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called a peptide bond (figure 3.5). The two amino acids linked by such a bond are not free to rotate around the N—C linkage because the peptide bond has a partial double-bond character, unlike the N—C and C—C bonds to the central carbon of the amino acid. The stiffness of the peptide bond is one factor that makes it p...
—— O N — H Proline (Pro) NONAROMATIC Nonpolar CH3 — CH3 CH3 — — CH — CH3 CH3 — — CH — CH2 — CH3 — CH2 — H — C — CH3 — — CH2 — NH ——— C — CH2 — H2N — C — C — OH — —— H O H2N — C — C — OH — —— H O H2N — C — C — OH — —— H O H2N — C — C — OH — —— H O H2N — C — C — OH — —— H O H2N — C — C — OH — ——— H O Alanine (Ala) Valin...
O Glutamic acid (Glu) Aspartic acid (Asp) Histidine (His) Lysine (Lys) Arginine (Arg) Chapter 3 The Chemical Building Blocks of Life 41 — — — — — — — — — — — — — A Protein’s Function Depends on the Shape of the Molecule HO O C The shape of a protein is very important because it determines the protein’s function. If we...
Protein Structure The structure of proteins is traditionally discussed in terms of four levels of structure, as primary, secondary, tertiary, and quaternary (figure 3.7). Because of progress in our knowledge of protein structure, two additional levels of structure are increasingly distinguished by molecular biologists...
variety of proteins is a β α β α β motif. A second motif that occurs in many proteins is the β barrel, a β sheet folded around to form a tube. A third type of motif, the α turn α motif, is important because many proteins use it to bind the DNA double helix. Tertiary Structure. The final folded shape of a globular prot...
polypeptide chain folds, the domains fold into their proper shape, each more-or-less independent of the others. This can be demonstrated experimentally by artificially producing the fragment of polypeptide that forms the domain in the intact protein, and showing that the fragment folds to form the same structure as it...
a view. Protein chains can fold in so many different ways that trial and error would simply take too long. In addition, as the open chain folds its way toward its final form, nonpolar “sticky” interior portions are exposed during intermediate stages. If these intermediate forms are placed in a test tube in the same pr...
Folding and Disease There are tantalizing suggestions that chaperone protein deficiencies may play a role in certain diseases by failing to facilitate the intricate folding of key proteins. Cystic fibrosis is a hereditary disorder in which a mutation disables a protein that plays a vital part in moving ions across cel...
of microorganisms and kept them from growing on the food. Most enzymes function within a very narrow range of physical parameters. Blood-borne enzymes that course through a human body at a pH of about 7.4 would rapidly become denatured in the highly acidic environment of the stomach. On the other hand, the proteindegr...
that builders use, and road maps store the information that tourists use. There are two varieties of nucleic acids: deoxyribonucleic acid (DNA; figure 3.11) and ribonucleic acid (RNA). The way in which DNA encodes the information used to assemble proteins is similar to the way in which the letters on a page encode inf...
would take 50,000 of them to equal the diameter of a human hair. FIGURE 3.12 A scanning tunneling micrograph of DNA (false color; 2,000,000×). The micrograph shows approximately three turns of the DNA double helix (see figure 3.15). The Structure of Nucleic Acids Nucleic acids are long polymers of repeating subunits c...
ines or pyrimidines. In DNA, thymine replaces the uracil found in RNA. Chapter 3 The Chemical Building Blocks of Life 47 DNA Organisms encode the information specifying the amino acid sequences of their proteins as sequences of nucleotides in the DNA. This method of encoding information is very similar to that by which...
acil in 48 Part I The Origin of Living Things place of thymine. Uracil has the same structure as thymine, except that one of its carbons lacks a methyl (— CH3) group. Transcribing the DNA message into a chemically different molecule such as RNA allows the cell to tell which is the original information storage molecule ...
