Unit 5: Mutations and Biotechnology Flashcards
Define
Mutation
Any change to DNA / genetic information
Two general categories of mutations
Small scale, or “point” mutations which affect one or a few nucleotides and only one gene
Large scale mutations, which affect overall chromosomal structures / arrangement, thereby affecting many genes
Two types of small scale mutations
Substitutions
Insertions / Deletions
Define and list the types of
Substitution Mutations
A change of a nucleotide for another
Types:
* Missense
* Nonsense
* Silent
Describe
Silent mutation
Change of a nucleotide that results in the same amino acid as in the original
Happens because of the redundancy of the genetic code - multiple codons can code for the same amino acid (see “wobble”)
The protein that forms is identical to the non-mutated but there may be slight differences in the expression of genes after a silent mutation
Describe
Missense mutation
Change of a nucleotide that results in the change of an amino acid
Effects can vary based on the properties of the amino acid (size, polarity) and what part of the protein is affected (ex: active site of an enzyme)
Can be harmful or have minimal effect. Can even be beneficial (rarely)
Describe
Nonsense mutation
Change of a nucleotide that results in a stop codon instead of an amino acid
Severity depends on where in the sequence the mutation occurs
Less detrimental nearer to the end of a protein (generally) but will result in nonfunctional protein if it happens closer to the start of the protein
Describe
Frameshift mutations
The insertion or deletion of nucleotides that results in a change to the reading from of the gene
All downstream amino acids are changed
Severity depends on where in the sequence the mutation occurs
Less detrimental nearer to the end of a protein (generally) but will result in nonfunctional protein if it happens closer to the start of the protein
What is important about mutations?
They are the source of all genetic variation, which is the basis of evolution by natural selection
The mutations themselves happen randomly BUT beneficial variations are favored by natural selection
When do spontaneous mutations happen?
During DNA replication
(Reminder: DNA polymerases add new nucleotides AND help proofread the new DNA to ensure proper base pairing)
Incidence rate of around 0.000 000 000 1
What are the results of mutations?
In normal body cells, mutations occur each time cell divides
These accumulate and eventually can lead to cancer and other age-related outcomes
Mutations can only be passed on to new generations if the error happens in the cell that produces the sperm or egg cell that is fertilized
Define
Mutagen
Any physical or chemical agent that causes mutations
List examples of
Mutagens
Radiation (such as UV, Xray, or nuclear radiation)
Chemical agents, which are often carcinogenic
Define
Genetic engineering
Alteration of genes for practical purposes
List some uses of genetic engineering
Medicine / health
Research
Criminal law
Agriculture
What is the basis for all genetic engineering?
Complementary base pairing
Understanding how bases pair together and how to break up stretches of DNA allows scientists to take DNA from different sources and join it together
Define
DNA cloning
The production of multiple copies of a specific DNA segment
What are two ways of cloning DNA?
Using plasmids to make recombinant bacteria, which copy the DNA each time it reproduces
PCR
Why is DNA cloning important?
Isolates just the gene / segment of DNA that is important
Makes a lot of copies so that it can be studied / manipulated more easily
Define
Restriction Enzyme
Restriction endonuclease
Enzyme that cuts DNA at specific location (based on sequence)
Found naturally in bacteria as a type of defense
Used in genetic engineering by acting as “molecular scissors”
Where do restriction enzymes work?
At specific restriction sites
These are usually palindromic / have the same sequence when read 5 -> 3 on either strand
Ex: 5’-GGATCC-3’, whose opposite strand is 3’-CCTAGG-5’
The restriction enzyme then cuts it to either make blunt or sticky ends
Define
Sticky End
A piece of DNA that was cut by a restriction enzyme in a way that left some of the nucleotides unpaired
This can allow for the joining of DNA from different sources
Summarize the process of making recombinant bacterial cultures
- Identify the gene of interest (GOI)
- Find a restriction site outside of the GOI
- Find a plasmid that has the same restriction sites
- Combine the GOI, plasmid, and restriction enzyme
- Use DNA ligase to rejoin the sticky ends
- Get bacteria to take up the plasmid
- Culture the bacteria
- Test bacteria to ensure it has taken up the GOI
Define
Competent
In reference to bacterial transformation
Competent bacteria are those able to take up plasmids from their environment
Usually requires causing some type of stress to the bacteria, such as by heat-shocking
What is gel electrophoresis?
A method of separating DNA fragments (usually cut into fragments by restriction enzymes) by size
Outline the process of gel electrophoresis
Solution containing DNA fragments are injected into wells within an agarose gel slab
A gel electrophoresis chamber applies a current through the gel, with a + electrode at one end
Small fragments of DNA are attracted to the + electrode and travel quickly through the agarose gel
Larger fragments are attracted to the + electrode but travel more slowly through the agarose
What is PCR?
Polymerase chain reaction
A method of amplifying a small quantity of DNA to make a huge number of copies
Describe the steps of PCR
DNA gene of interest, RNA primers, polymerase, and DNA nucleotides are placed into a test tube then go through repeated cycles of:
1. Heating, which separates the strands of DNA (denaturation)
2. Cooling, which allows primers to bind to the DNA (annealing)
3. Waiting, which allows the polymerase to build onto the primers and make new DNA strands
Each cycle doubles the amount of the gene present
