Download Nucleic Acids and DNA Replication

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
Number of Strands
Pentose Sugar
Nitrogenous Bases
RNA
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