Transcription and Translation Flashcards
gene expression
the process by which DNA directs protein synthesis, includes two stages: transcription and translation
transcription
the synthesis of RNA under the direction of DNA
what produces messenger RNA
(mRNA)
transcription
ribosomes
the sites of translation
translation
the synthesis of a polypeptide, which occurs under the direction of mRNA
RNA processing
how eukaryotic RNA transcripts are modified
primary transcript
the initial RNA transcript from any gene
central dogma
the concept that cells are governed by a cellular chain of command: DNA
→ RNA → protein
how many amino acids and nucleotide bases are there
20 amino acids, 4 bases
triplet code
a series of nonoverlapping, three-nucleotide words
template strand
one of the 2 DNA strands that provides a template for ordering the sequence of nucleotides in an RNA transcript
codons
the mRNA base triplets that are read in the 5’ to 3’ direction
what does each codon do
specifies the amino acid to be placed at the corresponding position along a
polypeptide
what does each codon specify
the addition of one of 20
amino acids
how do you read codons
in the correct reading frame (triplet groups)
RNA polymerase
catalyzes RNA synthesis and pries the DNA strands apart and hooks together the RNA nucleotides
promoter
the DNA sequence where RNA polymerase attaches
terminator
the sequence signaling the end of transcription
transcription unit
the stretch of DNA that is transcribed
three stages of transcription
– Initiation
– Elongation
– Termination
transcription factors
mediate the binding of RNA polymerase and the initiation of
transcription
transcription initiation complex
the completed assembly of transcription factors and RNA polymerase II bound to a promoter
TATA box
a promoter that is crucial in forming the initiation complex in eukaryotes
how does RNA polymerase work
moves along the DNA, it untwists the double helix, 10 to 20 bases at a time
what does the 5’ end receive during RNA processing
a modified nucleotide 5’ cap
what does the 3’ end receive during RNA processing
a poly-A tail
what do this modifications do
– They seem to facilitate the export of mRNA
– They protect mRNA from hydrolytic enzymes
– They help ribosomes attach to the 5’ end
introns(intervening sequences)
noncoding regions
exons
regions that do code and are eventually expressed
RNA splicing
removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
Spliceosomes
removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
ribosomes
catalytic RNA molecules that function as enzymes and can splice RNA
3 properties of RNA that enable it to function as an enzyme
- it can form a three dimensional structure because of its ability to base pair with itself
- some bases in RNA contain functional groups
- RNA may hydrogen bond with other nucleic acid molecules
alternative RNA splicing
segments that are treated as exons during RNA splicing
domains
molecular architecture consisting of discrete regions in proteins
are molecules of tRNA identical?
no
transfer RNA (tRNA)
what helps a cell translate an mRNA message into protein
anticodon
a sequence of nucleotides that correspond to a complementary codon on the mRNA
2 steps of translation
- a correct match between a tRNA and an amino acid
- a correct match between the tRNA anticodon and and an mRNA codon
aminoacyl-tRNA synthetase
an enzyme that matches a tRNA and an amino acid
wobble
flexible pairing at the third base of a codon which allows some tRNA to bind to more than one codon
ribosomal RNA (rRNA)
make up 2 ribosomal subunits
a ribosomes three binding sites of tRNA
- p site
- a site
- e site
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
3 stages of translation
- initiation
- elongation
- termination
initiation
it brings together mRNA, a tRNA with the first amino acid, and the 2 ribosomal subunits
- first a small ribosomal subunit binds with mRNA and a special initiator tRNA
- then the small subunit moves along the mRNA until it reaches the start codon
- proteins called initiation factors bring in the large subunit that completes the translation initiation complex
start codon
AUG
elongation
amino acids are added one by one to the preceding amino acid
3 steps of proteins called elongation factors
- codon recognition
- peptide bond formation
- translocation
when does termination occur
when a stop codon in the mRNA reaches the A site of a ribosome
muations
changes in the genetic material of a cell or virus
point mutations
chemical changes in just one base pair of a gene
2 categories of point mutation
- base pair substitutions
- base pair insertions or deletions
deletions
losses of nucleotide pairs in a gene
frameshift mutation
what is produced when insertion or deletion of nucleotides alter the reading frame
base pait substitutions
replaces one nucleotide and its parter with another pair of nucleotides
missense mutations
code for an animo acid, but not necessarily the right amino acid
nonsense muations
change an animo acids codon into a stop codon, nearly always leading to a nonfunctional protein
insertions
additions of nucleotide pairs in a gene
mutagenes
physical or chemical agents that can cause mutations
