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Biologia Celular 2001/2002Prof.Doutor José Cabeda Aula Teórica Nº 3 Fisiologia Celular Básica.

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Presentation on theme: "Biologia Celular 2001/2002Prof.Doutor José Cabeda Aula Teórica Nº 3 Fisiologia Celular Básica."— Presentation transcript:

1 Biologia Celular 2001/2002Prof.Doutor José Cabeda Aula Teórica Nº 3 Fisiologia Celular Básica

2 Biologia Celular 2001/2002Prof.Doutor José Cabeda Expressão Genética

3 Biologia Celular 2001/2002Prof. Doutor José Cabeda Molecular definition of a gene A gene is the entire nucleic acid sequence that is necessary for the synthesis of a functional polypeptide 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 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 In eukaryotes, genes lie amidst a large expanse of nonfunctional, noncoding DNA and genes may also contain regions of noncoding DNA

4 Biologia Celular 2001/2002Prof. Doutor José Cabeda Bacterial operons produce polycistronic mRNAs while most eukaryotic mRNAs are monocistronic and contain introns Figure 9-1

5 Biologia Celular 2001/2002Prof. Doutor José Cabeda Organizing cellular DNA into chromosomes Most bacterial chromosomes are circular with one replication origin Most bacterial chromosomes are circular with one replication origin Eukaryotic chromosomes each contain one linear DNA molecule and multiple origins of replication Eukaryotic chromosomes each contain one linear DNA 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 chromatin Eukaryotic DNA associates with histones to form chromatin

6 Biologia Celular 2001/2002Prof. Doutor José Cabeda Chromatin exists in extended and condensed forms Figure 9-29

7 Biologia Celular 2001/2002Prof. Doutor José Cabeda Nucleosomes are complexes of histones Figure 9-30

8 Biologia Celular 2001/2002Prof. Doutor José Cabeda The solenoid model of condensed chromatin Figure 9-31

9 Biologia Celular 2001/2002Prof. Doutor José Cabeda A model for chromatin packing in metaphase chromosomes Figure 9-35

10 Biologia Celular 2001/2002Prof. Doutor José Cabeda Stained chromosomes have characteristic banding patterns Figure 9-38

11 Biologia Celular 2001/2002Prof. Doutor José Cabeda Chromosome painting distinguishes each homologous pair by color Figure 9-0

12 Biologia Celular 2001/2002Prof. Doutor José Cabeda Mitochondrial genetic codes differ from the standard genetic code

13 Biologia Celular 2001/2002Prof. Doutor José Cabeda Bacterial gene control: the Jacob- Monod model Cis acting DNA sequences Trans-acting genes/proteins Figure 10-2

14 Biologia Celular 2001/2002Prof. Doutor José Cabeda 10.2 Bacterial transcription initiation RNA polymerase initiates transcription of most genes at a unique DNA position lying upstream of the coding sequence 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 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 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 Various proteins (RNA polymerase, activators, repressors) interact with DNA at or near the promoter to regulate transcription initiation

15 Biologia Celular 2001/2002Prof. Doutor José Cabeda DNase I footprinting assays identify protein-DNA interactions Figure 10-6

16 Biologia Celular 2001/2002Prof. Doutor José Cabeda Gel-shift assays identify protein-DNA interactions Figure 10-7

17 Biologia Celular 2001/2002Prof. Doutor José Cabeda Most bacterial repressors are dimers containing helices that insert into adjacent major grooves of operator DNA Figure 10-13

18 Biologia Celular 2001/2002Prof. Doutor José Cabeda Ligand-induced conformational changes alter affinity of many repressors for DNA Figure Tryptophan binding induces a conformational change in the trp aporepressor

19 Biologia Celular 2001/2002Prof. Doutor José Cabeda Many genes in higher eukaryotes are regulated by controlling their transcription Figure The nascent chain (run-on) assay allows measurement of the rate of transcription of a given gene

