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| What is the Central Dogma of biology (flow of information)? |
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Definition
| DNA (information storage) --> (transcription): mRNA (information carrier)--> (translation) Proteins |
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| is translated to make protein-coding genes |
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| functions in translation (facilitates it) |
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| snRNA (small nuclear RNA) |
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Definition
| important for messenger RNA processing |
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| important for regulation of translation |
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Term
| Describe the genetic code |
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Definition
| A three base code (known as triplet) is a universal genetic code for life as we know it. The code is redundant, meaning all amino acids except methionine and tryptophan are coded by more than one codon. The code is also non-overlapping, meaning once the ribosome locks onto the first codon, it then reads each separate codon one after another |
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| a single base change in DNA |
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-change in nucleotide sequence that does not change the amino acid specified by a codon
-no change in phenotype
-neutral with respect to fitness |
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-change in nucleotide sequence that changes the amino acid specified by codon
-change in primary structure of protein; may be beneficial, neutral, or deleterious |
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-change in nucleotide sequence that results in an early stop codon
-leads to mRNA breakdown or a shortened polypeptide
-usually deleterious |
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Term
| Frameshift Point Mutation |
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Definition
-addition or deletion of a nucleotide
-reading frame is shifted, altering the meaning of all subsequent codons; almost always deleterious |
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| T/F: In a silent point mutation, there will be a nonfunctional protein and a change in phenotype for a cell because all of the protein will not be made and stop |
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Definition
| False (nonsense point mutation) |
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Term
| In transcription, the strand that is read by the enzyme is the ________ strand and the other strand is the ______________ strand |
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| T/F: The template strand of a gene (DNA) is read in the 3' --> 5' direction. The new molecule of RNA is synthesized in the 5'--> 3' direction |
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| where RNA polymerase first binds |
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| a multipart enzyme consisting of a core enzyme (containing the active site for catalysis) along with other required proteins |
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| a bacterial protein that associates with the core RNA polymerase to allow recognition of promoters |
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| the enzyme responsible for catalysis in a multipart holoenzyme |
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| The purpose of the _______ _______ and _________ ________ in transcription is to form and bound to specific sections of DNA called promoters |
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Definition
| sigma factor; core enzyme |
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| RNA is often translated and transcribed at the same time because there is no nucleus |
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-one RNA polymerase
-promoter structure contains a -35 box and a -10 box
-proteins involved in recognizing promoter are sigma (different versions of sigma bind to different promoters)
-no RNA processing |
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Definition
-three RNA polymerases (each produces a different class of RNA)
-more variable promoter structures
-often includes a TATA box about -30 from the transcription start site
-many basal transcription factors are proteins involved in recognizing promoters
-RNA processing is extensive; several processing steps occur in the nucleus before RNA is exported to the cytoplasm
1)enzyme catalyzed addition of 5' cap on mRNAs
2)Splicing (intron removal), by spliceosome to produce mRNA
3) enzyme-catalyzed additino of 3' poly(A) tail on mRNAs |
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Definition
| transcription and translation of RNA cannot occur together, because transcription and RNA processing occur in the nucleus and translation occurs in the cytoplasm |
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Definition
-first step in mRNA processing
-sigma binds to the promoter, and RNA polymerase opens the DNA helix and threads the template strand through the active site |
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-second step during mRNA processing
-RNA polymerase begins moving along the DNA template synthesizing RNA |
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-third step during mRNA processing
-RNA polymerase transcribes a transcription termination signal, which codes for RNA that forms a hairpin; the RNA hairpin causes the RNA strand to separate from the RNA polymerase, terminating transcription |
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Term
| Explain how mRNA splicing occurs |
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Definition
1) snRNPs bind to start of intro and an A base within the intron
2) snRNPs assemble to form the spliceosome
3) Intron is cut and a loop forms
4) intron is released as a lariat; exons are joined together |
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Definition
| in eukaryotes, a large, complex assembly of snRNPs (small nuclear ribonucleoproteins) that catalyzes removal of introns from primary RNA transcripts |
