BIOLOGY SCORE

SB015Chapter 1: Molecules Of LifeBioScore

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BIOLOGY SCORE

CHAPTER 1 : MOLECULES OF LIFE SUBTOPIC : 1.1 Water

LEARNING OUTCOME:

i. Explain the structure of water molecule.

ii. Describe the properties of water and its importance:

Universal solvent

Low viscosity

High specific heat capacity

• High latent heat of vaporization

• High surface tension

• Maximum density at 4°C

MAIN IDEAS

/KEY POINT EXPLANATION NOTES

Water molecules

▪ Water has simple molecular formula. It composed of one oxygen atom

and two hydrogen atoms.

▪ A hydrogen atom combined with the oxygen atom by sharing of

electrons.

▪ Each hydrogen atom is covalently bonded to the oxygen via a shared

pair of electrons.

▪ Oxygen also has two unshared pairs of electrons. Thus, oxygen is more

electronegative compared to hydrogen.


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▪ The angle between the two covalent bonds is 104.5°

▪ Oppositely charged regions in neighboring water molecules are attracted

to each other by hydrogen bond_

Properties of

water and its

importance:

- universal

solvent due to its

polarity / polar

molecules

▪ The unequal sharing of electrons and water V-like shape make it a polar

molecule.

▪ When in contact with H2O, ions (eg :salts) and polar (eg: sugar) groups

are surrounded by H2O molecules

▪ Water separate the ions and molecules from each other

Example: Dissolving sodium chloride in water.

▪ The negative ends of water molecules are attracted to sodium ion

▪ The positive ends of the water molecules are attracted to chloride ions.

▪ This causes water molecules surround the individual sodium and

chloride ion and form hydration shell.


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Properties of

water and its

importance:

- low viscosity

▪ water has low viscosity so is a suitable medium for transportation in

living organisms

▪ in animals, low viscosity of water enable the blood plasma and lymph

to flow easily in the circulatory system.

▪ in plants, water in the xylem and phloem can move easily

Properties of

water and its

importance:

- high specific

heat capacity

▪ Water has high specific heat capacity so large amount of energy is

needed to break down the hydrogen bonds among water molecules

before the water molecules can begin to move about more freely and

therefore, causing an increase in temperature.

▪ Water resists changes in temperature and a lot of energy needed to

speed up its molecules.

▪ As a result, organism can maintain stable body temperature

Properties of

water and its

importance:

- High latent

heat of

vaporization

▪ Water has high latent heat of vaporization because hydrogen bonding

between molecules is difficult to be separated and vaporized

▪ When water is heated, it evaporates more rapidly than when it is

cooled. As a result, water,stabilizes temperature in lakes and ponds

provides a mechanism that prevents terrestrial organism from

overheating.

▪ Evaporation of sweat from human skin dissipates body heat and helps

prevent overheating on hot day or when excess heat is generated by

strenuous activity

Properties of

water and its

importance:

-high surface

tension

▪ Water has high surface tension due to cohesion. Cohesion is the linking

together of like water molecules by hydrogen bonds. High surface

tension allows insects (eg. water strider) to walk on pond without

breaking the surface


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▪ Adhesion is the clinging of water molecules to another substance.

▪ Cohesion and adhesion contribute to the transport of water and

dissolved nutrients against gravity in plants

Properties of

water and its

importance:

-Maximum

density at 4°C

▪ Water is less dense as a solid (ice) than as a liquid (water). Ice floats on

liquid water. Water molecules expand when solidify. Floating ice

insulate the water below preventing it from freezing. It allows marine

life to exist under the frozen surface .


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BIOLOGY SCORE

CHAPTER 1 : MOLECULES OF LIFE Subtopic : 1.2 Carbohydrates

Learning Outcome :

i. State the classes of carbohydrate

ii. Illustrate the formation and breakdown of maltose

iii. Compare the structures and functions of starch, glycogen and cellulose.

