THEME
 Metabolism

of carbohydrates
DIGESTION OF CARBOHYDRATES
Glycogen, starch and disaccharides (sucrose,
lactose and maltose) are hydrolyzed to
monosacchar...
α -amilase hydrolyzes the α -1-4-glycosidic
bonds randomly to produce smaller subunits like
maltose, dextrines and unbranc...
The intestinal juice contains enzymes hydrolyzing
disaccharides into monosaccharides (they are produced
in the intestinal ...
Galactose

lactase

Glucose

Lactase hydrolyses
lactose into glucose
and galactose
Lactose

Glucose

maltase

Maltase hydr...
ABSORPTION OF CARBOHYDRATES
Only monosaccharides are absorbed
The rate of absorption: galactose > glucose > fructose
Gluco...
Carrier protein is specific for D-glucose or Dgalactose.
L-forms are not transported.
There are competition between glucos...
Transport of glucose from blood into cells of different
organs is mainly by facilitated diffusion.
The protein facilitatin...
The fate of glucose molecule in the cell

Glucose
Glycogenesis
(synthesis of
glycogen) is
activated in well
fed, resting s...
Regulation of Glycolysis
The rate glycolysis is regulated to meet two major cellular needs:
(1) the production of ATP, and...
Inhibition
1) PFK-1 is
inhibited by ATP
and citrate
2) Pyruvate kinase
is inhibited by ATP
and alanine
3) Hexokinase is
in...
Gluconeogenesis - synthesis of "new" glucose from such
precursors as pyruvate, lactate, certain amino acids, and
intermedi...
Reactions Unique to Gluconeogenesis
The first of these bypass steps is the phosphorylation of pyruvate to
phosphoenolpyruvate. The first step is catalyzed by ...
In the last step of the bypass, oxaloacetate is acted upon by
phosphoenolpyruvate carboxykinase (GTP) to yield phosphoenol...
In some animal tissues, particularly the liver, kidney, and
intestinal epithelium, glucose 6-phosphate may be
dephosphoryl...
THE PENTOSE PHOSPHATE PATHWAY
Diabetes mellitus


Diabetes mellitus is a disorder in which blood
sugar (glucose) levels are abnormally high because
the...
 Doctors

often use the full name diabetes
mellitus, rather than diabetes alone, to
distinguish this disorder from diabet...
Types of Diabetes mellitus
 Type

1: In type 1 diabetes ( insulindependent diabetes or juvenile-onset
diabetes), more tha...
 Type

2: In type 2 diabetes ( non-insulindependent diabetes or adult-onset diabetes),
the pancreas continues to produce ...


Type 2 diabetes may occur in children and
adolescents, but usually begins in people older than
30 and becomes progressi...



Symptoms
The two types of diabetes have very similar symptoms. The first
symptoms are related to the direct effects o...
!!!Glycolysis, neoglucogenesis, the anaerobic degradation of glucose
!!!Glycolysis, neoglucogenesis, the anaerobic degradation of glucose
!!!Glycolysis, neoglucogenesis, the anaerobic degradation of glucose
!!!Glycolysis, neoglucogenesis, the anaerobic degradation of glucose
!!!Glycolysis, neoglucogenesis, the anaerobic degradation of glucose
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!!!Glycolysis, neoglucogenesis, the anaerobic degradation of glucose

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Glycolisis, gluconeogenesis, regulation of glucose synthesis

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!!!Glycolysis, neoglucogenesis, the anaerobic degradation of glucose

