LONG ESSAY QUESTIONS Directions: Read each question carefully and answer TWO of
ID: 74274 • Letter: L
Question
LONG ESSAY QUESTIONS
Directions: Read each question carefully and answer TWO of the FOUR questions below in their entirety. Make sure you answer all parts of the question.
Explain how proteins are made in a stomach cell and sent to lumen of the gut (which is outside the cell). Include detailed steps and the following processes:
1) Transcription (detailed steps)
2) mRNA processing (detailed steps)
3) Translation (detailed steps)
4) Processing in the Endomembrane system (detailed steps). Explain how it is processed to be shipped out of the cell.
5) Protein structure and Folding (detailed steps)
6) Exocytosis
Explanation / Answer
The pathway of protein synthesis and secretion:
The process of protein synthesis starts in the nucleus and ends in the cytoplasm. DNA stores the information about proteins, but the process of protein synthesis needs three types of RNA (ribonucleic acid), messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), which translate the DNA’s information to form proteins.
During protein synthesis, mRNA is synthesised under the direction of DNA. The message carried by the DNA is read by the mRNA, this process is called “transcription,” it takes place in the nucleus. This mRNA then carries the information to the tRNA and rRNA, which translate the genetic code into proteins, this process is called “translation” and this takes place in the cytoplasm (ribosomes).
Endoplasmic reticulum is physically continuous with the outer membrane of nuclear membrane. Based upon the presence of granules, which are studded with ribosomes, it is of two types, rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). RER contains ribosomes and hence capable to synthesise polypeptides. SER does not have attached ribosomes, it synthesises lipids (Eg: phospholipids and steroids).
(protein transport or transport of proteins) The process of protein synthesis and secretion starts from the endoplasmic reticulum. The polypeptide chain is formed in the ribosomes, and then transferred to the Golgi apparatus, where the final modifications are done. The Golgi apparatus sorts the modified poly peptide molecules and packages into new transport vesicles which reach their particular destinations.
The proteins generally contain endoplasmic reticulum signal sequence at their N-terminus, which directs them to the rough endoplasmic reticulum. After completion of translation process in the RER, the polypeptide chains get inserted into the ER membrane or into the lumen of ER. Some proteins move to the transport vesicles, which fuse together to form cis- Golgi vesicles, the cis-form again moves to trans-form. During this process, many proteins undergo modifications particularly at oligosaccharide chains. From the trans-Golgi vesicles, proteins move to cell membrane through small transportation vesicles.
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