BIOLOGY FORM 5-BIOCHEMISTRY
BIOLOGY FORM 5-BIOCHEMISTRY
ORGANIC CONSTITUENT OF THE CELLS.
Bio chemistry: is the study of structures, properties and functions of chemical constituents of the cells.
It is a great unifying theme in biology.
It finds applications in fields like;
- Agriculture; in developing pesticides and herbicides.
- Medicine; including all pharmaceuticals.
- Fermentation; baking products, food products and breweries.
- New development of biology eg genetic engineering.
ELEMENTS FOUND IN LIVING ORGANISMS ARE
- Chief/ macro elements: hydrogen (H), carbon(C), nitrogen (N), oxygen (O), phosphorous (P), sulphur(S).
- Ions – sodium(Na+) , magnesium (Mg2+) , chlorine( cl–) , calcium (Ca2+) etc.
- Trace elements – manganese(Mn) , iron(Fe) , cobalt(Co),copper (Cu) , molybdenum(Mo) and iodine(I).
Macromolecule is a giant molecule made from many repeating units. The molecules built are polymers and the individual units are monomers.
The units are joined together by a chemical process called CONDENSATION which means removal of water.
The units can be broken down again by an opposite process known as hydrolysis which means adding of water.
- The most important macromolecules in biology are;
- Polysaccharides( carbohydrates)
- Nucleic acids.
And their constituent monomers are; monosaccharide’s, amino acids, glycerol, fatty acids and nucleotides respectively.
- Adenosine triphosphate (ATP).
ORGANIC SUBSTANCES ( CHEMICAL NATURE AND IMPORTANCE)
They are substances which contain carbon, hydrogen and oxygen with the general formula of (CHO)n where n is a real number.
Characteristics of carbohydrates.
- They are either simple sugars or compound sugars.
The compound sugars are formed by condensation of simple `sugar molecules.
- They are hydrate of carbon from the proportion of hydrogen and oxygen in water.
- The basic carbohydrate unit is thus a sugar which is the derivative of a poly hydrosol alcohol.
- Alcohol is the paraffin compound with hydrogen atom replaced by the univalent hydroxyl (OH) group.
- Paraffin is aliphatic or chain of compounds of carbon and hydrogen in which the carbon atoms are linked by single bonds to adjacent atoms. (see Example above).
- The simpler hydroxyls are the glycol and glycerol and the simplest of sugar is the glycerose (glycerin).
The carbohydrate contains several hydroxyl groups.
4. Some contain aldehyde (-CHO) group and others contain ketone group ( -CO-)
- Glucose: is a pentahydroxyl alcohol with the aldehyde group.
- Fructose: is the pent hydroxyl alcohol with ketone group.
Complex sugars are built from the basic sugar units called monosaccharides through the process of condensation polymerization.
Many sugars are reducing sugars and others are non-reducing sugars but give rise to reducing sugars on hydrolysis with enzymes or mineral acid (mostly dilute HCL)
NB: Carbohydrates are called reducing sugar because they act as reducing agents supplying electrons from their functional groups i.e. the aldehyde and ketone groups which can reduce the cu2+ ions to cu+ ions which appear orange or yellow ppt (precipitate).
The true carbohydrates are saccharides with a combination of sugar units. These are divided into three main classes
- monosaccharides – with a single sugar unit
- Disaccharides – with two sugar units.
- Polysaccharides- with many sugar units.
Sugar which include mono and disaccharides are all soluble in water. They have a sweet taste.
They are crystalline and small molecules. Those with a potentially active aldehyde or ketone group are the reducing sugars e.g. glucose.
|Glucose||Plant juice and grape sugar|
|Maltose||From germinating seeds ( cereals)|
|Sacrose||From sugar cane ( in plants)|
Sugars without potentially active reducing groups are known as non-reducing sugars e.g.
- Have general formula (CnH2nOn)
- All are reducing sugars
- They are classified according to the number of carbon atoms e.g.;
Trioses have 3 carbon atoms
Tetraoses have 4 carbon atoms
Pentoses have 5 carbon atoms
Hexoses have 6 carbon atoms
Heptoses have 7 carbon atoms
– Of code, hexoses and pentoses are most common and triose being the true sugar.
– Pentose sugars are never occurring but only in combination with other groups of compounds.
Riboses- this occurs in one kind of nucleic acid. A derivative of deoxyribose
Hexose. The most important free sugar.
