Unit 1 - Structure and Replication of DNA Key Area 2 Flashcards
Key Area 2
What is DNA made up of?
DNA is made up of two strands each composed of repeating units called nucleotides
What is a DNA nucleotide made up of?
Nucleotides are made of deoxyribose sugar, phosphate and 1 of the four bases (ATGC)
In a DNA nucleotide what is attached to
a) Carbon 1-
b) Carbon 5-
The deoxyribose sugar in a nucleotide has a base attached to its carbon 1, and a phosphate attached to its carbon 5
Describe the sugar phosphate backbone of DNA
DNA has a sugar-phosphate backbone due to the strong chemical bonds forming between the phosphate of one nucleotide and the carbon 3 of the deoxyribose on another nucleotide
State the 4 DNA bases, and their complementary pair
Adenine - Thymine
Cytosine - Guanine
How are the 2 DNA strands joined together?
Hydrogen Bonding
Why is DNA described as antiparallel?
One end of a DNA strand has a phosphate attached at carbon 5, this is known as the 5’ end.
The other end has a deoxyribose sugar, this is known as the 3’ end.
The other DNA strand runs in the opposite direction forming a double helix.
This arrangement is described as being antiparallel.
What are the requirements for DNA replication?
Requirements for DNA replication:
- DNA template = the original strand
- DNA nucleotides
- Primers = short stands of nucleotides
- Enzymes
- DNA polymerase
- Ligase
Why does DNA need to be replicated?
DNA needs to replicate in order for cell division to take place. Remember cell division is required for growth, repair of damaged tissues and replacement of dead or damaged cells
State the stages involved in DNA Replication (1-5)
1) - DNA replication begins with the DNA molecule unwinding.
- Weak hydrogen bonds break between the two strands and the DNA separates(unzips) forming two template strands.
- This process exposes a y-shaped replication fork.
2) - The next stage of DNA replication requires a Primer.
- The short strand of DNA attaches to the 3’ end of the template DNA strand.
- This allows DNA polymerase to add DNA nucleotides to extend the strand.
3) - DNA polymerase is only able to add DNA nucleotides in the 5’ – 3’ direction
- This strand of DNA can be replicated continuously and is therefore called the leading strand.
- The second template strand of DNA is replicated in fragments and is called the lagging strand.
4) - A primer binds to different fragments and DNA polymerase adds nucleotides.
- An enzyme called ligase joins the fragments together.
What does PCR stand for?
Polymerase Chain Reaction (PCR)
What is PCR?
PCR is technique used to amplify DNA.
How does DNA find its target sequence?
PCR uses complementary primers for a specific target sequence.
How is DNA amplified?
Repeated cycles of heating and cooling
amplify the target region of DNA.
Describe the cycles of heating and cooling used to amplify DNA
- Repeated cycles of heating and cooling amplify this region of DNA.
- DNA is heated to between 92 and 98°C to
separate the strands. - It is then cooled to between 50 and 65°C to
allow primers to bind to target sequences. - It is then heated to between 70 and 80°C for
heat-tolerant DNA polymerase to replicate
the region of DNA.
