lecture 1 carbohydrate(glucose),metabolism & … 1 carbohydrate(glucose),metabolism & energy...

Lecture 1

Carbohydrate(glucose),Metabolism & Energy

Prof.Dr.Munaf Salih Daoud

Objectives :

1- Define carbohydrates & metabolism

2- Describe the role of ATP as an energy source

3- Explain what CHO are involved in by having an overview to their role in human metabolism

1 14الثاني، كانون 02

CHO Definition:

Most abundant organic molecules in nature of empiric formula (CH2O)n for simple ones, hence the name hydrate of carbon. Monosaccharides(glucose)disaccharides

(sucrose) oligosacchrides, polysaccharides

(starch)

Widely distributed in plants & animals.

Have important structural & metabolic roles.


In plants synthesized from CO2&H2O by photosynthesis & stored as starch or used to synthesize the cellulose of the cell walls.

Glucose (Glc):

Major monosaccharide of the blood.

Aldose=Aldohexose .D-form,α-form anomer .

Most food CHO are absorbed into bloodstream as Glc.Formed by hydrolysis of polysaccharide(starch),disaccharide(maltose,

lactose,sucrose). 3 14الثاني، كانون 02

Also other sugars like galactose(epimer of Glc)& fructose(isomer or ketohexose).

Major metabolic fuel of mammals & a universal fuel of the fetus.

Precursor for the synthesis of all other CHO in the body Glycogen(storage),Ribose &Deoxyribose of the

(Nucleic acid=DNA,RNA),Galactose in Lactose(milk)…etc


Diseases associated with CHO metabolism include diabetes mellitus(DM),galactosemia,Glycogen Storage disease & Lactose intolerance….

Monosaccharides:

Trioses (3-C ),

Tetroses(4-C),

Pentoses(5-C),

Hexoses(6-C).


● Aldose ;Aldohexose=Glc

●Ketose;Ketohexose =fructose

● Sugar alcohols or Polyols (Sorbitol produced by reduction from Glc (its alcohol) & is used in manufacture of foods for weight reduction & diabetics ) .


Metabolism:

Set of life-sustaining chemical transformation within living organism cells using enzymes & allow growth ,reproduction , respond to environments . Also digestion & intercellular transport of substances.


Absorption:

requires specific transports in the intestine & any disorder due to: hereditary (genetic)factor like enzyme deficiency or acquired (because of diseases or drugs) results in complications in the large intestine & a disease occurs.

Metabolic reactions are organized into multistep sequences ( pathways) e.g. glycolysis


Pathways are classified as:

1- Catabolic ( breakdown of molecules )

2- Anabolic ( Synthesis of molecules). 3- Amphibolic ( Both catabolism & anabolism )


Source of Energy ( E ): The ultimate source of E for all living matters is the sunlight which converts CO2 + H2O into CHO( starch) in plants. Starch is converted into glucose (Glc or G ) in the body which give E on oxidation. Plants(CO2+H2O)-sunlight photosynthesis → Glc → starch & in the body by digestion →Glc, & its oxidation & with ADP+Pi→ ATP ( E is conserved in ATP ).


ATP is a nucleotide ( Adenine+Ribose+ 3 phosphates). It has 2 high-energy phosphate bonds (2 ~P ). It acts as a donor of a ~P to form compounds of less free E of hydrolysis ( ∆G) like Glc6-P , Fructose(Frc)6-P …etc. Three major sources of ~P take part in E conservation (E capture). 1-Glycolysis 2- Kreb ̛s cycle 3- ETC &Ox.Phosph.


Phosphagen - act as storage forms of ~P e.g. Creatine~P found in skeletal muscles,heart,spermatozoa,brain).In rapid ATP utilization as a source of E for muscle contraction,phosphagens act as a donor of ~P to maintain its concentration & when ATP/ADP ratio is high,then phosphagens increase acting as a store.


Biological E are either: Exergonic- ∆G is negative, so reactions proceeds spontaneously with loss of free E ( E liberating) reactions .This occurs in Catabolic Reactions(molecules Breakdown) Glycogen→Glc→CO2 + H2O (Glycogenolysis & Glycolysis)


Endergonic- ∆G is positive so reactions proceeds only if free E can be gained (E is needed ). This occurs in Anabolic Reactions (molecules Synthesis). Glc → Glycogen ( glycogenesis)


Besides ATP,other nucleotides of high ~P are GTP,CTP,& UTP used to supply E in protein ,lipid, & polysaccharide synthesis,respectively. Each is formed by combination of ATP with GDP,CDP,& UDP in order by a kinase enzyme. 15 14الثاني، كانون 02

Lecture 2

Carbohydrates - Glucose metabolism Prof.Dr. Munaf Salih Daoud Objectives : 1- Explain glycolysis ( aerobic & anaerobic ) 2- Identify their medical & Clinical importance 3- Explain its regulation and the link with other pathways through intermediate compounds


CHO Metabolism

1- carried out in every cell in the body. 2- Found in cytoplasm ( Cytosol). Glycolysis,Glycogenesis,& Glycogenolysis. in mitochondria( Membranes& Matrix), TCA cycle, ETC & Ox. Phosph.. in both , Gluconeogenesis. 3- Alternative pathways are HMP shunt (PPP) , Uronic acid pathway.


