A* Summary notes with diagrams for 2.1.3 Nucleotides And Nucleic Acids, A level Biology

Nucleotides And Nucleic
Acids
Nucleotides consist of:

A pentose sugar

A phosphate group

A nitrogen containing organic (carbon based) base


DNA and RNA are polynucleotides (polymers) that are made up of
nucleotide monomers.



DNA nucleotides contain:

Penose sugar Phosphate group Bases

Deoxyribose (hydrogen at 2’ position) Present Adenine (A)

Thymine (T)

Cytosine (C)


Guanine (G)




Nucleotides And Nucleic Acids 1

, RNA nucleotides contain:

Phosphate
Penose sugar Bases
group

Adenine (A)

Ribose (has hydroxyl / OH group at 2’ Uracil (U)
position). The presence of the OH group Present
makes RNA more susceptible to hydrolysis. Cytosine (C)

Guanine (G)




There are 2 types of nitrogenous base.

Purines Pyrimidines

Adenine (A) Thymine (T)




Nucleotides And Nucleic Acids 2

, Guanine (G) Cytosine (C)




Purines have a double ring
structure and pyrimidines
have a single ring Uracil (U)
structure.


Between 2 antiparralel DNA
polynucleotide strands there
are hydrogen bonds between
complementary bases.
2 hydrogen bonds are formed
between Adenine (A) and
Thymine (T).
3 hydrogen bonds are formed
between Guanine (G) and
Cytosine (C).
These bases are known as
complementary pairs and are
vital in maintaining the
double helix structure of DNA.




Nucleotides And Nucleic Acids 3