Chapter 1 All

:

CHAPTER 1: MOLECULES OF LIFE

(7 HRS)

1.0 Molecules Of Life (7 hrs)

1.1 Water (1)

1.2 Carbohydrates (1)

1.3 Lipids (1)

1.4 Proteins (2)

1.5 Nucleic Acids (1)

Learning outcomes

a) Explain the structure of water molecule

b) Describe the properties of water and its importance

Structure:

1 oxygen atom & 2 hydrogen atoms (H2O)

Joined together by sharing electrons ~ covalent bond

3 atoms ~ arranged to form a triangle

Angle ~ 104.5

Learning Outcomes : 1.1 (a) Explain the structure of water molecule

H H

O


The sharing of electrons between O & H atoms are not equal

O atom ~ slightly negative charge (-)

H atoms ~ slightly positive charge (+)

Unequal charge distribution within a molecule ~ polar molecule

2-

+ +

O

H H

+ H atom of one water molecule is attracted to the - O atom of nearby water molecules

Water molecules are held together by hydrogen bonds

H bond is weak, represented by dotted lines

2-

+ +

2-

+

+

Hydrogen bond


1 water molecule can form maximum of 4 hydrogen bonds with 4 water molecules


Learning Outcomes : 1.1 (b) Describe the properties of water and its importance

Properties of water

1. Universal solvent

2. High specific heat capacity

3. High latent heat of vaporization

4. High surface tension

5. Maximum density at 4C

6. Low viscosity

mn

1. Universal Solvent Powerful solvent for ionic & polar substances (eg: NaCl)

NaCl are held together by ionic bonds between Na+ & Cl-


1. Universal Solvent Water is a polar molecule

The O atoms has a slightly negative charge & H atoms has a slightly positive charge

O atoms are attracted to the positively charged sodium ions

H atoms are attracted to the negatively charged chloride ions

Ionic bonds between NaCl molecules become weaker


1. Universal Solvent

Water molecules gather around the Na+ & Cl- to form a hydration shell, separating them from one another

Pulling these ions away from the salt crystal

Causes these ions to separate & dissolve


1. Universal Solvent

Importance:

Act as transport medium for solutes (eg: dissolved nutrients are carried throughout the body in blood plasma)

Water facilitates chemical reaction (solutes are more reactive when dissolved)



Definition : amount of energy needed to increase the temperature of 1 g of a substance by 1C

Large amount of energy is needed to increase the temperature of 1 g of water by 1oC

Heat is absorbed to break the H bonds between water molecules

Value = 1 cal/g (most substances have lower value)

A large body of water (ocean/lakes) has a relatively constant temperature although its surrounding temperature changes (temperature rises & falls slowly)



Importance:

Organisms can maintain their normal body temperature

Aquatic organisms can live in a relatively stable temperature (protected from rapid temperature changes)



Definition : Amount of energy needed to change 1 g of a

substance from liquid phase to vapor

A lot of energy is needed to change 1 g of water from

liquid state to vapor

Heat is absorbed to break the H bonds between water

molecules before they can move faster & vaporized

Value = 540 cal/g


Importance:

Cooling effect in organisms due to sweating (animals) or transpiration (plants)

Explanation:

As water absorbs heat, its energy increases

When water evaporates, it takes a lot of heat energy away lowering the temperature of the organism




H bonds make water molecules stick to each other cohesion

On the surface, water has greater attraction for each other than for molecules in the air



Water are also pulled downward by other water molecules beneath them

Produce a strong layer on the surface, hard to break the water surface create high surface tension

Water molecules can also stick to other substances adhesion



Importance:

Allow some organisms to move on water (eg: water strider)


As water cools, the molecules get closer together

Reach maximum density at 4C

At temperature below 4C, water molecules expand until it freezes/solidifies (at 0C)




H bonds in ice space the water molecules far apart & become stable

Ice is less dense than cold water floats



Importance:

Allow aquatic life to live under the frozen surface of water in cold climate region

Explanation:

The floating layer of ice insulates the water below, prevent them from losing heat & from freezing


6. Low viscosity

Weak H bonds between water molecules are constantly breaking & reforming.

