Unit 7

scientists seeking to determine which molecule is responsible for the transmission of characteristics from one generation to the next know that the molecule must (1) copy itself precisely, (2) be stable but able to be changed, and (3) be complex enough to determine the organism's phenotype. Explain how DNA meets each of the three criteria stated above

....

cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine

12

insulin is a protein that is made up of 51 amino acids. It would have been translated from an mRNA transcript that had at least

153 nucleotides

the following question refers to this table of codons. Which of the following sequences of nucleotides are possible in the template strand of DNA that would code for the polypeptide sequence Phe-Leu-Ile-Val

3'-AAA-GAA-TAA-CAA-5'

5'-ATG-CGC-GAC-GCG-ATT-TGA-C-3' one method for predicting the average temperature (in °C) at which a short DNA molecule binds with its complement is to calculate a melting temperature (Tm) using the following formula (Tm = 4(G+C) + 2(A+T)). Using the formula, what is the predicted Tm for the short single-stranded DNA molecule shown above

60°C

a researcher proposes that the transmembrane portion of a certain protein consists of 24 amino acids. Based on the proposed model, calculate the number of nucleotides in the mRNA that encode only for the amino acids in the transmembrane portion of the protein

72

sickle-cell anemia is associated with a mutation in the gene encoding the beta subunit of hemoglobin that results in a change from glutamic acid to valine at position 6. all other amino acids are identical to a normal hemoglobin molecule. based on the information above, which of the following mutations is the most likely cause of sickle-cell anemia

A single base-pair substitution in the gene encoding the beta subunit

altering patterns of gene expression in prokaryotes would most likely serve the organism's survival in which of the following ways

Allowing the organism to adjust to changes in environmental conditions

bacteriophages are viruses that infect bacteria. in an experiment, bacteriophages were labeled with either radioactive phosphorous or radioactive sulfur. the labeled bacteriophages were incubated with bacteria for a brief amount of time and then removed. the infected bacteria cells were found to contain significant amounts of radioactive phosphorous but not radioactive sulfur. Based on the results of the experiment, which of the following types of molecules did the bacteriophages most likely inject into the bacteria cells

DNA

which of the following removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments

DNA polymerase I

enzyme used to position nucleotides during DNA replication

DNA polymerase III

the genetic code is essentially the same for all organisms. From this, one can logically assume all of the following EXCEPT

DNA was the first genetic material

gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following

Eukaryotic exons may be spliced in alternative patterns

eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following

Gaps left at the 5' end of the lagging strand because of the need for a 3' onto which nucleotides can attach

what is the role of DNA ligase in the elongation of the lagging strand during DNA replication

Join Okazaki fragments together

5'-GACCGCAUGGUGACGAAAUUUGGCCAUUAA-3' Based on the universal genetic code, which of the following represents the correct polypeptide that will result from translation of the mRNA molecule shown, beginning with the first available start codon

Met-Val-Thr-Lys-Phe-Gly-His

DNA -(step 1)-> pre-mRNA -(step 2)-> mRNA -(step 3)-> protein which of the following best describes an event during step two in the simplified model above

Noncoding sequences are removed from a newly synthesized RNA molecules

the p53 protein regulates a cellular response to DNA damage. Based on the diagram above, which of the following best describes the role of p53 in the response to DNA damage

Phosphorylated p53 stimulates transcription of p21, and the resulting p21 protein suppresses cell division until the DNA damage is repaired

in eukaryotes, there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein

RNA polymerase II

for a repressible operon to be transcribed, which of the following must occur

RNA polymerase must bind to the promoter, and the repressor must be inactive

the following DNA sequence is a small part of the coding (nontemplate) strand from the open reading frame of the B-hemoglobin gene. Given the codon chart, what would be the effect of a mutation that deletes the G at the beginning of the DNA sequence 5'-GTT-TGT-CTG-TGG-TAC-CAC-GTG-GAC-TGA-3'

The reading frame of the sequence would shift, causing a change in the amino acid sequence after that point

from the following list, which is the first event in translation in eukaryotes

The small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

the table below shows the amino acid sequence of the carboxyl-terminal segment of a conserved polypeptide from four different, but related, species. Each amino acid is represented by a three-letter abbreviation, and the amino acid residues in the polypeptide chains are numbered from the amino end to the carboxyl end. Empty cells indicate no amino acid is present. a. assuming that species I is the ancestral species of the group, explain the most likely genetic change that produced the polypeptide in species II and the most likely genetic change that produced the polypeptide in species III b. predict the effects of the mutation on the structure and function of the resulting protein in species IV

a. the polypeptide in species two was most likely caused by a missense point mutation because species two only has one different amino acid (lysine). A different nucleotide was most likely substituted during transcription. The most likely genetic change that produced polypeptide three is a nonsense point mutation that caused a stop codon to be translated instead of glutamic acid b. the mutation in species four was most likely a frameshift mutation that added or deleted a nucleotide near the position of amino acid five. The resulting protein from species four will most likely have a very different structure and function because half of the amino acids are different.

the figure represents the process of expression of gene X in a eukaryotic cell. a. the primary transcript in the figure is 15 kilobases (kb) long, but the mature mRNA is 7kb in length. Describe the modification that most likely resulted in the 8kb difference in the length of the mature mRNA molecule. Identify in your response the location in the cell where the change occurs b. predict the length of the mature gene X mRNA if the full-length gene is introduced and expressed in prokaryotic cells. Justify your prediction

a. this was most likely caused by the splicing out of the introns from the primary transcript. this occurs in the nucleus before the mature mRNA exits and goes to the ribosome. b. the mature gene X mRNA, if introduced and expressed in prokaryotic cells, would most likely be 15kb long, because prokaryotic cells don't undergo RNA processing. Their transcription and translation occur simultaneously in the cytoplasm (since prokaryotes have no nucleus).

Muscle cells and nerve cells in one species of animal owe their differences in structure to

having different genes expressed

enzyme used to unwind and unzip DNA

helicase

the Trp operon is a coordinately regulated group of genes (trpA-trpE) that are required for tryptophan biosynthesis in E.coli. Based on the figure shown above, which of the following correctly describes the regulation of the Trp operon

in the presence of tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon

enzyme used during replication to attach Okazaki fragments to each other

ligase

steroid hormones, such as testosterone, pass through the plasma membrane and bind to an intracellular protein, as shown in the diagram below. The hormone-receptor complex then enters the nucleus, where it interacts with DNA to promote transcription of a specific gene. Based on the information presented, which of the following will also occur in response to steroid signaling

production of a specific mRNA will increase as a result of the binding of the hormone-receptor complex to the DNA

process in which naked DNA is taken up by a bacterial or yeast cell

reverse transcription

enzyme used to extend telomeres

telomerase

mutations in DNA are usually caused by chemical or radiation damage to DNA molecules, followed by imperfect repair of the damage. Immediately after this kind of imperfect repair, there may be a mismatched base pair in the DNA. The illustration below shows an example of a mismatch, with the relevant base pairs in bold. Which of the following best represents the DNA of the two daughter cells produced when a bacterial cell with this particular mismatch replicates its DNA and divides

the mutant has bases A and T bolded; the normal has bases G and C bolded

in both eukaryotes and prokaryotes, gene expression is primarily regulated at the level of

transcription

process in which RNA is produced by using a DNA template

transcription

process in which a protein is assembled at a ribosome

translation

the tryptophan operon is a repressible operon that is

turned off whenever tryptophan is added to the growth medium