DNA and its replication Flashcards
What is DNA
-Deoxyribonucleic acid
-It is the molecule of inheritence and it can direct its own replication.
-DNA forms the genetic code in its sequence of bases, this sequence of bases determines the organisms genotype and the structure of its proteins.
Describe the structure of DNA
DNA is made of repeating units called DNA nucleotides.
These are made of a phosphate (attached to carbon 5), a deoxyribose sugar and a base (attached to carbon 1)
Deoxyribose has 5 carbons.
How many different DNA nucleotides are there and how do they arrange themselvesand how are they joined ?
4, as there are four bases; Adenine, Thymine, Cytosine and Guanine.
These bases arrange themselves in a complementary configuration along the length of DNA, and are joined by weak hydrogen bonds.
How are DNA nucleotides connected.
-A stromg covalent bond forms between the phosphate ( carbon 5) of one nucleotide and the deoxyribose sugar on another nucleotide.
-These nucleotides join together in a long permanent strand, called the DNA molecules sugar-phosphate backbone.
-DNA takes the shape of a double-helix
What is anti parallel
-The two strands of DNA run anti-parallel to each other, they run in opposite directions.
- The 3’ end is an open deoxyribose sugar, the 5’ end is an open phosphate, it goes from 3’ to 5’
What is DNA polymerase
-Prior to cell division DNA has to be replicated by an enzyme called DNA polymerase.
-DNA polymerase is the enzyme that adds DNA nucletoides, using complimentary base pairings, to the deoxyribose (3’) end of the new DNA strand which is forming.
-DNA polymerase needs primers to start replication.
((3’) end of the primer, across from the 3’ end of the template strand)
What are primers
-A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing DNA polymerase to add DNA nucleotides
Describe the leading and lagging strand.
-Since DNA polymerase can only add nucleotides in one direction (5’ - 3’ on newly produced strand), the two strands replicate slighlt differently.
-The leading strand (3’-5’ on template strand, from bottom of replcation fork), replicates continuously.
-The lagging strand (5’ - 3’ on template strand, from bottom of replication fork), replicates in fragments.
Describe the stages of DNA replication of the leading strand.
1) The DNA helix unwinds.
2) Hydrogen bonds between complimentary base pairs unzip, allowing the two strands to separate. This forms a replication fork with two template strands.
3) A primer attaches to the 3’ end of each DNA template strand to start replication.
4) DNA polymerase adds complementary DNA nucleotides to the 3’ end of the new growing strand, while the lagging strand is replicated in fragments.
The replication of the leading and lagging strand occurs simultaneously to ensure the replication of thr full DNA molecule is complete at the same time.
Describe the stages of DNA replication in the lagging strand
1) The DNA helix unwinds.
2) Hydrogen bonds between complimentary base pairs unzip, allowing the two strands to separate. This forms a replication fork with two template strands.
3) A primer attaches to the 3’ end of each DNA template strand to start replication.
4) DNA polymerase adds complementary DNA nucleotides to the 3’ end of the new growing strand. Lagging strand (5’-3’) is replicated in fragments.
5) Fragments of the laggings strands are joined together using the enzyme ligase.
The replication of the leading and lagging strand occurs simultaneously to ensure the replication of thr full DNA molecule is complete at the same time.
What are the 6 requirments for DNA replication
1) Original DNA template
2) Primers (short sequence of nucleotides)
3) Supply of DNA nucleotides
4) Ligase Enzyme
5) Energy (ATP)
6) DNA Polymerase enzyme
What is PCR
-Polymerase chain reaction
-PCR amplifies DNA using complementary primers for specific target sequences, this occurs in vitro/outisde the body of an organism.
-It is done to get more DNA from a limited source to analyse.
Describe primers in PCR
-In PCR primers are short strands of nucleotides which are complmentary to specific target sequences at the two ends of the region of DNA to be amplified
What is thermal cycling
-PCR is repeated cycles of heating and cooling (thermal cycling) to amplify a target region of DNA
-Thermal cycling is repeated about 25-30 cycles, the quantity of DNA doubles after every cycle
What are the stages of PCR
1) DNA is heated to between 92-98°C to break the hydrogen bonds between complimentary bases, allowing the two strands to seperate.
2) DNA is cooled to between 50-65 °C which allows primers to bind to specific target sequences on the 3’ end of the template strands, at both ends of the target region of DNA to be amplified
3) DNA is heated to between 70-80°C, allowd heat-tolerant DNA polymerase to replicate the target region of DNA. optimal conditions: 72°C