Water molecules can slide easily over each other

It flows with less friction through narrow vessels.

Importance:

Act as medium of transportation in living organisms (eg: blood easily flow in the circulatory system)

Act as a good lubricant to reduce friction within body (eg: mucus facilitates movement of feces through the bowel)



1.1 Water (1)


1.3 Lipids (1)

1.4 Proteins (2)


Learning outcomes

a) Describe various forms & classes of carbohydrates

b) Describe the formation & breakdown of maltose

c) Describe the structures & functions of starch, glycogen and cellulose

Learning Outcomes : 1.2 (a) Describe various forms and classes of carbohydrates

Composed of carbon, hydrogen & oxygen atoms

Ratio of C, H & O ~ approximately 1:2:1 (CH2O)n

n = number of C atoms

Introduction

Classification

Monosaccharide Polysaccharide Disaccharide

1 sugar unit 2 sugar units Many sugar units

Classes of carbohydrates:


MONOSACCHARIDES

1. Small

2. Sweet

3. Soluble in water

4. Can crystallized

5. White / colourless

6. Reducing sugar

1 sugar molecule; simple sugar (3-7 carbon atoms)

Characteristics:


Based on the position of functional group

Aldose Ketose Triose 3C Pentose 5C Hexose 6C

Classification

Based on no. of C atom

Classes of monosaccharide:


Functional group ~ carbonyl group (C=O)

1. Aldose sugar

Carbonyl group is located at the end of carbon chain

Eg: glucose

2. Ketose sugar

Carbonyl group is located in the middle of carbon chain

Eg: fructose

Numbering of carbon chain begins with the carbon nearest to carbonyl group

Classes of monosaccharide: based on the position of functional group

Learning Outcomes : (a) Describe various forms and classes of carbohydrates


3 classes:

1. Triose sugar (3 C atoms)

Eg: glyceraldehyde & dihidroxyacetone; C3H6O3

2. Pentose sugar (5 C atoms) will be discussed in nucleic acid

Eg: ribose, ribulose; C5H10O5, & deoxyribose; C5H10O4

3. Hexose sugar (6 C atoms)

Eg: glucose, galactose, fructose; C6H12O6

When dissolved in water, pentose & hexose form ring structure; which is more stable

Classes of monosaccharide: based on the number of carbon atom


Same molecular formulas but different arrangements of atoms ~ isomers

Glucose ~ blood sugar, moderate sweetness, found in fruits & vegetables

Galactose ~ less sweet, found in milk & yoghurt

Fructose ~ fruit sugar, sweetest, found in fruits & honey

Hexose sugar (6 C atoms)


Linear and ring forms of glucose. To form the glucose ring, carbon 1 bonds to the oxygen attached to carbon 5.

Glucose

Each of these structure is glucose (C6H12O6)

a. All carbon atoms are clearly shown

b. The carbon atoms are omitted

c. The hydrogen atoms are omitted


Glucose

2 isomeric forms, according to the position of OH group at C1

above the ring plane = -glucose

below the ring plane = -glucose


Function of Monosaccharides

Energy source

Glucose ~ major respiratory substrate, primary energy source

Basic building units or monomers for disaccharide & polysaccharide


DISACCHARIDES

1. Sweet

2. Soluble in water

3. Can crystallized

4. White / colourless

2 sugar molecules or two monosaccharides

Joined together by a condensation process (removal of a water molecule)

Form covalent bond glycosidic bond

Can be broken down into monomers by hydrolysis process (addition of water molecule)

Characteristics:

