Ribosomes
The site of translation
What is a ribosome?
mRNA base triplets/words
What are codons (a.k.a. a Triplet code)
*always read in the 5' to 3' direction, redundant but not ambiguous*
The synthesis of RNA using DNA to produce mRNA
What is Transcription?
3' end of mRNA
What is a poly-A tail (50-250 adenine bases)?
*Joined to the sequence by polyadenylatition and the 3' UTR comes before it (coded by AAUAAA)*
The process of synthesising proteins from mRNA
What is translation?
Multiple ribosomes translating 1 strand of mRNA simultaneously
What is a polyribosome (or polysome)?
*allows cells to make many copied of a protein at once*
The correct group of codons, must be read this way for a specific polypeptides
What is a reading frame?
Stretch of DNA that is transcribed
What is the transcription unit?
5' end of mRNA
What is a 5' cap (guanine with three phosphates)?
Three phases of translation
What are:
1. Initiation (The process of bringing mRNA and tRNA [with an amino acid] together in a ribosome)
2. Elongation (Amino acids are added one by one)
3. Termination (protein!)
___ and proteins combined make up the large and small subunits of ribosomes
What is Ribosomal RNA (rRNA)?
What is a stop codon?
*64 codons, 3 are stop codons (UAG, UAA, UGA)*
The three steps of transcription
What are:
1. Initiation (RNA polymerase binds to DNA at the promoter, unwinds the DNA, and start the RNA transcript)
2. Elongation (RNA polymerase moves down the DNA and elongates the RNA transcript)
3. Termination (The transcript is complete and the polymerase terminates)
UTR stands for...
What is "Untranslated Region"?
*Also called an Intron-intervening sequences, not expressed*
The three steps of initiation (in translation)
What are:
1. The small unit of the ribosome binds with mRNA and a tRNA initiator
2. The small unit of the ribosome moves the mRNA to the start codon (AUG)
3. Initiation factors bring in the large unit of the ribosome and completes the initiation factor
What is an Exit Tunnel?
The codon on the tRNA that complements the mRNA
What is an anticodon?
Provides a template for complementary RNA transcript
What is a template strand?
Expressed regions of unprocessed RNA
What are exons
The three steps of elongation (in translation)
What are:
1. The codon is recognized and the tRNA bonds with it at the P site
2. A peptide bond is formed when the old polypeptide is moved to the amino acid on the tRNA in the P site
3. The old tRNA moves from the A site to the E site (and leaves) when the mRNA shifts (with the addition of a GTP), then the new tRNA moves to the A site
The three "sites" in a ribosome (and their function)
What are:
-The P site: hold the tRNA that carries the growing polypeptide chain
-The A site: hold the incoming tRNA
-The E site: where the tRNA leaves the ribosome
Flexible pairing at the 3rd base pair of the codon that allows tRNA to bind to more than one codon
What is a wobble?
Names of the RNA transcript before and after processing
What is Before = (primary transcript) and After = (RNA processing. Done by enzymes in the nucleus. ends of transcript are altered, interior parts are cut out, remaining is spliced)
*RNA Splicing= introns removed and exons joined*
Cellular chain of commands from DNA to RNA to Proteins
What is the Central Dogma?
The three steps of termination (in translation)
What are:
1. The stop codon in the mRNA eventually reaches the A site
2. The A site accepts a "release factor"
3. The release factor accepts a water molecule rather than an amino acid and the translation complex comes apart