Chapter 17 Flashcards
Gene expression
the process b which DNA directs the synthesis of proteins (sometimes RNA)
One Gene- One Polypeptide Hypothesis
Each gene codes for a polypeptide, which can constitute part of a protein
Transcription
Synthesis of RNA under the direction of DNA. Produces mRNA
mRNA
Messenger RNA that is produced during transcription
Carries the genetic message of the DNA to the ribosome (protein making machinery)
mRNA differences in Prokaryotes and Eukaryotes
Eukaryotes- Nuclear envelope separates transcription from translation
mRNA is modified through RNA processing to yield finished mRNA
Prokaryotes- mRNA produced by transcription is immediately translated without further processing
Translation
Production of a polypeptide chain using the mRNA transcript
Occurs in the ribosomes in the cytosol
Template Strand
The strand of DNA that is transcribed in transcription
mRNA is complementary to this strand of DNA
Codons
mRNA nucleotide triplets
Smallest units are uniform length that can code for all the amino acids
Genetic Code
Redundant because more than one codon codes for an amino acid , but they are never vague
Reading Frame
The correct groupings in order for the specific polypeptides to be produced
RNA polymerase
Catalyzes the RNA synthesis, which follows the same base pairing rule, except uracil substitutes for thymine
Promoter
DNA sequences where RNA polymerase attaches
Terminator
Sequence signaling the end of transcription in bacteria
Transcription Unit
Entire stretch of DNA that is transcibed
Transcription Initiation Complex
The completed assembly of transcription factors and RNA polymerase II bound to a promoter
Steps of Transcription
- Initiation- Transcription factors bind to the promoter which helps the RNA polymerase II be able to bind to the promoter, creating a transcription initiation complex
- Elongation- RNA polymerase II untwists the DNA and adds complementary RNA bases
- Termination- After RNA polymerase transcribes the terminator sequence in the DNA, the RNA transcript is released and the RNA polymerase detaches
Differences in Transcription between Prokayotes and Eukaryotes
RNA polymerase can bind to the promoter by itself in prokaryotes,
Prokaryotic polymerase stops transcription at the end of the terminator
Eukaryotes continues transcription after the pre-RNA is cleaved from the growing RNA chain, polymerase eventually falls of the DNA
TATA box
Promoter that is crucial in forming the initiation complex in eukaryote
Alteration of mRNA ends
Adds a 5’ cap to the 5’ end
The 3’ end receives a poly-A tail
Help to facilitate the export of mRNA, protects the mRNA from hydrolytic enzymes, and help ribosomes to attach to the 5’ end
RNA Splicing
Removes introns and joins exons together creating a mRNA molecule with a continuous coding sequence
Spliceosome
Consists of a variety of proteins and several small nuclear ribonucleicproteins that recognize splice sites
Ribozyme
Catalytic RNA molecules that function as enzymes and cal splice RNA
Rendered obsolete the belief that all biological catalysts are proteins
tRNA
Each tRNA carries specific amino acids on one end
Each has an anti codon on the opposite end that pairs with a codon on the mRNA
Acute Translation
- A correct match between the tRNA and an amino acid (joined by the enzyme aminoacyl-tRNA synthetase)
- Correct match between tRNA anti codon and mRNA codon
wobble
Flexible pairing at third base of a codon
Allows some tRNA to bind more than one codon
Ribosomes
Made out of rRNA
Facilitate the specific coupling of tRNA anti codons with mRNA codons in protein synthesis
Two ribosomal subunits (large and small) that are made of proteins and rRNA
3 Binding Sites
P- holds the tRNA that carries the polypeptide chain
A- holds he rRNA that carries the next amino acid to be added
E- Exit site, where discharged tRNA leave the ribosome
Steps of Translation
initiation- a small ribosomal subunit binds to mRNA , anticodon matches up with the start codon on the mRNA, and the large subunit attaches, allowing tRNA to attach to the P site
Elongation- Amino acids are added to the preceding amino acid
Termination- Stop codon is reached and translation stops
Signal Peptide
The sequence of the leading 20 or so amino acids that direct proteins to their final destination
Point Mutations
alterations of just one base pair in a gene
Missense mutation
substitutions that still allow for the codon to code for an amino acid
Nonense mutation
subsitutions that change a regular amino acid codon into a a stop codon, ceasing translation
Insertion/ Deletions
Additions and losses of nucleotide pairs in genes
Frameshift Mutation
causes mRNA to be read incorrectly
