المقرر الكود المستوى المحاضرات نوع المادة العلمية بيانات التواصل من 6 إلى آخر أساسيات وأيض 203 ك ح الثاني محاضرة بالفصل PDF 01003899211 الكربوهيدرات الدراسي الثاني Course of

General Metabolism

1. Lipids Metabolism (finished) 2. Metabolism 3. Proteins Metabolism Metabolism In living organisms

Microorganisms Plans Animals Human

We have learned metabolism from other organisms Biological process in living organisms

Digestion Absorption Excretion Metabolism Metabolism

The Greek metabole, meaning change. It is the totality of an organism's chemical processes to maintain life.

Anabolism Catabolism Amphibolic

Building compounds Oxidative process Links between the need energy release free energy other two pathways (~P) e.g. Protein synthesis e.g. Krebs Cycle e.g. Glycolysis Biomedical Importance of metabolism

Normal Metabolism Abnormal Metabolism

A knowledge of It results from: ●- Nutritional deficiency metabolism in normal ●- Enzyme deficiency animal is a prerequisite to ●- Abnormal secretion of Hormones understand abnormal ●- Genetic diseases state underlying many e.g. diabetes mellitus diseases. It includes the variations and adaptations in metabolism due to periods of Starvation, Exercise, Pregnancy, and Lactation. Carbohydrates In human body

1. : (Every cell).

2. Galactose : (Lactose of milk & Galactolipids ).

3. Fructose : (Liver & Seminal fluid).

4. Lactose : (Blood & Milk of lactating female).

5. Glycogen : (Liver & Muscles).

6. Ribose and Deoxy-ribose : (RNA & DNA).

7. Glycoproteins and mucoproteins: (Prothrombin & Mucin in saliva).

8. Mucopolysaccharides : (as heparin and hyaluronic acid in connective

tissues & as agglutinogens on RBCs giving what are called blood group antigens).

9. Others: (Vitamin C, D-, L-Ascorbic acid etc). Digestion of Carbohydrates ▲- A family of glycosidases degrade carbohydrates into monohexoses via catalyzing the hydrolysis of glycosidic bonds. ▲-These enzymes are usually specific to the type of bond to be broken. ▲-Each enzyme has its optimum pH. ▲-In the mouse, the digestion of complex carbohydrates starts by the action of amylase enzyme (pH= 6.8) 1. Metabolism

▲-After intake and absorption of glucose (e.g. after eating or drinking ), liver condenses extra glucose to glycogen. ▲-Then: ●1/3 of the body’s glycogen is stored in liver ● it is released as glucose to bloodstream ● If blood glucose falls ( e.g. during fasting) ● liver hydrolyzes glycogen to glucose Glycogen is bulky, so, we store only so much for short term energy supply ▲-You must know that:Fats are the long term energy supply Carbohydrate Metabolism (Continued) Metabolism The chemical needed changes that take place in a cell that produce energy and basic materials for important life processes -Millions of cells are included -Multiple organs (liver, adipose, heart, brain) are involved during such process -Thousands of enzymes are used during the metabolic -Various conditions (fed, fasted, exercise, stress) 1. Digestion & Absorption of Carbohydrates. 2. Glucose Oxidation:

i. Major Pathways:

(Mitochondrial or aerobic pathway, TCA cycle or Krebs cycle).

ii. Minor pathways:

( phosphate pathway + Uronic acid pathway)

3. Metabolism of Fructose, Galactose & Mannose.

4. Metabolism of Glycogen (Glycogenolysis + Glycogenesis).

5. Gluconeogenesis. Absorption of Carbohydrates

Target: Simple Sugars (Glucose, Fructose, Galactose)

Tissue Cell

The product of digestion provide the tissues with : (Fuel which are used to power the living process within the cells). Digestion of carbohydrates

A- Pre-stomach :

Via Salivary amylase a 1-4 endoglycosidase:

