bf 2: dna structure

storage of information

contain info needed to construct and maintain an organism

replication

must be able to be copied accurately so genetic info can be passed from cell to cell and generation to generation

expression of info

direct cellular processes to determine an organisms traits

variation by mutation

occasionally undergo changes to provide the genetic diversity necessary for evolution

federick griffith

transformation principle, dead s cells converted the harmless r cells into virulent s cells

nucleotides (building blocks)

dna is composed of nucleotides, the basic units of genetic material, consist of sugar, phosphate, and a base

dna strand ( linear polymer)

nucleotides form a strand through covalent phosphodiester bonds, one end has a 5’ phosphate group and the other 3’ hydroxyl group

double helix (two strand interact)

two dna strands, antiparallel, held together by hydrogen bonds between complementary bases, a-t, g-c

dna protein complex (chromatin organization)

dna wraps around histone proteins to form nucleosomes

chromosomes

fibers further folded and organized into chromosomes, each contain single continuous dna molecule with associated proteins

phosphate group

gives dna its negative charge and link nucleotides together

deoxyribose sugar

5 carbon sugar unique to dna, lacks oxygen on the 2’ carbon

nitrogenous base

one of 4

purines: adenine, guanine

pyrimidines: cytosine, thymine

erwin chargaff

a has the same amount of t, g has the same amount as t

rosalind franklin

x-ray diffraction to study dna fibers, image showed spiral, uniform helix, regular repeating pattern

james watson and francis crick

used data from chargaff and franklin to build 3d model of dna, double helix, antiparallel, sugar phosphate backbone