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DNA and Genetics 2
| Question | Answer |
|---|---|
| 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
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