Bisc 101 Nucleic Acids and DNA

Deoxyribonucleic acid (DNA)

-stores genetic information and is replicated using proteins.

-polymers of nucleotide monomers

RNA world hypothesis

-Proposes that there was a stage in the evolution of life when RNA both stored the genetic information and catalyzed its own replication.

Nucleic Acid

Polymers made of Nucleotides

Nucleotide

-monomers of Nucleic Acid

-building blocks, of DNA and RNA

(1) a phosphate group, (2) a five-carbon sugar, and (3) a nitrogenous base.

-sugar is the central component.

-5 types of bases:

Purines: adenine (A) and guanine (G)

Pyrimidines: cytosine (C), uracil (U), and thymine (T)

Ribonucleotide

-monomers of RNA

-sugar: Ribose, C 2’ is OH

-Uses Uracil

Deoxyribonucleotides

-monomers of DNA

-sugar: Deoxyribose, C2’ is Hydrogen

-Uses Thymine

Pyrimidines

cytosine (C), uracil (U), and thymine (T)

single ring structure

Purines

Adenine (A), Guanine (G)

two ring structure

Polymerization of nucleic acids

-Occurs through condensation reactions which forms a new covalent bond: a phosphodiester bond.

-Releases a molecule of water.

Phosphodiester bonds are covalent bonds

-catalyzed by enzymes. Joining of nucleotides is not spontaneous.

-Cells raise the potential energy of nucleotides before polymerization occurs.

DNA and RNA Strands Are Directional

-the sequence of nucleotides found in an RNA or DNA strand are always written in the 5′ -> 3′ direction.

-one end always has a free phosphate (5') and the other always has a free hydroxyl group. (3')

5’ outside ring, 3’ inside ring

Why Phosphates Store Energy

-Phosphates carry a negative charge.

-Linking multiple phosphates together creates a covalent bond that carries potential energy due to the repulsive forces.

-Energy is released when phosphates break off.

Antiparallel

-the two DNA strands run in opposite directions; one runs 5'→3' while the other runs 3'→5.

Base pair

-two nitrogenous bases held together by hydrogen bonds across the double helix

A-T base pair

2 hydrogen bonds

G-C base pair

3 hydrogen bond

Two grooves exist on the outside

Major groove: wider; where most proteins bind to DNA

Minor groove: narrower

What Stabilizes the Double Helix

-Hydrogen bonding between complementary base pairs.

-Bases are nonpolar and cluster in the interior.

-Van der Waals interactions between tightly stacked bases.

-DNA as a whole is water soluble because the phosphate backbone (exterior) is negatively charged and hydrophilic