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Chapter 1
Chemical constituents of the cell
The Chemical constituents of Cells
1. Carbohydrates
2. Proteins
3. Lipids
4. Nucleotides
5. Water
Types of Carbohydrates
Carbohydrates
Monosacchaides
Triose
Pentose
Hexose
e.g. glucose
fructose
Disaccharides
Polysaccharides
e.g. Maltose
Sucrose
e.g. starch,
cellulose
Monosaccharides
triose: 3- carbon sugar
pentose: 5-carbon sugar
hexose: 6-carbon sugar
Monosaccharide
Some monosaccharides possess aldehyde group.
Some monosaccharides possess ketone group.
What do you understand by the following sugars?
Aldohexose e.g. glucose
Ketohexose e.g. fructose
Altotriose
Aldopentose
Common monosaccharides
Ring form and Chain form of monosaccharides
From your knowledge, suggest a term used to describe the
relationship between glucose and fructose?
Structural isomer
Monosaccharides
Example of Hexose: glucose C6H12O6
6
CH2OH
5
H
6
O
5
H
H
4
HO
OH
CH2OH
H
3
2
H
OH
Alpha- glucose
Component of starch
H
1
4
OH
HO
O
OH
H
1
OH
3
H
H
2
H
OH
Beta- glucose
Component of cellulose
Monosaccharides
Examples of Hexose: -glucose and fructose
CH2OH
CH2OH
6
1
CH2OH
O
O
H
HO
H
H
OH
H
OH
2
5
H
H
OH
OH
3
4
H
OH
-glucose
OH
H
Fructose
-glucose and -glucose are stereoisomers.
Fructose and -glucose are
structural isomers.
Disaccharides
Each disaccharide molecule is formed by condensation of
two monosaccharide molecules.

Disaccharides C12H22O11
6
CH2OH
5
H
6
5
O
H
H
4
HO
OH
CH2OH
H
H
1
4
OH
HO
O
H
H
1
OH
H
OH
3
2
3
2
H
OH
H
OH
-glucose
-glucose
Disaccharides: Maltose
6
CH2OH
5
H
6
5
O
H
H
4
HO
H
1
OH
3
H
H
2
O
H
H
4
O
1,4 OH glycosidic
linkage
-glucose
CH2OH
1
OH
H
OH
3
2
H
OH
-glucose

CH2OH
CH2OH
1
O
H
6
CH2OH
O
H
H
2
HO
OH
H
OH
5
OH
OH
3
H
OH
-glucose
H
H
4
OH
Fructose
H
Disaccharide : Sucrose
CH2OH
6
CH2OH
O
5
H
1
4
HO
2
1
3
H
O
H
H
OH
6
CH2OH
5
O
H
2
OH
-glucose
OH
3
H
H
4
OH
Fructose
H
Hydrolysis of a disaccharide molecule forms two molecules of
monosaccharide.

