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Define the term gene expression.
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Define the term gene expression.
Gene expression is the process by which the genetic code in DNA influences the phenotype of an organism.
True or False?
Differences in phenotype occur as a result of the proteins produced in gene expression.
True.
Proteins produced through gene expression can impact the phenotype where different genes result in different proteins which lead to different phenotypes.
Why are genes expressed differently in different cells around the body?
Different cells have different functions and therefore require different proteins to perform its specific role. This allows cells to become specialised.
True or False?
Gene expression is determined by the process of transcription.
True.
Transcription is a stage where gene expression may be switched on or off. Transcription controls if and when a gene is expressed by converting DNA code to mRNA.
What role does mRNA play in gene expression?
mRNA carries the genetic code from DNA to ribosomes, where it is translated into proteins. The proteins then impact the phenotype of an individual.
Define the term promoter in the context of gene expression.
A promoter is a region of DNA, located at the start of a gene, that is involved with regulating gene expression. Proteins can bind to promoters in order to initiate or repress transcription.
Define the term enhancer in the context of gene expression.
An enhancer is a region of DNA, located at a distance from a gene, that is involved with regulating gene expression.
What is a transcription factor?
A transcription factor is a protein that regulates gene expression, e.g. by binding to a promoter to initiate/repress transcription.
How can transcription factors alter transcription rates?
Transcription factors can influence transcription by making it easier or harder for mRNA polymerase to bind to the promoter at the start of a gene.
How can nucleases regulate translation?
Nucleases can break down mRNA molecules in the cytoplasm, meaning that the mRNA can no longer be translated.
Define the term epigenesis.
Epigenesis is the development of patterns of differentiation in the cells of a multicellular organism.
True or False?
Epigenetic changes alter DNA base sequences.
False.
Epigenetic changes do not affect DNA base sequences; they affect phenotype but not genotype.
What is the difference between a genome and a proteome?
A genome is all of the genetic information present in an organisms, while a proteome is all the proteins synthesised within its cells.
Define the term transcriptome.
A transcriptome is the range of mRNA transcripts produced within a cell or tissue type.
True or False?
No cells express all of the genes present in their genome.
True.
No cell expresses all of its genes; the genes expressed by a cell will determine its structure and function.
What is the connection between gene expression and cell differentiation?
In order to differentiate into different cell types, cells express different genes; this results in the specific structure and function of specialised cells.
What is methylation in the context of epigenetics?
Methylation is the addition of a methyl group to DNA or histones.
How does methylation of DNA affect gene expression?
Methylation of DNA involves the direct addition of a methyl group to cytosine bases. This suppresses transcription of the affected gene by inhibiting the binding of transcription factors.
True or False?
Methylation of histones always represses gene expression.
False.
Methylation of histones can cause transcription to be either repressed or activated.
How can epigenetic inheritance occur?
Epigenetic inheritance can occur when epigenetic changes are not removed during mitosis or meiosis. This results in the passage of non-genetic variation from parents to offspring.
What is one example of the effect of an environmental factor on gene expression?
An example of the effect of an environmental factor on gene expression is:
air pollution can affect DNA methylation
Why do phenotypic differences exist between tigons and ligers?
There are phenotypic differences between tigons (male tiger and female lion hybrids) and ligers (male lion and female tiger hybrids) due to differences in the epigenetic tags passed on in the egg and sperm cells of lions and tigers.
Tigons are relatively small in size because female lions pass on epigenetic tags that limit growth
Ligers are relatively large in size because male lions do not pass on these epigenetic tags
True or False?
Monozygotic twin studies show the effects of both genetic and environmental factors on gene expression.
False.
Monozygotic twin studies show the effects of environmental factors on gene expression. Monozygotic twins have the same genetic information, meaning that phenotypic variation that arises can be attributed to epigenetic changes that may affect development.
True or False?
Chemicals in the environment can affect gene expression, while internal chemical signals cannot.
False.
Chemicals in the environment, e.g. lactose, and internal chemical signals, e.g. hormones, can both affect gene expression.