CHAPTER 4 A Tour of the Cell
Today Microscopic methods to study cells A picture show of cellular diversity Next times The components of cells Membranes and membrane proteins Cell wall /extracellular matrix Nucleus Ribosomes The endomembrane system Mitochondria and Chloroplasts (structure and origin) and chloroplasts Cytoskeleton, cilia and flagella Modern methods to visualize organelles
The Microscopic World of Cells Cells were discovered in 1665 by Robert Hooke. The microscopic observations later led to the cell theory. All living things are composed of cells. Cells are the smallest unit of life All cells are formed from previously existing cells.
Although cells are small, their complexity is comparable to that of an airplane. Each cell is a - micro-machine composed of nano-machines; - micro-reactor composed of nano-reactors; - micro-computer composed of nano-computers. The human eye can only resolve objects 0.1 mm = 100 µm but cells are usually <0.02 mm = 20 µm Animal cells 1 mm = 1,000 µm
Microscopes as a Window on the World of Cells Much of cell complexity is understood with the help of microscopes - Optical microscopes (LIGHT interacts with the sample) - Electron microscopes (ELECTRONS interact with the sample) - Scanning probe microscopes (A SCANNING PROBE interacts with the sample) - Most important scanning probe microscope: Atomic force microscope Several Nobel prizes were awarded for the invention of microscopes Atomic force microscope Copyright 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The light microscope The light microscope was the key tool that allowed discovery of the cell It is still used by most scientists Magnification ( 배율 ) = increase in the specimen s apparent size is up to 2,000x Resolving power ( 해상력 ) = ability to show two objects as separate is 0.2 µm Robert Hooke s microscope Current light microscope
Cultured cells Bright-field Phase contrast Differential-interferencecontrast Dark field
Stained cell preparations under the traditional light microscope Tissue section Blood cells Chromosomes
Using a laser, cells or groups of cells can be isolated under the microscope Laser-capture microdissection Before After Isolated cells http://www.bioopticsworld.com/articles/print/volume-5/issue-04/features/from-bench-to-business-nih-tech-transfer-needs-industry.html
Another application of lasers: The confocal laser scanning microscope Higher resolution Depth-dependent measurements (optical tomography)
High-resolution imaging of cell skeleton with confocal laser scanning microscopy
The electron microscope (EM) Uses a beam of electrons. Has a higher resolving power than the light microscope. Can magnify up to 2,000,000X Such power reveals the diverse parts within a cell.
The transmission electron microscope
Budding viruses Cell Protein molecules DNA molecules
The scanning electron microscope
Cell budding viruses Ant Cell surface with protein complexes (freeze-fracture technique)
The atomic force microscope (AFM) Advantages compared with electron microscope AFM does not require vacuum Does not require special sample treatment Provides a true 3D picture Has higher theoretical resolution than SEM
The atomic force microscope (AFM)
Tip of an atomic force microscope. A platinum electrode measuring one hundredth of a nanometer has been deposited on the tip via focused ion beam (FIB) deposition.
AFM image of a cell surface
AFM images of molecules Protein complexes Aquaporin Fo of ATP synthase AFM image of complex of DNA with DNA-cutting enzyme
The same cell type seen with different visualization methods The protist Euglena, photographed with three different methods
A eukaryotic cell with budding viruses
Light microscope can magnify up to 2 thousand times Electron Microscope can magnify up to 2 million times Atomic force microscopes can in principle visualize atoms (but only in vacuum) Atomic force microscope
The Two Major Categories of Cells Prokaryotic cells Eukaryotic cells
Prokaryotic cells Are smaller than eukaryotic cells. Lack internal structures surrounded by membranes. Lack a nucleus. DNA is coiled in a nucleoid region, which is not partitioned from the rest of the cell by membranes Copyright 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Examples of prokaryotic cells ( Try to identify the visualization method)
Examples of prokaryotic cells Cyanobacteria
Streptomyces (Eubacteria) Escherichia coli (Eubacteria)
Methanococcus (Archebacteria)
Halophiles (Archaebacteria)
Eukaryotic cells are much more complex than prokaryotic cells
A Panoramic View of Eukaryotic Cells An idealized animal cell An idealized plant cell Copyright 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Examples of eukaryotic cells
Ciliates (Protozoa)
Flagellates (Protozoa)
Amoeba (Protozoa) Yeast (Fungi)
Plant cells
Animal cells White blood cell (macrophage) eating bacteria White blood cell (lymphocyte) Nerve cell Glia cells
Endothelial cells (blood vessel wall)
Summary comparison: Prokaryotic and eukaryotic cells differ in several respects.
