Molecular biology 2.6-2.7 & 7.1-7.3 & 3.5

Question 1

DNA vs RNA

Answer 1

DNA: double stranded (double helix), Deoxyribose, Adenine, Guanine, Cytosine, Thymine
RNA: single stranded, Ribose, Adenine, Guanine, Cytosine, Uracil

Question 2

DNA structure

Answer 2

Nucleic acids linked into a single strand via condensation reactions (Phosphodiester bond)
H bonds between complimentary bases (2 between A and T, 3 between G and C)
antiparallel strands
double helix

Question 3

Watson and Crick

Answer 3

1953
models to visualize DNA
trial and error
success because of Rosalind Franklin’s X-ray crystallography, she showed DNA to be a double helix

Question 4

Messelson and Stahl

Answer 4

1958
DNA replication semi-conservative
radioactive nitrogen
centrifugation

Question 5

PCR

Answer 5

Polymerase Chain Reaction
Amplifies large quantities of a specific DNA sequence
Denaturation, Annealing, Elongation
Taq Polymerase (high temperature without denaturation)

Question 6

Insulin production transfer of genes

Answer 6

• gene responsible for insulin production extracted from a human cell
• spliced into a plasmid with a restriction enzyme
• connected by ligase
• plasmid inserted into a bacterial cell, which is then cultured
• bacteria now produce human insulin

Question 7

Hershey and Chase

Answer 7

1952
- Viruses grown in two different environments
- radioactive sulphur (S35) - radio-labeled proteins
- radioactive phosphorus (P32) - radio-labeled DNA
- then infected E.coli and were separated in a centrifuge
- bacteria were in pellet while viruses formed supernatant
Results:
- bacterial pellet found radioactive in P32 viruses (DNA)
- therefore, DNA carries genetic information

Question 8

Franklin and Wilkins

Answer 8

X-ray diffraction
DNA targeted by X-ray beam, X-ray pattern scattering recorded on film
Photo 51- first DNA structure evidence
double helix

Question 9

DNA replication enzymes

Answer 9

Helicase
DNA gyrase
single stranded binding proteins
DNA primase
DNA polymerase III
DNA polymerase I
Ligase

Question 10

Helicase

Answer 10

unwinds and separates two DNA strands by breaking H bonds between pairs, at specific regions creating a fork where strands run in antiparallel directions

Question 11

DNA Gyrase

Answer 11

reduces the tension put on both strands due to unwinding by relaxing supercoils

Question 12

Single Stranded Binding proteins

Answer 12

keep strands apart and prevent them from re-annealing

Question 13

DNA primase

Answer 13

generates a short RNA primer on each template strand

Question 14

DNA polymerase III

Answer 14

attaches to 3’ end of primer and joins free nucleotides in 5’ to 3’ direction
in opposite direction on both strands
leading strand - towards replication fork in a continuous replication
lagging strand- away from replication fork, in short fragments (Okazaki fragments)

Question 15

Okazaki fragments

Answer 15

short fragments of replicated DNA on the lagging strand