5. (8 points) Short answers to questions: a. Please match the characteristics of

Question

5. (8 points) Short answers to questions: a. Please match the characteristics of Prokaryotic vs. Eukaryotic gene expression: Translation is coupled to transcription Primary transcript has to undergo maturation to become mRNA Intron excision 3°-OH at the end of mRNA What is the function of the 5'Cap in mRNA during initiation of translation? b. Please match the characteristics of Prokaryotic vs. Eukaryotic transcriptional and translational cis- elements: Enhancer DNA sequence Shine-Dalgarng RNA sequence [TATAA] box at position (-25] on DNA Kozak consensus RNA sequence Describe key differences during translation initiation in Prokaryotes and Eukaryotes. Explain the function of SAM molecule in bacterial riboswitch that regulates translation of SAM- synthase. c. In Eukaryotes, initiation of transcription regulated by various Transcriptional Factors (TFs). What are the basal factors, where do they get recruited, and what is their main purpose? Describe the function of Activator. Which cis-element it associates with? Describe the mechanisms of action for Repressor and Corepressor during transcriptional repression.

Explanation / Answer

A)

5' capping of mRNA in eukaryotes, prevents the degradation of mRNA and also promotes translation by assisting the binding of the ribosome to the mRNA.

B)

The differences in translation initiation are

Two types of translation intitation seen

-cap depended

-cap independent

SAM or S- adenosylmethionine is a molecule that regulates the gene expression of genes invovled in methionine or cystiene biosynthesis.

WHen SAM is not bound to the riboswitch, the transcription terminator signal is not produced. THis results in the transcription of the genes and hence higher levels of proteins involved in biosynthesis of methionine or cystiene and consequently higher levels of methionine or cystiene.

However, when SAM is bound by the riboswitch, a terminator signal is produced. This results in the termination of transcriptionand thus leads to a decrese in levels of methionine or cystiene.

C)

Transcription factors that are required for the initiation of Transcription are called as basal transcription factors.

Ther are 7 important basal transcription factors

Transcription factors that activate transcription are known as activators. One of hte best examples for cis element activators is the lac operon, which is activated by lactose.

Factors that repress or inhibit transcription are called repressors. repressors can act by blocking the transcriptional factors or RNA polymerase, thus inhibiting their binding to the promoter DNA.

Corepressors are molecules that bind to repressors and activate them. THus a corepressor does not directly affect transcription but indirectly regulate gene expression.

Prokaryotes Eukaryotes Translation is coupled to transcription Primary transcript has to undergo maturation to become a mRNA 3' -OH at the end of mRNA Intron excision

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