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Genetics Chapter 9
gene expression
| Question | Answer |
|---|---|
| what is transcription? | process by which the polymerization of ribonucleotides, guided by complementary base pairing, produces an RNA transcript of a gene. |
| what are the three stages of transcripton? | initiation, elongation, and termination |
| how is transcription initiated in prokaryotes? | RNA polymerase binds tightly to a promoter, forming a closed promoter complex. then it unwinds part of the double helix. The enzyme identifies the template strand and guided by base pairing, it aligns the first two ribonucleotides at the 5’ end of the ne |
| is a signma factor in prokaryotes or eukaryotes? what role does it play in transcription? | it is found in prokaryotes, and it is responsible for reducing RNA polymerase’s general affinity for DNA and simultaneously increases the enzyme’s affinity for the promoter. |
| is a holoenzyme found in prokaryotes or eukaryotes? what is it? | it is found in prokaryotes, and it is the RNA polymerase consisting of a core unit and a sigma subunit only involved in initiation |
| in prokaryotes, what site does RNA polymerase bind on DNA? | RNA polymerase binds to the promoter on DNA |
| in prokaryotes, in what direction is RNA made? | it goes from the 5' to 3' end direction |
| in prokaryotes, what is required for transcription elongation to begin? | the enzyme has to leave the promoter in order to begin transcription elongation. |
| in prokayortes, is RNA made in an antiparallel direction? | yes it is |
| in prokaryotes, what are the two ways transcription is terminated? | Intrinsic terminators cause the RNA polymerase core enzyme to terminate transcription on its own. Extrinsic terminators require additional proteins – particularly a polypeptide called Rho – to bring about termination. |
| is Rho found in prokaryotes or eukaryotes? what is it? | Rho is found in prokaryotes, and they are polypeptides required for Extrinsic terminators to terminate transcription |
| are enhancers found in prokaryotes or eukaryotes? what are they? | they are found in eukaryotes, and they are DNA sequences that act as gene regulators in transcription |
| in eukaryotic cells, how is RNA processed? | primary transcripts undergo RNA processing in the nucleus before they migrate to the cytoplasm to direct protein synthesis. |
| is the 5' cap found in prokaryotes or eukaryotes? what is it? what nucleotide is involved here? | this is found in eukaryotic cells, and it is a Guanine nucleotide in reverse orientation from the rest of the molecule, and it is connected through a triphosphate linkage to the first nucleotide in the primary transcript |
| is the poly A tail found in prokaryotes or eukaryotes? what is it? | it is found in eukaryotic cells, and it is the 3' of mRNA that consists of 100-200 As |
| is the poly A tail coded for by the DNA? | no it is not coded for by the DNA |
| what is splicing in eukaryotic cells? | process that deletes introns and joins together successive exons to form a mature mRNA consisting only of exons. |
| are introns and exons found in prokaryotic or eukaryotic cells? | introns and exons are found in eukaryotic cells |
| what are exons? | Sequences found in both a gene’s DNA and the mature messenger RNA |
| what are introns? | sequences found in the DNA of the gene but not in the mature mRNA |
| what are splice donor sites, splice acceptor sites, and branch sites? | they are three types of short sequences within the primary transcript that help ensure the specificity of splicing |
| are spliceosomes found in prokaryotes or eukaryotes? what are they? | they are found in eukaryotic cells, and they are complicated intranuclear machines that ensures that all of the splicing reactions take place in concert |
| are ribozymes found in prokaryotes or eukaryotes? what are they? | they are found in eukaryotic cells, and they are rare primary transcripts that are also RNA molecules that can act as enzymes and catalyze a specific biochemical reaction |
| what is alternative splicing? | splicing that occurs between the splice donor site of one intron and the splice acceptor site of a different intron downstream. |
| what is translation? | the process by which the sequence of nucleotides in a messenger RNA directs assembly of the sequence of amino acids in the corresponding peptide |
| what is a ribosome? | cellular machines which coordinate the movements of transfer tRNAs carrying specific amino acids with the genetic instructions of an mRNA. |
| how is translation initiation started in prokaryotes? | 30S ribosomal subunit binds the mRNA’s Shine-Dalgarno box, tRNA binds to the mRNA’s initiation codon, and a 50S subunit associates with the 30S subunit |
| how does the ribosome bind to the mRNA in prokaryotes? | the Shine Dalgarno box |
| is the Shine Dalgarno box found in prokaryotes or eukaryotes? what is it? | it is found in prokaryotes, and it is a six-nucleotide sequence – usually 5’ ...AGGAGG ... 3’ |
| what is the initiation codon in prokaryotes? | mRNA’s ribosome binding site is the triplet 5’ AUG 3’ |
| is N-formylmethionine found in prokaryotes or eukaryotes? what is it? | it is found in prokaryotic cells; it is the initial amino acid coded for |
| how is translation initiation started in eukaryotes? | The complex of initiation factors plus 40S subunit then migrates along the circularized mRNA to the initiation site – usually the first AUG it encounters as it scans the mRNA in the 5’ to 3’ direction. |
| how does the ribosome bind to the mRNA in eukaryotes? | primarily at the 5' cap guided by initiation factors |
| what is the initiation codon in eukaryotes? what does it code for? | AUG; codes for methionine |
| what post translational modifications can be made to a protein? | phosphorylation, glycosylation, methylation and acetylation |
| are zymogens found in prokaryotes or eukaryotes? what is it? | they are found in eukaryotic cells and they are proteins that are synthesized in inactive forms |
| what is meant by the fact that transcription and translation are coupled in prokaryotes? | ribosomes start making protein from an mRNA strand while that mRNA is still being synthesized by RNA polymerase |
| are enhancers in prokaryotes and eukaryotes? what are they and where are they found? | enhancers are found in eukaryotes, and they are short DNA sequences that act as gene regulators to ultimately boost a target gene's transcription |
| are nucleosomes found in prokaryotes or eukaryotes? what are they and where are they found? | they are found in eukaryotes, and it is a segment of DNA wound around a core of about 8 histone proteins; they are found in the nucleus` |
| what is polycistronic mRNA and what cell types are they found in? | mRNA that carries genetic instructions for multiple proteins on a single mRNA strand |
| what is a silent mutation? | mutation that can change a codon into a mutant codon that calls for the same amino acid (change in a nucleotide) |
| what is a missense mutation? | mutation that changes a codon into a mutant codon that specifies for a different amino acid |
| what is a nonsense mutation? | changes an amino acid-specifying codon into an early stop codon |
| what is a frameshift mutation? | the insertion or deletion of nucleotides within the coding sequence, therefore changing the coding sequence calling for different amino acids |
| how can mutations outside of the coding sequence affect gene expression? | Mutations that alter promoter or enhancer sequences can reduce or block transcription by preventing RNA polymerase or transcription factors from binding. Likewise, mutations in termination signals can decrease mRNA production and lower gene expression. |
| what are loss of function mutations? | genetic changes that reduce or eliminate the normal activity of a gene or the protein it encodes. They often result in decreased protein function, nonfunctional proteins, or no protein being produced at all. |
| what are null mutations? | type of loss-of-function mutation in which the gene’s function is completely eliminated. They usually result in no functional protein being produced |
Created by:
angievelasco