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