Unit 6 FRQ Answers (SG)
The flow of genetic information from DNA to protein in eukaryotic cells is called the central dogma of biology. c)The central dogma does not apply to some viruses. Select a specific virus or type of virus and explain how it deviates from the central dogma.
A retrovirus like HIV deviates form the central dogma because instead of creating proteins from DNA, it uses host cells to create DNA from the virus's RNA.
Auxins are plant hormones that coordinate several aspects of root growth and development. Indole-3-acetic acid (IAA) is an auxin that is usually synthesized from the amino acid tryptophan (Figure 1). Gene Trp-T encodes an enzyme that converts tryptophan to indole-3-pyruvic acid (I3PA), which is then converted to IAA by an enzyme encoded by the gene YUC. e) A researcher removed a plant nodule and identified several "cheater" rhizobacteria that do not produce IAA or fix nitrogen. Describe the evolutionary advantage of being a bacterial cheater in a population composed predominantly of non-cheater bacteria. Plants can adjust the amount of carbon-containing molecules released into nodules in response to the amount of nitrogen fixed int the nodule. Predict the change in the bacterial population that would cause the plant to reduce the amount of carbon-containing molecules provided to the nodule.
Cheaters/bacteria that benefit without producing IAA/fixing nitrogen have more energy for reproduction. There will be a decrease in the nitrogen fixing/noncheater bacteria or a decrease in the amount of nitrogen fixed by bacteria.
Auxins are plant hormones that coordinate several aspects of root growth and development. Indole-3-acetic acid (IAA) is an auxin that is usually synthesized from the amino acid tryptophan (Figure 1). Gene Trp-T encodes an enzyme that converts tryptophan to indole-3-pyruvic acid (I3PA), which is then converted to IAA by an enzyme encoded by the gene YUC. a) Circle one arrow that represents transcription on the template pathway. Identify the molecule that would be absent if enxyme YUC is nonfunctional.
Circle either the arrow from Trp-T -> mRNA or YUC -> mRNA. Identify: IAA
A researcher is studying patterns of gene expression in mice. The researcher collected samples from six different tissues in a healthy mouse and measured the amount of mRNA from six genes. The data are shown in FIgure 1. a) Based on the data provided, identify the gene that is most likely to encode a protein that is an essential component of glycolysis. Provide reasoning to support your identification.
Gene G because Gene G is the only gene expressed in all 6 tissues and glycolysis occurs in all 6 tissues, mRNA is the only mRNA present in all 6 tissues only for Gene G.
Information flow in cells can be regulated by various mechanisms. d) Epigenetics is the study of heritable chagnes in the phenotype caused by mechanisms other than changes in the DNA sequence. Describe ONE example of epigenetic inheritance.
Histone acetylation: The acetylation of histone tails in the nucelosomes loosens the structure of a chromsome, therefore increasing the rate of expression of the more exposed genes.
Cell signaling in eukaryotes is often dependent on receptor proteins located in the plasma membrane. During the production of the mature mRNA molecules coding for these receptors, pre-mRNA molecules are processed to remove introns and to connect exons together. The exons contain the sequences that code for proteins. In certain instances, different mature mRNA molecules can be formed form the same pre-mRNA by alternating splicing, which results in different protein sequences in the resulting polypeptides. Figure 1 represents the expression of a gene with 5 exons that can be alternatively spliced to produce receptor protein A and receptor protein B. a)Explain how ligand A and ligand B can cause identical cellular responses in a cell.
Ligand A and Ligand B can cause identical cellular responses in a cell because they use the same secondary messenger and activate the same signal transduction pathway.
Auxins are plant hormones that coordinate several aspects of root growth and development. Indole-3-acetic acid (IAA) is an auxin that is usually synthesized from the amino acid tryptophan (Figure 1). Gene Trp-T encodes an enzyme that converts tryptophan to indole-3-pyruvic acid (I3PA), which is then converted to IAA by an enzyme encoded by the gene YUC. c) Explain one feedback mechanism by which a cell could prevent production of too much IAA without limiting I3PA production.
Negative feedback/feedback inhibition/increasing amounts of IAA inhibits the pathway. Production of YUC enzyme is inhibited or YUC enzyme activity is inhibited.
A research team has genetically engineered a strain of fruit flies to eliminate errors during DNA replication. The team claims that this will eliminate genetic variation in the engineered flies. A second research team claims that eliminating errors during DNA replication will not entirely eliminate genetic variation in the engineered flies. b) Describe ONE mechanism that could lead to genetic variation in the engineered strain of flies.
One mechanism that could lead to genetic variation would be crossing over in meiosis. This exchange of genetic material leads to more genetic variation because during meiosis, some parts of DNA are exchanged between adjacent chromosomes, which leads to different DNA sequences, which would cause genetic variation in the engineered group of flies.
Information flow in cells can be regulated by various mechanisms. a) Describe the role of THREE of the following in the regulation of protein synthesis.