D- Fructose these are the most common sugars.
Structure of Monosaccharides
Glucose in common with other hexoses and pentoses easily forms stable ring structure. At any one time most molecules oxists as rings rather than
In case of glucose carbon atom number 1 may combine with the oxygen atom an carbon 5. This form a six -sided structure known as a pyranose ring.
In case of fructose, carbon atom number 2 links with the oxygen an carbon atom number. This form a five sided structure known as furanose ring Both glucose and fructose can exist in beth pyranose ring.
In case of fructose, carbon atom number 2 links with the oxygen on number 5. This form a five sides structure known as furanose ring Both glucose and fructose can exist in both pyranose and furanose
and furanose ring form.
STRUCTURE PG 13 UB
- Most carbohydrate in common glucose can exists as a numbee of isomers (they posses the same molecular formula but differ in the arrangement of this atoms). one type of isomer called stereo isomerism. occurs when the atom, or group, are joined together but differ in Their arrangement in space one form of stereoisomer is called Optical Isomersm, result in isomer which can rotate the plane of polarized light. If the substance rotates the plane of polarisation to the right it is said to be dexTro-rotatory (d) and if to the left is laevo-rotatory (L) Optical isomerism is a property of any compound which can exist in two forms whose structure are minor image. Like right and left handed gloves
Stady the structure of glycerin (ghycer aldehyde)
L-Form isomer mirror. D-form isomer
Functions of monosaccharides.
PENTOSES (C5H10O5 ) e.g. ribose, deoxyribose, ribulose.
- Synthesis of nucleic acids e.g. Ribose is the chief constituent of the RNA.
- Synthesis of co-enzymes e.g. ribose synthesis (NAD and NADP)
HEXOSES (C6H12O6) e.g. fructose, glucose, galactose.
- Sources of energy when oxidized by respiration.
- Synthesis of disaccharides.
- Synthesis of polysaccharides.
TRIOSES (C3H6O3) e.g. glyceraldehydes, dihydroxyacetone.
- Intermediate in respiration (glycolysis).
- Photosynthesis (dark reaction) RUBP as an acceptor of CO2
- Carbohydrate metabolism.
*Disaccharides are formed by the condensation or polymerlization of two monosaccharides.
The most common disaccharides are;
- Maltose = glucose + glucose
- Lactose = glucose + galactose
- Sucrose = glucose + fructose.
In reducing sugars e.g. Lactose and maltose, one of the hexose residue retains its aldehyde or ketone groups as an intact unit as reducing sugar.
Maltose is a disaccharide produced upon incomplete hydrolysis of the polysaccharide starch.
- It is found in germinating seeds.
- It is also produced commercially for use in production of beer.
- Maltose is produced of two D-glucose units joined by a α-glycosidic bond between the anomeric carbon of one glucose unit and the number 4 carbon of the other glucose unit.
This specific bond formed an α-1,4-glycosidic bond also found in starch and glycogen.
NB: The numeric hydroxyl group of one of the glucose units participates in the glycosidic bond and
Therefore cannot be easily oxidized.
However the anumeric hydroxyl of the other glucose unit is not as occupied and this glucose unit exists in the equilibrium with free aldehyde solution.
Thus maltose is oxidized by Fehling’s solution, benedict’s solution or any other suitable reagent.
Constitutes some 3% to 5% of the milk of animal including cows and humans.
This disaccharide is composed of one galactose unit and one glucose unit joined by a glycosidic bond between the anomer of galactose and the number 4 carbon of glucose. A β-1, 4 –glycosidic bond.
Glucose unit of the lactose still exists as an equilibrium mixture of α and β anomers and
the free aldehyde in solution. Lactose is thus a reducing sugar.
- It is found in fruits and vegetables.
- Sugarcane and sugar beets are the commercial sources and used as table sugar.
- Sucrose is composed of one fructose unit joined by two glycosidic bonds.
Sucrose is not a reducing sugar since both anomeric carbons participates in the glycosidic bonds and thus no free aldehyde or ketone exists in solution.
NB: D is the hydroxyl group attached to the anomeric carbon atom (the anomeric hydroxyl group) is drawn on the same side of the ring as the last -CH2OH group for the β-anomer and the opposite side of the ring for the α-anomer.
