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Ryan Barrow Chris Romero
The Cell Packet #10 Ryan Barrow Chris Romero
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Overview: The Importance of Cells
All organisms are made of cells The cell is the simplest collection of matter that can live
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Cell structure is correlated to cellular function
10 µm Figure 6.1
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Concept 6.1: To study cells, biologists use microscopes and the tools of biochemistry
Scientists use microscopes to visualize cells too small to see with the naked eye Light microscopes (LMs) Pass visible light through a specimen Magnify cellular structures with lenses
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Types of Microscopes I Different types of microscopes
Unaided eye Different types of microscopes Can be used to visualize different sized cellular structures 1 m 0.1 nm 10 m 0.1 m 1 cm 1 mm 100 µm 10 µ m 1 µ m 100 nm 10 nm 1 nm Length of some nerve and muscle cells Chicken egg Frog egg Most plant and Animal cells Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Nucleus Most bacteria Mitochondrion Light microscope Electron microscope Figure 6.2 Human height Measurements 1 centimeter (cm) = 102 meter (m) = 0.4 inch 1 millimeter (mm) = 10–3 m 1 micrometer (µm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–3 mm = 10–9 m
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Use different methods for enhancing visualization of cellular structures
TECHNIQUE RESULT Brightfield (unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained, image has little contrast. [Parts (a)–(d) show a human cheek epithelial cell.] (a) Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved). (b) Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells. (c) 50 µm Figure 6.3
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Fluorescence. Shows the locations of specific
molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. These fluorescent substances absorb ultraviolet radiation and emit visible light, as shown here in a cell from an artery. Confocal. Uses lasers and special optics for “optical sectioning” of fluorescently-stained specimens. Only a single plane of focus is illuminated; out-of-focus fluorescence above and below the plane is subtracted by a computer. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry. 50 µm (d) (e) (f) Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences in density, making the image appear almost 3D.
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Electron microscopes (EMs)
Focus a beam of electrons through a specimen (TEM) or onto its surface (SEM) Very expensive Magnifications of up to 500,000 and a resolving power of less than 1nm **Viruses can only be seen using an electron microscope
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Scanning Electron Microscope (SEM)
Specimen is covered with metal and electron beam is swept over the coating Provides for detailed study of the surface of a specimen TECHNIQUE RESULTS Scanning electron micro- scopy (SEM). Micrographs taken with a scanning electron micro- scope show a 3D image of the surface of a specimen. This SEM shows the surface of a cell from a rabbit trachea (windpipe) covered with motile organelles called cilia. Beating of the cilia helps move inhaled debris upward toward the throat. (a) Cilia 1 µm Figure 6.4 (a)
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Transmission Electron Microscope (TEM)
Provides for detailed study of the internal ultrastructure of cells Transmission electron micro- scopy (TEM). A transmission electron microscope profiles a thin section of a specimen. Here we see a section through a tracheal cell, revealing its ultrastructure. In preparing the TEM, some cilia were cut along their lengths, creating longitudinal sections, while other cilia were cut straight across, creating cross sections. (b) Longitudinal section of cilium Cross section of cilium 1 µm Figure 6.4 (b)
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Isolating Organelles by Cell Fractionation
Takes cells apart and separates the major organelles from one another Individual function is isolated
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The centrifuge Is used to fractionate cells into their component parts
Spins with speeds up to 80,000 revolutions per minute Applies forces on particles up to 500,000 times the force of gravity
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The process of cell fractionation
Cell fractionation is used to isolate (fractionate) cell components, based on size and density. APPLICATION First, cells are homogenized in a blender to break them up. The resulting mixture (cell homogenate) is then centrifuged at various speeds and durations to fractionate the cell components, forming a series of pellets. TECHNIQUE Figure 6.5
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Differential centrifugation
