Question

Which of the following is involved in controlling gene expression? a. the occurrence of transcription b. activity of the polypeptide product c. life expectancy of the mRNA molecule in the cell d. All of these are involved.

Short answer

The correct answer is d. All of these are involved in controlling gene expression, as transcription, activity of the polypeptide product, and the life expectancy of the mRNA molecule in the cell all play essential roles in the regulation and control of gene expression.

Step-by-step solution

Define gene expression

Gene expression is the process by which genetic information stored in genes is used to produce functional products, such as proteins, necessary for the proper functioning of cells and organisms. This process is regulated at several levels, including transcription, translation, and post-translational events.

Evaluate the options

Now let's evaluate each option: a. the occurrence of transcription: Transcription is the first step of gene expression, where the genetic information in DNA is copied into mRNA. The occurrence of transcription determines which genes are expressed and at what levels, making it an essential factor in controlling gene expression. b. activity of the polypeptide product: After translation, proteins can undergo various modifications and regulatory processes that can impact their activity, stability, and localization in the cell. These modifications and processes can influence gene expression by altering the activity of the protein. c. life expectancy of the mRNA molecule in the cell: The stability and decay of mRNA molecules influence the levels of gene expression. An mRNA molecule with a longer life has a higher probability of being translated into protein, leading to a higher level of gene expression.

Determine the correct answer

As we can see, all three options play a role in controlling gene expression, so the correct answer is: d. All of these are involved.

Key concepts

Transcription

Transcription is the initial and critical step in the process of gene expression. It essentially acts as a blueprint copying mechanism that transfers the genetic information encoded in DNA into messenger RNA (mRNA). This step determines which genes are activated and how much mRNA is produced, thereby influencing the amount of protein synthesized.

• DNA is unzipped, exposing the sequence of nucleotides to be copied.
• An enzyme called RNA polymerase plays a pivotal role by attaching to the DNA template strand and synthesizing a complementary strand of RNA.
• The newly formed mRNA strand carries the genetic instructions necessary for protein synthesis.

By controlling transcription, cells can selectively express or silence genes as needed, responding to specific signals and environmental conditions.

Translational Regulation

Translational regulation refers to the control of the frequency and speed at which mRNA is translated into a polypeptide or protein. It is a layer of gene expression control that takes place after transcription and before the protein becomes fully functional. Cells use various mechanisms to regulate translation, including:

• The availability of ribosomes and translation initiation factors.
• The presence of specific regulatory proteins that can enhance or suppress translation.
• The initiation sequence of the mRNA itself, which can bind better or worse to ribosomal subunits.

This type of regulation ensures that proteins are synthesized at the right time and in the right amounts, conserving resources and optimizing the cell's response to changes.

mRNA Stability

mRNA stability significantly impacts gene expression levels by determining how long an mRNA can reside in the cell and be available for translation. The longer the mRNA remains intact, the higher the potential for protein synthesis from that message.

• Specific sequences or motifs in the mRNA can influence its stability, signalling the cell machinery to either protect or degrade the mRNA.
• RNA-chaperone proteins may bind to mRNA molecules to protect them from degradation.
• Various cellular and environmental signals can trigger mRNA decay when necessary, a process critical for resource management and cellular response adaptations.

By modulating mRNA stability, cells finely tune gene expression, ensuring proteins are produced in response to demand and conditions.