1- Glycolysis Used by all tissues for oxidation ( breakdown ) of Glc in 10 reactions to give E ( ATP )& intermediates for other metabolic pathways ( Link ). Aerobic (in presence of O2 ) Glc→ 2 pyruvates or pyruvic acids. Anaerobic ( in absence of O2 ) → 2 lactates or lactic acids.


Reactions: 1mole of glucose glucose 6 phosphate fructose 6 phosphate fructose1,6bisphosphate cleaved glyceraldehyde 3-phosphate & dihydroxyacetonephosphate (interconvertible) 20 14الثاني، كانون 02

2 moles glyceraldehyde 3-Phosphate → 2 NADH + 2 (1,3 bisphosphoglycerate) → 2 ( 3- phosphoglycerate ) → 2 ( 2-phosphoglycerate ) → 2 ( phosphoenolpyruvate ) → 2 (pyruvate ) aerobically . → 2 ( lactate ) anaerobically .


In RBCs : 2(1,3 bisphosphoglycerate ) 2( 2,3 bisphosphoglycerate)or ( 2,3 bisPG) 3- phosphoglycerte → 2-phosphoglycerte →→→ 2 lactates by LDH & this needs the 2NADH already formed.


The 2,3biPG of high concentration (4mM) equal to Hemoglobin ( Hb) binds to it & act as regulator of O2 transport by decreasing affinity of Hb to O2 thus allowing O2 release in tissue capillaries .


E production : Aerobic glycolysis produces 2ATP+2NADH(through malate shuttle) i.e. 8 ATP per 1 Glc oxidized to 2 pyruvates. Anaerobic glycolysis produces 2 ATP produced by substrate level phosphorylation. In exercised muscle ( due to lack of O2 or Hypoxia) or in RBCs ( lack of mitochondria),the NADH cannot be oxidized 02 24 14الثاني، كانون

through ETC but used by pyruvate to form lactate by LDH. This enzyme have Clinical significance & have 5 isoenzymes.The increased level of blood lactate above normal limit is known as Lactic Acidosis. (a pathological condition of many causes).


Anaerobic Glycolysis occurs in exercised muscle,RBCs,Cancer cells in CancerCachexia . Prolonged muscle exercise causes↑[lactate] in blood or hyperlactatemia. The lactate is one of the precurosrs of glucose in gluconeogenesis in liver ( Cori ̛s̛ cycle). Aerobic Glycolysis occurs in most tissues ( organs ) when O2 is available but it is low in Cardiac muscles


Ischemic heart diseases. The brain is highly dependent on Glc for its E supply & needs continuous supplement ,WHY ?. 1- can not synthesize it 2-can not store it 3- can not utilize other sugar than it 4- its uptake is not controlled by insulin.


Important enzymes : 1- Hexokinase(HK) & glucokinase (GK) 2- Phosphofructokinase -1 (PFK-1) 3- Aldolase A (cleavage enzyme) 4- Glyceraldehyde 3- phosphate Dehydrogenase (Glycer.3-PDH) 5- Pyruvate kinase (PK) 6- Lactate dehydrogenase ( LDH)


Regulation : The key enzymes are HK,PFK-1 & PK . 1- Allosteric activation or inhibition of HK,PFK-1 &PK by phosphorylation & dephosphorylation ( short- term influences , minutes-hours) 2- Hormonal influence on the amount of enzyme synthesized ( long- term increase of activity by 10-20 folds , hours-days).


3 - After a meal of CHO or high insulin → high enzyme activity. 4 - Starvation or Diabetes → low enzyme activity. 5- PK , activated by ATP, glucagon & epinephrine( adrenaline).


☻ Genetic defect , Inherited deficiences of HK & PK cause Hemolytic Anemia due to ↓[ATP] important in maintaining the biconcave shape of RBCs membranes and ↓[ 2,3 bisPG] important in O2 release in tissue capillaries . ☻glycolysis is inhibited by iodoacetate , arsenate& fluoride.


Other CHO that enters glycolysis: 1- Glycogen through formation of Glc6-P ( muscle). 2- Fructose through formation of Frc1-P ( isomer of Frc6-P) by fructokinase ( liver,kidney,intestine,testis) i.e. Fructolysis.


Lecture 3 2 –Kreb ̛s Cycle , Electron Transport Chain ( ETC) & Oxidative Phosphorylation (Ox.Phosph.): Objectives: 1- Outline the intermediates and enzyme activities & show steps that produce reduced coenzymes and high energy phosphate compounds. 2- Explain its regulation and the link with other pathways through intermediate compounds.


3- Describe the transport of electrons through the respiratory chain & ATP synthesis.