Tissue cells Homogenization Homogenate 1000 g (1000 times the force of gravity) 10 min Differential centrifugation Supernatant poured into next tube 20,000 g 20 min Pellet rich in nuclei and cellular debris mitochondria (and chloro- plasts if cells are from a plant) “microsomes” (pieces of plasma mem- branes and cells’ internal membranes) ribosomes 150,000 g 3 hr 80,000 g 60 min Figure 6.5
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The process of cell fractionation
RESULTS In the original experiments, the researchers used microscopy to identify the organelles in each pellet, establishing a baseline for further experiments. In the next series of experiments, researchers used biochemical methods to determine the metabolic functions associated with each type of organelle. Researchers currently use cell fractionation to isolate particular organelles in order to study further details of their function. Figure 6.5
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Concept 6.2 Eukaryotic cells have internal membranes that compartmentalize their functions Types of cells make organisms Prokaryotic Eukaryotic
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Comparing Prokaryotic and Eukaryotic Cells
All cells have several basic features in common They are bounded by a plasma membrane They contain a semifluid substance called the cytosol They all have ribosomes They have chromosomes
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Prokaryotic cells Before nucleus Do not contain a nucleus
Lack membrane bound organelles Have their DNA located in a region called the nucleoid May contain chlorophyll but no chloroplasts Flagella, if present, lack fibril arrangement Ribosomes are either 30S (subunits) or 60S
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Prokaryotic cells Contain plasmids
Small ring of DNA that carry accessory genes separate from those of a bacterial chromosome Details on plasmids to come later
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(b) A thin section through the
bacterium Bacillus coagulans (TEM) Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell’s DNA is located (not enclosed by a membrane) Ribosomes: organelles that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Cell wall: rigid structure outside the plasma membrane Capsule: jelly-like outer coating of many prokaryotes Flagella: locomotion organelles of some bacteria (a) A typical rod-shaped bacterium 0.5 µm Bacterial chromosome Figure 6.6 A, B
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Eukaryotic cells Contain a true nucleus, bounded by a membranous nuclear envelope Chlorophyll when present contained in chloroplasts Are generally quite a bit bigger than prokaryotic cells Cell wall present in some Mitosis and meiosis occur
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Eukaryotic Cells Ribosomes
Larger than those found in prokaryotic cells 80S Attached to the Endoplasmic Reticulum 70S Found in the mitochondria
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Cell Size The logistics of carrying out cellular metabolism sets limits on the size of cells
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Cell Size II A smaller cell
Has a higher surface to volume ratio, which facilitates the exchange of materials into and out of the cell Surface area increases while total volume remains constant 5 1 Total surface area (height width number of sides number of boxes) Total volume (height width length number of boxes) Surface-to-volume ratio (surface area volume) 6 150 125 12 750 Figure 6.7
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Plasma Membrane (More Later)
The plasma membrane Functions as a selective barrier Allows sufficient passage of nutrients and waste Outside of cell Inside of cell Hydrophilic region Hydrophobic (b) Structure of the plasma membrane Phospholipid Proteins TEM of a plasma membrane. The plasma membrane, here in a red blood cell, appears as a pair of dark bands separated by a light band. (a) 0.1 µm Carbohydrate side chain Figure 6.8 A, B
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A Panoramic View of the Eukaryotic Cell
Eukaryotic cells Have extensive and elaborately arranged internal membranes, which form organelles Animal Cells Plant Cells
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Plant and animal cells Have most of the same organelles
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Intermediate filaments ENDOPLASMIC RETICULUM (ER)
The Animal Cell Rough ER Smooth ER Centrosome CYTOSKELETON Microfilaments Microtubules Microvilli Peroxisome Lysosome Golgi apparatus Ribosomes In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) Nucleolus Chromatin NUCLEUS Flagelium Intermediate filaments ENDOPLASMIC RETICULUM (ER) Mitochondrion Nuclear envelope Plasma membrane Figure 6.9
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The Animal Cell No cellulose cell wall-only membrane No pits
No plasmodesmata Some vacuoles but usually small and numerous Cytoplasm throughout the cell Nucleus anywhere in cytoplasm by often central Only one cytoplasmic membrane Not normally any plastids Cilia common in higher animals Centrioles present