G G G G G a Limit dextrins G G G G G G G G G G G amylase G G G G G G G a 1-6 link G G maltotriose G G a 1-4 link G G G G G maltose G G isomaltose B-Small Intestine: • Pancreatic enzymes a-amylase

maltotriose maltose G G G G G G G G + G G a amylase amylose

G G G G G G G G G G G G G G G G G amylopectin a Limit dextrins In the Small intestine (continued):

- Portal for transport of virtually all nutrients - Water and electrolyte balance

Enzymes associated with intestinal Surface membranes i. Sucrase ii. a dextrinase iii.Glucoamylase (maltase) iv. Lactase v. peptidases Oligosaccharide digestion (cont.)

G G G G c-In The Stomach • No much carbohydrate digestion (because of the high G G pH of the stomach that inhibits salivary amylase) sucrase G • Acid and pepsin to unfold proteins a Limit dextrins • Ruminants have fore stomachs with extensive microbial populations to breakdown and an aerobically ferment G G feed G G maltase Glucoamylase (maltase) or G G G a- dextrinase

G G a- dextrinase G G G G G Maltase: Specifically removes a single glucose from the nonreducing end of a linear α1-4 glucose G G G chain…breaking down maltose into glucose. (exosaccharidases) G

Alpha dextinase : Cleaves 1,6-alpha glucosidic linkages

Glucose transporter Carbohydrate absorption (GLUT, 14 types) isoforms

GLUT1, GLUT3 and GLUT4: Are primarily Involved in Glucose transporter glucose uptake from the blood

-GLUT2: liver, kidney can either transport glucose to these cells (hyperglycemia) or from them into the blood ( fasting or hypoglycemia).

-GLUT5: Transporter of fructose in the small intestine and tests.

(PAGE 95) apical basolateral Defects of Carbohydrates Digestion & Absorption 1. Lactase deficiency: The presence of Lactose in the intestine causes an Increase in the osmotic pressure. So, water will be drawn from the tissues (causing Dehydration) into the large intestine, a process which causes Diarrhea. The increase in the fermentation of Lactose by bacteria lead to production of CO2 gas. This cause distention and abdominal cramps. Treatment: remove milk from diet. 2. Sucrase deficiency: Rare condition show the same symptoms of lactase deficiency. it occurs early in childhood. 3. Monosacchrides malabsorption: A defect in the carrier mechanism (congenital conditions) of glucose and galactose. Treatment: No treatment. Carbohydrate malabsorption

●Lactose intolerance (hypolactasia). ● Decline lactase with age ● Lactose fermented in LI – • Gas and volatile FA • Water retention • diarrhea/bloating ● Not all populations (incidence of the enzyme deficiency): • Northern European – low incidence • Asian/African Americans – High b 1-4 linkage Glycolysis Carbohydrates serve as primary source of energy in the cell and Central to all metabolic processes.

Glucose Cytosol - anaerobic

Hexokinase

Pentose Phosphate Glucose-6-P Glc-1- phosphate Shunt

Glycolysis glycogen

Pyruvate 1. Digestion & Absorption of Carbohydrates. a. Glucose Oxidation: i. Major Pathways: (Mitochondrial or aerobic pathway, TCA cycle or Krebs cycle). ii. Minor pathways: (Pentose phosphate pathway + Uronic acid pathway) b. Metabolism of Fructose, Galactose & Mannose. c. Metabolism of Glycogen (Glycogenolysis + Glycogenesis). d. Gluconeogenesis.

Glycolysis (continued)

* Oxidation of glucose is known as Glycolysis.

* Glucose is oxidized to either Pyruvate or Lactate.

•Under aerobic conditions (i.e. when oxygen is present), the dominant glycolytic product in most tissues is Pyruvate and the pathway is known as Aerobic Glycolysis.