The D-galactose only differs from the D-glucose only in the orientation of the groups bonded to Carbon no. 4. Ingested D-glucose (from milk and some other complex polysaccharide) is normally converted to D glucose in the human body.
The inability to perform this ionization (conversion of one isomer to another) results in a disease called galactosemis.
- Have high molecular weight formed by condensation of large number of monosaccharide units.
They include; Starch, glycogen, cellulose, chitin and insulin.
- All polysaccharides are insoluble in water forming colloidal solution.
- They are non –reducing sugars.
- They are Non- crystalline and as structural materials e.g. Cellulose.
- Represented by chemical formula ( C5H10O5) n or (C6H10O5)n where n is a whole number ranging from 300-400.
- Usually occur in a white powder-form at room temperature.
It forms a solution with hot water and a gel on cooling.
- During digestion, it is converted to a mixture of detrins. Later from maltose to glucose units.
- It is largely stored in plants and it is a result of photosynthesis.
- In plants, starch is found in the storage parts such as roots and stem tubers, corn and some rhizomes.
A starch granule is composed of
- A core of amylase
- Amyloplast membrane.
Diagrams of amylase and amylopectin.
NB: Amylase and amylopectin are two different forms of starch.
- Both have linear chains of glucose units joined by α-1, 4-glycosidic bond.
Amylase is linear polymer of α-1, 4-glucose unit and is insoluble in water.
Amylopectin is a branched polymer; the main chain of amylopectin is joined by α-1,4-glycosidic bond as in amylase. However about every 20-30 glucose units there are branches joined by α-1,6-glycosidic bond.
Amylopectin is not soluble in water.
When boiled to about 2000C starch is partially hydrolyzed to a mixture of dextrins. However, when heated with dilute mineral acids, starch is hydrolyzed via dextrin to glucose.
- In living things (tissues) the hydrolysis is of the following sequence.
- A suspension of glucose gives a blue black coloration with iodine.
- Amylopectin is compact as it has many branches of 1, 6- glycosidic bonds.
- Storage of food in seeds, example; cereals and legumes
- Important for human food.
- This is called animal starch formed by condensation polymerization of glucose on units.
- It is very similar to amylopectin in structure.
- It is a polymer of glucose units joined by α-1,4- bonds and with α-1,6- bonded branches . it is a white soluble powder and non reducing sugar.
- Mainly in vertebrates liver and muscles.
- Also some maize seeds and fungi.
Glycogen differs from amylopectin because it is more highly branched than amylopectin with one branch point about every 8 and 12 glucose units.
- It is important food storage in muscle and liver of vertebrates and fungi.
- It provides energy and is an energy substance.
This is an important structural material in plants.
It largely constitutes the chemistry of the cell wall.
Chemically cellulose is composed of several thousands of glucose units joined together by 1, 4- glycosidic bonds. The units are so arranged that the bonds alternate in appearance.
This lead to the cross links of hydrogen bonds between the parallel running cellulose molecules.
As a result of this, cellulose becomes tough with very high tensile strength.
The shape of a cellulose fibre is of the nature below.
Chemical structure of cellulose is presented as follows.
Hydrolysis of cellulose.
In the living tissues, hydrolysis of cellulose takes place in two stages;
Commercial use of cellulose
- It is a raw material in the manufacture of many industrial products such as papers, rayon and plastics.
- The rayon made from cellulose are used in the manufacture of industrial belts and tyre cords.
- Cellulose derivatives such as cellulose nitrate are used in the manufacture of films.
- Cotton, a pure form of cellulose is used in the manufacture of clothes.
This is closely related to cellulose in structure and function, being a structural polysaccharide. Structurally it is identical to cellulose except that the OH group at carbon 2 is replaced by – NH.CO. NH3.
This is a result of amino sugar (glucosamine) combine with acetyl group. Chitin is therefore a polymer of N-acetylglucoamine.
This is another storage carbohydrate which largely occurs of many plants. It also occurs in small quantities in many monocots. Hydrolysis by dilute mineral acids or specific enzymes e.g. inulin produce fructose only.
- It is a polymer of fructose molecule.
- Inulin inulase fructose
Summary roles of carbohydrates.
- They built up a cell plasma membrane. It is made up of carbohydrates and so they are used to build up the body of a living organism.
- They are used as a substrate in respiration (to produce energy) as raw materials. Glucose is the base raw material in glycolysis.
- Are useful in pollination. Nectar which attracts pollinators is made up of sugars.