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Ribosomes (small brwon dots)
The Plant Cell Ribosomes (small brwon dots) Central vacuole Microfilaments Intermediate filaments Microtubules Rough endoplasmic reticulum Smooth Chromatin NUCLEUS Nuclear envelope Nucleolus Chloroplast Plasmodesmata Wall of adjacent cell Cell wall Golgi apparatus Peroxisome Tonoplast Centrosome Plasma membrane Mitochondrion CYTOSKELETON In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata Figure 6.9
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The Plant Cell Cell wall that contains cellulose Pits in cell walls
Plasmodesmata is present Large vacuole filled with cell sap Cytoplasm is peripheral Nucleus usually peripheral Two cytoplasmic membranes Outer plasmodesmata Inner tonoplast Variety of plastids Chloroplast Leucolast Cilia and flagella absent in higher plants Centrioles absent in higher plants
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Plasmodesmata Plasmodesmata are microscopic channels of plants facilitating transport and communication between individual cells Cytoplasmic channels of plasmodesmata pierce the plant cell wall and connect all cells in a plant together Each plasmodesmata is lined with plasma membrane common to the two connected cells
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Cell Wall Formed like boxes
Enclose, protect and constrain the shape of each cell. Type of extracellular matrix that the plant cell secretes around itself
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Concept 6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes
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The Nucleus: Genetic Library of the Cell
Outer membrane is granular Inner membrane is smooth Contains most of the genes in the eukaryotic cell Plays essential role in cell division Within the membrane is a mesh of nucleoplasm interspersed with nuclear ribosomes and chromatin DNA bound to protein Acts as the control center for the cell
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Nucleolus Area within the nucleus that is responsible for the production of ribosomes
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Nuclear Envelope Encloses the nucleus, separating its contents from the cytoplasm Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Surface of nuclear envelope. Pore complexes (TEM). Nuclear lamina (TEM). Close-up of nuclear envelope Ribosome 1 µm 0.25 µm Figure 6.10
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Nuclear Envelope A double membrane which encloses the nucleus
Perforated with pores, nm in diameter, This is the membrane system surrounding the nucleus punctuated with pores, nm in diameter, that allow materials in and out.
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Ribosomes: Protein Factories in the Cell
Small complex particles made of ribosomal RNA and protein Cytoplasmic organelle that is the site for protein synthesis Bound ribosomes are attached to the outside of the endoplasmic reticulum Cells with high rates of protein synthesis have predominant nuclei and ribosomes Human liver cells have a few million
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TEM showing ER and ribosomes
Carry out protein synthesis Ribosomes Cytosol Free ribosomes Bound ribosomes Large subunit Small TEM showing ER and ribosomes Diagram of a ribosome 0.5 µm ER Endoplasmic reticulum (ER) Figure 6.11
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Concept 6.4 The endomembrane system regulates protein traffic and performs metabolic functions in the cell The endomembrane system Includes many different structures
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The Endoplasmic Reticulum: Biosynthetic Factory
The endoplasmic reticulum (ER) Accounts for more than half the total membrane in many eukaryotic cells
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The Endoplasmic Reticulum
The ER membrane Is continuous with the nuclear envelope Smooth ER Rough ER ER lumen Cisternae Ribosomes Transport vesicle Transitional ER 200 µm Nuclear envelope Figure 6.12
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Regions of the ER There are two distinct regions of ER
Smooth ER, which lacks ribosomes Rough ER, which contains ribosomes
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Functions of Smooth ER The smooth ER Synthesizes and transports lipids
Metabolizes carbohydrates Stores calcium Detoxifies poison There are no bound organelles
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Functions of Rough ER The rough ER Has bound ribosomes
Produces proteins and membranes, which are distributed by transport vesicles
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The Golgi Apparatus: Shipping and Receiving Center
Receives many of the transport vesicles produced in the rough ER Consists of flattened membranous sacs called cisternae
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The Golgi Apparatus Stack of membranous sacs
Functions of the Golgi apparatus include Modification of the products of the rough ER Packages and distributes lipids and proteins that were formed in the ER CIS Entry Trans Exit Manufacture of certain macromolecules
