Final Exam Flashcards
To get from DNA (nucleic acids) to protein
(amino acids) requires two major stages:
- TRANSCRIPTION
- TRANSLATION
Transcription
is the process of making RNA (copy gene to send to ribosome)
Prokaryotic vs Eukaryotic Transcription
- In bacteria, all transcription is performed by a single type of RNA polymerase
– polymerase contains four catalytic subunits and a single regulatory subunit known as sigma factor - In eukaryotes, there are 3 different RNA polymerases
– RNA polymerase I transcribes rRNA
– RNA polymerase II transcribes mRNA and some snRNA
– RNA polymerase III transcribes tRNA and some other small RNA
The two constituents of chromosomes
proteins and DNA
Translation
(synthesize protein at ribosome)
Transcription occurs in 3 stages
- Initiation
- Elongation
- Termination
Initiation
– RNA polymerase (RNAP) complex binds to DNA at a given “start” signal
– The RNAP unwinds the DNA helix, separating the strands and creating a transcription bubble
Elongation
RNA synthesized in the 5’-to-3’ direction as ribonucleotides are added by RNAP
Termination
– Marked by sequence that signals “stop” to polymerase
– RNA–DNA hybrid within the transcription bubble dissociates
– RNAP releases the DNA and DNA rewinds into helix
introns
Eukaryotic genes have regions of non-coding information
RNA editing
splicing of the mRNA transcript
Why have introns?
- Introns may help regulate gene expression
– Splicing process itself necessary for export of mRNA out of the nucleus
– Some introns contain sequences that control gene activity - Alternative splicing
– By changing pattern of splicing, different variations of a protein can be formed
– Clear illustration of why the proteome is more complex than the genome
Alternative splicing
can produce different forms of a protein from the same gene
Transcription is carefully regulated by the cell
Even the simplest cells are finely tuned to both internal and external signals that affect the rate of expression (transcription) of each gene
* In order to optimize the use of resources, cells carefully regulate transcription, expressing genes only when they are needed at a particular moment
* Some genes, however, are so important to a cell’s survival that they are expressed all the time. these are called housekeeping or constitutive genes
Transcription is carefully regulated by the cell
Even the simplest cells are finely tuned to both internal and external signals that affect the rate of expression (transcription) of each gene
* In order to optimize the use of resources, cells carefully regulate transcription, expressing genes only when they are needed at a particular moment
* Some genes, however, are so important to a cell’s survival that they are expressed all the time. these are called housekeeping or constitutive genes
key players in interpreting the code
the ribosome (made of two subunits) and tRNAs that bring amino acids to the ribosome
tRNA – the decoder
The “interpreter” of translation is an RNA molecule
* Bring correct amino acid to the ribosome
* Correct amino acid added based on “read” of codons on
mRNA
– Base-pairing interactions with anticodon loop
ribosome
is the catalytic machine that actually builds the peptide from the mRNA message
tRNA synthetases
- Catalyze the esterification of a specific amino acid to its compatible cognate tRNA to form an aminoacyl-tRNA
– requires energy in the form of ATP - “Match and attach” enzymes
- Have specific identity elements
– Some recognize anticodon loop sequence
– Some recognize acceptor arm sequence - Specifically, closing base-pair
Peptidyl transferase
– Enzymatic component of the ribosome
– Forms peptide bonds between amino acids
The ribosome has two primary functions
– Decode the mRNA
– Form peptide bonds
In eukaryotes, transcription and translation are spatially and temporally separated
mutation
a change in the normal base-pair sequence
Point mutations
alter a single base
– deletions, insertions
Base substitutions
substitute one base for another
