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

Triose Pentose

e.g. glucosefructose

Hexose

Monosacchaides

e.g. MaltoseSucrose

Disaccharides

e.g. starch,cellulose

Polysaccharides

Carbohydrates

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

Example of Hexose: glucose C6H12O6

Alpha- glucose Beta- glucose

Component of cellulose

Monosaccharides

Component of starch

O

CH2OH

H

OHH

OH

H

OH

H

HO

H

1

2

6

5

4

3

O

CH2OH

H

OH

H

OH

H

OH

H

HO

H

1

23

4

5

6

Examples of Hexose: -glucose and fructose

O

CH2OH

H

OHH

OH

H

OH

H

HO

H

-glucose Fructose

Monosaccharides

O

CH2OH CH2OH

OHOH

OH H

HH

1

2

34

5

6

-glucose and -glucose are stereo-isomers.

Fructose and -glucose are structural isomers.

Disaccharides

Each disaccharide molecule is formed by condensation of two monosaccharide molecules.

Disaccharides C12H22O11

O

CH2OH

H

OHH

OH

H

OH

H

HO

H

1

2

6

5

4

3

O

CH2OH

H

OHH

OH

H

OH

H

HO

H

1

2

6

5

4

3

-glucose -glucose

Disaccharides: Maltose

O

CH2OH

H

H

OH

H

OH

H

HO

H

1

2

6

5

4

3

O

CH2OH

H

OHH

OH

H

OH

H

H

1

2

6

5

4

3

-glucose -glucose

O

1,4 - glycosidic linkage

O

CH2OH

H

OHH

OH

H

OH

H

HO

H

O

CH2OHCH2OH

OHOH

OHH

HH

1

2

3 4

5

6

-glucose Fructose

Disaccharide : Sucrose

O

CH2OH

H

H

OH

H

OH

H

HO

H

O

CH2OHCH2OH

OH

OHH

HH

1

2

3 4

5

6

-glucose Fructose

O1

23

4

5

6

Hydrolysis of a disaccharide molecule forms two molecules of monosaccharide.

Amylose molecule

Polysaccharide

Polysaccharide

Amylose molecule

Polysaccharide

Amylopectin molecule

Polysaccharide

Starch consists of both amylose and amylopectin.

Glycogen consists of amylopectin only.

Polysaccharide: Cellulose

OH

HO

OH

HO

OH

HO

OH

HO

1,4 beta glycosidic linkage

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

Glycerol Fatty acids Triglyceride

C

C

C

OH

OH

OH

H

H

H

H

H

HO C

O

HO C

O

HO C

O

C

C

C

O

O

O

H

H

H

H

H

C

O

C

O

C

O

Lipid (I): Triglyceride (i.e. fat or oil)

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 saturationusually 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 tempera ture regulation in homiothermic animals.

5. Oxidation of triglycerides gives large amount of metabolic water, very important in desert animals.

Phospholipid

Lipid(II): Steroids

A B

C D

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

C C

H

H2N

RO

OH

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).

C C

H

H2N

RO

OH

C C

H

H2N

RO

O-

C C

H

H3N+

RO

O-

H+

Dipolar ion

In acidic medium, the zwitterion accepts H+ from the medium.

C C

H

H3N+

RO

O-

C C

H

H3N+

RO

OH

+ H+

C C

H

H3N+

RO

O-C C

H

H2N

RO

O-

+ OH-

+ H2O

In alkaline medium, the zwitterion provides H+ to neutralize the OH- in the medium.

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 non-essential 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.

 

  + ½ O2C

R

H

CO

OH

H2N C

R

CO

OH

O + NH3

An amino acid can be converted to another kind by a process called transamination.

H OH

C

R’

C

O

H2NC

R

C

O

OH

O+

C

R

H

C

O

OH

H2N C

R’

C

O

OH

O+

The amino acids join to form the primary structure called polypeptide.

C C

H

H2N

R O

OH C C

H

H2N

R O

OH C C

H

H2N

R O

OH

C C

H

N

R O

C C

H

N

R O

C C

H

N

R O

H H H

The polypeptide chains link by H-bond, ionic bond or disulphide linkage. It depends on what functional groups are present in the R groups.

C C

H

N

R O

C C

H

N

O

C C

H

N

O

H H H

R R

Linking through H-bonds:

C

O

OH

CO

OH

Linking through Ionic bonds

H3N+

C

O

O-

Linking through disulphide linkage

SH HS S S

Dehydrogenation

(- 2H)

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 amino acids form their structure.

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

O

CH2OH

OH

OHOH

HH

It has three parts:

pentose

Mononucleotide

O

CH2

OH

OHOH

HH

It has three parts:

pentose

phosphoric acid

P

Mononucleotide

It has three parts:

pentose

phosphoric acid

organic baseO

CH2

OHOH

HH

P

Organic base

1

23

4

5

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?

O

CH2

OHOH

HH

P

adenine

P

This molecule is called Adenosine Diphosphate (ADP).

O

CH2

OHOH

HH

P

adenine

P

P

Name this molecule.

Answer: Adenosine Triphosphate (ATP)

O

CH2

OHOH

HH

P

Organic base

O

CH2

OH

HH

P

Organic base

Dinucleotide

O

CH2

OHOH

HH

P

Adenine

O

CH2

OH

HH

P

Nicotinamide

O

CH2

OHOH

HH

P

Adenine

O

CH2

OH

HH

P

Flavin

Nicotinamide Adenine Dinucleotide (NAD) ?

Flavin Adenine Dinucleotide (FAD)

Polynucleotide

P

P

P

P

P

P

DNA molecule is made of TWO polynucleotide molecules.

P

P

P

P

P

P

P

P

P

P

P

P

Hydrogen bond

End of Chapter 1