Bio Ch 4

Dimer

a molecule made up of two subunits

What does the plasma memrane do?

allows passage of enough oxygen, nutrients, and wastes to service the entire cell (Figure 4.5).

Endosymbiont

one of the organisms lives inside the other

What are the main similarities of Euk/Pro?

plasma membrane, cytosol, chromosomes, and ribosomes

What are the parts of a prokaryotic cell?

Fimbriae: prokaryotes surface attachment structures Nucleoid: region where the cell's DNA is located (not enclosed by a membrane) Ribosomes: complexes that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Cell wall: rigid structure outside the plasma membrane Capsule: jellylike outer coating of many prokaryotes Flagella: long tailed organelles that allow for motion

What is the nucleoid?

region where the cell's DNA is located (not enclosed by a membrane)

What shape are bacterium?

rod-shaped bacterium

Prior to release of a vesicle what occurs in the golgi? Released from where?

sorting of the products and targets them for various parts of the cell and released by trans face.

Rough ER How named? Where located? Attached to what? What organ is this usually found on? What two main items does the ER create? How does the ER anchor new proteins to itself?

studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope. Ribosomes are also attached to the cytoplasmic side of the nuclear envelope's outer membrane, which is continuous with rough ER. Many types of cells secrete proteins produced by ribosomes attached to rough ER. For example, certain pancreatic cells synthesize the protein insulin in the ER and secrete this hormone into the bloodstream. As a polypeptide chain grows from a bound ribosome, the chain is threaded into the ER lumen through a pore formed by a protein complex in the ER membrane. As the new polypeptide enters the ER lumen, it folds into its functional shape. Most secretory proteins are glycoproteins, proteins that have carbohydrates covalently bonded to them. The carbohydrates are attached to the proteins in the ER by enzymes built into the ER membrane. the ER membrane keeps them separate from proteins that are produced by free ribosomes and that will remain in the cytosol. Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called transitional ER (see Figure 4.10). Vesicles in transit from one part of the cell to another are called transport vesicles. In addition to making secretory proteins, rough ER is a membrane factory for the cell; it grows in place by adding membrane proteins and phospholipids to its own membrane. As polypeptides destined to be membrane proteins grow from the ribosomes, they are inserted into the ER membrane itself and anchored there by their hydrophobic portions. Like the smooth ER, the rough ER also makes membrane phospholipids; enzymes built into the ER membrane assemble phospholipids from precursors in the cytosol. The ER membrane expands, and portions of it are transferred in the form of transport vesicles to other components of the endomembrane system.

What can cilium act as? Where used?

A cilium may also act as a signal-receiving antenna for the cell and transmit molecular signals from the cell's environment to its interior, triggering signaling pathways that may lead to changes in the cell's activities. Cilium-based signaling appears to be crucial to brain function and to embryonic development.

Lysosome What are they? Purpose? What environment do the enzymes work best? Where are they made/ transferred in the cell? How are lysosomal vesicles not destroyed by themselves?

A lysosome is a membranous sac of hydrolytic enzymes that an animal cell uses to digest (hydrolyze) macromolecules. Lysosomal enzymes work best in the acidic environment found in lysosomes. If a lysosome breaks open or leaks its contents, the released enzymes are not very active because the cytosol has a neutral pH. However, excessive leakage from a large number of lysosomes can destroy a cell by self-digestion. Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the Golgi apparatus for further processing. At least some lysosomes probably arise by budding from the trans face of the Golgi apparatus (see Figure 4.11). the three-dimensional shapes of these lysosomal proteins protect vulnerable inner membrane bonds from enzymatic attack.

Endosymbiont theory What did mitochondria/chloroplast evolve from?

According to this theory, the proposed ancestors of mitochondria were oxygen using nonphotosynthetic prokaryotes, while the proposed ancestors of chloroplasts were photosynthetic prokaryotes. This theory states that an early ancestor of eukaryotic cells engulfed an oxygen-using non- photosynthetic prokaryotic cell. Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont (a cell living within another cell). Indeed, over the course of evolution, the host cell and its endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion. At least one of these cells may have then taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells that contain chloroplasts.

What are desmosomes?

Desmosomes (also called anchoring junctions) function like rivets, fastening cells together into strong sheets. Intermediate filaments made of sturdy keratin proteins anchor desmosomes in the cytoplasm. Desmosomes attach muscle cells to each other in a muscle. Some "muscle tears" involve the rupture of desmosomes.

Endoplasmic Reticulum How big is the ER? Latin translations? What is the structure?

Accounts for more than half the total membrane in many eukaryotic cells. (The word endo- plasmic means "within the cytoplasm," and reticulum is Latin for "little net.") cisternae (from the Latin cisterna, liquid reservoir). endo cisterna reticulum The ER membrane separates the lumen internal compartment of the ER from the cytosol. the space between the two membranes of the nuclear envelope is continuous with the lumen of the ER (Figure 4.10).