. ATP 3.16). Although there is no chemical reason why RNA cannot form double helices as DNA does, cells do not possess the enzymes necessary to assemble double strands of RNA, as they do for DNA. Using two different molecules, one single-stranded and the other double-stranded, separates the role of DNA in storing hered...
ipid is a composite molecule, made up of three kinds of subunits: 1. Glycerol, a three-carbon alcohol, with each carbon bearing a hydroxyl group. Glycerol forms the backbone of the phospholipid molecule. 2. Fatty acids, long chains of C—H bonds (hydrocarbon chains) ending in a carboxyl (—COOH) group. Two fatty acids ar...
C CH2 CH3 CH OH CH2 CH2 CH2 CH2 CH2 (a) Phospholipid (phosphatidyl choline) (c) Terpene (citronellol) H CH O CH O CH b) Triacylglycerol molecule H3C CH2 CH2 CH3 CH CH2 CH CH3 CH3 CH3 HO (d) Steroid (cholesterol) FIGURE 3.19 Lipids. These structures represent four major classes of biologically important lipids: (a) pho...
aturated. Fats made from polyunsaturated fatty acids have low melting points because their fatty acid chains bend at the double bonds, preventing the fat molecules from aligning closely with one another. Consequently, a polyunsaturated fat such as corn oil is usually liquid at room temperature and is called an oil. In ...
(see next section), making fats much more efficient molecules for storing chemical energy. On the average, fats yield about 9 kilocalories (kcal) of chemical energy per gram, as compared with somewhat less than 4 kcal per gram for carbohydrates. All fats produced by animals are saturated (except some fish oils), while...
or (CH2O)6 The carbohydrates are a loosely defined group of molecules that contain carbon, hydrogen, and oxygen in the molar ratio 1:2:1. Their empirical formula (which lists the atoms in the molecule with subscripts to indicate how many there are of each) is (CH2O)n, where n is the number of carbon atoms. Because the...
! Chapter 3 The Chemical Building Blocks of Life 53 Disaccharides. Many familiar sugars like sucrose are “double sugars,” two monosaccharides joined by a covalent bond (figure 3.23). Called disaccharides, they often play a role in the transport of sugars, as we will discuss shortly. Polysaccharides. Polysaccharides are...
and glucose are called stereoisomers. Again, this seemingly slight difference has important consequences, as this hydroxyl group is often involved in creating polymers with distinct functions, such as starch (energy storage) and cellulose (structural support). Sugars are among the most important energy-storage molecul...
itself and many other monosaccharides, including fructose and galactose. When glucose forms a disaccharide with its structural isomer, fructose, the resulting disaccharide is sucrose, or table sugar (figure 3.25a). Sucrose is the form in which most plants transport glucose and the sugar that most humans (and other ani...
cuts these fragments into molecules of maltose. Finally, the maltose is cleaved into two glucose molecules, which cells are able to metabolize. Most plant starch, including the remaining 80% of potato starch, is a somewhat more complicated variant of amylose called amylopectin (figure 3.26b). Pectins are branched poly...
molecules, in that the hydroxyl group that binds a critical carbon atom is on the right side. However, “left-handed” sugars, in which the hydroxyl group is on the left side, can be made readily in the laboratory. These synthetic sugars are mirror-image chemical twins of the natural form, but the enzymes that break dow...
place either below or above the plane of the ring. If below, it is called the alpha form, and if above, the beta form. All of the glucose subunits of the starch chain are alpha-glucose. When a chain of glucose molecules consists of all beta-glucose subunits, a polysaccharide with very different properties results. Thi...
and fungi. FIGURE 3.28 Chitin. Chitin, which might be considered to be a modified form of cellulose, is the principal structural element in the external skeletons of many invertebrates, such as this lobster. Chapter 3 The Chemical Building Blocks of Life 57 Chapter 3 Summary 3.1 Molecules are the building blocks of li...
how are they arranged in the molecule? 7. Describe the differences between a saturated and an unsaturated fat. 3.5 Carbohydrates store energy and provide building materials. • Carbohydrates store considerable energy in their carbon-hydrogen (C—H) bonds. • The most metabolically important carbohydrate is glucose, a six...
