matriculation biology - molecule of life

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TOPIC 1 : MOLECULES OF LIFE

Retold by,

Amran Md SaidMatriculation College of Pahang

SUBTOPIC : 1.1 Water1.2 Carbohydrates1.3 Lipids1.4 Protein1.5 Nucleic acids

1.1 WATER

At the end of this topic, students should be able to:

explain the structure of water molecule describe the properties of water and its importance

Structure of a water molecule

A water molecule consist of an oxygen atom and two hydrogen atoms The two hydrogen atoms are combined with the oxygen atom by sharing of electrons The three atoms form a triangle, not a straight line

The water molecule is electrically neutral but there is a net negative charge on the oxygen atom and a net positive charge on both hydrogen atoms.

A molecule carrying such an unequal distribution of electrical charge is called a polar molecule.

The positively charged hydrogen atoms of one water molecule are attracted to the negatively charged oxygen atoms of nearby water molecules by forces called hydrogen bonds.


Hydrogen bonds largely account for the unique properties of water. weaker than covalent bonds.

But -> strong enough to hold water molecules together.

Because of their hydrogen bonds, water molecules are attracted to charged particles or charged surfaces.

Properties of water as vital constituent of life

1. Water as a universal solvent

powerful solvent for polar substances. These include ionic substances like sodium chloride (Na+ and Cl-), and also organic

molecules with ionized These cations (negatively charged ions) and anions (positively charged ions) become

surrounded by a shell of orientated water molecules. This makes them more reactive chemically than when they form part of an undissolve

solid. At the same time, non-polar substances are repelled by water, as in the case of oil on

the surface of water. Non-polar substances are hydrophobic.

2. Low viscosity of water

This unique property makes it suitable medium of transportation in living organisms. Helps in movement of food substances It also can act as a lubricants in joints

3. High specific heat capacity


A lot of energy is required to raise the temperature of water. Because, much energy is needed to break the hydrogen bonds . The head capacity of water is the amount of head required to raise the temperature of

1g of water by 1oC per calorie (cal) or 1 cal/g of water per oC This property of water is known as its high specific heat capacity. The specific heat capacity of water is the highest of any known substance. Aquatic environments like stream , lakes and seas are all very slow to change

temperature when the surrounding air temperature changes.

4. Latent heat of vaporization of water

When pure water is heated to 100oC, it boils The water molecules gain sufficient kinetic energy to escape into the air as water vapor The heat energy that is being used to produce this change is called the latent heat of

vaporization Water has a high latent heat of vaporization Because the hydrogen bonds between water molecules make it difficult for them to

be separated and vaporized

This means that much energy is needed to turn liquid water into water vapor. The amount of heat energy needed to melt ice is very high and the amount of heat that

must be removed from water to turn into ice is also great. Many living organism use this feature of water as cooling mechanism. For example, human sweat the liquid water in sweat absorbs heat energy from the

skin or in transpiration from green leaves to stop the leaves temperature from rising


too high on a hot day

5. Effect of temperature on water density

Most liquids contract on cooling, reaching their maximum density at their freezing point. Water is unusually reaching its maximum density at 4C. As water freezes, the ice formed is less dense than the cold As water freezes, the ice formed is less dense than the cold water around it. The icewater around it. The ice

floats on top.floats on top. The floating layer of ice insulates the water below.The floating layer of ice insulates the water below.

This is why the bulk of ponds, lakes or the sea rarely freeze solid. Aquatic life can generally survive a freeze-up.

6. High Surface Tension - adhesive and cohesive forces

Water adheres strongly to most surfaces It can be drown up into long columns through narrow tubes like the xylem vessels of

plant stems, without the water column breaking. Compared with other liquids, water has extremely strong adhesive and cohesive

properties that prevent the column breaking under tension. The outermost molecules of water form hydrogen bonds with water molecules below

them. This gives a very high surface tension to water- higher than that of any other liquid

except mercury. Surface skate. The insects waxy cuticle prevents wetting of its body, and the mass of the insect is not

great enough to break through the surface.


