Question

In the year 4525, humans have evolved to live underwater. One of the evolved adaptations for underwater life is the secretion of a new protein, aquaslickin, from epithelial cells in the skin, which provides a slick coating over the body to help glide through the water. List the steps that lead up to the secretion of aquaslickin in epithelial cells, starting with the transcription of the gene for aquaslickin into mRNA in the nucleus, and ending with the exocytosis of secretory vesicles containing aquaslickin.

Answer 1

Transcription Steps-

1. In the nucleus of epithelial cell the DNA is present which contains gene that codes for RNA molecule to make aquaslickin protein. This region has promoter and the end site terminator. It also contains regulatory sequences. DNA is used as a template to make RNA with the help of RNA polymerase.

2. Promoter region of DNA functions as a recognition site for polymerase, as polymerase binds it unwinds the DNA as the initiation process.

3. During elongation RNA polymerase slides on the template DNA stand, as complimentary bases pair up RNA polymerase links nucleotide to the 3^' end of growing RNA molecule.

4. Once RNA polymerase reaches to terminator portion of Template transcription is complete. RNA polymerase, DNA stand and mRNA dissociates from each other.

Splicing steps-

1. mRNA molecule produced from the trnascription contains intons(non coding region) and exons(coding region).

2. The mRNA has to get modified by the addition of poly A tail at 3' end,5'methylated cap and along with removal of introns.

3. Introns splicing is done by complex of protein and RNA called spliciosome. It removes introns and joins exons segments together.

4. The mature RNA molecule leaves the nucleus through nucleopore and enters cytoplasm for translation.

Translation steps-

1. Translation begins when small subunit of ribosome attaches the cap and moves to translation initiation site. tRNA containing codon and amino acid which will code for aquaslickin protein attaches to complimentary intiation site of mRNA.

2. The large subunit of ribosome binds to form peptidyl(P)site and aminoacyl(A)site. First tRNA enters the p site and second tRNA attaches to A site containingsecond complimentary codon.

3. Amino acid is then transferred to A site amino acid and first tRNA moves out. The second tRNA also does the same and moves out along with moving of ribosome sliding on mRNA. Growing peptide is continously transferred to A site.

4. When a stop codon enters A site a release factor is released and translation terminates as it terminates newly formed protein is released in the cytolpasm and ribosome dissociates.

Modification steps-

1. Modification occurs when specific sugar molecules are attached to core oligosaccharide that is attached to the protein. The sugar molecules are signal for a protein to be directed to its destination. It takes place in golgi apparatus.

2. Hydrolase is delivered from ER to golgi apparatus via cis cisternae. Modifaction of oligosaccharide begins by glycosylation. Protein which has to be sent to the cellular destination binds with it.

3. Hydrolase bind to receptor protein and vesicle is released from trans golgi cisternae and reaches endosome which gets modified into lysosome.

4. The vesicke fuses with the endosome and hydrolase is released . Receptors are send back to golgi apparatus.

5. The proteins are send to its proper cellular location with the help of sugar side chain. The enzymes in the lysosomes help tge protein to get activated and transfers it into its location.