Back to AI Flashcard MakerBiology /Biology IB HL - Translation and Protein Structure
Which ribosomes will have longer polypeptide chains?
Ribosomes located at the 3’-end of the polysome cluster will have longer polypeptide chains that those at the 5’-end
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Key Terms
Term
Definition
Which ribosomes will have longer polypeptide chains?
Ribosomes located at the 3’-end of the polysome cluster will have longer polypeptide chains that those at the 5’-end
Where are all proteins produced by eukaryotic synthesised?
All proteins produced by eukaryotic cells are initially synthesised by ribosomes found freely circulating within the cytosol
What determines whether the ribosomes are free in the cytosol or bound to the ER?
If the protein is targeted for intracellular use within the cytosol, the ribosome remains free and unattached. If the protein is targeted for secretio...
What determines protein destination?
Protein destination is determined by the presence or absence of an initial signal sequence on a nascent polypeptide chain
What does the presence of a signal sequence result in?
The presence of this signal sequence results in the recruitment of a signal recognition particle (SRP), which halts translation
Where do the SPR-ribosomes locate?
The SRP-ribosome complex then docks at a receptor located on the ER membrane (forming rough ER)
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| Term | Definition |
|---|---|
Which ribosomes will have longer polypeptide chains? | Ribosomes located at the 3’-end of the polysome cluster will have longer polypeptide chains that those at the 5’-end |
Where are all proteins produced by eukaryotic synthesised? | All proteins produced by eukaryotic cells are initially synthesised by ribosomes found freely circulating within the cytosol |
What determines whether the ribosomes are free in the cytosol or bound to the ER? | If the protein is targeted for intracellular use within the cytosol, the ribosome remains free and unattached. If the protein is targeted for secretion, membrane fixation or use in lysosomes, the ribosome becomes bound to the ER |
What determines protein destination? | Protein destination is determined by the presence or absence of an initial signal sequence on a nascent polypeptide chain |
What does the presence of a signal sequence result in? | The presence of this signal sequence results in the recruitment of a signal recognition particle (SRP), which halts translation |
Where do the SPR-ribosomes locate? | The SRP-ribosome complex then docks at a receptor located on the ER membrane (forming rough ER) |
What then causes translation to be re-initiated? | Translation is re-initiated and the polypeptide chain continues to grow via a transport channel into the lumen of the ER |
Where will the synthesised protein then be transported? | The synthesised protein will then be transported via a vesicle to the Golgi complex (for secretion) or the lysosome |
What happens to proteins synthesised for membrane fixation? | Proteins targeted for membrane fixation (e.g. integral proteins) get embedded into the ER membrane |
What happens to the signal sequence at the end? | The signal sequence is cleaved and the SRP recycled once the polypeptide is completely synthesised within the ER |
What is the primary sequence? | The first level of structural organisation in a protein is the order / sequence of amino acids which comprise the polypeptide chain |
How is the primary structure formed? | The primary structure is formed by covalent peptide bonds between the amine and carboxyl groups of adjacent amino acids |
Why is primary structure so important? | Primary structure controls all subsequent levels of protein organisation because it determines the nature of the interactions between R groups of different amino acids |
What is secondary structure? | The secondary structure is the way a polypeptide folds in a repeating arrangement to form α-helices and β-pleated sheets |
How is secondary structure formed? | This folding is a result of hydrogen bonding between the amine and carboxyl groups of non-adjacent amino acids |
What secondary structure will proteins that do not form alpha helices or beta pleated sheets have? | Sequences that do not form either an alpha helix or beta-pleated sheet will exist as a random coil |
What is the role of the secondary structure? | Secondary structure provides the polypeptide chain with a level of mechanical stability (due to the presence of hydrogen bonds) |
What is the tertiary structure? | The tertiary structure is the way the polypeptide chain coils and turns to form a complex molecular shape (i.e. the 3D shape) |
What creates the tertiary structure? | It is caused by interactions between R groups; including H-bonds, disulfide bridges, ionic bonds and hydrophobic interactions |
What is particularly important in the tertiary structure? | Relative amino acid positions are important (e.g. non-polar amino acids usually avoid exposure to aqueous solutions) |
Why may tertiary structure be important? | Tertiary structure may be important for the function of the protein (e.g. specificity of active site in enzymes) |
What is the quaternary structure? | Multiple polypeptides or prosthetic groups may interact to form a single, larger, biologically active protein (quaternary structure) |
What is a prosthetic group? | A prosthetic group is an inorganic compound involved in protein structure or function (e.g. the heme group in haemoglobin) |
What is a conjugated protein? | A protein containing a prosthetic group is called a conjugated protein |
What may hold the tertiary structure together? | Quaternary structures may be held together by a variety of bonds (similar to tertiary structure) |