1.2 CARBOHYDRATES

Learning Outcomes:

At the end of the lesson, student should be able to explain: 1. Describe various forms and classes 2. Describe the formation and breakdown of maltose 3. Structures and functions of starch, glycogen and cellulose.

Introduction

Organic molecule containing the element carbon, hydrogen and oxygen in a 1:2:1 ratioOrganic molecule containing the element carbon, hydrogen and oxygen in a 1:2:1 ratio Written as (CHWritten as (CH22O)O)nn ; n = number of carbon ; n = number of carbon

Use of carbohydrates:Use of carbohydrates:

Source of energy Source of energy Storage of energyStorage of energy Structural component of cell membranes and cell wallsStructural component of cell membranes and cell walls Carbohydrates can be classified into three classes:Carbohydrates can be classified into three classes:

1. monosaccharides :- single sugars 1. monosaccharides :- single sugars 2. disaccharides :- double sugars 2. disaccharides :- double sugars 3. polysaccharides :- many sugars3. polysaccharides :- many sugars

MONOSACCHARIDES

Physical Characteristic:1. Small2. White 3. Sweet


4. Soluble5. Can be crystallized

Chemistry Characteristic

1. reducing Benedict test

2. condensation reaction to form disaccharide or polysaccharide

Greek words, monos = simple; sacchar = sugar, generally have molecular formula that are some multiple of CH2O.

- (CH2O)n (CH2O)n For example, glucose has the formula C6H12O6. Most names for sugars end in -ose. basic unit or monomer unit or monomer

It can be classified by two ways : It can be classified by two ways :

1.1. By the number of carbons in the backboneBy the number of carbons in the backbone

2.2. By the functional groupBy the functional group

Classification by the number of carbon in the backbone Classification by the number of carbon in the backbone

Three carbon (3C) triose sugars . Example : glyseraldehyde and dihydroxyacetonThree carbon (3C) triose sugars . Example : glyseraldehyde and dihydroxyaceton Five carbon (5C) pentose sugars. Example : ribose and ribulose Five carbon (5C) pentose sugars. Example : ribose and ribulose Six carbon (6) hexose sugars Example : glucose and fructose Six carbon (6) hexose sugars Example : glucose and fructose


Ring Structure for pentose

Importance as synthesis of nucleic acid (RNA and DNA)

Ring Structure for hexose

Importance as source of energy in cell respiration


Classification by the functional groupClassification by the functional group

Example :Example :

Aldehyde group glyseraldehyde, ribose and glucoseAldehyde group glyseraldehyde, ribose and glucose

Ketone group dihydroxyaceton, ribulose and fructoseKetone group dihydroxyaceton, ribulose and fructose

Functional Groups

Differences between aldehyde and ketone groupDifferences between aldehyde and ketone group

All sugar contain the C = O. This is called a carbonyl groupAll sugar contain the C = O. This is called a carbonyl group

The monosaccharides which have a aldehyde group is called aldose sugarThe monosaccharides which have a aldehyde group is called aldose sugar The monosaccharides which have ketone group is called ketose sugarThe monosaccharides which have ketone group is called ketose sugar

Carbonyl GroupsCarbonyl Groups


If the location of carbonyl group is in the middle backbone of the corbon, it call ketose If the location of carbonyl group is in the middle backbone of the corbon, it call ketose

Reducing sugarReducing sugar

Aldehydes are reducing agents.Aldehydes are reducing agents. So aldose sugar have reducing agents, and are called reducing sugar.So aldose sugar have reducing agents, and are called reducing sugar. Ketose sugars do not have reducing agents, but in monosaccride form, it react asKetose sugars do not have reducing agents, but in monosaccride form, it react as

reducing agents because hydroxyl in functional group have free.reducing agents because hydroxyl in functional group have free.

Benedicts testBenedicts test

Benedicts reagent contains copper (II) ions, which give a blue colour to the BenedictsBenedicts reagent contains copper (II) ions, which give a blue colour to the Benedicts solution.solution.

