IB Bio B2.2

organelles

organelles

discrete subunits of cells that are adapted to perform specific functions

cell wall, cytoskeleton, cytoplasm, membrane

are not considered organelles because they don't have a _____

nuclei, vesicles, ribosomes, plasma membrane

are organelles

keeps dna safe, facilitates efficient post-transcriptional modification of mrna

advantages of the separation of the nucleus and cytoplasm into separate compartments

makes protein production more efficient

facilitates efficient post-transcriptional modification of mrna in simpler terms

cellular structures that are not organelles

1. cell walls (Extracurricular)

2. cytoplasm (not specialisd)

3. cytoskeleton (not descrete)

advantages of seperation

•In eukaryotes, keeping chromosomes inside the nucleus safeguards the DNA.

•In prokaryotes, there is no nucleus so DNA and ribosomes are together in the cytoplasm and translation can happen immediately after transcription.

•In eukaryotes, translation cannot happen until mRNA has passed out of the nucleus. This allows the mRNA to be modified after transcription but before translation.

Advantages of compartmentalisation in the cytoplasm of cells

•Enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm.

•Substances that could cause damage to the cell can be kept inside the membrane of an organelle. E.g. Digestive enzymes of lysosomes could kill a cell if they were not trapped inside the lysosome membrane.

•Conditions such as pH can be maintained at an ideal level or a particular process. Which may be different to the levels needed for other process in a cell.

Organelles with their contents can be moved around within the cell

lysomes as an example of the advantage of compartmentalisation

•All of the lysosomal enzymes are acid hydrolases, which are active at an acidic pH (about 5) that is maintained within lysosomes but not at the neutral pH (about 7.2) characteristic of the rest of the cytoplasm. To maintain their acidic internal pH, lysosomes must actively concentrate H+ ions.

•The requirement of these lysosomal hydrolases for acidic pH provides double protection against uncontrolled digestion of the contents of the cytoplasm; even if the lysosomal membrane were to break down, the released acid hydrolases would be inactive at the neutral pH of the cytosol.