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Tutor Victor


Question 1: Give the definitions:

Ribozyme:  Ribozyme are ribonucleic acids (RNA) catalyst enzymes used in biochemical reactions. They are useful in folding, and link the amino acids peptide bonds to form protein chains. Examples include hairpin, VS, Leadzyme ribozymes (Walter & Engelke, 2002).

Promoter:  promoters are specific regions in a DNA sequences that are rich with As and Ts. Their main function is to initiate transcription for particular genes. (Albert’s et al, 2013).

Operator: it is a segment of DNA that transcription regulator binds to in between the promoters. They are located downstream of the promoter and are either positive or negative (Albert’s et al, 2013).

 Activator:  activator is a DNA binding protein that increases transcription for a set of genes (Walter & Engelke, 2002).

 Repressor:  it is a RNA or DNA binding Protein that prohibits or stopstranscription through the operator (Alberts et al, 2013).

 Combinatory control of gene expression:  it is a process where genes are differentially expressed in complex transcriptions and bound to specific DNA elements. (Reményi, Scholer, & Wilmanns, 2004)

Transcription start site:  transcription start site marks beginning of the gene regulation in the DNA strand and indicates convergences cis & and trans-acting regulator mechanisms as indicated by promoters (Reményi, Scholer, & Wilmanns, 2004).

Riboswitch:  it is a special shape structure of RNA elements resulting from response to binding of a regulatory molecule (Henkin, T. M. (2008).

Operon: it is a transcribe genes that are similar to mRNA, it form the functional unit of the genomic DNA.  It made from polycistronic mRNA in prokaryotes (Alberts et al, 2013).

 Transcription regulator:   They are factors through which a cell regulatory DNA sequences controls the transcriptions activities (Alberts et al, 2013).

Enhancer:  enhancer is short region in Eukaryotes activators that are responsible for activating the transcription of genes upstream or downstream from transcription start site (Alberts et al, 2013).

 Polycistronic mRNA: it encodes different proteins (polypeptides) in prokaryotes that are from a similar mRNA (Alberts et al, 2013).

RNA interference:   it is a biological process where a mRNA can fold to itself, to inhibit gene expression causing destruction specific mRNA molecules (Alberts et al, 2013).

Translation start site:  it is the position that marks the start codon (AUG), . 2- Which of the following statements about transcriptional regulators is FALSE? Choose and explain?

  1. Transcriptional regulators usually interact with the sugar-phosphate backbone on the outside of the double helix to determine where to bind on the DNA helix.
  2. Transcriptional regulators will form hydrogen bonds, ionic bounds, and hydrophobic interactions with DNA.
  3. The DNA – binding motifs of transcriptional regulators usually bind in the major groove of the DNA helix.
  4. The binding of transcriptional regulators generally does not disrupt the hydrogen bonds that holds the double helix together is this statement false of true?. 

The answer is (1). The statement is false because, during the control of gene expression, DNA double helix’s major grooves are mainly inserted by proteins and interaction is usually by hydrogen bond bases. i.e. ion bonds (Alberts et al, 2013).

3- Which of the following statements about the Lac operon is FALSE? Choose and explain?

  1. The Lac repressor binds when lactose is present in the cell.
  2. Even when the CAP activator is bound to DNA, if lactose is not present, the     Lac operon will not be transcribed.
  3. The CAP activator can only bind DNA when it is bound to cAMP.
  4. The Lac operon only produces RNA when lactose is present and glucose is absent.

      The answer is (1).  The statement is false because the absence of glucose initiates the Transcription process. The lacrosse must also be present since the action involves bacteria, which prefer lactose. The absence of glucose triggers production of cAMP by the prokaryotes activating CAP. The transcription is switched of at the absence of glucose by binding of the repressor to the CAP operator.

4- Which of the following statements about miRNAs is FALSE? Choose and explain?

  1. One miRNAs can regulate the expression of many genes.
  2. miRNAs are transcribed in the nucleus from genomic DNA.
  3. miRNAs are produced from rRNAs.
  4.   miRNAs are made by RNA polymerase

The answer is (3). The statement is false because pre micro mRNAs are processed after the transcription of micro mRNA. The process further exports a mature mRNA to the cytosol because of the activity of the Dicer enzyme

5- Write a brief (1-2 sentences) definition about their functions

1/ Activator protein:  they facilitate the transcription process by binds to the operator to start transcription or enhance proximal elements (Alberts et al, 2013).

2/ Mediator:  they function within large protein complex works as transcription co activator to link the upstream and downstream transcription regulators in all eukaryotes. (Alberts et al, 2013).

3/ General transcription factors:  these are a class of proteinsprokaryotes that bind to promoters are recognize them in all genes  while initiating the opening  the double helix DNA and position RNA polymerase (Alberts et al, 2013).

4/ RNA polymerase:  they are Enzyme known DNA dependent and main function is to produce the primary transcript for the DNA strand into RNA (Alberts et al, 2013).

6- Combinatorial control of gene expression  …………………… choose and explain.

  1. involves every gene using a different combination of transcriptional regulators for its  proper expression
  2. Involves groups of transcriptional regulators working together to determine the expression of a gene.
  3. Involves only the use of gene activators used together to regulate genes appropriately.
  4. Is seen only when genes are arranged in operons.

The answer is (B).

Explanation: This process is critical for cell and encodes all RNA and protein molecules required for differentiation of a daughter’s cell from the parent cell (Alberts et al, 2013).

7- The MyoD transcriptional regulator is normally found in cells, which are differentiating into muscle cells, and participates in the transcription of genes that produce muscle-specific proteins, such as those needed in contractile tissue. Amazingly, artificial expression of Myod in fibroblasts causes these cells derived from skin connective tissue to produce protein normally only seen in muscles. However, some other cell types do not transcribe muscle-specific genes when Myod is also artificially expressed in them which of the following statements below are the best explanation of why Myod can cause fibroblasts to express muscle-specific genes. Choose and explain

  1. Unlike some other cell types, fibroblasts have not lost the muscle-specific genes from their genome.
  2. the muscle-specific genes must be in heterochromatin in fibroblasts
  3.  During their developmental history, fibroblasts have accumulated some transcriptional regulators in common with differentiating muscle cells.
  4.  The presence of MaoD is sufficient to activate the transcription of muscle-specific genes in all cell types

The answer is (C) “during their developmental history; fibroblasts have accumulated some transcriptional regulators in common with differentiating muscle cells”.

This is because Fibroblasts are derived from a different cell with same broad class of embryonic cells as muscle cells. Different cells express their Myod is complete the combinatorial Myod the final identity of the genes and the protein characteristics are expressed at the last stages of the transcription process (Alberts et al, 2013).


Walter, N. G., & Engelke, D. R. (2002). Ribozymes: catalytic RNAs that cut things, make things, and do odd and useful jobs. Biologist (London, England)49(5), 199.

Reményi, A., Scholer, H. R., & Wilmanns, M. (2004). Combinatorial control of gene expression. Nature structural & molecular biology11(9), 812-815.

Henkin, T. M. (2008). Riboswitch RNAs: using RNA to sense cellular metabolism. Genes & development22(24), 3383-3390.