Summary A tour of the cell Microscopes play a major role in the study of cells. Resolution of the human eye: ~0.1-0.2 mm (100 µm). Typical eukaryotic cells are 0.01 0.02 mm (10-20 µm). Typical prokaryotic cells are ~ 0.001 mm (1 µm). Microscopes probe the sample with light, electrons, or via electrostatic/van der Vaals interaction. Light microscope (resolution ~ 0.2 µm, magnification up to 2,000). Cells are often translucent; for microscopy they are stained (which may kill) or contrast-enhanced (phase contrast microscope); resolution is improved with the laser scanning confocal microscope. Structures seen: Eukaryotic cells, bacteria, cell organelles like nucleus, cytoskeletal fibers, condensed chromosomes. Electron microscope (resolution 0.2 nm, magnification typically up to 2,000,000). Transmission electron microscope (TEM): Electrons that penetrate the sample are measured. Used to visualize inner structures (membranes, substructure of organelles, viruses, large biomolecules). Scanning electron microscope (SEM): Measures reflections caused by electrons. Used to visualize details of surfaces, but only gives a pseudo-3d image (cannot measure the z-dimension). Atomic force microscope (resolution slightly better than electron microscope). A probe scans along the unaltered sample surface. No vacuum needed, gives a real 3D image (measures the z-dimension). Probes can also move atoms. The size of an atom: 0.03 0.3 nm. All cells on earth fall into two structural categories. Prokaryotes: 1 cell = 1 compartment ( box ). No details can be seen in the light microscope. Eukaryotes: 1 cell = many compartments (organelles such as nucleus, mitochondria, chloroplasts, Golgi, endoplasmic reticulum) ( boxes in a box ). The largest organelles can be seen in the light microscope.
요약 - 세포속으로여행 현미경은세포의연구에중요한역할을한다. 인간눈의해상도 : ~0.1-0.2 mm (100 um). 전형적인진핵세포들은 0.01-0.02 mm (10-20 um). 전형적인원핵세포들은 ~0.001 mm (1 um). 현미경은빛, 전자, 또는정전기 / 반데르발스상호작용을통해표본을검출할수있다. 광학현미경 ( 해상도 ~0.2 um, 최대배율 2,000 배 ). 세포들은대부분반투명하다 ; 현미경으로관찰을위해서세포들을염색하거나 ( 세포를죽일수도있음 ) 대비를높인다 ( 위상차현미경 ); 해상도는공초점레이져현미경으로향상할수있다. 볼수있는구조들 : 진핵세포, 원핵세포, 핵과같은세포소기관들, 세포골격섬유들, 응집된염색체들. 전자현미경 ( 해상도 0.2 nm, 일반적으로최대 2,000,000 배까지확대 ) 투과전자현미경 (TEM): 샘플을투과하는전자를측정. 내부구조들 ( 세포막들, 소기관들의구조, 바이러스, 큰생체분자들 ) 을확인하기위해사용되곤한다. 주사전자현미경 (SEM): 전자들에의해발생되는반사를측정한다. 표면의세부적인부분을가시화하기위해사용되곤하나, 오직가짜 -3D 영상만줄수있다 (z 축은측정할수없다 ). 원자간력현미경 ( 해상도는전자현미경보다약간더좋다.) 프로브는변하지않은시료의표면을따라탐색할수있다. 진공이필요없으며, 실제 3D 영상을줄수있다 (z 축을측정한다 ). 프로브는또한원자로이동할수있다. * 프로브 : 계측의목적으로사용되는빔 원자의크기 : 0.03-0.3 nm. 지구상의모든세포들은두개의구조적범위안에들어간다. 원핵세포들 : 1 개세포 = 1 칸 (" 박스 ). 광학현미경에서미세구조를확인할수없다. 진핵세포들 : 1 개세포 = 많은칸들 ( 핵, 미토콘드리아, 염록체, 골지체, 소포체와같은세포소기관들 ) ( 박스안의박스들 ). 광학현미경에서가장큰소기관들은확인할수있다.