Functions/ Dysfunctions-protiein Processing Flashcards
Central dogma of molecular biology
DNA—>RNA—>Protein
What is the purpose of the genetic code
To convert a nucleotide sequence of a gene into an amino acid sequence of a protein using mRNA as an intermediate
(Gene —> protein)
Code can be degenerate (some codons can code for more than one amino acid and some codons do not code for any aa)
Start codon
AUG
Coding for methionine
Stop codons
UAA,
UAG,
UGA
Which point mutation does not cause change in the amino acid being coded
Silent mutation
Which point mutation changes the amino acid in the protein but does not effect the protein function dramatically
Missense mutation
Which point mutation deletes or inserts one or more nucleotides into or out of frame.
Frameshift mutation
Which point mutation changes the codon into a stop codon causing premature termination. Causes the formation of the truncated version of a protein
Nonsense mutation (null mutation)
What disease arises from a missense mutation of the 6th codon in the allele for human B-glowing (subunit of hemoglobin) ?
Changes GAG -> GTG
- valine -> glutamate
- hydrophobic -> negative and hydrophilic
*OPPOSITE
SICKLE CELL ANEMIA
- Hgb starts to aggregate and form rigid rod like structures which causes sickle cell RBC’s
- poor O2 binding capacity of Hgb and Hgb tends to clog capillaries
Large frameshift deletions of the dystrophin gene which leads to defective dystrophin proteins
- causes muscle wasting and eventual wheelchair need
- 1:3,500 males
Duchenne Muscular Dystrophy
Severe form of Duchenne muscular dystrophy is caused by
Out of frame deletions that result in little/no expression of dystrophin proteins
What causes Becker muscular dystrophy
In frame deletions result in the expression of truncated forms of dystrophin. This version is more midl than DMD
*muscle becomes replaced with fat and fibroid
What is the cap on mRNA comprised of
5’ cap is made of guanosine and 3 phosphates
7-methylguanosine cap
What is the tail on mRNA called
Poly(A) tail at the 3’ end made up of adenine
. tRNA serves as an adaptor by having a binding site for both codons in mRNA and amino acids. TRNA matches amino acids to ____ in mRNA
Codons
Describe the structure of tRNA
- cloverleaf structure
- has 2 regions of unpaired nucleotides that are crucial to function
- Anticodon loop where mRNA complementary sequence binds
- 3’ CCA terminal region which binds the matching amino acid [attached is Phe]
It also has a T and D loop
What activates the amino acid that is esterfied to the CCA sequence of tRNA
aminoacyl tRNA synthetase enzyme
- serves as a second genetic code
- each amino acid has its own
- important to maintain fidelity of protein synthesis
Explain how aminoacyl tRNA synthetase functions
- Links amino acid to tRNA by high energy bond
- TRNA the binds to its mRNA codon
This enzyme also catalyze the addition of AMP to COOH end of the amino acid
Where does protein synthesis (translation) occur?
In the ribosome
T/F
Large and small ribosomal subunits assemble together into an active complex in the presence of mRNA
True
Difference between eukaryotic and prokaryotic ribosomal subunits
Eukaryotic - 60S and 40S
Prokaryotic - 50S and 30 S
Important for antibiotic function
What are the 3 sites of a ribosomal complex that are important for translation
- A site. Acceptor site is where the mRNA codon …
- P site- peptidyl site is where aminoacyl tRNA is attached
- E site- exit site is when the tRNA exits the ribosome
What direction does translation occur
5’ —> 3’
What are the 3 steps of translation
- Initiation
- Elongation
- Termination
What happens in the initiation step of translation
Formation of mRNA, small ribosomal subunit, and initiator tRNA pre-initiation complex
What happens in the elongation step of translation
Activated amino acids attached to initiating MET residue by forming a peptide bond
What happens in the termination step of translation
The peptide chain is released from the ribosomal complex as coded by the stop codons
What is e1F2 in the initiation step of translation
E1F2 is the eukaryotic intiation factor
-MET first binds to the P site and E1F2
What is EIFG?
Eukaryotic initiation factor
What is the reading frame for prokaryotic mRNA in translation?
Shine-Dalgarno (SDG) sequence (AGGAGG)
What is the eukaryotic mRNA reading frame for translation
5’ cap and 3’ poly A tail; the Kodak sequence
Label the steps of translation initiation
- Pre-initiator complex is first assembled
- Large subunit ribosome is then added to form initiaion complex
- Initiator tRNA attaches to P site of the small subunit
- Other initiation factors are added
- Large subunit is then added
- Translation begins with the start AUG codon
What is the initiatior tRNA for eukaryotes ?
Methioninyl tRNA
What are the translation initiation factors in eukaryotes and prokarytoes
IF- in prokaryotes
eIFs- in eukaryotes
What steps begins with the activated amino acid attached to the INITIATING METHIONINE via a PEPTIDE BOND
Elongation
What are the steps of elongation by the ribosome
- Aminoacyl tRNA is attached to a GTP-bound elongation factor
- Loading of aminoacyl tRNA so the anticodon pair is positioned on the A site
- Loading is possible by hydrolysis of GTP and release of factor from aminoacyl tRNA
What is the type of bond formed between the amino acids in the A and P site in translation? And what is the enzyme that catalyzes it?
- Peptide bond
- Peptidyl transferase
*nrg comes from bond between aa and tRNA
What step in translation is related to the release of the peptide chain from the ribosomal complex and the dissociation of the ribosomal complex
Termination step of translation
What triggers termination
The stop codons of UAA, UAG, and UGA
What recognizes the stop codons in the termination step of translation
Release factors (RF’s)
*are proteins that catalyze the addition of water (instead of an amino acid) and form a COOH bond at the end of the polypeptide