Nucleic acids

NUCLEIC ACIDS (DNA and RNA)

• Friedrich Miescher (1869):• He isolated a white substance from the nuclei of pus

cells, called it nuclein • Nuclein was shown to have acidic properties, hence it

became called nucleic acid• Nucleic acids constitute a fourth major class of biological

molecules important to life• Nucleic acids molecules are large polymer of smaller

building block units called nucleotides• The hereditary material called genes is composed of

nucleic acids• Nucleic acids convey information from the genes in the

nucleus to the rest of the cell• Nucleic acids are of two types• i) Deoxyribonucleic acid DNA ii) Ribonucleic acid (RNA)

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NUCLEOTIDES

• Nucleotides are the building block units of nucleic acids

• All nucleotides are composed of three components• 1) Pentose sugar. i) Deoxyribose (DNA) ii) ribose (RNA)• 2) Nitrogen-containing base. (Purines &Pyrimidines)

• 3) Phosphoric acid (Phosphate group) H3PO4

Nucleotide

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2.Nitrogen containing bases in DNA & RNA

• Nitrogenous bases are of two types• i) Purines (Adenine and Guanine)• ii) Pyrimidines ( Thymine, Cytosine & Uracil)

3.Phosphate group(H3PO4): Essential for nucleotide polymerization

P

O

O

O

O X

Phosphate group

Types of nucleotides

• Nucleotides are classified into three types• i) Mononucleotides ii) Dinucleotides iii) Polynucleotides• i) Mononucleotides: • They occur singly in the cell • The common mononucleotide is Adenosine triphosphate

(ATP) • Structure: ATP contain three phosphates. Linkage of

adenine base to ribose forms a structure called adenosine

• Adenosine Monophosphate:• When adenosine is bonded to a single phosphate it

forms a structure called Adenosine Monophosphate • Adenine + Ribose Adenosine• Adenosine + phosphate Adenosine

Monophosphate (AMP)Asghar khan lecturer in Botany GDC Totakan

Mononucleotides • Adenosine Diphosphate:• The attachment of another phosphate to AMP forms a

structure called adenosine diphosphate

• AMP + P Adenosine diphosphate (ADP) A-P-P• Adenosine Triphosphate: when another phosphate is

attached with ADP it forms a structure called adenosine Triphosphate (ATP)

• ADP + P Adenosine Triphosphate (ATP) A-P-P-P• ATP is an energy rich molecule• Also called energy currency of the cell. They are

formed during respiration• Provides energy to the cell on demands• The hydrolysis of ATP into ADP & Pi yields almost 7.3

Kcal energy• ATP + H2O ATPase ADP + Pi + 7.3 Kcal

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AMP,ADP AND ATP

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Dinucleotides • ii) Dinucleotides:• Linkage of two nucleotides results a dinucleotide.• If these nucleotides contain adenine as

nitrogenous base, then it is known as adenine dinucleotide

• Dnucleotide on attachment with vitamins forms Co-enzymes

• Examples of co-enzymes are• NAD+ (Nicotinamide adenine dinucleotide)• NADP (Nicotinamide adenine dinucleotide phosphate• FAD+ (Flavin adinine dinucleotide)

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Co-enzymes

• Coenzyme• A co-enzyme is a substance that works with

an enzyme to initiate or aid the function of the enzyme.

• Co-enzymes exist in two forms• In oxidized form co-enzymes act as hydrogen acceptor• NAD+ + 2H+ + 2e- NADH2• The oxidized form of co-enzyme is more reactive

than reduced form• They act as hydrogen carriers during electron

transport chain of glycolysis.

Oxidized form Reduced form

NAD+ NADH2

NADP+ NADPH2

FAD+ FADH2

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Polynucleotides (DNA & RNA)

• iii) Polynucloetides: Poly means many’’• When many nucleotides are bonded together, they

form a polynucleotide structures e.g. DNA & RNA (Nucleic acids )

• i) DNA (deoxyribonucleic acid)• Discovery of DNA• James Watson, Francis Crick and Maurice Wilkins (1916-2004) jointly received the noble prize in physiology or

medicine for their explanation of DNA Model in 1953. • MAIN PIONTS OF DNA MODEL: according to this

model:• i) DNA is a double helical/stranded structure• ii) The two helices are anti-parallel to each other• iii) The backbone of double stranded structure is

composed of sugar and phosphate.Asghar khan lecturer in Botany GDC Totakan

Bonding in DNA

• iv) The two stands of DNA are held together by hydrogen bond between Purines & pyrimidines

• Adenine form double hydrogen bond with Thymine • Guanine form triple hydrogen bond with cytosine• Diameter of DNA molecule is 2nm.• Distance between nitrogenous bases is 0.34nm.

DNA CHEMICAL COMPOSTION

• DNA is a polynucleotide chain structure.• Nucleotides are the building blocks of DNA

molecule• Nucleotide is composed of three components• 1) Pentose sugar. i) Deoxyribose (DNA)• 2) Nitrogenous bases. (Purines &Pyrimidines)• 3) Phosphoric acid (Phosphate group) • Four different types of nucleotides in DNA molecule are:• i) Adenine deoxyribonucleotide• ii) Gaunine deoxyribonucleotide• iii) Thymine deoxyribonucleotide• iv) Cytosine deoxyribonucleotide

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DNA double helix

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Structure of DNA• These four different nucleotides in DNA molecules

bonded to one another in such way that,• Sugar of one nucleotide is bonded to the

phosphate group of next nucleotide.• In this way the nucleotides form a linear DNA

molecule called a strand• The backbone of this DNA strand is made up of

sugar alternating with the phosphate group• The nitrogenous bases are projected towards

inside of the strands forming rungs of the ladder• The two strands twist about one another to form

a double helix• The sequence of nucleotides in the DNA of

different individual are different.

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