UNIT 12 Flashcards
(18 cards)
Describe the consequences of insertions and deletions.
Insertion/deletion of three/multiple of three bases results in extra/missing whole codons;
Polypeptide translated from mRNA will be unchanged except for an extra/missing amino acid;
Any other number of nucleotides is inserted/deleted is a frameshift mutation;
Every codon is changed from the insertion/deletion onwards in the direction of transcription/translation;
Frameshift mutations can introduce stop codons;
Results in earlier ending of translation/production of a truncated polypeptide, preventing proper functioning;
Outline causes of gene mutation.
Mutations often occur during DNA replication when there are errors in base pairing;
Mutagens increase the frequency of mutation, all mutagens are dangerous;
Chemical mutagens cause chemical changes in DNA that result in changes to the base sequence;
E.g. nitrosamines, mustard gas, benzene;
High energy radiation breaks bonds in DNA strands, allowing insertion/deletion of nucleotides;
May also cause chemical changes in bases resulting in base substitution;
E.g. x-rays, beta particles, UVB and UVC;
Mutations are usually random;
Substitutions between two purines/pyrimidines are more likely due to similar chemical structures;
Describe the consequences of mutations in somatic cells and germ cells.
Somatic cell mutations
Occurs in body cells/non-gamete cells, not inherited by offspring;
Can lead to uncontrolled cell division and tumour formation;
Potentially results in cancer if mutations affect genes controlling the cell cycle;
Germ cell mutations
Occurs in gametes/cells that develop into gametes, can be inherited by offspring;
Can lead to hereditary diseases/conditions in future generations;
May increase the risk of genetic disorders in descendants;
Discuss the ethical concerns regarding gene editing.
Safety concerns: whether there will be damage to other genes/long term effects uncertain/unknown health risks/issues/effects;
Difficulty in obtaining consent from future generations who may inherit edited genes;
Technology may be expensive/risk of increasing health disparity/genetic inequality;
Ambiguity over regulations regarding gene editing/different regulations in different countries;
Impact on natural biodiversity/if genetically modified animals are released into the wild;
Outline how gene knockout is used.
Intentional alteration of the DNA sequence in a gene;
Functions of genes can be investigated;
By making it uncooperative through gene editing;
Describe how CRISPR-Cas9 is used in gene editing, including an example of a successful use.
CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats;
gRNA is made by transcribing a spacer and a repeat from the CRISPR bacterial genome;
gRNA has base sequence complementary to target sequence;
gRNA binds to Cas9 enzyme;
Cas9 separates DNA strands by breaking hydrogen bonds;
Cas9 moves along DNA and finds target sequence using gRNA;
Cas9 makes a nick in other strand/strand without target sequence, creating 3’ and 5’ ends;
DNA strand on 3’ of the nick binds to primer binding site on gRNA;
Reverse transcriptase (attached to Cas9) adds DNA nucleotides to 3’ end using the template sequence in gRNA to determine the base sequence;
gRNA detaches from Cas9 and two DNA strainds pair up again;
Sequence assembled by reverse transcriptase displaces the sequence originally paired up with target sequence/becomes single-stranded flap;
Nucleotides in single-stranded flap are removed, editing out the original base sequence;
DNA proofreading for mispairing;
E.g. Sicilian Rouge High GABA tomatoes contain 4-5 times more GABA than previous varieties, gene for the enzyme converting GABA to glutamate was edited so enzyme is inactive, high concentrations of GABA persist until ripe/eaten, GABA claimed to reduce blood pressure;
Describe how conserved gene sequences are investigated.
Conserved sequences are identical/similar across species over long evolutionary periods;
Indicate essential functions of gene products;
Hypothesis: essential for protein function, leading to preservation OR certain genes mutate less frequently, aiding conservation/slower mutation rate;
Discuss the process, including potential risks and benefits, of using bacteria to genetically modify plant crop species.
Process
Genetic modification by gene transfer between species;
Gene transferred from bacterium to plant/crop;
Gene/DNA codes for/responsible for desired protein/gene product;
Bacteria have/produce plasmids / gene/DNA inserted into plasmid;
Using restriction endonuclease to cut DNA;
Using DNA ligase to join DNA;
Bacterium transfers modified plasmid to plant cell;
Benefits
Increase crop yields;
Increase pest/disease resistance / less pesticide/insecticide/fungicide used;
Improves nutritional/vitamin content;
Increased tolerance to saline soils/high/low temperatures/drought;
Risks
GM organisms could spread to sites (where they will cause harm);
Transferred gene could spread to other species / spread of herbicide resistance to weeds;
GM crops that produce pesticide could kill non-pest insects/monach butterflies / insect pests could develop resistance to pesticides/insecticides;
Distinguish between genome, transcriptome and proteome.
