Ch 15 The Genetic Code & Translation Flashcards
structure of amino acid
central carbon atom bonded to amino group, hydrogen atom, carboxyl group, and R group
what links amino acids
peptide bonds
free amino group
amino end (N-terminus)
free carboxyl end
carboxyl end (C-terminus)
how many common amino acids are there?
20 common amino acids
through what process is a peptide bond formed to link amino acids
dehydration synthesis (production of water molecule)
protein structure: sequence of amino acids
primary structure
protein structure: interactions between amino acids
secondary structure
common secondary structures
alpha helix, beta pleated sheets
protein structure: folding of secondary structures (R group interactions)
tertiary structure
protein structure: 2 or more polypeptide chains association
quaternary structure
group of amino acids forming a discrete functional unit in a protein
domain
set of three nucleotides that encode a single amino acid
codon
how many possible codons are there?
(4 possible bases): 4^3 = 64 possible codons
codons that encode amino acids
sense codons
codons that specify end of translation
nonsense/stop codons
explain degeneracy of genetic code
amino acids may be specified by more than one codon
codons that specify the same amino acid
synonymous codons
tRNAs that have different anticodons but accept the same amino acids
isoaccepting tRNAs
nonstandard base pairing at 3rd position (3’) of codon due to it pairing weakly and allowing flexibility
wobble
explain how one anticodon can pair with more than one codon
pairing at the third codon is weak (wobble)
more than one base can pair with that 3rd position
how is the genetic code considered nonoverlapping
each nucleotide is part of a single codon
how many potential reading frames are there for any sequence of nucleotides
three potential reading frames
first mRNA codon to specify an amino acid
initiation/start codon
what is the start codon and what does it encode in prokaryotes and eukaryotes?
AUG
prokaryotes: n-formyl methionine
eukaryotes: methionine
list the three stop/nonsense codons
UAA, UAG, UGA
do stop codons encode amino acids?
no, stop codons do NOT encode amino acids
what is meant by the genetic code is universal?
all forms of life mostly use the same genetic code
what are the four steps of protein synthesis (translation)
tRNA charging
initiation
elongation
termination
tRNA attaches to its appropriate amino acid
tRNA charging
what is required for tRNA charging?
energy (ATP)
how do amino acids attach to tRNA?
adenine nucleotide of CCA at 3’ end of tRNA binds to carboxyl group of amino acids
specificity of amino acids to tRNA is performed by
aminoacyl-tRNA synthetase
how do aminoacyl-tRNA synthetase recognize its appropriate amino acid and tRNA
amino acid: based on sizes, charges, R groups
tRNA: based on tRNA nucleotide sequence
describe the process of tRNA charging of translation
- amino acid reacts with ATP to produce aminoacyl-AMP
- amino acid is transferred to corresponding tRNA, where carboxyl group of amino acid attaches to A of CCA of tRNA
- AMP is released
what are the functional units of the ribosome
large subunit and small subunit
what is the only way mRNA can bind to subunits of ribosome
if they are separate
describe the process of initiation of translation in prokaryotes
- IF3 binds to small subunit, allowing small subunit to bind to Shine-Dalgarno sequence within mRNA
- t-RNA charged with fMET forms a complex with IF-2 and GTP, and binds to initiation/start codon
- IF-1 joins to the small subunit, causing all initiation factors to dissociate from the complex and GTP –> GDP
- large subunit joins to create 70S initiation complex
describe initiation of translation in eukaryotes
- initiation complex recognizes 5’ cap and binds ribosome there
- ribosome moves –> 3’ until AUG is reached
- proteins in 3’ poly(A) tail interact with cap-binding proteins, forming a loop and enhances the binding of ribosome to 5’end
describe the process of elongation of translation in prokaryotes
- fMET tRNA occupies P site of ribosome
- EF-Tu forms complex with GTP and charged tRNA and placed in A site of ribosome
- GTP –> GDP, and EF-Tu GDP complex is released
- EF-Ts regenerates EF-Tu-GDP into EF-Tu-GTP, which is ready to combine with another charged tRNA
- peptide bond forms between amino acids in P and A site and tRNA in the P site releases its amino acid
- EF-G and hydrolysis of GTP –> GDP allows translocation of ribosome down mRNA
- tRNA in P site moved to E site and exits into cytoplasm; tRNA in A site moved to P site and A site is open for another tRNA
3 sites of ribosome
Peptidyl (P) site
Aminoacyl (A) site
Exit (E) site
what characteristic of rRNA allows P site of amino acid to be released from its tRNA?
catalytic activity (rRNA is a ribozyme)
what’s the difference between elongation of translation in eukaryotes and prokaryotes
prokaryotesto have three elongation factors: EF-Tu, EF-Ts, EF-G
eukaryotes have at least three elongation factors
describe the process of termination of translation in prokaryotes
- ribosome translocates to a stop codon –> no tRNA pairs
- RF-1 or RF-2 bind to A site where the stop codon is
- RF-3 forms complex with GTP and binds to ribosome
- polypeptide is released from tRNA in the P site
- GTP with RF3 hydrolyzed to GDP
- tRNA, mRNA, and release factors are released from the ribosome
what’s the difference between termination of translation in eukaryotes and prokaryotes
prokaryotes have 3 release factors
eukaryotes have 2 release factors:
- eRF-1 recognizes all termination codons
- eRF-2 binds to GDP
mRNA with multiple ribosomes attached
polyribosomes
what’s the purpose of polyribosomes
allows mRNA to translate multiple proteins simultaneously
what are some post-translational modifications
- molecular chaperones fold polypeptide chains into their correct shapes
- cleavage and trimming
- removal of signal sequence
- addition of chemical groups
enhances dissociation of large and small subunits of ribosome
initiation factor 1 (IF-1)
binds GTP and delivers fMet-tRNA to initiation codon
initiation factor 2 (IF-2)
binds to 30S small ribosomal subunit and prevents association with large ribosomal subunit
initiation factor 3 (IF-3)
binds GTP and charged tRNA and delivers it to A site
elongation factor Tu (EF-Tu)
regenerates active EF-Tu-GDP
elongation factor Ts (EF-Ts)
stimulates translocation of ribosome to next codon
elongation factor G (EF-G)
bind to stop codons
release factor 1 (RF-1)
release factor 2 (RF-2)
binds with GTP and binds to ribosome to terminate translation
release factor 3 (RF-3)
