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DNA and Genetics 2

QuestionAnswer
The DNA with it's base sequence is held where within the cell? The nucleus.
Where are amino acids assembled into protein? In the ribosomes.
mRNA is created by what? Transcription.
What is the central dogma? DNA --transcription--> mRNA --translation--> Protein
What is epigenetics? Where the cell attaches chemical tags to DNA to influence gene expression in response to environmental conditions,
What is a promoter? A sequence of DNA that promotes the binding of RNA polymerase to allow the gene to be expressed. A promoter usually lies upstream of the 5' end of the coding sequence.
Where and what does a termination sequence do? A termination sequence is at the 3' end and it tells RNA polymerase to cease transcription.
Where are enhancers found? These DNA sequences lie within regions of non-coding DNA, and can be thousands of base pairs away from their target gene.
What is DNA wrapped around? Proteins called histones.
How can regions of DNA that are not close to one another in linear sequence enhance the expression of that gene? As the promoter region of the gene is brought close to the enhancer region through when the DNA is wrapped around histones.
What do transcription factors do? They can either bind the promoter or enhancer. These transcription factors then bind RNA polymerase.
What are transcription factors specific to? What are they required for? Transcription factors are specific for the promoters they associate with, and are required for transcription initiation.
What do inducers do? Inducers promote the association of transcription factors with their specific promoter and increase RNA polymerase association at the site.
When does transcription begin? Transcription begins when transcription factors recruit one subunit of RNA polymerase to the promoter on the *antisense strand* of DNA.
The RNA polymerase is made up of many subunits and is called a? Holoenzyme.
Genes are always transcribed from which strand? *Antisense strand* of DNA (so that the resulting mRNA is sense).
What does the RNA polymerase holoenzyme do? Unwinds and 'unzips' the DNA and builds a strand of mRNA that is complementary to the antisense strand using free ribonucleotides.
Transcription stops at what specific sequence? A specific transcription termination sequence (on the DNA at the 5' end of the gene). This forms a loops in the sequence called a *hairpin loop* which is used as a marker to tell RNA polymerase to stop.
When transcription is complete what happens? The mRNA transcript detaches from the RNA polymerase and therefore from the DNA template strand. The polymerase also detaches from the DNA, which reforms its double helical structure.
What are expressing regions which code for protein termed as? Exons.
What are intervening regions termed as? Introns.
What is splicing? Removal of the introns.
Where does splicing occur? At the spliceosome. A complex of snRNA (small nuclear RNA) and proteins that removes the introns from the primary mRNA transcript and splices the exons together.
What is one way to control gene expression at the level of RNA processing? At the stage of splicing the exons together.
What are snRNPs? small nuclear Ribonuclear Proteins.
After splicing, further processing of the mRNA transcript occurs at the 5' and 3' ends, what is this? 5' cap. 3' poly A tail.
Explain the 5' cap? The 5' cap of mRNA is added in the nucleus and involves the addition of a molecule of Guanine Triphosphate (GTP) to the 5' end of the mRNA transcript. 5' capping makes the mRNA more stable by preventing it from being degraded and assists ribosomal binding
Explain the 3' poly A tail? mRNA transcript is modified at the 3' end by the addition of multiple adenosine monophosphates (AMP) in a process called polyadenylation. As with 5' capping, a poly A tail also increases the stability of the transcript.
What is the 3' poly A ail required for? Nuclear export and for efficient protein synthesis.
Can simultaneous transcription and translation occur in prokaryotic cells? Yes.
What is an operon? A cluster of related DNA.
Give an example of an operon? The lac operon (controls lactose metabolism in E. coli). The lac operon is also an example of an inducible operon.
What is produced continuously and, in the absence of lactose, binds to a DNA sequence called the operator? A repressor protein.
What happens when the repressor protein is bound to the operator? RNA polymerase cannot bind to the promoter and therefore cannot transcribe the structural genes.
What happens when lactose is present? Lactose binds to the repressor protein, which becomes altered.
Why are operons advantageous? They use space effectively. Allows efficient expression of enzymes that are functionally related. Allows the co-ordination of gene regulation.
What happens when cells continue to grow and reproduce when it is not needed? A tumour forms.
What are the types of tumour? Benign, where they remain in one in the tissue they orginated in or cancerousm where they invade the surrounding tissue and spread to other regions of the body.
What are genes called that transform a cell into a cancer cell? Oncogenes.
The normal (non-mutated) version of oncogenes are called? Proto-oncogenes, because they do not cause cancer normally, but have the potential to do so if they mutate or their level of gene expression changes.
Where are oncogenes and proto-oncogenes involved? In checkpoints in the cell cycle, and are involved in cell signalling that drives the cell to survive ad grow.
Everyone has two copies of a proto-oncogene, one from each parent, and mutations are recessive - how many of the alleles have to be mutated for cancer to arise? Both.
Give an example of a proto-oncogene? Ras.
When mutated what does Ras do? When mutated Ras continuously signals to the cell that is has to grow and survive. Overactive Ras signalling can lead to cancer.
What is epigenetics? The study of changes in gene function that are heritable and that do not entail a change in a DNA sequence.
What are examples of environmental conditions that cause epigenetics modifications to DNA? Smoking, diet and gestational diabetes.
Are epigenetics inheritable? Yes.
Created by: Cleggat