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.
Give some examples of practical applications of PCR
PCR has many different practical applications including:
- solving crimes
- settling a paternity suit
- diagnosing genetic disorders.
a) What does a DNA polymerase do
b) How does it do this
a) DNA polymerase adds DNA nucleotides,
b) using complementary base pairing, to the
deoxyribose (3’) end of the new DNA strand
which is forming.
What is DNA replicated with?
DNA is replicated by a DNA polymerase.
What does DNA polymerase need to start replicaton
DNA polymerase needs primers to start replication.
a) what is a primer?
b) what does it do?
a) A primer is a short strand of nucleotides
b) which binds to the 3’ end of the template DNA strand allowing polymerase to add DNA nucleotides
Describe DNA Replication
- DNA is unwound and
- hydrogen bonds between bases are broken to form two template strands.
- DNA polymerase can only add DNA nucleotides in one direction
- resulting in the leading strand being replicated continuously and the lagging strand replicated in fragments.
How are the fragments joined together?
Fragments of DNA are joined together by
ligase.
What does the base sequence of DNA form?
The base sequence of DNA forms the
genetic code.
What are primers in PCR?
The primers are short stands of nucleotides which are complementary to specific target sequences at the two ends of the region of DNA to be amplified