Disaccharide

Maltose Sucrose Lactose

Learning Outcomes : 1.2 (b) Describe the formation and breakdown of maltose

Condensation

Hydrolysis

CONDENSATION PROCESS

HYDROLYSIS PROCESS


MALTOSE

Malt sugar

Monomers : -glucose + -glucose

Joined together by -1,4 glycosidic bond (between C1 of one glucose molecule and C4 of another molecule)

condensation

hydrolysis

-glucose (C6H12O6)

-glucose (C6H12O6)

Maltose (C12H22O11)

-1,4 glycosidic

bond

+

condensation

hydrolysis


POLYSACCHARIDES

1. Large molecule

2. Not sweet

3. Insoluble in water (form colloid)

Many sugar molecules; polymer (vary in length)

Joined together by condensation process (removal of a water molecules)

Form covalent bond glycosidic bond

Formation of polymer (large molecules made up of repeating units of monomers) polymerization

Can be broken down into monomers by hydrolysis process (addition of water molecules)

Characteristics:

Polysaccharide

Starch Glycogen Cellulose

Amylose Amylopectin

Learning Outcomes : 1.2 (c) Describe the structures and functions of starch, glycogen and cellulose

Energy storage in plants

Plants convert excess glucose into starch for storage in chloroplast

Monomers: -glucose molecules

Broken down by hydrolysis process with the help of amylase enzyme

Starch is a mixture of:

Amylose

Amylopectin

STARCH




Joined together by -1,4 glycosidic bond

Helical, due to the formation of H bonds

Unbranched chain (variable length of monomers)

Folded ~ very compact (ideal for storage)

AMYLOSE

O O

-1,4 glycosidic bond

O O O

OH

OH

CH2OH

1 4

2 3

5

6

OH

CH2OH

1 4

2 3

5

6

OH

OH

CH2OH

4 1

6

2 3

5

OH

OH

CH2OH

4 1

6

2 3

5

OH

-glucose -glucose -glucose -glucose


Joined together by -1,4 glycosidic bond & -1,6 glycosidic bond

Helical, branched chain (variable length of monomers)

Branches occur within 30 units

Folded & branched ~ very compact (ideal for storage)

AMYLOPECTIN


AMYLOPECTIN

O O O O O

OH

OH

CH2OH

1 4

2 3

5

6

OH

CH2OH

1 4

2 3

5

6

OH

OH 4 1

6

2 3

5

OH

OH

CH2OH

4 1

6

2 3

5

OH


OH

OH

CH2OH

4 1

6

2 3

5

OH

OH

CH2OH

4 1

6

2 3

5

O O

C H H



O


DIFFERENCES BETWEEN AMYLOSE &

AMYLOPECTIN

Features Amylose Amylopectin

Monomers -glucose -glucose

Bond

-1,4 glycosidic bond -1,4 glycosidic bond


Shape Helical, unbranched Helical, branched (within

30 units)

Function

Ideal for energy storage

(insoluble, coiled, compact)


Energy storage in animals (in liver & muscle)

Structure ~ similar to amylopectin

More branched than amylopectin

GLYCOGEN


Major component of plant cell wall

Monomers: -glucose

Bond: -1,4 glycosidic bond

Broken down by hydrolysis with the help of cellulase enzyme

Unbranched, long straight chain

CELLULOSE

O O


O

OH

OH

CH2OH

1 4

2 3

5

6

OH

CH2OH

1 4

2 3

5

6

OH

OH

CH2OH

4 1

6

2 3

5

OH

OH

CH2OH

4 1

6

2 3

5

OH



CELLULOSE



Straight chains are arranged parallel to one another

Linked together by hydrogen bonds (form microfibril)

Very stable & tough structure ~ provide support to plant cell

CELLULOSE


Functions of Polysaccharides

Energy Storage ~ eg: starch (in plant) & glycogen (in animals)