Golgi What does it receive and from whom? Mains purposes? Describe the structure/faces of the golgi. What is manufactured? Where is it located? How does it package? What does it specialize in? What food does it look like why? What moves packages from the ER to the golgi?

After leaving the ER, many transport vesicles travel to the Golgi apparatus. We can think of the Golgi primarily as a warehouse for receiving, sorting, and shipping, although some manufacturing also occurs there. In the Golgi, products of the ER, such as proteins, are modified and stored and then sent to other destinations. Not surprisingly, the Golgi apparatus is especially extensive in cells specialized for secretion. Structure: The Golgi apparatus consists of flattened membranous sacs—cisternae—look like stacked pita bread (Figure 4.11). A cell may have many, even hundreds, of these stacks. The membrane of each cisterna in a stack separates its internal space from the cytosol. Cis Face- receiving side of Golgi near ER Trans Face- shipping side of golgi Transfer vesicles concentrated in the vicinity of the Golgi apparatus are engaged in the transfer of material between parts of the Golgi and other structures. A Golgi stack has a distinct structural directionality, with the membranes of cisternae on opposite sides of the stack differing in thickness and molecular composition. The two sides of a Golgi stack are referred to as the cis face and the trans face; these act, respectively, as the receiving and shipping departments of the Golgi apparatus. Transport vesicles move material from the ER to the Golgi apparatus. A vesicle that buds from the ER can add its membrane and the contents of its lumen to the cis face by fusing with a Golgi membrane. The trans face gives rise to vesicles that pinch off and travel to other sites. Products of the endoplasmic reticulum are usually modified during their transit from the cis region to the trans region of the Golgi apparatus. For example, glycoproteins formed in the ER have their carbohydrates modified, first in the ER itself, then as they pass through the Golgi. The Golgi removes some sugar monomers and substitutes others, producing a large variety of carbohydrates. Membrane phospholipids may also be altered in the Golgi.

Overall what is the object of the endomembrane system?

As the membrane moves from the ER to the Golgi and then elsewhere, its molecular composition and metabolic functions are modified, along with those of its contents. The endomembrane system is a complex and dynamic player in the cell's compartmental organization. We'll continue our tour of the cell with some organelles that are not closely related to the endomembrane system but play crucial roles in the energy transformations carried out by cells.

How does the microtubule assembly produce the bending movements of flagella and motile cilia?

Bending involves large motor proteins called dyneins (red in the diagram) that are attached along each outer microtubule doublet. A typical dynein protein has two "feet" that "walk" along the microtubule of the adjacent doublet, using ATP for energy. One foot maintains contact while the other releases and reattaches farther along the microtubule (see Figure 4.21). The outer doublets and two central microtubules are held together by flexible cross-linking proteins. If the doublets were not held in place, the walking action would make them slide past each other. Instead, the movements of the dynein feet cause the microtubules—and the organelle as a whole—to bend.

Components of a Plant Cell

Cell wall: outer layer that maintains cell's shape and protects cell from mechanical damage; made of cellulose, other polysaccharides, and protein Central vacuole: prominent organelle in older plant cells; functions include storage, breakdown of waste products, hydrolysis of macromolecules; enlargement of vacuole is a major mechanism of plant growth Chloroplast: photosynthetic organelle; converts energy of sunlight to chemical energy stored in sugar molecules Cytoskeleton: Microfilaments Intermediate filaments Microtubules ER- rough/smooth Golgi apparatus Mitochondrion Peroxisome Plasma membrane Plasmodesmata: channels through cell walls that connect the cytoplasms of adjacent cells Ribosomes (small brown dots)

What two distinct types are every organism? What are w/in the domains of Euk/pro?

Cells the basic structural and functional units of every organism are of two distinct types: prokaryotic and eukaryotic. Organisms of the domains Bacteria and Archaea consist of prokaryotic cells. Protists, fungi, animals, and plants all consist of eukaryotic cells. (Euk FAPPs)

Components of an Animal Cell

Centrosome: region where the cell's microtubules are initiated; contains a pair of centrioles Chromatin: material consisting of DNA and proteins; visible in a dividing cell as individual condensed chromosomes CYTOSKELETON: reinforces cell's shape; functions in cell movement; components are made of protein. Includes: microfilaments, Intermediate filaments, and microtubules Microvilli: projections that increase the cell's surface area ENDOPLASMIC RETICULUM (ER): network of membranous sacs and tubes; active in membrane synthesis and other synthetic and metabolic processes; has rough (ribosome-studded) and smooth regions Flagellum: motility structure present in some animal cells, composed of a cluster of microtubules within an extension of the plasma membrane Golgi apparatus: organelle active in synthesis, modification, sorting, and secretion of cell products Lysosome: digestive organelle where macromolecules are hydrolyzed Mitochondrion: organelle where cellular respiration occurs and most ATP is generated Nuclear envelope: double membrane enclosing the nucleus; perforated by pores; continuous with ER Nucleolus: nonmembranous structure involved in production of ribosomes; a nucleus has one or more nucleoli Peroxisome: organelle with various specialized metabolic functions; produces hydrogen peroxide as a by-product, then converts it to water Plasma membrane: membrane enclosing the cell Ribosomes (small brown dots): complexes that make proteins; free in cytosol or bound to rough ER or nuclear envelope

Where are chloroplasts found? What do they do and how?