When heated with a reducing sugar, the copper (II) ions are reduced to copper (I) ions,When heated with a reducing sugar, the copper (II) ions are reduced to copper (I) ions, and an orange-red precipitate of copper (I) oxide is formed:and an orange-red precipitate of copper (I) oxide is formed:


reducing + Cureducing + Cu2+2+ oxidised + Cu oxidised + Cu++

sugar (oxidised) sugar (reduced) sugar (oxidised) sugar (reduced)

ISOMERISOMER

Isomer = molecules which have same chemical formula butIsomer = molecules which have same chemical formula but with different structurewith different structure

Example : glucose and fructose Example : glucose and fructose C C66HH1212OO66


and isomersisomers

Example : Example : - glucose and - glucose and - glucose- glucose

With six carbon atoms numbered.With six carbon atoms numbered.

At Carbon 1 , At Carbon 1 ,

glucose has OH downglucose has OH down

glucose has OH up glucose has OH up


DISACCHARIDESDISACCHARIDES

Disaccharides are formed when two monosaccharide joined together

Physic characteristic Physic characteristic

- Sweet- Sweet

- soluble in water.- soluble in water.

- Can be crystallized- Can be crystallized

Chemistry characteristicChemistry characteristic- - Reducing Benedict test (except sucrose)Reducing Benedict test (except sucrose)

A monosaccharide able joined together to form it by a A monosaccharide able joined together to form it by a condensation reaction.condensation reaction.

By hydrolysis reaction to form monosaccharide.

Types of DisaccharideTypes of Disaccharide

Maltose : Malt sugar, an ingredient for brewing beer, reducing sugar. Sucrose :Source sugar-cane, in plant (main form that is transportation in plant), non-

reducing sugar. Lactose :found in milk and, important energy source for young mammals, can only be

digested slowly.

Formation of disaccharideFormation of disaccharide

The two monosaccharide joined together by a condensation reactions in which water is removed

The bond formed between two monosaccharide as a result of condensation is called glycosidic bond

A glycosidic bond can also be broken down to release separate monomer units. This is called hydrolysis because water is needed to split up the bigger molecule

Maltose, malt sugar Maltose, malt sugar glucose + glucose glucose + glucose Sucrose, table sugar Sucrose, table sugar glucose + fructose . fructose . Lactose, milk sugar Lactose, milk sugar glucose + galactose glucose + galactose


Formation of disaccharide : MaltoseFormation of disaccharide : Maltose

lactoselactose

Milk sugar, is found exclusively in milk and is an important energy source for youngMilk sugar, is found exclusively in milk and is an important energy source for young mammalsmammals

It can only be digested slowly, so gives a slow steady release of energy.It can only be digested slowly, so gives a slow steady release of energy. Lactose = glucose + galactoseLactose = glucose + galactose

Formation of disaccharide : SucroseFormation of disaccharide : Sucrose


Reducing sugarReducing sugar

All monosaccharides and some disaccharide (maltose and lactose) are type of chemicalAll monosaccharides and some disaccharide (maltose and lactose) are type of chemical reaction knows as reduction.reaction knows as reduction.

Sucrose (non reducing sugar) and polysaccharide cant reducing Benedict test.Sucrose (non reducing sugar) and polysaccharide cant reducing Benedict test.

Reducing sugar : maltoseNon reducing sugar : sucrose

POLYSACCHARIDESPOLYSACCHARIDES

Are formed when many hundreds of monosaccharides condense (join) to form chains.Are formed when many hundreds of monosaccharides condense (join) to form chains. The chains formed may be:The chains formed may be:

- Variable in lengthVariable in length- Branched or unbranched- Branched or unbranched- Folded ideal for energy storage- Folded ideal for energy storage- Straight or coiled- Straight or coiled

Characteristic of polysaccharides:Characteristic of polysaccharides:- - large,large,- not sweet- not sweet- Insoluble in water- Insoluble in water

Polysaccharides are polymers of hundreds to thousands of monosaccharides joined by glycosidic linkages.

