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29 Cards in this Set
- Front
- Back
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The idea that genes dictate phenotypes through enzymes that catalyze specific chemical processes in the cell was first proposed in 1909 by the British physician
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Archibald Garrod
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synthesized everything else it needed. They identified three strains of Neurospora crassa, called auxotrophs, that required additional nutrients (e.g., amino acids, vitamins, and other nutrients) to survive and required a complete growth medium containing the additional nutrients.
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George Beadle and Edward Tatum
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An organism with specific nutritional requirements
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auxotrophs
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Which of the following describes a gene?
A It is the same thing as a chromosome. B It is a segment of DNA with the information for making a protein. C It is a triplet of three nucleotide bases. D It is a section of RNA that carries information to a ribosome. |
B is the correct answer, according to the one gene/one enzyme model. Choice A is incorrect because chromosomes contain thousands of genes. Choice C is a description of a codon. Choice D is a description of messenger RNA (mRNA).
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Beadle and Tatum's experiment demonstrated that each kind of mutant bread mold lacked a specific enzyme. This was conclusive evidence that...
A genes code for proteins. B mutations are caused by radiation. C enzymes can repair damaged DNA. D cells need specific enzymes in order to function. |
The correct answer is A. Genes contain the information for making specific proteins. Beadle and Tatum did use radiation to induce the mutations, but this was known before the experiment, therefore choice B is incorrect. C is also not correct; although enzymes can repair DNA, Beadle and Tatum's experiment was not proof. While it is true that cells need specific enzymes, this was the basis of the experiment, not the result, therefore choice D is incorrect.
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The DNA molecule transcribes the genetic code onto a single strand RNA molecule. Since the RNA molecule leaves the nucleus and moves through the cytoplasm to a ribosome, it is called messenger RNA, or mRNA.
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transcription
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messenger RNA, since the RNA molecules leave the nucleus and moves through the cytoplasm to a ribosome
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mRNA
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In the ribosome, the mRNA molecule translates the DNA information into a sequence of amino acids that are assembled by the machinery of the ribosome into polypeptides.
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translation
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What is the name of the process by which the information contained in a DNA molecule is copied onto a messenger RNA molecule?
A Transcription B Translation C Replication D Translocation |
A is the correct answer. The DNA sequence is transcribed onto mRNA. Choice B is the name of the process where the mRNA information is used to construct polypeptides. Choice C is incorrect because the strand is not copied exactly, so it is not replicated. Choice D is not a term used in cell processes.
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In a cell, the nucleotides GAT were temporarily paired with the nucleotides CUA. Where did this pairing most likely occur?
A In a double-stranded molecule of DNA in the cell nucleus B During translation in the ribosome when a protein is being made C During transcription when RNA is being made D In a double-stranded molecule of RNA in the cell nucleus |
C is the best answer because in RNA, uracil replaces thymine. Uracil rarely occurs anywhere else but in RNA, therefore choice A is incorrect. Choice B is incorrect because nucleotide bases are not paired during translation. Choice D is incorrect because RNA is single-stranded.
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a noncoding, intervening sequence within a eukaryotic gene
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introns
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a region of a gene that is present in the final functional transcript (mRNA) from that gene Any non-intron section of the coding sequence of a gene; together the exons constitute the mRNA and are translated into protein
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exons
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After a precursor mRNA molecule is transcribed from a eukaryotic gene, it is modified. ____ are cut out and ____ are spliced back together to produce a molecule of mRNA.
A promoters, terminators B terminators, promoters C exons, introns D introns, exons |
D is the correct answer. The introns are not expressed in the protein, so they are removed and the exons are spliced back together. Choices A and B are incorrect because terminators and promoters occur on the DNA molecule and mark genes or transcription segments. The terms are reversed in choice C and are therefore incorrect.
