Chapter 13 Flashcards
What is the central dogma?
DNA is used as instructions to make RNA, and RNA is used as instructions to make proteins
Define transcription
Use of DNA nucleotide sequences as instructions to make an RNA sequence
Define translation
Use of the RNA sequence as instructions to make the amino acid sequence of a protein. Triplets of nucleotides determine the amino acid.
Define a codon
Every 3 nucleotides (triplet) of an RNA sequence to specify an amino acid
What 5 characteristics does the genetic code have?
-unambiguous
-degenerate/redundant
-universal
-nonoverlapping
-ordered
What does it mean that the genetic code is unambiguous?
A given codon specifies for only ONE amino acid
What does it mean that the genetic code is degenerate/redundant?
A given amino acid can be specified by multiple codons
What does it mean that the genetic code is universal?
Almost all species use the same genetic code
*Exceptions apply
What does it mean that the genetic code is non-overlapping?
A given nucleotide is only part of one codon. (The RNA sequence is read in groupings of 3)
Define start codon
Genetic code only has 1 start codon - the first codon to be translated. AUG, aka methionine
Define stop codon
Genetic code has 3 stop codons - causing translation to end but do NOT code for an amino acid. UGA , UAA, and UAG
What is an example of altered codon-amino pairing (exception to the universal characteristic)
In most species AGA codes for aginine, but in the human mitochondria it is instead a stop codon.
Define open reading frames
ORFs are the 3-letter groupings read by the ribosome.
Define alternative ORFs
Shifting the start position up or down a nucleotide results in a different ORF, which creates a different protein.
How can alternative reading frames happen?
mRNAs being initiated at different positions. They can use or ignore start codons dependent on different environmental conditions and needs.
Define a gene
What is transcribed to produce an RNA molecule. It is a few thousand base pairs long.
Define RNA polymerase
Enzyme that transcribes the gene to produce an RNA molecule.
Define promoter
A few dozen base pairs that is before the gene, helping RNA polymerase to bind.
What does bacterial RNA polymerase consist of?
Core enzyme and sigma factor
What does the core enzyme of bacterial RNA polymerase do?
Catalyzes RNA production and has multiple protein subunits
Whats the sigma factor of bacterial RNA polymerase?
Helps to initiate transcription and binds to the promoter
Define holoenzyme
The core enzyme + the sigma factor (the entire enzyme)
Define template binding (bacterial)
Transcription begins at this point with the sigma factor binding to the template strand of DNA and scanning for the promoter.
Define template strand
Strand of DNA that RNA polymerase reads
Define coding strand
Strand of DNA that is NOT being read
Define antisense strand
AKA template. Reading strand
Define sense strand
AKA coding. NON-reading strand
Define consensus sequence
The nucleotide sequence of the promoters that is the average/most similar among these many sequences. This is how the sigma factor recognizes promoters, as it is designed to bind to the consensus sequence.
What happens once the sigma factor binds to the promoter? (bacterial)
DNA strands are then unraveled, and then the sigma factor leaves. RNA polymerase then reads the template strand to create a complementary RNA sequence.
Define proofread
3’->5’ exonuclease ability. RNA polymerase recognizes its mistakes, excises them, then adds the right nucleotide.
How does transcription end in bacteria?
The new RNA forms a hairpin structure at the 3’ end. Then, either intrinsic or Rho-dependent termination occurs
What does the rho protein do? (Rho-dependent termination) (bacterial)
Binds to RNA and detaches it from DNA to help end transcription. It does this by binding to the 5’ side and moving in the 3’ direction, breaking RNA-DNA base pairing.
What are the 3 steps of bacterial transcription?
- Initiation - binding to DNA
- Elongation - reading of DNA
- Termination - detaching from DNA