4- List some inhibitors (blockers) of ETC ,pathological & inherited disorders of both. ……………………………………… ▪ The link between glycolysis & TCA cycle Pyruvate ( cytosol) enters the mitochondria ( matrix)and irreversibly converts into Acetyl CoA.


2pyruvate + CoASH +2NAD→2 AcetylCoA + 2 NADH + 2 CO2

by Pyruvate dehydrogenase complex Enzyme ( PDC or PDH ) an enzyme of 4 distinct enzymatic activities & 5 coenzymes namely; [Thiamine pyrophosphate(TPP), Coenzyme A ( CoA), NAD, FAD & lipoic acid]. PDH is inhibited by dietary deficiency of Thiamine(vit.B1), arsenite , mercuric ions.


☻PDH genetic defect ( inborn error ) leads to ↑ [pyruvate] & also [lactate] i.e. Lactic Acidosis & Neurological disorders .


Series of 9 enzymatically catalyzed mitochondrial reactions that form a common pathway for the final oxidation of all metabolic fuels ( CHO , lipids, & proteins)giving Glc. ,free fatty acids ( FFAs also called unesterified FAs) and amino acids(AAs) which are catabolized to Acetyl CoA ( the substrate of TCA ).


TCA cycle reactions are both Catabolic & Anabolic & so called Amphibolic pathway. Oxidation of Acetyl CoA to form intermediate compounds, E & CO2 is catabolic reactions. Citrate formed can move out of mitochondria when there surplus (excess) of E & Glc as in cases of ↑ Eating & ↓ physical activities ( sitting all the time) with no exercises or sport, 02 38 14الثاني، كانون

,this Citrate can be reconverted into Acetyl CoA ( a precursor of FAs synthesis that is esterified with glycerol forming Triglycerides ( Fat) in lipogenesis pathway in liver to go into adipose tissues to be stored causing Obesity. Lipogenesis is Anabolic pathway.


TCA cycle provides much of the E for respiration .The electrons generated by this cycle in the form of reducing equivalents (reduced coenzymes) like NADH & FADH2 are transferred to the ETC & produce ATP by Oxidative Phosphorylation . Net Reaction : Acetyl CoA + 3 NAD+ + FAD+ +GDP + Pi + 2H2O → 2CO2 + 3 NADH + FADH2 + GTP + 2H+ + CoA .


Energy production: 3 NADH → 9ATP 1 FADH2 → 2 ATP 1 GTP → 1 ATP i.e. 1Acetyl CoA → 12 ATP & 2AcetylCoA→ 24 ATP Regulation : The 3 important regulatory enzymes are 1- Citrate Synthase 2- Isocitrate dehydrogenase ( IDH ) 3- α- ketoglutarate dehydrogenase (α-KG DH ) are inhibited in E sufficieny when ATP , NADH Succinyl CoA are ↑ . ADP act as Activator.


Genetic defects of enzymes are associated with severe Neurological damage due to ↓↓ ATP formation in CNS.[ N.B. the enzyme α-KGDH needs coenzymes like Coenzyme A ( CoA) & Thiamine pyrophosphate (TPP).Thiamine is vitamin B1 and its deficiency in food affect this step in CAC].


Pathological Cases: Deficiency of 1- an enzyme causing inherited disorders. 2- a coenzyme e.g. nutritional vitamin deficiency. 3- oxygen ( hypoxia). 4- substrates and 5- due to effect of chemical inhibitors.


ETC is the final common pathway in Aerobic cells by which eˉ derived from various substrates are transferred to O2 to form H2O. Series of highly organized Ox.-Red. enzymes & reactions represented as: Red. A + Ox. B ↔ Ox. A + Red. B the enzymes use NAD+ or FAD+ as eˉ acceptor cofactors ( Coenzymes ).


Ox. Phosph. is the main source of E in Aerobic cells , it is the process whereby free E released when eˉ are transferred along ETC , is coupled to form ATP from ADP + Pi.


In intact mitochondria, eˉ transport & ADP phosphorylation are tightly coupled reactions But in damaged ones , these reactions may occur unaccompanied and free E is released as heat ( i.e. NO ATP production ). 48 14الثاني، كانون 02

ETC & Ox.Phosph. occur in the Inner mitochondrial membrane (Coupling Membrane ). It has high selective permeability for specific substances e.g. ATP & other nucleotides , pyruvate, succinate… etc


Sources of eˉ are NADH ,FADH2. ETC is organized into 4 complexes ( 9 reactions ) Complex I : Substrates → NADH→

FMNH2 → Quinone ( Q ) by NADH dehydrogenase ( inhibited by Rotenone - insecticide ) Complex II : Succinate → FADH2 → Q by Succ. DH (inhibited by Carboxine ).


Complex III: Q → Cytochrome b →

Cyto. c → Cyto.aa3 by Cyt.Reductase (inhibited by Antimycin) Complex IV: Cyto.aa3 → O2 → H2O by Cyto. Oxidase [inhibited by cyanide (CN), Carbon monooxide(CO), Hydrogen Sulfide(H2S), Azide )].


