Prokaryotic and Eukaryotic Gene Regulation & RNA Processing

Transcription (Prokaryotes)

Occurs in cytoplasm; transcription and translation happen at the same time; no mRNA processing

Transcription (Eukaryotes)

Occurs in nucleus; mRNA is processed (5' cap, splicing, poly-A tail); translation happens later

Spliceopathies

Diseases caused by incorrect RNA splicing → faulty proteins

HATs

Add acetyl groups to histones → DNA loosens → genes ON

HDACs

Remove acetyl groups → DNA tightens → genes OFF

DNMTs

Add methyl groups to DNA → genes OFF

Neurotransmitters in Addiction

Dopamine increases reward/pleasure → drugs overstimulate → dependence forms

Promoters

DNA sequences where RNA polymerase binds to start transcription

Epigenetics (general)

Changes in gene expression without changing DNA sequence

Epigenetics & Cancer

Tumor suppressor genes silenced (methylation); oncogenes activated

mRNA Stability

How long mRNA lasts; longer life = more protein made

Decapping Enzymes

Remove 5' cap → mRNA degraded faster

Polyadenylation

Adds poly-A tail → protects mRNA + increases translation

miRNA

Binds imperfectly to mRNA → blocks translation

siRNA

Binds perfectly → cuts and destroys mRNA

lncRNA

Long RNA that regulates gene expression in many ways

PABP

Binds poly-A tail → stabilizes mRNA

eIF4E (Elf4E)

Binds 5' cap → starts translation

eIF4G (Elf4G)

Scaffold protein that helps assemble translation complex

Maskin

Blocks translation by preventing eIF4E interaction

CPEB

Controls poly-A tail length → regulates translation

PARN

Shortens poly-A tail → decreases translation

Src

Kinase that activates proteins via phosphorylation

ZBP1

Controls where mRNA is located in the cell

Phosphorylation

Adds phosphate group → turns proteins ON/OFF

Ubiquitination

Tags protein for destruction

Methylation

Adds methyl group → often silences genes

Acetylation

Adds acetyl group → activates gene expression

Genomic Imprinting

Only one parent's gene copy is expressed; the other is silenced

Lac Operon (normal)

Lactose absent: OFF; lactose present: ON

Lac Operon Mutation (repressor broken)

Always ON

Lac Operon Mutation (operator mutated)

Repressor can't bind → always ON

Lac Operon Mutation (promoter mutated)

No transcription

Negative Control

Repressor blocks transcription

Positive Control

Activator increases transcription

Trp Operon (high tryptophan)

Repressor active → operon OFF

Trp Operon (low tryptophan)

Operon ON → makes tryptophan

mRNA Surveillance

Detects and destroys faulty mRNA (ex: premature stop codons)

Mutagens

Agents that damage DNA (UV, chemicals, radiation) → cause mutations

SWI/SNF Complex

Moves nucleosomes → makes DNA accessible for transcription

Gal Operon

Controls galactose metabolism; activated when galactose is present

AREs (AU-rich elements)

Sequences that make mRNA unstable → quick degradation