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Functions of the Golgi apparatus
cis face (“receiving” side of Golgi apparatus) Vesicles move from ER to Golgi Vesicles also transport certain proteins back to ER Vesicles coalesce to form new cis Golgi cisternae Cisternal maturation: Golgi cisternae move in a cis- to-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma mem- brane for secretion Vesicles transport specific proteins backward to newer Cisternae trans face (“shipping” side of 0.1 0 µm 1 6 5 2 3 4 Golgi apparatus Figure 6.13 TEM of Golgi apparatus
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Lysosomes: Digestive Compartments
A lysosome Is a membranous sac of hydrolytic enzymes Can digest all kinds of macromolecules Degrades the cell and other malfunctioning organelles
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(a) Phagocytosis: lysosome digesting food
Lysosomes Lysosomes carry out intracellular digestion by Phagocytosis (a) Phagocytosis: lysosome digesting food 1 µm Lysosome contains active hydrolytic enzymes Food vacuole fuses with lysosome Hydrolytic enzymes digest food particles Digestion Food vacuole Plasma membrane Lysosome Digestive Nucleus Figure 6.14 A
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(b) Autophagy: lysosome breaking down damaged organelle
Lysosomes Autophagy (b) Autophagy: lysosome breaking down damaged organelle Lysosome containing two damaged organelles 1 µ m Mitochondrion fragment Peroxisome Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Vesicle containing damaged mitochondrion Digestion Lysosome Figure 6.14 B
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Vacuoles: Diverse Maintenance Compartments
A plant or fungal cell May have one or several vacuoles Food vacuoles Are formed by phagocytosis Contractile vacuoles Pump excess water out of protist cels
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Central Vacuole Are found in plant cells
Hold reserves of important organic compounds and water Central vacuole Cytosol Tonoplast Central vacuole Nucleus Cell wall Chloroplast 5 µm Figure 6.15
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The Endomembrane System: A Review
Is a complex and dynamic player in the cell’s compartmental organization
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Putting it All Together
Relationships among organelles of the endomembrane system Plasma membrane expands by fusion of vesicles; proteins are secreted from cell Transport vesicle carries proteins to plasma membrane for secretion Lysosome available for fusion with another vesicle for digestion 4 5 6 Nuclear envelope is connected to rough ER, which is also continuous with smooth ER Nucleus Rough ER Smooth ER cis Golgi trans Golgi Membranes and proteins produced by the ER flow in the form of transport vesicles to the Golgi Nuclear envelop Golgi pinches off transport Vesicles and other vesicles that give rise to lysosomes and Vacuoles 1 3 2 Plasma membrane Figure 6.16
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Concept 6.5 Mitochondria and chloroplasts change energy from one form to another Mitochondria Are the sites of cellular respiration Details on Cell Respiration later Chloroplasts Found only in plants, are the sites of photosynthesis Details on photosynthesis later
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Mitochondria: Chemical Energy Conversion
Are found in nearly all eukaryotic cells
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Mitochondria II Mitochondria are enclosed by two membranes
A smooth outer membrane An inner membrane folded into cristae Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Mitochondrial DNA Inner Cristae Matrix 100 µm Figure 6.17
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Chloroplasts: Capture of Light Energy
The chloroplast Is a specialized member of a family of closely related plant organelles called plastids Contains chlorophyll Chloroplast structure includes Thylakoids, membranous sacs Stroma, the internal fluid Chloroplasts II
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Chloroplasts II Chloroplasts
Are found in leaves and other green organs of plants and in algae Chloroplast DNA Ribosomes Stroma Inner and outer membranes Thylakoid 1 µm Granum Figure 6.18
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Peroxisomes: Oxidation
Produce hydrogen peroxide and convert it to water Chloroplast Peroxisome Mitochondrion 1 µm Figure 6.19
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Cell Walls of Plants The cell wall
Is an extracellular structure of plant cells that distinguishes them from animal cells
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Plant Cell Walls Plant cell walls
Are made of cellulose fibers embedded in other polysaccharides and protein May have multiple layers Central vacuole of cell Plasma membrane Secondary cell wall Primary Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata Figure 6.28
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