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Description
Flashcards by J yadonknow, updated more than 1 year ago
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Created by J yadonknow
over 6 years ago
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| Question | Answer |
| Define a Ribosome - | An organelle that provides the interface for translation of the genetic code into the formation of a functional protein |
| Describe the functions of a ribosome | Provide an interface for mRNA and aminoacyl tRNAs Ribosomes catalyse the formation of peptide bonds |
| How does a ribosome facilitate tRNA binding? | The ribosome has 3 tRNA binding sites: The (E) exit site The (P) peptidyl site The (A) aminoacyl site |
| What are ribosomes composed of? | By mass ~35%/40% protein 60%/65% RNA |
| How is the size of a ribosome measured? | Measured in Svedbergs (S) - Rate of sedimentation during centrifugation - Bigger the particle, faster it moves down a centrifugation tube |
| What are the subunits of a ribosome? | Small 30s subunit, which binds to the mRNA being translated Large 50s subunit which catalyses peptide bond formation Size in total is 70s!!! Not 80s! (confusing, right?) |
| Draw a diagram of an E. Coli cell ribosome. | 20nm high Large 50s subunit made of rRNA and proteins Small 30s subunit made of 16s rRNA and 21 proteins EPA sites |
| Human ribosome | Large 60s subunit small 40s subunit EPA site overall size is 80s |
| How do mitochondrial ribosomes differ to human ribosomes | Mitochondria have 55s ribosomes that are more similar to bacterial ribosomes than cytoplasmic ribosomes |
| Draw a diagram showing the process of translation | Coding strand/promoter/coding region/terminator transcription (RNA polymerase) translation (tRNAs and ribosomes) Protein NH3+-COO- |
| Describe very briefly this translation | mRNA is read 5'-3' Protein is synthesised NH3+-COO- |
| What is the first amino acid encoded in prokaryotes? | N-formyl-methionine instead of methionine |
| Describe the process of initiation in E.Coli | Small (30s) subunit assemble and binds to the ribosome binding site on the mRNA strand as a result of complementary base-pairing between it and the 16s rRNA. |
| What is this sequence known as? | The Shine-Dalgarno sequence, exists just before the 1st AUG codon. |
| Describe the binding of the tRNA molecule to the ribosome | F-met-tRNA^met binds to the initiation codon The 50s ribosome subunit then binds to generate the complete ribosome |
| Draw a diagram showing this binding | corfu 06 |
| Describe translation initiation in Eukaryotes | First amino acid is methionine, not N-formyl-methionine 40s and met-tRNA^met combine prior to binding to mRNA |
| How does the ribosome bind to the mRNA molecule? | There is no ribosome binding site on mRNA Instead, the 40s subunit recognises the cap at the 5' end of the mRNA |
| Draw a diagram you cunt | well done you cunt |
| Draw a diagram translation elogation | 1. Met-tRNA^met bound at P site 2. Binding of tRNA to A site, facilitated by EF-Tu/EF-Tα, requires 1 ATP equiv. 3. Peptidyl transferase reaction, peptide bond formed 4. Translocation, needs EF-G/EF-2 and ATP equiv. tRNA move along by 1 binding site 5.Release of 1st tRNA, binding of 3rd tRNA at A site, requires ATP equiv. 6. carries on until a termination codon is reached |
| What does the elongation cycle consist of? | Repeated cycles of: Binding of aminoacyl-tRNA (needs GTPs) The peptidyl transferase reaction Translocation - movement of the ribosome one codon along the mNRA (needs GTP) |
| What is the result of each cycle? | Incorporation of one amino acid into the protein |
| What terminates a cycle? | Reaching a stop codon |
| Why does a stop codon terminate a cycle? | As there is no tRNA molecule complementary to a stop codon |
| What is the energy expenditure during translation? | Equivalent of 3 ATP used for each amino acid incorporated |
| What is each molecule equivalent of ATP used for? | One to link the amino acid to its tRNA One is used when the aminoacyl-tRNA binds to the ribosome One is used to faciliate translocation |
| Peptidyl transferase diagram. Cunt. | Well done. Prick. |
| What component of the ribosome catalyses the peptidyl-transferase reaction in E.Coli? | The 23s rRNA |
| How do we know this? | An E.Coli ribosome that has had ~95% of its proteins removed can still catalyse peptide formation X-ray crystallography shows that the active site for peptidyl transferase contains 23s rRNA but no proteins |
| What are elongation factors? | Accessory proteins that are not part of the ribosome required for translation |
| Name the elongation factors required for prokaryotic elongation and its eukaryotic equivalent | EF-Tu and EF-1α |
| Describe Step 1 of Elongation | Deliver aminoacyl-tRNAs to the ribosome |
| Describe Step 2 of Elongation | EF-G (EF-2 in eu) uses energy provided by the hydrolysis of GTP to move the ribosome along the mRNA during translocation Look at your notes here in detail to note the EPA site translocation |
| Compare eukaryotic and prokaryotic ribosomes | Eu ribosomes larger Initiation is different: Recog of ribosomal binding sites (Pro) or cap (Eu) Elongation is very similar Both very sensitive to antibiotics and inhibitors |
| Name and describe the effects of a class of antibiotics that effect ribosomes | Erythromycin/Clarithromycin target prokaryotic large ribosomal subunit Inhibits peptidyl transferase reaction & translocation |
| Name and describe the effects of a class of antibiotics that effect ribosomes cont. | Cholramphenicol targets prokaryotic and mitochondrial large subunit Inhibits peptidyl transferase reaction |
| Name and describe the effects of a class of antibiotics that effect ribosomes (Cont. cont.) | Ricin Targets Eu 60s subunit Catalytic action, removes a base fom rRNA, lethal dose in humans is approx 10^-4g |
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