
glyceraldehyde 3-phosphate dehydrogenase
NB: Arsenic poison inhibit this pass way by competing with inorganic phosphate as a substrate for
glyceraldehyde 3-phosphate dehydrogenase,
Then it forming a complex (1-arseno-3-phosphoglycerate) that spontaneously hydrolyzes to form
3-phosphoglycerate and bypass 1,3-bisphosphoglycerate formation and cause energy deprivation.

31. Step-7 Synthesis of 3-phosphoglycerate producing ATP
• This reaction is catalyzed by phosphoglycerate kinase
• This kinase reaction replaces the two ATP molecules consumed by preparatory
phase.
• This is an example of substrate-level phosphorylation

32. Step-8 Shift of the phosphate group from carbon 3 to carbon 2
• The shift of the phosphate group from carbon 3 to carbon 2 of phosphoglycerate
• Catalyzed by phosphoglycerate mutase

33. Step-9 Dehydration of 2-phosphoglycerate
 Fluoride inhibit enolase
 Sodium fluoride is used along with K-oxalate for collection of blood for glucose estimation.
 If K-oxalate is used alone, then in vitro glycolysis will reduce the glucose value in the sample.
 Functions of Fluoride
 Inhibits in vitro glycolysis by inhibiting enzyme enolase
 Also acts as anticoagulant, and an antiseptic

34. Step-10 Formation of pyruvate
• The conversion of PEP to pyruvate is catalyzed by pyruvate kinase
• This is another example of substrate-level phosphorylation

35. In anaerobic
Lactate formation is necessary for reconversion of NADH to NAD+ during anaerobic

36. Summary of glycolysis pathway

37. Comparison of aerobic and anaerobic glycolysis
B. In Glycolysis—in Absence of O2 (Anaerobic
Phase)
 In absence of O2, reoxidation of NADH at
glyceraldehyde- 3-P-dehydrogenase stage cannot
take place in electron-transport chain.
 But the cells have limited coenzyme. Hence to
continue the glycolytic cycle NADH must be
oxidized to NAD+.
 This is achieved by reoxidation of NADH by
 conversion of pyruvate to lactate (without
producing ATP) by the enzyme lactate
dehydrogenase.
 In anaerobic phase per molecule of glucose
oxidation
 4 – 2 = 2 ATP will be produced.

38. Glycolysis regulation

39. Anaerobic glycolysis and Cori cycle

40. Students are expected to know
1. What is glycogenesis and glycogenolysis
2. Where do glycogenesis and glycogenolysis take place(organ and organelles)
3. When do glycogenesis and glycogenolysis take place
4. How many gram of glycogen stored in liver and muscle
5. Why do glycogenesis and glycogenolysis take place
6. What are the steps of glycogenesis and glycogenolysis take place
7. What are the enzymes involve in glycogenesis and glycogenolysis take place

41. Glycogen Metabolism

42. Glycogen metabolism
The constant source of glucose supply is absolutely required for cells.
B/c glucose is the preferred energy source for brain and absolute source for mature
RBC.
The three source of blood glucose are
1. dietary intake of glucose,
2. glycogen degradation and
3. gluconeogenesis

43. Cont.,,,,
Dietary intake of glucose in the form of complex CHO is sporadic and not
reliable source of glucose.
Gluconeogenesis have sustainability but slowly response to low glucose.
Due to this our body has developed mechanisms for storing a supply of glucose in
a rapidly mobilizable form called glycogen

44. Where do glycogen synthesis take place?
The major site for store of glycogen in the body is skeletal muscle and liver.
Muscle glycogen used to provide energy to muscle during exercise, not use for
other cells.
Liver glycogen is to maintain blood glucose particularly during early fasting.
400g of glycogen stored in muscle and account 2% of muscle fresh weight
whereas 100g of glycogen store in liver and account 10% of liver weight.
In glycogen storage disease the amount of store is high in both muscle and liver.

45. Glycogen
• Glycogen is a multibranched polysaccharide of glucose that serves as a form of
energy storage in animals, fungi, and bacteria.

46. Glycogen structure
Picture taken from Lippincott illustrated 4th edition. Branched structure of glycogen, showing
α(1→4) and (1→6) linkages

47. Where is exact glycogen storage in cell
• Glycogen molecules exist in cytoplasmic granules associated with its degradatory
and synthetic enzymes.
• During early fasting liver glycogen depleted muscle glycogen depleted after
prolonged fasting, why??????

48. 1. Glycogen synthesis
o Glycogen synthesis is called glycogenesis
o Glycogen synthesis require primer for starting synthesis
o Primer is usually glycogen fragment or protein called glycogenin.
o Glycogenin elongated with a few UDP-glucose until glycogen synthase become
active by the process called autoglucosylation.

