3 pts. Proteins are what genes code for. They do much of the work of the cell, a

ID: 195913 • Letter: 3

Question

3 pts. Proteins are what genes code for. They do much of the work of the cell, and as we discussed, there are many kinds of proteins. Each organelle of the cell and the cytosol has proteins that do specific jobs. All proteins are made on ribosomes. If the location in which a protein functions is the cytosol, nucleus, mitochondria or peroxisome then that protein is made on a ribosome that is free in the cytosol.

If the location in which a protein functions is the endomembrane system then the protein is made on a ribosome attached to the outside of the rough endoplasmic reticulum. As the protein is made it is forced through a pore so that it ends up inside the RER.

For each enzyme listed or described below state the kind of ribosome on which it’s made (cytosolic or RER). If it’s made on a RER ribosome, state the final destination of the protein in the endomembrane system.

protein

Ribosome type

Location in endomembrane system (if applicable)

RNA polymerase (synthesizes RNA during transcription)

Testosterone synthesizing enzyme

Glucose Na+ symporter (brings glucose into the cell)

DNA Polymerase (makes DNA)

Actin, which polymerizes into actin filaments, aka microfilaments

A mature acid hydrolase that will function as an intracellular peptidase

Endomembrane System

2 pts. Although we will not encounter protein synthesis and secretion in detail until later in the semester, you already have enough information about these processes to place in order the seven events that are now listed randomly below. Order events 1-7 so that they represent the correct sequence of events corresponding to steps a-g, tracing a typical secretory protein (so a protein secreted outside of the cell) from the initial transcription (readout) of the relevant genetic information in the nucleus to the eventual secretion of the protein from the cell by exocytosis. Please remember that all proteins are not synthesized and processed using this series of events. Only those proteins destined to be secreted, or to wind up within one of the organelles involved in the endomembrane system or in the lysosome will be processed in this way. Other proteins are made by free ribosomes in the cytosol and are transported to their final destinations in other ways.

Transcription à (a) à (b) à (c) à (d) à (d) à (f) à (g) à secretion.

The protein is partially glycosylated within the lumen of the ER.

The secretory vesicle arrives at and fuses with the plasma membrane.

The RNA transcript is transported from the nucleus to the cytoplasm.

As the protein is synthesized, it passes across the ER membrane into the lumen of a cistern.

The enzyme is packaged into a secretory vesicle and released from the Golgi complex.

The final sugar groups are added to the protein in the Golgi complex.

The RNA message associates with a ribosome and begins synthesis of the desired protein on the surface of the rough ER.

Place the steps 1-7 in the appropriate order…..

a) _____ b) _____ c) _____ d) _____ e) _____ f) _____ g) _____

protein

Ribosome type

Location in endomembrane system (if applicable)

RNA polymerase (synthesizes RNA during transcription)

Testosterone synthesizing enzyme

Glucose Na+ symporter (brings glucose into the cell)

DNA Polymerase (makes DNA)

Actin, which polymerizes into actin filaments, aka microfilaments

A mature acid hydrolase that will function as an intracellular peptidase

Explanation / Answer

The sequence of events for the said process are as follows

a) RNA transcript is transported from Nucleus to cytoplasm

b) RNA message associates with Ribosome and begins protein synthesis

c) as the protein is synthesized ,it passes through the pore across ER ,into it's lumen

d) protein is partially glycosylated in ER lumen

e) final sugar groups are added to the protein in Golgi complex

f) Enzyme is packaged into a secretory vesicle and released from golgi complex

g)the secretory vesicle arrives and fuses with the plasma membrane

Protein Ribosome type Location in endomembrane system RNA polymerase Cytosolic Not applicable Testosterone synthesizing enzyme (as testosterone is a lipid harmone , it's synthesized in SER , a part of endomembrane system) RER SER Glucose Na+ transporter RER Plasma membrane DNA polymerase (acts within Nucleus) cytosolic Nucleus Actin (polymerise in Cytosolic to form microfilaments) cytosolic cytosol Mature acid hydrolase (acts in lysosomes if inside the cells ,and lysosomes are part of endomembrane system) RER Lysosomes