3.9 : DNA replication and The Genetic Code Flashcards
Describe the process of semi - conservative replication
Double helix unwinds and separates into two strands, which results in the hydrogen bonds breaking.
Free DNA nucleotides then pair with their complementary bases, which have been exposed as the strands separate. Hydrogen bonds are formed between them.
The new nucleotides join to their adjacent nucleotides with phosphodiester bonds.
What are they roles of enzymes in DNA replication?
DNA helicase : unwinding and separating of DNA. It travels along the DNA backbone, catalysing reactions that break the hydrogen bonds between complementary base pairs.
DNA polymerase catalysed the formation of phosphodiester bonds between the new nucleotides.
How are mutations formed?
An incorrect sequence may occur in the newly-copied strand. These errors occur randomly and spontaneously and lead to a change in the sequence of bases, known as a mutation.
What is genetic code?
DNA carries the instructions needed to synthesise the many different proteins needed by organisms.
Proteins are the foundation for different physical and biochemical characteristics of living things.
They are made up of a sequence of amino acids, folded into complex structures. Therefore DNA must code for a sequence of amino acids.
This is called the genetic code.
What codes for amino acids and what codes for proteins?
A codon, which is a sequence of three bases, codes for one amino acid.
A section of DNA that contains the complete sequence of bases to code for an entire protein is called a gene.
Why is the genetic code universal?
All organisms use this same code
Why is the genetic code degenerate?
More than one sequence of three bases ( condons) can code for the same amino acid.
This is because there are 64 possible codons but only 20 different amino acids.
What are start and stop codes?
One codon acts as the start codon which comes at the beginning of a gene, signalling the start of a sequence that codes for a protein.
If it is in the middle of a gene, it codes for the amino acid methionine.
There are also three ‘stop’ codons that do not code for any amino acids and signal the end of the sequence.
