Structure & Replication of DNA Flashcards
What does DNA consist of
Two strands of nucleotides twisted into a double helix
What do DNA nucleotides contain
Deoxyribose sugar, phosphate and a base (Adenine, Thymine, Cytosine or Guanine)
Deoxyribose has a base attached to
It’s carbon 1, and a phosphate attached to its carbon 5 (this forms the 5’ end)
What is the DNA sugar-phosphate backbone held together by
Strong chemical bonds
The 2 DNA strands are antiparallel
With deoxyribose sugar and phosphate at 3’ and 5’ ends of each strand
Adenine pairs with
Thymine
Cytosine pairs with
Guanine
What is the genetic code formed by
The base sequence of DNA (the order of bases)
What do chromosomes consist of
Tightly coiled DNA packaged around bundles of protein
What must happen before a cell divides
The DNA must be replicated
DNA is replicated by
The enzyme DNA polymerase
Replication of the DNA template strand with the 3’ end is
Continuous and forms the “leading strand”
DNA chain of nucleotides can only grow by
Adding nucleotides to its 3’ end
What does DNA polymerase bring about the formation of
The sugar–phosphate bonds between individual nucleotides
What does the enzyme ligase do
Joins fragments of DNA together to form the “lagging strand”
Requirements for DNA replication:
DNA, primers, enzymes, DNA nucleotides and ATP
What end of the DNA strand is the deoxyribose on
The 3’ prime end
The phosphate is on the 5’ end
What is a DNA primer made of
A short sequence of nucleotides which binds to the 3’ end of the template DNA strand
Replication of the lagging strand is
Discontinuous as this strand starts with the 5‘ end
What happens during the first stage of DNA replication
The DNA double helix unwinds and the weak hydrogen bonds between bases break
Why are primers required
To create an existing chain for DNA polymerase to add DNA nucleotides to
What is polymerase chain reaction (PCR)
A technique used to create many copies of a piece of DNA
What does PCR use
Complimentary primers for specific target sequences to “amplify” the DNA
Firstly DNA is heated
To between 92 and 98°C to separate the DNA strands
Next the DNA is cooled
To between 50 and 65°C allowing primers to bind to target sequences
Finally DNA is heated
To between 70 and 80°C for heat-tolerant DNA polymerase to replicate the region of DNA
What does the PCR technique help
Solve crimes, settle paternity disputes and diagnose genetic disorders
