lecture 1 & 2

Question 1

name 2 popular misconceptions from before Mendel

Answer 1

blending inheritance- red and white flowers make pink flowers

preformationism (homunculus)

Question 2

name 3 prerequisite characteristics for genetic material

Answer 2

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

Question 3

name 3 experiments involved in identification of genetic material

Answer 3

1- Griffith: transformation

2- Avery, MacLeod, McCarty: transforming principle

3- Hershey and Chase: bacteriophage genetic material = DNA

Question 4

describe Griffith’s experiment with transformation

Answer 4

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

Question 5

describe Avery and transforming principle

Answer 5

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

Question 6

bacteriophage is 50% ___ and 50% ___

Answer 6

protein
DNA

Question 7

Hershey & Chase

Answer 7

• 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)

Question 8

Watson & Crick

Answer 8

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

Question 9

ribose has hydroxyl in __’ carbon

Answer 9

2’

Question 10

nucleotides (monomer) are connected by ___ bonds to form nucleic acids (polymer)

Answer 10

phosphodiester

Question 11

structure of a nucleotide consists of a ___, ___, ___

Answer 11

phosphate group, sugar, nitrogenous base

Question 12

purine has ___ rings
pyrimidine has ___ rings

Answer 12

2
1

Question 13

name the purines and pyrimidines

Answer 13

purines: adenine & guanine

pyrimidines: uracil & cytosine & thymine

Question 14

what is the difference between a nucleotide and a nucleoside

Answer 14

nucleotide = nitrogenous base (purine/prym) & sugar & phosphate

nucleoside = nitrogenous base & sugar

Question 15

describe the linkage of nucleotides by phosphodiester bonds

Answer 15

5’ phosphate of one nucleotide unit is linked to 3’ hydroxyl group of next nucleotide unit

Question 16

Uracil in RNA replaces ___ in DNA

Answer 16

thymine

Question 17

describe complementary base pairing

Answer 17

• purine pairs with pyrimidine

adenine & thymine (uracil)

guanine & cytosine

Question 18

name 4 characteristics of DNA structure

Answer 18

• base pairing
• complementary
• “constant” width
• antiparallel

Question 19

which form is the “ideal” DNA structure

Answer 19

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

Question 20

describe A form of double helix

Answer 20

• shorter
• 11 bp per turn
• bases tilted
• DNA when “dehydrated”
• in vivo, dsRNA and RNA/DNA hybrids resemble A-form

Question 21

describe Z form of DNA double helix

Answer 21

• 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

Question 22

name 4 unusual structures that certain sequences can adopt

Answer 22

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)

Question 23

describe DNA triple helix

Answer 23

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)

Question 24

DNA tetraplex or quadruplex

Answer 24

only DNA sequences with high proportions of G (end of the chromosomes)