| What are ribosomes? | Large macromolecules (not organelle) composed of two subunits a big and a small one, made of two classes of molecules, rRNA and ribosomal proteins. |
| Why are ribosomes not organelles? | They are complex structures not enveloped by a membrane which doesn't classify it as an organelle |
| How is the morphology of ribosomes? | Size about 25 nm seen on EM, do not have a regular definite shape. |
| What is the role of ribosomes? | Translation of mRNA into polypeptide chains (three tRNA binding sites A, P and E and a groove for mRNA evacuation and tunnel for polypeptide release. |
| Where are ribosomes found? | Free or on ER or on membrane, assemble only during translation. |
| Are ribosomes the same in eukaryotes and prokaryotes? | No, the differ in size shape amount of composing particles, (sedimentation coefficient). |
| Give the composition of eukaryotic and prokaryotic ribosomes. | Eukaryotes ( number of rRNA species: 4 / sedimentation coefficient of small subunit= 40s / rRNA species present= 18s / number of proteins = 33/ Large subunit sedimentation coefficient= 60s / rRNA species= 28s 5.8s and 5s/ number of proteins= 49)
Prokaryotes have all together 3 rRNA species. |
| What are the genes that encode the rRNA? | Located either in nucleolus (48s that makes 28s, 18s and 5.8s) forming the NOR (nucleolar organization region) or outside the nucleolus (5s) in nucleus called rDNA or rRNA- encoding genes. |
| How are ribosomes synthesized? | ribosomal proteins are translated from a gene, then they head towards the nucleolus and assemble with the rRNA encoded sequences, producing the small and large subunit that go independent and only assemble when translation occurs. |
| Are ribosomal proteins distributed randomly? | NO, each have a catalytic role, like peptidyl transferase that catalyzes peptide bonds, some for recognition, some for movement... |
| Talk about ribosomes of mitochondria and chloroplast. | differ from cytoplasmic ones with the same function, chloroplast ones are almost the same in all plant cells, whereas mitochondrial ones differ among species. |
| How is a gene expressed? | Transcription and translation. |
| What are the differences between prokaryotic and eukaryotic transcription? | -processing
-enzymes
-translation and transcription co-relation. |
| What are polysomes? | Many ribosomes simultanously translating the same mRNA producing many copies of the same protein. |