Phosphorylation occurs in Complex V & ATP is formed as follows: 2 ADP + 2Pi + 2H+ + E → 2 ATP + 2H2O by ATP synthase ( ATPase ) ( inhibited by Oligomycin) The most widely accepted theory of ETC & Ox. Phosph. is the Chemiosmotic or Mitchell ̛s Theory.


Control of Ox. Phosph. : 1- Availability of ADP , substrates & O2 . 2- The capacity of ETC itself. [ N.B. uncouplers of Ox. Phosph. are compounds that cause normal ETC but NO production of ATP e.g. 2,4 dinitrophenol & dicumarol ] .


Sites of coupling for ATP formation Complex I , Complex III , Complex IV NADH gives 3ATP ; FADH2 gives 2ATP. ☻Several inherited defects ( NADH dehydrogenase & Cyt. Oxidase ) of Mitochondria occur and cause Myopathy & Encephalopathy. Pathological Cases: Poisoning with chemicals like CN ,CO , insecticides ….. etc


Lecture 4 Glycogen Metabolism & Uronic Acid Pathway

Objectives: 1- Describe glycogen synthesis(Glycogenesis) and degradation ( glycogenolysis) and their control & hormonal regulation (epinephrine , glucagon ) at cell surface. 2-Identify the uronic acid pathway & its role in mucopolysaccharide synthesis &detoxification.

3-List some inherited disorders of both . 56 14الثاني، كانون 02

Glycogen is a storage form of Glc, highly branched very large Glc polymer linked by α-1,4 glycosidic linkage ( bond ) and branches by α-1,6 glycosidic bond at every several Glc residues , found in cytosol as granules & its major sites are muscle & liver ( concentration is higher in liver than muscle but amount is larger in muscle than liver ). 57 14الثاني، كانون 02

Liver glycogen release Glc into blood but not the muscle glycogen because the enzyme glucose 6 phosphatase (Glc6Pase) is absent in the muscle. The duration of liver glycogen exhaustion is about 12 hours ( i.e. enough for ≈ 12 hrs) then gluconeogenesis starts.


Synthesis ( Glycogenesis ) It starts with Glc6P → Glc1P which reacts with UTP → UDP-Glc by pyrophosphorylase enzyme. UDP-Glc , a high energy compound starts adding Glc residue to a preexisting glycogen chain ( Glycogen primer ) formed on a protein primer known as Glycogenin.


UDP is released after addition & Glc is added successively in the 1→ 4 position ( 1,4 glycosidic bond ) by Glycogen Synthase ( straight chain molecule known as Amylose chain is formed ). When segments of Amylose chain are elongated then branching is formed by the Branching enzyme glucosyl-4:6 transferase linked at C-6 OH. 02 63 14الثاني، كانون

This new branch is further elongated by glycogen synthase to form new amylose chain. This process goes on ( repeated ) until Amylopectin is formed and the whole branched Glycogen structure is formed.


Degradation ( Glycogenolysis) 1- A phosphorylitic cleavage (removal) of Glc of the terminal ( outermost chains ) α-1,4 glycosidic bond of Glycogen by Glycogen Phosphorylase to give Glc1-P. Removal goes on sequentially until about 4 Glc –residues remain. 2- Removal of branch chains: This is catalyzed by the Debranching enzyme system ; it has 2 enzymatic activities.


a- α ( 1,4→1,4 ) glucantransferase ( glucosyl transferase ) b- α- 1,6 glucosidase 3- In lysosomes another enzyme α-1,4 glucosidase is involved in glycogen degradation to give Glc.


Regulation: 1- Hormonal ,Glucagon(liver) and epinephrine(liver & muscle) stimulates glycogenolysis & inhibit glycogenesis while insulin stimulates glycogenesis in both liver & muscle . 2- Covalent modification i.e. Phosphorylation or dephosphorylation by cAMP. 67 14الثاني، كانون 02

Allosteric mechanisms & covalent modification by reversible phosphorylation of enzyme protein in response to hormone action. cAMP is formed from ATP by Adenylate cyclase at the inner surface of cell membranes in response to hormones such as epinephrine & glucagon. 02 68 14الثاني، كانون

cAMP is hydrolyzed by Phophodiesterase to AMP , so ending hormone action and insulin increase the activity of this enzyme in the liver. Phosphorylated enzyme can be dephosphorylated by a phosphatase enzyme e.g. removal of P from Phosphorylase a ( active ) →

Phosphorylase b ( inactive ). 69 14الثاني، كانون 02

☻Genetic defects ( inborn errors of glycogen metabolism) Glycogen Storage Diseases ( GSDs)are inherited disorders ( more than 10 characterized by deposition of an abnormally type or quantity of glycogen in tissues, or failure to mobilize glycogen e.g. vonGierke ̛s̛ disease –Type I.


Effect of Epinephrine and /or glucagon regulation at cell membrane receptors Epinephrine Adenylate Cyclase(Ia) → Adenylate Cyclase(a)

ATP → cAMP → AMP

Protein Kinase(Ia) Protein Kinase(a)

( Ia is for inactive & a for active ).