Major component of cell walls ~ provide structural support to

plant cell ~ eg: cellulose



1.1 Water (1)


1.3 Lipids (1)

1.4 Proteins (2)


Learning outcomes

a) State the types of lipid

b) Describe the structure of glycerol & fatty acids

c) Describe the formation & breakdown of triglycerides

Learning Outcomes : 1.3 (a) State the types of lipid: fats, phospholipids and steroids

LIPIDS

Fats Steroids Phospholipids

Consist of mainly carbon & hydrogen atoms; few oxygen atom

Group of hydrophobic molecules ~ insoluble in water

3 major types:

LIPIDS

Eg: oil, butter Eg: lecithin Eg: cholesterol


Building block

1 Glycerol 3 Fatty acids

Saturated Unsaturated

Most abundant

Also known as (a.k.a) : Triglyceride / Triacylglycerol

FATS

a) Structure of glycerol and b) general structure of fatty acids

Learning Outcomes : 1.3 (b) Describe the structure of glycerols and fatty acids

.

A.k.a : glycerine

3C alcohol with 3 OH groups (soluble in water)

C

C

C

OH

OH

OH

H

H

H

H

H

Glycerol

.

Fatty Acids

Has 2 regions:

Hydrophilic head (a carboxyl group, COOH at 1 end ) ~ acid

Hydrophobic tail ~ long unbranched hydrocarbon chain (known as side chain, R)

HO C1

O

C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14

H H H H H H H H H H H H H

H H H H H H H H H H H H H

H

Carboxyl group Hydrocarbon chain

R


. Hydrophobic tail vary in length

Different fatty acids has different number of C atoms (usually 16 or 18)

C2 HO C3 C4 C5 C6 C7 C8 C9 C1

H H H H H H H O

H H H H H H H H

C10

H H

C11 C12 C13 C15 C14

H H H H H

H H H H

C16 C18 C17

H H H

H H H

H

H H

Eg: Stearic acid (stearate) C18H36O2

Fatty Acids


. Based on the presence of double bonds within hydrocarbon

chain:

Saturated fatty acids

~ no double bond between C atoms; eg: stearic acid

Unsaturated fatty acids

~ has double bonds between C atoms; eg: oleic acid

C2 HO C3 C4 C5 C6 C7 C8 C9 C1

H H H H H H H O

H H H H H H H H

C10

H H

C11 C12 C13 C15 C14

H H H H H

H H H H

C16 C18 C17

H H H

H H H

H

H H

Eg: Stearic acid (stearate) C18H36O2

Classification of Fatty Acids


. Has maximum number

of H atoms

Straight chain, fatty acids can be closely packed

Solid at room temperature

SATURATED FATTY ACID


.


Fats that consist of saturated fatty acids ~ saturated fat

Mostly animal fats (eg: butter, lard)


Double bond causes

bending in

unsaturated fatty

acids

Fatty acids cannot be

closely packed

Liquid at room

temperature

UNSATURATED FATTY ACID


UNSATURATED FATTY ACID

Fats that consist of unsaturated fatty acids ~ unsaturated fat

Mostly plant & fishes fats (eg: oil)


Fatty acids stearic acid (saturated fat) and oleic acid (unsaturated fat).

. Based on the ability to be synthesized in the body:

