2.4.4Inquiry Process
Organelles in Protein Synthesis — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 58 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 6Two Sites of Translation
The destination of a protein decides where its ribosome is located.
Free ribosomes
- Free ribosomes Float in the cytoplasm and make proteins used inside the cell, such as enzymes of glycolysis.
Bound ribosomes
- Bound ribosomes Attached to the rough ER, they make proteins that are secreted, built into membranes or sent to lysosomes.
Signal sequence
- Signal sequence A short stretch of amino acids on the new polypeptide directs the ribosome to the ER.
Same machinery
- Same machinery Both kinds of ribosome are identical; their position depends on the protein being made.
| Protein destination | Made on |
|---|---|
| Cytoplasm, nucleus, mitochondria | Free ribosomes |
| Secretion, membranes, lysosomes | Rough ER ribosomes |
Section 2 of 6Processing Route
1
DNA in the nucleus is transcribed to mRNA, which exits via nuclear pores.
2
The ribosome translates the mRNA and the polypeptide enters the rough ER lumen.
3
Inside the ER the protein folds and may have carbohydrate added.
4
A transport vesicle carries it to the Golgi apparatus for further modification and sorting.
5
Secretory vesicles carry the finished protein to the plasma membrane for release.
Section 3 of 6Role of Each Organelle
Role of Each Organelle
Nucleus
- Nucleus Holds the gene and produces mRNA, separating transcription from translation.
Rough ER
- Rough ER Provides a space for folding and a first stage of modification of proteins.
Golgi
- Golgi Modifies, sorts and packages proteins into the correct vesicles.
Mitochondria
- Mitochondria Supply ATP needed for amino acid activation, translation and vesicle movement.
Section 4 of 6Evidence from Experiments
Cell structure gives clues about how proteins travel.
Pulse-chase
- Pulse-chase Radioactive amino acids given briefly appear first in the ER, then in the Golgi and later in vesicles.
Pancreatic cells
- Pancreatic cells Cells making digestive enzymes have extensive rough ER and many Golgi stacks.
Antibody producers
- Antibody producers Plasma cells packed with rough ER secrete large amounts of antibody.
Interpretation
- Interpretation Abundant organelles match high demand for secreted protein.
Section 5 of 6Worked Example
Question
- A pancreatic cell secretes digestive enzymes.
- Predict which organelles will be abundant and justify your answer.
- The enzymes are proteins for export, so they are made on ribosomes attached to rough ER.
- They are modified and packaged in the Golgi apparatus and carried in secretory vesicles.
- Making and moving so much protein needs a lot of ATP, so many mitochondria are expected.
Answer Abundant rough ER, Golgi apparatus, secretory vesicles and mitochondria.
Section 6 of 6Exam Checklist & Tips
2.4.4 – Key Points for the Exam
- Free ribosome A ribosome in the cytoplasm that makes proteins for use inside the cell.
- Rough ER Endoplasmic reticulum with attached ribosomes.
- Golgi apparatus An organelle that modifies and packages proteins.
- Signal sequence A short sequence directing a protein to a specific location.
- Secretory vesicle A vesicle that carries proteins to the plasma membrane for release.
Common Mistakes
- Saying the ribosome makes mRNA; it translates it.
- Placing protein synthesis in the Golgi apparatus.
- Stating that all proteins go through the Golgi.
- Forgetting the role of mitochondria in supplying ATP.
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