FaCEN_nucleo celular

8/4/2019 FaCEN_nucleo celular

1/8

Figure 4-9. (Alberts4e) A cross-sectional view of a typical cell nucleus. The nuclear envelope consists of two membranes, the outer one being continuous with the endoplasmicreticulum membrane (see also Figure 12-9). The space inside the endoplasmic reticulum (the ER lumen) is coloredyellow; it is continuous with the space between the two nuclear membranes.

The lipid bilayers of the inner and outer nuclear membranes are connected at each nuclear pore. Two networks of intermediate filaments (green) provide mechanical support for the nuclear

envelope; the intermediate filaments inside the nucleus form a special supporting structure called the nuclear lamina.

UNIVERSIDAD NACIONAL

DE ASUNCIN

FACULTAD DE CIENCIAS

EXACTAS Y NATURALES

CTEDRA DE

BIOLOGA CELULAR

PROF. LIC. GLORIA YALUFF

ELABORADO POR

DANILO FERNNDEZ ROS
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.2155


2/8

Figure 12-10. (Alberts4e) The arrangement of nuclear pore complexes in the nuclear envelope.(A) A small region of the nuclear envelope. In cross section, a nuclear pore complex seems to have four structural building blocks:

column subunits, which form the bulk of the pore wall; annular subunits, which extend "spokes" (not shown) toward the center of the

pore; lumenal subunits, which contain transmembrane proteins that anchor the complex to the nuclear membrane; and ring subunits,

which form the cytosolic and nuclear faces of the complex. In addition, fibrils protrude from both the cytosolic and the nuclear sides

of the complex. On the nuclear side, the fibrils converge to form basketlike structures. Localization studies using immunoelectron

microscopy techniques showed that the proteins that make up the core of the nuclear pore complex are symmetrically distributed

across the nuclear envelope so that the nuclear and cytosolic sides look identical. This is in contrast to proteins that make up the

fibrils, which are different on each side of the cytosolic or the nuclear side.

(B) A scanning electron micrograph of the nuclear side of the nuclear envelope of an oocyte.

(C) The continuity of the inner and outer nuclear membrane at the pore is apparent in this thin section electron micrograph, showinga side view of two nuclear pore complexes (brackets).

(D) This electron micrograph shows face-on views of negatively stained nuclear pore complexes from which the membrane has been

removed by detergent extraction. (B, from M.W. Goldberg and T.D. Allen, J. Cell Biol. 119:1429 1440, 1992. The Rockefeller

University Press; C, courtesy of Werner Franke and Ulrich Scheer; D, courtesy of Ron Milligan.)

Figure 12-11. (Alberts4e) Possible paths for free diffusion through the nuclear pore complex. This drawing shows ahypothetical diaphragm (gray) inserted into the pore to restrict the size of the open channel to 9 nm, the pore size estimated from diffusion

measurements. Nine nanometers is a much smaller diameter than that of the central opening apparent on the images of the nuclear pore complex

derived from electron micrographs. It is also smaller than the opening estimated during active transport, when the pore dilates to allow the transport ofparticles of up to 26 nm in diameter (arrow). Thus, it is likely that some pore components are lost during the preparation of specimens for electron

microscopy, and that these normally restrict free diffusion through the central opening. Such components may form a diaphragm (or plug) that opens

and closes to allow the passage of large objects during active transport, which depends on sorting signals (discussed below). Although plugs can beseen in some preparations, it is not clear whether they are components of the pore complex or material that is being transported through it. Three-

dimensional computer reconstructions suggest that the channels permitting free diffusion might be located near the rim of the pore complex, between

the column subunits, rather than at its center (see Figure 12-10A); this would mean that passive diffusion and active transport take place through

different parts of the complex.


DE ASUNCIN


EXACTAS Y NATURALES

CTEDRA DE

BIOLOGA CELULAR


ELABORADO POR

DANILO FERNNDEZ ROS


3/8


4/8

Figure 4-22. (Alberts4e) The three DNA sequences required to produce a eucaryotic chromosome thatcan be replicated and then segregated at mitosis.


DE ASUNCIN


EXACTAS Y NATURALES

CTEDRA DE

BIOLOGA CELULAR


ELABORADO POR

DANILO FERNNDEZ ROS


5/8

Figure 4-25. (Alberts4e) The structure of a

nucleosome core particle, as determined by

x-ray diffraction analyses of crystals. Eachhistone is colored according to the scheme of

Figure 4-24, with the DNA double helix in light

gray. (Reprinted by permission from K. Luger etal., Nature 389:251 260, 1997. Macmillan

Magazines Ltd.)

Figure 4-24. (Alberts4e) Structural organization of the nucleosome. A nucleosome contains a proteincore made of eight histone molecules. As indicated, the nucleosome core particle is released from chromatin by

digestion of the linker DNA with a nuclease, an enzyme that breaks down DNA. (The nuclease can degrade the

exposed linker DNA but cannot attack the DNA wound tightly around the nucleosome core.) After dissociation of

the isolated nucleosome into its protein core and DNA, the length of the DNA that was wound around the corecan be determined. This length of 146 nucleotide pairs is sufficient to wrap 1.65 times around the histone core.


DE ASUNCIN


EXACTAS Y NATURALES

CTEDRA DE

BIOLOGA CELULAR


ELABORADO PORDANILO FERNNDEZ ROS


6/8

Figura 10-24. (Lodish5e) Modelo de empaquetamiento de la cromatina y del armazn cromosmico en los cromosomas en metafase. En loscromosomas en interfase, largas extensiones de cromatina de 30 nm forman bucles hacia fuera de los armazones extendidos. En los cromosomas metafsicos, el armazn se

pliega adicionalemente para formar una estructura muy compacta cuya geometra precisa an no se ha determinado.


DE ASUNCIN


EXACTAS Y NATURALES

CTEDRA DE

BIOLOGA CELULAR


ELABORADO POR

DANILO FERNNDEZ ROS


7/8

Figura 10-1. (Lodish5e) Vista general de

la estructura de genes y cromosomas


DE ASUNCIN


EXACTAS Y NATURALES

CTEDRA DE

BIOLOGA CELULAR


ELABORADO POR

DANILO FERNNDEZ ROS


8/8

FIGURA EXPERIMENTAL 10-23. (Lodish5e) Una micrografa electrnica de un

cromosoma en metafase sin histonas revela el armazn alrededor del cual seorganiza el DNA. Los bucles largos de DNA son visibles extendindose del armaznde protena no histona (la estructura oscura). La forma del armazn refleja la del

mismo cromosoma metafsico. El cromosoma fue preparado a partir de clulas HeLa

mediante tratamiento con un detergente suave. (De J. R. Paulson y U. K. Laemmli,

1977, Cell 12:817. Copyright 1977 MIT.)


DE ASUNCIN


EXACTAS Y NATURALES

CTEDRA DE

BIOLOGA CELULAR


ELABORADO POR

DANILO FERNNDEZ ROS

Documents

FaCEN_nucleo celular