CH 17 Flashcards
Gene expression
-process by which DNA directs protein synthesis
-2 stages transcription and translation
Transcription
-the synthesis of RNA using information in DNA
messenger RNA (mRNA)
-attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein
Translation
-the synthesis of a polypeptide, using information in the mRNA
Ribosomes
-sites of translation
primary transcript
-the initial RNA transcript from any gene prior to processing
triplet code
-a series of nonoverlapping, three-nucleotide words
template strand
-DNA strand that provides template/pattern for complimentary base pairing
codons
-mRNA base triplets
-read in the 5′ → 3′ direction
reading frame
-how they are grouped
RNA polymerase
-catalyzes RNA synthisis
-pries the DNA strands apart and joins together the RNA nucleotides
promoter
-The DNA sequence where RNA polymerase attaches
terminator
-the sequence signaling the end of transcription in bacteria
transcription unit
-stretch of DNA that is transcribed
Transcription factors
-mediate the binding of RNA polymerase and the initiation of transcription
transcription initiation complex
-completed assembly of transcription factors and RNA polymerase II bound to a promoter
TATA box
-crucial in forming the initiation complex in eukaryotes
5’ cap
-modified form of guanine added on to end of 5’ strand
poly-A tail
-enzyme adds 50-250 adenine at the end of the 3’ strand
introns
-noncoding regions
exons
-other regions
-eventually expressed, usually translated into amino acid sequences
RNA splicing
-removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
Spliceosomes
-consist of a variety of proteins and several small RNAs that recognize the splice sites
Ribozymes
-catalytic RNA molecules that function as enzymes and can splice RNA
alternative RNA splicing
-Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing
domains
-Proteins often have a modular architecture consisting of discrete regions
transfer RNA (tRNA)
-transfer amino acids to the growing polypeptide in a ribosome
anticodon
-base-pairs with a complementary codon on mRNA
aminoacyl-tRNA synthetase
-carries out the correct matching of tRNA and amino acids
wobble
-Flexible pairing at the third base of a codon
-allows some tRNAs to bind to more than one codon
ribosomal RNA (rRNA)
-RNA molecules (and proteins) that make up ribosomes
P site
-holds the tRNA that carries the growing polypeptide chain
A site
-holds the tRNA that carries the next amino acid to be added to the chain
E site
-the exit site, where discharged tRNAs leave the ribosome
signal peptide
-marks Polypeptides destined for the ER or for secretion
signal-recognition particle (SRP)
-binds to the signal peptide
-escorts the ribosome to a receptor protein built into the ER membrane
polyribosome/polysome
-formed by Multiple ribosomes that translate a single mRNA simultaneously
Mutations
-changes in the genetic information of a cell
Point mutations
-changes in just one nucleotide pair of a gene
nucleotide-pair substitution
-replaces one nucleotide and its partner with another pair of nucleotides
Silent mutations
-have no effect on the amino acid produced by a codon because of redundancy in the genetic code
Missense mutations
-still code for an amino acid, but not the correct amino acid
Nonsense mutations
-change an amino acid codon into a stop codon; most lead to a nonfunctional protein
Insertions/deletions
-additions or losses of nucleotide pairs in a gene
frameshift mutation
-produced by the Insertion or deletion of nucleotides may alter the reading frame
Mutagens
-physical or chemical agents that can cause mutations