Genome: the entire set of genetic information in an organism;
Transcriptome: the entire set of mRNAs transcribed in a cell;
Proteome: the entire set of proteins produced by a cell;
Describe the role of promoters, enhancers and transcription factors.
Promoter: short sequence of bases on DNA that allows RNA polymerase to bind (e.g. TATA box);
Enhancer: base sequences located upstream/downstream of a gene that increase the rate of transcription;
Transcription factors: proteins that bind to DNA to activate/silence a gene/regulate transcription;
Explain the control of gene expression in eukaryotes.
mRNA conveys genetic information from DNA to ribosomes;
Gene expression requires the production of specific mRNA through transcription;
Most genes are turned off/not being transcribed at any one time/regulated / some genes are only expressed at certain times;
Some genes are only expressed in certain cells/tissues / cell differentiation involves changes in gene expression;
Transcription factors/proteins can increase/decrease transcription rate;
Hormones/chemical environment of cell can affect gene expression;
Example of chemical environment;
Transcription factors/proteins may prevent or enhance the biniding of RNA polymerase;
Nucleosomes limit access of transcription factors to DNA/regulate gene expression/transcription / activate/silence genes;
DNA methylation/acetylation appears to control gene expression (as epigenetic factors) / methylated genes are silenced;
Some DNA mtehylation patterns are inherited;
Introns may contain positive or negative gene regulators / gene expression can be regulated by post-transcriptional modification/splicing/mRNA processing;
Outline how nucleosomes affect the transcription of DNA.
Promote and inhibit transcription/expression of genes;
Can prevent transcription by supercoiling;
Allow/prevent binding of RNA polymerase/transcription factors;
Methylation/acetylation/tagging of nucleosomes/histones can promote/inhibit transcription;
Movement of histones/nucleosomes (along DNA) can affect which genes are transcribed;
Explain the role of lactose in the expression of the gene for lactase production.
Lac operon mechanism;
Lactose binds to repressor protein;
Repressor protein cannot block/bind to promoter/operator;
RNA polymerase binds to promoter/transcribes the gene;
Lactase produced (if actors present)/lactase production inhibited if lactose absent;
Without lactose, repressor protein binds to promotor/operator and blocks RNA polymerase from binding to promoter
Explain how methylation acts as epigenetic tags.
Epigenetic tags change the pattern of gene expression in a cell;
Methylation is the addition of a methyl group;
DNA is wrapped around histone proteins/nucleosome;
Methylation of histones allows chromatin to supercoil;
Prevents transcription;
Acetylation is the opposite of methylation/promotes transcription;
Methylation of DNA bases (cytosine) in the promoter prevents transcription factors from binding;
RNA polymerase does not transcribe the gene downstream of the promoter/gene is not expressed;
Outline epigenetic inheritance.
Some epigenetic tags can be inherited as most but not all are removed (during meiosis);
Results in daughter cells containing the same epigenetic modifications as parent cells;
Phenotypic changes resulting from epigenetic modifications can be inherited without changes in DNA base sequence;
Removal of epigenetic tags results in no transgenerational epigenetic inheritance;
Describe the consequences of removing most but not all epigenetic tags using an example.
99% of epigenetic tags removed during gamete production/meiosis;
Some can be inherited/epigenetic inheritance;
Offspring inherit one allele of each autosomal gene from mother and father;
(usually) dominant allele is expressed but if silenced by epigenetic tags recessive allele is expressed instead;
E.g. Tigons and Ligers / female lion has genes to inhibit growth/male lion has genes to promote growth/tigers do not have either gene / male lion + female tiger = genes to promote growth/smaller body size / male tiger + female lion = genes to inhibit growth/smaller body size;
State the reason why identical twins may show different methylation patterns as they grow older.
Different environment;
Explain the effects that the environment can have on DNA in living organisms.
Environment can cause mutation;
Mutations are random changes in the base sequence of DNA;
Radiation/UV/gamma rays can cause mutations;
Chemical mutagens/carcinogenic chemicals can cause mutations (e.g. mustard gas);
Environment can also cause changes to gene expression (e.g. air pollution);
Methylation patterns in DNA changed as a result of environmental factors;
Methylation inhibits gene transcription / acetylation promotes gene transcription;
Body temperature/stress/diet (can affect gene expression);
Lion male has gene to promote growth
Lion female has gene to suppress growth
No special genes in tiger
Promote growth + no suppress = large
Suppress growth + no suppress = small