Essential fatty acids

~ cannot be synthesized in the body

~ must be present in the diet

~ eg: linoleic, linolenic and arachidonic acids

Non-essential fatty acids

~ can be synthesized in the body

~ eg: stearic acid & others

Classification of Fatty Acids


PHOSPHOLIPIDS

Building block

1 Glycerol 2 Fatty acids Phosphate group

Major component of cell membrane; eg: lecithin

Amphipathic molecule

i.e one end hydrophilic polar, another end hydrophobic non-polar



PHOSPHOLIPIDS

Composed of 3 fatty acids & 1 glycerol backbone

Fats are formed when 3 condensation reaction occurs ~ also

known as esterification

Water is removed by extracting the OH from the carboxyl

group (of fatty acid) and H from the glycerols hydroxyl group

Triglyceride can be broken down by hydrolysis

TRIGLYCERIDE

Learning Outcomes : 1.3 (c) Describe the formation & breakdown of triglycerides


Formation of Triglycerides

C OH H

H

H

R HO

O

C

C OH H

C OH H

R HO

O

C

R HO

O

C

C O H

H

H

R

O

C

C O H

C O H

R

O

C

R

O

C

1 glycerol 3 fatty acids

Condensation

Triglyceride

+ 3H2O

Hydrolysis

Ester bond

Ester bond

Ester bond

Importance of Lipids

Main energy storage in animals (due to higher number of

hydrogen atom)

1 g of fat has > twice energy than same weight of starch

Lighter ~ hydrophobic nature, doesnt associates with

water

Improve buoyancy in aquatic animals

Provide better thermal insulation of mammals

Act as padding for internal organs

Phospholipid ~ major component of plasma membrane

Steroid ~ some are hormones that regulates metabolism



1.1 Water (1)


1.3 Lipids (1)

1.4 Proteins (2)


Learning outcomes

a) Describe the basic structure of amino acids

b) Explain how amino acids are grouped

c) Describe the formation and breakdown of dipeptide

d) Explain primary, secondary, tertiary & quaternary levels of proteins & the types of bonds involved

e) Classify proteins according to their structure

f) Explain the effect of pH & temperature on the structure of protein

Learning Outcomes : 1.4 (a) Describe the basic structure of amino acids

PROTEIN

Polymer

Building blocks ~ amino acids

Joined together to form a long chain ~ polypeptide

Protein consist of 1 or more polypeptide chains which folded & coiled into specific conformation

Mostly composed of C, H, O, N & sometimes S

BASIC STRUCTURE OF AMINO ACIDS

C H2N COOH

R

H

Amino acids consist of 4 components attached to a central carbon

These components include:

a. a hydrogen atom

b. a carboxyl group

c. an amino group

d. a variable R group (or side chain).

amino group carboxyl group


BASIC STRUCTURE OF AMINO ACIDS

i. COOH (carboxyl group)

ii. NH2 (amino group) : basic

: acidic

C H2N COOH

R

H

2 functional groups:


Amino acids are amphoteric; have both acidic & basic properties


Learning Outcomes : 1.4 (b) Explain how amino acids are grouped

20 types of amino acids commonly found in proteins

All have the same basic structure but differ in the side chain, R

Amino acids are grouped based on the properties of R group

GROUP OF AMINO ACIDS

C H2N COOH

R

H


Serine (ser)

Aspartic acid (asp)

Lysine (Lys)

Glycine (gly)

4 groups

Non-polar Basic Polar Acidic

Hydrophilic Has COOH group Has NH2 group Hydrophobic


i. Essential amino acids (for human)

Cannot be synthesized in sufficient amount, must be

obtained through food or supplement intake

8 amino acids; eg: isoleucine, leucine, lysine, methionine,

phenylalanine, threonine, tryptophan, valine

For infants : histidine

ii. Non-essential amino acids

Can be synthesized in the body

Eg: alanine, arginine, asparagine, aspartic acid, cysteine,

glutamic acid, glycine, proline, serine, tyrosine, glutamine

GROUP OF AMINO ACIDS


Learning Outcomes : 1.4 (c) Describe the formation and breakdown of dipeptide

2 amino acids are joined by condensation process to form a dipeptide

By removal of a hydroxyl group from the carboxyl end of one amino acid and a hydrogen from the amino group of another amino acid.

Form a covalent bond ~ peptide bond

Formation of the dipeptide

Learning Outcomes : (c) describe the formation and breakdown of dipeptide

OH C N C

O R1

H

H

H

H C N C OH

O R2

H H

Peptide bond

C N C

O R1

H

H

H

C N C OH

O R2

H H

H2O

Condensation

H2O

Hydrolysis

C-terminal N-terminal

Formation & breakdown of the dipeptide


Dipeptide is hydrolysed into 2 amino acids by hydrolysis process (addition of water).