•Under anaerobic conditions (i.e. when oxygen is depleted) as for instance during prolonged vigorous exercise, the dominant glycolytic product in many tissues is Lactate and the pathway is known as Anaerobic Glycolysis. Glycolysis

Stage 1 Energy requiring (consuming) stage

- ATP

- ATP Glycolysis Stage 2 (Energy producing stage) 2 Molecules.

+ 2 ATP

+ 2 ATP Oxygen requiring step

Pathway of Cytoplasmic Glycolysis of Glucose Special feature of Anaerobic Glycolysis in RBCs

1. RBCs contain no mitochondria. Therefore, they depend only on anaerobic glycolysis to produce 2 ATP. 2. The RBCs have the ability to form 2,3 Bisphospho- glycerate (2,3-DPG) through Rapoport- Luebering cycle using mutase enzyme. *. The presence of 2,3 DPG lowers the affinity of Hb

to O2 leading to good oxygenation of tissues and formation of Rapoport-Luebering cycle pyruvate. Special Features of Anaerobic Glycolysis in RBCs Clinical significance of 2,3-DPG: 1. During storage of blood in blood banks, 2,3-DPG concentration decreases gradually to reach 0.5 mg after 10 days (normal: 4.5 mg).

This lead to high O2 affinity of the stored blood which is not desirable for blood transfusion.

*. As 2,3 DPG can not penetrate RBCs, addition of Inosine (a substance can penetrate erythrocytes and changed into 2,3-DPG through HMP pathway) is advisable.

2. Also, persons living at high altitudes undergo a state of low O2 affinity due to increase of 2,3-DPG. *. This disappears on returning to the Sea Level I.e. a state of normal oxygen affinity is obtained. 3. Moreover, fetal hemoglobin (HbF) binds less strongly with 2.3-DPG than

adult hemoglobin (HbA) consequently it has a higher O2 affinity. This may be a source of pathogenesis in patients carrying such type of haemoglobin. Energy (ATP) Production of Cytoplasmic Glycolysis

Generally, ATP Production = ATP Produced – ATP Utilized

1-Anaerobic Glycolysis:

Anaerobic ATP production = 4 ATP – 2 ATP = 2

2-Aerobic Glycolysis (if oxygen get available)

Aerobic aATP p)roduction == 4 + 6* (or 4 + 4*) ATP – 2 ATP = 8 (or 6)

•From extra-mitochondrial oxidation of 2 NADH + H+ by respiratory chain phosphorylation in mitochondria using two special carriers for hydrogen. Carbohydrates • Serve as primary source of energy in the cell • Central to all metabolic processes

Glucose Cytosol - anaerobic

Hexokinase

Pentose Phosphate Glucose-6-P Glc-1- phosphate Shunt

glycolysis glycogen

Pyruvate cytosol Pyruvate mitochondria (aerobic) Aceytl CoA FATTY ACIDS

Krebs Reducing cycle equivalents AMINO ACIDS

Oxidative Phosphorylation (ATP) Glucose metabolism in different tissues:

Glucose No mitochondria Glucose Glucose

Glucose The Full Glycogen Monty Lactate Fasted State

Glucose Need 13.8 kJ/mol ATP = -30 kJ/mol G-6-Pase Hexokinase -16.7 kJ/mol

Pentose Phosphate Glucose-6-P Glc-1- phosphate Shunt

glycolysis GNG glycogen

Pyruvate Controlling Metabolic Flux

1. Control enzyme levels

2. Control of enzyme activity (activation or inhibition)

3. Compartamentalization Fatty acid oxidation occurs in mitochondrial matrix Fatty acid synthesis occurs in endoplasmic reticulum membrane exposed to the cytoplasm of the cell.