Function is as an energy storage macromolecule that is hydrolyzed as needed.

Others serve as building materials for the cell or whole organism.


STARCHSTARCH

Starch Starch is a storage polysaccharide in plants. is a storage polysaccharide in plants.

monomers are joined by 1-4 linkages between the monomers are joined by 1-4 linkages between the glucose, known as glucose, known as -1,4 glycosidic-1,4 glycosidic bondbond . .

unbranched form of starch unbranched form of starch amylose amylose forms a helix. forms a helix.

Branched forms Branched forms amylopectin. amylopectin.

AmyloseAmylose

Made from -glucose molecules Made from -glucose molecules

Forming unbranched helical chain of 300 units in length.Forming unbranched helical chain of 300 units in length.

Each -glucose is joined by a glycosidic bond between neighbouring C1 and C4 atoms.Each -glucose is joined by a glycosidic bond between neighbouring C1 and C4 atoms.


AmylopectinAmylopectin

Made from -glucose moleculesMade from -glucose molecules Forming branched chains of up to 1500 unitsForming branched chains of up to 1500 units Branches occur every 30 units and are formed between neighbouring C1 and C6Branches occur every 30 units and are formed between neighbouring C1 and C6

atoms which are then held together by glycosidic bond.atoms which are then held together by glycosidic bond.

amylose

amylopectin

GlycogenGlycogen

Animals also store glucose in a polysaccharide called Animals also store glucose in a polysaccharide called glycogenglycogen.. Glycogen is highly branched, like amylopectin.Glycogen is highly branched, like amylopectin. Found in liver and muscle tissue and made up of short branched chains of -glucoseFound in liver and muscle tissue and made up of short branched chains of -glucose

units.units.


CelluloseCellulose

Major component of the tough wall of plant cells.Major component of the tough wall of plant cells. Long chains of Long chains of -glucose-glucose units which are unbranched units which are unbranched but parallel strands of cellulose are linked by means of hydrogen bonds, making thebut parallel strands of cellulose are linked by means of hydrogen bonds, making the

cell wall a very stable structure.cell wall a very stable structure.

The enzymes that digest starch cannot hydrolyze the beta linkages in cellulose.The enzymes that digest starch cannot hydrolyze the beta linkages in cellulose. Cellulose in our food passes through the digestive tract and is eliminated in feces asCellulose in our food passes through the digestive tract and is eliminated in feces as

insoluble fiber.insoluble fiber. As it travels through the digestive tract, it abrades the intestinal walls and stimulatesAs it travels through the digestive tract, it abrades the intestinal walls and stimulates

the secretion of mucus.the secretion of mucus. Some microbes can digest cellulose to its glucose monomers through the use ofSome microbes can digest cellulose to its glucose monomers through the use of

cellulase enzymes.cellulase enzymes. Herbivores, like cows , have symbiotic relationships with cellulolytic microbes, allowingHerbivores, like cows , have symbiotic relationships with cellulolytic microbes, allowing

them access to this rich source of energy.them access to this rich source of energy. Cows do have enzymes Cows do have enzymes amylases, which can break amylases, which can break - 1,4 glicosidic bonds in - 1,4 glicosidic bonds in

starch but which cannot recognize starch but which cannot recognize - 1,4 glicosidic bonds in cellulose, - 1,4 glicosidic bonds in cellulose, the bacteria in the rumen do produce enzymes called cellulles which can recognizethe bacteria in the rumen do produce enzymes called cellulles which can recognize

and break and break - 1,4 glicosidic bonds in cellulose - 1,4 glicosidic bonds in cellulose


TOPIC 1 : MOLECULES OF LIFE

Retold by,


1.3 LIPIDS

General term for any water-insoluble organic molecules that can be extracted from cells by ethers, benzene, or other nonpolar solvents.

