Theme 2C Flashcards
What are the three components of translational regulation of gene expression?
- Initiation
- Elongation
- Termination
What is translation?
The assembly of amino acids into polypeptides/proteins
What do amino acids contain?
- Amino group
- Carboxyl group
- R group (variable and determines unique character of amino acid)
What is a dehydration reaction?
Two amino acids are joined together via a covalent peptide bond between the carboxyl group and amino group
What are polypeptides?
Linear chains of amino acids linked by peptide bonds
What are proteins?
Folded (3D structure) and contain multiple polypeptides
What are non-polar amino acids?
R groups are usually CH2 or CH3, and not soluble in water
What are uncharged polar amino acids?
R groups usually contain oxygen (hydroxyl group or double bond)
What are charged amino acids?
R groups contain acids or bases that can ionize (have a positive or negative charge)
What are aromatic amino acids?
R groups that contain a carbon ring with alternating single and double bonds
What are the special functional amino acids?
- Methionine: first amino acid in polypeptide (start codon)
- Proline: causes bend in polypeptide chains
- Cysteine: disulfide bridge (2 cysteins next to each other) contributes to structure of polypeptides
What is the primary protein structure?
Amino acid sequence, determines protein folding and 3D structure which is critical for proper function
What is the secondary protein structure?
has alpha helices and beta sheets, depends on hydrogen bonding in the polypeptide backbone
What is the tertiary protein structure?
The 3D structure of a single polypeptide and is composed of interactions between amino acid side chains (disulfide bonds and charged regions)
What is the quaternary protein structure?
Interactions between more than one polypeptide to form a multisubunit protein (like hemoglobin)
What are chaperones?
Function to protect slow-folding or denatured proteins by preventing their aggregation
What are codons?
They are written in the 5’-3’ as they appear in mRNA.
- UAG, UAA, and UGA are stop codons and do not code for amino acids
- Non-overlapping, message contains no gaps
- Message translated in fixed reading frame set by start codon
What is degeneracy in the genetic code?
Most amino acids are specified by more than one codon
What are tRNA’s?
The adaptor between codons (mRNA0 and amino acids.
- Acceptor stem is where amino acid is attached
- Anticodon is at the bottom loop of the tRNA contains a 3 nucleotide sequence that recognizes the mRNA codon
- tRNA molecules do not bind to stop codons
What is wobble pairing?
The base at the 5’ end of the anticodon can form H-bonds with more than one type of base located at the 3’ end of the codon (in the mRNA)
How is aminoacyl-tRNA made?
“charging”: adding the amino acid to the tRNA to create an aminoacyl-tRNA (20 different versions for 20 different amino acids)
What are ribosomes composed of?
The large subunit made of rRNA, proteins, and contains a peptidyl transferase center for formation of peptide bonds.
The small subunit is pretty much the same except it has a decoding center where charged tRNAs read and decode the codon of mRNA.
- Each subunit is seperate in cytoplasm, but together on mRNA
- Eukaryotic ribosomes are bigger
What are the tRNA binding sites of ribosomes?
A. Aminoacyl: binds to the tRNA carrying the next amino acid to be added
P. Peptidyl: binds to the tRNA attached to the growing peptide chain
E. Exit: binds to the tRNA that carried the previous amino acid added
Describe translation initiation.
An initiation complex (ribosome, mRNA, initiator tRNA) is formed after binding to methionine.
- Initiator tRNA brought to P site of small ribosome subunit (needs GTP)
- tRNA + small subunit complex recruited to 5’cap of mRNA and scans 5’-3’ until first AUG
- Complementary base pairing between initiator tRNA anticodon and mRNA start codon
- Large subunit binds to small subunit to form initiation complex, which is now ready to accept first tRNA to A site
- GTP hydrolyzed to GDP, translation begins now
