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Biology Chapter 15
Genes and Proteins part 2 (15.3-15.5)
| Question | Answer |
|---|---|
| What is the most important difference between prokaryotic and eukaryotic transcription? | Eukaryotes have membrane-bound nucleuses and organelles. |
| What does monogenetic mean? | That mRNAs specify a single protein. |
| What do eukaryotes need so that the DNA polymerase can bind to the template strand? | Eukaryotes need transcription factors. These factors first bind to the promoter region and then acquire the correct polymerase. |
| Describe the eukaryotic polymerases. | There are three different polymerases made of 10 subunits or more. Each has own transcription factors to attract it. |
| Describe RNA polymerase 1. | It is found in the nucleolus (where ribosomal RNA is made an assembled into ribosomes). This polymerase makes all the rRNAs from duplicated sets of 18S, 5.8S, and 28S. |
| Describe RNA polymerase 2. | In nucleus and makes all protein-coding nuclear pre-mRNAs and it transcribes the majority of eukaryotic genes. |
| Describe RNA polymerase 3. | In nucleus and it transcribes a variety of structural RNAs including 5s, pre-rRNAs, pre-tRNAs, and small nuclear pre-RNAs. |
| What does transfer RNA (tRNA) do? | It serves in translation as the adaptor molecules between mRNA template and growing polypeptide chain. |
| What do small nuclear RNAs do? | They splice pre-mRNAs and regulating transcription factors. |
| What is greek a amanitin? | An oligopeptide toxin. RNA pol 1 is insensitive to it; RNA pol 2 is very sensitive to it (will not function in its presence); RNA pol 3 is moderately sensitive to it. |
| What are basal transcription factors? | These are transcription factors that bind to the promotor. Called TF2 |
| Name the common "boxes" for promotors in eukaryotes. | TATA box at -25 to -35 (TATAAA); CAAT box at -80 (GGCCAATCT); GC-rich box (GGCG); and octamer box (ATTTGCAT). |
| What do these "boxes" do? | They bind cellular factors that increase the efficiency of transcription initiation. |
| What is FACT? | This protein "facilitates chromatin transcription" by disassembling nucleosomes ahead of a transcribing RNA polymerase 2 and reassembling them after the polymerase passes. |
| How is each polymerase terminated? | RNA pol 1 and 3 require termination proteins and pol 2 is removed by cleavage during mRNA processing. |
| What is an exon? | Nucleotide sequence present in protein-coding mRNA after completion of pre-mRNA splicing. |
| What is an intron? | Non-protein coding intervening sequences that are removed from mRNA during processing. |
| What are the 3 most important steps of pre-mRNA processing? | The addition of stabilizing and signaling factors at the 5' and 3' ends of the molecule, & the removal of the introns. |
| What is 5' capping? | It add a 7-methylguanosine cap to protect nascent mRNA from degradation. |
| What is a 3' poly-A tail? | A long "tail" of 200 A nucleotides at the end of the cleaved pre-mRNA strand. This protects it and is a binding site for a protein needed for exporting it to the cytoplasm. |
| What is pre-mRNA splicing? | The removal of introns from exons. |
| What make up 50% of each ribosome? | Mature rRNAs. |
| What is an anticodon? | It is a 3-nucleotide sequence in a tRNA that interacts with an mRNA codon through complementary base pairing. |
| How are polypeptide bonds formed? | When the amino group of one amino acid forms an amide (peptide) bond with the carboxyl group of another amino acid. |
| What does translation require? | Input of mRNA template, ribosomes, tRNAs, and various enzymatic factors. |
| What is a ribosome? | It is a complex macromolecule made of structural and catalytic rRNAs and many distinct polypeptides. The nucleolus is made specifically for the making and assembly of rRNAs. |
| Ribosomes dissociates into small and large subunits. What do they do? | When not making proteins, ribosomes breakdown into small (40S) and large (60S) subunits. The small subunit binds the mRNA template while the large binds tRNAs. |
| What is a polysome? | mRNA molecule being translated by many ribosomes all going in the same direction of 5' to 3'. |
| What are tRNAs? | They are structural RNA molecules transcribed from genes by RNA pol 3. They each carry a specific amino acid and recognizes 1 or more of the mRNA codons that define the order of amino acids in a protein. |
| What are tRNAs actually responsible? | They translate the language of RNA into the language of proteins. |
| What is an aminoacyl tRNA synthetase? | An enzyme that "charges" tRNA molecules by catalyzing a bond between the tRNA and a corresponding amino acid. |
| What is an initiator tRNA? | A tRNA that interacts with a start codon, binds to the ribosome P site, and links to a special methionine to begin a polypeptide chain. |
| What are Kozak's rules? | Determines the correct inition AUG in a euk mRNA; this must appear around the AUG: 5'-GCC(purine A or G)CCAUGG-3' |
| What is peptidyl transferase? | An RNA-based enzyme that catalyzed the formation of each peptide bond. |
| What terminates translation? | When a nonsense codon (UAA, UAG, or UGA) is encountered. |
| What is a signal sequence? | A short sequence at the amino end of a protein that directs it to a specific cellular compartment. |
| What is a chaperone? | A helper protein that prevents proteins from spontaneously folding incorrectly in the folding process. |
| The AUC and AUA codons in mRNA both specify isoleucine. What feature of the genetic code explains this? | Degeneracy. |
| How many nucleotides are in 12 mRNA codons? | 36. (3x12=36) |
| What event contradicts the central dogma of molecular biology? | Scientists use reverse transcriptase enzymes to make DNA from RNA. |
| Which subunit of the E. coli polymerase confers specificity to transcription? | Greek letter o. |
| The -10 & -35 regions of prokaryotic promoters are called consensus sequence because ________ | they are similar in all bacterial species. |
| Which feature of promoters can be found in both eukaryotes and prokaryotes? | The TATA box can be found in both euk and prok. |
| What transcription will be most affected by low levels of greek a-amanitin? | pre-mRNAs will be most affected. |
| How do enhancers and promoters differ? | Enhancers increase the efficiency of gene ecpression, but are not essential for transcription. Promoter recognition is essential to transcription initiation. |
| Which pre-mRNA processing step is important for initiating translation? A) poly-A tail B) RNA editing C) splicing D) 7-methylguanosine cap. | D) 7-methylguanosine cap. |
| What processing step enhances the stability of pre-tRNAs and pre-rRNAs? | Methylation enhances stability. |
| The RNA components of ribosomes are synthesized in the _______ | nucleolus. |
| In any given species, there are at least how many types of aminoacyl tRNA synthetases? A) 20 B) 40 C) 100 D) 200 | A) 20 aminoacyl tRNA synthetases. |
| Define RNA editing. | Direct alteration of one or more nucleotides in an mRNA that already has been synthesized. |
| What is the Shine-Dalgarno sequence? | (AGGAGG) initiates prok translation by interacting with rRNA molecules comprising the 30S ribosome. |
Created by:
tali_Alley
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