Genes and Geneomes Flashcards
When do DNA strands need to be separated? (Double helix unwound)
To act as templates for DNA.
Describe in detail the helical structure of DNA
Two sugar-phosphate backbones intertwine and are linked by non-covalent hydrogen bonding. Uneven coiling generates ‘major’ and ‘minor’ grooves.
What base does adenine always pair with?
Thymine
What base does guanine always pair with?
Cytosine.
Name the four base nucleotides in DNA and state how they are paired.
Thymine pairs with adenine
Guanine pairs with cytosine
What feature of the A:T and G:C pairing ensures that the sugar phosphate backbones are held at a constant distance from each other?
The overall length of an A:T base pair is approximately equal to G:C pair so the distance between the backbones is maintained.
What is the origin of replication?
A point on the genome where a particular sequence of base pairs initiates replication.
What is the replication complex?
A number of molecules and enzymes needed for replication form a large protein complex called the replication complex, which recognises and binds to the origins of replication.
It includes:
1) helicases, which separate the base pairs and unwind the two DNA strands.
2) single-strand DNA binding (SSB) proteins, which prevent the strands from reannealing to reform the duplex.
3) DNA polymerases, the enzymes which actually assemble the nucleotides into the new DNA strands.
What is DNA polymerase?
The enzymes that assemble the nucleotides of new DNA strands.
What are helicases?
The enzymes which separate base pairs of DNA ready for replication.
What are single-strand DNA binding proteins?
Proteins which bind to unwound single strands of DNA in order to prevent them from reannealing while awaiting replication.
What is the replication bubble?
The separation of DNA strands causes a replication bubble with a replication fork at each end. Helicases continue to unwind the DNA at each of these forks, extending the replication bubble in both directions.
What is the enzyme DNA topoisometase?
An enzyme which ‘nicks’ one of the DNA strands, it cuts the sugar-phosphate backbone, allowing the DNA helix to swivel around itself & resells it.
This prevents torsional stress ahead of the replication fork.
What is a nuclease?
They break links between nucleotides.
How does DNA polymerase act as a proof reading mechanism?
Each time a new nucleotide is added, the polymerase ‘checks’ that the base pair that it has just formed is correct, if not the polymerase reverses and it’s nuclease activity removes the incorrect nucleotide before synthesis is resumed.
