Week 7 & 8 Flashcards
RNA sequences required in process of translation
Messenger RNA (mRNA): plan/info to build protein(s) (it contains the coding information of an amino acid sequence of a protein)
Transfer RNA (tRNA): adds amino acids (it carries specific amino acids to the ribosome to form the polypeptide chain) (serves to deliver the appropriate amino acid to the growing peptide chain)
Ribosomal RNA (rRNA): reads mRNA sequence (it is associated with proteins to form ribosomes)
Transcription DNA to RNA steps (go see PowerPoints to identify the structures)
- Initiation: RNA polymerase binds to promoter, then transcription of mRNA is initiated. The RNA will be copied from 5’ to 3’.
- Elongation: Transcription by RNA polymerase III.
- Termination: RNA polymerase III encounters terminator sequence and unbinds from DNA. mRNA transcript is then completed (5’ to 3’).
Compare formation and processing of mRNA in bacteria vs Eukaryotes
Transcription in bacteria (for mRNA):
- Transcription takes place in cytoplasm
- Translation begins (in cytoplasm) while mRNA is still being transcribed (translation takes place immediately when RNA takes place)
- Several genes transcribed in a single mRNA (operon)
Transcription in Eukaryotes (for mRNA):
- Transcription occurs in nucleus
- Pre-mRNA transcript processed to mature mRNA: there will be an addition of 5’-CAP (It protects the transcript from being broken down) & Poly A-Tail (it makes the RNA molecule more stable and prevents its degradation) and there will be an RNA splicing (Introns will be taken away leaving only Exons)
- Mature mRNA exported to cytoplasm for translation
Bacteria mRNA makes multiple proteins at the same time in the cytoplasm, while the Eukaryotic mRNA makes one protein at a time in the nucleus.
Define intron/exon and describe the process of splicing
Exon: Coding segment (exons are expressed) (it contains information to code proteins and peptides sequence)
Intron: Non-coding segment (it gives you variations) (introns in trash) (it does not code for proteins and interrupt the sequence)
During RNA splicing introns will be taken away so it will leave only exon. The introns will be taken away from the pre-mRNA
If the introns would not be removed, the RNA would be translated into a nonfunctional protein.
What are benefits of alternative splicing?
The overall function of alternative splicing is to increase the diversity of the mRNA expressed from the genome.
One of the benefits is that it allows a single gene to produce two or more mature mRNA variants that are similar but not identical.
Define genetic code and indicate its importance
The genetic code is composed of nucleotide triplets which are codons (every three nucleotides)
In mRNA specify for one amino acid
The genetic code is non-overlapping (each nucleotide belongs to one codon). It contains a ‘’stop’’ and ‘’start’’ (AUG) codons. The start codon marks where the translation sequence begins and the stop codon marks where the translation ends.
There is 64 possible codons (4 possible basis x 3 letters per codon)
Explain how mRNA and tRNA interact, by relating it to the genetic code
During translation, the anticodons of tRNA will bind with a few specific mRNA codon. This action will ensure that the correct amino acid will be added to the growing polypeptide chain. Therefore, the tRNA will be able to convert the code (genetic code) in mRNA.
Describe ribosome and detail the steps in formation of polypeptide (see PowerPoint for image)
Ribosomes are responsible for protein synthesis. They decode the message of the mRNA and form the peptide bonds. They are made of rRNA protein.
The 5 main steps involved in polypeptide synthesis are:
- Activation of amino acid
- Transfer of amino acid to tRNA
- Initiation of polypeptide chain
- Chain termination
- Protein translocation (move between cellular compartments)
- Initiation
- Codon recognition
- Peptide bond formation
- Translocation
Relate mutations to protein sequence, structure and function
A protein’s structure and function is determined by its amino acid sequence.
Mutation can cause the effect of a change in the amino acid sequence of a protein since it will change the structure which will then make the protein have a different function.
What are the different type of mutations and the different point mutations? What are there results/consequences?
Types of mutation:
- Substitution (replaces a triple sequence)
- Inversion (reverses the triple sequence)
- Point mutation (there is only one letter that has been changed)
- Insertion (one extra letter has been added)
- Deletion (one letter has been taken away)
Point mutation:
- Silent: Has no effect on the protein sequence (the polypeptide stays the same but the codons are different by one letter)
- Missense: Results in an amino acid substitution (removes a full triple sequence and changes it)
- Nonsense: Substitutes a stop codon for an amino acid (it changes the last amino acid for a stop codon)
