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
Why is DNA negatively charged?
Because of the negative charges on the phosphate groups
What features of DNA give it a high melting point?
It is precipitated with NaAcetate and ethanol
Also high content of CG base pairs
What makes DNA compact?
Hydrogen bonding
Also DNA bases can pi-stack together to form a compact core
What are the three main forms of DNA?
1) A-DNA
2) B-DNA
3) Z-DNA
What is A-DNA?
Right-handed helix
11 base pairs per turn
Typically forms on dehydration
What is B-DNA?
The more common form of DNA
Right-handed helix
Has deep major and minor grooves
Approx. 10 base pairs per helical turn
What is Z-DNA?
Left-handed helix
Often formed transiently during unfolding
Describe what happens during DNA replication.
The DNA must be unzipped
New strands are generated on each of the parent strands by DNA polymerase which only adds bases to the 3’ end
Involves the attachment of nucleoside triphosphates to the 3’ end
What are nucleoside triphosphates?
Precursors for building nucleic acid chains.
Describe what happens during transcription.
DNA must be unzipped
RNA strand is generated on the template strand by RNA polymerase
RNA polymerase only adds bases to the 3’ end
Describe the structure of RNA.
Remains single-stranded
Can fold up by base pairing (i.e. in tRNA)
What does tRNA do?
Carries an amino acid to add to the chain during protein synthesis
It matches its anticodon to the mRNA encoding the protein within a ribosome
The ribosome moves along the mRNA to synthesise the protein