- Are useful in storage purpose for future metabolism eg starch, glycogen and laminarin.
- Used in the balance of osmotic pressure as they make solutes in the blood.
- Are used in inheritance and control of the body activities as they make the genes e.g. deoxyribose of DNA and ribose of RNA are pentose sugars.
- Other uses are from the above discussions.
These are organic compound made up of elements carbon, hydrogen and oxygen in which its proportion of oxygen is smaller than that of hydrogen (i.e. not in the ratio of carbon dioxide of 2:1)
Properties of lipids.
The features that characterize the lipids include the following;
- They are either liquids or non-crystalline solids at room temperatures.
- They are higher than water ( less dense than water)
- They are hydrolyzed by alkaline into their respective constituent compounds. This process is called saponification.
- They contain either saturated or unsaturated hydrocarbon chains.
- In the presence of water and alcohol they form an emulsion.
- They are esters of higher aliphatic alcohols.
- All lipids are insoluble in water but soluble in organic compounds or solvents e.g. ether, chloroform and hot alcohol.
They occur in adipose tissues of animals and some are a component of the protoplasm of all living cells.
Lipids have ester linkage.
Because of unsaturated bonds which are easy to break, that are why they are liquid at room temperature, solids contain saturated bonds.
Simple lipids are oils and fats of which are esters of glycerol. (Higher alcohol). Than glycerol forms the ester called waxes.
- Oils and fats are formed by the combination of fatty acids and glycerol e.g. oleic acid which are widely distributed in many fats and oils.
- They are also known as triglycerides.
Natural fats and oils.
They are a mixture of glycerides (esters) of fatty acids and glycerol.
Oils: contain greater proportion of unsaturated fatty acids; they are liquid at 200C.
Fats: contain a greater proportion of saturated fatty acids; they are solids at 200C.
BIOLOGICAL IMPORTANCE OF LIPIDS.
- They form an insulation material thus prevent heat loss in organisms and animals particularly.
- Prevent water loss, form water proof in organisms, plants and insects.
- Can be a stored form of energy in the body of an organism e.g. amoeba and seed like units.
- Form the basic constituent of the cell membrane as well as the cell components.eg phospholipids
- Enables large aquatic organisms like whales to have buoyancy.
- Contains basic fat soluble vitamins A, B, D and K.
- Forms the natural rubber.
- It is a constituent of hormones like steroids e.g. oestrogen, progesterone, also acdysome hormone in insects and crustacea are made up of lipids.
- Gives more energy in metabolism.
- Used to make bile salts (sodium taurochlorate and sodium glycochorate) for emulsification in the duodenum.
- Limits the linkage of small molecules across plasma membrane (cholesterol).
- Constituent of myelin sheath; helps to prevent outward flow of ions which would short circuit the movement of ions along the nerve. Also enhance the salutatory condition.
BIOLOGY FORM 5-BIOCHEMISTRY
Proteins are nitrogenous compounds formed by condensation polymerization of larger number of amino acids.
- Proteins are thus polymer molecules of amino acids.
Element present in proteins are carbon, hydrogen, oxygen, nitrogen, sulphur acid and phosphorous and iron.
THE AMINO ACIDS
There are 20 amino acids which are polymerized to give many types of proteins.
- They are colorless.
- They are Crystalline solid.
- Form colloidal solution.
- Coagulate on – heating
- Strong acid or base
- Presence of heavy metal
- Organic detergent.
- They are specific in nature of action.
Substances which are protein in nature are;
- Albumin – egg albumin and serum albumin.
- Histone – make the chromosome of nucleus.
- Globular- blood fibrinogen, prothrombine and antibodies.
- Schleroproteins- keratin (of hair and feathers) also keratin of skin, collagen which makes tendon, bone, connective tissue myosin (muscles), silk (spiders web).
GENERAL PROPERTIES OF PROTEINS
- They are polymers of amino acids.
Many are large dimmers with many amino acid units. Eg serum globulin of human blood have 736 amino acids, myosin of muscle has 780 amino acids.
- Colloidal in nature.
- Amphoteric properties.
- Every amino acid regardless of its side chain has an acidic carboxylic group and a basic amino group or it has acid-base properties i.e. is said to be amphoteric.
- In solid state the amino acid have base salt like properties because they have both a positive charge part and a negative charge part such substances are called zwitterions.