They contain carbon, hydrogen and oxygen, with far more hydrogen and carbon compared with oxygen than in carbohydrates;

They are insoluble in water . 3 major classes of lipids

1. triglycerises e.g. Fat & oil 2. phospholipids e.g. Lecithin 3. steroids e.g. Cholesterol & Testosterone

Importance of lipids

Energy storage Component of cell membrane Insulation : blubber Emulsifiers Important carriers or precursors of important flavor and odor compounds. Transports fat-soluble vitamins Immune system Contributes to obesity, coronary heart disease and other health problems.

TRYGLYCERIDE

Composed of 3 fatty acid molecules attached to a glycerol backbone


Triglycerides with reletively short fatty acid chains, or with unsaturated fatty acids, tend to be liquid at normal temperaturated and called oils.

Triglycerides with longer fatty acid chains, or with saturated fatty acid, are more likely to be solid and are called fats.

Triglycerides, like all lipids, are insoluble in water. This is because they have no dipoles and no charges which can attract water molecules.

Are especially useful as energy stores, because they contain much energy per gram than either carbohydrates or proteins.


Formation via condensation breakdown by hydrolysis

FATTY ACIDS

Long linear hydrocarbon chains One end - contains a carboxylic acid group The other end is the methyl, "n" or omega end.

Classification of fats based on fatty acids

1. Saturated fat : saturated fatty acid eg. Stearic acid2. Unsaturated fat : unsaturated fatty acid eg. oleic acid


Classification of essential

Essential fatty acids- Body cant produce own fatty acids, so its needed from food.

Non-essential fatty acids. Body can synthesise fatty acids itself

PHOSPHOLIPIDS

Example : Lecithin (in cell membrane structure).


Importance of lecithin in cell membrane structure:-

Polarization leads to solubility in water. It act as a permeability barrier, so that exchanges across this membrane are very limited and very slow.

Permeable to water molecules, but not to ions such as Na+, K+, and Cl-.

STEROIDS

Examples : Cholesterol & Testosterone. Structure of Steroids.


PROTEIN

At the end of the lesson, student should be able to:

Describe the basic structure and classes of amino acids Explain how amino acids are grouped Describe the formation and breakdown of dipeptide Explain structure levels of proteins and the types of bonds involved Explain the effect of pH and temperature on the structure of protein Classify of proteins according to their structure

Protein

Protein are polymers whose molecules are made from many amino acid molecules linked together.

Protein consists of carbon, hydrogen, oxygen and nitrogen. Function of protein:

- Enzymatic catalysis .- Transport of respiratory gases and storage.- Structure and support- Contacts or co-ordination (hormones) - Immunity.- Growth and development membrane proteins.- Heredity

Protein molecule

Each different proteins molecule is made under the direction of its own gene and performs its precise function.

The shape of it is determined by its amino acids sequence. Amino acids are the building blocks from which protein are made. There are about 20 commonly occuring amino acids in protein. All have the same basic structure but differ in their RESIDUAL CHAIN ( R ). Amino Acid Structure


An amino acid is a molecule containing an amino group (-NH2), a carboxyl group (-COOH), and a hydrogen atom.

Amino group (-NH2) has characteristics such as basic. Carboxyl group (-COOH) has characteristics such as acidic. Each amino acid has unique chemical properties determine by the nature of the side

group (indicated by R). For example, when the side group is CH2OH, the amino acid (serine) is polar, but

when the side group is CH3, amino acid (alanine) is nonpolar. Type of amino acid, Base on side chain group

- Polar eg. Serine (Ser)- Non polar eg. Glycine (Gly)- Acidic eg. Aspartic acid (Asp)- Basic eg. Lysine (Lys).


Formation of Polypeptides

Two amino acids can be joined by a condensation reaction to form a dipeptide. If any amino acids are joined together by peptide bonds then a polypeptide is formed. A polypeptide usually contains hundreds of amino acids. The repeated sequence (-N-C-C-N-) is the polypeptide backbone.


amino acids are structure of protein The twenty commonly occurring amino acids can be arranged in an enormous variety

of different ways in giving rise to many different proteins A plant can synthesis all amino acids as needed from simple component. But an animal cant synthesis apart of amino acids Base on essential, amino acids divide 2 categories

i) Essential amino acid eg. Methionine, lysine and Valineii) Non-essential amino acid eg. Glycine, alanine and Cysteine.

