chapter 9 part 2 Flashcards
start codon
AUG - methionine
stop codons
UAA. UAG, UGA
kinase
what are release factors
ALL organisms use these to bind a stop codon in the A-site, which then makes the polypeptide bond to the tRNA at the P-site release & the RF is ejected- then ribosomal subunits separate
what are the release factors in bacteria
-RF1: recognize UAG & UAA
-RF2: recognize UGA & UAA
-RF3: recycles RF1
what is the release factor in eukaryotes & archaea
-eRF1 recognizes all three stop codons
-eukaryotes have a second release factor that recycles eRF1
how many ribosomes do bacteria cells contain & how much percent of the cell mass do they make up?
-20,000
-25%
what are polyribosomes
structures containing groups of ribosomes all actively translating the same mRNA
where are mRNAs produced in eukaroytes?
the nucleus
-must be processed to form mature mRNAs & then exported to the cytoplasm for translation
is monocistronic in eukaroytes or prokaryotes
eukaryotes
monocistronic
an RNA that directs synthesis of a single kind of polypeptide
what produces polycistronic mRNAs in bactera
operons
what are polycistronic mRNAs?
these lead to the synthesis of several different proteins
-contain more than one polypeptide-producing segment
-each segment has a start & stop codon
-most segments have shine-delgarno sequences
what separates the segments is polycistronic mRNA
intercistronic spacer sequences
are intercistronic spacer sequences translated?
no!
when can intact ribosomes proceed to the next start codon after finishing translation of the previous segment without disassembly
when the intercistronic spacer is short
transfer RNAs
adaptor molecules that interpret & then act on infromation carried in mRNA
codons
groups of three consecutive nucleotides in an mRNA each correspond to one amino acid
how many codons does to genetic code contain?
64
what are synonymous codons?
code for the same amino acids (ex: ser has seven different codons)
how many different tRNA genes do most genomes have?
30-50
isoaccepting tRNAs
tRNA molecules with different anticodons that carry the same amino acid
is genetic code universal?
yes, in fact bacteria can be used to produce important proteins from plants & animals
what are aminoacyl-tRNA synthetases or tRNA synthetases
enzymes that catalyze the addition of the correct amino acid to tRNAs
-a large molecule that contacts several points on the tRNA in the recognition process
acceptor stem
the correct tRNA fits into the active site of the tRNA synethetase
what provides energy for the tRNA synethetase attachment of amino acid
ATP
who determined that an overlapping genetic code was no possible?
sidney brenner
what did fraenkel-conrat find?
single nucleotide changes led to a single amino acid change
how did we get proof of a triplet genetic code?
when researchers created mutations by insertion or deletion of single nucleotides into the rII gene in T4 bacteriophage
what is the reading frame?
this refers to the specific codon sequence as determined by the start codon
what are frameshift mutations?
mutations that alter the reading frame
-all the codons after the addition or deletion will specify the wrong amino acids
what are the two categories of post-translational events
-post-translational polypeptide processing
-protein sorting
Post-translational polypeptide processing
-modifies polypeptides into functional proteins by removal or chemical alteration of amino acids
protein sorting
-uses signal sequences/leader sequences to direct proteins to their cellular destinations
is fMet found in functional bacterial proteins?
no
T/F: methionine is always the first amino acid in eukaryotic proteins
False
what is the most common amino acid modification?
phosporylation
what is phosphorylation?
it is carried out by kinase enzymes that add phosphates to proteins
it can activate or inactivate a protein
what are other enzymes that may add other functional groups to amino acids?
methyl- methylase
hydroxyl- hydroxylase
acetyl- acetylase
-carbohydrate side chains are also added to some proteins
insulin
-first produced as proproinsulin
-cleaved at the N-terminus to proinsulin
-cleaved again after froming disulfide bonds to make insulin
what does insulin consist of?
A-chain & B-chain segments
what do signal sequences do?
-15 to 20 amino acids at the N-terminal direct proteins to their cellular destinations
what is the signal hypothesis?
proposes that the first 15 to 20 amino acids of many polypeptides contain an “address label”
what did Blobel suggest?
that the signal sequence directs proteins to the endoplasmic reticulum (ER) & then the Gogli Apparatus, where they are sorted for their specific destinations
what do proteins destined for the ER have?
a N-terminal signal sequence that direct the forming polypeptide into the ER lumen or membrane
where are polypeptides destined for secretion produced?
at the rough ER
transmembrane proteins
Cotranslation of proteins into the ER lumen are deposited within the membrane itself
conformational diseases
-when large amounts of mutant proteins accumulate
-often neurodegenerative disorders & dementias
types of conformational diseases
-alzheimer disease
-parkinson’s disease (a form of it)
-huntington’s disease
Most synonymous codons can be grouped so they differ only in ____ _____ ____.
the third base
what does the third base wobble create
flexible pairing at the 3’ nucelotide of the codon