Peptide bond is broken down and produces 2 amino acids.

Breakdown of dipeptide


Many amino acids are joined by condensation process to form a polypeptide

Bond ~ peptide bonds

Polypeptide backbone ~ repeated sequence of (-N-C-C-)

Formation of polypeptide

OH H C N C

O R2

H H

H C N C OH

O R3

H H

Peptide bond

H OH C N C

O R1

H H

Peptide bond


Formation of tripeptide


Two ways based on:-

Level of protein structure

i. Primary

ii. Secondary

iii. Tertiary

iv. Quaternary

Structure

i. Fibrous

ii. Globular

iii. Conjugated

Classification of Protein

Learning Outcomes : 1.4 (d) Explain primary, secondary, tertiary & quaternary levels of proteins & the types of bonds involved

Learning Outcomes : (d) explain primary, secondary, tertiary and quaternary levels of proteins and the types of bonds involved

Learning Outcomes : (d) explain primary, secondary, tertiary and quaternary levels of proteins and the types of bonds involved Learning Outcomes :

1.4 (d) Explain primary, secondary, tertiary & quaternary levels of proteins & the types of bonds involved

Primary structure

Refers to the linear sequence of amino acids joined by peptide bonds within a polypeptide chain

Each protein has a unique sequence of amino acids, determined by specific DNA code

Different sequence results in the formation of different bonds between amino acids

Causes a polypeptide chain to fold & coil into a unique 3 dimensional shape of protein

Eg : lysozyme & all protein that has been sequenced


Primary structure


Secondary structure

Linear chain of amino acids will coil or fold spontaneously

Due to the formation of H bonds between the backbones (between H of the NH groups & O of the C=O groups of amino acids in the primary chain)

2 types

-helix

-pleated sheet


Secondary structure


-helix

Helical coil

H bonds is formed between 1 amino acid & the 4th amino acid away from it

Can stretch under tension ~ provide elasticity

Because the hydrogen bonds can be reformed

Eg: keratin in hair, nails & wool

| S |

S |

| S |

S |


-pleated sheet

Zig-zag pattern ~ provide strength & flexibility

Eg: silk, spider web


Tertiary structure

1 polypeptide chain in secondary structure may further coiled into a globular shape which is maintained by bonds and interactions among R groups

Globular shape unique to each polypeptide chain

Mantained by 4 interactions between R groups:-

Disulfide bonds (covalent bonds) between R groups with sulfhydryl groups

Ionic bonds between +ve & -ve charged R groups

Hydrogen bonds between + & - charged R groups

Hydrophobic / Van der Waals interaction between non-polar R groups


Tertiary structure


Features Primary Secondary Tertiary

Type of

bond exist

i. Peptide

bond

i. Peptide bond

ii. H bond (between

C=O & NH group of

backbone)

i. Peptide bond

ii. H bond (between C=O

& NH group of

backbone)

iii. Disulfide bond

iv. Ionic bond

v. H bond (between R

groups)

vi. Hydrophobic (van der

Waals) interaction

Tertiary structure

Eg: enzymes, hormones, antibodies

Type of bonds exist in different levels of protein:


Quaternary structure

Refers to a single protein that is formed when two or more polypeptide chain joins

Bonds exist ~ same as tertiary structure

Eg: hemoglobin (consist of 4 polypeptide chains, two chains and two chains)


4 Levels of Protein


Classification of Protein

FIBROUS

Mostly secondary structure

Form long parallel filaments or strands

Insoluble & stable

Function : mechanical & structural support

Eg:

Keratin, actin, myosin, collagen, silk

Fibrous Globular Conjugated

Based on Structure

Learning Outcomes : 1.4 (e) Classify proteins according to their structure

Globular Protein

Mostly tertiary/quaternary structure

Folded to form compact spherical shaped

Relatively unstable

Relatively soluble ~ colloid

Function : metabolic & chemical process

Eg:

Enzyme

Antibodies

Hormone

Hemoglobin


Conjugated Proteins

Conjugated Protein Prosthetic group Location

Glycoprotein Polysaccharide Component of cell membrane

Mucin (in saliva)

Lipoprotein Lipid Component of cell membrane

Lipid transported in blood

plasma

Chromoprotein Pigment Myoglobin, hemoglobin

Nucleoprotein Nucleic acid Chromosome, ribosome

Protein that can function well if it joins with other compound

Non-protein compound ~ prosthetic group


Effect of pH and Temperature

Structure of protein is affected by:-

1. pH

2. temperature

Globular protein is relatively unstable because it is maintained

by weak ionic bonds, hydrogen bonds & hydrophobic

interactions

When protein is heated or exposed to an extreme pH

changes, those bonds are broken

Causes it to uncoiled & change its conformation

Lose its biological function ~ denatured protein coagulate

Usually irreversible (sometimes, renaturation may occur)

Learning Outcomes : 1.4 (f) Explain the effect of pH and temperature on the structure of protein

Factor Effect to the protein structure

Heat or radiation Increased kinetic energy

Protein atoms vibrate

H & ionic bonds, van der Waals interaction break

Strong acids & alkali

H & ionic bonds, van der Waals interaction break

Breakdown of peptide bonds occur if exposed very long

Effect of pH and Temperature

Learning Outcomes : 1.4 (f) Explain the effect of pH and temperature on the structure of protein


1.1 Water (1)


1.3 Lipids (1)

1.4 Proteins (2)


Learning outcomes

a) Describe the structure of nucleotide as the monomer of nucleic acid (DNA & RNA)

b) Describe the structure of DNA based on the Watson & Crick Model

c) State the types & function of RNA

d) State the differences of DNA & RNA

Learning Outcomes : 1.5 (a) Describe the structure of nucleotide as the monomer of nucleic acid (DNA and RNA)

Nucleic acid is polynucleotide ~ polymer of nucleotides

Building blocks ~ nucleotide

Mostly composed of C, H, O, P & N

Introduction

NUCLEIC ACIDS

2 types

Deoxyribonucleic Acid (DNA)

Ribonucleic Acid (RNA)


Structure of nucleotides

Each nucleotide has 3 components:-

Nucleotide

Pentose sugar Phosphate group Nitrogenous base


Ribose (in RNA)

Deoxyribose (in DNA)

Pentose Sugar (5 C sugars)

Ribose ~ component of RNA nucleotide

Deoxyribose ~ component of DNA nucleotide

At 2nd carbon atom ~ in deoxyribose; one H atom

~ in ribose; one OH group

C5H10O4 C5H10O5


Nitrogenous base

Based on the number of C ring

2 groups

Pyrimidine Purine

Cytosine (C) Uracil (U) Thymine (T) Adenine (A) Guanine (G)

Single ring Double rings

In RNA In DNA


Learning Outcomes : (a) Describe the structure of nucleotide as the basic composition of nucleic acid (DNA and RNA)

Nitrogenous base

Nitrogenous base in DNA:

i. Guanine

ii. Adenine

iii. Thymine

iv. Cytosine

Nitrogenous base in RNA:

i. Guanine

ii. Adenine

iii. Uracil

iv. Cytosine


Nitrogenous Base

CH2

H

O

H

OH H

H

H

OH

HO P O

O

Pentose Sugar ~ deoxyribose

Phosphate Group

1

2 3

4

5

Learning Outcomes : (a) Describe the structure of nucleotide as the basic composition of nucleic acid (DNA and RNA)

