WEEK 2 - CARBOHYDRATEMETABOLISM L1.pdf

8/10/2019 WEEK 2 - CARBOHYDRATEMETABOLISM L1.pdf

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Taif University

College of Medicine

Second Year Students

BIOCHEMISTRY

LECTURE 1

Dr. Gaber Shehab


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Intended Learning Outcomes (ILOs)

Explain digestion, absorption and the fate of absorbed

g ucose.

Discuss the steps and importance of glycolysis and Cori cycle

Discuss the steps and importance of gluconeogenesis

Illustrate the steps of Kerb's cycle and its importance

Point out hexose monophosphate shunt and its function.

Describe glycogen metabolism (glycogenesis & glycogenolysis)


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Digestion,

Overview to carbohydrate Metabolism

fate of absorbedglucose.


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Dietary Carbohydrates:

Polysaccharides:

rom p ant origin: starc compose oamylose and amylopectin) and cellulose.

From animal origin: glycogen.

Disaccharides:Sucrose, lactose and maltose (by hydrolysisof starch).

Monosaccharides:Glucose, fructose and galactose

in fruits and honey & obtained byhydrolysis of oligo- & polysaccharides.


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Stage 1: Digestion of carbohydratesOverview to carbohydrate Metabolism

cleaves the

(14) bond

cleaves the(14) bond

cleaves the (16) bond in isomaltosecleaves the (14) bond in maltosecleaves the (14) bond in lactosecleaves the ,(12) bond in sucrose


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Degradation of dietary polysaccharides bysalivary or pancreatic -amylase



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Ingested polysaccharides and disaccharides are converted to monosaccharides


Digestion of Carbohydrates

y intestina y ro ytic enzymes, an t e monosacc ari es t en enter intestina

cells and are transported to the liver or other tissues.


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Digestion of Carbohydrates


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9

-

Stage 1: Digestion of Carbohydrates

bonds in polysaccharides to give smallerpolysaccharides (dextrins), maltose, isomaltose andsome glucose.

In the small intestine, pancreatic amylase hydrolyzesdextrins to maltose, isomaltose and glucose.

, ,

isomaltose are hydrolyzed to monosaccharides. The monosaccharides enter the bloodstream for

transport to the cells.


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Absorption of monosaccharides

1. Simple diffusion:


intestinal lumen and mucosal cells.

e.g. Fructose

2. Facilitated transport:It requires a transporter.

e. . Glucose Fructose and alactose

3. Active transport (cotransport):

It needs energy derived from the hydrolysis of ATP.

glucose & galactose are actively transported against

their concentration gradients by this mechanism.


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Fate of absorbed monosaccharides


In the liver,

fructose and

galactose areconverted to

g ucose.

O i b h d M b li


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If carbohydrate degradation is deficient (as a result of


Abnormal degradation of disaccharides

, , ,the mucosa of the small intestine), undigested carbohydrate

will pass into the large intestine, where it can cause osmotic

diarrhea (water is drawn from the mucosa into the largeintestine).

volumes of CO2 and H2 gas, causing abdominal cramps,diarrhea, and flatulence.

Lactose intolerance, caused by a lack of lactase, is by far

the most common of these deficiencies.

O i t b h d t M t b li


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Abnormal lactose metabolism

O i t b h d t M t b li


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What is the fate of Glucose?




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Glucose in the body undergoes one of the following metabolic fates:

1. Oxidation to roduce ener : Ma or athwa s l col sis &


Fates of Glucose

Krebs' cycle).2. Conversion to other substances:

Such as:

- Carbohydrates: pentoses (hexose monophosphate pathway) &uronic acid (uronic acid pathway)

Lipids: Non-essential fatty acids and Glycerol-3 Phosphate.

Proteins: Non-essential amino acids which enter in theformation of proteins.

3. Storage of excess glucose:

as glycogen in liver and muscles,and TAG in adipose tissue.


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Atlas of Biochemistry, page 113


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Glucose Oxidation

Extracting Energy from Glucose:

There are 3 major biochemical processes that occur in cells to

progressively breakdown glucose with the release of various

packets of energy:

Glycolysis (occurs in the cytoplasm and is only moderately efficient).

Krebs' cycle (takes place in the matrix of the mitochondria and

results in a great release of energy).

Electron transport chain (occurs in the mitochondria)


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Atlas of Biochemistry, page 113

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WEEK 2 - CARBOHYDRATEMETABOLISM L1.pdf