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a complex cell organelle constructed in the nucleolus, functioning as the site of protein synthesis in the cytoplasm that is composed of proteins plus rRNA and that catalyzes translation of messenger RNA into an amino acid sequence Ribosomes are made up of two non-identical subunits each consisting of a different rRNA and a different set of proteins
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ribosome
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(tRNA) – small RNA molecules that carry amino acids to the ribosome for polymerization into a polypeptide During translation the amino acid is inserted into the growing polypeptide chain when the anticodon of the tRNA pairs with a codon on the mRNA being translated
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transfer RNA
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An mRNA molecule with a complementary codon is transcribed from the DNA codon ACT. In the process of protein synthesis, a tRNA pairs with the mRNA codon. What is the nucleotide sequence of the tRNA anticodon?
A UGA B ACT C ACU D UCA |
C is the correct answer. The anticodon on the tRNA will match the original codon on the DNA except that uracil will replace thymine. The tRNA anticodon will pair up with a codon on the mRNA molecule following base pairing rules. Choice A is incorrect because this is the sequence on the mRNA molecule. Choice B is incorrect because it contains the base thymine. In RNA molecules, thymine is replaced by uracil. Choice D has the correct bases but in reversed sequence.
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changes in the genetic material of a cell or virus
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mutations
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How many individual chromosomes (not pairs) does each cell in an individual with Down syndrome have?
A 23 B 24 C 46 D 47 |
D is the correct answer. Persons with Down syndrome have an extra copy of chromosome 21, for a total of 47 chromosomes. Choices A and C are both incorrect because humans normally have 23 pairs of chromosomes or 46 individual chromosomes. Choice B refers to chimpanzees, which have 24 pairs of chromosomes.
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changes in one or a few base pairs in a single gene. These can be substitutions, insertions, or deletions
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point mutations
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a mutation in which there is an addition or deletion of one, two or a small number (not a multiple of three) of nucleotides that causes the codon reading frame to shift to one of two others from the point
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frameshifts
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the most common type of mutation involving a base-pair substitution within a gene that changes a codon, but the new codon makes sense in that it still codes for an amino acid
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missense substitutions
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a mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein
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nonsense substitutions
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One wrong base in a sequence might have no effect on the organism at all. The mistake could occur in an intron, so protein production is not affected. In other cases, the wrong base might be in the third position in a codon. There are many synonymous codons, so the wrong base might not result in the wrong amino acid in the polypeptide.
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silent mutations
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Which statement could explain why a particular point mutation had no affect on the polypeptide expressed by a gene?
A The mutation was the deletion of a single nucleotide. B The mutation was the addition of an additional stop codon. C The mutation was the addition of a single nucleotide. D The mutation was the substitution of a single nucleotide. |
D is the correct answer. If the substitution occurred in the third place in a nucleotide triplet, the expressed amino acid might not be changed. Choices A and C are unlikely because a deletion or insertion would cause a frameshift. Choice B is unlikely because the stop codon would prematurely terminate the polypeptide chain, almost certainly making it nonfunctional.
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2 primary sources of variation origins
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One is any mutation within a gene. The other is the reshuffling and recombination of chromosomes during sexual reproduction.
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Since chromosomes are randomly mixed but not destroyed during sexual reproduction, the same set of genes, commonly called the gene pool, is preserved for future generations unless something happens to the population.
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recombination
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Which of the following processes is a result of environmental pressure on the genotypic variation in populations?
A Meiosis B Mitosis C Sexual reproduction D Evolution |
D is the correct answer. Evolution requires changes in the genotypes of a population over time. Choices A, B, and C are all incorrect because cell division does not require variation.
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During Prophase I, the homologous chromosomes adhere closely together, something like the halves of a zipper. The pairing is precisely gene-by-gene. During this phase, the homologous chromosomes can exchange segments.This is an important source of genetic variation that results from sexual reproduction.
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crossing over
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Which of the following statements describes crossing over?
A Homologous chromosomes exchange corresponding genes. B Chromosomes are sorted independently during meiosis. C The transfer of genetic material from one chromosome to a nonhomologous chromosome. D Insertion of extra bases during transcription of DNA to RNA. |
A is the correct answer. When homologous chromosomes exchange corresponding genes, novel but viable chromosomes are created. Choice B is an important process that produces new combinations of chromosomes but does not change the individual chromosome. Choice C is the process of translocation, which typically produces nonviable or harmful changes in chromosome structure. Choice D is a description of errors that occur during gene replication, not meiosis.
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