DNA structure and replication
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what is a nucleotide composed of
a sugar (e.g deoxyribose), a base and a phosphate
what are the four types of bases in DNA
• Thymine • Adenine • Guanine • Cytosine
which bases pair up with each other
• A and T • G and C
what type of bond forms between complementary bases
Hydrogen bond
which two components of a nucleotide for the backbone of DNA
the sugar and phosphate form the sugar phosphate backbone
why is DNA said to have an antiparallel structure
• one strand starts at the 3 end’ and ends at the 5’ end (starts with a deoxyribose sugar and ends with a phosphate) • the other strand starts at the 5’ end and ends at the 3’ end (starts with a phosphate and ends with a deoxyribose sugar)
what final shape does DNA form
Double helix
how many bases code for an amino acid
3 bases code for an amino acid
what is the purpose of DNA replication
to allow a cell to make an identical copy of its DNA
what must occur prior to mitosis to ensure the daughter cells have an identical copy of DNA
DNA replication
what are the requirements for DNA replication
• DNA • primers • Enzymes (DNA polymerase and ligase) • free nucleotides • ATP
what is a primer
A short strand of nucleotides that will bind to the 3’ end of the template DNA strand allowing DNA polymerase to add free nucleotides
what must occur to allow DNA replication to begin
DNA double helix must be unwound and unzipped
what enzyme adds free DNA nucleotides to the 3’ end of the primer during DNA replication
DNA polymerase
what are the two strands formed during DNA replication
• leading strand • lagging strand
in what direction does DNA polymerase add nucleotides
5’-3’ direction
what is the difference between the leading and lagging strand
• the leading strand is synthesised continuously • the lagging strand is synthesized in fragments
why is the lagging strand synthesized in fragments
nucleotides can only be added in a 5’-3’ direction
which enzymes joins together the fragments of the lagging strand
ligase
what is PCR
a technique used to amplify specific target DNA sequences
what are the practical applications of PCR
• provide DNA samples for criminal investigations • diagnosis of genetic conditions • proving the identity of a child’s father
what is needed to perform PCR
• DNA • complementary primers • a thermal cycler • HEAT TOLERANT DNA POLYMERASE • a supply of nucleotides
what Is the first stage of PCR
DNA is heated between 92 and 98 degrees to denature DNA and separate the two strands
what is stage two of PCR
DNA is cooled between 50 and 65 degrees to allow primers to bind to the target DNA sequences