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What are the three main parts of an RNA nucleotide?
A ribose molecule, a phosphate group, and a nitrogenous base
What might be the effect of a mutation in the promoter sequence of a gene?
RNA polymerase might be unable to bind to the promoter, and, as a result, the gene would not be transcribed.
What must happen to a DNA molecule before RNA polymerase can begin to assemble nucleotides into a new RNA strand?
The DNA molecule must be separated into two strands.
How many amino acids could be specified if codons consisted of two nucleotides instead of three? What problem would this present for an organism making proteins using all 20 amino acids?
There could be 16 combinations of nucleotides, which is too few combinations for all 20 amino acid to have a unique code.
Within a cell, where does translation take place?
on ribosomes in the cytoplasm.
Describe the functions of the three kinds of RNA illustrated in Figure 13–8.
Messenger RNA provides the code for the translation, ribosomal RNA reads the code, and a tRNA molecule brings the next amino acid specified by the code.
What is the central dogma of molecular biology?Information is transferred from DNA to RNA to protein.
What is a polyploid organism?
has many sets of chromosomes.
What is one beneficial mutation that has happened in humans?
mutations that made stronger bones and better disease resistance.
Why is it beneficial for E. coli to have the ability to regulate the expression of the lac genes, rather than just express them all the time?
It would waste the cell’s energy and resources to build the lac proteins when they are not needed, as when E. coli are in an environment that has no lactose.
How does miRNA function to help block gene expression?
A molecule of miRNA is a small loop of RNA that combines with proteins to create a silencing complex that binds to and destroys mRNA that matches the miRNA’s sequence.
Explain why the Hox genes that are found in different animals are so similar to each other.
The Hox genes descended from the genes of common ancestors.
How do internal and external factors work together to regulate gene expression in the metamorphosis of a frog?
External forces (such as a drying pond) trigger internal factors (such as hormonal changes) that change the rate of metamorphosis.
Infer From which labeled structure in Figure 13–9 is structure D made? Identify that labeled structure.
Structure D is made from structure A, which is one of the strands of DNA.
Interpret Visuals Identify structure F in Figure 13–9. What does it specify?
Structure F is a codon that specifies the amino acid alanine.
Interpret Visuals What is structure E in Figure 13–9? What does it specify?Structure E is the start codon, which specifies the amino acid methionine.
Predict What would happen to structure F in Figure 13–9 if structure C were deleted?
The base sequence of the codon (structure F) would change from GCU to GUG.
Predict In Figure 13–9, what effect would the deletion of structure C have on the process that occurs during step Y?
The deletion of structure C would shift the reading frame of the codons during translation. As a result, the sequence of the amino acids that follows after structure C might change.
Interpret Visuals What process is illustrated in Figure 13–10? Translation
Interpret Visuals Identify structure C in Figure 13–10. ribosome.
Interpret Visuals Which labeled structure in Figure 13–10 is a codon? Structure F
Infer What is the relationship between the codons and anticodons? How is this relationship important to the structure of proteins? Use Figure 13–10 to explain your answer.
The codons and anticodons have complementary nitrogenous bases, allowing them to base pair. Because the kind of amino acid attached to a tRNA depends on the tRNA’s anticodon, the base pairing between the anticodons and codons brings a specific sequence of amino acids to the ribosomes. For example, the codon labeled F is complementary to the anticodon UAC and codes for the amino acid methionine.
Predict In Figure 13–10, what will happen after the ribosome joins the methionine and phenylalanine?
The bond between the methionine and its tRNA will be broken. The tRNA will move away from the ribosome, allowing it to bind with another methionine. The ribosome will move down the mRNA to the next codon.
Classify What term describes the general type of mutation occurring in A, B, C, and D in Figure 13–5? A chromosomal mutation
Interpret Visuals In Figure 13–5, which process or processes involve two chromosomes?
Process D involves two chromosomes.
Compare and Contrast Contrast process A and process B in Figure 13–5.
Process A results in the deletion of a segment of a chromosome. Process B results in the duplication of a segment of a chromosome.
Interpret Visuals During which process in Figure 13–5 does a segment of a chromosome become oriented in the reverse direction?
A segment of a chromosome becomes oriented in the reverse direction during process C.
Interpret Visuals In Figure 13–5, which process is a translocation? Process D is a translocation.
Contrast the functions of the three main types of RNA.
