Question 1#

The process that occurs during translational control of eukaryotic gene expression is:

A. Protein degradation

Four major steps in the control of eukaryotic gene expression (Fig. below). Transcriptional and posttranscriptional control determine the level of messenger RNA (mRNA) that is available to make a protein, while translational and posttranslational control determine the final outcome of functional proteins. Note that posttranscriptional and posttranslational controls consist of several steps. 

Four major steps in the control of eukaryotic gene expression. Transcriptional and posttranscriptional control determine the level of messenger RNA (mRNA) that is available to make a protein, while translational and posttranslational control determine the final outcome of functional proteins. Note that posttranscriptional and posttranslational controls consist of several steps.

 

Question 2#

All of the following transcription mechanisms occur in eukaryotes EXCEPT:

A. Chromatin structure changes to allow DNA to be accessible to the polymerase

Transcription mechanisms in eukaryotes differ from those in prokaryotes. The unique features of eukaryotic transcription are as follows:

1. Three separate RNA polymerases are involved in eukaryotes: RNA polymerase I transcribes the precursor of S.SS, ISS, and 28S rRNAs; RNA polymerase II synthesizes the precursors of messenger RNA (mRNA) as well as microRNA; and RNA polymerase III makes tRNAs and 5S rRNAs.
2. In eukaryotes, the initial transcript is often the precursor to final mRNAs, tRNAs, and rRNAs. The precursor is then modified and/or processed into its final functional form. RNA splicing is one type of processing to remove the noncoding introns (the region between coding exons) on an mRNA.
3. In contrast to bacterial DNA, eukaryotic DNA often is packaged with histone and nonhistone proteins into chromatins. Transcription will only occur when the chromatin structure changes in such a way that DNA is accessible to the polymerase.
4. RNA is made in the nucleus and transported into cytoplasm, where translation occurs. Therefore, unlike bacteria, eukaryotes undergo uncoupled transcription and translation.

Question 3#

The human genome contains approximately:

A. 35,000 to 40,000 genes

Genome is a collective term for all genes present in one organism. The human genome contains DNA sequences of 3 billion base pairs, carried by 23 pairs of chromosomes. The human genome has an estimated 25,000 to 30,000 genes, and overall, it is 99.9% identical in all people. Approximately 3 million locations where single-base DNA differences exist have been identified and termed single nucleotide polymorphisms. Single nucleotide polymorphisms may be critical determinants of human variation in disease susceptibility and responses to environmental factors.

Question 4#

If cyclin-dependent kinase (CDK) is to a cell as an engine is to a car, then cyclins and CKI are:

A. The key and ignition, respectively

The cell cycle is connected with signal transduction pathways as well as gene expression. Although the S and M phases rarely are subjected to changes imposed by extracellular signals, the G1 and G2 phases are the primary periods when cells decide whether or not to move on to the next phase. During the G1 phase, cells receive green- or red-light signals, S phase entry or G 1 arrest, respectively. Growing cells proliferate only when supplied with appropriate mitogenic growth factors. Cells become committed to entry of the cell cycle only toward the end of G1. Mitogenic signals stimulate the activity of early Gl cyclin-dependent kinases (CDKs) (eg, cyclin D/CDK4) that inhibit the activity of pRb protein and activate the transcription factor called E2F to induce the expression of batteries of genes essential for G1-S progression. Meanwhile, cells also receive antiproliferative signals such as those from tumor suppressors. These antiproliferative signals also act in the G1 phase to stop cells' progress into the S phase by inducing CKI production. For example, when DNA is damaged, cells will repair the damage before entering the S phase. Therefore, G1 contains one of the most important checkpoints for cell cycle progression. If the analogy is made that CDK is to a cell as an engine is to a car, then cyclins and CKI are the gas pedal and brakes, respectively. Accelerated proliferation or improper cell cycle progression with damaged DNA would be disastrous. Genetic gain-of-function mutations in oncogenes (that often promote expression or activity of the cyclin/CDK complex) or loss-of-function mutations in tumor suppressor (that stimulate production of CKI) are causal factors for malignant transformation.

Question 5#

In cellular apoptosis, the release of cytochrome c activates the:

A. Fas receptor

A simplified view of the apoptosis pathways (Fig. below). Extracellular death receptor pathways include the activation of Fas and tumor necrosis factor (TNF) receptors, and consequent activation of the caspase pathway. Intracellular death pathway indicates the release of cytochrome c from mitochondria, which also triggers the activation of the caspase cascade. During apoptosis, cells undergo DNA fragmentation, nuclear and cell membrane breakdown, and are eventually digested by other cells.

 A simplified view of the apoptosis pathways. Extracellular death receptor pathways include the activation of Fas and tumor necrosis factor (TNF) receptors, and consequent activation of the caspase pathway. Intracellular death pathway indicates the release of cytochrome c from mitochondria, which also triggers the activation of the caspase cascade. During apoptosis, cells undergo DNA fragmentation, nuclear and cell membrane breakdown, and are eventually digested by other cells.