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Organelles Involved in Protein Synthesis and Transport

Laura Armstrong

Teacher

Laura Armstrong

Contents

Topic Explainer Videos

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Overview of the Process

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Step-by-Step Process

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Recall Questions

This topic requires prior knowledge of animal and plant cell structures. You can test your knowledge on these below.

What is the function of ribosomes in a eukaryotic cell?

Ribosomes are the site of protein synthesis. They assemble amino acids into polypeptide chains.

What is the function of the golgi apparatus?

  • It modifies lipids and proteins e.g. adds sugar (to form a glycolipid or glycoprotein). 
  • It packages lipids and proteins into secretory vesicles to be transported outside of the cell.
  • It forms lysosomes (vesicles which contain hydrolytic enzymes for digestion).

Describe the structure of the rough endoplasmic reticulum.

  • A 3D system of sheet-like membranes. 
  • The membranes form a series of flattened sacs called cisternae.
  • The Rough ER has ribosomes attached to its surface.

Topic Explainer Videos

Check out this @LauraDoesBiology video that explains organelles involved in protein synthesis and transport or read the full notes below. Once you've gone through the whole note, try out the practice questions!

Overview of the Process

The synthesis and transport of proteins in a eukaryotic cell involve several organelles working together:

  1. Nucleus: Contains DNA, which codes for the sequence of amino acids in a polypeptide.
  2. Ribosomes & Rough Endoplasmic Reticulum (RER): Site of protein synthesis.
  3. Golgi Apparatus: Modifies, sorts, and packages proteins into secretory vesicles.
  4. Secretory Vesicles: Transport proteins within the cell and out of the cell (to the cell surface membrane).
  5. Mitochondria: Provide ATP for protein synthesis and the movement of vesicles.
  6. Cell Surface Membrane: Controls the release of proteins via exocytosis.

Step-by-Step Process

The Nucleus

  • DNA contains genetic instructions for proteins.
  • The sequence of bases in DNA will determine the sequence of amino acids in a polypeptide.

The Ribosomes & RER

  • Ribosomes in the cytoplasm and on the rough endoplasmic reticulum join amino acids together to form a polypeptide. This requires energy from ATP.
  • The polypeptide is folded and processed in the lumen of the RER.
  • Vesicles bud off from the RER carrying the protein.
  • Vesicles fuse with the Golgi apparatus for further processing.

The Golgi Apparatus

  • Proteins are modified (e.g. carbohydrate chains are added to form glycoproteins).
  • The proteins are then sorted and packaged into secretory vesicles.
  • Hydrolytic enzymes are packaged into vesicles called lysosomes which remain in the cell.

Transport to Cell Surface or Other Locations

  • Secretory vesicles move towards the cell surface membrane.
  • Proteins can then be secreted out of the cell via exocytosis.

Exocytosis at the Cell Surface Membrane

  • Vesicles fuse with the plasma membrane.
  • Proteins are released outside the cell.

Key Terms 

  • Nucleus: Contains DNA which codes for polypeptides.
  • Ribosome: Site of protein synthesis.
  • Rough Endoplasmic Reticulum (RER): Network of membranes with ribosomes on surface for protein synthesis and transport to the golgi apparatus.
  • Golgi Apparatus: Modifies and packages proteins into vesicles for secretion.
  • Vesicles: Transport proteins to different parts of the cell or outside the cell.
  • Mitochondria: Make ATP, needed for protein synthesis and transport of vesicles.
  • Exocytosis: Process where vesicles fuse with the plasma membrane to release contents outside the cell.
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Exam Tip

Don’t abbreviate rough endoplasmic reticulum in the exam. Write it out fully!

No answer provided.

Describe the roles of organelles involved in the production and secretion of extracellular proteins. (6 marks)

  1.  The nucleus contains DNA, which determines the sequence of amino acids in a polypeptide.
  2.  Ribosomes and the rough endoplasmic reticulum synthesise proteins.
  3. Mitochondria produce ATP which provides energy for protein synthesis.
  4.  Vesicles transport proteins from the rough endoplasmic reticulum to the Golgi apparatus.
  5. The Golgi modifies proteins (e.g. forms glycoproteins) and packages them into secretory vesicles.
  6. Vesicles move to the cell surface membrane and release the protein via exocytosis.

Practice Question

Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!

Plant cell structure Prokaryotic cell structure