Molecular Biology2.6 Structure of DNA and RNA

Nucleic AcidsThe nucleic acids DNA and RNA are polymers of nucleotides

Nucleic Acids Nucleotides consist of 3 parts:

A sugar 5 carbon sugars = pentose sugars

A base contains nitrogen 1 or 2 rings of atoms

1 ring = Pyrimidine 2 rings = Purine

A phosphate group negatively charged

acidic

Nucleic Acids Covalent bonds are

formed between the phosphate of one nucleotide and the sugar of the next.

This creates a “backbone” of alternating sugar and phosphate.

Nucleic Acids The bonds holding the

phosphate group to the sugar and the base to the sugar are both products of condensation reactions.

Water is eliminated when they form.

The oxygen to form the water has come from the sugar's -OH groups.

Nucleic AcidsDNA differs from RNA in the number of strands normally present, the base composition and the type of pentose

Make a chart

DNA # of strands

Base composition

Sugar

RNA

Nucleic Acids DNA has 2 polymers of nucleotides

(double-stranded) RNA has 1 polymer (single-stranded)

Nucleic Acids The sugar within DNA is deoxyribose The sugar with RNA is ribose

Draw both sugars. Compare the structures.Predict the reason for the difference in their names.Compare to the previously examined carbohydratesugars.

Nucleic Acids There are 4

different bases for each type of nucleic acid

These can be linked in any sequence

Draw the 2 generic base types.

Complete the “data-based question” p109

Nucleic Acids Data-based #1

Nucleic Acids Data-based question #2

Nucleic Acids Data-based #3 and #4

Nucleic AcidsThe amino acid sequence of polypeptides is coded for by genesThe sequence of nucleotide bases provides the code3 bases of the gene are needed to code for each amino acid

More about this later

Nucleic Acids The variety of

combinations of bases is the key to nucleic acids acting as a store of genetic information.

Nucleic AcidsDNA Pyrimidines =

Thymine (T) and Cytosine (C)

Purines = Adenine (A) and

Guanine (G)

Nucleic AcidsRNA Pyrimidines =

Uracil (U) and Cytosine (C)

Purines = Adenine (A) and

Guanine (G)

Note the change from T to U

Nucleic AcidsDNA is a double helix made of 2 antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs

Nucleic Acids The strands are held together

by hydrogen bonds between the complementary base pairs. Adenine always pairs with

Thymine Guanine always pairs with

Cytosine The 2 strands are parallel but

run in opposite directions one runs 5’ to 3’ the other 3’ to 5’

Nucleic AcidsDraw simple diagrams of DNA using circles, pentagons, and rectangles to represent phosphates, pentoses, and bases. The base is attached to the

C1

The phosphate is linked to the C5

The phosphate of another nucleotide will link to the C3

Review quiz http://www.rsc.org/Education/Teachers/R

esources/cfb/quiz.cfm?qzid=15