4. Hormonal control 1-Control of enzymes activities

Rate limiting step insulin 2-Control via hormonal levels e.g. insulin IR P

Protein Kinase B Protein Kinase B (inactive) OH P (active)

Glycogen synthase kinase OH P Glycogen synthase kinase (active) (inactive)

P OH

Glycogen synthase Glycogen synthase (inactive) (active)

Glycogen formation Glucose Utilization Stage 1:postparandial All tissues utilize glucose Stage 2 :Postabsorptive KEY – Maintain blood glucose Glycogenolysis Glucogneogenesis Lactate Pyruvate Glycerol AA Propionate Spare glucose by metabolizing fat

Stage 3: Early starvation Glucogneogenesis Stave 4: Intermediate starvation gluconeogenesis Ketone bodies Stage 5 – Starvation Carbohydrate Metabolism/ Utilization &Tissue Specificity

• Muscle – cardiac and skeletal – Oxidize glucose/produce and store glycogen (fed) – Breakdown glycogen (fasted state) – Shift to other fuels in fasting state (fatty acids) • Adipose and liver – Glucose  acetyl CoA – Glucose to glycerol for triglyceride synthesis – Liver releases glucose for other tissues • Nervous system – Always use glucose except during extreme fasts • Reproductive tract/mammary – Glucose required by fetus – Lactose  major milk carbohydrate • Red blood cells – No mitochondria – Oxidize glucose to lactate – Lactate returned to liver for Gluconeogenesis Regulation of Glycolysis 1. Hormonal regulation Insulin: Stimulate synthesis of all 3 key enzymes of glycolysis (Glucokinase/Hexokinase, Phosphofructokinase-1, Pyruvate kinase). These enzymes catalysed what is called committed reactions of the pathway. It secreted after meal in response to high blood glucose level. Glucagon: Inhibits the activity of all key enzymes of glycolysis. It is secreted in response to low blood glucose level. 2. Energy regulation High level of ATP inhibits PFK-1 and PK. High level of ADP and AMP stimulate PFK-1. 3. Substrate regulation Glucose 6-phosphate inhibits hexokinase (and not glucokinase). Fructose 2,6 bisphosphate stimulates PFK-1. Fructose 1,6 bisphosphate stimulates pyruvate kinase. 2. Tri-Carboxylic Acid or Citric Acid cycle

It is the final pathway where the oxidative metabolism of carbohydrates, amino acids, and fatty acids converge. It occurs in the mitochonderia in close proximity to the reactions of electron transport, which oxidise the reduced coenzymes produced by the cycle

5 Oxalloacetate

4

1 3

2 Energy Production in TCA cycle

Enzyme Method of ATP Production No. ATP

Isocitrate dehydrogenase Oxidation of NADH + H by 3 ATP respiratory chin phosphorylation Oxidation of NADH + H by α-Ketoglutarate 3 ATP respiratory chin phosphorylation dehydrogenase Succinyl CoA thiokinase Substrate level phosphorylation 1 ATP

Succinate dehydrogenase Oxidation of FADH by respiratory 2 ATP chin phosphorylation Malate dehydrogenase Oxidation of NADH + H by 3 ATP respiratory chin phosphorylation Total 12 ATP

*Oxidation of one molecule of one molecule of Acetyl Co-A in TCA produce 12 ATP molecules (11 by respiratory chain phosphorylation and 1 by substrate level phosphorylation). The function (significance) of TCA

*The cycle is amphibolic (i.e. has catabolic and anabolic functions) a) Production of energy (12 ATP per pyruvate molecule). b) Catabolic functions: Oxidation of carbohydrates, Fates, and Proteins. c) Anabolic functions: Formation of several components: i. Amino acids (a-ketoglutrate or Oxaloacetate Glutamate and Aspartate. ii. Glucose a-ketoglutrate Gluconeogenesis. iii. Heme Synthesis Succinyl CoA. iv. Fatty acid and cholesterol Citrate (diffuse to cytoplasm). Oxaloacetate + Acetyl CoA Fatty acid and cholesterol.

v. CO2 production which is used in several CO2 fixation reactions. Pentose Phosphate Pathway *. Steps of reactions: This pathway occurs in two phases:

1. Oxidative phase (irreversible): Where 3 molecules of Glucose are converted into 3 molecules of Ribulose-5-phosphate with production of + NADPH, H and CO2.