  1. 1. THEME  Metabolism of carbohydrates
  2. 2. DIGESTION OF CARBOHYDRATES Glycogen, starch and disaccharides (sucrose, lactose and maltose) are hydrolyzed to monosaccharide units in the gastrointestinal tract. The process of digestion starts in the mouth by the salivary enzyme α –amilase. The time for digestion in mouth is limited. Salivary α -amilase is inhibited in stomach due to the action of hydrochloric acid. Another α -amilase is produced in pancreas and is available in the intestine.
  3. 3. α -amilase hydrolyzes the α -1-4-glycosidic bonds randomly to produce smaller subunits like maltose, dextrines and unbranched oligosaccharides. α -amilase
  4. 4. The intestinal juice contains enzymes hydrolyzing disaccharides into monosaccharides (they are produced in the intestinal wall) Sucrase hydrolyses sucrose into glucose and fructose Glucose sucrase Fructose Sucrose
  5. 5. Galactose lactase Glucose Lactase hydrolyses lactose into glucose and galactose Lactose Glucose maltase Maltase hydrolyses maltose into two glucose molecules Maltose Glucose
  6. 6. ABSORPTION OF CARBOHYDRATES Only monosaccharides are absorbed The rate of absorption: galactose > glucose > fructose Glucose and galactose from the intestine into endothelial cells are absorbed by secondary active transport Na+ Protein Glucose Protein
  7. 7. Carrier protein is specific for D-glucose or Dgalactose. L-forms are not transported. There are competition between glucose and galactose for the same carrier molecule; thus glucose can inhibit absorption of galactose. Fructose is absorbed from intestine into intestinal cells by facilitated diffusion. Absorption of glucose from intestinal cells into bloodstream is by facilitated diffusion.
  8. 8. Transport of glucose from blood into cells of different organs is mainly by facilitated diffusion. The protein facilitating the glucose transport is called glucose transporter (GluT). GluT are of 5 types. GluT1 is seen in erythrocytes and endothelial cells; GluT2 is located mainly in hepatocytes membranes (it transport glucose into cells when blood sugar is high); GluT3 is located in neuronal cells (has higher affinity to glucose); GluT4 - in muscles and fat cells. GluT5 – in intestine and kidneys;
  9. 9. The fate of glucose molecule in the cell Glucose Glycogenesis (synthesis of glycogen) is activated in well fed, resting state Glucose-6phosphate Gluconeoge nesis is activated if glucose is required Glycogen Glycogenolysis (degradation of glycogen) Pentose phosphate pathway supplies the NADPH for lipid synthesis and pentoses for nucleic acid synthesis Pyruvate Glycolysis is activated if energy is required Ribose, NADPH
  10. 10. Regulation of Glycolysis The rate glycolysis is regulated to meet two major cellular needs: (1) the production of ATP, and (2) the provision of building blocks for synthetic reactions. There are three control sites in glycolysis - the reactions catalyzed by hexokinase, phosphofructokinase 1, and pyruvate kinase These reactions are irreversible. Their activities are regulated by the reversible binding of allosteric effectors by covalent modification by the regulation of transcription (change of the enzymes amounts). The time required for allosteric control, regulation by phosphorylation, and transcriptional control is typically in milliseconds, seconds, and hours, respectively.
  11. 11. Inhibition 1) PFK-1 is inhibited by ATP and citrate 2) Pyruvate kinase is inhibited by ATP and alanine 3) Hexokinase is inhibited by excess glucose 6phosphate Regulation of Glycolysis Stimulation 1) AMP and fructose 2,6bisphosphate (F2,6BP) relieve the inhibition of PFK-1 by ATP 2) F1,6BP stimulate the activity of pyruvate kinase Alanine
  12. 12. Gluconeogenesis - synthesis of "new" glucose from such precursors as pyruvate, lactate, certain amino acids, and intermediates of the tricarboxylic acid cycle. Most of the reaction steps in the pathway from pyruvate to glucose 6-phosphate are catalyzed by enzymes of the glycolytic sequence and thus proceed by reversal of steps employed in glycolysis. However, there are two irreversible steps in the normal "downhill" glycolytic pathway which cannot be utilized in the "uphill" conversion of pyruvate to glucose 6-phosphate. In the biosynthetic direction these steps are bypassed by alternative reactions.
  13. 13. Reactions Unique to Gluconeogenesis
