Topic 7 - Modern Genetics Flashcards
(27 cards)
What is the Genome?
The genome is the total of all the genetic material in an organism.
What are Exons?
Exons are the segments of DNA which contain information for the synthesis of proteins/peptide chains.
What are Introns?
Introns are the segments of DNA which do not code for proteins/peptide chains.
What does PCR stand for?
Polymerase Chain Reaction.
How is PCR used in DNA profiling?
- PCR can Amplify small traces of DNA to create a large enough sample.
- (DNA profiling requires at least 1 microgram of DNA)
What was the initial problem for scientists when trying to develop a way to replicate (amplify) DNA?
- DNA samples need to be heated to 90-95 ℃ to separate the strands (to make them available for replication).
- This temperature would destroy DNA polymerase from most organisms
What is needed for a PCR?
- DNA sample (to be amplified)
- Taq DNA Polymerase
- Primers
- Supply of the 4 nucleotide bases
- Buffer
- PCR machine
What are the three steps in a Polymerase Chain Reaction (PCR) ?
Step 1 - Heat a mixture of the DNA sample, Taq polymerase, buffer, free DNA nucleotides and finally primers at 90-95 ℃ for 30 seconds.
Step 2 - Cool the mixture to 50-55 ℃ for 20 seconds to let the primers bind to the DNA strands.
Step 3 - Heat the mixture again to 72℃ for at least a minute to let the Taq DNA polymerase build up complementary strands of DNA.
What are each of the three steps in PCR called?
Step 1 - Separating the DNA strands
Step 2 - Annealing
Step 3 - Elongation
What is the role of Primers in PCR?
- A pair of Primers will attach to each strand of DNA to mark the start points for the Taq DNA polymerase.
- In other words, primers highlight what section of the DNA is to be amplified.
What is the role of Taq DNA Polymerase in PCR?
- Like any other polymerase, Taq Polymerase is involved in attaching DNA Nucleotides together to synthesise a strand of DNA.
What is DNA sequencing?
DNA sequencing is the process of working out the order of bases in a strand of DNA.
What is a terminator base?
- (In DNA sequencing) A Terminator base is a modified version of one of the 4 nucleotide bases.
- Terminator bases act as the the stop point for any further synthesis of DNA.
How do Terminator Bases stop the further synthesis of DNA?
- Terminator Bases are modified so that they lack the -OH group (which is usually on Carbon 3 of the deoxyribose sugar).
- This results in the Terminator base being unable to bind with the phosphate group of another nucleotide and forming a phosphodiester bond.
- Therefore the strand of DNA stops extending.
What are satellites? (DNA Profiling)
Satellites are short sequences of DNA bases that are repeated many times throughout the genome.
What is the difference between Mini-satellites & Micro-satellites?
Mini-satellites have a longer base sequence (10-100 base pairs in a sequence) and are repeated more times throughout the genome.
Micro-satellites have shorter base sequences (2-6 base pairs in a sequence) and are repeated much less throughout the genome.
What are VNTRs in DNA?
- Variable Number Tandem Repeats (VNTRs)
- Refers to the number of repeating sequences (satellites) found in DNA which differ in each individual.
- Unless in the case of Identical Twins.
What are Restriction Endonucleases?
Restriction Endonucleases are a type of enzyme that cut up DNA at a specific sequence of bases called ‘Recognition Sites’.
What is a Recognition site?
- A recognition site is a specific sequence of nucleotides in DNA which a Restricition Endonuclease (enzyme) recognises & digests.
What do Specific Restriction Endonucleases do in DNA profiling?
- Specific Restriction Endonucleases are used to cut DNA in to fragments, whilst leaving VNTRs intact.
Since Restriction Endonucleases don’t digest VNTRs, how does this create a specific DNA profile for an individual?
- Since VNTRs differ in length in each individual & Restriction Endonucleases don’t digest them, each individual will have a DNA profile consisting of different sizes of DNA fragments.
What process separates the DNA Fragments based on size to create the DNA profile?
Gel Electrophoresis.
How does Gel Electrophoresis separate DNA strands in terms of size?
- DNA molecules contain negatively charged phosphate backbones.
- The Gel Electrophoresis apparatus consists of a positive electrode on one side of an Agarose gel medium (DNA is on the opposite side in wells)
- The DNA strands will be attracted to this positive charge and will move towards the positive electrode.
- Larger DNA strands move slower and shorter DNA strands move faster.
- Therefore at the end of a certain time period (usually 45 minutes) the strands will have a been separated based on size.
In Gel Electrophoresis, how do we make sure that the DNA strands don’t run off the end of the apparatus?
- A dye is added with the strands of DNA.
- This dye does not bind with the DNA but instead moves slightly faster than the DNA.
- Therefore when the dye reaches the end, we can stop the electric current in the apparatus to stop DNA strands running off the end.