MAIN IDEAS

/KEY POINT EXPLANATION NOTES

Carbohydrates

▪ Organic compounds containing carbon, hydrogen and oxygen with

the ratio of 1:2:1 ▪ Empirical formula (CH2O)n

Classes of

carbohydrates

Three classes of carbohydrates :

Classes Example

Monosaccharides Glucose, fructose and

galactose

Disaccharides Maltose, sucrose and

lactose

Polysaccharides Starch, glycogen and

cellulose

Characteristics

of

monosaccharides

▪ Sweet tasting ▪ Primary source of energy ▪ Readily soluble in water ▪ Reducing sugar – benedict test ▪ Can be crystallized ▪ Have a carbonyl group (CO) and multiple hydroxyl groups (-OH)

Classification of

monosaccharides

Depending on the location of the carbonyl group, sugar are grouped

into Aldoses or Ketoses

Aldoses Ketoses

Carbonyl group is located

at the terminal carbon in

the chain/ carbon skeleton

Carbonyl group is located

at a carbon that is not at the

end of the chain/carbonyl

group is in the middle of the

carbon skeleton.

Example:

ribose, glucose , galactose

and glyceraldehyde

dihydroxyacetone, ribulose

and fructose


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Interconvertible

forms of glucose

α – glucose β –glucose

-OH group of the first

carbon atom is located

below the plane of the ring

-OH group of the first

carbon atom is located

above the plane of the ring

Disaccharides ▪ Consists of two monosaccharides joined by a glycosidic bond which

formed by a condensation reaction. ▪ Example of disaccharides :Sucrose, maltose and lactose ▪ Characteristics of disaccharides: Same as monosaccharides.

Polysaccharides ▪ Macromolecules, polymers of monosaccharides which joined by

glycosidic linkage.

Formation and

breakdown of

maltose.

▪ Disaccharides are formed by the condensation reactions of two

simple sugar molecules. ▪ Two OH groups, one from each sugar molecule, combine together

to release water and form an oxygen bridge between them .


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Comparison

between the

structures and

functions:

Starch

▪ A granular, tasteless, insoluble in cold water and organic molecule

that is produced by all green plants ▪ The basic chemical formula of the starch molecule is (C6H10O5)n.

Starch is polysaccharide comprising of glucose monomers joined

by α -1,4 glycosidic bonds linkages. ▪ The simplest form of starch is the

o Amylose - linear polymer; o Amylopectin - the branched form.

Amylose

▪ A linear unbranched polymer: straight chain ▪ Amylose chain coils into helix:

o held by hydrogen bonds formed between hydroxyl groups ▪ Glucose units joined by α -1,4 glycosidic bonds

Amylopectin

▪ a branched polymer ▪ linear chains held together by α -1,4 glycosidic bonds ▪ short branches: intervals of approximately 25- 30 monomers where

α -1,6 glycosidic bonds occur

http://global.britannica.com/topic/chemical-formula

http://global.britannica.com/science/polysaccharide

http://global.britannica.com/science/glucose


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Glycogen

▪ Function as major storage in animals ▪ Insoluble in water ▪ Structure similar to amylopectin but larger and with more

extensively branched ▪ The linear chain of α glucose are held together by α -1,4 glycosidic

bond and branches are held by α -1,6 glycosidic bonds

Cellulose

▪ Structural polysaccharides in plant cell walls. ▪ Composed of long unbranched chains of β- glucose subunits linked

by β -1,4 glycosidic bond


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BIOLOGY SCORE

CHAPTER 1 : MOLECULES OF LIFE Subtopic : 1.3Lipids

Learning Outcome :

i. State the types of lipid: triglycerides (fat and oil), phospholipids and steroids.

ii. Describe the structure of fatty acids and glycerols.

iii. Explain the formation and breakdown of triglycerides.

MAIN

IDEAS /KEY

POINT

EXPLANATION NOTES

Lipid

▪ Lipids are organic compounds.

▪ Consist of carbon, hydrogen and oxygen.

▪ Proportion of oxygen is lower than in carbohydrates.

▪ General formula : CnH2nO2

▪ Can store large amount of energy.

