Nucleic Acids Flashcards
What are the 3 main components of nucleic acids?
- Base pair
- Phosphodiester / phosphate
- Deoxyribose
What do phosphates do and in what position?
They link up sugars on the outside of the helix. The 5’ position of the sugar to the 3’ position of the next sugar.
What are the two different types of nucleobases and what is the difference?
- Pyrimidine - Benzene ring but 2 of the C’s are replaced with N’s
- Purine - Pyrimidine fused to something else
What are the nucleobases?
- Thymine
- Uridine
- Cytosine
- Adenine
- Guanine
What is the basic chemistry of nucleobases?
- Planar
- Rigid
- Aromatic units
- Sp2 hybridisation
What does adenine compliment?
Thymine
What does Guanine compliment?
Cytosine
What happens as the strand gets longer?
Complimentsry interactions
You get more complimentary interactions and the double helix will become more stable and harder to separate. This is due to more hydrogen bonding
Which complementary pair has more hydrogen bonding and therefore makes the double helix more stable?
Guanine and cytosine have more hydrogen bonds, specifically 3 whereas Adenine and Thymine only have 2.
Phosphates & stacking
Why does the DNA duplex have a helical structure?
- Phosphates have negative charges which repel each other so they can get as far away as possible in the helix form
- The hydrogen bonding between the base pairs
- Stacking nucleobases through hydrophobic / van der waals vertically compacts the structure. It also stabilises the structure due to the hydrophobic effect.
What are the different forms of DNA?
- B-DNA: Right handed
- A-DNA: Right handed
- Z-DNA: Left handed
What is the difference between the different forms of DNA?
- B-DNA: Right handed - Normal helical structure
- A-DNA: Right handed - More twisted than B, minor becomes huge and major becomes small, anti-parallel
- Z-DNA: Left handed - less common, sugars are in an alternating arrangement, phosphates are on the outside, interacts differently with enzymes and is associated with diseases.
What is triplex DNA?
Nucleobase
- Purine nucleobase, 4 hydrogen bonds with the additional nitrogen.
What is Quadruplex DNA?
Layers
- Guanine quadruplex, the strand has fewer Gs in them, made of two strands, layers of guanine quartets
nucleophile
What is the difference between DNA and RNA?
- RNA has an additional hydroxyl group attached which provides more ways hydrogen bonding can occur and can act as a nucleophile against a phosphate and catalyse the hydrolysis.
- Uridine replaces thymine
- Usually single stranded
What is the difference between thymine and uridine?
Methyl group
- It doesn’t have the methyl group that thymine has which means it has more flexibility.
- It has the same hydrogen bonding.
What are nucleosomes and what are they for?
DNA
- DNA is coiled around proteins called histones which are further packed to produce chromosomes.
- This provides a way for an organism to find the right bit of DNA easier.
How many protein units are required for each nucleosome?
Eight
What does the central dogma of biology deal with?
Residue-by-residue transfer
The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid.
Whats it called when DNA is changed to RNA?
Transcription
What’s it called when RNA is converted into DNA?
Reverse transcription
What’s it called when RNA is turned into protein?
Translation
What does copper isomerase do?
It’s an enzyme which straightens out the DNA.
What does helicase do?
It splits up the two strands.
