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
Overview to carbohydrate Metabolism
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Ingested polysaccharides and disaccharides are converted to monosaccharides
Overview to carbohydrate Metabolism
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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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:
Overview to carbohydrate Metabolism
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
Overview to carbohydrate Metabolism
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
Overview to carbohydrate Metabolism
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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Overview to carbohydrate Metabolism
Abnormal lactose metabolism
O i t b h d t M t b li
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What is the fate of Glucose?
Overview to carbohydrate Metabolism
Overview to carbohydrate Metabolism
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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 &
Overview to carbohydrate Metabolism
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