▪ The ratio of energy storing C-H bonds in fats is more than twice that

carbohydrates / more C and H

▪ Insoluble in water but soluble in organic solvent

▪ Three types of lipids

● Triglycerides

● Phospholipids

● Steroids

Triglycerides

▪ Triglyceride consist of 1 molecule of glycerol joined to three molecules of

fatty acids by ester bonds. ▪ Glycerol is a three-carbon alcohol that contains three hydroxyl group (-OH) ▪ A fatty acid is a long, unbranched hydrocarbon chain with carboxyl group (-

COOH) at one end. ▪ Form fats and oils mainly for energy storage

Ester bond


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Saturated Fat

Unsaturated Fat

Contain saturated fatty acids Contain unsaturated fatty acids

Solid state at room temperature Liquid state at room temperature

Found in animals

Can be found in plant and fish

No double bond between carbon

atoms

Has one or more double bonds between

carbon atoms which reduces the number

of bonded hydrogen atoms

Phospholipids

▪ Similar to a fat molecule but has only two fatty acids attached to glycerol

rather than three.

▪ The third hydroxyl group of glycerol is joined to a phosphate group, which

has a negative charge.

▪ Essential for cells because they make up the cell membrane

Steroids

▪ Many hormones , as well as cholesterol, are steroids, which are lipids

characterized by a carbon skeleton.

▪ Have a basic four- ring hydrocarbon structure with different functional side

chains.

Formation

and

breakdown

of

Triglycerides

▪ Triglycerides are formed by combining one glycerol with three fatty acid

molecules through the process of condensation . Alcohols have a hydroxyl

(HO–) group. Organic acids have a carboxyl (–COOH) group.


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▪ Alcohols and organic acids join to form esters.


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BIOLOGY SCORE

CHAPTER 1 : MOLECULES OF LIFE

Subtopic : 1.4 Proteins

Learning Outcome :

i. Describe the basic structure of amino acids.

ii. State how amino acids are grouped

iii. Describe primary, secondary, tertiary and quaternary levels of proteins and the types of bonds

involved.

iv. Describe the effects of pH and temperature on the structure of protein.

v. Explain the formation and breakdown of dipeptide.

vi. Classify proteins according to their structure and composition.

MAIN IDEAS /

KEY POINT

EXPLANATION NOTES

Protein ● Organic compounds containing carbon, hydrogen , oxygen

and nitrogen.

● Are polymers with repeated units of monomers ( amino acids)

Protein

monomer

● Amino acids joined together by peptide bond formed a

polypeptide chain or protein.

● Molecules contains amino group, a carboxyl group, a

hydrogen atom and a side chain (specific to each amino acid).

● Amino acids are grouped according to the properties of their

side chain (R group) :

a) Nonpolar amino acid

b) Polar amino acid

c) Acidic amino acid

d) Basic amino acid


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Levels of

proteins

● There are 4 levels of proteins and types of bonds involved :

Levels of

proteins

Bond(s) E.g :

Primary (1ͦ) Peptide Insulin

Secondary (2)ͦ Hydrogen Keratin, spider

cobweb, silk

Tertiary (3ͦ)

(consist of

single

polypeptide

chain)

Hydrogen bond, Ionic

bond, disulphide bridge,

hydrophobic and van de

Waals interaction

Myoglobin,

enzyme

Quaternary (4)ͦ

(consist of more

than one

polypeptide

chain)

Hydrogen bond, Ionic

bond, disulphide bridge,

hydrophobic and van de

Waals interaction

Haemoglobin


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Effects of pH

and temperature

Explain Examples

Temperature • Heat increases the kinetic

energy of the protein chain.

• Excessive motion can

break relatively weak

hydrogen bonds, electrostatic

interactions (ionic bond) and

hydrophobic interactions.

• Protein chain is free to

rearrange after disrupting.

• E.g : Fried

egg white

pH • Extreme pH can cause

protein to denature.

• Change the charges of

acidic and basic functional

groups of proteins.

• Those functional groups will

lose or gain a proton.

• Break hydrogen bonds

between acidic and basic R

groups and disrupt ionic

bonds.

E.g: Enzymes

are affected by

changes in pH.


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Denature/

Renature

Denaturation :

High temperature or various

chemical treatments will

denature a protein, causing it

to loose its shape and hence

ability to function.

