Biological Molecules 3: Nucleotides Flashcards
What are nucleotides?
Small molecules which are used to build up the long chains of DNA and RNA which store and distribute genetic information
What are the three components of nucleotides?
1) Ribose sugar
2) Phosphate group
3) Base
What is ATP?
Adenosine triphosphate
Stores energy in the phosphoanhydride/pyrophosphate bonds
These can be hydrolysed one at a time to release energy
ATP –> ADP + Pi + energy
How can you increase the energetic favourability of a chemical reaction?
By coupling it to another spontaneously ouccuring chemical reaction
Enables it to be driven energetically uphill
What is the importance of the adenosine group in ATP?
Allows ATP to be recognised and selectively bound by an enzymes active site
What is a common reaction that is coupled with ATP hydrolysis?
Formation of glycosidic bonds in sucrose
Allows storage of energy
All steps are enzyme controlled
Give three examples of dinucleotides.
NAD
NADP
FAD
Each of which are used as hydride carriers during respiration and photosynthesis
Which bases are purines?
Adenine and guanine
Which bases are pyrimidine?
Cytosine, thymine, and uracil
Why is RNA not as stable as DNA?
Because the 2’ hydroxyl group in RNA can break the phosphodiester bond
This only occurs slowly but it cannot occur in DNA
This makes DNA better for long-term storage of genetic information
Describe the hydrogen bonding between adenine and thymine.
Two hydrogen bonds form
Each base donates one lone pair
Describe the hydrogen bonding between cytosine and guanine.
Three hydrogen bonds form
Cytosine donates one lone pair
Guanine donates two lone pairs
Why does hydrogen bonding only occur from A-T or C-G?
Most favourable interactions
Prevents mismatching
High selectivity enables accuracy in replication and transcription
How are DNA sequences written conventionally?
From the 5’ end
How is the double helix of DNA formed?
The backbones of each strand must twist to enable the bases to match efficiently