-RNA Splicing: introns are removed by splicesomes, therefore allowing exons to be joined together. -Repressor proteins: can bind to the promoter region of an operon in DNA, therefore preventing the attachment of RNA polymerase and therefore preventing the expression of that gene. -siRNA: facilitates degradation of mRNA, therefore inhibiting translation
Information flow in cells can be regulated by various mechanisms. c) Epigenetics is the study of heritable changes in the phenotype caused by mechanisms other than changes in the DNA sequence. Describe ONE example of epigenetic inheritance.
1. Carcinogens (ex. cigarette smoke)Effect: DNA is altered/damaged which affects the products of the affected genes 2. Viruses: disrupt gene sequence
Information flow in cells can be regulated by various mechanisms. b) Identify TWO environmental factors that increase the mutation rate in an organism, and discuss their effect on the genome of the organism.
1. Silent mutation: when a one nucleotide is changed and there is no change in the amino acid/protein sequence 2. Substitution (missense): when one nucleotide change causes a new codon, therefore a different amino acid/protein sequence 3. Substitution (nonsense): when one nucleotide change causes a stop codon, therefore the protein is truncated or not formed at all
A research team has genetically engineered a strain of fruit flies to eliminate errors during DNA replication. The team claims that this will eliminate genetic variation in the engineered flies. A second research team claims that eliminating errors during DNA replication will not entirely eliminate genetic variation in the engineered flies. c) Describe how genetic variation in a population contributes to the process of evolution in the population.
Genetic variation contributes to the process of evolution because it leads to the expression of different phenotypes. Depending on environmental conditions, one phenotype may be more advantageous for an organism than another. For example, if there are two types of birds, one short beaked and one long beak, and the long beak allows the bird to gain more access to food, the long beak phenotype is more fit than the short beak version. This will ultimately mean that the long beak bird has more chance of living to reproductive age, and will therefore have more offspring, and will help the long beak trait continue to thrive, meaning there will be more long beaked birds than short beak birds.
The flow of genetic information from DNA to protein in eukaryotic cells is called the central dogma of biology. b)Cells regulate both protein synthesis and protein activity. Discuss TWO specific mechanisms of protein regulation in eukaryotic cells.
Protein regulation includes histone acetylation and DNA methylation. Histone acetylation brings acetyl groups that are positively charged and cause the 41 histones to not bind to each other as tightly. This loose packaging of the DNA allows RNA polymerase better access to DNA to transcribe for that protein. In reverse, DNA methylation affects methyl groups that induce tighter packaging of the DNA. This DNA is less likely to be transcribed and have proteins synthesized. In addition operons can be activated or inactivated to have its protein that it codes for synthesized. Repressible operons are always having their proteins synthesized unless an enzyme binds to the active site, stopping the RNA molecule from being able to transcribe genes. Inducible operons are always turned off and not transcribed until the enzyme that is bound to its active site is stimulated to let go, granting access to RNA polymerase.
The flow of genetic information from DNA to protein in eukaryotic cells is called the central dogma of biology. a) Explain the role of each of the following in protein synthesis in eukaryotic cells. - RNA Polymerase -Splicesomes (snRNPs) -Codons -Ribosomes -tRNA
RNA polymerase is an enzyme that attaches to a DNA sequence and begins transcribing it to mRNA. Before the mRNA can leave the nucleus, it undergoes RNA splicing by the splicesomes. These enzymes cut out the intron part of the DNA that isn't going to be translated, and leaves the exons to be translated. The final mRNA then leaves the nucleus and is patterned into codons. Codons are the mRNA sub units consisting of 3 nucleotides each. A ribosome attaches itself to the mRNA to stabilize it. Ribosomes are where proteins are made. Protein making is done by tRNA anticodons attaching itself to their respective complementary mRNA codons. When tRNA attaches, it brings with it an amino acid. These amino acids combine to the next amino acid brought by the next tRNA until the stop codon tells the tRNA to stop coding. Then the collected amino acids form a protein are released.
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.
In species 2, the most likely genetic change was a point mutation in which a single nucleotide is altered, which changes the amino acid being coded for. In species 3, the most likely genetic change was a point mutation that coded for a stop codon which halted production of the polypeptide prematurely.
A research team has genetically engineered a strain of fruit flies to eliminate errors during DNA replication. The team claims that this will eliminate genetic variation in the engineered flies. A second research team claims that eliminating errors during DNA replication will not entirely eliminate genetic variation in the engineered flies. a) Provide ONE piece of evidence that would indicate new genetic variation has occurred in the engineered flies.
One piece of evidence that would indicate a new variation has occurred in the engineered flies would be the appearance of a new phenotype. If all the flies were engineered to have black eyes and if some generations down the line, a red eyed fly appeared, genetic variation would have occurred.
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. b) Predict the effects of the mutation on the structure of the resulting protein in species IV. Justify your prediction.
