1. Two couples in which both partners have albinism each have three children. All three of the first coupleâs children have albinism, while all of the second coupleâs children have normal pigmentation. How can you explain these findings given that the development of pigmentation is a multi-step biochemical pathway?
2. All of the genome is replicated during the DNA synthesis phase of the cell cycle, but only part of the genome is transcribed each time transcription is initiated. How is it determined which base pairs of thegenome are transcribed into RNA?
3. To encode all 20 amino acids using a genetic code that is unambiguous, what would be the minimum codon size if there were ________ different bases (rather than four)?
a) two
b) five
c) Suppose that only the first two nucleotides of a three nucleotide codon are base-specific, and position three is dependent on whether it is occupied by a purine or pyrimidine, how many triplets of different meaning would there be?
4. A segment of a polypeptide chain is Arg-Gly-Ser-Phe-Val-Asp-Arg. If it is encoded by the followingsegment of DNA, which DNA strand acts as the template for transcription? Appropriately label the ends ofeach DNA strand with 5â and 3â.
- G G C T A G C T G C T T C C T T G G G G A â- C C G A T C G A C G A A G G A A C C C C T -
1. Two couples in which both partners have albinism each have three children. All three of the first coupleâs children have albinism, while all of the second coupleâs children have normal pigmentation. How can you explain these findings given that the development of pigmentation is a multi-step biochemical pathway?
2. All of the genome is replicated during the DNA synthesis phase of the cell cycle, but only part of the genome is transcribed each time transcription is initiated. How is it determined which base pairs of thegenome are transcribed into RNA?
3. To encode all 20 amino acids using a genetic code that is unambiguous, what would be the minimum codon size if there were ________ different bases (rather than four)?
a) two
b) five
c) Suppose that only the first two nucleotides of a three nucleotide codon are base-specific, and position three is dependent on whether it is occupied by a purine or pyrimidine, how many triplets of different meaning would there be?
4. A segment of a polypeptide chain is Arg-Gly-Ser-Phe-Val-Asp-Arg. If it is encoded by the followingsegment of DNA, which DNA strand acts as the template for transcription? Appropriately label the ends ofeach DNA strand with 5â and 3â.
- G G C T A G C T G C T T C C T T G G G G A â- C C G A T C G A C G A A G G A A C C C C T -
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Its one problem with 7 questions
A) Most eukaryotic cells transcribe a relatively high portion of their genome, but most of those RNA transcripts are likely not encoding for proteins. Elucidating the function(s) of that "junk" RNA is one of the next big challenges in molecular cell biology. You isolate one of those transcripts and determine that its sequence consists of 50% C, 30% U, and 20% A. What is the percentage of Gs in this transcript? (don't write the unit)
B) Which stop codon(s) can be encoded by the RNA in the previous question ("How many times do we need to tell you to stop? 1").
List the codon(s) alphabetically. If you need to enter fewer codons than the alloted number of "blanks", enter N/A .
C) From what you can tell, the sequence of the transcript you isolated in the previous question* appears quite random. Assuming that it is random, you can expect to see the various combinations of any three nucleotides at a probability that depends of the frequency of each of the nucleotides. For example, you naturally should expect to see the triplet CCC more times than AAA. What is the expected percentage of triplets corresponding to stop codon(s) in this transcript (round to one decimal place and enter just the number without "%")? *(How many times do we need to tell you to stop? 1)
D) If the length of the transcript in the previous two questions is 2,500 nucleotides, how many stop codons do you expect to find in it, based on the frequency you calculated above?
E) On average, how many bases separate each of the occurrence of the stop codon(s) (round to the nearest integer).
F) The sequence between two potential stop codons is an "open reading frame" (ORF*). Upon closer examination of the RNA sequence from the previous questions** you determine the presence of an ORF that may encode for a putative protein which is 600 amino acid residues-long. How long is the ORF?
*Open reading frame: a stretch of DNA or RNA which is uninterrupted by a stop codon and may therefore encode for a protein.
