17. When errors in nucleotide sequencing occur,

a. DNA polymerases replaces the incorrect nucleotide with the correct nucleotide
b. enzymes dissolve the incorrect nucleotide so DNA polymerase can add the correct one
c. purines replace pyrimidines in the DNA molecule
d. DNA polymerase proofreads for errors while another enzyme corrects it
A?

18. Which of the following is NOT a step in transcription?
a. RNA polymerase unwinds the double helix of the transfer RNA
b. RNA polymerase attaches to a gene's promoter region on a strand of DNA
c. RNA polymerase adds complementary RNA nucleotides to the growing strand of RNA
d. RNA polymerase unwinds and separates the DNA strands
D?

19. During translation, the amino acid detaches from the transfer RNA molecule and attaches to the end of a growing protein chain when
a. the ribosomal RNA anticodon binds to the messenger RNA codon
b. the transfer RNA anticodon binds to the messenger RNA codon
c. a "stop" codon is encountered
d. the protein chain sends a signal through the nerve cells to the brain
Not sure...

21. Which of the following procedures is NOT a usual step in a genetic engineering experiment?
a. inducing a mutation in a source of chromosome
b. cleaving DNA with a restriction enzyme
c. recombining pieces of DNA from different species
d. cloning and screening target cells
I'm not sure between A and C, but I think it's C...

Thanks
-MC

17. The correct answer is d. DNA polymerase proofreads for errors while another enzyme corrects it.

To determine the correct answer, we need to understand the process of nucleotide sequencing and how errors are corrected. During nucleotide sequencing, DNA polymerase adds complementary nucleotides to the growing DNA strand. However, sometimes errors can occur in this process, such as the incorporation of an incorrect nucleotide.

In order to correct these errors, DNA polymerase has a built-in proofreading function. It checks each nucleotide it adds to the growing strand for accuracy. If an incorrect nucleotide is detected, DNA polymerase removes it and replaces it with the correct nucleotide. This proofreading function helps to maintain the integrity and accuracy of the DNA sequence.

Additionally, there are other enzymes involved in the error correction process. For example, exonucleases can remove incorrect nucleotides from the DNA strand, enabling DNA polymerase to add the correct nucleotide.

Therefore, the correct answer is d. DNA polymerase proofreads for errors while another enzyme corrects it.

18. The correct answer is a. RNA polymerase unwinds the double helix of the transfer RNA.

To determine the correct answer, we need to understand the process of transcription. Transcription is the synthesis of RNA from a DNA template. It involves several steps:

1. RNA polymerase binds to a gene's promoter region on a strand of DNA.
2. RNA polymerase unwinds and separates the DNA strands.
3. RNA polymerase adds complementary RNA nucleotides to the growing strand of RNA.
4. RNA polymerase continues transcribing until it reaches a termination signal or "stop" codon.

Based on these steps, we can see that DNA double helix unwinding occurs during transcription. However, the unwinding specifically involves the separation of the DNA strands, not the transfer RNA (tRNA) as mentioned in option a. Therefore, the correct answer is a. RNA polymerase unwinds the double helix of the transfer RNA.

19. The correct answer is c. a "stop" codon is encountered.

During translation, the process of protein synthesis, the amino acids are added to a growing protein chain based on the instructions provided by messenger RNA (mRNA). This process involves the interaction between transfer RNA (tRNA) and mRNA.

Each tRNA molecule has an anticodon that corresponds to a specific codon on the mRNA. The codons on mRNA specify the sequence of amino acids in the protein. The interaction between the tRNA anticodon and the mRNA codon ensures that the correct amino acid is incorporated into the growing protein chain.

However, when a "stop" codon is encountered in the mRNA sequence, it signifies the end of protein synthesis. At this point, the amino acid detaches from the tRNA molecule and attaches to the end of the growing protein chain. Therefore, the correct answer is c. a "stop" codon is encountered.

21. The correct answer is a. inducing a mutation in a source of chromosome.

In genetic engineering experiments, various procedures are performed to manipulate DNA and create desired genetic modifications. These procedures may involve techniques such as gene cloning, DNA sequencing, and gene transfer.

However, inducing a mutation in a source of chromosome is not a usual step in a genetic engineering experiment. Mutations refer to changes in the DNA sequence, which can occur naturally or as a result of environmental factors. Genetic engineering experiments typically focus on altering specific genes or introducing foreign DNA, rather than inducing random mutations in a chromosome.

On the other hand, the other options are commonly used steps in genetic engineering experiments:
- Cleaving DNA with a restriction enzyme is a common technique to cut DNA at specific sites.
- Recombining pieces of DNA from different species is a key step in creating recombinant DNA molecules.
- Cloning and screening target cells involve the replication and analysis of genetically modified cells.

Therefore, the correct answer is a. inducing a mutation in a source of chromosome.