Topic 8- Gene Expression Flashcards
What are the 4 types of DNA mutations?
- Deletion/ insertion: where one or more nucleotide pairs are inserted or deleted from the sequence.
Causes frame shift. - Duplication: One or more bases are repeated.
Causes frame shift. - Inversion: A group of bases is separated from the DNA sequence and then rejoins at at the same position but in reverse order.
- Translocation: A group of bases is separated for the DNA sequence on one chromosome and are inserted into the DNA sequence on another chromosome.
Explain how a single base substitution causes a change in the structure of a polypeptide.
Don’t include transcription or translation.
(3 marks)
1) Change in sequence of amino acids/ of primary structure.
2) Change in hydrogen bonds.
3) Alters tertiary structure.
Describe how alterations to the tumour suppressor gene can lead to the development of tumours.
(3 marks)
1) increased methylation of tumour suppressor genes.
2) Mutation in tumour suppressor gene.
3) Tumour suppressor genes are not transcribed/ expressed.
OR Amino acid sequence is altered.
What is restriction endonuclease? (in vivo)
Enzymes that are used to cut out the DNA fragment of interest.
Usually at staggered points to create sticky ends.
What modifications are made to the DNA fragments to ensure transcription? (In vivo)
A promotor region- added to start of fragment, this sequence of DNA is the binding site for RNA polymerase and allows transcription to occur.
A terminator region- added to the end of fragment, this causes RNA polymerase to detach and stop transcription, so only one gene is copied onto mRNA at a time.
What ensures multiple genes are not copied onto an mRNA molecule at the same time? (In vivo)
A terminator region causes RNA polymerase to detach and stop transcription.
What is a vector?
Something to carry the isolated DNA fragment into the host cell.
How do DNA fragments attach to the plasmids? (In vivo)
The plasmid is cut open using the same restriction endonuclease as the DNA, creating the same sticky ends. Therefore, the DNA fragment sticky ends are complementary to the plasmid sticky ends.
Explain hoe the DNA and plasmid are stuck together? (In vivo)
The enzyme ligase sticks them together and ligase analyses the condensation reaction to form phosphdiester bonds between nucleotides.
How is the plasmid with the recombinant DNA inserted into the host cell? (In vivo)
To increase the permeability of the cell membrane of the host cell, the host cells are mixed wit calcium ions and heat shocked.
What equipment is needed for PCR?
(In vitro)
A thermocyler
DNA fragment to amplify
DNA (taq) polymerase
Primers
DNA nucleotides.
What is the PCR method?
(In vitro)
1) Temperature increases to 95, breaking hydrogen bonds and splitting the DNA into single strands.
2) Temperature is decreased to 55 so that primers can attach.
3) Temperature is increased to 72 (taq DNA polymerase optimum), DNA polymerase attaches to complementary free nucleotides and makes a new strand to align next to template.
Advantages of PCR.
-Efficient as it is automated.
-Rapid
-Doesn’t require living cells
What is epigenetic?
Environmental changes in gene function without changing the DNA sequence.
What is an epigenome?
A single layer of chemical tags on the DNA, this impact the shape of the DNA-histone complex. (wether tightly wound or not)
What is the effect of increased methylation of DNA?
Increased methylation inhibits transcription.
Methyl groups bind to cytosine bases.
This prevent transcription factors from binding and attracting proteins that condense the DNA-histone complex.
What is the effect of decreased acetylation o associated histones?
Inhibits transcription.
If acetyl groups are removed from the DNA, the histones become more positive and are attracted more to the phosphate group on DNA, making DNA and histones more strongly associated and making it harder for transcription factors to bind.
Explain what would happen if there was a mutation of the tumour suppressor gene.
The tumour suppressor gene would not produce the proteins to control cell division, and mutated cells would not be identified and destroyed.
What would the result of hypermethylation of a tumour suppressor gene be?
Increased number of methyl groups attach to TSG, resulting in the gene being inactivated and becoming turned off.
What would be the result of Hypomethylation of oncogenes?
Reduced number of methyl groups attached to the oncogenes, this results in the gene being permanently switched off.
Outline how additional transcription factors can cause a cell to become specialised.
(4 marks)
1) Transcription factors bind to promotor region of DNA.
2) Block RNA polymerase AND
3)prevent genes from being transcribed.
4) Allows binding of RNA polymerase AND
5) Enables genes to be transcribed.
6) Proteins produced in cell cause cell to become specialised.
What is a DNA probe
(2 marks)
1) single short strand of DNA
2) bases are complementary
Suggest why the virus genetic material needs to undergo reverse transcriptase before it can be tested in PCR.
(1 mark)
PCR amplifies DNA, viruses have RNA.
State the type of bond formed by the catalytic action of Taq polymerase.
(1 marks)
Phosphodiester bond
