Name: 3d imaging with electron microscopy
Uploaded: 2023-04-30T12:01:40.000Z
Duration: 1 min 7 s
Channel: JoVE

A estrutura 3D de amostras biológicas pode ser determinada usando duas técnicas de microscopia crioeletrônica - tomografia eletrônica e reconstrução de partícula única.
Na tomografia eletrônica, uma amostra é progressivamente inclinada em relação ao feixe de elétrons, capturando uma série de imagens 2D de diferentes ângulos. Essas imagens 2D são então empilhadas usando software de computador para gerar a imagem 3D ou tomograma da amostra.
A tomografia eletrônica mantém a integridade estrutural in vivo da amostra e é usada principalmente para visualização 3D de células, organelas e macromoléculas em seu ambiente nativo.
Na reconstrução de partícula única, amostras isoladas in vitro, como uma amostra de proteína purificada, são distribuídas uniformemente em uma grade.
Uma imagem 2D das moléculas de proteína individuais em orientações aleatórias é capturada. Milhares dessas imagens são então calculadas e alinhadas para reconstruir a imagem 3D da amostra.

tomografia por microscópio eletrônico e reconstrução de partícula Única

Electron Microscope Tomography and Single-particle Reconstruction

A microscopia eletrônica de transmissão (MET) pode ser usada para determinar a estrutura 3D de amostras biológicas com a ajuda de técnicas como tomografia de microscópio eletrônico e reconstrução de partícula única. Embora a reconstrução de partícula única possa examinar macromoléculas e complexos macromoleculares apenas em condições in vitro, a tomografia permite o estudo de componentes celulares ou células pequenas in vivo.

 Tomografia Eletrônica 

 A tomografia eletrônica pode ser realizada no modo MET ou MEVT (microscopia eletrônica de varredura e transmissão). A MEVT é uma técnica usada principalmente para obter tomogramas de amostras biológicas espessas. Ela combina a metodologia de varredura da superfície da amostra da microscopia eletrônica de varredura, de modo que os elétrons transmitidos ou espalhados em cada ponto onde o feixe de elétrons atinge a amostra sejam coletados por uma série de detectores. 

 Uma variação da técnica convencional de tomografia eletrônica é a tomografia de eixo duplo, onde a amostra é inclinada em torno de dois eixos em relação ao feixe de elétrons. Isto resulta em dois tomogramas separados que são então alinhados para gerar uma imagem 3D da amostra. A tomografia de eixo duplo tem duas vantagens sobre a tomografia de eixo único: uma melhor reconstrução das características expandidas da amostra e maior resolução da profundidade da amostra. 

 Outra variação é a criotomografia eletrônica, na qual as amostras são fotografadas em condições criogênicas, porque a fixação e a desidratação podem danificar as estruturas biológicas. O método é usado principalmente para amostras finas, com menos de 500 nm de espessura, porque amostras espessas bloqueiam o feixe de elétrons. Portanto, a técnica tem sido limitada a complexos macromoleculares purificados, vírus ou células pequenas, como células bacterianas. 

 Reconstrução de partícula única 

 A análise de partículas únicas é normalmente usada com microscopia crioeletrônica para gerar estruturas 3D com resolução quase atômica. Ela é mais adequada para complexos macromoleculares grandes ou dinâmicos que são difíceis de cristalizar, tornando-a uma substituta para a cristalografia de raios X. Para complexos que podem ser cristalizados, a análise de partículas únicas é o método de escolha para a obtenção de estruturas de alta resolução. A técnica tem sido usada para estudar proteínas de membrana, complexos proteicos, a estrutura da cromatina e de máquinas macromoleculares, como ribossomos e proteassomos.

Tomografia por Microscópio Eletrônico e Reconstrução de Partícula Única

A microscopia eletrônica de transmissão (MET) pode ser usada para determinar a estrutura 3D de amostras biológicas com a ajuda de técnicas como ...

electron-microscope-tomography-and-single-particle-reconstruction

Education

JoVE Core

Cell Biology

Biologia Celular

Unit 1

Unidade 1

Visualizing Cells, Tissues, and Molecules

Visualizando Células, Tecidos e Moléculas

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

3d imaging with electron microscopy

Transmission electron microscopy (TEM) can build 3D images of biological samples. It does this with electron microscope tomography and single-particle reconstruction. Tomography can show cell parts or small cells in vivo, while single-particle reconstruction is used for macromolecules and macromolecular complexes in vitro only.

Electron tomography can be done in TEM or in STEM, which stands for scanning transmission electron microscopy. STEM is mainly used for thick biological specimens. It combines sample scanning with detectors that collect electrons transmitted or scattered where the beam hits the sample.

A common variation is dual-axis tomography. In this method, the sample is tilted around two axes relative to the electron beam. The two tomograms are then aligned to form a 3D image. Dual-axis tomography can improve the reconstruction of expanded features and increase depth resolution compared with single-axis tomography.