Messenger RNA carries copies of instructions for assembling proteins from DNA to the ribosomes. Ribosomal RNA is a component of the ribosomes. Transfer RNA carries amino acids to the ribosomes for assembly into proteins
Describe the process in which a molecule of pre-mRNA is converted into a final mRNA molecule.
After being transcribed from DNA, portions of the pre-mRNA molecule—called introns—are cut out from it. The remaining pieces, called exons, are then spliced together. Next, a cap and a tail are added to the opposite ends of the mRNA molecule, forming the final mRNA molecule.
How does transcription differ from DNA replication? Describe at least four differences.
Accept any four of the following answers: RNA polymerase is involved in transcription, whereas DNA polymerase is involved in DNA replication. During transcription, free nucleotides base pair with the nucleotides on only one strand of a DNA molecule, not both strands as in DNA replication. In transcription, the free nucleotides are RNA nucleotides, not DNA nucleotides. Transcription continues until a stop signal is reached on the DNA strand. DNA replication continues until the entire chromosome is replicated. At the end of transcription, one single-stranded RNA molecule is formed, not two double-stranded DNA molecules. The newly formed RNA molecule leaves the nucleus, whereas the newly formed DNA molecules stay in the nucleus.
Some substitution mutations have no effect on the final protein that is assembled by the ribosome. Use Figure 13–3 to provide specific examples that explain how having multiple codons specify the same amino acid makes this possible.
Most amino acids can be specified by more than one codon. This can help neutralize the effect of some substitution mutations. If a substitution mutation results in a new codon that specifies the same amino acid, the mutation will have no effect. For example, if a substitution mutation occurs in a “CUG,” codon, and a U is substituted for the C, the resulting codon, “UUG,” still codes for the amino acid Leu. In fact, if another substitution mutation happens and “UUG,” is changed to “UUA,” the codon would still specify Leu.
Explain the process of translation.
After a molecule of mRNA is transcribed in the nucleus it moves to the cytoplasm. A ribosome then positions itself at the start codon on the mRNA molecule. As each successive codon passes the ribosome, a molecule of tRNA brings an amino acid to the ribosome. Only a tRNA molecule with an anticodon that is complementary to the codon on the mRNA can attach an amino acid to the growing polypeptide chain. The ribosome attaches each new amino acid to the chain, and the bond holding the tRNA to the amino acid is broken. The ribosome moves to the next codon, and the process repeats until the entire mRNA molecule is translated.
Why is pesticide resistance considered a beneficial mutation in mosquitoes?
When pesticides are present, mosquitoes that have a mutation that allows them to be resistant to pesticides have an advantage over mosquitoes without that mutation. In an area being sprayed with pesticide, mosquitoes lacking the mutation would die, and the resistant mosquitoes would live. So, having the mutation is beneficial to the mosquitoes.
What might be the effects of a mutation in the gene that codes for the lac repressor in E. coli?
The lac repressor might be unable to bind with the operator. As a result, RNA polymerase would not be prevented from beginning the process of transcription, and the lac genes would be turned on permanently. Another effect of the mutation might be that the lac repressor would be unable to bind with lactose. As a result, the repressor would permanently bind with the operator, RNA polymerase would be prevented from binding to the promoter, and the lac genes would be turned off permanently.
How do eukaryotic cells regulate gene expression?
Eukaryotic cells also use RNA interference to block gene expression. A Dicer enzyme cuts a small loop of miRNA into tiny pieces. Then, the pieces bind with proteins to make a silencing complex. When the complex finds a piece of mRNA that has a code that matches its own code, it sticks to the mRNA and shuts it down.
Why is gene regulation necessary in the development of multicellular organisms? Use a specific example to support your argument.
Every cell that has a nucleus in a multicellular organism has all the genes to build that organism. But not every cell needs every gene, so it is important that the unneeded genes are switched off. For example, nerve tissue needs to be flexible, not stiff and rigid. So, the genes that code for the proteins that create the rigidity of bones would be inappropriate in nerves. Genes that create bone structure need to be turned off in nerve cells.
Why do some kinds of point mutations generally result in greater changes in proteins than others?
Point mutations include substitutions, insertions, and deletions of single nucleotides in DNA. Insertions and deletions have a greater effect on proteins than do substitutions, because insertions and deletions can affect every amino acid that is specified by the nucleotides that follow the point of mutation. In contrast, a substitution affects a single amino acid. A change in more than one amino acid is more likely to alter the ability of the protein to function normally than is a change in a single amino acid.