  14. 14. The first of these bypass steps is the phosphorylation of pyruvate to phosphoenolpyruvate. The first step is catalyzed by pyruvate carboxylase of mitochondria: pyruvate + CO2 + ATP → oxaloacetate + ADP + P The oxaloacetate formed in this mitochondrial reaction is then reduced to malate at the expense of NADH by the mitochondrial form of malate dehydrogenase: oxaloacetate + NADH + H+ → malate + NAD+ The malate so formed may then leave the mitochondria and in the cytosol the malate is then reoxidized by the cytoplasmic form of NAD-linked malate dehydrogenase to form extramitochondrial oxaloacetate: malate + NAD+ → oxaloacetate + NADH + H+
  15. 15. In the last step of the bypass, oxaloacetate is acted upon by phosphoenolpyruvate carboxykinase (GTP) to yield phosphoenolpyruvate and CO2, a reaction in which GTP serves as the phosphate donor: oxaloacetate + GTP → phosphoenolpyruvate + CO2 + GDP. The second crucial point in gluconeogenesis in which a reaction of the downhill glycolytic sequence is bypassed is conversion of fructose 1,6diphosphate into fructose 6-phosphate: fructose 1,6-diphosphate + H2O → fructose 6-phosphate + P. This reaction is catalized by the enzyme fructose diphosphatase.
  16. 16. In some animal tissues, particularly the liver, kidney, and intestinal epithelium, glucose 6-phosphate may be dephosphorylated to form free glucose; the liver is the major site of formation of blood glucose. The hydrolytic cleavage of glucose 6-phosphate does not occur by reversal of the hexokinase reaction but is brought about by glucose-6-phosphatase: glucose 6-phosphate + H2O → glucose + P Glucose-6-phosphatase is not present in muscles or in the brain, which thus cannot donate free glucose to the blood.
  17. 17. THE PENTOSE PHOSPHATE PATHWAY
  18. 18. Diabetes mellitus  Diabetes mellitus is a disorder in which blood sugar (glucose) levels are abnormally high because the body does not produce enough insulin.Insulin a hormone released from the pancreas, controls the amount of sugar in the blood.The levels of sugar in the blood vary normally throughout the day. They rise after a meal and return to normal within about 2 hours after eating. Once the levels of sugar in the blood return to normal
  19. 19.  Doctors often use the full name diabetes mellitus, rather than diabetes alone, to distinguish this disorder from diabetes insipidus, a relatively rare disease that does not affect blood sugar.
  20. 20. Types of Diabetes mellitus  Type 1: In type 1 diabetes ( insulindependent diabetes or juvenile-onset diabetes), more than 90% of the insulinproducing cells of the pancreas are permanently destroyed. The pancreas, therefore, produces little or no insulin Only about 10% of all people with diabetes have type 1 disease. Most people who have type 1 diabetes develop the disease before age 30.
  21. 21.  Type 2: In type 2 diabetes ( non-insulindependent diabetes or adult-onset diabetes), the pancreas continues to produce insulin, sometimes even at higher-than-normal levels. However, the body develops resistance to the effects of insulin, so there is not enough insulin to meet the body's needs.
  22. 22.  Type 2 diabetes may occur in children and adolescents, but usually begins in people older than 30 and becomes progressively more common with age. About 15% of people older than 70 have type 2 diabetes. Obesity is the chief risk factor for developing type 2 diabetes, and 80 to 90% of people with this disease are obese. Because obesity causes insulin resistance, obese people need very large amounts of insulin to maintain normal blood sugar levels.
  23. 23.   Symptoms The two types of diabetes have very similar symptoms. The first symptoms are related to the direct effects of high blood sugar levels (hyperglycemia). When the blood sugar level rises above 160 to 180 mg/dL, sugar spills into the urine (glucoseuria). When the level of sugar in the urine rises even higher, the kidneys excrete additional water to dilute the large amount of sugar. Because the kidneys produce excessive urine, a person with diabetes urinates large volumes frequently (polyuria). The excessive urination creates abnormal thirst (polydipsia). Because excessive calories are lost in the urine, the person loses weight. To compensate, the person often feels excessively hungry. Other symptoms include blurred vision, drowsiness, nausea, and decreased endurance during exercise.

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