Lecture 8 Flashcards
Housekeeping gene
Found in ALL cells (NOT specialized)
Multiple regulation mechanisms at
EACH of steps
Some cells make messages that by default will
NOT be translated
mRNAs contain sequences that control their translation
A bacterial gene’s expression can be controlled by regulating translation of its mRNA
- Stem loop: Secondary structure formed in prokaryotes; if this is the state of the cell, the protein will be made
- Repressor may bind and block the ribosome binding site = NO protein
- Bacterial genes have sequences within mRNA that regulate translation
- When temp is increased, the stem loop will dissolve or come apart and will expose the binding site and start codon, then it can be translated
Thermosensor
Found in many pathogenic bacteria; temp increases, stem loop dissolves = oxposed binding site
Regulatory RNAs control the expression of thousands of genes
MicroRNAs direct the destruction of target mRNAs
Small interfereing RNAs protect cells from infections
sRNAs (small RNAs) are used to regulate gene expression
An miRNA targets a complementary mRNA molecule for destruction
MANY genes for these; ~1/3 of protein-encoding genes are regulated by miRNA
Loop structures cut off and exported to cytoplasm -> RISC enters -> search cell for complement mRNA that isn’t needed to be translated anymore, some will have a perfect match to some message = message degraded
Micro RNAs: many complementary bases, folds back to form secondary structure (recognize as miRNA)
1) Stem loop structures cut off
2) Transported to cytoplasm; in the cytoplasm, it associates wtih the RISC (RNA induced silencing complex)
3) Get only one miRNA strand and RISC protein - search for complement to miRNA (the complement iwll be an mRNA)
4) mRNA will no longer get translated
- Could have perfect match or partial match; message is degraded regardless
miRNAs are encoded in YOUR genome; it is a way that you regulate your OWN messages
siRNAs are produced from double-stranded, foreign RNAs during the process of RNA interference
Small interfering RNA: siRNA
You do NOT encode for these, this is from a foreign source
1) Infected with double-stranded RNA -> cut up by dicer
2) Double stranded pieces of RNA associate with RISC
3) Singel stranded siRNA and RISC search for complementary message from a VIRUS
4) Degrade mRNA complement (this one can also be perfect or partial match)
RISC comes from you
siRNA cleaved by dicer -> RISC associates to siRNA -> single-stranded RNA -> search for complementary message (from virus, NOT you) -> degrade cell OR -> viral proteins produced and make you sick
miRNA is in OUR genome
siRNA is a FOREIGN piece
miRNA targets YOUR messages (preventing translation)
siRNA targets FOREIGN messages
RNAi can also trigger transcriptional silencing
RNAi = RNA interference
Can occur during process of transcription; mRNA doesn’t have to be completely processed and out in the cytoplasm for it to work
This RECRUITS proteins that will result in proteins being shut off
Transcription silencer
sRNAs associate, can occur during process of transcription, too; can recruit proteins that will turn transcription off
Thousands of long noncoding RNAs may also regulate mammalian gene activity
Long, noncoding RNAs are generally a couple hundred bases
Can also regulate gene activity: act as a scaffold or docking site
Long noncoding RNAs can serve as scaffolds, bringing together proteins that function in the same cell process
Long noncoding RNA: Act as docking site for other proteins (transcriptional activators or repressors); there to recruit anything necessary to turn transcription on or off; we regulate our genes using these as well
There is NEVER a role for double-stranded RNA in the cell; usually there because it’s a virus