It seems probable that life has evolved on other worlds besides our own. The possible presence of life in the warm waters beneath the surface of Europa, a moon of Jupiter, is a source of current speculation. FIGURE 4.1 The origin of life. The fortuitous mix of physical events and chemical elements at the right place a...
to write a definition of “life,” you will find that it is not an easy task, because of the loose manner in which the term is used. Imagine a situation in which two astronauts encounter a large, amorphous blob on the surface of a planet. How would they determine whether it is alive? Movement. One of the first things th...
criterion of life, but it is not sufficient in itself to identify living things because many complex things are not alive. To determine whether the blob is alive, the astronauts would have to learn more about it. Probably the best thing they could do would be to examine it more carefully and determine whether it resem...
a mechanism for the preservation of improvement. Heredity. All organisms on earth possess a genetic system that is based on the replication of a long, complex molecule called DNA. This mechanism allows for adaptation and evolution over time, also distinguishing characteristics of living things. To understand the role o...
divine God created life is at the core of most major religions. The oldest hypothesis about life’s origins, it is also the most widely accepted. Far more Americans, for example, believe that God created life on earth than believe in the other two hypotheses. Many take a more extreme position, accepting the biblical ac...
old. They tell us that life originated during the first billion years of the history of our planet. As we attempt to determine how this process took place, we will first focus on how organic molecules may have originated (figure 4.5), and then we will consider how those molecules might have become organized into livin...
Our atmosphere changed once organisms began to carry out photosynthesis, harnessing the energy in sunlight to split water molecules and form complex carbon molecules, giving off gaseous oxygen molecules in the process. The earth’s atmosphere is now approximately 21% oxygen. Critics of the reducing atmosphere hypothesi...
for negatively charged organic molecules. In part, the current popularity of this hypothesis comes from the new science of genomics, which suggests that the ancestors of today’s prokaryotes are most closely related to the bacteria that live on the deep-sea vents. No one is sure whether life originated at the ocean’s e...
ine, alanine, glutamic acid, valine, proline, and aspartic acid. Other biologically important molecules were also formed in these experiments. For example, hydrogen cyanide contributed to the production of a complex ring-shaped molecule called adenine—one of the bases found in DNA and RNA. Thus, the key molecules of li...
of nucleic acids such as RNA, are too complex to have formed spontaneously, and certainly too complex to form spontaneously again and again. While there is no doubt that simple proteins are easier to synthesize from abiotic components than nucleotides, both can form in the laboratory under the right conditions. Decidi...
Molecules that are the building blocks of living organisms form spontaneously under conditions designed to simulate those of the primitive earth. Chapter 4 The Origin and Early History of Life 65 4.3 The first cells had little internal structure. Theories about the Origin of Cells The evolution of cells required early...
by means of a cell membrane, and concentrating materials within themselves. He termed these early, chemical-concentrating bubblelike structures protobionts. 66 Part I The Origin of Living Things Oparin’s theories were published in English in 1938, and for awhile most scientists ignored them. However, Harold Urey, an a...
bubbles that were better able to incorporate molecules and energy from the lifeless oceans of the early earth would have tended to persist longer than the others. Also favored would have been the microdrops that could use these molecules to expand in size, growing large enough to divide into “daughter” 4. Bombarded by...
Eventually, DNA took the place of RNA as the replicator in the cell and the storage molecule for genetic information. DNA, because it is a double helix, stores information in a more stable fashion than RNA, which is single-stranded. Little is known about how the first cells originated. Current hypotheses involve chemi...
first to be studied in detail have been the methanogens, or methane-producing bacteria, among the most primitive bacteria that exist today. These organisms are typically simple in form and are able to grow only in an oxygen-free environment; in fact, oxygen poisons them. For this reason they are said to grow “without ...
many kinds of thermophilic archaebacteria thrive at temperatures of 110°C (230°F). Because these thermophiles live at high temperatures similar to those that may have existed when life first evolved, microbiologists speculate that thermophilic archaebacteria may be relics of earth’s first organisms. Just how different...