- Zwitterions are produced from the molecular form of the amino acid by internal-acid base reaction.
NOTE: in the reaction above, neither the molecular form nor the zwitterions form has a net electrical charge. In aqueous solution these two forms are in equilibrium but the equilibrium overwhelmingly favors the zwitterions at any pH.
At any pH, some of the alamine in solution exists in the positive ion form. Some of it in the negative ion form, some in the zwitterions form and some in molecular form.
- If the solution pH is very high that is ( H3O+) or (H+) is very low, both of the equilibrium in the reaction is shifted to form the right and the negative ion form of alamine predomination.
- On the other hand, if the solution pH is very low that is (H3O+) 0r (H+) is very high- both equillibria in reaction above are shifted to the left and the positive form of alamine predominates.
- At the pH of human cell and fluids (pH7) alanine exists primarily as the zwitterions.
In solution that are predominantly basic (i.e. pH btn 8.5 to 10.5), no single form of alanine predominates. In this pH range, there are roughly comparable amount of zwitterions and the negative charged.
- Similarly in moderately acidic solution there are roughly comparable amount of the zwitterions and the positively charged form of alanine.
- The amount of positive or negative charge is affected by pH. Each molecule has a specific pH which the total positive charge is exactly equally to the total negative charge. It is electrically neutral and has no tendency to move to either the anode of cathodes of an electric field. This is known as isoelectric point.
At higher pH protein and amino acid become more negative while at low pH they become more positively charged.
Properties of isoelectric point.
- Solubility- have greater tendency to precipitate or coagulate.
- Stability- as emulsion colloids.
- Osmotic pressure- swelling by inhibition of water.
- Viscosity and acid and base bonding properties.
- They have large size molecule e.g. hemoglobin of mass 6000 and more. The enzyme urease nearly 500,000.
- Denaturation – there are easily denatured by heat, ultraviolent reactor and chemicals. Denaturation alters the structure of proteins.
Structure of amino acids.
The amino acid consists of an α carbon surrounded by;
- Hydrogen atom(H)
- Amino group or amine group (-NH2), giving the nature of amino acid.
- The carboxyl (-COOH) giving the acidic nature of amino acid.
- The R-group known as the side chain. It presents the hydrogen atom or any other group as alkyl group.
How peptide bonds are formed.
Proteins are polymers of amino acids joined together by peptide bond.
OTHER BONDS FOUND IN PROTEINS.
- Ionic bonds: is an electrostatic attraction between positive and negative charge.
- Hydrogen bond: this occurs between hydrogen atom and more electronegative atoms.
- Disulphide bond: the bond between two crystalline molecules.
- Van-de-Waal forces: these are weak non-attraction forces (hydrophobic interactions) created between –CH3 groups which are non-polar.
CLASSIFICATION OF PROTEINS.
- Level of organization.
- According to function.
- According to composition.
- To whether they contain essential amino acids.
- According to structure.
ACCORDING TO LEVEL OR ORGANISATION.
- Primary structure.
- Secondary structure.
- Tertiary structure.
- Quaternary structure.
- Primary structure.
This is a linear sequence of amino acids joined together by peptide bonds. Also disulphide bond may be found.
- Secondary structure
This is due to coiling or twisting of the polypeptide.
This is due to attraction of various amino acids. This is a component of hair, claws, nails, as well as skin.
β pleated sheets (zig zag structures)
Collagen is a compound of tissues like bones and cartilage. Collagen is an example of β pleated sheets.
- Tertiary structure.
Tertiary structure is due to coiling and twisting of the polypeptide helix forming a globular or spherical shape.
Bonds present in the coiled structure are ionic bond, hydrogen bonds, hydrophobic interactions, disulphide bridges.
Examples of tertiary structures. (They are very soluble).
- Immune globin( antibodies)
- Quaternary structure.
Quaternary structure is due to coiling and twisting of various polypeptide chains usually the structure is associated with non-protein parts called prosthetic groups e.g. hemoglobin.
Hemoglobin has four polypeptide chains, two α-chains and two β chains each surrounding an iron atom.
The hemoglobin consists of protein parts. The protein part consist of 4 polypeptide chains, of the four polypeptide chains, 2α chains and 2 β chains and is called globin. The non protein parts is called HAEM consist of poiphyding surrounding an iron atom.
