Download Biochemistry 1 (BASIC-106)

•Dr. Tarek El Sewedy
Intended Learning Outcomes
By the end of this lecture, students will learn:
1.
Biological function of carbohydrates.
2.
Characteristics of carbohydrates
Lecture content
 Biological function of carbohydrates.
 Monosacharides
 Disacharides
 Polysacharides
 Physical Properties of Carbohydrates
 Chemical Properties of carbohydrates
Biomolecules of life
1.
Carbohydrates
2. Proteins.
3. Lipids
4. Nucleic acids
Carbohydrate Function
• Sources of Immediate energy (ATP) as produced by
glucose catabolism(Glycolysis and Krebs cycle).
• Source of stored energy (Glycogen stored in liver).
• Intermediates in the biosynthesis of other basic
biomolecules (fats and proteins).
• Associated with other molecules such as vitamins
and antibiotics.
Cont, Carbohydrate function
• Structural function: ex. Ribose, deoxyribose and
cellulose and starch in plants.
• Involved in many cell functions such cell-cell
recognition and protein folding.
Digestion of carbohydrates
a) α-amylase (in saliva) randomly hydrolyzes
all the glycosidic bonds of starch.
b) Digestion continues in the small
intestines with pancreatic amylase. This
degrades the starch to maltose .
c) Further digestion occurs down the
digestive tract in the small intestine. The
resulting monosaccharides are absorbed by
the small intestine and transported into the
blood stream.
• In living organisms, most carbohydrates are found bound to
other compounds rather than as simple sugars

Glycoproteins (hormones, antibodies)

