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Aula Teórica Nº 3
Fisiologia Celular Básica
2001/2002
Prof.Doutor José Cabeda
Biologia Celular
Expressão Genética
2001/2002
Prof.Doutor José Cabeda
Biologia Celular
Molecular definition of a gene
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A gene is the entire nucleic acid sequence that is
necessary for the synthesis of a functional
polypeptide
DNA regions that code for RNA molecules such as
tRNA and rRNA may also be considered genes
In eukaryotes, genes lie amidst a large expanse of
nonfunctional, noncoding DNA and genes may also
contain regions of noncoding DNA
2001/2002
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Biologia Celular
Bacterial operons produce polycistronic
mRNAs while most eukaryotic mRNAs
are monocistronic and contain introns
Figure 9-1
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Organizing cellular DNA into
chromosomes
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Most bacterial chromosomes are circular with one
replication origin
Eukaryotic chromosomes each contain one linear
DNA molecule and multiple origins of replication
Bacterial DNA is associated with polyamines
Eukaryotic DNA associates with histones to form
chromatin
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Chromatin exists in extended and
condensed forms
Figure 9-29
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Nucleosomes are complexes of
histones
Figure 9-30
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The solenoid model of condensed
chromatin
Figure 9-31
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A model for chromatin packing in
metaphase chromosomes
Figure 9-35
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Stained chromosomes have
characteristic banding patterns
Figure 9-38
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Chromosome painting distinguishes
each homologous pair by color
Figure 9-0
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Mitochondrial genetic codes differ
from the standard genetic code
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Bacterial gene control: the JacobMonod model
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Cis acting DNA sequences
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Trans-acting genes/proteins
Figure 10-2
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10.2 Bacterial transcription initiation
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RNA polymerase initiates transcription of most genes
at a unique DNA position lying upstream of the coding
sequence
The base pair where transcription initiates is termed
the transcription-initiation site or start site
By convention, the transcription-initiation site in the
DNA sequence is designated +1, and base pairs
extending in the direction of transcription
(downstream) are assigned positive numbers which
those extending in the opposite direction (upstream)
are assigned negative numbers
Various proteins (RNA polymerase, activators,
repressors) interact with DNA at or near the promoter
to regulate transcription initiation
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DNase I footprinting assays identify
protein-DNA interactions
Figure 10-6
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Gel-shift assays identify protein-DNA
interactions
Figure 10-7
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Most bacterial repressors are dimers
containing  helices that insert into
adjacent major grooves of operator DNA
Figure 10-13
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Ligand-induced conformational changes
alter affinity of many repressors for DNA
Tryptophan binding
induces a
conformational change
in the trp aporepressor
Figure 10-14
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Many genes in higher eukaryotes are
regulated by controlling their transcription
The nascent chain (run-on)
assay allows measurement
of the rate of transcription of
a given gene
Figure 10-22
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Regulatory elements in eukaryotic
DNA often are many kilobases from
start sites
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The basic principles that control transcription in bacteria also
apply to eukaryotic organisms: transcription is initiated at a
specific base pair and is controlled by the binding of transacting proteins (transcription factors) to cis-acting regulatory
DNA sequences
However, eukaryotic cis-acting elements are often much
further from the promoter they regulate, and transcription
from a single promoter may be regulated by binding of
multiple transcription factors to alternative control elements
Transcription control sequences can be identified by analysis
of a 5-deletion series
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Construction and analysis of a 5deletion series
Figure 10-24
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Three eukaryotic polymerases
catalyze formation of different RNAs
I: pre-rRNA
II: mRNA
III: tRNAs, 5S rRNA,
small stable RNAs
Figure 10-25
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The TATA box is a highly conserved
promoter in eukaryotic DNA
Alternative promoters in eukaryotes include initiators and CpG islands
Figure 10-30
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Most eukaryotic genes are regulated
by multiple transcription control
mechanisms
Figure 10-34
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Transcriptional activators are modular
proteins composed of distinct functional
domains
Figure 10-39
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DNA-binding domains can be
classified into numerous structural
types
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Homeodomain proteins
