Question

1. A biologist discovers a new unicellular organism and isolates various components making up the organism. One component contains phosphate, uracil, adenine, ribose, guanine, and cytosine. Which of the following could be the identity of this component? (1 point)
DNA
repressor
tRNA
All of the above are correct.

2. Which of the following are necessary for transcription? (1 point)
RNA polymerase, DNA, ribonucleotides
DNA polymerase, RNA, deoxyribonucleotides
RNA polymerase, DNA polymerase, DNA
ribosome, tRNA, amino acids

3. What peptide would you expect to result from a 21-nucleotide-long DNA sequence that contains only the base adenine?
a peptide composed of 7 phe
a peptide composed of 21 phe
a peptide composed of 7 lys
a peptide composed of 21 lys

4. After a strain of bacterial cells is exposed to a chemical mutagen, 30% of the cells produce new colonies that continue to grow. Which of the following can be concluded?
Some cells underwent beneficial mutations.
Some cells underwent neutral mutations.
Some cells underwent lethal mutations.
All of the above are correct.
5. A DNA sequence reads -A-C-C-T-G-C-. Which of the following statements is plausible?
Mutation to -A-C-G-T-G-C- is a neutral mutation.
Mutation to -A-A-G-T-G-C- is a frameshift mutation.
Mutation to -A-C-C-T-G-T- is an advantageous mutation.
Mutation to -A-A-G-T-G-C- is a lethal mutation.

Answer 1

Q1. The answer is tRNA.
Through the process of elimination, a repressor is a protein and, thus, consists of amino acids. On the other hand, DNA and tRNA consist of phosphate, adenine, guanine, and cytosine. However, among mentioned components, uracil and ribose are characteristic of  RNAs. DNA consists of a phosphate, deoxyribose and bases: adenine, thymine, guanine, cytosine. RNA (tRNA, mRNA, rRNA) consists of phosphate, ribose and bases: adenine, uracil, guanine, cytosine.

Q2. The answer is RNA polymerase, DNA, ribonucleotides.
Transcription is a process in which DNA sequence transcribes into messenger RNA (mRNA). RNA polymerase is an enzyme necessary for this process. It attaches to DNA sequence and helps ribonucleotides to bind to complementary bases on DNA. After mRNA is transcribed, RNA polymerase de-attaches from DNA sequence and mRNA is free.

Q3. The answer is a peptide composed of 7 phe
Three nucleotide bases on mRNA are called codon. Each codon codes for specific amino acid. Genetic codon chart has summarised RNA codons and their amino acids.
Now, we have a 21-nucleotide-long DNA sequence that contains only the base adenine: AAAAAAAAAAAAAAAAAAAAA
Next, we must transcribe it into mRNA so we can read codon chart. According to the base complementarity rule, adenine will bind to uracil in RNA:
DNA:   AAAAAAAAAAAAAAAAAAAAA
RNA:   UUUUUUUUUUUUUUUUUUUU
We now have a 21-nucleotide-long RNA sequence that contains only the base uracil, and let separate it on triplets (three nucleotide bases):
RNA:   UUU-UUU-UUU-UUU-UUU-UUU-UUU
After taking a look at genetic codon chart, amino acid that is appropriate for UUU triplet is Phe:
RNA:        UUU-UUU-UUU-UUU-UUU-UUU-UUU
Protein:    Phe - Phe - Phe -Phe- Phe - Phe - Phe
After counting, there are 7 phe amino acids in the protein.

Q4. The answer is Some cells underwent beneficial mutations.
A chemical mutagen was added to the bacterial strain in order to kill all of the bacteria. However, 30% of the bacteria survived. This means that they underwent some mutations. Since that mutation helped them survive, it had some beneficial effect on bacterial survival. Therefore, some bacteria underwent beneficial mutations.

Q5. The answer is Mutation to -A-C-C-T-G-T- is an advantageous mutation.
A DNA sequence is -A-C-C-T-G-C- . It should be transcribed to mRNA sequence according to the base complementarity rule by which, in RNA, adenine will bind uracil, and guanine will bind cytosine:
Normal sequence:                                             Mutated sequence:
DNA: -A-C-C-T-G-C-                                           DNA: -A-C-C-T-G-T-
RNA: -U-G-G-A-C-G-                                          RNA:  -U-G-G-A-C-A-
Now, after comparing RNA triplets to amino acids in genetic codon chart:
Normal sequence:                                             Mutated sequence:
RNA:       -UGG-ACG-                                         RNA:        -UGG-ACA-
Protein:   - Trp - Thr -                                          Protein:   - Trp  - Thr -
This mutation might  be advantageous among all other mentioned choices.