BIOL2142 Module 4

Which of the following cellular components could NOT be described as an organelle microtubules glycoproteins endoplasmic reticulum a nucleus

Glycoproteins

Where are proteins in the chloroplast synthesised? in the cytoplasm in the chloroplast in the endoplasmic reticulum in both the cytoplasm and the chloroplast

Chloroplast proteins are synthesised in the cytosol and in the chloroplast. Most chloroplast proteins are sysnthesised in the cytoplasm and have plastid targeting sequences. The chloroplast genome contains around 100 genes which also encode some of the chloroplast proteins and are synthesised on ribosomes in the chloroplast stroma.

Choose the sequence that best describes the progress of an enzyme from synthesis to its final destination in a lysosome: Rough endoplasmic reticulum; cis face of Golgi appartus, trans face of golgi apparatus, endolysosome, vesicle Smooth endoplasmic reticulum; cis face of Golgi appartus, trans face of Golgi apparatus, vesicle, endolysosome Rough endoplasmic reticulum; cis face of Golgi apparatus, trans face of Golgi apparatus, vesicle, endolysosome Rough endoplasmic reticulum; trans face of Golgi apparatus, cis face of Golgi apparatus, vesicle, endolysosome

Rough endoplasmic reticulum; cis face of Golgi apparatus, trans face of Golgi apparatus, vesicle, endolysosome

In which cells of an organisms would you expect to find the highest number of mitochondria? Those involved in structural support Those most metabolically active Those providing protective outer layers None of the above - all cells in a given organism have the same number of mitochondria

Those most metabolically active

A gene regulatory protein, A, contains a typical nuclear localization signal but surprisingly is usually found in the cytosol. When the cell is exposed to hormones, protein A moves from the cytosol into the nucleus, where it turns on genes involved in cell division. When you purify protein A from cells that have not been treated with hormones, you find that protein B is always complexed with it. To determine the function of protein B, you engineer cells lacking the gene for protein B. You compare normal and defective cells by using differential centrifugation to separate the nuclear fraction from the cytoplasmic fraction and then separate the proteins in these fractions by gel electrophoresis. You identify the presence of protein A and protein B by looking for their characteristic bands on the gel. The gel you run is shown in the Figure below. On the basis of these results, what is the function of protein B? Decide whether the following possible mechanism/function for protein B is true or false. The data on the gel show that protein A is always found in the nucleus in the absence of protein B. Therefore, any mechanism that is proposed must explain this result. One possible answer is that protein B binds protein A and masks the nuclear localisation signal. In the presence of hormone, protein B interacts with the hormone, which changes its conformation so that it can no longer bind protein A. When protein B no longer binds to protein A, the nuclear localisation signal on protein A is now exposed and protein A can enter the nucleus. Therefore, in the absence of protein B, the nuclear localisation signal on protein A is always exposed and protein A resides in the nucleus.

True Response Feedback: Well done! I hope this wasn't a guess! Proteins with an NLS do not necessarily automatically enter the nucleus. Certain proteins are regulated in their entry in response to certain cellular signals, such as hormones, and then enter the nucleus to exert their effect. Certain transcription factors, that regulate gene experssion may do this. In the scenario described in the question, protein B acts like a negative regualtor of protein A, preventing its entry to the nucleus. The increase of the hormone, perhaps in response to some change in physiology of the organsim, leads to dissociation of protein B from protein A, which then exposes its NLS, which allows importins to bind to protein A and facilitate entry to the nucleus. protein A then might bind to a promoter of one or more genes to regulate their expression, to switch on or switch off the genes for example.

Chlorophyll molecules are found: associated with the thylakoid membrane of chloroplasts in the stroma of chloroplasts only evenly distributed in the chloroplast in amyloplasts and chromoplasts

associated with the thylakoid membrane of chloroplasts

After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode? a. soluble secreted proteins b. ER membrane proteins c. plasma membrane proteins d. all of the above.

d. all of the above. Response Feedback: The rough ER consists of ER membranes and polyribosomes that are in the process of translating and translocating proteins into the ER membrane and lumen. Thus all proteins that end up in the lysosome, Golgi apparatus, or plasma membrane, or are secreted, will be encoded by the RNAs associated with the rough ER.

Your friend has just joined a research lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. She wants to start designing some experiments but wasn't listening carefully when she was told about the molecular defect of this cell line. She's too embarrassed to ask and comes to you (as knowledgeable first year cell biologist!) for help. She does recall that this cell line forms coated pits but vesicle budding and the removal of coat proteins doesn't happen. Which of the following proteins might be lacking in this cell line? clathrin adaptin Rab dynamin

dynamin Correct! The question asks you to integrate several aspects of the processes of vesicle budding. Not all of these proteins listed are required for vesicle budding, so you had to be selective.

Where are proteins in the chloroplast synthesised? in the cytoplasm in the chloroplast in the endoplasmic reticulum in both the cytoplasm and the chloroplast

in both the cytoplasm and the chloroplast Chloroplast proteins are synthesised in the cytosol and in the chloroplast. Most chloroplast proteins are sysnthesised in the cytoplasm and have plastid targeting sequences. The chloroplast genome contains around 100 genes which also encode some of the chloroplast proteins and are synthesised on ribosomes in the chloroplast stroma.

In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins? the nucleus on the rough ER in the cytosol in the cytosol, chloroplasts and mitochondria

in the cytosol, chloroplasts and mitochondria Ribosomes are cytoplasmic structures and thus their protein components are translated in the cytosol. However, the chloroplast and mitochondrial protein synthesis machineries require ribosomes as well and these are encoded within these organelle genomes as well. For translation of nuclear encoded genes, ribosomes are drawn from a common cytoplasmic pool.

Which of the following pairs is mismatched? nucleolus : ribosomal RNA nucleus : DNA replication lysosome : protein synthesis cell membrane : lipid bilayer cytoskeleton : microtubules

lysosome : protein synthesis

The Golgi apparatus is found only in prokaryotes is the main site of lipid production for membranes is a network of tubular membranes processes and packages many different substances for transport to other sites in the cell

processes and packages many different substances for transport to other sites in the cell

What does a polyribosome consist of? several ribosomes translating a single mRNA molecule a ribosome simultaneously translating several mRNA molecules ribosomes attached to rough ER a ribosome specialized for synthesis of a polypeptide a bundle of ribosomes in the nucleus

several ribosomes translating a single mRNA molecule

If electron micrographs consistently show mitochondria to be grouped around a particular structure in a particular kind of cell, one might infer that the: cell is dead or dying structure requires a considerable supply of energy cell contains DNA structure is involved in secretion cell is carrying out protein synthesis

structure requires a considerable supply of energy