20 Biologia Celular 2001/2002Prof. Doutor José Cabeda Regulatory elements in eukaryotic DNA often are many kilobases from start sites 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 trans- acting proteins (transcription factors) to cis-acting regulatory DNA sequences 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 trans- acting 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 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 Transcription control sequences can be identified by analysis of a 5 -deletion series

21 Biologia Celular 2001/2002Prof. Doutor José Cabeda Construction and analysis of a 5 - deletion series Figure 10-24

22 Biologia Celular 2001/2002Prof. Doutor José Cabeda Three eukaryotic polymerases catalyze formation of different RNAs Figure I: pre-rRNA II: mRNA III: tRNAs, 5S rRNA, small stable RNAs

23 Biologia Celular 2001/2002Prof. Doutor José Cabeda The TATA box is a highly conserved promoter in eukaryotic DNA Figure Alternative promoters in eukaryotes include initiators and CpG islands

24 Biologia Celular 2001/2002Prof. Doutor José Cabeda Most eukaryotic genes are regulated by multiple transcription control mechanisms Figure 10-34

25 Biologia Celular 2001/2002Prof. Doutor José Cabeda Transcriptional activators are modular proteins composed of distinct functional domains Figure 10-39

26 Biologia Celular 2001/2002Prof. Doutor José Cabeda DNA-binding domains can be classified into numerous structural types Homeodomain proteins Homeodomain proteins Zinc-finger proteins Zinc-finger proteins Winged-helix (forkhead) proteins Winged-helix (forkhead) proteins Leucine-zipper proteins Leucine-zipper proteins Helix-loop-helix proteins Helix-loop-helix proteins

27 Biologia Celular 2001/2002Prof. Doutor José Cabeda Homeodomain from Engrailed protein interacting with its specific DNA recognition site Figure 10-40

28 Biologia Celular 2001/2002Prof. Doutor José Cabeda Interactions of C 2 H 2 and C 4 zinc- finger domains with DNA Figure 10-41

29 Biologia Celular 2001/2002Prof. Doutor José Cabeda Interaction between a C 6 zinc-finger protein (Gal4) and DNA Figure 10-42

30 Biologia Celular 2001/2002Prof. Doutor José Cabeda Interaction of a homodimeric leucine-zipper protein and DNA Figure 10-43

31 Biologia Celular 2001/2002Prof. Doutor José Cabeda Interaction of a helix-loop-helix in a homodimeric protein and DNA Figure 10-44

32 Biologia Celular 2001/2002Prof. Doutor José Cabeda Schematic model of silencing at yeast telomeres Figure 10-57

33 Biologia Celular 2001/2002Prof. Doutor José Cabeda Repressors and activators can direct histone deactylation at specific genes Figure 10-58

34 Biologia Celular 2001/2002Prof. Doutor José Cabeda Model for cooperative assembly of an activated transcription-initiation complex in the TTR promoter Figure 10-61

35 Biologia Celular 2001/2002Prof. Doutor José Cabeda Repressors interfere directly with transcription initiation in several ways Figure 10-62

36 Biologia Celular 2001/2002Prof. Doutor José Cabeda Lipid-soluble hormones control the activities of nuclear receptors Figure 10-63

37 Biologia Celular 2001/2002Prof. Doutor José Cabeda Processing of eukaryotic mRNA Figure 11-7

38 Biologia Celular 2001/2002Prof. Doutor José Cabeda The 5 -cap is added to nascent RNAs after initiation by RNA polymerase II Figure 11-8

39 Biologia Celular 2001/2002Prof. Doutor José Cabeda Multiple protein isoforms are common in the vertebrate nervous system Figure Alternative splicing of slo mRNA, which encodes a Ca 2+ -gated K + channel in auditory hair cells, contributes to the perception of sounds of different frequencies

40 Biologia Celular 2001/2002Prof. Doutor José Cabeda Model for passage of mRNPs through nuclear pore complexes Figure 11-31

