In need of help for these two questions. Thank you in advance!
Restriction Enzyme A has the recognition sequence 5′- CTGCAG -3′. Restriction Enzyme B has the recognition sequence 5′- GCGC -3′. Based on this information, you can infer that:
A. Enzyme A will cut the genome into fewer pieces than will Enzyme B.
B. Enzyme A will cut a genome into more pieces than will Enzyme B.
C. Enzyme A will generate DNA pieces with blunt ends and Enzyme B will generate DNA pieces with sticky ends.
D. NONE OF THESE
Which of the following types of gene mutation in a protein-coding gene usually has the least-
severe (i.e., least-deleterious) phenotype?
A. base deletions
B. All generate equally severe phenotypes.
C. missense substitutions
D. nonsense substitutions
1)
2) C. missense substitutions
To answer the first question about restriction enzymes A and B, we need to compare their recognition sequences.
Enzyme A has the recognition sequence 5′- CTGCAG -3′, which means it recognizes the sequence CTGCAG on the DNA strand. Enzyme B has the recognition sequence 5′- GCGC -3′, which means it recognizes the sequence GCGC on the DNA strand.
From this information, we can determine that the correct answer is C. Enzyme A will generate DNA pieces with blunt ends, and Enzyme B will generate DNA pieces with sticky ends.
To explain how we arrived at this answer, restriction enzymes work by recognizing specific sequences on a DNA molecule and cutting the DNA at or near those sequences. The recognition sequences are usually palindromic, meaning they read the same forward and backward on both DNA strands.
In this case, Enzyme A recognizes the sequence CTGCAG, which is palindromic, while Enzyme B recognizes the sequence GCGC, which is also palindromic.
When Enzyme A cuts the DNA, it will create blunt ends, where both ends of the DNA fragment have no overhanging single-stranded sequences. On the other hand, Enzyme B will cut the DNA and leave short, single-stranded overhangs of GCGC sequences called sticky ends. These sticky ends can base pair with complementary DNA sequences, allowing for easier manipulation in genetic engineering techniques like DNA cloning.
Now let's move on to the second question about gene mutations in a protein-coding gene and the phenotype associated with each mutation.
Different types of gene mutations can have different effects on the phenotype. The question asks for the type of mutation that usually has the least severe or least deleterious phenotype.
The correct answer is C. missense substitutions.
To explain why, let's briefly define the types of mutations mentioned:
1. Base deletions: These mutations involve the removal of one or more nucleotides from the DNA sequence. They can result in frameshift mutations, where the reading frame is shifted and subsequent codons are incorrect, leading to non-functional or truncated proteins.
2. Missense substitutions: These mutations involve the substitution of one nucleotide for another, resulting in a different amino acid being encoded in the protein sequence. Depending on the specific change, missense mutations can have varying effects on protein structure and function. Some missense mutations can be neutral and have no effect on the protein's function, while others can lead to mild or moderate changes in function.
3. Nonsense substitutions: These mutations involve the substitution of a nucleotide that changes an amino acid-coding codon into a premature stop codon. This results in the production of a truncated protein that is usually non-functional.
Based on this information, we can infer that missense substitutions usually have the least severe phenotype. While missense mutations can potentially alter the function of a protein, they do not always result in a complete loss of function or a non-functional protein like nonsense substitutions. Additionally, the effects of missense mutations can vary depending on the specific amino acid change and its location within the protein.
Therefore, the least severe or least deleterious phenotype is associated with missense substitutions (option C).