Eukaryotic Genome Control Mechanisms for Gene expression AP Biology Eukaryotic Genome Control Mechanisms for Gene expression

Chromatin vs. Chromosomes appearance within the cell.

Histone Proteins and Supercoiling 2 nm DNA double helix His- tones Histone tails Histone H1 10 nm Linker DNA (“string”) Nucleosome (“bead”) Nucleosomes (10-nm fiber)

Supercoiling of Chromatin

Euchromatin vs. Heterochromatin (The dark spots are the hetero)

DNA Control stages in Protein Synthesis Signal NUCLEUS Chromatin DNA Gene available for transcription Gene Transcription RNA Exon Primary transcript Intro RNA processing Tail Cap mRNA in nucleus Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Degradation of mRNA Translation Polypeptide Cleavage Chemical modification Transport to cellular destination Active protein Degradation of protein Degraded protein

Methylation

. Histone tails DNA double helix Amino acids available for chemical modification Histone tails protrude outward from a nucleosome Unacetylated histones Acetylated histones Acetylation of histone tails promotes loose chromatin structure that permits transcription

“Build the factory”

Enhancers Distal control element Activators Promoter Gene DNA Enhancer TATA box General transcription factors DNA-bending protein Group of mediator proteins RNA polymerase II RNA polymerase II Transcription Initiation complex RNA synthesis

Notice the different nucleotide control sequences (red vs, pink) Liver cell nucleus Lens cell nucleus Available activators Available activators Enhancer Promoter Control elements Albumin gene Albumin gene not expressed Crystallin gene Albumin gene expressed Crystallin gene not expressed Crystallin gene expressed Liver cell Lens cell

miRNA &siRNA Protein complex Degradation of mRNA Dicer OR miRNA Target mRNA Hydrogen bond Blockage of translation

Control of exons

How many As on the tail?

“Build the factory”

Chaperonin Protein will stay in the cell

RER Protein will leave the cell

Proteosomes Proteasome and ubiquitin to be recycled Ubiquitin Protein to be degraded Ubiquitinated protein Protein fragments (peptides) Protein entering a proteasome