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


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


Bacterial operons produce polycistronic mRNAs while most eukaryotic mRNAs are monocistronic and contain introns

Figure 9-1


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


Chromatin exists in extended and condensed forms

Figure 9-29


Nucleosomes are complexes of histones

Figure 9-30


The solenoid model of condensed chromatin

Figure 9-31


A model for chromatin packing in metaphase chromosomes

Figure 9-35


Stained chromosomes have characteristic banding patterns

Figure 9-38


Chromosome painting distinguishes each homologous pair by color

Figure 9-0


Mitochondrial genetic codes differ from the standard genetic code


Bacterial gene control: the Jacob-Monod model

Cis acting DNA sequencesCis acting DNA sequences

Trans-acting genes/proteinsTrans-acting genes/proteins

Figure 10-2


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


DNase I footprinting assays identify protein-DNA interactions

Figure 10-6


Gel-shift assays identify protein-DNA interactions

Figure 10-7


Most bacterial repressors are dimers containing helices that insert into adjacent major grooves of operator DNA

Figure 10-13


Ligand-induced conformational changes alter affinity of many repressors for DNA

Figure 10-14

Tryptophan binding induces a conformational change in the trp aporepressor


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


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


Construction and analysis of a 5-deletion series

Figure 10-24


Three eukaryotic polymerases catalyze formation of different RNAs

Figure 10-25

I: pre-rRNAII: mRNAIII: tRNAs, 5S rRNA, small stable RNAs


The TATA box is a highly conserved promoter in eukaryotic DNA

Figure 10-30

Alternative promoters in eukaryotes include initiators and CpG islands


Most eukaryotic genes are regulated by multiple transcription control mechanisms

Figure 10-34


Transcriptional activators are modular proteins composed of distinct functional domains

Figure 10-39


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


Homeodomain from Engrailed protein interacting with its specific DNA recognition site

Figure 10-40


Interactions of C2H2 and C4 zinc-finger domains with DNA

Figure 10-41


Interaction between a C6 zinc-finger protein (Gal4) and DNA

Figure 10-42


Interaction of a homodimeric leucine-zipper protein and DNA

Figure 10-43


Interaction of a helix-loop-helix in a homodimeric protein and DNA

Figure 10-44


Schematic model of silencing at yeast telomeres

Figure 10-57


Repressors and activators can direct histone deactylation at specific

genes

Figure 10-58


Model for cooperative assembly of an activated transcription-initiation complex in the TTR promoter

Figure 10-61


Repressors interfere directly with transcription initiation in several ways

Figure 10-62


Lipid-soluble hormones control the activities of nuclear receptors

Figure 10-63


Processing of eukaryotic mRNA

Figure 11-7


The 5-cap is added to nascent RNAs after initiation by RNA polymerase II

Figure 11-8


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


Model for passage of mRNPs through nuclear pore complexes

Figure 11-31


Proteins with a nuclear-localization signal (NLS) are recognized by receptors and

transported into the nucleus

Figure 11-35


A model for the import of cytosolic cargo proteins bearing a basic NLS

Figure 11-37


The roles of RNA in protein synthesis

Figure 4-20


The genetic code is a triplet code


The genetic code can be read in different frames

Figure 4-21


Simultaneous translation by multiple ribosomes and their rapid recycling increases the efficiency of protein synthesis

Figure 4-42


Animações

TranscriçãoPós-tradução


Processos fisiológicos dependentes de membranas


As membranas biológicas exibem permeabilidade selectiva


Transporte passivo

Figure 15-2


Overview of membrane transport proteins

Figure 15-3


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


A comparison of the uptake rate of glucose by facilitated diffusion and

passive diffusion

Figure 15-5


Ionic gradients and an electric potential are maintained across the

plasma membrane


The membrane potential in animal cells depends largely on K+ resting

potential

Figure 15-8


Active transport by ATP-powered pumps

Figure 15-10


AE1 protein, a Cl-/HCO3- antiporter, is

crucial to CO2 transport by erythrocytes

Figure 15-20


Transepithelial movement of glucose and amino acids requires multiple

transport proteins

Figure 15-25


Parietal cells acidify the stomach contents while maintaining a neutral

cytosolic pH

Figure 15-26


Osmotic pressure causes water to move across membranes

Figure 15-30


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


The structure of aquaporin, a water channel protein in the erythocyte plasma membrane

Figure 15-33


Changes in intracellular osmotic pressure cause leaf stomata to open

Figure 15-34

biologia celular 2001/2002prof.doutor josé cabeda aula teórica nº 3 fisiologia celular básica

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