current level of 21%. As the concentration of oxygen increased, so did the amount of ozone in the upper layers of the atmosphere. The thickening ozone layer afforded protection from most of the ultraviolet radiation from the sun, radiation that is highly destructive to proteins and nucleic acids. Certain cyanobacteria...
earance of iron from oceans and formation of iron oxides Oldest definite fossils Oldest dated rocks Millions of years ago 570 600 1500 2500 3500 4500 Life forms Appearance of first multicellular organisms Appearance of first eukaryotes Appearance of aerobic (oxygen-using) respiration Appearance of oxygen-forming photos...
within other larger bacteria, leading to the evolution of chloroplasts, the photosynthetic organelles of plants and algae. Bacteria with flagella, long whiplike cellular appendages used for propulsion, may have become symbiotically involved with nonflagellated bacteria to produce larger, motile cells. The fact that we...
anobacterium Archaeoglobus Halococcus Halobacterium (a) Borrelia burgdorferiAquifex Methanococcus jannaschii FIGURE 4.15 The three domains of life. The kingdoms Archaebacteria and Eubacteria are as different from each other as from eukaryotes, so biologists have assigned them a higher category, a “domain.” (a) A three-...
learned about living things, particularly from the newer evidence that DNA studies provide, scientists will continue to reevaluate the relationships among the kingdoms of life. For at least the first 1 billion years of life on earth, all organisms were bacteria. About 1.5 billion years ago, the first eukaryotes appear...
as a whole, the evidence of bacterial life associated with the Mars meteorite is not compelling. Clearly, more painstaking research remains to be done before the discovery can claim a scientific consensus. However, while there is no conclusive evidence of bacterial life associated with this meteorite, it seems very po...
• Experiments recreating the atmosphere of primitive earth, with the energy sources and temperatures thought to be prevalent at that time, have led to the spontaneous formation of amino acids and other biologically significant molecules. 4.3 The first cells had little internal structure. • The first cells are thought ...
�s History 6. When did the first eukaryotes appear? By what mechanism are they thought to have evolved from the earlier prokaryotes? 7. What sorts of organisms are contained in each of the six kingdoms of life recognized by biologists? Part II Biology of the Cell How Do the Cells of a Growing Plant Know in Which Direct...
microtubules. Cortical microtubules in epidermal cells of a fava bean are tagged with a flourescent protein so that their ordered array can be seen. organized in bands perpendicular to the axis of elongation, like steel belts. These tough bands reinforce the plant cell wall laterally, so that when the cell sucks in wa...
toplasts exposed to APM, a microtubule disrupting chemical, exhibited random cell elongation with or without centrifugation. The Experiment This question has been addressed experimentally in a simple and direct way in the laboratory of Richard Cyr at Pennsylvania State University. Rigid plant cells conduct mechanical f...
were not centrifuged but were more ordered in protoplasts that had been centrifuged. The microtubules in these cells were oriented parallel to the direction of the force, in a direction approximately perpendicular to the axis of elongation (graph a above). These results support the hypothesis that plant cell growth re...
. Vesicles: Enzyme Storehouses. Sacs that contain enzymes digest or modify particles in the cell, while other vesicles transport substances in and out of cells. Ribosomes: Sites of Protein Synthesis. An RNA-protein complex directs the production of proteins. Organelles That Contain DNA. Some organelles with very differ...
asm. The Plasma Membrane Surrounds the Cell The plasma membrane encloses a cell and separates its contents from its surroundings. The plasma membrane is a phospholipid bilayer about 5 to 10 nanometers (5 to 10 billionths of a meter) thick with proteins embedded in it. Viewed in cross-section with the electron microscop...
ukaryotes is contained in the nucleus, which is surrounded by two membranes. In both types of organisms, the DNA contains the genes that code for the proteins synthesized by the cell. The Cytoplasm Comprises the Rest of the Cell’s Interior A semifluid matrix called the cytoplasm fills the interior of the cell, exclusiv...
cells, and the life processes of metabolism and heredity occur within these cells. 2. Cells are the smallest living things, the basic units of organization of all organisms. 3. Cells arise only by division of a previously existing cell. Although life likely evolved spontaneously in the environment of the early earth, ...
