Chapter 17: Gene Expression Flashcards
3 steps of translation
- Initiation; req. E
- Elongation
- Termination
Introns
“nonsense” coding
may help regulate gene expression
Missense mutation
1 of 4 types of substitution mutations
when a nucleotide change still codes for an amino acid, but not the one you wanted
initiator tRNA
tRNA that carries the first amino acid [usually methionine (Met)] to the initiation complex so it can start translating protein
special factor that brings the bottom/small ribosomal sub-unit to the mRNA strand
Genetic disorders/hereditary dx
when a mutation has an adverse effect on phenotype
Frameshift mutation
when a single extra based gets inserted into a series of DNA’s codons, changing the triplet groups (reading frame) of the RNA
results in different amino acids being synthesized
Spliceosomes
protein/RNA complex that recognizes and removed introns
proteins and nuclear ribonucleoproteins (snRNPs) that recognize splice sites (for cutting out introns) and sometimes catalyzing splicing of introns
Substitution Mutations (4)
- nucleotide-repair substitution
- silent mutation
- missense mutation
- nonsenese mutation
template strand
the part of the unzipped DNA that RNA attaches to during transcription
Deletion mutations
LOSS of nucleotide pairs in a gene that may alter the reading frame can cause frameshift mutations
more disastrous than substitution mutations
(Beadle & Tatum’s) correct 1 gene: 1 polypeptide hypothesis
the idea that each gene dictates production of a specific polypeptide/protein
Transcription factors
mediate the binding of RNA polymerase and the initiation of transcription
Reading frames
correct groupings of codons required for polypeptide production
Initiation (translation)
complex of mRNA, tRNA, the first amino acid, small/bottom ribosomal sub-unit, and large/top ribosomal sub-unit come together
Anticodon
region in the tRNA whose triplet sequence matches that of the codons during translation
Signal peptides
markers on proteins that tell the proteins to go to the ER or to get secreted out of the cell
bind to Signal recognition particles (SRP)
RNA polymerase
binds to DNA (initiation), then untwists DNA to creates new RNA strand (elongation)
Works in the DNA’s 5 to 3 prime direction, adding bases to the RNA’s 3 to 5 prime direction
Multiple pols can be working on the gene at the same time
Usually transcribes 10-20 bases at a time, 40 per second in eukaryotes
Mutation
changes in the genetic material of a cell or virus
Wobble
flexible pairing of the third base of a codon
allows some tRNAs to bind to more than one codon; alternate version not ideal, but good enough
alternative RNA splicing
exon shuffling
(variability in the way) segments of DNA strands are treated as exons
may result in evolution of new proteins
Terminator
DNA sequence that tells RNA polymerase where to STOP working (in transcription)
Pol usually falls off about 10 to 35 bases later
codon/base triplet code
the 3-nucleotide segment of a DNA strand; one for each amino acid
64 three letter combos possible, enough to code for all 20 amino acids 61 codons) and stop signals (3 codons)
Signal cleaving enzyme
cuts off a ribosome/polypeptide’s signal peptide once the complex has been delivered/bound to the ribosome
Nucleotide-pair substitution
1 of 4 types of substitution mutations
when a nucleotide and its partner are replaced with another pair of nucleotides
Promotor
DNA sequence that tells RNA polymerase where to start working (in transcription)
RNA processing
Last step in transcription before translation
5 cap added, poly- A tail added (approx. 50-250 bases), introns removed, exons liked together
This eases transport, protects mRNA from hydrolytic enzymes, help ribosomes attach to the 5 prime end
Where polypeptide synthesis happens
in the cytosol (except for when the ribosomes leave the cytosol and bind to the ER to make endomembrane system proteins).
Domains
regions of proteins that are coded for by different exons
Silent mutation
1 of 4 types of substitution mutations
when the effect of a change has no effect on the amino acid produced because it is overshadowed by redundancy in the genetic code
Translocation complex
complex on the ER membrane where the signal recognition particles (SRP) can attach temporarily in order to bind the signal peptide and ribosome it was carrying
tRNA
houses the anticodons and carries the corresponding amino acids into ribosomes for translation
about 80 bases long, takes 3D shape bc of Hydrogen bonding
Runs 3 to 5 prime!
Polyribosome
aka polysome; looks a bit like a bead necklace
When a bunch of ribosomes are working (still 5 to 3) on a single mRNA at the same time
works very quickly
Gene expression
the process by which DNA directs transcription and translation
Insertion mutations
ADDITION of nucleotide pairs in a gene that may alter the reading frame can cause frameshift mutations
more disastrous than substitution mutations
Transcription unit/region
Stretch of DNA being transcribed during transcription
Point mutation (2 types)
chemical changes in just one base pair of a gene
- Nucleotide-pair substitutions
- One or more nucleotide-pair insertions or deletions
TATA box
section of the promotor sequence that helps the polymerase know where to attach so it can start transcribing and so it can read in the right direction (but not all eukaryotes have it)
Similar to -10 or -35 element in bacteria
form the initiation complex by consisting of As and Ts that make the strand easier to unzip
Polyadenylation “stop” signal
tells pol to drop off???
Ribosome
made in the nucleus, excreted through pore complex
organelle in cytosol or bound in the rough ER or nuclear envelope that synthesizes polypeptide chains from the codons on the mRNA chains made during transcription
How bacteria handles transcription and translation faster
transcription and translation are coupled together
Conformation
when a completed polypeptide chain folds into is 3D shape (bc of hydrogen attractions/bonds)
Central dogma
the idea that cells are governed by a cellular chain of command:
DNA to RNA to Protein. Thanks, Sal!
Initiation factors
proteins that bring the large/top ribosomal sub-unit to the part for translation
Req. GTP to GDP exergy
ribosomal RNA
What dreams and ribosome are made of
Signal recognition particles (SRP)
bind to signal peptides and brings them (and their ribosomes) to the ER
After delivering signal peptides/ribosomes to ER, signal protein breaks off of ER
aminoacyl-tRNA synthetase
Enzyme that matches/binds tRNA triplet to the appropriate amino acid (w covalent bond) before it enters the ribosome
requires ATP to AMP
happens before the tRNA’s anticodon is matched with the mRNA’s codon triplet in the ribosome
Stop signals
DNA sequences that tell the RNA polymerase to stop coding
Primary transcript
the RNA strand you have (in transcription) before its ‘processed’
(Beadle & Tatum’s) debunked 1 gene: 1 enzyme hypothesis
the idea that each gene dictates production of a specific enzyme
3 binding sites of ribosome
E (exit)
P (peptidyl tRNA binding site); peptide chain made
A (aminoacyl tRNA binding site); tRNA enters ribosome
Redundancy
Phenomenon where multiple codons can code for the same amino acids (even though each codon can only code for 1 amino acid)
Ribozymes
RNAs that act as enzymes (by speeding up the binding of nucleic acids)
catalytic RNA molecules
can splice RNA
function as enzymes (bc they can take on 3d structure, they have functional grps that can participate in catalysis, and they may hydrogen bond with other nucleic acid molecules)
Nonsense mutations
1 of 4 types of substitution mutations
when a amino acid codon is changed into a stop codon
proteins with this problem are nearly always nonfunctional
transcription initiation complex
completed assembly of transcription factors and RNA polymerase II (pol II) bound to a promoter
