6.1 DNA and RNA Structure

Rosalind Franklin

discovered double helix shape of DNA

Chargaff

discovered that A=T and C=G

Purines

double ring structure

A and G

adenine and guanine

Pyridimines

single ring structure

C, U, T

cytosine, uracil, and thymine

A and T

2 hydrogen bonds

C and G

3 hydrogen bonds

Watson and Crick

combined findings of Franklin (helix shape) and Chargaff (base pairing) to create the first 3D, double helix model of DNA

DNA structure

1. double stranded helix

-sugar phosphate backbone

-nucleotides pairing in the center

2. antiparallel

-one strand runs 5’ to 3’, the other strand runs in the opposite, upside-down direction 3’ to 5’

-5’ end has the free phosphate group

-3’ end has the free hydroxyl group

DNA function

primary source of heritable information

genetic information is stored in and passed from one generation to the next through DNA

exception: RNA is the primary source of heritable information in some viruses

Eukaryotic DNA

DNA found in nucleus

linear chromosomes

Prokaryotic DNA

DNA is in nucleoid region

chromosomes are circular

contain plasmids

Plasmids

small, circular DNA molecules that are separate from the chromosomes

replicate independently from the chromosomal DNA

primarily found in prokaryotes, but found in some eukaryotes

contain genes that may be useful to the prokaryote when it is in a particular environment, but may not be required for survival ex. virus being able to go undercover in someone’s body and not being targeted

can be manipulated in laboratories

-plasmids can be removed from bacteria, then a gene of interest can be inserted into the plasmid to form recombinant plasmid DNA

-when the recombinant plasmid is inserted back into the bacteria, the gene will be expressed

bacteria can exchange genes found on plasmids with neighboring bacteria

-once DNA is exchanged, the bacteria can express the genes acquired(sexual)

-helps with survival of prokaryotes

RNA vs. DNA

RNA:

ribonucleic acid

single stranded

ribose

A=U

C=G

DNA:

deoxyribonucleic acid

double stranded

deoxyribose

A=T

C=G