wenhoek assisted the eye by interposing a glass lens between object and eye. The glass lens adds additional focusing power. Because the glass lens makes the object appear closer, the image on the back of the eye is bigger than it would be without the lens. Modern light microscopes use two magnifying lenses (and a varie...
many biological and physical phenomena (figure 5.3c). Cell radius (r) Surface area (4r2) Volume r3) (4 – 3 1 cm 12.57 cm2 4.189 cm3 10 cm 1257 cm2 4189 cm3 FIGURE 5.4 Surface area-to-volume ratio. As a cell gets larger, its volume increases at a faster rate than its surface area. If the cell radius increases by 10 tim...
cell. Also, some large cells actively move material around their cytoplasm so that diffusion is not a limiting factor. Lastly, some large cells, like your own neurons, are long and skinny so that any given point in the cytoplasm is close to the plasma membrane, and thus diffusion between the inside and outside of the ...
ilayered and does not retain the purple dye after Gram staining; such bacteria exhibit the background red dye and are characterized as gramnegative. The susceptibility of bacteria to antibiotics often depends on the structure of their cell walls. Penicillin and vancomycin, for example, interfere with the ability of bac...
by rotating their flagella. (a) The photograph is of Vibrio cholerae, the microbe that causes the serious disease cholera. The unsheathed core visible at the top of the photograph is composed of a single crystal of the protein flagellin. (b) In intact flagella, the core is surrounded by a flexible sheath. Imagine that...
ukaryotic cell is compartmentalization. The interiors of eukaryotic cells contain numerous organelles, membrane-bounded structures that close off compartments within which multiple biochemical processes can proceed simultaneously and independently. Plant cells often have a large membrane-bounded sac called a central va...
oplasmic reticulum Cytoplasm Nucleus Cell wall Plasmodesma (b) Plasma membrane Mitochondrion Chapter 5 Cell Structure 85 5.3 Take a tour of a eukaryotic cell. The Nucleus: Information Center for the Cell The largest and most easily seen organelle within a eukaryotic cell is the nucleus (Latin, for kernel or nut), first...
the nuclear envelope, like craters on the moon, are shallow depressions called nuclear pores. These pores form 50 to 80 nanometers apart at locations where the two membrane layers of the nuclear envelope pinch together. Rather than being empty, nuclear pores are filled with proteins that act as molecular channels, per...
FIGURE 5.12 Eukaryotic chromosomes. These condensed chromosomes within an onion root tip are visible under the light microscope (500×). Chapter 5 Cell Structure 87 The Endoplasmic Reticulum: Compartmentalizing the Cell The interior of a eukaryotic cell is packed with membranes (table 5.1). So thin that they are invisi...
interior ER compartment, the cisternal space, from which it is transported by vesicles to the Golgi apparatus (figure 5.14). The protein then travels within vesicles to the inner surface of the plasma membrane, where it is released to the outside of the cell. Structure Cell wall Cytoskeleton Flagella (cilia) Table 5.1...
izing Internal Activities Regions of the ER with relatively few bound ribosomes are referred to as smooth ER. The membranes of the smooth ER contain many embedded enzymes, most of them active only when associated with a membrane. Enzymes anchored within the ER, for example, catalyze the synthesis of a variety of carboh...
packaging, and distribution of molecules synthesized at one place in the cell and utilized at another location in the cell. A Golgi body has a front and a back, with distinctly different membrane compositions at the opposite ends. The front, or receiving end, is called the cis face, and is usually located near ER. Mat...
15 The Golgi apparatus. The Golgi apparatus is a smooth, concave membranous structure located near the middle of the cell. It receives material for processing on one surface and sends the material packaged in vesicles off the other. The substance in a vesicle could be for export out of the cell or for distribution to a...
