Download Chromatin Structure and Gene Regulation

Eukaryotic Genome Structure
and Gene Regulation
19.1 & 19.2
Lesson 4.6
Chromatin
• Chromatin – DNA/protein
complex in eukaryotic cells
• All the DNA in a cell, if
spread out, would be
thousands of times longer
than the diameter of the
cell – which is why
chromatin folding is
necessary
DNA Packing
Cell Differentiation
• Cells which produce proteins which are very
specialized to its function
– e.g. muscle cells
• Almost all cells of an organism have an
identical genome, but only certain genes are
expressed in each type of cell
– Differential gene expression – cause of expression
of different genes by cells with the same genome
Where Gene Regulation Occurs
Types of Regulation
• Regulation on Chromatin Structure
– Histone modifications
– DNA Methylation
• Regulation of Transcription Initiation
• Post-Transcriptional Regulation
– RNA Processing
– mRNA Degradation
– Initiation of Translation
– Protein Processing and Degredation
Regulation of Chromatin Structure:
Histone Modifications
• Histone Acetylation – attaching an acetyl
group to the end of a histone, neutralizing
these ends so they cannot bind to other
nucleosomes
– This gives transcription proteins easier access to
genes
– If histones are deacetylated, transcription of those
genes cannot occur
Regulation of Chromatin Structure:
DNA Methylation
• Methylation (attachment of a methyl group to
DNA) causes most genes to be inactive
• Removal of the methyl group on these genes
will cause expression
• Methylation or demethylation during
embryonic development is responsible for if
maternal or paternal alleles are expressed –
genomic imprinting
Transcription of the Eukaryotic
Genome
• Transcription Factors must be in place for
polymerases to act, but most transcription
factors cannot recognize promoters in the
same way that enzymes do
mRNA Degradation
• In prokaryotic cells, mRNA degrades quickly,
within minutes, of being in the cytoplasm
• In eukaryotes, it could be up to weeks, allowing
them to be translated multiple times if
necessary
– When it is degraded, enzymes shorten the poly-A
tale and 5’ Cap, allowing the mRNA to be degraded
– There are nucleotide sequences in the poly-A tail
that code for how long it will be until it is degraded
(scientists removed those sequences and
immediately it degraded)