3.8 The control of gene expression Flashcards
Addition mutation
When a nucleotide is added to a segment of DNA
Results in frame shift
Deletion mutation
When a nucleotide is removed to a segment of DNA
Results in frame shift
Substitution mutation
When a nucleotide is switched out for a different nucleotide in a segment of DNA
Doesn’t result in frame shift
Inversion mutation
When multiple nucleotides are reversed in order
Doesn’t result in frameshift
Duplication mutation
When multiple nucleotides are duplicated within the DNA segment
Can result in frame shift
Translocation mutation
When nucleotides are transferred to another part of the DNA sequence
Can result in frame shift
What can increase number of mutations
Mutagenic agents
What is a mutation
Changes to a base sequence in DNA
How can a mutation result in a different/dysfunctional protein
- Change in base sequence
- Change in primary structure
- Different hydrogen bonding in secondary structure as different binding sites
- Different binding in tertiary structure by H bonds/disulfide bridges/ionic bonds
- Different/dysfunctional protein
Properties of DNA
Non-overlapping - each base only read once and is part of only one triplet
Degenerate - Multiple triplets code for the same amino acid
Universal - All organisms share same 4 nucleotides (A,T,C,G)
Stem cell definition
A cell that can divide by mitosis an unlimited number of times and can become differentiated
Totipotent cells
Stem cells that can differentiate into any body cell + embryonic cells. Found in mammalian embryo
Pluripotent cells
Stem cells that can differentiate into any body cell. Found in mammalian embryo
Multipotent cells
Stem cells that can differentiate into multiple different cells. e.g Found in bone marrow
Unipotent cells
Stem cells that can differentiate into only one type of cell. e.g. cardiomyocytes
How are Induced pluripotent stem cells produced
From adult somatic cells, using an appropriate transcription factor
How do cells specialise
Only certain parts of the DNA is translated.
Controlled by transcription factors
Oestrogen
- Lipid soluble so diffuses through phospholipid bilayer
- Binds to receptors on transcription factor in cytoplasm
- Causes DNA binding site on TF to be altered
- TF enters nucleus
- TF binds to promoter region of DNA - activating transciption
What is DNA amplification
When a fragment of DNA is replicated
PCR steps
- Requires DNA fragment, primers and nucleotide
- Heat to 95 degrees to break hydrogen bonds
- Reduce temperature so primers bind to DNA
- Increase temp, DNA polymerase joins nucleotides
- Repeat
Epigenetics definition
involves heritable changes in gene function, without changes to the base sequence of DNA
Two epigenetic changes
- Increased methylation - supresses gene transcription, prevents binding of TF’s
- Decreased acetylation - increases positive charge of histone, so they bind more tightly to the DNA, TF’s can no longer access DNA
How does RNAi inhibit translation of mRNA
- Complimentary to mRNA base sequence
- Bind to mRNA
- Break it down
- Prevent its translation
Cancer definition
Uncontrolled cell division
Role of tumour suppressor genes
Slow down/regulate cell division
Role of protooncogenes
Produces proteins that stimulate cell division
Cause apoptosis
How can increased oestrogen concentration cause cancer
More TF’s bind to DNA
More transcription
More cell division - uncontrollable
How do oncogenes cause cancer
Abnormal methylation
Protooncogenes become hyperactivated
Cause uncontrolled cell division
No programmed cell death (apoptosis)
How do mutated tumour suppressor genes cause cancer
Abnormal methylation
Tumour suppressor genes not translated
Cell division not regulated
Uncontrollable cell division
Applications of genome projects
Identification of antigens for vaccines
Human genome project
Identifying genetic diseases
Tracing ancestry
Why is it harder to translate the genome of more complex organisms into the proteome
Non-coding DNA
Regulatory genes
What is recombinant DNA technology
Involves the transfer or DNA from one organism/species to another. This can be translated as DNA is universal
3 methods of producing DNA fragments
- Reverse transcriptase
- Restriction enzymes
- Gene machine
What does in vitro mean
In glass
What does in vivo mean
In life
Role of reverse transcriptase in producing DNA fragment
- Extract desired mRNA from virus/bacteria
- Reverse transcriptase catalyses the production of DNA to mRNA
Role of restriction endonucleases in producing DNA fragment
Restriction endonucleases cut gene from DNA
Same enzyme cuts host DNA
Ligase joins sticky ends together
In vitro
- Isolation - 3 methods
- Insertion
- Transformation -
- Identification
- Growth/cloning
Gene machine
- Protein amino acid sequence
- mRNA codons
- DNA triplet code
- Computer produces synthetic gene
Insertion (step 2)
- Add a promoter region and a terminator region
- So that RNA polymerase/TF can attach and transcribe base sequence
- Insertion of DNA fragment into a vector
- Vector transports DNA fragment to host cell
Transformation (step 3)
Transforming the bacteria by introducing the recombinant plasmid
Identification (step 4)
Fluorescent die
Radioactive marker
Growth/cloning (step 5)
Allow bacteria to divide
What is a DNA probe
Single stranded section of DNA that has complimentary base pairing with target gene
Why are DNA probes made in same amounts
They can be amplified using PCR
Uses of DNA probes
Indicate where harmful alleles are by using a radioactive material of fluorescent dye
Prevent genetic diseases
Screen patients for heritable conditions, drug responses or health risks.
Gel electrophoresis
The negatively charged DNA fragments move through the pores in the gel, towards the positively charged electrode
Smaller DNA fragments are able to move at a faster rate through the pores and so they travel a further distance
The fragments separate according to size and charge, producing bands in the gel
What are VNTRs
Variable Number Tandem Repeats. Short sequence of nucleotides repeated a variable number of times. The probability of two people having the same VNTRs is very low.
Recombinant DNA definition
DNA that has been formed artificially
USes of genetic fingerprinting
Forensics
Medical diagnosis
Animal/plant breeding
The scientists used a radioactively labelled DNA probe to show that the cells of tobacco plant leaves contained the SUT1 gene.
Describe how they would do this.
Do not include PCR in your answer.
- Extract DNA and add restriction endonucleases/restriction enzymes;
- Separate fragments using electrophoresis;
- (Treat DNA to) form single strands
- The probe will bind to/hybridise/base pair with the SUT1/gene;
- Use autoradiography (to show the bound probe);
Why is DNA treated to form single strands for testing
So that the DNA probe can bind
What is meant by a non-coding base sequence?
Does not code for amino acid/tRNA/rRNA
Explain the role of reverse transcriptase in RT-PCR.
Produces DNA using RNA
Why is the gene machine used over enzyme catalysed reactions
It is much faster
Suggest and explain how the viruses became able to infect other species of frog.
- Mutation in the viral DNA
- Altered (tertiary structure of the) viral attachment protein
- Allows virus to bind to receptors of other species