Lysosomes contain hydrolytic enzymes that digest particles or cells taken into the cell by phagocytosis and break down old organelles. The digestive enzymes in lysosomes function best in an acidic environment. Lysosomes actively engaged in digestion keep their battery of hydrolytic enzymes (enzymes that catalyze the h...
cytoplasm, which often involves adding hydrogen atoms to oxygen. The name peroxisome refers to the hydrogen peroxide produced as a by-product of the activities of the oxidative enzymes in the microbody. Hydrogen peroxide is dangerous to cells because of its violent chemical reactivity. However, peroxisomes also contai...
copies of the portion of the DNA encoding the rRNA are clustered together on the chromosome. By transcribing RNA molecules from this cluster, the cell rapidly generates large numbers of the molecules needed to produce ribosomes. At any given moment, many rRNA molecules dangle from the chromosome at the sites of these ...
it, are proteins that carry out oxidative metabolism, the oxygen-requiring process by which energy in macromolecules is stored in ATP. Mitochondria have their own DNA; this DNA contains several genes that produce proteins essential to the mitochondrion’s role in oxidative metabolism. All of these genes are copied into...
On the surface of the thylakoids are the light-capturing photosynthetic pigments, to be discussed in depth in chapter 10. Surrounding the thylakoid is a fluid matrix called the stroma. Like mitochondria, chloroplasts contain DNA, but many of the genes that specify chloroplast components are also located in the nucleus...
their functions, but both depend on nuclear genes for other functions. Some centrioles also contain DNA, which apparently helps control the synthesis of their structural proteins. (a) 0.09 µm Microtubule triplet (b) FIGURE 5.23 Centrioles. (a) This electron micrograph shows a pair of centrioles (75,000×). The round sh...
MTOC nucleation centers near the center of the cell and radiate toward the periphery. They are in a constant state of flux, continually polymerizing and depolymerizing (the average halflife of a microtubule ranges from 10 minutes in a nondividing animal cell to as short as 20 seconds in a dividing animal cell), unless...
that imparts tremendous mechanical strength to the cell. 3. Intermediate filaments. The most durable element of the cytoskeleton in animal cells is a system of tough, fibrous protein molecules twined together in an overlapping arrangement (figure 5.25c). These fibers are characteristically 8 to 10 nanometers in diamet...
wound healing, and the spread of cancer. White blood cells in particular exhibit this ability. Produced in the bone marrow, these cells are released into the circulatory system and then eventually crawl out of capillaries and into the tissues to destroy potential pathogens. Cells exist in a gel-sol state; that is, at ...
toplasm. Many of the enzymes involved in cell metabolism, for example, bind to actin filaments; so do ribosomes. By moving and anchoring particular enzymes near one another, the cytoskeleton, like the endoplasmic reticulum, organizes the cell’s activities. Intracellular Molecular Motors Certain eukaryotic cells must mo...
Paramecium is covered with a dense forest of cilia. the cell periphery, dragging the vesicle with it as it travels along the microtubule. Another vesicle protein (or perhaps a slight modification of kinesin—further research is needed to determine which) binds vesicles to the motor protein dynein, which directs movemen...
also contain cilia; sound waves bend these cilia, the initial sensory input of hearing. Thus, the 9 + 2 structure of flagella and cilia appears to be a fundamental component of eukaryotic cells. Some eukaryotic cells use pseudopodia to crawl about within multicellular organisms, while many protists swim using flagella...
cell is young. Thicker secondary cell walls may be added later when the cell is fully grown. 100 Part II Biology of the Cell 5.4 Symbiosis played a key role in the origin of some eukaryotic organelles. Endosymbiosis Symbiosis is a close relationship between organisms of different species that live together. The theory...
ose) Present Flagella May be present (single strand) May be present Absent except in sperm of a few species INTERIOR STRUCTURES ER Absent Ribosomes Microtubules Centrioles Golgi apparatus Nucleus Mitochondria Chloroplasts Present Absent Absent Absent Absent Absent Absent Usually present Usually present Present Present ...
cell. • The cytoskeleton encompasses a variety of fibrous proteins that provide structural support and perform other functions for the cell. • Many eukaryotic cells possess flagella or cilia having a 9 + 2 arrangement of microtubules; sliding of the microtubules past one another bends these cellular appendages. • Cell...