After activation of protein kinase , there are 2

pathways :

1- Protein Kinase ( a )

Glycogen Synthase I → GlycogenSynthase D

active inactive

dephosphorylated phosphorylated

inhibits

UDP-Glc → Glycogen ( glycogenesis stops )


2- Protein kinase ( a ) ↓ Phosphorylase kinase → Phosphorylase kinase dephosphorylated phosphorylated inactive active ↓ Ca+²

Phosphorylase b → Phosphorylase a

inactive( dephospho.) active ( phospho.)

↓ stimulates

Glycogen → Glc-1P ( glycogenolysis starts)


Uronic Acid ( Uronate ) pathway ●In liver, Glc is converted to Glucuronic acid or Glucuronate (GluUA) , Ascorbic acid( vit.C) but not in human , and Pentoses ● Like PPP , NO ATP is produced . ● Reactions: 1- Glc6-P → Glc1-P + UTP → UDP-Glc (uridine diphosphate-glucose) 2- UDP-Glc + NAD+ → NADH + UDP-Glucuronate


3- UDP-Glucuronate is used for conjugation with the aminosugars ( Glucosamine& Galactosamine) in the synthesis of Mucopolysaccharides (MPS) or Glycosaminoglycans (GAGs) having various functions in the body e.g. Hyaluronic acid (HA) found in eye , Synovial fluid,Placenta ; Chondroitin sulfate (CS) found in cartilage; and Heparin found in blood .


4- UDP-Glucuronate is also used for conjugation with steroid hormones, bilirubin & a number of drugs that are excreted in urine or bile as glucuronide conjugates.


5- This pathway is linked to others like Pentose Phosphate Pathway by its Xylulose 5-P & Glycolysis by its Fructose 6-Phosphate. 6- L – Xylulose is a pentose sugar that is formed in this pathway and its enzyme reductase deficiency causes its accumulation in the blood , This genetic defect (Inherited disorder =Inborn error ) is Essential Pentosuria


☻7- Mucopolysaccharidoses ( another inborn error) A group of 10 related disorders due to inherited defect of Lysosomal hydrolases enzymes that degrade MPs ( GAGs ). Hurler & Hunter Syndromes due to deficiency of Iduronidase & Sulfatase , respectively. MPs are accumulated in tissues & excess are excreted in urine.


Lecture 5 Gluconeogenesis , Galactose & Lactose Metabolism Objectives : 1-Describe the physiological states in which gluconeogenesis is active , the substrates & tissues involved.


2-Explain the recipricol regulation between glycolysis and gluconeogenesis. 3- Describe galactose & lactose metabolism. 4-List some inherited disorders of both


● Synthesis of a new Glc from non-CHO precursor like lactate ,pyruvate ,glycerol , amino acids ( AAs) called glucogenic AAs . Location: liver , kidney ( main sites ) & less in the intestine.


Function: The liver acts as a productive organ of Glc to compensate the low level of blood glucose , so gluconeogenesis is active during : 1- During fasting & starvation ( periods of limited CHO intake & liver glycogen exhaustion). 2- During prolonged muscle exercise as mentioned before. The Cori̛ s̛ cycle of lactate ( lactic acid cycle).


3- The triglyceride(Fat) or TAG hydrolyzed by lipases (Lipolysis) in adipose tissue to give Glycerol & fatty acids. Glycerol moves into the liver & by kinase → Glycerol 3-P then by dehydrogenase → DHAP & then by isomerase→ Glyceraldehyde 3-P ( triose 3-P ) & then by reverse reactions of glycolysis(gluconeogenesis) into Glc. to supply the brain.


4- Tissue protein breakdown (Proteolysis)contribute to form Glc by different amino acids ( glucogenic AAs).These AAs on deamination or transamination ( catabolic reactions of AAs ) give α- keto acid of that AA. e.g.1 Alanine(Ala)→ NH2 + pyruvic acid (pyruvate) ( glycolysis end product)


e.g.2 Glutamate(Glu)→ NH2 + α-ketoglutaric acid ( α-KG , TCA cycle intermediate ) Pyruvates & α-KG are both gluconeogenic substrates & can produce Glc. Gluconeogenesis is the reversal of glycolysis except three steps must be bypassed :


1- Phosphorylation of Glc by HK. 2- Conversion of Frc6-P to Frc1,6bisP by PFK-1. 3- Conversion of PEP to pyruvate by PK. A good example is Muscle alanine (Ala) Ala(muscle)→ Ala(blood)→Ala(liver)by transamination → pyruvate(liver) → Glc(liver) → Glc ( blood).