Another form is electron cryo-tomography. Samples are imaged under cryogenic conditions because fixation and dehydration can damage biological structures. This method is mainly used for thin samples, usually less than 500 nm thick, because thicker samples block the electron beam. It has therefore been limited to purified macromolecular complexes, viruses, and small cells such as bacterial cells.

Single-particle analysis is usually paired with cryo-electron microscopy to produce 3D structures with near-atomic resolution. It works best for large or dynamic macromolecular complexes that are hard to crystallize, so it can serve as an alternative to X-ray crystallography. When complexes can be crystallized, single-particle analysis is still a method of choice for obtaining high-resolution structures. It has been used to study membrane proteins, protein complexes, chromatin structure, and macromolecular machines such as ribosomes and proteasomes.

3D Imaging with Electron Microscopy

imaging biological samples with optical microscopy

imaging-biological-samples-with-optical-microscopy

How Light Microscopes Bring Samples Into View

Optical microscopy uses light and lenses to make tiny biological samples visible. Antonie van Leeuwenhoek built the first compound optical microscope in the 17th century to view blood cells, bacteria, and yeast cells. In 1830, Joseph Jackson Lister developed an essentially modern light microscope. During the 20th century, microscopes gained better magnification and resolution. A sample is placed on a glass slide and clipped onto the stage, which is the flat platform of the microscope. The...

phase contrast and differential interference contrast microscopy

phase-contrast-and-differential-interference-contrast-microscopy

Microscope Contrast for Live, Unstained Cells

Phase-contrast and differential interference contrast microscopy help scientists see live cells without stains. Both methods boost contrast so thin, transparent structures become easier to study under the microscope. Phase-contrast microscopes use interference between light that passes straight through a cell and light that is refracted by cell parts. The microscope uses an annular stop in the condenser to make a hollow cone of light. The objective lens also contains a phase plate with a phase...

fixation and sectioning

Microscope Slide Prep and Staining

Microscope slide preparation includes wet mounts, fixation, and staining. These steps help make specimens easier to see under a light microscope. They also help preserve cells and highlight important structures. A wet mount is the simplest slide preparation. The specimen is placed in a drop of liquid on the slide. A liquid sample can be added directly with a dropper, and a solid sample, such as a skin scraping, can be placed on the slide before the liquid is added. The liquid is sometimes...

immunofluorescence microscopy

Fluorescent Antibody Staining in Cells

Fluorescent antibody staining uses a fluorescence microscope to make cells and microbes visible in bright colors against a dark background. The microscope works with fluorochromes, which are fluorescent dyes that absorb energy from a light source and then give off visible light. Some fluorochromes are natural, such as chlorophylls. Others are added to the specimen to improve contrast. Common examples of fluorochromes include Texas red and FITC. The method can also use nucleic acid dyes such as...

immunocytochemistry and immunohistochemistry

immunocytochemistry-and-immunohistochemistry

Antibody Staining in Cells and Tissues

Immunocytochemistry (ICC) and immunohistochemistry (IHC) use antibodies to detect specific proteins or antigens in samples. ICC focuses on individual cells, such as blood cells and stem cells. IHC is used for tissue samples. These methods were first published by Albert Coons in 1941, when they were used to detect pneumococcal antigen in mouse tissue sections from mice infected with Pneumococcus. Both techniques can produce either a colored signal or a fluorescent signal. Enzyme-conjugated...

confocal fluorescence microscopy

Confocal Microscopy for Sharp Cell Images

Confocal microscopy is an advanced imaging method used to capture sharp fluorescence images. Its main advantage is that it blocks out-of-focus light from the sample with pinholes. That helps produce high-resolution images with strong contrast. Unlike a standard optical microscope, a confocal microscope uses a focused laser beam to scan the sample surface at different z-planes. This makes it especially useful for thick specimens, such as biofilms. These samples can often be examined alive and...

protein dynamics in living cells

Fluorescent Methods for Protein Movement

Protein movement in living cells can be measured with fluorescence-based methods such as FRAP, FRET, and PET. These techniques help scientists track how proteins move, interact, and change distance inside the cell. Fluorescent recovery after photobleaching, or FRAP, measures protein movement rates within the cell. In this method, a small region is exposed to a strong laser beam. The beam permanently bleaches fluorophore-tagged proteins in that area. Over time, bleached proteins diffuse away...

total internal reflection fluorescence microscopy

total-internal-reflection-fluorescence-microscopy

Surface-Only Imaging with TIRF Microscopy

Total internal reflection fluorescence microscopy, or TIRF, is a microscope method used to view fluorophores near a solid surface with a higher refractive index, such as a glass coverslip. It is useful when scientists want to study signals close to the cell surface. TIRF works when light from a medium with a lower refractive index, such as air, hits the glass coverslip at a critical angle. Instead of entering the glass, the light undergoes total internal reflection. This reflection creates an...