THE FOUR LEVELS OF PROTEIN STRUCTURE
ii. BASED ON WHETHER THEY CONTAIN ESSENTIAL OR NON ESSENTIAL AMINO ACIDS.
Essential amino acids Vs non essential amino acids
Essential amino acids are those which cannot be synthesized by human cells but are obtained from food.
All of the 20 α amino acids are needed to make different proteins in the body of a human.
Twelve of these amino acids can be synthesized by the cells from other substances that are present in the body; these are called non-essential amino acids.
The other eight cannot be synthesized by the body and must be included in the persons diet are called essential amino acids.
iii. BASED ON COMPOSITION.
- Simple proteins
Simple proteins are made up of amino acids only.
E.g. – Histones (nucleoprotein)
- Globulin( immunoglobulin)
- Schleroproteins ( e.g. Keratin)
- Conjugated proteins.
Made up of amino acids; are globular proteins associated with non protein materials. E.g. haemoglobin glycoprotein (components of cell membrane), mucin (component of saliva), lipoproteins (components of cell membrane).
iv. ACCORDING TO FUNCTION.
NOTE:these are also functions proteins.
Adrenaline corticotrophic hormone (ACTH).
||Transports fatty acids and lipids in the blood.|
NEUTRAL AMINO ACIDS.
This is because their side chains have no charge at the pH of body cell. Thus are divided into;-
- Natural hydrophobic amino acids.
- Natural hydrophilic amino acids.
Natural hydrophobic amino acids.
Seven natural amino acids have side chains(R) that are non polar or hydrophobic. These hydrophobic are either alkyl or aromatic in nature.
- Alanine (ala).
- Valine (Val).
- Leusine (leu).
- Iso leusine.
- Phenyl donine (phe)
- Tryptophan (trp).
Neutral hydrophilic amino acids.
Eight amino acids are classified as hydrophilic.
- In general these amino acids are more soluble than hydrophobic amino acids.
- The acid chain of glycine (gly) is just hydrogen. The other seven neutral hydrophilic amino acids have side chains that can form either strong or weak hydrogen bond with water.
- These have hydroxyl group in either side chain serine (ser) theorine (Thr) or tyrosine (try). Two contain an amino functional group, asparagines (asp) and glutamine (gln). The remaining two contain a sulphur atom cysterine (cys) and methionine (met).
Others include: tyrosine, asparagines, cysterine, glutamine, and methionine.
ACIDIC AMINO ACIDS
Acidic amino acids have side chains that contain a second carbonyl group.
At the pH of cells in the body, these carboxylic groups exist primarily as negative charged carboxylate ions and this interact strongly with water molecules.
- Aspartic acid (asp)
- Glutamic acid (glu)
BASIC AMINO ACIDS.
Three of the amino acids contain a side chain that act as a proton acceptor or base. They are thus classified as basic amino acids, these are lysine (lys), arginine (arg) and histamine.
v. BASED ON STRUCTURE
a. fibrous protein.
- Have a secondary structure and little or no tertiary structure.
- Insoluble in water.
- Physically tough.
- Form long polypeptide chain cross linked at intervals forming long fibres or sheets.
Functions of fibrous proteins.
Perform structural function in cell and organism e.g. collagen (tendon, bones, connective tissues) myosin in muscles, (silk) spider web, keratin (nail, hair, feathers).
b. globular proteins.
- Found mostly in tertiary structure.
- Polypeptide chain highly folded to form spherical shape.
- Easily soluble in water.
Functions of globular proteins.
Forms enzymes, antibodies and some hormone e.g. insulin.
c. intermediate protein.
Fibrous in nature but soluble in water e.g. fibrinogen.
Function of intermediate protein.
Fibrinogen forms insoluble fibrin when blood clots.
Like proteins, nucleic acids are largely polymers made up of small number of different building blocks called nucleotides.
Each nucleotide is in turn composed of 3 smaller parts.
- A phosphate group.
- A nitrogen containing base.
The term nucleotide is used to refer to nitrogenous base bound to a monosaccharides. And the nucleotide is a nucleotide phosphate.
There are two major types of nucleic acids.
- deoxyribose nucleic acids (DNA).
- ribonucleic acid (RNA).