41 Biologia Celular 2001/2002Prof. Doutor José Cabeda Proteins with a nuclear-localization signal (NLS) are recognized by receptors and transported into the nucleus Figure 11-35

42 Biologia Celular 2001/2002Prof. Doutor José Cabeda A model for the import of cytosolic cargo proteins bearing a basic NLS Figure 11-37

43 Biologia Celular 2001/2002Prof. Doutor José Cabeda The roles of RNA in protein synthesis Figure 4-20

44 Biologia Celular 2001/2002Prof. Doutor José Cabeda The genetic code is a triplet code

45 Biologia Celular 2001/2002Prof. Doutor José Cabeda The genetic code can be read in different frames Figure 4-21

46 Biologia Celular 2001/2002Prof. Doutor José Cabeda Simultaneous translation by multiple ribosomes and their rapid recycling increases the efficiency of protein synthesis Figure 4-42

47 Biologia Celular 2001/2002Prof. Doutor José Cabeda Animações Transcrição Pós-tradução

48 Biologia Celular 2001/2002Prof.Doutor José Cabeda Processos fisiológicos dependentes de membranas

49 Biologia Celular 2001/2002Prof. Doutor José Cabeda As membranas biológicas exibem permeabilidade selectiva

50 Biologia Celular 2001/2002Prof. Doutor José Cabeda Transporte passivo Figure 15-2

51 Biologia Celular 2001/2002Prof. Doutor José Cabeda Overview of membrane transport proteins Figure 15-3

52 Biologia Celular 2001/2002Prof. Doutor José Cabeda Uniporter-catalyzed transport Uniporters accelerate a reaction that is already thermodynamically favored (similar to enzymes) Uniporters accelerate a reaction that is already thermodynamically favored (similar to enzymes) This type of transport is termed facilitated transport or facilitated diffusion This type of transport is termed facilitated transport or facilitated diffusion Three main features distinguish uniport transport (facilitated diffusion) from passive diffusion Three main features distinguish uniport transport (facilitated diffusion) from passive diffusion The rate of facilitated diffusion is much higher than passive diffusion The rate of facilitated diffusion is much higher than passive diffusion Transport is specific Transport is specific Transport occurs via a limited number of uniporters Transport occurs via a limited number of uniporters

53 Biologia Celular 2001/2002Prof. Doutor José Cabeda A comparison of the uptake rate of glucose by facilitated diffusion and passive diffusion Figure 15-5

54 Biologia Celular 2001/2002Prof. Doutor José Cabeda Ionic gradients and an electric potential are maintained across the plasma membrane

55 Biologia Celular 2001/2002Prof. Doutor José Cabeda The membrane potential in animal cells depends largely on K + resting potential Figure 15-8

56 Biologia Celular 2001/2002Prof. Doutor José Cabeda Active transport by ATP-powered pumps Figure 15-10

57 Biologia Celular 2001/2002Prof. Doutor José Cabeda AE1 protein, a Cl - /HCO 3 - antiporter, is crucial to CO 2 transport by erythrocytes Figure 15-20

58 Biologia Celular 2001/2002Prof. Doutor José Cabeda Transepithelial movement of glucose and amino acids requires multiple transport proteins Figure 15-25

59 Biologia Celular 2001/2002Prof. Doutor José Cabeda Parietal cells acidify the stomach contents while maintaining a neutral cytosolic pH Figure 15-26

60 Biologia Celular 2001/2002Prof. Doutor José Cabeda Osmotic pressure causes water to move across membranes Figure 15-30

61 Biologia Celular 2001/2002Prof. Doutor José Cabeda Water channels are necessary for bulk flow of water across cell membranes Figure Aquaporin is a water channel that increases a membranes permeability to water

62 Biologia Celular 2001/2002Prof. Doutor José Cabeda The structure of aquaporin, a water channel protein in the erythocyte plasma membrane Figure 15-33

63 Biologia Celular 2001/2002Prof. Doutor José Cabeda Changes in intracellular osmotic pressure cause leaf stomata to open Figure 15-34


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