Transcription+Translation Flashcards
transposons
can be copied and inserted elsewhere in the genome
this is why they account for a large percentage of the repeated DNA sequences
lateral gene transfer
genetic information is transferred from one species to another
very common in prokaryotes
Sources of new genes
gene duplication
Gene duplication causes
often caused by mistakes in crossing over repeated elements
What does gene duplication result in?
gene ‘families’
Gene family
genes with similar sequences and often similar functions
Example of a gene family
hemoglobin groups
have different genes for oxygen carrying during different points in development
B-globin
How do transposons work?
- RNA polymerase makes mRNA of whole transposon
- LINE mRNA leaves the nucleus to be translated
- mRNA returns to nucleus
- Reverse transcriptase converts mRNA to LINE cDNA
- Integrase cuts the chromosomal DNA and inserts the LINE cDNA
What does integrase do?
cuts the chromosomal DNA in order for the LINE cDNA to be inserted
Where does LINE DNA originate from?
part of the chromosomal DNA sequence
Initiation of transcription in prokaryotes
sigma proteins bind to RNA polymerase and promoter sequences on DNA to bring them together
Promoter
sequence of genes
How do prokaryotes control gene transcription?
there are different sigma proteins that express different genes depending on what is needed
Elongation of transcription in prokaryotes
RNA polymerase moves in 5’ to 3’ direction to synthesize mRNA
What is the advantage of using RNA polymerase?
there is no need for a primer
What end does RNA polymerase add bases to?
3’ -OH end
What direction is an RNA template read in?
3’ to 5’
Termination of transcription in prokaryotes
transcription termination signal that codes for hairpin structure of RNA
How is RNA hairpin formed?
RNA binds to itself
Are genes in an operon transcribed together?
yes
operon has 1 promoter and 1 transcription termination signal
Are genes in an operon translated together?
no
ribosomes bind at different points along the operon
AUG encodes for which protein
methionine
How does the ribosome read mRNA?
5’ to 3’
which direction is the growing polypeptide synthesized?
N->C terminus
termination in translation of prokaryotes
when stop codon is encountered a release factor enters the ribosome and causes it to release the peptide and disassemble
release factor
looks like a tRNA that binds to the stop codon, but contains no amino acid
Advantage of the operon
energy is conserved
genes can be turned off when not needed
Energy used in synthesis of proteins
4 ATP are used for every base and there are 3 bases in each amino acid (codon). Roughly 300 amino acids in a prokaryotic protein, so that is a lot of energy!
Initiation of transcription in eukaryotes
Transcription factors bind to the promoter sequence and RNA polymerase
What do eukaryotic transcription factors help do?
they allow greater control of transcription
Elongation and termination of transcription in eukaryotes
similar to prokaryotes
mRNA processing
occurs in eukaryotes
splicing of introns, exons joined
5’ cap added
polyA tail added
Initiation of translation in eukaryotes
lots of proteins and complex
proteins bind to the 5’ cap and bind the ribosome
ribosome ‘scans’ forward on the mRNA until it reaches the start codon
