Flashcards in Chapter 17 - From Gene to Protein Deck (27):
What is Transcription?
creating an RNA copy of a DNA code
What does Transcription consist of?
Initiation - the beginning of the copying
Elongation - the creation of the RNA copy
Termination - the end of the copy
What happens in initiation?
The promoter (a section of DNA often includes a TAT box and ~25 nucleotides upstream from the start point) of a gene includes within it the transcription start point.
- Transcription factors attach to the TATA box
- then an RNA polymerase II binds to the promoter after transcription factors are present and attached to the TATA box.
- The RNA polymerase II will separate the two DNA strands and will make a copy of RNA
What are the components of the Transcription Initiation Complex?
Promoter, Transcription factors, RNA Polymerase II and the other transcription factors that bind to the DNA when RNA polymerase II binds.
What is the elongation process?
The RNA Polymerase II will move along the DNA strand, it will unzip the double helix.
- RNA nucleotides are bound together from 5' to 3' making a copy of the DNA
*remember that in RNA, Thymine is replaced with Uracil
How is transcription terminated?
The RNA polymerase II will transcribe a sequence on the DNA called the Polyadenylation signal sequence
- then at ~a0-35 nucleotides downstream from the AAUAAA, proteins associated with the growing RNA will cut it free from the polymerase.
- releases a pre-mRNA for processing
What happens in RNA processing?
After RNA is transcribed a modified guanin nucleotide is added to the 5' end called the 5' cap.
- At the 3' end an enzyme adds 50-250 more adenine nucleotides forming what is called the poly-a-tail.
How does a copy of RNA turn into a mRNa (messenger RNA)?
when an RNA copy is made there are regions made up of coding and non-coding regions. Non-coding regions need to be cut out.
- The coding regions are called Exons and the non-coding regions are Introns
- When the 5' cap, Poly-A tail, and the introns are removed the molecule becomes a messenger RNA.
Translation consists of...
mRNA that has the genetic code that will be made into proteins.
- Transfer RNA (tRNA) is a folded up piece of RNA that binds to amino acids to transfer them to the new protein
- Ribosomes act as a work bench for the adding of amino acids into a polypeptide chain.
What are tRNA?
RNA that is folded up (typically three times).
It will have an attachment site on one end with a genetic code that matches with an amino acid.
What is an Anticodon?
the nucleotides that are exposed from one of the three loops in the tRNA.
What is an aminoacyl-tRNA synthetase?
It is an enzyme that binds an amino acid to a tRNA molecule
What are tRNA and amino acid that are bound together called?
Aminoacyl tRNA (sometimes called "charged tRNA)
What happens to the charged tRNA?
It will wait until the bound amino acid is needed in the ribosome to make the polypeptide.
What function does the ribosome have in translation?
- The ribosome acts as a workbench for translation of the mRNA into a polypeptide chain.
What composes the ribosome?
The small subunit - Has a binding site for the mRNA
The Large subunit - Has a site for the Aminoacyl tRNA to enter, a site where the amino acids are bound to each other, and an exit site where the tRNA leaves the ribosome.
Exit tunnel - where the growing polypeptide chain leaves.
What is the initiation process in Translation?
The mRNA is bound to the small ribosomal subunit.
- Every three nucleotides are codons with specific codes to make amino acids.
- An initiator tRNA will bind to a codon AUG with UAC to start the process.
- The large subunit is then added and completes the Translation Initiation Complex.
*This process also requires initiation factors and energy from GTP
What is the elongation process of Translation?
- A codon in site A will bind to a tRNA with the corresponding code.
- a peptide bond will form between the amino acids
- Moves from Site A to P to E and out of the ribosome.
- Then repeated until the polypeptide is complete.
What is the Termination process of Translation?
- At the end of the mRNA sequence for the polypeptide there will be a stop codon (UAG, UAA, UGA)
- a release factor that is similar to a tRNA is accepted and bound to the codon.
- The release facto promotes hydrolysis of the bond between tRNA and the last amino acid
- This will free the peptide from the ribosome
- With hydrolysis of at least 2 GTP the ribosome subunits and mRNA are dissociated.
What is the start codon?
What are the stop codons?
UAA, UGA, UAG
What are mutations?
They are changes to the genetic information
What are the different type of mutations?
Point mutations, Insertions, Deletions, Frameshift mutation
What are the different types of point mutations?
Silent - No effect on amino acid sequence
Missense - Changes amino acid for another amino acid (may have little effect
Nonsense - change from an amino acid codon for a stop codon
What is an Insertion mutation?
An addition of nucleotide pairs
What is a Deletion mutation?
The loss of nucleotide pairs