2. Non-oxidative phase (reversible): Where the 3 molecules of Ribulose-5-phosphate are interacted and converted into 2 molecules of Glucose 6- phosphate and one molecule of Glyceraldehyde-3- phosphate. Pentose Phosphate Pathway 1. The Oxidative Phase of PPP: Pentose Phosphate Pathway 2. The Non-Oxidative Phase of PPP: Uronic Acid Pathway The uronic acid pathway is utilized to synthesize UDP-glucuronate, Glucuronate and L-Ascorbate. Uronic Acid Pathway

*Importance of Uronic Acid Pathway:

The this pathway produces glucuronic acid that is important for:

1. Synthesis of substrates e.g. glucosaminoglycans, Vitmin C, L- ascorbic acid (not in human), Mucopolysaccharides formation.

2. Conjugation reactions: UDP-gluconic acid is used for conjugation with many compounds to make them more soluble before excretion e.g. steroid hormones and bilirubin.

3. Detoxification reactions. This function can be considered a hydrotropic action of glucuronic acid which is important in steroid hormones excretion in urine. Metabolism of Other Important Sugars 1. Fructose Metabolism *Dietary Sources of Fructose: i. Sucrose (table sugar): Hydrolysis of Sucrose gives Glucose and Fructose. ii. Fructose as monosaccharide is present in honey and many fruits and vegetables.

*Importance of Fructose: i. Energy production (15% of dietary energy is derived from fructose). ii. Main nutrient for sperms in the seminal vesicle. iii. Its deficiency in semen correlates with male infertility. Metabolism of Other Important Sugars Fructose Metabolism *Metabolic pathway: ii. In Muscles: *. Fructose is metabolized by hexokinase (Fructokinase is not available in extrahepatic tissues). *. G-3-P and DHAP will be oxidized to Pyruvate. Metabolism of Other Important Sugars 2. Galactose Metabolism *. Dietary Sources of Galactose: i. Lactose (milk sugar): Hydrolysis of lactose gives Glucose and Galactose. *. Importance of Galactose: It enters in the structure of : Milk sugar, Glycolipids, glycoproteins and proteoglycans. *. Metabolic pathway: *. Galactose enters glycolysis by its conversion into glucose-1-phosphate through phosphorylation to Gal-1P and epimerization to Glu-1P via Uridine diphospho-glucose (UDP- glucose) catalyzed by uridyl transferase. Metabolism of Other Important Sugars 3. Mannose Metabolism *Dietary Sources of Mannose: *. The digestion of many polysaccharides and glycoproteins yields Mannose, the C-2 epimer of glucose.

*Metabolic pathway: *. Mannose is phosphorylated by hexokinase to generate mannose-6- phosphate which is converted to fructose-6- phosphate, by the enzyme phosphomannose isomerase . Then, it enters the glycolytic pathway or is converted to glucose-6-phosphate by the gluconeogenic pathway of hepatocytes . Carbohydrates Metabolism Glycogen synthesis

*. Definition: It is the formation of glycogen in liver and muscles.

*. Substrates for glycogen synthesis: i. In liver: Carbohydrate sources: Blood glucose, other hexoses (Fructose and Galactose). Non-carbohydrate sources: Glycerol and Lactate. ii. In muscles: Blood glucose only Carbohydrates Metabolism Glycogen Synthesis Mechanism:

I. Formation of Uridine diphosphate-glucose:

*. Glucose is converted into G6P in liver by glucokinase and in muscle by hexokinase

*. Cleavage of PPi is the only energy cost for glycogen synthesis (one ~P bond per *UDP-glucose is the glucose residue). immediate precursor

for glycogen synthesis. PPi + H2O = 2 Pi Carbohydrates Metabolism Glycogen Synthesis II. Formation of Glycogen:

*. UDP-glucose reacts with glycogen primer, which may be: a) Few molecules of glucose linked together by a 1-4 linkage b) A protein called glycogenin c) Glycogen synthase

1. A glycosidic bond is formed between the anomeric C1 of the glucose moiety derived from UDP- glucose and the hydroxyl oxygen of a tyrosine side- chain of Glycogenin.