individual phospholipid molecules do not bind to one another, the lipid bilayer of membranes is a fluid. 6.2 Proteins embedded within the plasma membrane determine its character. The Fluid Mosaic Model. A varied collection of proteins float within the lipid bilayer. Examining Cell Membranes. Visualizing a plasma membr...
on one another would just equal the thickness of this sheet of paper. The lipid layer that forms the foundation of a cell membrane is composed of molecules called phospholipids (figure 6.2). Phospholipids Like the fat molecules you studied in chapter 3, a phospholipid has a backbone derived from a three-carbon molecul...
the Cell Fatty acid Fatty acid G L Y C E R O L Phosphorylated alcohol (a) Polar (hydrophilic) region Nonpolar (hydrophobic) region (b) FIGURE 6.2 Phospholipid structure. (a) A phospholipid is a composite molecule similar to a triacylglycerol, except that only two fatty acids are bound to the glycerol backbone; a phosp...
This can be demonstrated vividly by fusing cells and watching their proteins reassort (figure 6.4). Phospholipid bilayers are fluid, with the viscosity of olive oil (and like oil, their viscosity increases as the temperature decreases). Some membranes are more fluid than others, however. The tails of individual phosph...
ielli model suggests, then their nonpolar portions would separate the polar portions of the phospholipids from water, causing the bilayer to dissolve! Because this doesn’t happen, there is clearly something wrong with the model. In 1972, S. Singer and G. Nicolson revised the model in a simple but profound way: they pro...
transport molecules across membrane Transmit information into cell Interior protein network Spectrins Determine shape of cell Clathrins Anchor certain proteins to specific sites, especially on the exterior cell membrane in receptor-mediated endocytosis Cell surface markers Glycoproteins “Self ”-recognition Glycolipid ...
fluid mosaic model proposes that membrane proteins are embedded within the lipid bilayer. Membranes are composed of a lipid bilayer within which proteins are anchored. Plasma membranes are supported by a network of fibers and coated on the exterior with cell identity markers. Chapter 6 Membranes 107 Examining Cell Mem...
is embedded in epoxy and allowed to harden. Knife Tissue Epoxy Forceps Grid Section Tissue 4. A tissue section is mounted on a small grid. 3. A diamond knife sections the tissue-epoxy block like a loaf of bread, creating slices 25 nm thick. Lead "stain" Section Grid 5. The section on the grid is "stained" with an elec...
cytoskeleton Figure 6.7 Functions of plasma membrane proteins. Membrane proteins act as transporters, enzymes, cell surface receptors, and cell surface markers, as well as aiding in cell-to-cell adhesion and securing the cytoskeleton. Chapter 6 Membranes 109 Structure of Membrane Proteins If proteins float on lipid bi...
In this way, information outside the cell is translated into action within the cell. The mechanisms of cell signaling will be addressed in detail in chapter 7. Channels. Other proteins have several helical segments that thread their way back and forth through the membrane, forming a channel like the hole in a doughnut...
dimer, attached to the membrane by special proteins such as junctional complexes and ankyrin; glycophorins can also be involved in attachments. This cytoskeletal protein network confers resiliency to cells like the red blood cell. H+ Porin monomer Retinal chromophore NH2 -pleated sheets Bacterial outer membrane Nonpol...
its own type of transporter (that is, it has its own channel which fits it like a glove and cannot be used by other molecules). Each channel is said to be selective for that type of molecule, and thus to be selectively permeable, as only molecules admitted by the channels it possesses can enter it. The plasma membrane...
. Molecules bind to a receptor on the extracellular side of the cell and are conducted through the plasma membrane by a membrane protein. Facilitated Diffusion Outside of cell Carriers, another class of membrane proteins, transport ions as well as other solutes like sugars and amino acids across the membrane. Like chan...
to its original shape. It is then available to bind the next glucose molecule that approaches the outside of the cell. Transport through Selective Channels Saturates A characteristic feature of transport through selective channels is that its rate is saturable. In other words, if the concentration gradient of a substa...

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