Structure of proteins

A typical protein consists of one or more polypeptide chains which may be folded, branched and cross-linked at intervals.

Each proteins has a specific three-dimensional shape. In describing the structure of a protein, it is usual to refer to four separate levels of

organization. Primary (10), secondary (20), tertiary (30) and quaternary (40) levels of protein.

Primary structure This discribe the sequence of amino acids in the protein and usually determines its

eventual shape and biological function.


Secondary structure Once a linear chain of amino acids is formed it spontaneously folds to form helix or

pleated sheet. Hydrogen bonds holds the secondary structure together.


Tertiary structure

Once they have been folded by hydrogen bonds, polypeptides may then fold into a globular shape which is maintained by - hydrogen bonds, - ionic bonds - disulphide bridgeExample myoglobin.

Hydrogen bond bond between polar side chains Ionic bond bond between positively and negatively charged side chains disulphide bridge (covalent bonds between sulphur atoms in the residual chains of the

amino acids.) Hydrophobic interactions & van der Waals interactions Nonpolar R group with

another nonpolar R group

Quaternary structure

Consists of more than one polypeptide chains to form a single functional molecule Held together by hydrophobic interactions, hydrogen bonds, ionic bonds and disulfide

bridges Associated with non-protein groups into a large complex protein molecule


Human haemoglobin is an example.

It consists of four chains (two -polypeptide chains and two -polypeptide chains) wrapped around an iron hem group.

Effect of pH and temperature on structure of protein

Structure of protein maintain by hydrogen bond ( 2 , 3 and 4); ionic bond, hydrophobic interaction, disulfide bridge and van de waals interaction ( 3, 4)

Breakage the bond causes loss of specific three-dimensional shape of a protein molecule

They change may be temporary or permanent

But amino acid sequence remains unaffected Change shape of protein denaturation Denaturation occurs under extreme conditions such as extreme pH and temperature. Molecule unfolds and can no longer perform its normal biological function

If the temperature or pH exceeds a proteins range of tolerance, its polypeptide chains will unwind or change shape, causing to lose its conformation and hence its ability to function

Example: Proteins are easily damaged by heat (temperatures greater than 40 0C) due to breakage of their cross linkages


This cause the protein molecules to open up, straighten the folds and assume a random configuration

For some proteins, denaturation might be reserved when normal conditions are restored

Classifation base on structure Divided by 3 classification base on structure.

- Conjugated protein- Globular protein- Fibrous protein

Conjugated Protein

protein joined with non protein component/ prosthetic group Protein structure merge with with non protein group (prosthetic group) Eg. Haemoglobin contains the prosthetic group containing iron, which is the haem. It is

with in the haem group that carries the oxygen molecule through the binding of the oxygen molecule to the iron ion (Fe2+) found in the haem group

Globular Protein

Mostly, that protein related in tertiary and quaternary structure. Usually water soluble (can to form colloid) Long polypeptide with helix to form globular or spherical example: globulin (blood serum), enzymes, antibody, hormone


Fibrous Protein

Mostly, that protein related in secondary structure. Insoluble in water and very strong because its make from long polypeptide example: collagen, myosin, fibrin and keratin

Differences between fibrous protein and globular proteins

Properties of protein

Amphoteric Buffering capacity Colloidal properties Denaturation

Note :Properties of Protein, just for extra knowledge

Properties of protein

1. Amphoteric

In aqueous as neutral (pH 7), amino acid such as dipole, its called zwitterions Amphoteric because have characteristic both acidic and basic.


In aqueous acidic (< pH 7), protein receive H+ and make its positive charge. In aqueous alkaline (>pH 7), donate H+ and make its negative charge. Charge at zwitterions depend on pH pH at amino acid as neutral like electric its call isoelectric All amino acids have own characteristic as isoelectric point (pI).