Reactions: 1- Pyruvate Carboxylation(matrix) Pyru. + ATP + Mg+² + CO2 + Biotin by Carboxylase → OAA (matrix) →

malate(matrix) 2- malate ( matrix) → malate ( cytosol)→OAA (cytosol)→ PEP (cytosol ) 3- PEP→→→→→→ Frc1,6bisP


This conversion occurs by sequential reactions catalyzed by 6 enzymes ( simply the reverse of glycolytic ones). 4- Frc1,6 bisP by Frc1,6 bisphosphatase ( Frc1,6bisPase) → Frc6-P. [ Frc1,6bisPase is an allosteric enzyme ] 5- Frc6-P by isomerase → Glc6-P 89 14الثاني، كانون 02

6- Glc6-P by glucose 6 phosphatase → Glc.+ Pi This enzyme is found in liver , kidney , small

intestine but not in muscles, so muscles do not contribute Glc to the blood.

The conversion of 2 Pyruvates to 1 Glc uses 4 ATP & 2 GTP = 6 ATP. That is Why Gluconeogenesis is unlike glycolysis is an E- consuming pathway.


Regulation : Stimulated by : 1- glucagon , glucocorticoids, epinephrine ( adrenaline) & cAMP.

2- Substrates like glucogenic AAs. 3- Starvation since Acetyl CoA acts as allosteric activator of pyruvate carboxylase (PC). 4- Inhibited by Insulin & after CHO feeding ( meal )


Key enzymes :

1- Carboxylase

2- PEP carboxykinse

3- Frc1,6 bisPase

4- Glc6Pase (G6Pase).

☻Genetic defect ( Multiple Carboxylase

deficiency ).

Glycolysis versus Gluconeogenesis When blood Glc level is increased after a meal of CHO ( fed state) , insulin is largely secreted from 02 92 14الثاني، كانون

the pancreas to stimulate (induce) Glc uptake in muscles & adipose tissues and also cause increased glycolytic enzyme activity in liver ( GK , PFK-1 , PK) . Certainly gluconeogenesis is not required in this condition. But,in case of prolonged (fast state)- Starvation ( Bl. Glc level is decreased ) 02 93 14الثاني، كانون

and in case of Diabetes mellitus [ Glc level is high due to insulin deficiency or tissue insensitivity ( resistivity )],then insulin antagonists hormones ( glucagon,epinephrine & glucocorticoids) stimulate gluconeogenesis enzymes activity (PC , PEP carboxykinase ,G6Pase ).


Galactose ( Gal) It is important in cerebrocytes , brain & cartilage and also + Glc forms the disaccharide lactose in mammary glands. Reactions: Gal + ATP by galactokinase → Gal 1-P Gal 1-P + UDP-Glc by Gal1-P Uridyltransferase ( Gal1PUT) → Glc1-P + UDP-Gal UDP-Gal by 4-Epimerase ↔ UDP-Glc


☻Genetic defect; Deficiency of : galactokinase – Galactosemia & Galactosuria Gal1PUT – Classical Galactosemia 4- epimerase - Galactosemia


Galactosemia – is an Inborn error of CHO ( Gal) ↑ Gal(blood) → ↑ Gal diffusion into Eye lens & by H2 Reductase → Galactitol (impermeable) & accumulate in lens → ↑osmotic pressure & H2O retention (swelling) → Myopia ( damage of lens tissues → Cataracts. 97 14الثاني، كانون 02

Case: a male infant exhibits difficulty to feed, diarrhea ,vomiting & failure to thrive ( grow). At 5 days of age, exhibits mild jaundice & enlarged liver (Hepatomegaly).


Gal is necessary for Lac formation in Mammary gland.UDP-Gal + Glc by Lac Synthetase ,Gal transferase(Protein A ) + Cofactor α-Lactalbumin (Protein B) → Lactose. Protein B ( α- Lactalbumin) occurs in the last 3 months of pregnancy (Trimester 7,8,9 months) and after birth when progesterone level is decreased. 02 99 14الثاني، كانون

Prior to & during pregnancy ( absence of protein B) the mammary gland synthesize Acetyllactosamine: UDP-Gal + N-AcetylGlcN(Acetylglucosamine)→ N-Acetyllactosamine


Progesterone inhibits the synthesis of Protein B and after birth Progesterone Levels ↓ significantly leading to ↑ synthesis of Prolactin leading to ↑ α- Lactalbumin . UDP-Gal is also used in the synthesis of Glycolipids , Glycoproteins and Glycosaminoglycans (GAGs). 101 14الثاني، كانون 02

Lactose (Gal + Glc) source: milk ( synthesized in mammary gland) ☺How can Glc synthesize Lactose? Glc→ Glc 6-P → Glc1-P → UDP-Glc→ UDP-Gal + Glc → Lactose Lactase( B-galactosidase )found in intestine hydrolyse it into Gal+Glc to be transported by portal circulation to the liver.


☻Genetic defect: Deficiency of Lactase called Alactasia → Lactose Intolerance. Abnormally lactose move to Large Intestine to be broken down by Bacteria into H2, 3-C & 2-C metabolites and CO2 causing Bloating ( flatulance),Diarrhea & Dehydration. H2 can be measured in the breath .


This case occurs in Infants, milk which is their primary food is not tolerable & lactose-free formula is used instead ( soya milk ). In adults , the condition is less serious & is treated by avoiding milk & its products.


