Biology Assignment 5

Question 1: Give the definition:

• Ribozyme:
• Promoter:
• Operator:
•  Activator:
• Repressor:
• Combinatory control of gene expression
• Transcription start site
• Riboswitch
• Operon
• Transcription regulator
• Enhancer
• Polycistronic mRNA
• RNA interference
• Translation start site

2- Which of the following statements about transcriptional regulators is FALSE? Choose and explain?

• 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.
• Transcriptional regulators will form hydrogen bonds, ionic bounds , and hydrophobic interactions with DNA.
• The DNA – binding motifs of transcriptional regulators usually bind in the major groove of the DNA helix.
• The binding of transcriptional regulators generally does not disrupt the hydrogen bonds that holds the double helix together.

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

• The Lac repressor binds when lactose is present in the cell.
• Even when the CAP activator is bound to DNA, If lactose is not present, the Lac operon will not be transcribed.
• The CAP activator can only bind DNA when it is bound to cAMP .
• The Lac operon only produce RNA when lactose is present and glucose is absent.

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

• One miRNAs can regulate the expression of many genes.
• miRNAs are transcribed in the nucleus from genomic DNA.
• miRNAs are produced from rRNAs.
• D) miRNAs are made by RNA polymerase

5- Write a brief (1-2 sentences) definition about their function…?

1/ Activator protein

2/ Mediator

3/ General transcription factors

4/ RNA polymerase

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

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

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 is the best explanation of why myod can cause fibroblasts to express muscle-specific genes ? choose and explain

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