atomic force microscopy

Atomic Force Microscopy for Surface Mapping

Atomic force microscopy is used to map the surface details of materials. It can examine ceramics, glass, polymers, and biological samples. The method gives far more resolution than an optical imaging system and produces three-dimensional surface profiles instead of flat 2D images. The probe is the key part of an AFM setup. It includes the cantilever and tip assembly, and it is also the part that is replaced most often. Constant contact with samples wears down the tip, so probe choice depends...

super-resolution fluorescence microscopy

Sharper Cell Images with Fluorescence Microscopy

Super-resolution fluorescence microscopy gives sharper images than standard fluorescence microscopy by reducing the point spread function, or PSF. The PSF is the light pattern from a point source that makes it look blurred. Because of this blur, each fluorescent spot appears larger than it really is. Nearby fluorophores can also overlap through their PSFs and make the image less clear. Several super-resolution methods have been developed to improve image detail. Photoactivated localization...

overview of electron microscopy

Electron Microscopy: TEM vs SEM

Electron microscopy uses electrons instead of visible light to make images with much higher detail than a light microscope. Visible light limits the resolution of light microscopes, which usually magnify up to 1000X, and sometimes up to 1500X. Electrons have a much shorter wavelength, about 0.005 nm, so they can produce resolution as fine as 0.05 nm. An electron microscope can also magnify images up to 2,000,000X and reveal subcellular structures and some molecular structures, including single...

scanning electron microscopy

How SEM Reveals Surface Details

A scanning electron microscope (SEM) reveals the surface details of a sample with an electron beam. The beam scans across the sample in a two-dimensional pattern. SEM can image areas from about 1 centimeter down to 5 micrometers wide. SEM is useful for studying bacteria, viruses, tissues, and larger samples such as insects. Conventional SEM can produce magnification from 20X to 30,000X. It also offers spatial resolution of about 50 to 100 nanometers. The process starts when the electron gun...

transmission electron microscopy

How TEM Reveals Tiny Structures

Transmission electron microscopy uses electrons to reveal very small structures inside a specimen. The technique grew from the first electron microscope prototype developed in 1931 by physicist Ernst Ruska. He built on the idea that magnetic fields can direct an electron beam, just as lenses direct light in an optical microscope. In a transmission electron microscope, a hot tungsten element produces electrons. An electron gun then accelerates them with a potential difference, giving the beam...

preparation of samples for electron microscopy

preparation-of-samples-for-electron-microscopy

Electron Microscopy Sample Prep Methods

Electron microscopy sample prep methods help biological samples survive imaging in TEM and SEM. Before a specimen can be viewed, it must be fixed, or stabilized, so the electron beam does not damage it. It also must be dried well, or desiccated, because the microscope uses a vacuum. Fixation should happen as quickly as possible. Once a sample leaves its natural environment, its properties begin to change. In tissue samples, oxygen levels can drop and change the appearance of mitochondria. That...

immunogold electron microscopy

Immunogold Labeling in Electron Microscopy

Immunogold labeling in electron microscopy uses antibodies and tiny gold particles to find specific proteins in cells and tissues. The gold particles are very electron-dense, which means they show up clearly in electron microscope images. This gives researchers a high-resolution way to see where proteins are located and to compare their amounts under different stimulation conditions. The method can reveal proteins on the cell surface and inside cells. It has been used to study proteins...

cryo-electron microscopy

Cryo-EM for Native Biomolecule Imaging

Cryo-EM, or cryo-electron microscopy, lets scientists image biomolecules in their frozen, native state. It avoids the dehydration, fixation, and staining used in conventional electron microscopy, which can distort samples and create artifacts. It also reduces damage from the electron beam by using gentler imaging conditions. This method is useful when other structure tools have limits. X-ray diffraction needs a molecule to form a crystal, and that is not always possible. Even when...

electron microscope tomography and single-particle reconstruction

Transmission electron microscopy (TEM) can build 3D images of biological samples. It does this with electron microscope tomography and single-particle reconstruction. Tomography can show cell parts or small cells in vivo, while single-particle reconstruction is used for macromolecules and macromolecular complexes in vitro only. Electron tomography can be done in TEM or in STEM, which stands for scanning transmission electron microscopy. STEM is mainly used for thick biological specimens. It...

key terms and concepts

Learn how TEM creates 3D biological images using tomography and single-particle reconstruction, including STEM, dual-axis, and cryo-tomography methods.

3D Imaging with Electron Microscopy | JoVE K12

cell biology

JoVE Core - Biologia Celular ilustra processos celulares complexos em vídeos de animação fáceis de entender e, ao mesmo tempo, abrangentes. Esta coleção foca nos componentes e funções essenciais das células, incluindo organelas e membranas, transporte celular e energia celular. É complementado por vídeos de Cientistas em ação que demonstram a aplicação da biologia celular em experimentos de pesquisa do mundo real.

3D Imaging with Electron Microscopy

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