Polysaccharide
Amylose molecule
Polysaccharide
Amylose molecule
Polysaccharide
Amylopectin molecule
Polysaccharide
Starch consists of both amylose and amylopectin.
Glycogen consists of amylopectin only.
Polysaccharide: Cellulose
OH
HO
OH
OH
HO
1,4 beta glycosidic linkage
HO
HO
OH
In cellulose molecule, cross bridges exist among the
linear chains. The cross bridge is hydrogen bond.
Functions of carbohydrates
Monosaccharide and disaccharide are respiratory
substrate.
Monosaccharide and disaccharide are osmotically
active substances, contributing to the solute potential
of cell sap.
Cellulose is structural materials to build up cell wall.
Starch and glycogen are storage materials.
Types of Lipids
Triglyceride
Steroid
Phospholipid
Wax
Lipoprotein
Lipid (I): Triglyceride (i.e. fat or oil)
H
O
H
O
H
C
OH
HO
C
O
H
C
O
C
O
H
C
OH
HO
C
O
H
C
O
C
O
H
C
OH
C
H
C
O
C
HO
H
Glycerol
H
Fatty acids
Triglyceride
Degree of saturation of the fatty acids determines
the melting point of the triglyceride. The more
saturation the fatty acids have, the higher melting
point the triglyceride has. More unsaturation leads
to lower melting point.
Animal fat with more saturationusually solid at
room temperature.
Plant oil with more unsaturation liquid at room
temperature.
But high degree of unsaturation is not edible.
Unsaturation may be converted to saturation by
catalytic hydrogenation.
Properties of triglycerides
1.
Soluble in organic solvent, but insoluble in
water; not affect water potential of cell.
2.
High energy content, respiratory fuel.
3.
Chemically more stable than proteins and
carbohydrates.
4.
Heat insulator. Therefore it is important in
temperature regulation in homiothermic animals.
5.
Oxidation of triglycerides gives large
amount of metabolic water, very important in desert
animals.
Phospholipid
Lipid(II): Steroids
C
A
D
B
Many hormones are steroid. e.g. testosterone, oestrogen
Cholesterol is a steroid. Cholesterol is the precursor of all
steroid hormones.
Amino acid: the basic unit of protein
R
O
H2N
C
C
OH
H
The -NH2 group is called amino group which is basic in
property.
The -COOH group is called carboxylic group which is acidic
property.
Therefore amino acid is amphoteric(having both acidic and
basic properties).
Amino acid forms dipolar ion (zwitterion).
R
R
O
O
H2N
C
H2N
C
C
C
O-
OH
H
H
H+
R
O
H3N+
C
Dipolar ion
C
O-
H
In acidic medium, the zwitterion accepts H+ from the medium.
R
R
O
H3N+
C
O
+ H+
C
H3N+
C
C
O-
OH
H
H
In alkaline medium, the zwitterion provides H+ to neutralize the OHin the medium.
R
R
O
H3N+
C
+ OH-
C
O-
H
O
H2N
C
C
O-
H
+ H2O
In human beings, 10 kinds of amino acids
can be synthesized. These are called non-essential
amino acids. Another 10 kinds are called essential
amino acids which cannot be synthesized and
should be obtained from the diet.
The first class proteins contain all kinds of nonessential amino acids. This is usually animal
proteins.
Excess amino acids are deaminated in liver to form
alpha keto-acids and ammonia. The latter, being too toxic, is
converted to urea.
R
H2N
C
H
R
O
C
+ ½ O2
OH
O
C
O
C
OH
+ NH3
An amino acid can be converted to another kind by a process called
transamination.
R’
R
O
O
H2N
C
C
+
O
C
C
OH
OH
H
R
R’
O
O
H2N
C
H
+
C
OH
O
C
C
OH
The amino acids join to form the primary structure called
polypeptide.
R
H2N
C
O
OH
C
H2N
H
O
C
C
OH H2N
R
O
C
C
H
R
O
C
C
H
H
H
N
R
R
O
N
C
C
H
H
N
H
R
O
C
C
H
OH
The polypeptide chains link by H-bond, ionic bond or disulphide
linkage. It depends on what functional groups are present in the R
groups.
N
H
R
O
C
C
H
R
O
N
C
C
H
H
N
H
R
O
C
C
H
Linking through H-bonds:
OH
O
C
O
OH
Linking through Ionic bonds
O
C
O-
H3N+
Linking through disulphide linkage
Dehydrogenation
SH
HS
(- 2H)
S
S
Classification of proteins according to their structure
1.Globular protein:
polypeptide chains in it are folded. The molecular shape is
globe like. It is water soluble. They form functional proteins such
as enzyme, hormone, plasma proteins.
2.Fibrous proteins:
The polypeptide chains in it are straight and unfolded. The
molecular shape is elongated. It is insoluble in water.
The cross bridge between polypeptide chains is very strong,
giving strength to the molecule.
They are structural protein e.g. collagen, myosin.
Classification of proteins according to composition
1.Simple proteins-only
structure.
amino
acids
form
their
2.Conjugated proteins-complex with nonprotein
portion called prosthetic group forming an integral
part. e.g. glycoprotein, nucleoprotein, flavoprotein.
Four Structural levels of protein
Primary structure: refers to the amino acids sequence along
the polypeptide chain.
Secondary structure: refers to whether the polypeptide forms a
helical (alpha-helix) or parallel structure (beta-sheet).
Tertiary structure: refers to the helical structure furthers fold
to form a globular form.
Quaternary structure: Several globular polypeptides combine
to form a complex protein structure.
The FOUR structural levels
of Haemoglobin molecule.
Functions of proteins:
1. Structural materials of cells.
2. Reserve materials for energy production.
3. Functional materials e.g. enzymes, some hormones,
antibodies, haemoglobin
Types of Nucleotides
1. Mononucleotide/ Nucleotide
2. Dinucleotide
3. Polynucleotide
Mononucleotide
It has three parts:
pentose
CH2OH
O
OH
H
H
OH
OH
Mononucleotide
It has three parts:
P
pentose
CH2
phosphoric acid
O
OH
H
H
OH
OH
Mononucleotide
It has three parts:
P
pentose
CH2
phosphoric acid
5
O
Organic base
organic base
1
4
H
H
3
OH
2
OH
Types of organic bases:
Adenine
Thymine
Cytosine
Guanine
Uracil
Nicotinamide
Flavin
If the organic base is adenine, the mononucleotide is
called adenine monophosphate or adenosine
monophosphate.(AMP)
If the organic base is thymine, the mononucleotide
is called thymine monophosphate.(TMP)
Can you name the molecule if its organic base is
uracil, cytosine or guanine?
This molecule is called Adenosine Diphosphate (ADP).
P
P
CH2
O
adenine
H
H
OH
OH
Name this molecule.
P
P
Answer: Adenosine
Triphosphate (ATP)
P
CH2
O
adenine
H
H
OH
OH
Dinucleotide
P
Organic
base
CH2
O
H
H
OH
P
CH2
O
H
Organic
base
H
OH
OH
Nicotinamide Adenine
Dinucleotide (NAD)
Flavin Adenine
? Dinucleotide (FAD)
P
P
CH2
CH2
Nicotinamide
O
H
H
H
OH
P
Flavin
O
H
OH
P
CH2
CH2
Adenine
O
H
H
OH
OH
Adenine
O
H
H
OH
OH
Polynucleotide
P
P
P
P
P
P
DNA molecule is made of TWO polynucleotide molecules.
P
P
Hydrogen bond
P
P
P
P
End of Chapter 1