Gene Expression: The Flow of Information from DNA to RNA to Protein III

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  1. In E. coli and other proks, transcription takes place in an _____ ________ space undivided by a nuclear membrane. Translation occurs in the same open space and is sometimes coupled directly with _______
    • open intracellular
    • transcription
  2. This coupling is possible because transcription extends mRNAs in the same ________ direction as the ribosome moves along the mRNA. (Result?)
    • 5' to 3' direction
    • Result: ribosomes can begin to translate a partial mRNA that the RNA polymerase is still in the process of trasncribing from the DNA
  3. Differences in prokaryotes and eukaryotes (5-overview)-4(transcription)-3(translation) (*specific)
    pg 282
  4. Because of this scanning mechanism, initiation in euks takes place at only a single site on the mRNA, and each mRNA is _________ (meaning) it contains the info for translating only _____ kind of _______
    monocistronic: mRNA containing the coding region of only one gene 

    • one
    • polypeptide
  5. Immediately after translation, euk polypeptides all have _____ instead of ______ at their N termini. Posttranslational cleavage events in both proks and euks often create mature proteins that no longer have N-termini _____ or _____
    • Met 
    • fMet
    • fMet 
    • Met
  6. One consequence of the code's degeneracy is that some mutations, known as ______ mutations, can change a codon into a mutant codon that specifies exactly the same amino acid
    silent mutations
  7. The majority of silent mutations change the ______ nucleotide of a codon, the position at which most codons for the same amino acid ______
    • third 
    • differ
  8. Why do silent mutations usually have no effect on any of the phenotypes influenced by the gene
    because silent mutations do not alter the amino acid composition of the encoded polypeptide
  9. Missense mutations
    Mutations that change a codon into a mutant codon that specifies a different amino acid
  10. If the substituted amino acid has chemical properties similar to the one it replaces, then it may have _____ or ____ effect on protein function. Such subs are ________
    • little or no
    • conservative
  11. By contrast, ___________ missense mutations that cause substitution of an amino acid with very different properties are likely to have more noticeable consequences
    • nonconservative
    • *(Ex): A change of the same GAC codon for aspartic acid to GCC, a codon for alanine (an amino acid with an uncharged, nonpolar R group), is an example of a nonconservative substitution.
  12. Why is the effect on phenotype of any missense mutation difficult to predict?
    because it depends on how a particular amino acid subsitution changes a protein's structure and function
  13. Nonsense mutation
    changes an amino acid (specifying codon to a premature stop codon)
  14. Nonsense mutations result in the production of ________ proteins lacking all amino acids between the amino acid encoded by the mutant codon and the C terminus of the normal polypeptide. The mutant polypeptide will be _______ to function if it requires the missing amino acids for its activity.
    • truncated
    • unable
  15. Frameshift mutations result from the ________ or ________ of nucleotides within the coding sequence
    insertion or deletion
  16. If the number of extra or missing nucleotides is not divisible by ____, the insertion or deletion will skew the _______ ______ downstream of the mutation.
    • 3
    • reading frame
  17. As a result, frameshift mutations cause unrelated _____ ______ or premature _____ _______ to appear in place of amino acids critical to protein activity, destroying or diminishing polypeptide function
    • amino acids
    • stop codons
  18. Name all of the mutations depicted 
    Image Upload
    Image Upload
  19. Mutations that produce a variant phenotype are not restricted to alterations in _______
  20. Gene expression depends on several signals other than the actual coding sequence (result)
    changes in any of these critical signals can disrupt the process
  21. Changes in the sequence of a promoter that make it hard or impossible for RNA polymerase to associate with the promoter diminish or prevent _________.
