Module 9: V6 - V11 Flashcards
Where does translation occur?
in the cytoplasm
What is required for translation to occur?
tRNA needs to have the amino acid attached to it
the first tRNA and the small subunit of the ribosome are going to bind to the mRNA
What sets the frame that the mRNA is going to be read by?
the start codon (AUG) and the methionine tRNA that is going to bind to it
What occurs after the first tRNA and small subunit of the ribosome bind to the mRNA?
the large subunit of the ribosome will bind and then the next tRNA can come in and the process of peptide bond formation can start
What happens once the stop codon is reached during translation?
termination occurs in which the mRNA and protein dissociate, and the ribosomal subunits are recycled -> protein folding and posttranslational processing
What are structures in the tRNA which are vital for its function?
the anticodon which binds to the codon (reverse complement) and the section which is bound to the amino acid (amino acid arm)
What is the role of aminoacyl-tRNA synthetases?
add the amino acid to the amino acid arm of tRNA
What are the different classes of aminoacyl-tRNA synthetases?
class I and class II one is monomeric and the other is dimeric
Which end of the amino acid is attached to tRNA?
the carboxyl end
What is the role of inosine in the anticodon?
allows one tRNA to read more than one codon
this is because inosine allows ‘wobble’ in the third base of a codon
Which bases can inosine pair with?
A, U and C
What is the ribosome made of?
protein and RNA
Which part of the ribosome carries out catalysis?
RNA not protein
How is the AUG start codon distinguished from other AUG codons in prokaryotes?
binding of the ribosome is guided by the Shine-Dalgarno sequence which is a ribosome binding site upstream of the first AUG codon (initiation codon)
How is the AUG start codon distinguished from other AUG codons in prokaryotes?
there is a 5’ cap which the ribosome binds to and then slides down the mRNA
the first tRNA will bind with the first AUG codon
Which sites are found on the mRNA binding site?
the A-site, P-site and E-site
What happens when a new tRNA binds to the A-site?
a bond forms between the two amino acids on the tRNAs in the A- and P-site and the bond is broken between the tRNA in the P-site and its respective amino acid
What happens once the tRNA in the A-site is bound to the entire polypeptide chain?
the large subunit of the ribosome will slide across along with the small subunit and now the tRNA that was once in the A-site will be in the P-site and the tRNA that was once in the P-site will be in the E-site (process repeats until STOP)
What happens once a STOP codon is reached?
binding of release factor to the A-site and hydroxylation of the carboxyl end to the final tRNA is catalysed (release of polypeptide chain)
What happens when an operon contains several genes?
results in the production of polycistronic mRNA which has multiple ribosome binding sites where translation can occur separately from the other genes
Why is transcription and translation able to happen at the same time in prokaryotes?
because there is no nucleus
Where can ribosomes be found in eukaryotes?
in the cytoplasm or rough endoplasmic reticulum because there are some proteins which may need to be modified and sent to other parts of the cell or transported out of the cell
How is a protein translocated to the correct location in the cell?
the cell uses signal sequences
Where is a signal peptide found?
at the start of the protein sequence for those proteins that are modified, trafficked and secreted
What is the role of reverse transcriptase in retrovirus?
converts viral RNA into a DNA copy which can then be inserted into the genome and from that transcription can produce another viral genome in RNA
What are retrotransposons?
remnants of retrovirus which can no longer make coat or leave the cell and are only involved in the process of DNA integration
Why does reverse transcriptase invalidate the central dogma?
because the central dogma describes DNA replication, transcription of DNA to RNA and translation of RNA to protein, not reverse transcription or RNA replication
What is a transposon?
an active piece of DNA that can move from place to place
they are usually between genes or inside introns
What are DNA transposons?
transposons which move using a DNA intermediate
What are retrotranspsons?
transposons which move using an RNA intermediate
not really moving, they are making a new copy of themselves that inserts somewhere else
What do LINEs encode for?
reverse transcriptase so can move autonomously
Do SINEs encode for reverse transcriptase?
no, because they are too short and therefore cannot move autonomously
What would allow a SINE to move from one place to another in a genome?
the only way a SINE could move from one place to the other in a genome is if there is a LINE element that is producing RT that can then act on the RNA of a SINE element
How much of the genome is coding?
only about 1.5% as there is a lot of non-coding sequence within genes (introns), and space between genes
What are characteristics of the mitochondrial genome?
very little space between genes, no introns, circular (more like a bacterial genome structure), 4 of the 64 codons encode a different thing compared to the nuclear genome, fewer tRNAs
What does mitochondrial disease affect?
energy, development, vision, cause seizures
Where are the genes that can cause mitochondrial diseases when there are mutations?
can be caused by mutations in the mitochondrial genome OR the mitochondrial genes in the nuclear genome
