DNALayal Fahad MadaFatimaEntesarHila AhmedNahlaSaja

Purine and Pyrimidine Structures :• Purines and pyrimidines are two of the building blocks of

nucleic acids. Only two purines and three pyrimidines occur widely in nucleic acids.

• # The four nitrogen bases are :• Purine: Adenine (A) and Guanine (G)• Pyrimidines: Thymine (T) and Cytosine (C)• Purines are always bonded to a pyrimidine (A-T, C-G)• Reason: size of base and number of hydrogen bonds. • A=T 2 bonds C≡G 3 bonds

Purine and Pyrimidine Structures : - contd..

Ribose & Deoxyribose :

• The 5-carbon sugars ribose and deoxyribose are important components of nucleotides, and are found in RNA and DNA, respectively.

• The sugars found in nucleic acids are pentose sugars; a pentose sugar has five carbon atoms.• A combination of a base and a sugar is called a nucleoside

Ribose & Deoxyribose : - Contd ..• Deoxyribose, found in DNA, is a modified sugar, lacking one

oxygen atom (hence the name "deoxy"). This difference of one oxygen atom is important for the enzymes that recognize DNA and RNA, because it allows these two molecules to be easily distinguished inside organisms.•

Ribose and deoxyribose are pentose.Ribose is also called ribofuranose because of the structural relationship to furane. The only structural difference between ribose and deoxyribose is the loss of an -OH group in position 2 in the ring. 

Phosphate : • Attaching a phosphate group :

• The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA.• This backbone is composed of alternating

sugar and phosphate groups, and defines directionality of the molecule.

• The sugar-phosphate backbone is negatively charged and hydrophilic, which allows the DNA backbone to form bonds with water.

Nucleoside & Nucleotide :• A nucleoside consists of a• nitrogenous base covalently attached to a sugar (ribose or

deoxyribose) but without the phosphate group. A nucleotide consists of a nitrogenous base, a sugar (ribose or deoxyribose) and one to three phosphate groups. • Nucleoside = Sugar + Base • Nucleotide = Sugar + Base + Phosphate

DNA Structure

• DNA is Deoxyribonucleic acid• is a molecule that carries most of the

genetic information of all living organisms and many viruses. • DNA Composed of four nucleotides ,

each nucleotide consist of a phosphate group , sugar (deoxyribose) and a nitrogen base.• Two strands of twisted nucleotides =

double helix.

DNA Structure - Contd ..

• All DNA strands are read from the 5' to the 3' end• where the 5' end terminates in a phosphate group• and the 3' end terminates in a sugar molecule.

• The four nitrogen bases are:• Purine : Adenine and Guanine . ( A & G )• Pyrymidine : Thyamine and Cytosine . (T & C )

• A = T• G ≡ C

FUNCTION :

• Function of DNA Stores genetic information that instructs the

cell on what proteins to make and where to make them

Responsible for determining all organism’s traits such as eye

color, body structure, and cellular enzyme production (exact

words from a previous TAKS test).