Glycolipids

Nucleic acid.
Monosaccharaides
• Monosaccharaides are also known as “simple sugars”
• They are classified by:
1. Number of carbons.
2. Whether they are aldoses or ketoses.
• D-glyceraldehyde is the simplest of the aldoses.
• Glucose is the most widely known
Glucose
 Glucose is a monosaccharide with formula C6H12O6
 It is absorbed directly into the bloodstream during digestion.
 Bread, rice, pasta are rich in glucose.
 Glucose is a common medical analyte measured in blood samples.
 The hormone insulin, regulates the concentration of glucose in
the blood.
 A high fasting blood sugar level is an indication of diabetic
conditions
 Organisms use glucose as a precursor for the synthesis of several important
substances. Starch, cellulose, and glycogen ("animal starch").
 Some of these polymers like starch or glycogen serve as energy stores while
others like cellulose have structural roles.
 In animals, glucose results from the breakdown of glycogen, a process known
as Glycogenolysis.
 Glucose can also be synthesized in the liver and kidneys from non-
carbohydrate intermediates, such as pyruvate and glycerol, by a process
known as Gluconeogenesis.
 Glucose is produced commercially via the enzymatic hydrolysis of starch.
Many crops can be used as the source of starch. Maize, rice, wheat
 Glucose is classified as a monosaccharide, an aldose, a
hexose, and is a reducing sugar.
Fructose
Fructose
 Fructose is found naturally in fruits and
vegetables.
 Fructose is metabolized differently than
glucose and other sugars, doesn’t stimulate
insulin and is characteristically low
glycemic. For these reasons, it’s often used
in low-glycemic food applications
 15 to 80% sweeter than sucrose, and tastes
particularly sweet when cold or in solution
Disaccharides
Disaccharides
 Disaccharides are formed when two monosaccharaides are joined
together and a molecule of water is removed.
 Milk sugar (lactose) is made from glucose and galactose
 sugar cane sugar (sucrose) is made from glucose and fructose.
 Maltose is made up of two glucose molecules.
 The two monosaccharides are bonded via a glycosidic bond
 Can be degraded to monosaccharides by hydrolysis producing
water.
Sucrose
Sucrose
• Formed of Glucose and fructose monomers joined together.
• known as table sugar
• Commercially obtained from sugar cane or sugar beet
• Used pharmaceutically to make syrups
Lactose
• Lactose is a famous disaccharide, resulting from a galactose
joining to glucose.
• Milk is the most famous source of Lactose.
• Used in infant formulations, and as a diluent in pharmaceuticals
Maltose
 Made up of two glucose molecules.
 Produced when amylase breaks down starch.
 Obtained from malt sugar and when glucose is caramelized.
Polysaccharides
Starch
 Starch or Amylum is a carbohydrate consisting of a large
number of glucose units joined together by glycosidic bonds.
 produced by all green plants as an energy store
 It is the most common carbohydrate in the human diet like
potatoes, wheat, maize (corn), rice.
Cont, Starch
•
consists of two types of molecules: the linear and helical amylose and the branched
amylopectin.
•
Glycogen, the glucose store of animals, is a more branched version of amylopectin.
 Used as an additive for food processing, typically used as thickeners and stabilizers in foods
such as puddings, custards, soups, and salad dressings, and to make noodles and pastas.
 Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80%
amylopectin by weight.
Glycogen
• Glycogen is also known as “animal starch”.
• It is stored in muscle and liver tissue
• Complete hydrolysis yields glucose
Glycogen
• Glycogen is the glucose storage polymer in animals, is
similar in structure to amylopectin, but glycogen has
more branches
• The highly branched structure permits rapid release of
glucose from glycogen stores, i.e. in muscle during
exercise. The ability to rapidly mobilize glucose is more
essential to animals than to plants
A. Physical properties of carbohydrates
D and L forms of sugars
 Asymmetric carbon atom: It is a carbon atom
attached to four different atoms or groups.
 Any compound has asymmetric carbon posses
the following properties:
1-Formation of isomers.
2-Having optical activity
 Isomers exist in two forms:
1-D-form (when the hydroxyl group lies
on right side to the asymmetric carbon atom)
2-L-form (when the hydroxyl group lies
on left side to the asymmetric carbon atom).
 In nature, glucose is found in the D form only.
Asymmetric carbon atom
Cyclic and linear forms
 Monosaccharides of five or more carbon atoms are present
in ring forms.
 In solutions, cyclic forms are in equilibrium with minute
amounts of the linear forms.
Enantiomers (Anomers)
• The anomeric carbon atom (C#1) can exist as two different isomers called α and β.
• α and β differ only in configuration of OH of the anomeric carbon compared to C #6
• Though almost exactly the same, they operate differently in our bodies.
For example: Humans have the α-amylase enzyme for the digestion of starch, but not the
β-amylase enzyme for the digestion of cellulose.
∴ We can digest starch products such as pasta (α-Form) and not paper or wood (β- form).
β-D-Glucose
α-D-Glucose
B. Chemical properties of carbohydrates
 Reduction of monosaccharides
producing sugar alcohol:
The aldehyde and keto group of
monosaccharides can be reduced by H2 +
catalyst(non enzymatically) or by enzymes
producing the corresponding alcohol.
 Ester formation:
The most common esters of
monosaccharidesa are phosphate esters.
Ex; Adenosine triphosphate (ATP),
glyceraldehydes-3-phosphate.
Alcohol
Acid
Ester
 Reaction with acids:
Concentrated acid remove three water molecules from sugar forming furfural
from pentose and hydroxyl furfural from hexose. The furfurals further react
with phenols (naphthol) present in to produce a purple ring interface.
 Reaction with bases:
Strong alkali as concentrated NaOH on heating leads to condensation of
monosaccharides forming yellow and brown resin and caramel formation.
Deoxygenation of Hydroxyl Groups
 The hydroxyl groups on Carbon atom#2 of Monosaccharides can
be replaced with hydrogen atoms to form deoxy-sugars.
 Deoxygenation of ribose within a ribonucleotide to form the 2-
deoxyribonucleotide is a critical reaction in DNA biosynthesis.
Biomolecules
Interconversion
(Acetyl CoA)
Please Remember
Students selected for assignment
 ‫حنان حلمي أبراهيم‬
 ‫أيمان محمد أحمد‬
ASSIGNMENTS
The students are requested to prepare slides about the following
topics and delivered before next lecture:
1. Importance of cellulose in plants.()
2. Hypoglycemia.()
3. Hyperglycemia.()
4. Carbohydrates and immunity.()
5. Carbohydrates and cell signaling.()
6. Carbohydrates and as building blocks.()
7. Carbohydrate as fuel()
Study Questions
 Mention 3 different functions of carbohydrates
Complete:
 Monosaccharaides can be aldoses or …………….
 The starch of human body is called---------.
 The major carbohydrates in plants is called……………...
 Mention 4 functions of carbohydrates.
Suggested readings:
• Harper’s Biochemistry 26th edition