**Questions "How many times do we need to tell you to stop" 1 through 5.
| 27 bases | ||
| 1,800 bases | ||
| 2,500 bases | ||
| 259 bases | ||
| 600 bases | ||
| 83 bases | ||
| 200 bases |
G) What may be the ramifications of your analyses of the RNA you isolated*? It is clearly containing an ORF which is longer than what you expected to find based on the sequence analysis you have conducted. What would be a logical conclusions based on the comparison of the lengths of the actual and predicted ORFs? Questions "How many times do we need to tell you to stop" 1 through 6. Pick 1, 2 or 3 below
| 1) The difference between the actual and predicted sizes of the ORF is not big enough to be significant and therefore your initial hypothesis that sequence is random is clearly random, is supported. | ||
| 2) Nature is random and your results, using the Bard's words, may be "full of sound and fury" but are really "signifying nothing". | ||
| 3) The difference between the actual and predicted sizes of the ORF is rather big and may suggest that the sequence of the RNA may not be as random as it first appeared. This raises the hypothesis that what started as piece of "junk" RNA may be actually encoding for a protein. |
13. The arms of a human and the wing of a bat are _________________ structures, composed of the same bones that have been modified for different functions.
| a. | analogous |
| b. | vestigial |
| c. | homologous |
| d. | convergent |
14. Xeroderma pigmentosum is an autosomal recessive genetic disorder. People who are homozygous for the disease-causing allele have skin that is damaged by exposure to ultraviolet radiation; this can lead to skin cancer at an early age. The mutation that causes this disorder is in a gene that functions:
| a. | to repair DNA by excising (removing) nucleotides damaged by UV light. |
| b. | in lysosomes, to break down lipids that otherwise accumulate in the nervous system. |
| c. | to produce the UV blocking pigment melanin in the skin cells |
| d. | in red blood cells to carry oxygen to the skin. |
15. The Amish are a religious sect descended from a small group of colonists who came to the United States over 200 years ago. Their religious beliefs have kept them isolated from society. The Amish have a much higher than average incidence of both polydactyly (extra fingers and toes) and dwarfism in their communities. This is most likely explained by:
| a. | inheritance of acquired characters. |
| b. | the founder effect. |
| c. | disruptive selection. |
| d. | natural selection. |
16. In the structure of DNA that Watson and Crick proposed, the sides of the "ladder" of the DNA molecule are always the same distance apart, making the molecule a constant width. This occurs because when the bases hydrogen bond to form the rungs of the "ladder", a:
| a. | purine always pairs with a pyrimidine. |
| b. | purine always pairs with a purine. |
| c. | pyrimidine always pairs with a pyrmidine. |
| d. | The structure of the double helix is not determined by how the bases pair. |
17. The RNA transcript of DNA that travels to the cytoplasm, carrying the instructions to make a protein, is called:
| a. | rRNA. |
| b. | tRNA. |
| c. | mRNA. |
| d. | RNA polymerase. |
18. When DNA is replicated, the error rate is approximately one error for every 10,000 nucleotides copied. However, that error rate is reduced to only 1 error for every 1 billion nucleotides. The DNA sequence is "corrected" by:
| a. | repeating S phase to see if the error rate is lower the second time around. |
| b. | enzymes that proofread the DNA and repair errors. |
| c. | messenger RNA during the process of transcription. |
| d. | Any errors made during DNA replication cannot be corrected. If errors are detected after S phase, the cell is destroyed. |
19. Mendel's principle of segregation says that:
| a. | when gametes are formed, each gamete receives only one allele for a particular gene. |
| b. | some genes are dominant to others. |
| c. | a testcross must be used to determine the genotype of an organism with a dominant phenotype. |
| d. | all of the above |
20. Tay-Sachs disease is lethal before reproductive age, but the allele persists in Louisiana French Canadians because:
| a. | it is a dominant allele. |
| b. | new mutations causing this disease are common in that population. |
| c. | it is not expressed in the phenotype of heterozygous individuals. |
| d. | the disease is contagious and can be transmitted by nonheritable means. |
21. Physical features that are similar in organisms which are not closely related to each other are most likely a result of ____________. A good example of this is the similarities seen between some marsupial and placental mammals.
| a. | natural selection. |
| b. | adaptation to similar environments |
| c. | convergent evolution |
| d. | All of the above phrases can be used to correctly fill this blank. |
22. In humans, which of the following sex chromosome compliments could be found in males?
| a. | XY |
| b. | XX |
| c. | Y |
23. The proteins that are associated with eukaryotic chromosomes:
| a. | help to package the DNA within the nucleus. |
| b. | are involved in gene expression, through binding with the DNA. |
| c. | may be replicating or transcribing the DNA. |
| d. | All of these are true of proteins that are associated with eukaryotic chromosomes. |
24. A sequence of DNA nucleotides that contains the information to produce a single protein is a(n):
| a. | codon. |
| b. | gene. |
| c. | polypeptide. |
| d. | anticodon. |