  22. Likewise, mutations in enhancers that disrupt them from being recognized by ________ ______ also diminish the transcription of euk genes
    transcription factors
  23. Mutations in a termination signals can diminish the amount of ______ produced and thus the amount of ______ product
    • mRNA 
    • gene
  24. Three sites in euks that allow splicing to join exons together with precision in the mature mRNA
    splice acceptor sites, splice donor sites and branch sites
  25. Changes in any of those three sites can obstruct _________. In some cases, the result will be the absence of ______ ______ and thus no _________. In other cases, the splicing errors can yield aberrantly _______ mRNAs that encode _______ forms of the protein
    • splicing 
    • mature mRNA
    • polypeptide
    • spliced
    • altered
  26. Mature mRNAs have ribosome binding sites and in-frame stop codons indicating where translation should _____ and ____
    start and stop
  27. Mutation affect phenotype in 2 ways. Name them
    • changing either the amino acid sequence of a protein 
    • changing the amount of protein produced
  28. What do we call any mutation inside or outside a coding region that reduces or abolishes protein activity in one of the many ways prev. described
    loss of function mutation
  29. Loss of function alleles that completely block the function of a protein are called _____ or ________ mutations. (What are the two possible results)
    • null or amorphic mutations
    • Either prevent production of the protein 
    • Or promote synthesis of a protein incapable of carrying out any function
  30. Explain why null or amorphic alleles are usually recessive to wild-type alleles using the figure (3-story)
    Image Upload
    pg 285
  31. hypomorphic mutation
    Image Upload
    a loss of function allele that produces either less of the wild-type protein or a mutant protein that functions less effectively than the wild-type protein (a2)
  32. Hypomorphic alleles are usually _______ to wild-type alleles for the same reason that amorphic alleles are usually ________
    • recessive 
    • recessive
  33. Some combinations of alleles generate phenotypes that vary continuously with the amount of functional gene product, giving rise to Incomplete dominance. Explain with the example presented in the figure (4-story)
    Image Upload
    pg 285
  34. With phenotypes that are exquisitely sensitive to the amount of functional protein produced, even a relatively small change of ______ or less can cause a switch between distinct phenotypes. Therefore, a heterozygote for a loss of function mutation that generates less than the normal amount of functional gene product may look ________ from the wild-type organism
    • twofold
    • (completely) different
  35. Haploinsufficient
    a rare form of dominance in which an individual heterozygous for a wild-type allele and a loss of function allele shows an abnormal phenotype because the level of gene activity is not enough to produce a normal phenotype
  36. The number of haploinsuff. genes in humans is ~ _____. Detail an example
    • 800
    • GLI3 gene: it encodes a transcription factor important for the specification of digits. Heterozygotes for loss of function mutation in GLI3 causes one form of polydactyly (extra fingers and toes)
    • Image Upload
  37. Why are the large majority of mutations in most genes loss of function alleles?
    Because there are many ways to interfere with a gene's ability to make sufficient amounts of active proteins
  38. However, rare mutations that either enhance a protein's function, confer a new activity on a protein, or express a protein at the wrong time or place act as _________ __________ ________
    gain of function alleles
  39. Why are gain of function alleles almost always dominant to wild-type alleles?
    because a single such allele by itself usually produces a protein that can alter phenotype even in the presence of the normal protein
  40. Many dominant mutant alleles are _____ when homozygous
  41. Hypermorphic mutations (define)
    How do you know if it is dominant?
    • generates either more protein than the wild-type allele or the same amount of a more efficient protein.
    • If excess protein activity alters phenotype, the hypermorphic allele is dominant
  42. A hypermorphic mutation in the human FGFR3 gene results in ________, the most common form of dwarfism (how)
    • achondroplasia
    • The FGFR3 gene encodes a signaling protein (fibroblast growth factor receptor 3) that inhibits bone growth
  43. Achondroplasia/FGF 4-story:
    Image Upload
  44. Neomorphic mutation
    rare mutations that produce a novel phenotype due to production of a protein with a new function or due to ectopic expression of the protein
  45. Ectopic expression
    gene expression that occurs outside the cell or tissue where the gene is not normally expressed
  46. Some neomorphic alleles produce mutant proteins with a ____ function, while others cause genes to produce the normal protein but at an inappropriate _____ or _____ (______ _______)
    • new
    • time or place (ectopic expression)
  47. Neomorphic allele that expresses a normal protein ectopically is the AntpNs mutant allele of the Drosophila gene Antennapedia
    Image Upload
    • Flies that are AntpNs/Antp+ heterozygotes have legs on their heads in place of antennae
    • The Antp gene encodes a protein that promotes leg development; accordingly, the wild-type allele Antp+ is transcribed in tissues that will become the fly's legs.
    • A mutation within the transcriptional control region of the gene instead causes the AntpNs allele to express normal protein in tissues destined to become the antennae
  48. Why is AntpNs dominant?
    because the Antp+ allele does not prevent the ectopic expression of Antp protein in the cells normally destined to become antennae
  49. Dominant negative alleles
    aka antimorphic alleles: dominant mutant alleles of genes encode proteins that not only fail to provide the activity of the wild-type protein but also prevent the normal protein from functioning
  50. Explain dominant negative (aka antimorphic genes) by considering a gene encoding polypeptide that associates with three other identical polypeptides in a four subunit enzyme (4-Story) 
    Image Upload
    pg 287
  51. If more than one gene encoded the same molecule with a role in gene expression, a mutation in one of these genes would not necessarily be _____ and might even be ______. Bacterial geneticists have found, that mutations in certain tRNA genes can suppress the effect of a _______ mutation in other genes. The tRNA-gene mutations that have this effect give rise to _______ ________ _______.
    • lethal 
    • useful
    • nonsense 
    • nonsense suppressor tRNAs
  52. Explain nonsense suppressor t-RNAs by considering the otherwise wild-type E. coli population with an in-frame UAG nonsense mutation in the tryptophan synthetase gene (4-story)
    • pg 288
    • Free points for now ask professor how much we need to know about this
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Gene Expression: The Flow of Information from DNA to RNA to Protein III
2017-11-05 05:08:51
Genetics Exam II
Ch 8.4-end
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