2. Buffering capacity

Amphoteric characteristic of amino acids, its make such as buffer A buffer solution is one which resist the tendency to alter its pH even when small

amounts of acid or alkali are added to. That mean a buffer solution cant change spontaneously, while added pH increase

(basic) . Amino acids will donate hydrogen ionic. While pH reduce (acidic), amino acids will receive hydrogen ionic.

3. Colloidal properties

4. Denaturation

The structure of a protein can be change if the bonds which hold it in shape are broken. This process is called Denaturation.

High temperatures break hydrogen bond and van der Waals forces. In a globular protein a long chain instead of a curled-up ball. The molecules will no longer be soluble in water.

Extremes of pH break ionic bond, because they alter the charges on R groups. Reducing agents break disulphide bond. This is made use of when perming hair.

Keratin, from which hair is made, contains disulphide bond that hold the shape in shape.

NUCLEIC ACID

Topic distinguish

At the end of the lesson, students should be able to:

Describe the structure of nucleotide as the basic composition of nucleic acid (DNA and RNA)

Describe the structure of DNA based on the Watson and Crick Model. State the type and function of RNA State the differences of DNA and RNA


Nucleic acids The amino acid sequence of a polypeptide is programmed by a gene. A gene consists of regions of DNA, a polymer of nucleic acids. DNA (and their genes) is passed by the mechanisms of inheritance.

Structure of nucleotide

Nucleic acids are polymers of monomers called nucleotides. Each nucleotide consists of three smaller molecules. These are :1. A phosphate group2. A pentose sugar3. A nitrogenous base

Phosphate group


Pentose sugar

Nitrogenous base


3 components are combined by CONDENSATION reaction. 3 components are breakdown by HYDROLYSIS reaction.


DNA

Double stranded polymer of nucleotides Contains 4 bases (not include uracil (U) ):

i.Adenine (A)ii.Guanine (G)iii.Cytosine (C)iv.Thymine (T)

Long and thin strand Amount between A and T and G and C usually equal to each other because A always

pairing with T and G with C Helix shape is maintained by HYDROGEN BONDS

James Watson and Francis Crick postulated double helix of 2 nucleotides strands Nucleotide strands being linked together by pairs of nitrogenous bases which are

joined by hydrogen bonds Purines ; double ring structures form longer links if paired together than pyrimidide Only by pairing 1 purine with 1 pyrimidine consistent separation of 3 rings width can

be achieved Deoxyribose and phosphate units form the uprights while nitrogenous base pairings

form the rungs 2 chains that form the uprights run in opposite direction (antiparallel)


RNA

Single stranded polymer of nucleotides Pentose sugar ribose Organic bases Guanine, Cytosine, Adenine and Uracil (replacing thymine) 3 types of RNA :

i.Messenger RNA (mRNA) ii.Transfer RNA (tRNA) iii.Ribosomal RNA (rRNA)

rRNA

Large,complex molecule Made up of double and single helix Manufactured by DNA of the nucleus Found in ribosome Comprises of more than half the mass of the total RNA of the cell The Base sequence is similar in all organisms

tRNA

Small molecule, comprising single strand Manufactured by nuclear DNA Made up 10 -15 % of cells RNA All type are fundamentally similar Form clover-leaf shape, one end of the chain ending with C-C-A sequence Which amino acid attaches itself 20 types of tRNA, carrying different amino acid


At an intermediate point along the chain is an important sequence of 3 bases anticodon

mRNA

Long stranded molecule, up to thousands of nucleotides form into helix Manufactured in nucleus Mirror copy of a part of a strand of DNA There is hence an immense variety of types Enter the cytoplasm associate with ribosomes and acts as template for protein

synthesis Made up less than 5% of total cellular RNA Easily and quickly broken down, sometimes existing for only a matter of minutes.


Edited on Mei, 31 2011Retold by,


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matriculation biology - molecule of life

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