Tour of the Cell 1 (Ch. 6)

Dead White Men Who Discovered (and were made of) Cells: Anton Van Leeuwenhoek Robert Hooke

Where the Magic Happened

Microscopy is certainly a Perspective Changer (sorry in advance)

Brightfield (unstained specimen). Light Microscopy TECHNIQUE RESULTS 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

Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences in density, making the image appear almost 3D. 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)

Scanning electron micro- Transmission electron micro- Electron Microscopy 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) 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) Cilia 1 µm Longitudinal section of cilium Cross section of cilium

Differential centrifugation Cell Fractionation APPLICATION Cell fractionation is used to isolate (fractionate) cell components, based on size and density. 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. Homogenization Tissue cells 1000 g (1000 times the force of gravity) 10 min Homogenate TECHNIQUE Differential centrifugation Supernatant poured into next tube 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. 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris 150,000 g 3 hr Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma mem- branes and cells’ internal membranes) Pellet rich in ribosomes

The size range of cells 10 m Human height 1 m Length of some nerve and muscle cells 0.1 m Unaided eye Chicken egg 1 cm Frog egg 1 mm 100 µm Most plant and animal cells Light microscope 10 µm nucleus Nucleus Most bacteria Most bacteria Mitochondrion 1 µm Electron microscope Smallest bacteria 100 nm Viruses Ribosomes 10 nm Proteins Lipids Measurements 1 centimeter (cm) = 102 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 µm = 10 9 m 1 nm Small molecules 0.1 nm Atoms

Comparing the size of a virus, a bacterium, and an animal cell Animal cell nucleus While we’re on the topic of size...

Why Cells Are So Small: The SA:V Ratio 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

Prokaryote bacteria cells Eukaryote animal cells Types of cells Prokaryote bacteria cells - no organelles - organelles Eukaryote animal cells Eukaryote plant cells

Why organelles? Specialized structures specialized functions Containers Compartments = different local environments pH, concentration differences distinct & incompatible functions lysosome & its digestive enzymes Membranes as sites for chemical reactions Unique lipids & proteins embedded enzymes & reaction centers chloroplasts & mitochondria Why organelles? There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions. Organelles as specialized structures An example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move. Organelles as Containers Nothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it. Organelle membranes as sites for chemical reactions An example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast.

Cells gotta work to live! make proteins proteins control every cell function make energy for daily life for growth make more cells growth repair renewal

Proteins do all the work! cells DNA Repeat after me… Proteins do all the work! organism

Cell functions Building proteins copy DNA DNA -> RNA build proteins process proteins Folding, modifying Remove amino acids Add molecules (e.g. glycoproteins) address & transport proteins

Protein Synthesis Organelles involved nucleus ribosomes endoplasmic reticulum (ER) Golgi apparatus vesicles The Protein Assembly Line Golgi apparatus nucleus ribosome ER vesicles The Endomembrane System

What kind of molecules need to pass through? Nucleus histone protein chromosome DNA Function protects DNA Structure nuclear envelope double membrane membrane fused in spots to create pores nuclear pores pore nuclear envelope nucleolus What kind of molecules need to pass through?

production of mRNA from DNA in nucleus nuclear membrane 1 production of mRNA from DNA in nucleus small ribosomal subunit large cytoplasm mRNA nuclear pore 2 mRNA travels from nucleus to ribosome in cytoplasm through nuclear pore

Nucleolus Function ribosome production build ribosome subunits from rRNA & proteins Ribosome assembly is completed in cytoplasm small subunit large subunit ribosome rRNA & proteins nucleolus

Ribosomes Function protein production Structure rRNA & protein small subunit large Function protein production Structure rRNA & protein 2 subunits combine 0.08mm Ribosomes Rough ER Smooth The genes for rRNA have the greatest commonality among all living things. There is very little difference in the DNA sequence of the rRNA genes in a humans vs. a bacteria. Means that this function (building of a ribosome) is so integral to life that every cell does it almost exactly the same way. Change a base and this changes the structure of the RNA which causes it to not function.

Types of Ribosomes Free ribosomes suspended in cytosol synthesize proteins that stay in cytosol Bound ribosomes attached to endoplasmic reticulum synthesize proteins for export or membranes membrane proteins

Endoplasmic Reticulum Function processes proteins manufactures membrane synthesis & hydrolysis of many compounds Structure membrane connected to nuclear envelope & extends throughout cell accounts for 50% membranes in eukaryotic cell

Types of ER rough smooth

Smooth ER function Membrane production Metabolic processes Lipid Synthesis Glycogen hydrolysis (in liver) Drug detoxification (in liver)

Membrane Factory Build new membrane synthesize phospholipids ER membrane expands buds off & transfers to other parts of cell.

Which cells have lot of rough ER? Rough ER function Produces proteins for export out of cell protein secreting cells packaged into transport vesicles for export Which cells have lot of rough ER? Which cells have a lot of ER? protein production cells like pancreas = production of digestive enzymes (rough endoplasmic reticulum from a cell of exocrine pancreas (88000X))

Synthesizing proteins cytoplasm cisternal space mRNA ribosome membrane of endoplasmic reticulum polypeptide signal sequence ribosome

Which cells have lots of Golgi? Golgi Apparatus Function finishes, sorts, tags & ships products like “UPS shipping department” ships products in vesicles membrane sacs “UPS trucks” transport vesicles secretory vesicles Which cells have lots of Golgi? Cells specialized for secretion? endocrine glands: produce hormones pituitary, pancreas, adrenal, testes, ovaries exocrine glands: produce digestive enzymes & other products pancreas, mammary glands, sweat glands

Golgi Apparatus

Vesicle transport vesicle budding from rough ER fusion of vesicle with Golgi apparatus migrating transport protein ribosome

The Endomembrane System Putting it together… The Endomembrane System proteins transport vesicle Golgi apparatus smooth ER rough ER nuclear pore nucleus ribosome cell membrane protein secreted cytoplasm

Any Questions!!

Can I offer you something in A Computer Animation?

Or perhaps something more in a silly rap song?!?

Review Questions

1.. In which cell would you expect to find the most smooth endoplasmic reticulum? Muscle cell in the thigh muscle of a long-distance runner Pancreatic cell that manufactures digestive enzymes Macrophage (white blood cell) that engulfs bacteria Epithelial cells lining the digestive tract Ovarian cell that produces estrogen (a steroid hormone) Answer: e Source: Taylor - Student Study Guide for Biology, Sixth Edition, Test Your Knowledge Question #18

2. In which cell would you expect to find the most bound ribosomes? Muscle cell in the thigh muscle of a long-distance runner Pancreatic cell that manufactures digestive enzymes Macrophage (white blood cell) that engulfs bacteria Epithelial cells lining the digestive tract Ovarian cell that produces estrogen (a steroid hormone) Answer: b Source: Taylor - Student Study Guide for Biology, Sixth Edition, Test Your Knowledge Question #19

3. Of the following, which is probably the most common route for membrane flow in the endomembrane system? Golgi → lysosome → ER → plasma membrane tonoplast → plasma membrane → nuclear envelope → smooth ER nuclear envelope → lysosome → Golgi → plasma membrane rough ER → vesicles → Golgi → plasma membrane ER → chloroplasts → mitochondrion → cell membrane Answer: d Source: Barstow - Test Bank for Biology, Sixth Edition, Question #20