Chapter 11
What are the three sites for tRNA on a ribosome
1. Aminoacyl (A) site (binding site) 2. Polytidyl (P) site (addition of amino acid site) 3. Exit (E) site (leaving site)
How are the introns removed?
1. Breaks are introduced at the splice sites (5' and 3' end) of the introns 2. Sequences at the splice sites have been conserved through time
What is the process for creating mRNA?
1. Created by RNA polymerase II 2. Aided by a specific transcription factors called General Transcription Factors (GTFs) 3. RNA polymerase and the GTFs together create the preinitiation complex 4. RNA polymerase moves from the 5 to 3' direction along the DNA adding complimentary trinucleotide precursers 5. As it moves DNA returns to helix and creates a pre-mRNA 6. Only portions of the pre-mRNA are used in the mRNA molecule 7. This is due to intervening sequences in the DNA gene, which are sequences seen in the pre-mRNA but not the mRNA 8. Genes with intervening sequences are called split genes 9. The portions of the slit gene which contribute to the mRNA are called exons and the portions that are not incorporated are called introns 10. At the 3' end a poly- A tail is added 11. At the 5' end a guanosine cap is added 12. Introns are excluded 13. Exons are linked together
What are the 5 overall steps seen in transcription and translation?
1. Creation of pre-mRNA from DNA template 2. Creation of mRNA from pre-mRNA 3. Movement of mRNA out of nucleus to ribosome in cytoplasm 4. Translation of mRNA in ribosome 5. Creation of protein in cytoplasm
What are the 5 aspects that all mRNA in eukaryotes share?
1. Each mRNA codes for only one protein 2. All mRNAs are found in the cytoplasm 3. They all attach to a ribosome when they are translated 4. Most have large areas of nucleotides that will never be translated 5. At the 3' end there is a poly-A tail 6. At the 5' end there is a guanasine cap
What are the 3 steps of translation.
1. Initiation 2. Elongation 3. Termination
What is the process of transcription?
1. RNA polymerase attaches to the promotor region of the DNA template with the aid of transcription factors 2. The RNA polymerase moves in a 3-5' direction along the template, adding nucleotides 3. These added nucleotides enter the RNA as trinucleotide precursers (putting them together is polymerization) 4. As RNA polymerase moves along the RNA-DNA hybrid dissociates and the DNA becomes a helix again 5. The RNA polymerase is responsible for polymerizing the nucleotides and for digesting of incorrect nucleotides
What are the steps involved in termination?
1. Release factors notice one of the three stop codons 2. Ribosome disociates from the mRNA
What are the steps involved in initiation?
1. Ribosome binds to intiation sequence (AUG) 2. Small portion of ribosome binds to the correct sequence with the help of initiation factors 3. It finds the 5' end of the message and looks for the 1st AUG 4. t-RNA brings in the first amino acid which is represent by AUG 5. two different types tRNA for this amino acid, one for initiation site and one for the middles portions of the mRNA 6. After initiator tRNA is bound the large portion of the ribosome joins 7.
What are the three stop codons?
1. UAA 2. UAG 3. UGA
What are the steps involved in elongation?
1. tRNA enters protein at the A site 2. Moves to the P-site where the amino acid is added to polypeptide chain 3. As it enters the P site another tRNA enters the A site 4. The amino acid is added to the chain by peptidyl transferase 5. Ribosome translocates which is when it moves in the 5- 3 prime direction in 3 nucleotides at a time
What is the sequence of the splice site at the 5' end?
3. At the 5 end the slice point is G/GU Gu is part of the intron
What is a codon?
A codon is a three nucleotide sequence that codes for an amino acid?
What is a polyribosome?
A complex of multiple ribosomes on one mRNA which allows the mRNA to be transcribed faster
What is a silent mutation?
A mutation that does not change the amino acid and has no effect other then a possibly different IEP
What is a nonsense mutation?
A mutation that produces a stop codon that should not be there creates a protein that stops before it is complete
What is a missense mutation?
A mutation which incorporates a wrong amino acid
What is the consensus sequence in bacteria?
A sequence found in the DNA that is usually 35 base pairs upstream of the promotor region
What is the sequence of the splice site at the 3' end?
AG/G AG is part of the intron
How is translocation driven?
By conformational changes in the elongation factor of the ribosome
What is RNA polymerase?
It is an enzyme that is able to encode DNA template strand into mRNA strand
What is mRNA?
It is messenger RNA, it is created from pre-mRNA which is created from the DNA template
What is pre-RNA?
It is the RNA molecule that is equivalent in length and compliment to the DNA strand
What is the Pribnow box?
It is the sequence on the DNA upstream of the promotor region where transcription begins
What direction does RNA polymerase move on the DNA strand?
It moves in a 3' to 5' direction the opposite of DNA replication
What is the purpose of miRNA and siRNA
Micro-RNA and small-interfering-RNA are responsible for binding to a complementary region of mRNA and inhibit the translation of its message
How do these sites differ?
RIbosomem oves the tRNA through each of the three sites in successive steps
What are the three types of RNA polymerases found in eukayotic cells?
RNA polymerase I RNA polymerase II RNA polymerse III
What is tRNA?
RNA that is responsible for translating the mRNA code to the ribosome
What splices the RNA at the splice sites?
Small nuclear RNA (snRNA)
What is the sequence of the Pribnow box?
TATA
What is the sequence of the consensus sequence in bacteria?
TTGACA
What is the name of the DNA that a pre-RNA is transcribed from?
The Transcription Unit
What is meant by upstream?
The area of DNA template that is preceeding the initiation site (towards the 3' end)
What is meant by down stream?
The area of DNA that is towards the 5' end
What is the genetic code?
The code that is exhibited in a gene
What is a splicosome?
The complex between the snRNA and the splice site sequence where the snRNA cuts the intron out of the mRNA
How do you use the chart for the genetic code?
The left column represents the first nucleotide, the top column represents the second nucleotide and the third column represents the third nucleotide
What is translation?
The process in which proteins are synthesized in the cytoplasm from a mRNA template
What is transcription?
The process of creating RNA from a DNA template
What is the promotor region?
The promotor region is the area on the DNA where the RNA polymerase binds to
How many codons can code for the same amino acid?
There are multiple codons that can code for the same amino acid.
How many polymerases are found bacteria?
There is only one polymerase in bacteria
What are transcription factors?
They are proteins which allow the RNA polymerase to identify the promotor region of the DNA
What is the function of RNA polymerase I?
Transcribe rRNA
What is the function of RNA polymerase II?
Transcribes mRNA
What is the function of RNA polymerase III?
Transcribes tRNA
What is rRNA?
ribosomal RNA which recongnizes molecules, provides structural support and catalyzes chemical reactions in which amino acids are joing to one another
