A1.2 Nucleic Acid

DNA

A double helix made of two antiparallel strands of nucleotides with two strands linked by

hydrogen bonding between complementary base pairs

RNA

Sugar–phosphate bonding and the sugar–phosphate “backbone” of DNA and RNA

Sugar–phosphate bonding makes a continuous chain of covalently bonded atoms in each strand of DNA or RNA nucleotides, which forms a strong “backbone” in the molecule.

Nitrogenous Base Names

Adenine, Guanine (Purine-double ring structures), Cytosine, Thymine/Uracil (single-ring structure)

-Uracil is found exclusively in RNA, replacing thymine)

AT, CG

Differences between DNA and RNA

DNA: Double helix, two strands. Deoxyribose sugar (one oxygen atom) ATGC

RNA: One strand. Ribose sugar (one hydroxyl -OH group) AUGC

Nucleic Acid Examples

DNA: Nuclear DNA, mitochondrial DNA, chloroplast DNA

RNA: mRNA, tRNA, rRNA / ribosomal

Complementary base pairing

the specific matching of nitrogenous bases in nucleic acids (DNA and RNA) held together by hydrogen bonds

Diversity of DNA Base Sequences/Limited capacity of DNA for storing information

Diversity by any length of DNA molecule and any base sequence is possible. DNA has an enormous capacity to store data

Universal Genetic Code

The conservation and near-universality of the genetic code across nearly all known life forms.

Antiparallel orientation

5’ to 3’ phosphate sugar inkages

-double stranded DNA consists of two strands running in opposite directions, one 5’ to 3’ and the other 3’ to 5’

Purine to Pyrimidine Bonding as a component of DNA helix stability

Adenine-Thyine (A-T) and Cytosine-Guanine (C-G) pairs have equal length, so the DNA helix has the same 3D structure regardless of base sequence

Structure of a Nucleosome

DNA molecule wrapped around a core of eight histone proteins held together by an additional

histone protein attached to linker DNA.

Hershey–Chase experiment evidence showing that DNA is the genetic material

The experiment showed that only viral DNA enters a host bacterial cell during infection

Infection: labled viruses infected w/ E. coli baceria

Blending: a blender knocked the empty viral protein coats off the outside of the bacterial cells

Chargaff’s data

Erwin Chargaff measured the amounts of purines (large bases: Adenine and Guanine) and pyrimidines (small bases: Thymine and Cytosine) in various organisms.

The amounts of bases are not equal (\(A \neq G\)). However, the amount of Adenine always equals Thymine (\(A = T\)), and Guanine always equals Cytosine (\(G = C\))

(Basically, DNA does not contain equal amounts of all four bases, which permanently destroyed the old tetranucleotide hypothesis)