What is an intron
Noncoding DNA seqeunces, bacteria do not have introns
Colinearity
A direct relationship between DNA sequence and amino acid sequence (1:1 relationship between DNA and amino acids)
not true in eukaryotes
Exons
Part of the genome that are expressed, coding sequences
pre-mRNA
A class of introns in nuclear protein-coding genes that are removed by the spliceosome-mediated splicing
5’ cap
guanine
poly-A tail
adenine on the 3’ end
What is the sequence of an mRNA
5’ - UTR - Shine delgarno sequence - coding region - 3’ UTR - Poly A tail
Shine delgarno sequence
A consensus sequence for the ribosome to sit down
What are ribosomes made of
rRNA, a piece of RNA is complementary to Shine delgarno sequence to be able to bind
spliceosome
Made up of snRNPs that match to the beginning of the intron
splices the intron and creates a lariat (the cut out intron)
mature mRNA
Has a cap, a tail, no intron sequence, only exon sequence
What kind of RNA functions in splicing and is associated with the spliceosome
snRNA (small nuclear RNA)
Alternative Processing
A method to take the same RNA transcript and mix and match the exons. Same gene sequence can make different types of proteins
alternative splicing
A single gene can produce multiple different mRNA, allowing one gene to code for many proteins
intron late hypothesis
proposes that introns were absent from ancient organisms but were later acquired by eukaryotes
Intron early hypothesis
proposes that ealy ancestors of bacteria, archaea and eukaryotes possessed introns that were later lost by prokaryotes and simple eukaryotes
How are different introns differentiated?
Introns are differentiated by how the intron is removed from RNA
Group I introns
found in some genes of bacteria, bacteriophages and eukaryotes, are self splicing: they can catalyze their own removal
Group II introns
present in some genes of mitochondria, chloroplasts, archaea, and a few bacteria, self splicing but mechanism differs from group I introns
Nuclear pre-mRNA introns
-most studied
- include introns located in the protein encoding genes of the eukaryotic nucleus
-Splicing similar to group II introns not self splicing
-removal requires a large structure called a spliceosome that includes snRNAPs
Transfer RNA introns
-found in tRNA genes of bacteria, archaea and eukaryotes
- removed by a splicing mechanism that relies on enzymes to cut and reseal the RNA
What are two general characteristics of the splicing process?
the splicing of all pre-mRNA introns takes place in the nucleus
the order of exons in DNA is usually maintained in the spliced RNA (the coding sequences may be split up but not usually jumbled up)
Where does protein synthesis take place?
in the cytoplasm
What functions as a template for protein synthesis?
messenger RNA (mRNA) which carries genetic information from DNA to a ribosome
