Lecture 2 - Exam 3 Flashcards
- Is it guaranteed that a transcript will make it to a protein in the cell?
- What happens the longer a mRNA persists?
- Stability often depends on what?
- NO!
- The longer a mRNA persists the more protein can be made off of it.
- Stability often depends on the length of the poly-A tail that is added to the mRNA transcript’s 3’UTR.
What does Sense and Antisense strands mean?
Sense: 5’ to 3’
Antisense: 3’ to 5’
How many tRNAs are there?
40 tRNAs, more than amino acids.
With the wobble base, what bases have to be correct and which ones can be incorrect?
The first two bases must be correct, and the third base can be incorrect… hence, the wobble base.
Describe the structure of the 60S ribosomal subunit.
tRNA molecules, ribosomal proteins, and ribosomal RNA (rRNA). The ribosome has three tRNA-binding sites, designated P (peptidyl), A (aminoacyl), and E (exit).
Note: Unsure, but in class mentioned that it is half protein/half RNA
- It was first thought that rRNAs played only a structural role in ribosomes. It was later shown that rRNA does what?
- What is the proof of catalytic activity?
- The role of rRNA in the formation of peptide bonds extends the catalytic activities of RNA beyond…? This may provide an important link for understanding what of cells?
- rRNAs also play a largely _______ role.
- It was later shown that rRNA has catalytic activity and they are responsible for the peptidyl transferase reaction to occur.
- Ribosomal proteins are absent from the site of the peptidyl transferase reaction, showing that rRNA is responsible for catalyzing peptide bond formation.
- The role of rRNA in the formation of peptide bonds extends the catalytic activities of RNA beyond self-replication to direction involvement in protein synthesis.
This may provide an important link for understanding the early evolution of cells. - structural
Describe the primitive atmosphere when the first cell emerged ~3.8 billion years ago, 750 million years after Earth was formed.
Don’t forget Stanley Miller’s experiments! What did his experiments show?
No oxygen! Reducing conditions in the atmosphere = very reactive compounds + energy.
Miller’s experiments in the 1950s showed that organic molecules could form spontaneously in conditions thought to have existed on early Earth. These molecules included amino acids… Other experiments showed that organic molecules can spontaneously polymerize (heating amino acids causes them to polymerize).
Describe the process of production of B-globin and hemoglobin.
The gene (DNA) for B-Globin will be transcribed. Nuclear RNA (nRNA) will be the result of this. This includes exons and introns, along with the m7 Cap and poly-A tail. The next step is nuclear RNA being processed. This will remove introns from the RNA and will result in messenger RNA (mRNA). (5’ cap is still present is necessary for translation and prevents degradation & will not end up being part of the protein). The next step is the mRNA being translated into the B-Globin protein sequence (now, the 5’ cap and poly-A tail are absent). The final step is posttranslational modification, resulting in the hemoglobin protein.
- What are the three stages of translation?
- What recognizes Eukaryotic mRNAs?
- What happens after the eukaryotic mRNAs are recognized?
- How many ribosomes are required to translate one mRNA? What is this called?
- Initiation, elongation, and termination.
- Eukaryotic mRNAs are recognized by the 7-methylguanosine cap at the 5’ end (5’ cap).
- The ribosomes then scans downstream of this cap until they encounter the initiation codon.
- One mRNA is typically translated by multiple ribosomes. This is called a polyribosome or polysome.
In what directions are all mRNAs read in? What way are polypeptide chains synthesized?
All mRNAs are read in the 5’ to 3’ direction, and polypeptide chains are synthesized from the amino (N) to the carboxyl (C) terminus.
Step 1: Initiation
1. In eukaryotes, initiation is complex, and requires at least how many proteins? What are these called?
2. What is eIF4E? What is it involved in? How what forms do they exist in? Do all cellular mRNAs require eIF4E?
- It requires at least 12 proteins, designated eIFs (eukaryotic initiation factors).
- eIF4E, eukaryotic initiation factor 4E, is a protein that in humans is encoded by the EIF4E gene. eIF4E is involved in directing ribosomes to the cap structure of mRNAs. They exist as both a free form and as part of the eIF4F pre-initiation complex (mediating the mRNA-ribosome interaction). Almost all cellular mRNAs require eIF4E to be translated into protein.
Describe the initiation of translation in eukaryotic cells.
- Initiation factors eIF1, eIF1A, and eIF3 bind to the 40s ribosomal subunit.
- The initiator methionine tRNA is bound by eIF2 (complexed to GTP) and forms a complex with the 40S subunit and eIF5.
- The mRNA is brought to the 40S subunit by eIF4E (which binds to the 5’ cap), eIF4G (which binds to both eIF4E at the 5’ cap and PABP [Poly-A binding protein] at the 3’ poly-A tail), eIF4A, and eIF4B.
- The ribosome then scans down the mRNA to identify the first AUG initiation codon. This scanning require energy and is accompanied by ATP hydrolysis.
- When the initiating AUG is identified, eIF5 triggers the hydrolysis of GTP bound to eIF2, followed by the release of eIF2 (complexed to GDP) and other initiation factors.
- The 60S ribosomal subunit then joins the 40S complex facilitated by eIF5B.
Technique: What are Morpholino Oligonucleotides used for?
Morpholino Oligonucleotides are uncharged, stable molecules used to block complementary sequences of RNA. There are translation blocking or splice blocking versions.
It uses steric hindrance to impede:
translation or mRNA processing.
What does steric mean?
What about steric hindrance?
Relating to the spatial arrangement of atoms in a molecule, especially as it affects chemical reactions.
Steric hindrance is the slowing down of chemical reactions.
Mutations in what can alter the ultimate expression of a particular gene?
Mutations in splicing sites.
