REPLICTION OF DNA U1 Flashcards
State when DNA replication occurs and the role of DNA polymerase and primers
DNA replication occurs prior to cell division.
DNA polymerase is the enzyme that replicates DNA.
DNA polymerase requires a primer to start DNA replication.
A primer is a short strand of nucleotides which binds to the 3’ end of the template (parent/original) DNA strand. This allows DNA polymerase to add new nucleotides.
Give examples of other molecules required for DNA replication
DNA replication requires the use of ATP, free DNA nucleotides and other enzymes throughout the process.
Describe the process of DNA replication
The process of DNA replication can be summarised:
1- DNA is unwound and hydrogen bonds between bases are broken – forming two template strands.
2-Primer attaches to a short sequence on the DNA allowing the DNA polymerase to bind.
3-DNA polymerase will add nucleotides using the complementary base pairing rule to the deoxyribose (3’) end of the NEW strand which is forming.
Describe the replication of the leading strand of DNA formed during DNA replication
DNA polymerase works in a 5’ to 3’ direction. DNA polymerase can only add nucleotides to the 3’end of the growing strand. This means that one strand is replicated continuously, and we call this the leading strand.
Describe the replication of the lagging strand formed during DNA replication
Due to the antiparallel structure of DNA the fact that DNA polymerase can only add nucleotides onto the 3’end, the opposite strand has to be replicated in fragments. This is known as the lagging strand. This requires the use of many primers and the fragments produced are joined together by the enzyme ligase.
State the function of the polymerase chain reaction (PCR) and describe the function of the primers used
The polymerase chain reaction amplifies DNA using complementary primers for specific target sequences.
Primers are short strands of nucleotides which are complementary to specific target sequences at the two ends of the region of DNA to be amplified. The DNA to be amplified will be your sample DNA.
Describe the processes of the polymerase chain reaction
State the stages
The polymerase chain reaction consists of repeated cycles of heating and cooling to amplify the target DNA. Here are the stages:
DNA is heated between 92°C and 98°C to break the hydrogen bonds between bases and separate the two strands.
The DNA is then cooled to between 50°C and 65°C to allow primers to bind to target sequences.
It is then heated to between 70°C and 80°C for heat tolerant DNA polymerase (Taq polymerase) to replicate the region of DNA.
This would be just one cycle, so a single sample of one DNA molecule is amplified into two. This cycle is repeated 20-30 times, yielding millions of copies of the original sample of DNA.
Describe the practical applications (uses) of the polymerase chain reaction
The practical applications of PCR are to amplify DNA to help solve crimes, settle paternity suits and diagnose genetic disorders. There are many others too.
