ribosomes & er- sc.912.l.14.2: relate structure to function for the components of plant and animal cells. explain the role of cell membranes as a highly selective barrier.
1. describe the structure and function of ribosomes.

2. in what two places might ribosomes be found in a cell?

3. describe the structure of the endoplasmic reticulum.

4. what are the two types of endoplasmic reticula? what does each do?

5. explain how ribosomes, endoplasmic reticulum, and the golgi apparatus function together in protein synthesis.

Question

ribosomes & er- sc.912.l.14.2: relate structure to function for the components of plant and animal cells. explain the role of cell membranes as a highly selective barrier.
1. describe the structure and function of ribosomes.

2. in what two places might ribosomes be found in a cell?

3. describe the structure of the endoplasmic reticulum.

4. what are the two types of endoplasmic reticula? what does each do?

5. explain how ribosomes, endoplasmic reticulum, and the golgi apparatus function together in protein synthesis.

Accepted Answer

### Question 1
# Brief Explanations:
Ribosomes are made of ribosomal RNA (rRNA) and proteins, structured as two subunits (large and small). Their function is to synthesize proteins by translating mRNA into polypeptide chains.
# Answer:
Structure: Composed of rRNA and proteins, has two subunits (large and small). Function: Site of protein synthesis (translates mRNA to make polypeptides).

### Question 2
# Brief Explanations:
Ribosomes can be free - floating in the cytoplasm (making proteins for the cell's own use) or attached to the rough endoplasmic reticulum (making proteins for export or for cell membrane).
# Answer:
Free in the cytoplasm and attached to the rough endoplasmic reticulum.

### Question 3
# Brief Explanations:
The endoplasmic reticulum (ER) is a network of membranous tubules and sacs (cisternae). It is continuous with the nuclear envelope. The membrane encloses a lumen (internal space).
# Answer:
The endoplasmic reticulum is a network of membranous tubules and flattened sacs (cisternae). It is connected to the nuclear envelope and has an internal lumen.

### Question 4
# Brief Explanations:
- Rough ER: Has ribosomes attached to its surface. Its function is to synthesize proteins (especially those for export, insertion into the cell membrane, or for the Golgi apparatus). It also helps in protein folding and modification.
- Smooth ER: Lacks ribosomes. It is involved in lipid synthesis (e.g., phospholipids for cell membranes, steroids), detoxification of drugs and poisons (in liver cells), and storage/release of calcium ions (in muscle cells for muscle contraction).
# Answer:
- Rough Endoplasmic Reticulum (Rough ER): Has ribosomes on its surface. Function: Synthesizes proteins (for export, cell membrane, etc.), aids in protein folding/modification.
- Smooth Endoplasmic Reticulum (Smooth ER): No ribosomes. Function: Lipid synthesis, detoxification, calcium ion regulation.

### Question 5
# Brief Explanations:
1. Ribosomes (either free or on rough ER) synthesize proteins. If on rough ER, the newly made protein enters the ER lumen.
2. In the rough ER, the protein is folded and may be modified (e.g., addition of sugar groups - glycosylation).
3. The protein is then transported in a vesicle from the rough ER to the Golgi apparatus.
4. The Golgi apparatus modifies, sorts, and packages the protein (e.g., further glycosylation, adding phosphate groups). It then sends the protein in a vesicle to its final destination: either outside the cell (via exocytosis), to the cell membrane, or to other organelles. If the ribosome is free in the cytoplasm, the protein may be used within the cell, or it can also be transported to the Golgi via vesicles for further processing if needed.
# Answer:
1. Ribosomes synthesize proteins. If on rough ER, the protein enters the ER lumen.
2. Rough ER folds/modifies the protein and sends it in a vesicle to the Golgi.
3. Golgi modifies, sorts, and packages the protein.
4. Golgi sends the protein (in a vesicle) to its destination (e.g., cell membrane for export, cell membrane, or other organelles). Free ribosomes - made proteins may also be sent to Golgi for processing if needed.

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