DNA Replication Flashcards
Why is DNA replication needed
As every time that a cell undergoes cell division, all of its DNA is copied.
What is DNA replication
The process by which DNA is copied
What happens when parent cells prepare to divide
The two strands of DNA’s double helix separate and each strand serves as a template for the creation of a new double stranded DNA molecule.
What ensures that the two new strands are identical to the original
Complementary base pairing
What is the first enzyme that is involved in DNA replication
DNA helicase attaches to the DNA molecule.
What does DNA helicase do
It causes the hydrogen bonds between complementary bases to break. This results in the two polynucleotide strands separating from each other.
What happens after the two strands of DNA separate
Free nucleotides then line up with the complementary bases on the DNA strands.
What are the free nucleotides held together by at this stage
They are held together by hydrogen bonds between complementary bases. They aren’t bonded to each other by phosphodiester bonds.
What type of nucleotides are the free nucleotides and how are they different from normal nucleotides.
They are activated nucleotides. Which contain three phosphate groups whereas a normal nucleotide only contains one phosphate group.
What is the second enzyme involved in DNA replication
DNA polymerase
What does the second enzyme do
It moves down the molecule and catalyses the formation of a phosphodiester bond between activated nucleotides.
What happens to the activated nucleotides when the phosphodiester bonds form
The activated nucleotides lose two of their phosphate groups whereas
What do the two phosphate groups that are lost provide
They provide energy for the reaction when they leave
After DNA polymerase has finished working on the DNA molecule what happens
We have two copies of the double stranded DNA molecule.
What does each new strand of DNA have
It has one strand from the original DNA molecule and one strand which is new.
What type of replication is this
Semi conservative DNA replication
What happens when incorrect bases are inserted into the polynucleotide
The DNA sequence is changed which is called a mutation.
What is a feature of mutations
They are random and occur spontaneously
Where the instructions that DNA contains found
They are contained in the sequence of bases along the chain of the polynucleotide that makes up the 2 strands of DNA.
What type of code is the base sequence and what is it called
It is a triplet code, where a sequence of 3 bases is called a codon.
What does each codon code for
It codes for an amino acid
What is a gene
A section of DNA that contains the complete sequence of bases to code for an entire protein
What is a feature of the genetic code
It is universal meaning all organisms use the same code
How many different codons are possible
As there are 4 different bases it means that there are 64 different codons possible.
How many different start and stop codons are present and what do they do
There is one start codon that codes for protein synthesis at the beginning of a gene and 3 stop codons at the end of a gene that signals the end of the sequence.
If a start codon is present in the middle of a gene what happens
It codes for the amino acid methionine
How many naturally occurring amino acids are present
They are only 20 naturally occurring amino acids
What does the number of naturally occurring amino acids mean
That an amino acid can be coded for by one or more codon.
