Question

In a eukaryotic cell, the hydrophilic ligand CUE binds the enzyme-linked receptor CUE receptor. Describe a hypothetical but realistic signal transduction cascade, that eventually leads to the transcription of the GRAD gene. The GRAD protein is secreted by the cell. Describe the critical steps in gene transcription, RNA processing and in translation, and which structures and organelles are involved.

A detailed description of transcription and translation, and all proteins involved, is NOT expected, but a description of the main steps is.

Include:

RNA polymerase

a signal transduction cascade

transcription factors

amplification

how the signal reaches the nucleus

transcription factors

ribosomes

organelles involved

secretion from the cell

This question is worth 12 points

Answer 1

Transcription is the process of decoding genetic DNA sequence into mRNA sequence that occurs in nucleus of eukaryotes typically the three steps called initiation, elongation, and termination. RNA polymerases are the enzymes that carry out transcription process along with number of accessory proteins called transcription factors which can specifically bind to enhancer and promoter sequences in DNA in order to recruit RNA polymerase to an appropriate transcription site. Post-transcriptional modification is the process of chemically altering mRNA molecules formed by transcription to produce a mature, functional RNA molecule that can then leave the nucleus and undergo translation. Some common  post- transcriptional modifications include 5' capping, addition of the poly A tail, and splicing. Once the functional mRNA molecule transported out of nucleus to the special organelle in the cell called the ribosome that is located in the cytoplasm of the cell where protein synthesis occur. The molecules involved in translation are mRNA, ribosomes, and tRNA. The process which transforms mRNA as  codons of three bases. Each 'codon' codes for a particular amino acid. Translation also occur in three phases called: initiation, elongation adn termination. Aminoacid sequence synthesized by translation is put into post translational modification and some common PTMs are: phosphorylation; acetylation; hydroxylation and methylation. Formed proteinsa re secreted out of the EP via secretory pathway: rough ER → ER-to-Golgi transport vesicles → Golgi cisternae → secretory or transport vesicles → cell surface from where it expelled out by exocytosis.