There are two main differences between the deoxyribonucleotide components of DNA and the ribonucleotide component of RNA.
||– Has its sugar D-ribose lacking hydroxyl group in carbon #2 of ribose; hence the prefix De-oxy is used to denote the absence of oxygen at that position.||– Has its sugar D-ribose having oxygen at carbon number 2.|
||– Have four possible organic bases, 3 of which are adenine, guamine and cytosine and the fourth is thymine which is lacking in RNA.||– Have four possible organic bases, 3 of which are adenine, guamine and cytosine and the fourth is uracil which is lacking in DNA.|
JOINING THE NUCLEOTIDES TO FORM A POLYMER OF DNA OR RNA.
The bond that holds these polymers together are ester linkage formed between the phosphate on the number 5 carbon of ribose in one nucleotide and the hydroxyl on the number 3 carbon of ribose in the next nucleotide (deoxyribose in the case of DNA)
Two nucleic acids are said to have 3l5l– phosphate ester bridge/bond between their nucleotide components
Diagram of a long nucleic acid.
- The DNA consists of two long polynucleotide strands and the base components of each nucleotide on one strong can form hydrogen bonds with only one specific nucleotide base on the other strand.
- Guamine (G) can hydrogen bond only to cytosine in another DNA strands form a base pair.
- Adenine (A) can hydrogen bond with thymine (T).
ATP (ADENINE TRIPHOSPHATE)
- ATP is formed from the nucleotide adenosine monophosphate by the addition of two further phosphate molecules.
- ATP is an energy store, because the last branches are highly energetic on breaking.
- The hydrolysis of ATP to ADP is catalyzed by the enzyme ATPase and the removal of the terminal phosphate yield 30.6kj mol-1 of free energy. So does the second one to from ADP and AMP respectively. AMP and ADP may be re-converted to ATP by the addition of phosphate molecule in a process called phosphorylation of which there two main forms.
- Photosynthetic phosphorylation– occurring during photosynthesis in chlorophyll-containing cells.
- Oxidative phosphorylation – occurring during cellular respiration in all aerobic cells.
USES OF ATP.
A metabolic active cell may require up to two million ATP molecules every second. ATP is the source of energy for;
- Anabolic processes. It provides the energy needed to build up macromolecules from components units.
- Polysaccharide synthesis from monosaccharide.
- Protein synthesize from amino acids.
- DNA replication.
- Movement- it provides the energy for many forms of cellular movements, including;
- Muscle contraction
- Cilliary actioning
- Spindle action in cell division.
- Active transport – it provides the energy necessary to move materials against concentration gradient e.g. ion pumps.
- Secretion – it is secreted to form the vesicle in the secretions of the cell product.
- Activation of chemicals – it makes chemicals more enabling them in reacting (more readily) e.g. the phosphorylation of glucose at the start of glycolysis.
- Enzymes are simple or compound organic proteins which are organic catalysts catalyzing reactions in living tissues.
ENZYME: Greek word “en” means in and “zyme” means yeast cell.
They are bio catalysts found in living things.
- Catalysts accelerate chemical reactions although a catalyst is a participant in a reaction and undergoes physical change during the reaction. It reverts to its original state when the reaction is complete.
- Enzymes are protein catalysts for chemical reactions in biological systems. Most chemical reactions of living cells would occur very slowly, were it not for catalyzing enzymes as illustrated below.
Energy diagram under catalyst action showing progress of the reaction.
Fig. reduction of necessary activation energy by enzymes.
NB: as seen in the above graph, the activation energy (Ea) necessary to initiate the reaction is much less in the presence of the catalyst than in its absence.
- It is this lowering of activation energy barrier by enzyme catalysts that makes possible most of the chemical reactions in life.
- By contrast to non-protein catalyst (e.g. H+, OH –, or metal ions) each enzyme catalyze a small number of reactions, frequently only one and thus enzymes are reaction –specific catalysts.
- Most inorganic catalysts are relatively non specific for example platinum, often used to catalyze the formation of water from hydrogen gas and oxygen gas. Will catalyze almost any reaction in which H2 is one of the reactants and the reaction of materials as well.
Properties of enzymes.
- They generally work fast than inorganic catalysts and greatly lower the activation energy.
- Enzymes are not consumed by the reaction they catalyze i.e. a given molecule of an enzyme can be used indefinitely if the conditions are kept suitable.
- Enzymes can work in either direction i.e. catalyze reversible reactions. This is due to the fact that metabolic reactions are reversible and the direction of the reaction depends on the relative amount of substrates and products present.
- Enzymes are denatured by excess heat (temperature) by the virtue of their proteineous nature.
