Download Biochemistry 3(Dr.Kawa) Polysaccharide (Complex Carbohydrates

Biochemistry 3(Dr.Kawa)
Polysaccharide (Complex Carbohydrates)
These are polymerized products of many monosaccharide units. They
may be:A- Homoglycans: - homopolysaccharides contains only one type of
monosaccharide.
Starch
A polymer of the monosaccharide glucose, the storage polysaccharide
of higher plants consists of two components, amylose and amylopectin
forming α-glucosidic chain. The amylose component consists of glucose
units linked in a linear fraction by α-1 4 linkages which is a non
branching helical chain and comprise of (15-20%) of starch.
Amylopectin is a branched chain polysaccharide and comprise of (8085%) composed of 24 - 30 glucose residues united by 1 4 linkage in
the chain and by 1 6 linkage at the branch point.
Glycogen
Glycogen is the analogue of starch, a glucose polymer in plants, and is
sometimes referred to as animal starch, having a similar structure to
amylopectin but more extensively branched and compact than starch.
Glycogen is a polymer of α (1→4) glycosidic bonds linked, with α
(1→6)-linked branches.
Cellulose
polysaccharide consisting of a linear chain of several hundred to over
ten thousand β(1→4) linked D-glucose units .Cellulose is derived from
D-glucose units, which condense through β(1→4)-glycosidic bonds.
This linkage design contrasts with that for α(1→4)-glycosidic bonds
present in starch, glycogen, and other carbohydrates. Cellulose, also
known as plant fiber, cannot be digested by the human; therefore
cellulose passes through the digestive tract without being absorbed
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into the body. cows and sheep contain certain symbiotic anaerobic
bacteria (like Cellulomonas) in the flora of the rumen, and these
bacteria produce enzymes called cellulases that help the
microorganism to break down cellulose; the breakdown products are
then used by the bacteria for increasing the number.
Hemicellulose
A polysaccharide related to cellulose that comprises ca. 20% of the
biomass of most plants. In contrast to cellulose, hemicellulose is
derived from several sugars in addition to glucose, especially xylose
but also including mannose, galactose, rhamnose, and arabinose.
Hemicellulose consists of shorter chains – around 200 sugar units.
Furthermore, hemicellulose is branched, whereas cellulose is
unbranched.
Inulin
Inulins are polymers composed mainly of fructose units, and typically
have a terminal glucose. The fructose units in inulins are joined by β
(2→1) glycosidic bond. In general, plant inulins contain between 20
and several thousand fructose units. Smaller compounds are called
fructooligosaccharides, the simplest being 1-kestose, which has 2
fructose units and 1 glucose unit.
B- Heteroglycans: heteropolysaccharides containing residues of
more than one type of monosaccharide:
Agar
It is prepared from sea weeds. It contains galactose, glucose and
other sugars. It dissolved in water at 100 C° which upon cooling sets
into a gel. Agar cannot be digested by bacteria and hence used
widely as supporting agent to culture bacterial colonies.
Mucopolysaccharides
Mucopolysaccharides or glycosamino glycans (GAG) are
heteropolysaccharides containing uronic acid and amino sugars.
Acetylated amino groups sulfate and carboxyl groups are also
generally present. Because of the presence of these charged groups,
they attract water molecules and so they produce viscous solutions.
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Examples: 1.Hyaluronic acid
, 2.Heparin, 3.Chondroitin sulfate,
4.Dermatin sulfate and 5.Keratin sulfate.
Digest Carbohydrate
In simple terms, our digestion system - from the mouth to the small
intestine - is designed to break down disaccharides and
polysaccharides into monosaccharides, the monosaccharide (glucose)
are absorbed into the blood stream and taken to the liver, where it is
stored or distributed to cells throughout the body for producing the
energy.
The liver regulates blood glucose levels to provide sufficient energy
for the body. For example, excess glucose (a cause of hyperglycemia)
is converted in the liver to glycogen (glycogenosis) in response to the
hormone insulin and stored.
Likewise, if blood sugar levels fall, (e.g. between meals), the glycogen
is re-converted to glucose (glycogenolysis) in response to messages
conveyed by the hormone glucagon ,to prevent hypoglycemia.
Metabolism of glucose:Polysaccharide  disaccharide  Monosaccharide glucose which
absorbed and converted to:a – Glycogen and stored in liver cells.
b- Metabolized to CO2 + H2O to provide energy.
c- Keto acids + amino acids + proteins.
d- Fats and stored in adipose tissues.
There are 4 processes regulate the metabolism of carbohydrates in
the body:
1-Glycogenesis: The process that convert glucose to glycogen in liver
cells.
2- Glycogenolysis: The process of breakdown of glycogen to glucose
and other intermediate products in liver cells.
3-Gluconeogenesis: The process of glucose formation from noncarbohydrates such as amino acids and fatty acids.
4- Glycolysis: The process that convert glucose to Lactate or pyruvate.
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Hyperglycemia: high level of glucose in the blood.
Hypoglycemia: low level of glucose in the blood.
Blood sugar
The blood sugar level is the amount of glucose (sugar) in the blood .
Normally blood glucose levels stay within narrow limits throughout
the day: 80 to 120mg/dl. But they are higher after meals and usually
lowest in the morning
Diabetes mellitus: - Disease characterized by insufficient blood levels of
active insulin and this deficiency leads to inability of glucose to enter
muscle and liver cells with abnormal metabolism of proteins and fats
leading to ketosis and possible diabetic coma.
Types of Diabetes mellitus (DM)
The classical symptoms of diabetes is polyuria, polydipsia and polyphagia
Type 1 diabetes (Insulin dependent diabetes mellitus) (IDDM): is
characterized by loss of the insulin-producing beta cells of the islets of
Langerhans in the pancreas leading to a deficiency of insulin
Type 2 diabetes Insulin independent diabetes mellitus (IIDM): is
characterized differently and is due to insulin resistance or reduced
insulin sensitivity
Gestational diabetes (GDM): It occurs in about 2%–5% of all
pregnancies and may improve or disappear after delivery.
Estimation of blood glucose
Several different types of blood glucose tests are used.
1- Fasting blood sugar (FBS) measures blood glucose after you have
not eaten for at least 8 hours.Normal value : 80-100mg/dl
2- 2-hour postprandial blood sugar measures blood glucose
exactly 2 hours after you eat a meal. Normal value :
<140mg/dl
3- Random blood sugar (RBS) measures blood glucose regardless of
when you last ate. Normal value : 100-120mg/dl
4- Oral glucose tolerance test (OGTT) is used to diagnose
prediabetes and diabetes.
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