Nitrogenous Base

CH2

H

O

H

OH OH

H

H

OH

HO P O

O

Pentose Sugar ~ ribose

Phosphate Group

1

2 3

4

5

deoxyribose ribose

DNA nucleotide RNA nucleotide

In a nucleotide :

nitrogenous base is joined to the 1st carbon of the pentose

phosphate group is joined to the 5th carbon of the pentose


2 nucleotides are combined by condensation process ~ dinucleotide

Between OH group in phosphate group (of 1 nucleotide) and the OH group at the 3rd carbon in pentose sugar (of the other nucleotide)

Joined together by phosphodiester bond

FORMATION OF DINUCLEOTIDE


FORMATION OF DINUCLEOTIDE

CH2

H

O

H

OH H

H

H

OH

HO P O

O 1

2 3

4

5

deoxyribose

CH2

H

O

H

OH H

H

H

OH

HO P O

O 1

2 3

4

5

deoxyribose

CH2

H

O

H

H

H

H

OH

HO P O

O 1

2 3

4

5

deoxyribose

CH2

H

O

H

OH H

H

H

O

HO P O

O 1

2 3

4

5

deoxyribose

phosphodiester bond

condensation


Many nucleotides joined together ~ polynucleotide

Elongation ~ from 5 to 3

Forming a backbone with repeating sugar-phosphate units

Breakdown by hydrolysis process

5

3

FORMATION OF POLYNUCLEOTIDE


Based on Watson & Crick Model

DNA Structure

Learning Outcomes : 1.5 (b) Describe the structure of DNA based on the Watson & Crick Model

Consist of 2 polynucleotide chains

Both polynucleotide chains are twisted to form a double helix

Each polynucleotide chain is made up of nucleotide

Nucleotides are joined together by phosphodiester bond

Each full turn of a double helix has 10 base pairs

DNA Structure


2 polynucleotide chains are arranged in opposite direction (antiparallel)

One strand ends with a 3 hydroxyl group while the other strand ends with a 5 phosphate group

5 '

3 '

3 '

5 '

DNA Structure


Sugar-phosphate forms the backbone

The 2 backbones are on the outside, the nitrogenous bases are paired inside the helix

DNA Structure


Both chains are held together by hydrogen bonds between complementary base pair;

Adenine with Thymine, Cytosine with Guanine

Between Adenine & Thymine ~ 2 hydrogen bonds

Between Cytosine & Guanine ~ 3 hydrogen bonds

Specific base-pairing rule ~ the numbers of A=T, G=C

5 '

3 '

3 '

5 '

DNA Structure


Importance:

As genetic material which carries genetic information that control all activities of a cell

DNA


Single stranded polynucleotide

Pentose sugar ~ ribose

Nitrogenous bases ~ Guanine, Adenine, Cytosine, Uracil

3 types:

RNA

Messenger RNA (mRNA)

Transfer RNA (tRNA)

Ribosomal RNA (rRNA)

RNA

Learning Outcomes : 1.5 (c) State the types & function of RNA

Function :

Carries genetic information copied from DNA which act as a template for protein synthesis

mRNA


Function :

Forms ribosomal subunits (together with proteins)

rRNA


Function :

Transfer specific amino acids to ribosome during protein synthesis

tRNA


RNA


DNA RNA

2 polynucleotide chains 1 polynucleotide chain

pentose sugar ~ deoxyribose pentose sugar ~ ribose

nitrogenous base ~ G, A, T, C nitrogenous base ~ G, A, C, U

shape ~ double helix shape ~ linear (mRNA)

longer chain / larger molecular

mass

shorter chain / smaller molecular

mass

Only 1 type Has 3 types : mRNA, rRNA &

tRNA

Differences between DNA & RNA

Learning Outcomes : 1.5 (d) State the differences of DNA & RNA

Reference

Campbell N.A & Reece, J.B., Biology, 6th ed. (2002), Pearson Education, Inc.

Solomon E.P & Berg, L.R, Biology, 7th ed. (2005) Thomson Learning, Inc.

Mader, S.S Biology, 8th ed. (2004) McGraw-Hill Companies, Inc.

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