*. UDP is released as a product. Carbohydrates Metabolism Glycogen Synthesis II. Formation of Glycogen (cont.): 2. Glycogenin then catalyzes glucosylation at C4 of the attached glucose, with UDP- glucose again being the glucose donor. *. The product is an O-linked disaccharide with an a(1-4) glycosidic linkage.

3. This process is repeated until a short linear glucose polymer with a(1-4) glycosidic linkages is built up on the Glycogenin.

4. Glycogen Synthase catalyzes elongation of glycogen chains.

5. A branching enzyme transfers a segment from the end of a glycogen chain to the C6 hydroxyl of a glucose residue of glycogen to yield a branch with an a(1-6) linkage. Carbohydrates Metabolism Glycogen Synthesis

*. Glycogen Synthase catalyzes elongation of glycogen chains.

*. A branching enzyme transfers a segment from the end of a glycogen chain to the C6 hydroxyl of a glucose residue of glycogen to yield a branch with an a(1-6) linkage. Carbohydrates Metabolism Glycogenolysis

*. Definition: It is the breakdown of glycogen into glucose (in liver) and lactic acid (in muscles). *. Steps for glycogenolysis: 1. Phosphorylase: It acts on the branches containing more than 4 glucosyl units. It breaks a 1-4 bonds down and removes glucose in the form of glucose 1-phosphate. 2. Transferase: When the branch contains 4 units, 3 of them are transferred to a next branch by transferase enzyme and the last one is removed by debranching enzyme (a 1-6 bond). Carbohydrates Metabolism Glycogenolysis *. Steps for glycogenolysis (cont).: 3. Mutase: It converts G1P to glucose-6- phosphate

4. G6p Phosphatase It converts G6P to glucose in liver only (not found in muscles Carbohydrates Metabolism (Gluconeogenesis) *. Definition: It is the biosynthesis of glucose from non-carbohydrate sources. These sources (glucogenic substances or substrates) include: 1. Lactate 2. Pyruvate (Common) 3. Some amino acids 4. Glycerol 5. Propionate *. Functions of gluconeogenesis: 1. Supplies the body with glucose which is: essential for energy production, Precursor of milk sugar (lactose) in mammary glands, Required during low carbohydrate diet or when liver glycogen is depleted (12-18 hr fasting). 2. Clears the blood from the waste products as Lactate (produced by muscles and RBCs) and glycerol (produced by adipose tissue).

Give a brief account on the biosynthesis of glucose from non- carbohydrate sources. Follow up Examination 1-Define the following terms: 1-Enzyme 2-substrate 3-inhibition

2-What are the effects of the following on the enzyme activity: 1- pH 2- time

3-How can our bodies synthesize the following: 1-Pyruvate from Alanine 2-Glutaric acid from Aspartic 3-Pyruvic from Lactic 4-Ammonia from Urea, Please write the enzyme group for which each of these enzymes belong.

These are the results of one of the in-patients of King Khalid Hospital: ALT 30 IUs/ml (N. Up to 45 IUs/ml) AST 95 IUs/ml (N. Up to 40 IUs/ml) CPK 80 IUs/ml (N. Up to 20 IUs/m) LDH 75 IUs/ml (N. Up to 25 IUs/ml) a-What is most probable Diagnosis? b- Isoenzyme of CPK which may be elevated c-enzyme group d-Suggest if the CPK will be elevated at first or LDH. Best Regards & Good Luck