Nucleic Acids and DNA Replication

1. What is the role of nucleic acid?

2. What is the monomer of a nucleic acid?

3. The monomer of a nucleic acid is made up of 3 things: a phosphate, base, and a _________________.

4. What is the difference between DNA and RNA?

5. A always pairs with T, and G always pairs with ____.

Nucleotides• Include DNA and RNA

Components of a Nucleotide• Phosphate Group (5’ end)

• Pentose Sugar (3’ end)• Ribose in RNA• Deoxyribose in DNA

• Nitrogenous bases• Purine (2 rings)

• Adenine, A• Guanine, G

• Pyrimidines (1 ring)• Cytosine, C• Thymine, T (only in DNA)• Uracil, U (only in RNA)

Formation of Polynucleotides• Dehydration reactions link nucleotides together

• Phosphodiester linkages are the bonds between the sugar of one nucleotide and the phosphate of the next

• New nucleotides can only be added to the 3’ end where there is an exposed hydroxyl group (from the sugar)

• This is why we say that DNA is built in a 5’ to 3’ direction

• Directionality in the structure of the DNA molecule influences how it functions

Formation of Polynucleotides

The DNA Double Helix

The DNA Double Helix• The two strands of the double helix are arranged in an

antiparallel fashion, one of them going 5’-3’ and the other one going in the opposite direction

The “Backbone”• Made up of alternating sugars and phosphates

• Connected by covalent bonds called phosphodiester linkages by dehydration reactions

The “rungs” of the Ladder• Made up of nitrogenous bases

• Hydrogen bonded to each other

• The bases are hydrophobic and in their position inside the molecule they are shielded from the aqueous environment of the nucleus

Complimentary Base Pairing• Each purine is bound to a pyrimidine

• A always to T (with 2 hydrogen bonds)

• C always to G (with 3 hydrogen bonds)

• Chargraff’s Rule: for any given species the % of Ts will by equivalent of the % of As while the % of Cs will be equivalent to the % of Gs

The DNA Double Helix

DNA vs. RNA

  DNA RNA

Number of Strands

Pentose Sugar

Nitrogenous Bases

Functions of DNA• provides directions for its own replication

• directs RNA synthesis

• through RNA, controls protein synthesis (blueprints of the cell)

Function of Ribosomal RNA• rRNA

• Together with proteins makes up the structure of the ribosomes, the site of protein synthesis

Function of Transfer RNA• tRNA

• Recognizes the 3 base sequence on the messenger RNA and brings the appropriate amino acid to the ribosome fro protein synthesis