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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
Histones
Histone
tails
Histone H1
Linker DNA
(“string”)
Nucleosomes (10-nm fiber)
Nucleosome
(“bead”)
10 nm
Supercoiling of Chromatin
 Histones-proteins
DNA wraps around
 Nucleosome-unit of DNA wrapped
around histones
 Supercoiling-Chromatinchromosomes
 Heterochromatin-remains condensed
 Euchromatin-loose during interphase
 Cellular differentiation-making cells
different; accomplished by turning genes
“on” or “off”differential gene expression
Euchromatin vs.
Heterochromatin
(The dark spots are the hetero)
During Transcription
 DNA
Methylation-heavy coat-preventssource of genomic imprinting
 Histone acetylation-breaks bond btwn
DNA and proteins;allows RNA polymerase
to attach

piwi-associated RNAs(piRNAs) induce
formation of heterochromatin
 Building


transcription initiation complex
Enhancers& activators-control rate
Repressor or silencer sit on TATA box
Signal
NUCLEUS
Chromatin
DNA
Gene available
for transcription
Gene
Transcription
RNA
DNA Control
stages in Protein
Synthesis
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
TATA
box
Enhancer
General
transcription
factors
DNA-bending
protein
Group of
mediator proteins
RNA
polymerase II
RNA
polymerase II
Transcription
Initiation complex
RNA synthesis
Liver cell
nucleus
Notice the different
nucleotide control
sequences
(red vs, pink)
Available
activators
Enhancer
Control
elements
Lens cell
nucleus
Available
activators
Promoter
Albumin
gene
Crystallin
gene
Albumin
gene not
expressed
Albumin
gene
expressed
Crystallin gene
not expressed
Liver cell
Crystallin gene
expressed
Lens cell
miRNA &siRNA
Protein
complex
Degradation of mRNA
Dicer
OR
miRNA
Target mRNA
Hydrogen
bond
Blockage of translation
 Coordinated
control of genes familiesmultiple copies of same gene, all
transcribed at one
 MicroRNA (miRNA) and small interfering
RNA (siRNA)-little pieces that attach to
mRNA to control transcription
 Post transcription Regulation


Alternative RNA Splicing using snRPS
Cytoplasmic degradation
Control of exons
Translation control
mechanisms
 Build
Translation Initiation Complex
 Faulty cap
 Tail too short
How many As on the tail?
“Build the factory”
Post Translation control
 Chaperonin
or SRP
 Phosphorylation-turns on or off
 Proteosomes-control how long protein
lasts-mainly work on intracellularly
produced proteins ex. Cyclins, remove
transcription factors, recycle amino acids
 (Lysosomes work on extracellularly
produced proteins)
Chaperonin
Protein will stay in the cell
RER
Protein will leave the cell
Proteosomes
Proteasome
and ubiquitin
to be recycled
Ubiquitin
Proteasome
Protein to
be degraded
Ubiquitinated
protein
Protein entering a
proteasome
Protein
fragments
(peptides)
Nuclear membrane’s role?
What is Dark Matter?
A
five-year project called ENCODE, for
"Encyclopedia of DNA Elements," found
that about 80 percent of the human
genome is biologically active, influencing
how nearby genes are expressed and in
which types of cells. It's not junk DNA,
which was previously thought — instead,
these non-coding regions of DNA could
have major bearing on diseases and
genetic mutations, researchers say.
Epigenetic
 Inheritance
of traits not directly involving
nucleotide sequence
 Modifications of chromatin can be
reversed
 Methylation
 ID twins: one normal; one schizophrenic