Question

1. The virus hijacks the cell, and RNA polymerases produce the complement to the positive stranded RNA genome. We can call these strands negative strands, and they then serve as templates for RNA polymerases to produce their complement. How does the sequence of these strands, the complement to the negative strands, compare with the original viral genome?

2-1. RNA polymerases lack proofreading ability. Define proofreading ability and describe its importance in replication of DNA genomes.

a. Why is this a critical function for human DNA polymerases?

b. What advantage might its absence give RNA viruses like SARS-CoV-2?

2-2. The positive stranded RNA serves as the template for protein synthesis.

a. What is the process called that involves converting the RNA sequence into a sequence of amino acids?

b. ​​​​​​​What is the cellular “workbench” of this process, and what is this “workbench” composed of (i.e., what structure accomplishes protein synthesis)?

c. ​​​​​​​How is the sequence of RNA converted into a sequence of amino acids?

d. ​​​​​​​Where does this process take place in the human cell?

3. Following protein synthesis, RNA genome and proteins assemble to form virus particles that then bud into the endoplasmic reticulum (ER) lumen and then on to the Golgi apparatus. Next, they are transported via Golgi vesicles to the cell membrane, where they are released via exocytosis. Define ER, Golgi apparatus, and exocytosis, and explain how this process undertaken by these viruses is comparable to processes regularly used by the cell.

4-1. Restriction enzymes ______.

-are naturally produced by bacteria to protect them from viral infections

-are like molecular "scissors" that cut at a specific DNA sequence

-are enzymes that restrict entry into cells by invading pathogens

-are isolated from human cells and are named after the cell type that produces them

4-2. BRCAII is a tumor suppressor gene located on chromosome pair 13. Inherited mutations in  BRCAII can predispose an individual to breast cancer. If Scarlet carries an inherited mutation for BRCAII and her husband Scott does not, what is the probability that their son inherited the mutated allele?

Answer 1

Ans. 1. The virus hijacks the cell and produces negative strand which is complementary to the positive stranded RNA genome. This negative strand is produced in the 3' to 5' direction. The complement to negative strand is again in 5' to 3' direction and it is similar in sequence to original viral genome, except that RNA polymerase does not have any proof reading ability. So, any defect in the sequence while incorporation of nucleotides is not corrected.

2-1. RNA polymerases produce complementary RNA sequence to original DNA strand. The synthesis of new RNA strand follows the principle of complementarity. So, A in the template strand pairs with U in the daughter RNA strand; G pairs with C and vice versa; T pairs with A. Now, if for any reason this pairing is mistaken and a nucleotide is paired with another nucleotide other than the assigned one, then the wrong nucleotide is removed by proofreading ability. This ensures that proper pairing between nucleotide sequences of DNA and RNA strand takes place.

a. This is a critical function for DNA polymerase as this enzyme is involved in a delicate process of DNA replication. If one daughter strand of DNA becomes defective due to improper proof reading ability of DNA polymerase, then it leads to formation of subsequent generations of defective daughter DNA strands. So, this is a critical function of the enzyme DNA polymerase.

b. Absence of this enzyme gives advantages to viruses like SARS-CoV-2 is that they can manipulate host genetic machinery more efficiently. They will gradually evolve by the production of novel proteins which gives them genetic advantage. These strains will then come out in more virulent forms which can pose serious threat to the health of the patient.

2-2. a. The process that converts RNA sequence to amino acid sequence of proteins is called translation.

b. The cellular "workbench" of this process is cell cytoplasm. The main part of the cell involved in this process is ribosome.

c. The sequence if RNA is converted to the sequence of amino acids with the help of tRNA. Ribosomes read the frame of RNA in sequence of three nucleotides called codons. The appropriate tRNA bearing the complementary anticodon is incorporated in the ribosome. Each codon encodes for a specific amino acid which is incorporated by ribosomes to form a chain of protein.

d. This process takes place in the cell cytoplasm just outside the nucleus. Certain ribosomes are attached to endoplasmic reticulum that carry out these functions.

(NOTE: I have answered all the subparts of questions 1 & 2 as per our guidelines. Please re post questions 3 and 4 separately, hope to help you soon. Thanks.)