460937
Description
| Question | Answer |
| What is an aminoacyl tRNA molecule called? | tRNA molecule bound to an amino acid |
| What is a decylated/uncharged tRNA molecule? | A tRNA molecule which has had its amino acid removed |
| What is a peptidyl tRNA molecule? | A tRNA molecule bound to a growing polypeptide chain |
| Which codon is the start codon? | AUG (methionine) |
| Which codons are stop codons? | UAG, UAA, UGA |
| What can the deletion or insertion of a base cause? | A shift in the reading frame which can change the corresponding amino acids and therefore the structure of the protein. |
| Why does protein synthesis take place outside the nucleus? | DNA is too big to leave the nucleus therefore DNA is transcribed in mRNA as it is small and mobile. |
| What is the 5' cap composed of that is added to pre-mRNA? | Phosphorylated 7-methyl guanosine |
| What adds the 5' cap to the pre-mRNA? | Guanyltransferase |
| Why is a 5' cap added to the pre-mRNA? | Ensures mRNA is transported out of the nucleus, blocks degradation of mRNA 5' exonucleases and promotes translation |
| How is a 3' poly-A-tail added to the pre-mRNA? | The pre-mRNA is cleaved by an endonuclease near a signal AUAAAA sequence at the 3' end. 200 adenosine residues are then added at the cleavage site by poly-A-polymerase |
| Why is a poly-A-tail added? | It protects the mRNA from degradation by 3' endonucleases. The tail also aids in the termination of transcription, ensures export from the nucleus and is important in translation. |
| What is splicing of pre-mRNA? | pre-mRNA contains regions which code for proteins known as exons and unused base sequence know as introns which need to be sliced off. |
| What does alternative splicing mean? | That a single gene can code for many different proteins |
| What does the mRNA do after transcription? | Leaves the nucleus and travels to ribosomes for translation |
| What do ribosomes consist of? | 40s subunit and 60s subunit |
| What is initiation? | The binding of a ribosome to the 5' end of the mRNA and hydrogen binding of the anticodon of an aminoacylated tRNA carrying methionine on the AUG start codon. |
| What is elongation? | The addition of further amino acids to the growing polypeptide chain brought by corresponding aminoacylated tRNAs. Peptidyl transferase creates covalent peptide bonds between the amino acids |
| What is termination? | When the stop codon is reached and the peptide and ribosomal subunits are released |
| Where are proteins destined for use in the cytoplasm synthesised? | On free ribosomes |
| Where are proteins destined for secretion out of the cell synthesised? | On ribosomes attached to the RER |
| What is the name given to the cavities of the RER and golgi? | Lumen |
| What mutation occurs in sickle cell anaemia? | Glutamine becomes valine |
| What happens to blood cells in sickle cell anaemia? | Haemoglobin crystallises when oxygen levels are low, causing the sickle shape which gets stuck in small vessels |
| What are the clinical consequences of sickle cell anaemia? | Downstream tissue ischemia, causing pain and infarction. Organ damage and ischemic stroke. |
| Where is sickle cell anaemia common? | In sub-Saharan Africa where sickled red blood cells provide protection against malarial parasite, thus giving individuals with the mutation a selective advantage |
| Where can the nucleotides required for mRNA synthesis be found? | The nucleus |
| Why does alternative splicing mean that more than one protein can be synthesised from a gene? | Particular exons will be included and excluded from mRNA which will produce different amino acid sequences |
| Is the product of translation the finished protein? | No because it hasn't been folded yet |
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