1. The document describes the process of chromatin remodeling from a loose structure to a highly condensed structure. It progresses from nucleosomes forming a beads-on-a-string structure, to a 30nm fiber, then loops and folds to form a metaphase chromosome hundreds of nanometers in length.
2. It explains how histone acetylation promotes a loose chromatin structure allowing transcription, while unacetylated histones result in a tighter structure preventing transcription.
3. The stages of gene expression are outlined, from transcription to RNA processing and export from the nucleus for translation into protein in the cytoplasm.
17. LE 19-3
Signal
NUCLEUS
DNA
RNA
Chromatin
Gene available
for transcription
Gene
Exon
Intro
Transcription
Primary transcript
RNA processing
Cap
Tail
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Translation
Degradation
of mRNA
Polypeptide
Cleavage
Chemical modification
Transport to cellular
destination
Degradation of protein
Active protein
Degraded protein
Chromatin modification:
DNA unpacking involving
histone acetylation and
DNA demethylation
18. LE 19-4
Histone
tails
Amino acids
available
for chemical
modification
DNA
double helix
Histone tails protrude outward from a nucleosome
Acetylation of histone tails promotes loose chromatin
structure that permits transcription
Unacetylated histones Acetylated histones
20. LE 19-4b
Acetylation of histone tails promotes loose chromatin
structure that permits transcription
Unacetylated histones Acetylated histones
21.
22. LE 19-5
Enhancer
(distal control elements)
Proximal
control elements
Upstream
DNA
Promoter
Exon Intron Exon Intron Exon
Downstream
Transcription
Poly-A signal
sequence
Termination
region
Intron Exon Intron Exon
RNA processing:
Cap and tail added;
introns excised and
exons spliced together
Poly-A signal
Cleaved 3′ end
of primary
transcript
3′
Poly-A
tail
3′ UTR
(untranslated
region)
5′ UTR
(untranslated
region)
Start
codon
Stop
codon
Coding segment
Intron RNA
5′ Cap
mRNA
Primary RNA
transcript
(pre-mRNA)
5′
Exon
23. LE 19-6
Distal control
element Activators
Enhancer
DNA
DNA-bending
protein
TATA
box
Promoter
Gene
General
transcription
factors
Group of
mediator proteins
RNA
polymerase II
RNA
polymerase II
RNA synthesis
Transcription
Initiation complex
27. LE 19-10
Protein to
be degraded
Ubiquitinated
protein
Proteasome
Protein entering a
proteasome
Protein
fragments
(peptides)
Proteasome
and ubiquitin
to be recycled
Ubiquitin
28. LE 19-11
Proto-oncogene
DNA
Translocation or transposition:
gene moved to new locus,
under new controls
New
promoter
Gene amplification:
multiple copies of the gene
Point mutation
within a control
element
Oncogene Oncogene
Point mutation
within the gene
Normal growth-stimulating
protein in excess
Normal growth-stimulating
protein in excess
Normal growth-stimulating
protein in excess
Hyperactive or
degradation-
resistant protein
29. LE 19-12_1
Cell cycle-stimulating
pathway
Growth
factor
G protein
Receptor
MUTATION
Protein kinases
(phosphorylation
cascade)
NUCLEUS
Hyperactive
Ras protein
(product of
oncogene
issues signals
on its own.
