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Biology IB HL - 7.1 DNA Structure Part 3

Biology25 CardsCreated about 1 month ago

This deck covers key concepts related to DNA structure, the role of DNA polymerase, and the process of DNA sequencing, including the Sanger method and the characteristics of non-coding DNA.

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In what form do free nucleotides exist in?

Free nucleotides exist as deoxynucleoside triphosphates (dNTPs) – they have 3 phosphate groups
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Key Terms

Term
Definition
In what form do free nucleotides exist in?
Free nucleotides exist as deoxynucleoside triphosphates (dNTPs) – they have 3 phosphate groups
How does DNA polymerase create the chain?
DNA polymerase cleaves the two additional phosphates and uses the energy released to form a phosphodiester bond with the 3’ end of a nucleotide chain
Why does DNA polymerase move in different directions?
Because double-stranded DNA is antiparallel, DNA polymerase must move in opposite directions on the two strands
In what direction does DNA polymerase move on the leading strand?
On the leading strand, DNA polymerase is moving towards the replication fork and so can copy continuously
In what direction does DNA polymerase move on the lagging strand?
On the lagging strand, DNA polymerase is moving away from the replication fork, meaning copying is discontinuous
Why is the lagging strand discontinuous?
As DNA polymerase is moving away from helicase, it must constantly return to copy newly separated stretches of DNA
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Biology IB HL - 7.1 DNA Structure Part 3
TermDefinition
In what form do free nucleotides exist in?
Free nucleotides exist as deoxynucleoside triphosphates (dNTPs) – they have 3 phosphate groups
How does DNA polymerase create the chain?
DNA polymerase cleaves the two additional phosphates and uses the energy released to form a phosphodiester bond with the 3’ end of a nucleotide chain
Why does DNA polymerase move in different directions?
Because double-stranded DNA is antiparallel, DNA polymerase must move in opposite directions on the two strands
In what direction does DNA polymerase move on the leading strand?
On the leading strand, DNA polymerase is moving towards the replication fork and so can copy continuously
In what direction does DNA polymerase move on the lagging strand?
On the lagging strand, DNA polymerase is moving away from the replication fork, meaning copying is discontinuous
Why is the lagging strand discontinuous?
As DNA polymerase is moving away from helicase, it must constantly return to copy newly separated stretches of DNA
What is the lagging strand built up in?
This means the lagging strand is copied as a series of short fragments (Okazaki fragments), each preceded by a primer
What must be done before the Okazaki fragments can be joined?
The primers are replaced with DNA bases and the fragments joined together by a combination of DNA pol I and DNA ligase
What is DNA sequencing?
DNA sequencing refers to the process by which the base order of a nucleotide sequence is elucidated
What is the most widely used method for DNA sequencing?
The most widely used method for DNA sequencing involves the use of chain-terminating dideoxynucleotides
How are dideoxynucleotides unique?
Dideoxynucleotides (ddNTPs) lack the 3’-hydroxyl group necessary for forming a phosphodiester bond (structure)
How do dideoxynucleotides affect the DNA chain?
Consequently, ddNTPs prevent further elongation of a nucleotide chain and effectively terminate replication
What is the point of using dideoxynucleotides?
The resulting length of a DNA sequence will reflect the specific nucleotide position at which the ddNTP was incorporated
What method is used to determine the DNA sequence using dideoxynucleotides?
Dideoxynucleotides can be used to determine DNA sequence using the Sanger method
What is set up? Sanger method 1
Four PCR mixes are set up, each containing stocks of normal nucleotides plus one dideoxynucleotide (ddA, ddT, ddC or ddG)
Why are PSR mixes used? sanger method
As a typical PCR will generate over 1 billion DNA molecules, each PCR mix should generate all the possible terminating fragments for that particular base
How are the fragments separated? Sanger method
When the fragments are separated using gel electrophoresis, the base sequence can be determined by ordering fragments according to length
What can be done to the fragments to make detection easier?
If a distinct radioactive or fluorescently labelled primer is included in each mix, the fragments can be detected by automated sequencing machines
What will happen if the Sanger method is conducted on the coding strand?
If the Sanger method is conducted on the coding strand (non-template strand), the resulting sequence elucidated will be identical to the template strand
What is the vast majority of the human genome composed of?
The vast majority of the human genome is comprised of non-coding DNA (genes only account for ~ 1.5% of the total sequence)
What are the 5 types of noncoding DNA?
satellite DNA; Telomeres; Introns; Non-coding RNA genes; Gene regulatory sequences; STING
What are 3 characteristics of satellite DNA?
tandemly repeating sequences of DNA structural component of heterochromatin and centromeres commonly used for DNA Profiling
What are 2 characteristics of telomeres?
role and structure regions of repetitive DNA at the end of a chromosome Protects against chromosomal deterioration during replication
What are 2 characteristics of introns?
role and structure non-coding sequences within genes are removed by RNA splicing prior to the formation of mRNA
What are 2 characteristics of non-coding RNA Genes?
role and structure codes for RNA molecules that are not translated into protein e.g genes for tRNA