Protein Pathway Supplement (2) Flashcards
Three stop codons
UAA
UAG
UGA
How many codons code for the 20 known amino acids
61
What is on the 5’ cap of mRNA
What is on the 3’ tail of mRNA
A 7-methylguanosine A Poly(A) tail
What is the general structure of tRNA
A cloverleaf with two distinct regions of unpaired nucleotides
Anticodon loop
A set of three consecutive nucleotides that paid with a complementary codon in mRNA
What is an aminoacyl tRNA
A complex of tRNA with amino acid
The AA needs to be activated by aminoacyl tRNA synthetases
Two step process for activation of amino acids
- Aminoacyl tRNA synthase catalyzes AMP to COOH end of AA
2. AA transferred to cognate tRNA
Why is it relevant that the structures of prokaryotic ribosomes and eukaryotic ribosomes are different
We can target prokaryotic ones with antibiotics
Describe the A site, P site, and E site
Where mRNA codon is exposed to receive aminoacyl tRNA
Where aminoacyl tRNA is attached
Location occupied by empty tRNA before exiting ribosome
What direction does translation occur
5 - 3
Three steps of translation
- Initiation - formation of mRNA, small ribosomal subunit and initiator tRNA pre-initiation complex
- Elongation - activated AA attached to initiating Met by forming a peptide bond
- Termination - peptide chain is release from ribosomal complex
Translation begins with what
AUG (methionine)
What in eukaryotes determines the reading frame for the whole sequence
5’, 3’ poly(A), kozak sequence, and the ATP dependent mRNA scan
The activated AA is attached to initiating methionine how
Via a peptide bond
What three steps involve elongating the peptide chain
- Loading of an amionacyl tRNA onto the ribosome
- Prior to loading, aminoacyl tRNA is attached to a GTP bound elongation factor
- Loading is accompanied by GTP hydrolysis
What enzyme catalyzes the formation of the peptide bond between AA in A and P sites
Peptidyl transferase
How do RF’s work
Bind to A site and cleave the ester bond between C terminus of the polypeptide and the tRNA
Describe the cytoplasmic pathway
Used for proteins destined for cytosol, mitochondria, mucleus, and peroxisomes
Protein synthesis begins and ends on free ribosomes in cytoplasm
Describe the secretory pathway
Used by proteins destined for the ER, lysosomes, plasma membranes, or for secretion
Translation begins on free ribosomes but terminates on ribosomes sent to ER
Proteins synthesized in cytoplasmic pathway have no what
No translocation signals
Translocation sequences are recognized by what
Transporter in inner membrane (TIM)
Transporter in outer membrane (TOM)
What is the signal sequence for ER Lumen proteins
KDEL
Lysine, aspartic acid, glutamic acid, leucine
What is the signal for lysosomal proteins
Mannose-6-phsophate
What is the signal for membrane proteins
N-terminal apolar regions
What is the signal for secretory proteins
Tryptophan domain
Glycoproteins can be either what or what
O or N
O-Link - formed with the hydroxyl bond of Ser of Thr
N-Link - always with Asparagine
Describe phosphorylation
Formaiton of an ester bond between phosphate and OH of amino acid through serine/threonine and tyrosine kinase
The phosphate is removed by phosphatases
Regulates enzyme activity and protein function
How does glycosylation attach to a protein
O - linked - through an OH group
N - linked - through a CONH2 group (amide)
How does phosphorylation attach to a protein
Through the formation of an ester bond between phosphate and the OH of the amino acid
How do disulfide bonds attach to proteins
Through the formation of a thiol (SH) group of two cystine residues
How does acetylation attach to proteins
Through Acetyl CoA
The histones are acetylated and deacetylated on their N-terminus Lysines
Silent mutation
No change to the amino acid
Missense mutation
Changes an amino acid within the protein
Frameshift mutation
One or more nucleotides are deleted or inserted which causes a change in the codon sequence and alteration in the amino acid
