DNA

1. DNA
Layal Fahad
Mada
Fatima
Entesar
Hila Ahmed
Nahla
Saja

2. 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

3. Purine and Pyrimidine Structures : - contd..

4. 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

5. 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.

6. 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.

7. 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

8. DNAStructure
• 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.

9. 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

10. 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).