- Enzymes are sensitive to pH. Every enzyme has its own range of pH at which it functions effectively.
- Enzymes are specific in the action they catalyze. Normally a given enzyme will catalyze only one reaction or one type of reaction.
- Enzymes react in only small amount. A very small amount of catalyst will transfer in a very large amount of reactants.
- They are colloidal in nature and thus provide large surface area for reaction to take place.
- Enzyme activity can be accelerated or inhibited. The accelerators are called activators e.g. Cu, Zn, Co, Cl, Ca. while the inhibitors are for example DOT, Pb, and Hg etc.
NATURE AND MODES OF ENZYME ACTIVITY.
Hypothesis explains the nature and mode of enzyme activity.
- The lock and key theory (hypothesis) by Fischer.
In the model the three dimensional configuration of the enzyme represented the lock (the active title) into which particular substrate (key) will fit.
The active site presumes to be rigid.
- The induced fit model by Koshland.
Originally little more than an attractive hypothesis, this model now has received considerable experiment support.
An essential feature is the flexibility of the region of the active site. In this mode, the substrate induce the conformation change in an enzyme just like the shape of a glove is affected hand wearing.
MOLECULAR STRUCTURE OF ENZYMES.
Enzymes are either composed of;
- Protein alone-simple enzymes.
- Protein and other non-protein molecule( i.e. conjugated enzymes)
The protein part of an enzyme is called Apanzyme.
Non- protein part is called co-enzyme.
The protein part of an enzyme is made up of enzyme protein zymoprotein.
The two component (the apoenzyme and coenzymes) make up the active enzymes called holloenzymes.
Holoenzymes = coenzyme + apoenzyme.
Prosthetic groups are usually metallic ions such as Co, Mg, Ni, Cu, Zn (mineral salt). This is also a non-protein part, the well known co-enzyme are those which function as hydrogen carriers, in-oxidation-reduction in energy metabolism. For instance coenzyme NAD, NADP, Q, A. Coenzyme A is involved in transfer of an acetyl group.
These are substances which increase the activity of the halo enzymes. Their absence may retard the catalytic activity of the enzymes or preventing it from acting.
Activators are usually inorganic ions e.g. Ca2+ for thrombo kinase, Cl– for ptyalin, Mg2+ for phosphate.
Coenzymes and activators are needed by the enzymes for proper activities.
FACTORS AFFECTING ENZYMATIC ACTIVITY.
- Over a limited range of temperature, the velocity of enzyme catalyzed reactions increase as the temperature rises. The exact ratio by which the velocity change for a 100C temperature rise is the Q10 or temperature coefficient.
The velocity of many biological reactions roughly doubles with a 100C rise in temperature ( Q10 = 2) and is halved if the temperature is decreased by 100C. Many physiological processes e.g. the rate of contraction of an exercised heart- consequently exhibit Q10 of about 2.
When the rate of enzyme catalyzed reaction is measured at several temperature the result shows in the figure below is typical. There is an optimal temperature which the reaction is most rapid. Above this reaction the rate decrease sharply due to heat denaturation of the enzyme and below this the energy content of enzymes is too low to make them participate in their reaction.
Fig. enzymes activity as a function of temperature.
- Although temperature sensitivity varies somewhat from one enzyme to another the curve shown here may be taken as applying to an average enzyme.
Its activity rises steadily with temperature (approximately) doubling for each 100C increase until thermal denaturation cause a sudden sharp decline, beginning between 400C and 450C. The enzyme because completely ineffective/ inactive at temperature above 600C presumably because its three dimensional configuration has been severely disrupted.
Denaturation of a protein enzyme by heat is the loss of it biological activity. This can be done also by heat, acid or high salt concentration.
Moderate pH changes affect the ionic state of the enzyme and frequently that of the substrate also.
When enzyme activity is measured as several pH values optimal activity is generally observed between pH values of 5 and 9. However the few enzymes eg pepsin is active at pH values well outside this range. The shape of pH activity curves is determined by the following factors.
- Enzyme denaturation.
At extremely high or low pH values.
- Since the only forms that will interact are SH+ and E–. Extreme pH values will lower the effective concentrations of E– and SH+ thus lowering the reaction velocity as shown below.
Only the crossed-hatched area of S and E in the appropriate ionic state and thermal concentration of E and S are correctly charged at X the result is a bell-shaped pH activity curve