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Term
| During translation, mRNA contains _______ and tRNA contains _________ |
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Definition
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| T/F: During translation, the mRNA template is read 5'--> 3' but synthesized 3'--> 5' |
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| the AUG triplet in mRNA at which protein synthesis begins; codes for the amino acid methionine |
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| bears f-met and binds to the start codon |
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Term
| Describe the structure (shape) of a tRNA molecule |
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Definition
| all the tRNAs in a cell have the same general structure (tertiary), shaped like an upside-down L. They vary at the anticodon and attached amino acid |
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Term
| Initiation of translation |
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Definition
-mRNA binds to small subunit
-initiator aminoacyl tRNA binds to start codon
-large subunit of ribosome of ribosome binds, completign ribosome assembly (translation can now begin) |
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Term
| Elongation of the protein |
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Definition
-incoming aminoacyl tRNA
-peptide bond formation
-translocation
repeats |
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Term
| Termination of translation |
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Definition
-release factor binds to stop codon; polypeptide and uncharged tRNAs are released
-ribosome subunits separate |
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| the tRNA with growing polypeptide attached |
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-a messenger RNA molecule along with more than one attached ribosome and their growing peptide strands
-enable the cell to produce many copies of a protein from a single mRNA |
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Term
| Which of the following is an important exception to the central dogma of molecular biology? |
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Definition
| many genes code for RNAs that function directly in the cell |
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Term
| Why does a single-base deletion mutation within a protein-coding sequence usually have more severe effect than a deletion of three adjacent bases? |
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Definition
| because single-base deletions change the reading frame |
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| When researchers discovered that a combination of three deletion mutations or three addition mutations would restore the function of a gene, most biologists were convinced that the genetic code was read in triplets. Explain the logic behind this conclusion. |
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Definition
| In a triplet code, addition or deletion of 1-2 bases disrupts the reading frame "downstream" of the mutation site(s), resulting in a dysfunctional protein. But addition or deletion of 3 bases restores the reading frame--the normal sequence is disrupted only between the first and third mutation. The resulting protein is altered but may still be able to function normally. Only a triplet code would show these patterns |
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| Explain why all point mutations change the genotype, but why only some point mutations change the phenotype |
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Definition
| A point mutation changes the nucleotide sequence of an existing allele, creating a new one, so it always changes the genotype. But because the genetic code is redundant, and because point mutations can occur in DNA sequences that do not code for amino acids, these point mutations do not change the protein product and therefore do not change the phenotype |
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Term
| Where is the start codon located? |
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Definition
| at the downstream end of the 5' unstranslated region (UTR) |
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| What does a bacterial RNA polymerase produce when it transcribes a protein-coding gene |
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Definition
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| Where is an amino acid attached to a tRNA |
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Definition
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| Describe the sequences of events that occurs during translation as a protein elongates by one amino acid and the ribosome moves down the mRNA. Your answer should specify what is happening in the ribosome’s A site, P site, and E site. |
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Definition
| After a peptide bond forms between the polypeptide and the amino acid held by the tRNA in the A site, the ribosome moves down the mRNA. As it does, an uncharged tRNA leaves the E site. The now-uncharged tRNA that was in the P site enters the E site. The now-uncharged tRNA that was in the P site enters the E site, the tRNA holding the polypeptide chain moves from the A site to the P site, and a new aminoacyl tRNA enters the A site. |
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| The 5’ cap and poly(A) tail in eukaryotic mRNAs protect the message from degradation by ribonucleases. But why do ribonucleases exist? What function would an enzyme that destroys messages serve? Answer this question using the example of an mRNA for a hormone that causes human heart rate to increase. |
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Definition
| Ribonucleases degrade mRNAs that are no longer needed by the cell. If an mRNA for a hormone that increased heart rate were never degraded, the hormone would be produced continuously and heart rate would stay elevated—a dangerous situation. |
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