Zinc-finger proteins
Winged-helix (forkhead) proteins
Leucine-zipper proteins
Helix-loop-helix proteins
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Homeodomain from Engrailed protein
interacting with its specific DNA
recognition site
Figure 10-40
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Interactions of C2H2 and C4 zincfinger domains with DNA
Figure 10-41
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Interaction between a C6 zinc-finger
protein (Gal4) and DNA
Figure 10-42
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Interaction of a homodimeric
leucine-zipper protein and DNA
Figure 10-43
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Interaction of a helix-loop-helix in a
homodimeric protein and DNA
Figure 10-44
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Schematic model of silencing at
yeast telomeres
Figure 10-57
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Repressors and activators can direct
histone deactylation at specific
genes
Figure 10-58
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Model for cooperative assembly of an
activated transcription-initiation complex
in the TTR promoter
Figure 10-61
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Repressors interfere directly with
transcription initiation in several ways
Figure 10-62
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Lipid-soluble hormones control the
activities of nuclear receptors
Figure 10-63
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Processing of eukaryotic mRNA
Figure 11-7
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The 5-cap is added to nascent RNAs
after initiation by RNA polymerase II
Figure 11-8
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Multiple protein isoforms are
common in the vertebrate nervous
system
Alternative splicing of slo mRNA, which encodes a Ca2+-gated K+ channel in
auditory hair cells, contributes to the perception of sounds of different
frequencies
Figure 11-27
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Model for passage of mRNPs through
nuclear pore complexes
Figure 11-31
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Proteins with a nuclear-localization signal
(NLS) are recognized by receptors and
transported into the nucleus
Figure 11-35
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A model for the import of cytosolic
cargo proteins bearing a basic NLS
Figure 11-37
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The roles of RNA in protein
synthesis
Figure 4-20
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The genetic code is a triplet code
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The genetic code can be read in
different frames
Figure 4-21
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Simultaneous translation by multiple
ribosomes and their rapid recycling increases
the efficiency of protein synthesis
Figure 4-42
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Animações
Transcrição
Pós-tradução
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Processos fisiológicos
dependentes de membranas
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As membranas biológicas exibem
permeabilidade selectiva
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Transporte passivo
Figure 15-2
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Overview of membrane transport
proteins
Figure 15-3
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Uniporter-catalyzed transport
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Uniporters accelerate a reaction that is already
thermodynamically favored (similar to enzymes)
This type of transport is termed facilitated
transport or facilitated diffusion
Three main features distinguish uniport transport
(facilitated diffusion) from passive diffusion
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The rate of facilitated diffusion is much higher than
passive diffusion
Transport is specific
Transport occurs via a limited number of uniporters
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A comparison of the uptake rate of
glucose by facilitated diffusion and
passive diffusion
Figure 15-5
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Ionic gradients and an electric
potential are maintained across the
plasma membrane
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The membrane potential in animal
cells depends largely on K+ resting
potential
Figure 15-8
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Active transport by ATP-powered
pumps
Figure 15-10
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AE1 protein, a Cl-/HCO3- antiporter, is
crucial to CO2 transport by
erythrocytes
Figure 15-20
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Transepithelial movement of glucose
and amino acids requires multiple
transport proteins
Figure 15-25
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Parietal cells acidify the stomach
contents while maintaining a neutral
cytosolic pH
Figure 15-26
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Osmotic pressure causes water to
move across membranes
Figure 15-30
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Water channels are necessary for
bulk flow of water across cell
membranes
Aquaporin is a water channel that increases a membrane’s permeability to water
Figure 15-32
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The structure of aquaporin, a water
channel protein in the erythocyte
plasma membrane
Figure 15-33
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Changes in intracellular osmotic
pressure cause leaf stomata to open
Figure 15-34
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Biologia Celular