Lecture 6 Pentose Phosphate Pathway ( PPP) & Fructose Metabolism Objectives: 1-Evaluate the importance of PPP in cells of certain tissues particularly erythrocytes. 2-Describe the metabolism of fructose and the deleterious effect of excess ingestion. 3-Identify the inherited disorders of both.


PPP ; also called hexose monophosphate (HMP) shunt

Location: liver, lactating mammary glands, adipose tissue , adrenal cortex , gonads ,RBCs…etc but not in skeletal muscle. Functions:

1- Provides NADPH an important reduced & phosphorylated coenzyme used


in Reductive Biosynthesis Reactions of fatty acids(FAs) , steroids, glutathione..etc. 2- Provides Ribose5-P( used in the synthesis of nucleotides & nucleic acids). 3- Provides a route for the use of Pentose & their conversion to intermediates of glycolysis like Glyceraldehyde 3-P & Fructose 6-P.


4- NADPH is essential in RBCs to keep the antioxidant Glutathione ( Glycine-Cysteine-Glutamate) ; tripeptide (Gly-Cys-Glu) in the reduced state (GSH) important to prevent cell hydrogen peroxide (H2O2) toxicity from oxidizing the membrane component causing lysis ( hemolysis ) →

Hemolytic Anemia. 108 14الثاني، كانون 02

NADPH + GSSG → NADP+ + GSH by Glutathione Reductase GSH + H2O2 → GSSG + H2O by Glutathione Peroxidase Reactions: 1- 3 Glc6-P + 6NADP+ →→→ 6 NADPH + 3CO2 + Ribulose 5-P Three oxidative, irreversible reactions result in NADPH & CO2 & Ribulose 5-P by glucose 6-P dehydrogenase ( G6PD)


2-Ribulose5-P ( 5-C) → Ribose5-P ( 5-C ) ( nucleotides & nucleic acid )by isomerase 3-Ribulose5-P enters in non-oxidative , reversible ( interconversion ) of sugar phosphate to give Fructose6-P & Glyceraldehyde3-P & The Ribulose5-P ↔ Xylulose5-P by Epimerase


4- Xylulose 5-P + Ribose 5-P ↔ Sedoheptulose7-P ( 7-C) + Glycerald.3-P(3-C) by Transketolase & Thiamine pyrophosphate ( TPP) an active Vit.B1 act as a coenzyme. Glycerald. 3-P is an intermediate of glycolysis and this point is a link between HMP shunt & glycolysis .


5- Sedoheptulose.7-P + Glycerald.3-P ↔ Erythrose-P ( 4-C) + Frc6-P ( 6-C) by Transaldolase 6- Xyl.5-P( 5-C) + Eryth.4-P ( 4-C) ↔ Frc6-P ( 6-C) + Glycerald.3-P ( 3-C) by Transketolase & TPP.


● Regulation : 1- availability of NADP+ 2- G6PD is activated by CHO feeding & inhibited by starvation & DM. 3- G6PD is activated by TPP.


☻Genetic defect ,deficiency of G6PD in some people in the Mediterranean region lead to Hemolytic Anemia. This is due to drugs like Aspirin , antimalarial primaquine or food ( Fava Beans ) causing Favism .


Chronic deficiency of thiamine ( vitamin B1) lead to Wernicke̛s Korsakoff Syndrome. Pathological cases: deficiency of G6PD ( glucose 6 phosphate dehydrogenase ).


Fructose ( Frc ) metabolism source: sucrose,fruits,honey Reactions: ▪ Frc.+ATP by fructokinase →Frc1-P+ADP ▪Frc1-P by AldolaseB→DHAP+Glyceraldehyde ▪ DHAP by isomerase → Glycerald.3-P ( link with Glycolysis)


Glyceraldehyde activated by kinase → Glyceraldehyde 3-P or reduced to glycerol ( link with glycolysis & gluconeogenesis ) or oxidized to glycerate ( in serine synthesis ) Aldolase B ( cleavage enzyme) found predominantly in liver.


Fructokinase ( liver ,kidney , intestine) , specific for Frc. , not affected by feeding-fasting cycles nor by insulin levels ( which may explain why it is cleared from blood of Diabetic patients at a normal rate ). ☻ Genetic defect; Deficiency of Fructokinase → Essential Fructosuria Aldolase B → HereditaryFrc.Intolerance(HFI)


▪ In Essential Fructosuria , Frc. is accumulated & in HFI , Frc1P is accumulated. ● Diets high in Sucrose or High-Frc Syrup ( HFS) used in manufactured foods & beverages → ↑ Frc & Glc entering the liver. Frc undergoes more rapid glycolysis ( fructolysis) in the liver than Glc ,


because it bypass the regulatory step catalyzed by PFK-1 allowing Frc to flood the pathways & lead to enhanced fatty acid synthesis, ↑ esterification of fatty acids & ↑ VLDL secretion → ↑ Triglyceride ( i.e. TAG) & then ↑ LDL-cholesterol .

