DNA and RNA Flashcards
What 3 classic experiments led to Watson and Crock suggesting the double helical model for DNA structure in 1953
- Griffith 1928: Discovered the Transforming Principle
- Avery, MacLeod + McCarty 1944: Established transforming principle was DNA
- Hershey + Chase 1952: Demonstrated that a biological organism (bacteriophage T2) had DNA as its genetic material
Describe the basis for Griffith’s 1928 experiment
- Uses Streptococcus pneumonia
- Descovered two different strains defined by serotypes
- Serotype ll: no capsule - ‘rough’ colony (R) - non-pathogenic. When injected into mice they could fight it off
- Serotype lll: Capsule - ‘smooth’ colony (S) - pathogenic in mice causing them to die
Describe Griffith’s (1928) experiment
- If the Smooth type lll bacteria were heat-killed the mouse would survive
- However if the Smooth type lll bacteria were heat-killed and then Rough type ll bacteria were added, the mice would die
- Transformation occurs because DNA is released from heat killed smooth type bacteria and taken up by living rough type bacteria and incorporated into their genome changing their properties
Describe Dawson’s (1931) experiment
- In vitro = in a test tube rather than using live mice
- Heat killed smooth type lll cells will transform living rough type ll cells in vitro
- Living smooth type lll cells recovered without injection into mice
What did Avery, MacLeod and McCarty (1944) discover
That the transforming principle was DNA
Describe the experiment done by Avery, MacLeod and McCarty (1944)
- Used 75L of heat killed smooth type lll cells to give a soluble extract containing the transforming principle
- Successively removed different components (including lipids, protein and polysaccharide)
- The only thing remaining was DNA
- This confirmed in a final experiment where they treated with an enzyme DNAse which breaks down DNA and finally the activity by the transforming principle was lost
What did Avery, MacLeod and McCarty’s experiment (1944) fail to show
It didn’t fully demonstrate that biological organisms use nucleic acids as their genetic material
Describe the life cycle of a Bacteriophage
Describe Hershey-Chase’s experiment (1952)
- The experiment demonstrated that the genetic material of Phage T2 is DNA
- They had two batches of phage labelled with different radioisotopes: 35S which was a coat protein and 32P which attached to DNA
- The 35S lable remained in the supernant as phage ghost parts, while the 32P became intergrated into the bacterial cells and ended up in a pellet
What other experiment by Wilkins, Franklin and Gosling also played a key part of the Watson and Crock proposing the structure of DNA
They used x-ray diffraction to study DNA fibres
The image created showed spots forming a cross in the centre denote a helical structure
Heavy bands at the left and right arise from the recurring bases
What new piece of information was found about DNA resulting in Chargaff’s Laws (1949-1959)
- Total number of pyrimidines (T, C) = total purines (A, G)
- Hence deducing that A bonds with T and C bonds with G
Which is the major and which in the minor grove on the diagram
DNA strands run
antiparallel
The two DNA strands are held together by hydrogen bonds
How many bonds form between C+G and A+T
3 bonds between G+C pairs
2 bonds between A+T pairs
Because there are only 2 bonds between A+T bases, these two bases are found at higher quantities at
Places where the DNA will need to unwind to all the start of transcription
In a basic unit of a nucleic acid (nucleotide), what determines if it is a DNA or RNA nucleotide
Carbon 2 position determines whether DNA or RNA
hydroxyl group forms the sugar ribose (RNA)
hydrogen atom forms the sugar deoxyribose (DNA)
Which carbon is the phosphate attached to of the pentose sugar
Carbon 5
What affect does the phosphate group have on the DNA
It cause it to have a negative charge
Which carbon does the Purine/Pyrimidine base attach to
At carbon 1
In RNA, adenine bind to which base?
Uracil
What is the main difference between purine and pyrimidines
Purine - double nitrogenous ring structure
Pydrimidines - single ring structure
Through which group on the nitrogenous bases do they bind to the pentose sugar
N-H groups
For purine, the group on the smallest carbon ring
For pyrimidine, the group next to the carboxyl and methyl group
Using which function groups on Adenine and Thymine, will they form hydrogen bonds
Using which functional groups on Guanine and Cytosine, will they form hydrogen bonds
What is the difference between a nucleoside and a nucleotide
Nucleoside: sugar + base
Nucleotide: sugar + base + phosphate
What does dAMP, dGMP, dCMP and dTMP stand form
deoxyadenosine monophosphate
deoxyguanosine monophosphate
deoxycytidine monophosphate
deoxythymidine monophosphate
Bases are said to be stacked in a what arrangement in DNA
Bases are stacked in a planar arrangement - horizontal running up through the centre of the DNA
What is the significance of the major and minor grove
There is a lot more space in the major grove for proteins to come and interact with the bases within DNA
DNA is a right-hand helix, meaning?
It spins to the right
How is the phosphodiester bond formed in DNA
is the ester bond formed between the hydroxyl group on the 3’ carbon and the carboxyl group on the phosphate AND the ester bond between the hydroxyl group on the 5’ carbon and another carboxyl group on the phosphate
There is other forms of DNA, how do they differ from regular DNA
A - form similar to normal but squashed down form of DNA (found in double stranded RNA)
Z - form is a left handed helix that zig zags rather than coils elegantly (found in vitro in repeated DNA)
For normal DNA, how many base pairs are there per turn?
In Å, what is the distance between base pairs
And in Å, what is the diamter of the helix
Base pairs per turn: 10
Distance between BP: 3.4Å
Diameter of helix: 19Å
What property of DNA in vivo (in cells) but also in labs, is important
The double helix can denature when heat is applied which breaks the hydrogen bonds between the strands
What is the main two differences between DNA and RNA on a molecular level
- RNA contain uracil instead of thymine
- has ribose sugar, instead of deoxyribose
What are the 3 most important types of RNA within cells
mRNA, rRNA, tRNA
What is mRNA
messenger RNA - copied from DNA and used to make protein (intermediate between DNA and protein)
What is rRNA
Ribosomal RNA - functional RNA component of the ribosome (translational machinery in cells)
What is tRNA
transfer RNA - involved in process of translation - tRNA brings amino acids to ribosomes during translation
What is the basic structure of t-RNA
- RNA is single stranded but folds up on itself to form complicated 3D structure. Base pairing between different parts of the molecule to form stem and loop structures
- Forms these stem and loop structures
