Lecture #15 - DNA structure and function Flashcards
What are the components of DNA and RNA?
Base + Deoxyribose sugar + phosphate = nucleotide
Base: cYtosine + thYmine (pYramidines) and adenosine + guanine (purines)
What are nucleotide units linked together through?
Linked through the phosphate groups, forming the “backbone” of the molecule
1 What does the “tetranucleotide hypothesis” state? (two things) and what’s the problem to do with that? So what was L___’s conclusion?
Stated:
- Nucleotides are present as tetranucleotide repeats
- 1:1:1:1 ratio of A, T, C, G
Problem:
- DNA (and RNA) only contained four bases
- Such a “simple” molecule could not possibly encode the complexity of life.
LEVEN’S conclusion:
-Proteins, and not DNA, on the chromosome are the bearers of genetic information
2 C___ disproved Levene’s tetranucleotide hypothesis What were his two significant findings? What was his conclusion? (based on his first or second finding?)
- First rule: [A] = [T] and [G] = [C]
- Second rule: The composition of DNA varies between species
CHARGAFF’S conclusion based on SECOND rule : As there is significant DNA,variation between species, DNA is feasible to be the genetic material
3 G____ identified what? Explain the difference between the two Outline this guy’s experiment What was his conclusion?
GRIFFITH identified two strains of Streptococcus pneumoniae:
- S strain: smooth cells, PATHOGENIC so kill (hv a protective capsule so immune system can’t recognise it)
- R strain; rough cells, NON-PATHOGENIC so harmless (no capsule so immune system destroys)
Experiment
- Injected mouse with LIVING S STRAIN (virulent) –> mouse dies (found in heart)
- Injected mouse with LIVING R STRAIN (nonvirulent) –> mouse is healthy (not found in body)
- KILLED S STRAIN by heating and injected –> mouse healthy (not found)
- DEAD S STRAIN + LIVING R STRAIN ——-> mouse dead! (S strain found in heart!)
- Conclusion: the info that determines a bacteria’s strain and virulence must be encoded in a NON-LIVING CHEMICAL, as this info can be transferred from dead to living bacteria (aka DNA moves from dead S to live R and made R deadly).
Griffith’s conclusion:
A chemical substance (transforming principle - transforms R to S) is the bearer of genetic information
4 A____’s experiment was what? What was his conclusion?
AVERY’S experiment:
- Took heat-killed S strain and live R cells and in three test tubes
- DESTROYED RNA (found R converted to S) -
- DESTROYED PROTEINS (found R converted to S)
- DESTROYED DNA (NO conversion! So DNA must’ve been the “transforming principle”
- Avery’s conclusion”
- DNA is the chemical substance that causes transformation i.e. is the genetic material)
The technique of X-ray crystallography can be used to determine what? What did early X-ray studies on molecules suggest?
The technique of X-ray crystallography can be used to determine the 3D STRUCTURE OF BOTH SMALL AND LARGE MOLECULES.
Early X-ray studies on molecules of DNA were suggestive that DNA HAD A HELICAL STRUCTURE and that the BASES WERE PERPENDICULAR TO THE LENGTH OF DNA MOLECULES.
What’s the difference between RNA and DNA?
The group on the 2nd carbon (deoxy = no oxygen so just H)
Nucleotide monomers (deoxyribonucleotides) are joined together with what bonds to form what?
Nucleotide monomers (deoxyribonucleotides) are joined together with phosphodiester bonds to form a polynucleotide = nucleic acid (deoxyribonucleic acid for DNA)
Formation of the phosodiester bond:
The OH group on the 3rd carbon of one nucleotide reacts with the phosphate group attached to the 5th carbon on another nucleotide
DNA strans grow in the 5’ —–> 3’ direction
The Watson-Crick model of DNA structure:
- DNA has what structure?
- What’s on the outside and inside?
- How is it stabalised?
- The two polynucleotide strans are oritented how?
- DNA has a double stranded helical structure
- The sugar phosphate backbone is on the outside and the bases are on the inside
- Stabilised by hydrogen bonds
• The two polynucleotide strands are oriented in opposite directions