The protein produced in species 4 will have a much different structure, and the function will be radically different. The frame shift mutation that resulted in the polypeptide completely altered the polypeptide chain which in turn will change the interactions between amino acids so the structure is changed. The altered amino acid will cause the proteins function to shift.
A molecule of messenger RNA (mRNA) has just been synthesized in the nucleus of a human cell. a) What types of modifications may occur to this RNA before it leaves the nucleus?
The RNA needs a GTP cap added to the 5' end, a polyA tail added to the 3' end. Also, splicing must occur, where the spliceosome must attach to the introns and remove them. It also needs to splice exons together in order to produce mature RNA. The exons need to be expressed as protein.
A researcher is studying patterns of gene expression in mice. The researcher collected samples from six different tissues in a healthy mouse and measured the amount of mRNA from six genes. The data are shown in Figure 1. b) The researcher observed that tissues with a high level of gene H mRNA did not always have gene H protein. Provide reasoning to explain how tissues with high gene H mRNA levels can have no gene H protein.
The mRNA is not exported from the nucleus, Gene H mRNA is not translated since RNA interference prevents translation, and post-transcriptional modifications.
A molecule of messenger RNA (mRNA) has just been synthesized in the nucleus of a human cell. b)Once in the cytoplasm, how is the mRNA translated to a protein.
The mRNA will attach to the small ribosomal unit and then the large ribosomal unit. Then the mRNA will be decoded with its codon's tRNA. The anticodon will bring amino acids from the cytoplasm to the mRNA. The tRNA will come in at the A site and a peptide bond will form between amino acids at the A and P sites. Now the empty tRNA will exit the ribosome and this will continue until the stop sequence is reached.
A molecule of messenger RNA (mRNA) has just been synthesized in the nucleus of a human cell. c) If the cell is a secretory cell, how is the protein from part (b) eventually targeted, packaged, and secreted to the exterior of the cell?
The protein needs an srp signal which will send it to the ER, and then on to the golgi bodies, which will pack it away in vesicles, which will transfer it to the cell membrane where it can exit through exocytosis.
Cell signaling in eukaryotes is often dependent on receptor proteins located in the plasma membrane. During the production of the mature mRNA molecules coding for these receptors, pre-mRNA molecules are processed to remove introns and to connect exons together. The exons contain the sequences that code for proteins. In certain instances, different mature mRNA molecules can be formed form the same pre-mRNA by alternating splicing, which results in different protein sequences in the resulting polypeptides. Figure 1 represents the expression of a gene with 5 exons that can be alternatively spliced to produce receptor protein A and receptor protein B. b) Predict the most likely effect of a two-nucleotide deletion in the middle of the intron located between exons 4 and 5 on the structure of protein A. Justify your prediction.
There is no change because the intron does not contain protein coding info.
Auxins are plant hormones that coordinate several aspects of root growth and development. Indole-3-acetic acid (IAA) is an auxin that is usually synthesized from the amino acid tryptophan (Figure 1). Gene Trp-T encodes an enzyme that converts tryptophan to indole-3-pyruvic acid (I3PA), which is then converted to IAA by an enzyme encoded by the gene YUC. b)Predict how the deletion of one base pair in the fourth codon of the coding region of gene Trp-T would most likely affect the production of IAA. Justify your prediction.
There would be a reduction in IAA production or no production of IAA. The mutation will result in the translation of an inactive/nonfunctional Trp-T enzyme, no translation of Trp-T enzyme, and no/reduced production of I3PA.
Information transfer is fundamental to all living organisms. For the following examples explain in detail how the transfer of information is accomplished. A gene in a eukaryotic cell is transcribed and translated to produce a protein.
Transcription is a sequence of DNA translated into a sequence of mRNA. RNA polymerase binds to the promoter and makes complimentary RNA strand using uracil instead of thymine, adding a 5' cap and 3 poly-A tail. snRNPs cut out introns and bind exons. Translation is mRNA base sequences being translated into amino acids. There are two ribosomal subunits with three action sites. tRNA carries over start codon to being synthesis and also has anticodons complementary to mRNA codons. Amino acids are coded by a triplet code of bases and once the stop codon is reached, the polypeptide chain is released and ribosomal subunits detach.
P450 encodes an ezyme that detoxifies insecticides. Abc8 encodes a transporter protein that pumps insecticides out of cells. Cps encodes an external structural protein located in the exoskeleton that greatly reduces the absoprtion of insecticides. Based on this information and the data in Figure 1, explain how a deletion of both P450 and Abc8 results in lower survival in bedbugs compared with a deletion of Cps only.
When both Abc8 and P450 are deleted the cell can t get rid of the insecticide that has been absorbed. SO because Cps doesn't encode for an exoskeleton that completely stops the insecticide from getting into the cell, only insecticide that does get into the cell remains toxic and has no way of leaving. When Cps is deleted, the survival rate is much higher because although a higher concentration of insecticide is getting into the cell it is getting detoxified and being removed through the transporter dumps encoded by Abc8.