49. Steps in glycogenesis
Primer required.
The glycogen primer is formed by autoglucosylation of glycogenin.
Glycogenin is a dimeric protein, the monomers glycosylating each other using UDP-glucose till
seven glucose units are added.
Step-1 Glucose activation step
• First G-6-P is converted to G-1-P by phosphoglucomutase enzyme.
.

50. Step in glycogenesis cont.…
Step-1 glucose activation. G-1-P + UTP------UDP-Glucose + PPi by UDP-glucose
pyro phosphorylase
Step-2 Elongation of glycogen by glycogen synthase.

51. Glycogenesis
Step-3 formation of branch/branching
The amylo-α(1→4) → α(1→6)-glucotransferase enzyme first cut 8 glucosyl
residues from the long glycogen.
 Then it form branch with new nonreducing end.
Then after, elongation of branch will continues by glycogen synthase.

52. Glycogen synthesis

53. Glycogenesis
Adopted from Textbook of biochemistry for medical student
The enzyme amylo- 1, 4→1, 6-transglucosidase
(branching enzyme) forms the alpha-1, 6 linkage

54. 2. Glycogen degradation (glycogenolysis)
• Glycogen degradation is the mobilization of stored glucose in liver and muscle.
• It is not the reverse of glycogen synthesis as it involve different enzyme.
Step-1 shortening of the long glucose by glycogen phosphorylase
• Glycogen phosphorylase use pyrophosphate(PLP) as coenzyme and cleave 1-4
bond until 4 glucosyl residues remain before branch of 1-6.
• This short structure called limit dextrin.

55. Glycogenolysis
Step-2 branch removing/debranching
• The three glucose before branch is removed out and attached to another
nonreducing end by amylo-α(1→4) → α(1→4) glucotransferase(4:4 transferase).
• The remaining branching glucosyl residue removed by amylo-α(1→6) glucosidase
to free glucose.
• These two enzyme called debranching

56. Glycogenolysis summary

57. Is glycogenolysis in liver and muscle exactly similar???

58. Glycogenolysis in liver maintain blood glucose
• In the liver, glucose 6-phosphate is translocated into the endoplasmic reticulum
(ER) by glucose 6-phosphate translocase.
• There it is converted to glucose by glucose 6-phosphatase.
• The resulting glucose is then transported out of the ER to the cytosol by GLUT-7.
• Hepatocytes release glycogen-derived glucose into the blood to help maintain
blood glucose
• This process used to maintain blood glucose until the gluconeogenic pathway is
actively producing glucose.

59. Muscle glycogenolysis
• Unlike to liver muscle glycogen muscle glycogen do not use to maintain blood
glucose
• Because muscle has no enzyme to convert Glucose-6-phosphate to free glucose
• Muscle derived glucose used as energy source for muscle itself
• Muscle glycogenolysis is the major energy source for muscle during strenuous
exercise

60. Glycogenolysis in muscle and liver

61. Glycogen metabolism regulation
In order to maintain blood glucose, glycogen synthesis and degradation should be tightly regulated
Glycogen synthesis in liver accelerated during well fed and degradation accelerated during fasting.
In muscle degradation accelerated during exercise and synthesis after exercise/at rest.
1.Allosteric regulation
Both glycogen synthase and glycogen phosphorylase regulated by the metabolites and energy
level of the cell
The availability of substrate like G-6-P and high energy(ATP) allosterically activate glycogen
synthase enzyme and inhibit glycogen phosphorylase

62. Glycogen metabolism regulation cont.…
Taken from Lippincott illustrated 4th ed. Allosteric regulation of glycogen synthesis and degradation.

63. 2. Hormonal regulation of glycogen metabolism
Hormone like glucagon and catecholamine release during fasting bind to their
specific membrane receptor.
When they bind they activate receptor and then G-couple receptor finally cAMP
increase
cAMP activate cAMP-dependent protein kinase through binding to its R-subunit
Activated cAMP-dependent protein kinase phosphorylate glycogen
phosphorylase(inactive-b-form) to active-a form.

64. Hormonal regulation of glycogen metabolism

65. 3. Glycogen degradation activation in muscle by Ca++
 During muscle contraction energy is needed as ATP for the muscle cells
 This energy is supplied by degradation of stored glycogen by muscle. How?
 Nerve impulse cause muscle membrane depolarization that cause the release of
Ca++ from muscle sarcoplasm reticulum to cytoplasm of muscle.
 The released muscle bind to calmodulin(4Ca2+-calmodulin complex) formed.
 This complex bind to protein kinase in cytoplasm w/c is Camp-dependent kinase.

66. Muscle glycogen phosphorylase regulation by Ca++
• Activated protein kinase phosphorylate glycogen phosphorylase
• Then, muscle glycogen breakdown enhanced and G-6-P for ATP released
• When muscle relax released Ca++ returned to sarcoplasmic reticulum and kinase become inactive
.

67. Glycogen storage diseases

68. QUIZ
• The energy yield from one glucose residue derived from glycogen is 3 ATP
molecules, why?

69. END
ANY QUESTION??