lecture 1 & 2 Flashcards
name 2 popular misconceptions from before Mendel
blending inheritance- red and white flowers make pink flowers
preformationism (homunculus)
name 3 prerequisite characteristics for genetic material
1- genetic material must store very large amounts of information
2- genetic material must have the capacity to be replicated accurately to be transmitted “unchanged” to the next generation
3- genetic material must “encode” phenotype
name 3 experiments involved in identification of genetic material
1- Griffith: transformation
2- Avery, MacLeod, McCarty: transforming principle
3- Hershey and Chase: bacteriophage genetic material = DNA
describe Griffith’s experiment with transformation
S strain (smooth, virulent) — mouse dies
R strain (rough, nonvirulent) — mouse lives
heat-killed S cells — mouse lives
living R cells + heat-killed S cells — mouse dies
transformation- some cellular component is taken up by live R bacteria (Streptococcus pneumonia) from dead S bacteria, making them virulent
describe Avery and transforming principle
tried to determine the identity of the transforming principle from Griffith’s experiment
- established that S-cell extract could transform R-cells in culture, determined it was DNA
- Avery postulated that genes = DNA
bacteriophage is 50% ___ and 50% ___
protein
DNA
Hershey & Chase
- radioactive isotypes of phosphorus(DNA) and sulfur(protein)
- most of the radioactive phosphorus entered the cell, most of the proteins remained on the outer surface of bacteria
bacteriophage genetic material is DNA (DNA was the phosphorus)
Watson & Crick
DNA double helix- structure forms an alpha helix, pH 7: find DNA mostly in B form (10.5 bp per round) — backbone of DNA has phosphate and sugar inside nitrogenous bases (super hydrophobic)– 2 DNA helices are antiparallel 5’ phosphate and 3’ hydroxyl
- used data of many experiments done before
- DNA vs. RNA to build the model of DNA structure
ribose has hydroxyl in __’ carbon
2’
nucleotides (monomer) are connected by ___ bonds to form nucleic acids (polymer)
phosphodiester
structure of a nucleotide consists of a ___, ___, ___
phosphate group, sugar, nitrogenous base
purine has ___ rings
pyrimidine has ___ rings
2
1
name the purines and pyrimidines
purines: adenine & guanine
pyrimidines: uracil & cytosine & thymine
what is the difference between a nucleotide and a nucleoside
nucleotide = nitrogenous base (purine/prym) & sugar & phosphate
nucleoside = nitrogenous base & sugar
describe the linkage of nucleotides by phosphodiester bonds
5’ phosphate of one nucleotide unit is linked to 3’ hydroxyl group of next nucleotide unit
Uracil in RNA replaces ___ in DNA
thymine
describe complementary base pairing
- purine pairs with pyrimidine
adenine & thymine (uracil)
guanine & cytosine
name 4 characteristics of DNA structure
- base pairing
- complementary
- “constant” width
- antiparallel
which form is the “ideal” DNA structure
B form
- spiral staircases with bases being treads
- flat base pairs perpendicular to backbone
- hydrated in vivo conditions, saw:
- right-handed double helix
- on outside, major and minor grooves
- theoretically, 10 bp per turn, but in the cell, closer to 10.5
describe A form of double helix
- shorter
- 11 bp per turn
- bases tilted
- DNA when “dehydrated”
- in vivo, dsRNA and RNA/DNA hybrids resemble A-form
describe Z form of DNA double helix
- longer and thinner
- 12 bp/turn
- backbone is zig-zag
- left- handed
- formation favored by high concentrations of positively charged ions and long (GC) or (AT) stretches in vitro
name 4 unusual structures that certain sequences can adopt
1- palindromes- same when reading 5’ to 3’ on either strand
2- hairpins- double-stranded in the stem region
3- cruciforms- double hairpin structure
4- mirror repeats- mirrored (not palindromic)
describe DNA triple helix
H-DNA (Hoogsteen base pairs)
“sideways” pairing forms C=G=C or T=A=T triangle
- one purine interacting with two pyrimidines
(very unlikely in the cell- very low pH)
DNA tetraplex or quadruplex
only DNA sequences with high proportions of G (end of the chromosomes)