1.2 Structure and replication of DNA Flashcards
Describe the structure of a DNA molecule.
DNA is a large double stranded helix made up of repeated units called nucleotides
Name the four nucleotide bases
Adenine
Thymine
Cytosine
Guanine
What are nucleotides
Nucleotides in a chain are joined together by sugar phosphate bonds to make long chains of nucleotides called polynucleotides
How are sugar phosphate backbones made
A strong chemical bond forms between the phosphate group of one nucleotide and the carbon 3 of the deoxyribose sugar on another one. neighbouring nucleotides become joined together ina long permanent strand in which sugar molecules alternate with phosphate groups forming the DNAs strong sugar phosphate back bone
Explain the terms of anti parallel in terms of DNA
The arrangement of the two strands with there sugar phosphate backbones running in opposite directions. The double helix is described as having two anti-parallel chains of nucleotides
Identify and describe the 3 prime and 5 prime ends in a DNA double stranded molecule
Primer is added to the 3 end of DNA
Strand A is lagging and B is leading
Stage one of DNA replication
Double stranded helix unwinds
Stage two of DNA replication
Hydrogen bonds between nucleotide bases break seperating the strands
Stage three of DNA replication
A primer attaches to each template strands
Stage four of DNA replication
DNA polymerase adds free complementary nucleotides to the 3 end of a growing dna strand
Stage five of DNA replication
Hydrogen bonds form between bases
Stage six of DNA replication
Strong bonds form between sugars and phosphates creating strong sugar phosphate backbones.
When does DNA replication within a cell take place
DNA replicates prior to cell division (mitosis) and identical copies of DNA are passes to daughter cells
Identify and explain the roles of the key essential substances required for DNA replication
DNA molecule -
Primers
Nucleotides
Enzymes (ligase, polymerase)
ATP
Why is ligase needed in dna replication
In DNA replication, ligase joins together fragments of newly synthesized DNA to form a seamless strand1.
Why is a DNA molecule needed in DNA replication
To act as a template for a new DNA molecule to be made
Why are primers needed in DNA replication
DNA polymerases can only attach new DNA nucleotides to an existing strand of nucleotides
Why is polymerase needed in DNA replication
it creates new DNA strands by adding nucleotides that are complementary to the template strand
State the purpose of the polymerase chain reaction
PCR is a labotory technique for the amplification of DNA. This is a technique that can be used to create many copies of a piece of DNA in vitro (outside the body) Scientests use PCR machines to amplify DNA outside an organism
State the role of primers in PCR
PCR amplifies DNA using complimentary primers for specific target sequences.
What is a primer?
A primer is a single stranded piece of dna complementary to a specific target sequence at the 3 end of the DNA strand to be replicated
State the role of enzymes in pcr
The polymerase is called taq polymerase which is heat tolerant and replicates the region of DNA
Stage one of PCR
DNA is heated to 90 degrees. This denatures DNA which breaks the hydrogen bonds separating the bases.
Stage two of PCR
Cool to 50 degrees. Primers are added which anneals (binds) to specific target sequences of DNA
Stage three of PCR
Heat to 70 degrees. Taq polymerase adds free DNA nucleotides to complamentery DNA nucleotides
Give examples of the practical applications of PCR
-Forensics in solving crime
- Settle paternity disputes
- Diagnose genetic disorders