This is not happening in other tissues ( Muscles & Adipose) because Glc inhibits phosphorylation of Frc .


HFI occurs in Infants after ablactation (breast feeding stop ) & food ( sucrose ) intake associated with the condition of Deficiency of the enzyme fructose 1,6 bisPhosphatase (Frc1,6 bisPase) lead to Frc1P & Frc1,6bisP accumulation in liver. These two compounds will allosterically inhibit liver Glycogen phosphorylase, despite the presence of high Glycogen reserves. 121 14الثاني، كانون 02

This inhibition causes Frc-induced Hypoglycemia . ● Frc also causes Sequestration of phosphate (Pi) . ↑ Frc ingestion → ↑ATP utilization for phosphorylation → ↓ [ ATP] and ↓[ Pi] available to participate in other essential metabolic reactions & ↑ [ ADP ]. The depletion of ATP & repletion of ADP cause


↑ levels of Purine nitrogenous base (Adenine) and → ↑Uric acid formation causing Hyperuricemia & Gout. ● In case of hyperglycemia (e.g. Uncontrolled DM) large amounts of Glc enter different tissue cells .Glc is utilized for E production by Glycolysis ; But when Glc is in excess, utilization differs according to the tissue:


1- Liver, Seminal vesicles, Ovaries & Sperm cells Excess Glc + NADPH by Aldose Reductase → Sorbitol + NADP+ Sorbitol + NAD+ by Sorbitol Dehydrogenase → Frc + NADH This pathway of Glc conversion to Frc by way of Sorbitol is called Polyol pathway .


2- Kidney , Nerve ,Eye ( Lens & Retina) cells Sorbitol is trapped inside the cells because its Dehydrogenase is low or absent . It accumulates causing strong Osmotic effects (H2O move into the cells causing H2O retention) resulting in Swelling. Some pathologic alterations associated with Diabetes mellitus can be attributed to this phenomenon i.e. Nephropathy , Neuropathy & Retinopathy .


Abbreviation (To know but not to memorize): CHO – carbohydrate ATP – adenosine triphosphate ADP – adenosine diphosphate Pi – inorganic phosphate E – energy ETC – electron transport chain Ox.Phosph. – oxidative phosphorylation TCA cycle- tricarboxylic acid cycle CAC – citric acid cycle ~P – high-energy phosphate bond

UTP – uridine triphosphate

GTP – guanosine triphosphate CTP – cytidine triphosphate MSD


HMP shunt – hexose monophosphate shunt PPP – pentose phosphate pathway UA – uronic acid pathway Glc or G – glucose Frc – fructose Glc 6-P – glucose 6- phosphate Glc 1-P – glucose 1-phosphate Frc 6-P – fructose 6 phosphate Frc I,6 bisP – fructose 1,6 bisphosphate Frc 2,6bisP – fructose 2,6 bisphosphate Glycerald.3-P – glyceraldehyde 3-phosphate DHAP – dihydroxyacetone phosphate 1,3 bisPG – 1,3 bisphosphoglycerate 2,3 bisPG – 2,3 bisphosphoglycerate MSD


3 PG – 3 phosphoglycerate 2PG – 2 phosphoglycerate PEP – phosphoenolpyruvate HK – hexokinase GK – glucokinase PFK – phosphofructokinase Frc 1,6bisPase – fructose 1,6 bisphosphatase PK – pyruvate kinase PC – pyruvate carboxylase PDC or PDH – pyruvate dehydrogenase complex Glc6Pase or G6Pase – glucose 6 phosphatase G6PD – glucose 6 phosphate dehydrogenase NADH – nicotinamide adenine dinucleotide(reduced) NAD – nicotinamide adenine dinucleotide ( oxidized) MSD 02 128 14الثاني، كانون

NADPH – nicotinamide adenine dinucleotide phosphate ( reduced ) NADP - nicotinamide adenine dinucleotide phosphate ( oxidized ) FADH2 - Flavine adenine dinucleotide ( reduced ) FAD - Flavine adenine dinucleotide ( oxidized ) AA – amino acid FA – fatty acid cAMP – cyclic adenosine monophosphate TPP – thiamine pyrophosphate CoA – coenzyme A TAG or TG – triacylglycerol or triglyceride DM – Diabetes mellitus MSD


UDP-Glc – uridine diphosphate glucose UDP-GluUA - uridine diphosphate glucuronate ( glucuronic acid ) α-KG – alpha ketoglutarate

OAA – oxaloacetic acid or oxaloacetate

Rib.5P – ribose 5 phosphate

Ribul. 5P – ribulose 5 phosphate

Xylul.5P – xylulose 5 phosphate

Sedoheptul.7P– sedoheptulose 7 phosphate

Eryth.4P – erythrose 4 phosphate

GSH – glutathione (reduced)

GSSG – glutathione ( oxidized ) H2O2 – hydrogen peroxide MSD


lecture 1 carbohydrate(glucose),metabolism & … 1 carbohydrate(glucose),metabolism & energy...

Documents