Rough ER, Golgi and Lysosomes Explained
How the rough endoplasmic reticulum, Golgi apparatus, Golgi vesicles and lysosomes work together to make, modify, package and secrete proteins. Includes the 4-mark exam question, a worked model answer and the examiner trap on saying the Golgi modifies and packages, not makes.
Chapters (9)
Exam question [4 marks]
Describe the roles of the rough endoplasmic reticulum, the Golgi apparatus and lysosomes in a cell.
Try it on paper first, then check the mark scheme below. The question is original and was written for this lesson.
Mark scheme
| Mark | Mark point | Also accept | Do not accept |
|---|---|---|---|
| 1 | Rough endoplasmic reticulum has ribosomes (on its surface) that make proteins, which are folded / transported inside it | "RER has ribosomes, makes / synthesises proteins", "proteins pass into the lumen", "folds proteins" | "smooth ER has ribosomes"; "RER makes lipids"; "ribosomes are made in the RER" |
| 2 | Golgi apparatus receives vesicles (of proteins) from the rough endoplasmic reticulum and modifies the proteins | "processes proteins", "adds carbohydrate / makes glycoproteins" | "Golgi makes proteins"; "Golgi makes ribosomes" |
| 3 | Golgi packages the proteins into (Golgi) vesicles, for secretion / to become lysosomes | "forms secretory vesicles", "vesicles move to / fuse with the cell-surface membrane", "packages and sends out" | "stores proteins forever"; "Golgi vesicles are made by the nucleus" |
| 4 | Lysosome is a membrane-bound organelle containing hydrolytic enzymes that break down worn-out organelles / material taken into the cell (e.g. bacteria) | "digestive enzymes that hydrolyse", "digests old organelles", "destroys pathogens" | "lysosomes get rid of waste" alone; "lysosomes contain acid" alone; "lysosomes make energy" |
Each mark names a structure and gives its function. Mark 1 needs the ribosomes and the protein link; "rough" alone is not enough. Mark 2 needs the word modify / process; "makes proteins" for the Golgi is a common error. For mark 4, the phrase "hydrolytic enzymes" (or clearly equivalent) with a use is required. Smooth ER (lipid synthesis, no ribosomes) is taught as a contrast but is not credited in this question.
Model answer (4/4)
The rough endoplasmic reticulum has ribosomes on its surface that make proteins, which are folded and transported inside it. The Golgi apparatus receives vesicles from the rough endoplasmic reticulum and modifies the proteins. It then packages them into vesicles, either for secretion or to become lysosomes. A lysosome is a membrane-bound organelle containing hydrolytic enzymes, which break down worn-out organelles or material taken into the cell.
Examiner trap
- Mixing which ER has ribosomes
- Not saying lysosomes contain hydrolytic enzymes
- Describing Golgi as 'making' proteins instead of modifying and packaging
Key terms
- rough endoplasmic reticulum
- smooth endoplasmic reticulum
- Golgi apparatus
- Golgi vesicle
- lysosome
- hydrolytic enzymes
- protein processing
- lipid synthesis
- secretion
Lesson notes
A written version of the video, chapter by chapter, for revision. Times link to the video.
0:25Rough ER: making proteins
Start next to the nucleus, with the rough endoplasmic reticulum. It is a system of flattened, membrane-bound sacs. The word rough comes from the ribosomes dotted all over its outer surface. Those ribosomes make proteins, and the proteins pass into the inside of the sacs.
Inside, they are folded into their shape, and then carried onwards.
0:49Vesicles carry the protein
The finished protein does not just drift off. The edge of the sac pinches off a tiny bubble of membrane, called a vesicle, with the protein inside. That vesicle moves through the cytoplasm to the next stop.
1:02The Golgi apparatus
That next stop is the Golgi apparatus. It is a stack of flattened, membrane-bound sacs, a bit like a pile of curved pancakes. The vesicle fuses with the Golgi, and the protein is processed inside it. Notice the word. The Golgi modifies proteins. It does not make them.
For example, it can add a carbohydrate to a protein. Then it packages the finished protein into new vesicles, called Golgi vesicles, which bud off the far side.
1:32Secretion at the cell surface
Some Golgi vesicles travel to the cell-surface membrane. They fuse with it, and release the protein outside the cell. That is secretion. So the pathway is: rough endoplasmic reticulum, vesicle, Golgi, vesicle, cell-surface membrane.
1:50Lysosomes
Not every Golgi vesicle leaves the cell. Some stay inside, and become lysosomes. A lysosome is a small, membrane-bound sac full of hydrolytic enzymes, which it releases to break things down. The membrane keeps those enzymes separate from the rest of the cell, so they cannot digest it.
Lysosomes break down worn-out organelles. They also break down material taken into the cell, such as bacteria, by hydrolysis.
2:18Smooth ER compared
One last structure to compare. Smooth endoplasmic reticulum has the same folded membrane, but no ribosomes. So it does not make proteins. It makes lipids. Rough for proteins, smooth for lipids. Don't swap them.
3:16Examiner trap and recap
The trap. Saying the Golgi makes proteins loses the mark. Say it modifies and packages them. And for lysosomes, always say hydrolytic enzymes.
Recap. Ribosomes on rough endoplasmic reticulum make proteins, the Golgi modifies and packages them, and lysosomes contain hydrolytic enzymes that break down worn-out organelles and material taken in.
Next time: the cell-surface membrane, cell wall and vacuole, and how specialised cells are adapted.
Watch first
This lesson builds on:
- Nucleus, Mitochondria and Chloroplasts · AQA 7402 · 3.2.1.1
Keep going
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- Nucleus, Mitochondria and Chloroplasts · AQA 7402 · 3.2.1.1
- Cell Wall, Vacuole and Specialised Cells · AQA 7402 · 3.2.1.1
- Prokaryotic vs Eukaryotic Cells · AQA 7402 · 3.2.1.2
- Viruses: Structure and Non-Living Status · AQA 7402 · 3.2.1.2
Independent revision resource, not affiliated with or endorsed by AQA. The exam question is original and was written for this lesson; it is not an AQA question. Spotted an error? Email info@medservatory.com with the lesson code AB-023.