Ch 11 From DNA to Proteins: Translation Flashcards
one-gene, one-enzyme hypothesis
Beadle and Tatum developed this which suggested that genes function by encoding enzymes and that each gene encodes a separate enzyme
one-gene, one-polypeptide hypothesis
some proteins are composed of more than one polypeptide chain and that different polypeptide chains are encoded by separate genes
amino acids
all proteins are polymers composed of these linked end to end
each consists of a central carbon atom bonded to an amino group, a hydrogen atom, a carboxyl group, and an R (radical) group that differs for each amino acid
peptide bonds
amino acids in proteins are joined together by these to form polypeptide chains; a protein consists of one or more polypeptide chains
polypeptide
have polarity: one end has a free amino group (NH3+) and the other end has a free carboxyl group (COO-)
two common secondary structures found in proteins
beta pleated sheet and the alpha helix
polynucleotide phosphorylase
does not require a template
it randomly links together any RNA nucleotides that happen to be available
sense codons
61 codons encode amino acids
degenerate
amino acids may be specified by more than one codon
synonymous codons
codons that specify the same amino acid
isoaccepting tRNAs
different tRNAs that accept the same amino acid but have different anticodons
wobble
when bases pair weakly, may be flexibility
the hypothesis proposed that there could be some nonstandard pairings of bases at the third position of a codon
nonoverlapping
each nucleotide is a part of a single codon
reading frame
each different way of reading the sequence and any sequence of nucleotides has three potential reading frames
initiation (start codon)
the reading frame is set by this which is the first codon of the mRNA to specify an amino acid
stop codons, termination codons, nonsense codons
UAA, UAG, and UGA signal the end of the protein in both bacterial and eukaryotic cells
universal
genetic code was assumed to be this meaning that each codon specifies the same amino acid in all organisms
aminoacyl-tRNA synthetases
the key to specificity between an amino acid and its tRNA is a set of enzymes
each recognizes a particular amino acid as well as all the tRNAs that accept that amino acid
tRNA charging
attachment of a tRNA to its appropriate amino acid, requires energy which is supplied by adenosine triphosphate (ATP)
initiation factor 3 (IF-3)
binds to the small subunit of the ribosome and prevents the large subunit from binding during initiatioin
initiation factor 1 (IF-1)
enhances the disassociation of the large and small ribosomal subunits
initiation factor 2 (IF-2)
required for the attachment between initiator tRNA and the initiation codon
30S initiation complex
complex consisting of 1) the small subunit of the ribosome, 2) the mRNA, 3) the initiator tRNA with its amino acid, 4) one molecule of GTP, and 5) several initiation factors
70S initiation complex
when the large subunit has joined the initiation complex
Kozak sequence
the identification of the start codon is facilitated by the presence of a consensus sequence that surrounds the start codon
a ribosome has three sites that can be occupied by tRNAs
the aminoacyl (A) site, the peptidyl (P) site, and the exit (E) site
elongation factor Tu (EF-Tu)
a charged tRNA binds to the A site; binding takes place when this joins with GTP and then with a charged tRNA to form a three-part complex
elongation factor Ts (EF-Ts)
regenerates EF-Tu-GTP from EF-Tu-GDP
translocation
third step in elongation
the movement of the ribosome down the mRNA in the 5’-3’ direction
elongation factor G (EF-G)
translocation positions the ribosome over the next codon and requires this
release factors
bind to the ribosome
E. coli has three release factors: RF-1, RF-2, and RF-3
polyribosome
an mRNA with several ribosomes attached; often just a polysome
molecular chaperones
correct folding may initially require the participation of other molecules
