Question

Question 1

Regulated exocytosis involves __________vesicles that contain cargo such as hormones, mucus or ______________and are released in response to an __________signal. In contrast, unregulated exocytosis involves cargo of macromolecules like ____________ and soluble proteins and are released ____________ an external signal.

Question 2                

When is the signal sequence for the ER cleaved off a protein that is being translated on the ER?

1. It is always cleaved off.

2. Only when the a soluble protein is translated into the ER lumen.

3. For soluble proteins and single-pass transmembrane proteins.

4. Only when the protein is embedded into the ER membrane.

Question 3                

Where does translation always start in the cell?

1. On a free ribosome in the cytosol

2. On a ribosome on the ER for a secreted protein

3. In the nucleus

4. On a ribosome on the ER for a membrane protein

Question 4

If a protein is to be imbedded as a multi-pass protein in the ER membrane, what part of the protein will have a signal sequence?

1. Interior of the protein
2. 5’ end of the protein
3. carboxyl terminal end
4. amino terminal end

Answer 1

Answer 1. Exocytosis is an important cellular process that involves the transport of molecules from the cell to the outside environment. The process is carried out by membrane-bound vesicle which carries the content to be secreted out and achieved by fusion of vesicle to the plasma membrane and release of vesicle content outside the cell. Exocytosis is an important phenomenon as it involves the removal of waste from the cell, rebuilding of the cell membrane by transporting membrane proteins and lipids. Cells communicate information through exocytosis such as immune cells, neural cells (neurotransmitters), etc. Exocytosis can constitutive (unregulated) or non-constitutive (regulated). Constitutive exocytosis is performed by all cells and involves regular secretion of molecules such as membrane proteins, lipids. In contrast to constitutive, non-constitutive exocytosis is not performed by all cell but it is more common in secretory cells and needs an extracellular signal to occur. For example, cells secrete hormones, digestive enzymes once they receive a signal.

Regulated exocytosis involves secretory vesicles that contain cargo such as hormones, mucus or neurotransmitter and are released in response to an external signal. In contrast, unregulated exocytosis involves cargos of macromolecules like lipids and soluble proteins and are released outside as an external signal.

Answer 2. Signal sequences are short peptide which is present at the N-terminus of the newly synthesized proteins and facilitate the transport of proteins to their destined region. The endoplasmic reticulum (ER) signal sequence is a sequence of hydrophobic amino acids that are recognized by a single-recognition particle and then binds to its receptor which is present on the rough ER. The ER signal sequence is cleaved into the ER lumen. It is always cleaved off is the right answer.

Answer.3 Translation is the process through which proteins are synthesized from an RNA template. Translation always starts on a free ribosome in the cytosol is the right answer. The first 3-50 amino acids are synthesized on a free ribosome which carries the signal peptide for endoplasmic reticulum and once this ribosome-protein complex is formed ribosome directed towards the rough endoplasmic reticulum and attached to it for further protein synthesis and modification to take place. Both types of membrane, as well as secretory proteins, are synthesized in the ER. The nucleus is not the site of translation in eukaryotes.