Transcription
factor (activator)
DNA
Gene expression
Protein that
stimulates
the cell cycle
30. LE 19-12_2
Active
form
of p53
DNA
DNA damage
in genome
UV
light
Protein kinases
MUTATION
Defective or
missing
transcription
factor, such as
p53, cannot
activate
transcription
Protein kinases
(phosphorylation
cascade)
Cell cycle-inhibiting
pathway
Cell cycle-stimulating
pathway
Protein that
stimulates
the cell cycle
NUCLEUS
DNA
Gene expression
Transcription
factor (activator)
Receptor
G protein
Growth
factor
MUTATION
Hyperactive
Ras protein
(product of
oncogene)
issues signals
on its own
Protein that
inhibits
the cell cycle
31. LE 19-12_3
Protein overexpressed
EFFECTS OF MUTATIONS
Protein absent
Cell cycle not
inhibited
Increased cell
division
Cell cycle overstimulate
Effects of
mutations
Active
form
of p53
DNA
DNA damage
in genome
UV
light
Protein kinases
MUTATION
Defective or
missing
transcription
factor, such as
p53, cannot
activate
transcription
Protein kinases
(phosphorylation
cascade)
Cell cycle-inhibiting
pathway
Cell cycle-stimulating
pathway
Protein that
inhibits
the cell cycle
NUCLEUS
DNA
Gene expression
Transcription
factor (activator)
Receptor
G protein
Growth
factor
MUTATION
Hyperactive
Ras protein
(product of
oncogene)
issues signals
on its own
Protein that
stimulates
the cell cycle
32. LE 19-13
Colon
Colon wall
Loss of
tumor-
suppressor
gene APC (or
other)
Normal colon
epithelial cells
Small benign
growth (polyp)
Larger benign
growth (adenoma)
Activation of
ras oncogene
Loss of
tumor-
suppressor
gene DCC
Loss of
tumor-
suppressor
gene p53
Additional
mutations
Malignant tumor
(carcinoma)
33. LE 19-14
Exons (regions of genes coding
for protein, rRNA, or tRNA) (1.5%)
Alu elements
(10%)
Simple sequence
DNA (3%)
Large-segment
duplications (5–6%)
Unique
noncoding
DNA (15%)
Introns and
regulatory
sequences
(24%)
Repetitive
DNA that
includes
transposable
elements
and related
sequences
(44%)
Repetitive
DNA
unrelated to
transposable
elements
(about 15%)
35. LE 19-16
DNA of genome
Transposon
is copied
Mobile transposon
Transposon
Insertion
New copy of
transposon
Transposon movement (“copy-and-paste” mechanism)
Retrotransposon movement
DNA of genome
Insertion
RNA
Reverse
transcriptase
Retrotransposon
New copy of
retrotransposon
36. LE 19-16a
DNA of genome
Transposon
is copied
Mobile transposon
Transposon
Insertion
New copy of
transposon
Transposon movement (“copy-and-paste” mechanism)
38. LE 19-17
DNA
Non-transcribed
spacer
RNA transcripts
Transcription unit
DNA
18S 5.8S 28S
rRNA
18S
5.8S
28S
Part of the ribosomal RNA gene family
Heme
Hemoglobin
α-Globin
β-Globin
α-Globin gene family β-Globin gene family
Chromosome 11Chromosome 16
ζ ψζ ψα2 ψα1 α1α2
ψβ δ βGγ∍ Aγ
Embryo Embryo Fetus Adult
Fetus
and adult
The human α-golbin and β-globin gene families
42. LE 19-19
Duplication of
ancestral gene
Mutation in
both copies
Transposition
to different
chromosomes
Further
duplications
and mutations
Ancestral globin gene
ζ ψζ ψα2
ψα1 α1α2
ψβ δ βGγ∍ Aγ
α-Globin gene family
on chromosome 16
ψϑ
β-Globin gene family
on chromosome 11
ζ α
α
α β
β
∍
βγ
Evolutionarytime
44. LE 19-20
Epidermal growth
factor gene with multiple
EGF exons (green)
EGF EGF EGF EGF
F F F F
Fibronectin gene with multiple
“finger” exons (orange)
K
K KEGFF
Plasminogen gene with a
“kringle” exon (blue)
Portions of ancestral genes TPA gene as it exists today
Exon
shuffling
Exon
shuffling
Exon
duplication
Notas del editor
Estructura del operón.
Estructura del operón triptófano
Regulación positiva. La proteína CAP es una proteína reguladora que activa genes catabólicos).
Cuando hay glucosa en E.coli los niveles de AMPc son bajos y el complejo CAP-AMPc no se forma. Cuando la glucosa se agota, aumentan los niveles de AMPc y se forma el complejo CAP-AMPc uniéndose al promotor, permitiendo la transcripción.
Silenciamiento del ARN:
ARNi micro ARN: ARNss de 21 a 25 nucleótidos con capacidad de regular la trasncripción por interferencia al unirse por complementariedad a ARNm bloqueando la transcripción o permitiendo la degradación del ARNm. Tienen una importante función en la defensa contra la invasión de los virus y en el silenciamiento de los transposones.
ARNmi: 19 a 14 nucleótidos bloqueando la traducción
regulación post-traduccional.
Barbara McClintock y los transposones. Maíz con variaciones en la pigmentación por causa de elementos transponibles