What happens to a polypeptide in the lumen of the rER?

It is folded into its 3D shape and may be modified.

How do proteins move from the rER to the Golgi apparatus?

In transport vesicles that bud off the rER and fuse with the Golgi.

What does the Golgi apparatus do to proteins?

Modifies them (e.g. adds carbohydrate groups), then sorts and packages them into vesicles.

What is a glycoprotein?

A protein with carbohydrate groups attached.

Release of substances from a cell when a vesicle fuses with the cell-surface membrane.

Why do pancreatic cells have extensive rER?

They make large quantities of digestive enzymes for secretion, so need many ribosomes.

Give the full route of an extracellular enzyme from gene to secretion.

Nucleus (transcription), rER ribosome (translation), rER lumen, Golgi, secretory vesicle, exocytosis.

What happens to proteins made on free ribosomes?

They stay in the cell, for use in the cytoplasm.

What is a pulse-chase experiment?

A short period with radioactive amino acids, then unlabelled medium, to follow the labelled proteins.

Why does radioactivity appear first in the rER in a pulse-chase experiment?

Ribosomes on the rER use the labelled amino acids to make polypeptides.

What would a toxin that stops rER vesicles fusing with the Golgi do?

Protein would build up in the rER and secretion would fall.

Protein processing: rER and GolgiEdexcel A-Level Biology A: Flashcards

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Where are proteins for secretion made?

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Where are proteins for secretion made?: On ribosomes attached to the rough endoplasmic reticulum.
What happens to a polypeptide in the lumen of the rER?: It is folded into its 3D shape and may be modified.
How do proteins move from the rER to the Golgi apparatus?: In transport vesicles that bud off the rER and fuse with the Golgi.
What does the Golgi apparatus do to proteins?: Modifies them (e.g. adds carbohydrate groups), then sorts and packages them into vesicles.
What is a glycoprotein?: A protein with carbohydrate groups attached.
What is exocytosis?: Release of substances from a cell when a vesicle fuses with the cell-surface membrane.
Why do pancreatic cells have extensive rER?: They make large quantities of digestive enzymes for secretion, so need many ribosomes.
Give the full route of an extracellular enzyme from gene to secretion.: Nucleus (transcription), rER ribosome (translation), rER lumen, Golgi, secretory vesicle, exocytosis.
What happens to proteins made on free ribosomes?: They stay in the cell, for use in the cytoplasm.
What is a pulse-chase experiment?: A short period with radioactive amino acids, then unlabelled medium, to follow the labelled proteins.
Why does radioactivity appear first in the rER in a pulse-chase experiment?: Ribosomes on the rER use the labelled amino acids to make polypeptides.
What would a toxin that stops rER vesicles fusing with the Golgi do?: Protein would build up in the rER and secretion would fall.
Which organelle supplies the ATP for protein processing and transport?: Mitochondria.

Exam questions on Protein processing: rER and Golgi

Acinar cells of the pancreas make and secrete large quantities of the digestive enzyme amylase into the pancreatic duct. Electron micrographs of these cells show extensive rough endoplasmic reticulum, a prominent Golgi apparatus and many vesicles close to the cell-surface membrane.
Explain why these cells have extensive rough endoplasmic reticulum.2 marks
Pancreatic cells were incubated for three minutes in a medium containing radioactively labelled amino acids and then transferred to a medium containing only unlabelled amino acids. Samples were taken at intervals and the position of the radioactivity in the cells was found. After 5 minutes most of the radioactivity was in the rough endoplasmic reticulum, after 20 minutes it was mostly in the Golgi apparatus, and after 60 minutes it was in vesicles near the cell-surface membrane and in the surrounding medium.
Explain why radioactivity was found first in the rough endoplasmic reticulum.2 marks
A researcher treats pancreatic cells with a toxin that prevents vesicles from the rough endoplasmic reticulum from fusing with the Golgi apparatus. The untreated cells normally secrete digestive enzymes.
Predict and explain the effect of the toxin on the position of enzyme proteins in the cell and on the secretion of enzymes.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).