Renaturation:

Denatured proteins remains

dissolved, it may renature

when the chemical and

physical aspects of its

environment are restore to

normal.

Formation and

breakdown of

dipeptide

● Amino acids are joined together by a condensation /

dehydration reaction.


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● Breakdown of dipeptide during hydrolysis (water molecules

adds) across the peptide bond forming amino acids.


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Protein

classification

according to

their structure

and

composition.

● Classes of proteins based on the structure:

Class Fibrous Globular

Characteristic

s

Long

polypeptide

chains,

Insoluble in

water, stable

and tough

Compact

polypeptide

chain, tightly

folded, soluble in

water to form

colloidal

suspension and

unstable structure

Examples Collagen, α-

keratin ,elastin,

Enzyme,

antibody,

haemoglobin

● Classification of protein based on composition.


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BIOLOGY SCORE

CHAPTER 1 : MOLECULES OF LIFE

SUBTOPIC : 1.5 : DNA and RNA molecules

LEARNING OUTCOME:

i. State the structure of nucleotide as the basic components of nucleic acid (DNA and RNA).

ii. Illustrate the structure of DNA based on the Watson and Crick Model.

iii. State the types of RNA.

iv. Compare DNA and RNA.

MAIN IDEAS /

KEY POINT

EXPLANATION NOTES

Nucleic acids

● Macromolecules / polymers called polynucleotide.

● TWO types of nucleic acids : DNA and RNA

● Monomer of nucleic acids is nucleotide that made up of :

a) pentose sugar

b) Phosphate group

c) Nitrogenous bases

Components of nucleotide


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● The portion of a nucleotide WITHOUT the phosphate group is

called nucleoside

● Nitrogenous bases are divided into two families :

a) Purines

b) Pyrimidines

● Nitrogenous bases in nucleic acids :

Ring structure Base Symbol Found in

Purines

( double)

Adenine

Guanine

A

G

DNA/RNA

DNA/RNA

Pyrimidines

( single)

Cytosine

Thymine

Uracil

C

T

U

DNA/RNA

DNA

RNA

● Phosphodiester bond between phosphate group at C5 of one

pentose sugar and hydroxyl group (OH) at C3 of the next

pemtose through condensation process.

● Breakdown : hydrolysis


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● Sugar and phosphate group of adjacent nucleotides are linked

together by phosphodiester bond forming a sugar phosphate

backbone of a polynucleotide strand.

Structure of

DNA based on

the Watson and

Crick Model

● James Watson and Francis Crick proposed the double helix model

of DNA in 1953.

● DNA consist of two polynucleotide strands that coiled in a spiral

(anti parallel) to form a double helix structure.

● One strand runs 5’ to 3’ ends while the other strand runs from 3’

and 5’ ends

● Each strand must be complementary to each other

● Complementary base pairing:

● Adenine always pair with thymine

● Guanine always pair with cytosine

● Amount of A = T, amount of G = C

● Held together (base pairs) by hydrogen bond.

● A and T : Two hydrogen bonds

● G and C : Three hydrogen bonds

● The type of pentose sugar is called deoxyribose .

RNA

● RNA structure is a single stranded polymer of nucleotide.

● Functions of RNA:

a) Main genetic material in virus

b) Involve in protein synthesis

● If pairing of base occur, A will pair with U instead of T.

● The type of pentose sugar is ribose.

● 3 basic forms of RNA:

✔ Messenger RNA (mRNA)

✔ Transfer RNA (tRNA)

✔ Ribosomal RNA (rRNA)


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Differences

between

DNA and RNA

DNA RNA

Consist of two polynucleotide chains //

double stranded

Consist of single polynucleotide

chain // single stranded

Pentose sugar is deoxyribose Pentose sugar is ribose.

Organic bases: A, T, C, G

* Base Thymine (T)

Organic bases: A, U, C, G

* Base Uracil (U)

Manufactured and found in nucleus Manufactured in nucleus but

found throughout the cell

Chemically very stable Chemically much less stable

Permanent Temporary existing

Only one basic form 3 basic forms : mRNA, rRNA

and tRNA

END OF CHAPTER 1 : MOLECULES OF LIFE

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