B2.2 - organelles and compartmentalisation

Question 1

what are organelles?

Answer 1

organelles are discrete subunits of cells that are adapted to perform specific functions
- most organelles are surrounded by a membrane

Question 2

what are examples of organelles?

Answer 2

examples: nuclei, vesicles, and ribosomes

Question 3

what are non-examples of organelles?

Answer 3

non-examples: cell wall, plasma membrane, cytoskeleton and cytoplasm

Question 4

when did the study of the function of individual organelles become possible?

Answer 4

when ultra-centrifuges had been invented and methods of using them for cell fractionation had been developed

Question 5

what is fractenation?

Answer 5

fractenation involves breaking down a membrane and spinning the sample at high speeds so the heavier components move further down the tube

Question 6

what were the results from fractenation?

Answer 6

allowed different sizes of ribosomes to be detected as the smaller, less dense 70S was found higher in the fraction than the larger, more dense 80S

Question 7

what is an advantage of separation of the nucleus and cytoplasm into separate components?

Answer 7

allows separation of the activities of gene transcription and translation
- post-transcriptional modification of mRNA can occur before it meets ribosomes in the cytoplasm
- not possible in prokaryotes

Question 8

what are advantages of compartmentalisation in the cytoplasm of cells?

Answer 8

• allows accumulation of metabolites and enzymes at high concentrations
• separates incompatible biochemical processes

Question 9

what are 2 examples of compartmentalisation?

Answer 9

lyosomes - contain hydrolytic enzymes and free radicals which digest biological molecules
- prevents useful molecules being digested and cell damage

phagocytic vacuoles - contain pathogen engulfed by endocytosis
- protects cellular contents from damage by the pathogen