final exam 183
Is it possible to generate two polypeptides with the same amino acid sequences from translation of two mRNAs that have different sequences?
Yes
Which of the following correctly describe(s) tRNAs?
tRNAs interact with mRNAs via hydrogen bonds formed between complementary nucleotides.
What does it mean if a particular type of tRNA can wobble?
tRNAs with that sequence can interact with multiple codons that all correspond to the same amino acid
In the context of cellular information processing, what is a mutation?
A change in the DNA sequence
If there's 15% adenine (A) nucleotides, what is the percentage of cytosine (C) in the DNA?
35% the percentage of A in a helix is equal to the percentage of T. The remaining percentage consists of C's and G's, and is equally split between the two nucleotides because they pair up. For this question, the helix has 15% A, 15% T, 35% C, and 35% G.
Which feature of the genetic code ensures that translation of a single mRNA sequence will always result in the same amino acid sequence?
A codon only corresponds to one type of amino acid.
Which of the following nonsense mutations would be most likely to have the LEAST effect in a cell?
A nonsense mutation at the very end of the coding region.
Which of the following correctly describes silent mutations?
A silent mutation changes the DNA sequence of a gene and the mRNA sequence produced by transcription of the gene, but does not alter the polypeptide sequence generated by translation.
Which of the following correctly describes tRNAs in cells?
A. A specific type of tRNA can only be attached to one type of amino acid. B. The anticodon of a tRNA determines with which codon of an mRNA it interacts. C. The enzymes that attach amino acids to tRNAs determine which codons correspond to which amino acids. D. A tRNA only has one anticodon. E. All of the above --> right ans
Which of the following correctly describe(s) nucleic acids?
A. Both DNA and RNA are chains of nucleotides connected by covalent bonds B. The nucleotides present in RNA are different from the nucleotides present in DNA C. DNA molecules have two nucleic acid strands, while RNA molecules are single-stranded D. DNA functions as information storage, while RNAs serve as temporary messages E. All of the above --> Right answer
Select ALL statements that correctly describe gene expression.
All genes must be transcribed to be expressed, but expression of some genes does not require translation. Different types of cells in a multicellular organism all have the same genes.
Which of the following correctly describes the role of RNA primers in DNA replication?
An RNA primer is required to start formation of all new DNA strands.
Select ALL statements that correctly describe nucleotides.
Both DNA and RNA nucleotides that are complementary interact via hydrogen bonds formed between their nitrogenous bases. The nitrogenous base cytosine (C) is present in both DNA and RNA nucleotides.
Which of the following correctly describes mutations?
Both nonsense mutations and frameshift mutations alter the length of the polypeptide produced by expression of the gene.
Select ALL statements that correctly describe translation.
Covalent bonds are formed between amino acids An mRNA is translated in a specific direction Ribosomes move along an mRNA
Which of the following correctly describes the chemical bonds in a DNA molecule?
Covalent bonds connect nucleotides within a strand; hydrogen bonds hold the two strands of a DNA molecule together.
___________ allow complementary RNA nucleotides to interact with the template DNA strand. RNA polymerase forms ___________ to connect nucleotides in a strand.
Hydrogen bonds; phosphodiester (covalent) bonds
During transcription, RNA polymerase incorrectly adds a G instead of an A in the strand it is forming. This mistake changes a codon that normally corresponds to Thr to a codon that corresponds to Ala. What effect will this mistake have in a cell?
Multiple protein molecules in a cell will have Ala instead of Thr at one position in the polypeptide chain because an mRNA is translated multiple times.
Transcription involves using DNA as a template to generate a new RNA strand. In what way(s) are DNA and RNA different?
Nucleotides in DNA have the nitrogenous base thymine, but not uracil; RNA nucleotides have uracil, but not thymine
What part of DNA's structure allows it to be copied?
Nucleotides pair up in a specific way
select ALL statements that correctly describe a difference between DNA and RNA molecules
RNA is involved in both transcription and translation; DNA is involved in transcription, but not translation. DNA is only present in the nucleus of eukaryotic cells; RNA is present in both the nucleus and cytoplasm of eukaryotic cells
Which of the following statements accurately describes transcription of a gene?
RNA polymerase transcribes one strand of a gene strand in one direction.
Select ALL statements that correctly describe splicing.
Splicing takes place in the nucleus of eukaryotic cells. Splicing allows different polypeptides to be produced under different conditions by expression of the same gene.
A nucleotide is inserted in the middle of the coding region of a gene. What are the potential effects on the polypeptide produced by expression of the gene?
The insertion has the potential to alter only amino acids specified by codons after the inserted nucleotide, and could change the length of the polypeptide chain.
What feature of DNA's structure helps explain why the two strands of a DNA helix at a replication fork are copied via slightly different processes (one in a single piece, and the other in multiple pieces)?
The two strands of a DNA double helix go in opposite directions.
Why is the melting temperature of a DNA molecule that has mostly A-T base pairs lower than the melting temperature of a DNA molecule that has the same total number of base pairs, but is mostly G-C base pairs?
There are fewer hydrogen bonds between the two strands
Which of the following, if any, correctly describes stop codons?
There are no tRNAs that interact with stop codons.
Which of the following correctly describe(s) the three main processes involved in cellular information processing?
Translation is only involved in expression of genes that contain information to produce proteins. In DNA replication, all DNA in a cell is copied, but in transcription, only some DNA is copied. Transcription is the first step in expression of all genes. All of the above --> right answer.
The melting temperature of a DNA molecule is the temperature at which the two strands of the helix become separated from each other. If the two strands of a DNA molecule are held together more tightly, the melting temperature is higher because it takes more energy (heat) to separate them. If the two strands are held together less tightly, the melting temperature is lower. Based on what you know about the structure of DNA molecules, it is reasonable to predict that if you compare two DNA molecules with the same total number of base pairs,
a DNA helix that has mostly A-T base pairs will have a lower melting temperature than one with mostly G-C base pairs.
A gene contains the information for a protein with 612 amino acids. Which of the following mutations in the coding region of the gene would be most likely to result in a dysfunctional protein when the gene is expressed?
a substitution mutation that changed the codon for the third amino acid to a stop codon
A mutation in the DNA sequence of a gene results in the start codon of a gene being altered. Which of the following outcomes is a reasonable prediction?
mRNAs generated by expression of the gene might not be translated.
You isolate an RNA molecule from a cell and determine that it is composed of 20% cytosine (C) nucleotides. Can you determine the percentage of guanine (G) in the RNA?
no Because an RNA molecule is just one strand (single-stranded), the number of Cs and Gs (or As and Us) are not necessarily equal. A single strand of RNA can fold into different shapes due to the hydrogen bonds that form between complementary nucleotides (G with C and A with T). However, because there isn't a second, complementary strand in RNA (like there is in DNA), it isn't guaranteed that for every C there is a G or that for every A there is a U.
What type(s) of substitution mutations can change the length of the polypeptide chain generated by expression of a gene?
nonsense
Select ALL statements below that correctly describe BOTH DNA replication and transcription.
process requires a template DNA strand new strands are formed in a specific direction a polymerase enzyme forms a complementary strand a specific DNA sequence indicates start
You isolate DNA from a prokaryotic cell and determine that the DNA is composed of 15% adenine (A) nucleotides. Can you determine the percentage of cytosine (C) in the DNA?
yes