Chloroplasts, found in plants and algae, are the sites of photosynthesis. These organelles convert solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water.

What are the parts of the cytoskeleton? Made of what? What can separate chromosomes?

Cytoskeleton: Microtubules are the thickest. Hollows rods made of tubulin (a dimer) which are made of α-tubulin and β-tubulin. Can separate Microfilaments (actin filaments) are the thinnest Intermediate filaments are fibers with diameters in a middle range.

Major difference b/w prokaryotes and eukaryotes?

DNA location: In a eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane (see Figure 4.7). In a prokaryotic cell, the DNA is concentrated in the nucleoid,a region that is not bounded by a membrane (Figure 4.4). The interior of either type of cell is called the cytoplasm; in eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane. Within the cytoplasm of a eukaryotic cell, suspended in cytosol, are a variety of organelles of specialized form and function. These membrane-bounded structures are absent in prokaryotic cells. Thus, the presence or absence of a true nucleus is just one aspect of the disparity in structural complexity between the two types of cells. Eukaryotic cells are generally much larger than prokaryotic cells (see Figure 4.2). Size is a general feature of cell structure that relates to function. The logistics of carrying out cellular metabolism sets limits on cell size. At the lower limit, the smallest cells known are bacteria called mycoplasmas, which have diameters between 0.1 and 1.0 μm. These are perhaps the smallest packages with enough DNA to program metabo- lism and enough enzymes and other cellular equipment to carry out the activities necessary for a cell to sustain itself and reproduce. Typical bacteria are 1-5 μm in diameter, about ten times the size of mycoplasmas. Eukaryotic cells are typically 10-100 μm in diameter.

Types of Vacuoles?

Food vacuoles, formed by phagocytosis, have already been mentioned (see Figure 4.12). Many freshwater protists have contractile vacuoles that pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell (see Figure 5.12). In plants and fungi, certain vacuoles carry out enzymatic hydrolysis, a function shared by lysosomes in animal cells. (In fact, some biologists consider these hydrolytic vacuoles to be a type of lysosome.) In plants, small vacuoles can hold reserves of important organic compounds, such as the proteins stockpiled in the storage cells in seeds. Vacuoles may also help protect the plant against herbivores by storing compounds that are poisonous or unpalat- able to animals. Some plant vacuoles contain pigments, such as the red and blue pigments of petals that help attract pollinating insects to flowers.

Things not in animal/plant cells

In animal cells but not plant cells: Lysosomes Centrosomes, with centrioles Flagella (but present in some plant sperm) (Flagella swims the centrosomes over to get lysosomed) In plant cells but not animal cells: Chloroplasts Central vacuole Cell wall Plasmodesmata (Triple C P - plasma cannon shooting chloroplasts at a cacuole penetrates and hits the cell wall)

What is a centrosome? Purpose? What is a centriole?

In animal cells, microtubules grow out from a centrosome, a region that is often located near the nucleus and is considered a "microtubule- organizing center." These microtubules function as compression resisting girders of the cytoskeleton. Within the centrosome is a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring (Figure 4.22). Before an animal cell divides, the centrioles replicate.

What is flagella/Cilia? Use/Purpose? Examples? difference?

In eukaryotes, a specialized arrangement of microtubules is responsible for the beating of flagella (singular, flagellum) and cilia (singular, cilium), microtubule- containing extensions that project from some cells. (The bacterial flagellum, shown in Figure 4.4, has a completely different structure.) Many unicellular eukaryotes are propelled through water by cilia or flagella that act as locomotor appendages, and the sperm of animals, algae, and some plants have flagella. When cilia or flagella extend from cells that are held in place as part of a tissue layer, they can move fluid over the surface of the tissue. For example, the ciliated lining of the trachea (wind- pipe) sweeps mucus containing debris out of the lungs (see the EMs in Figure 4.3). In a woman's reproductive tract, the cilia lining the oviducts help move an egg toward the uterus. A flagellum has an undulating motion like the tail of a fish (fish named flagella). In contrast, cilia work more like oars (cilia the viking), with alternating power and recovery strokes.

What is autophagy? How does it work?

Lysosomes also use their hydrolytic enzymes to recycle the cell's own organic material, a process called autophagy. During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane, and a lysosome fuses with the outer membrane of this vesicle (Figure 4.13). The lysosomal enzymes dismantle the enclosed material, and the resulting small organic compounds are released to the cy- tosol for reuse. With the help of lysosomes, the cell continually renews itself. A human liver cell, for example, recycles half of its macromolecules each week.

What lifeforms use lysosomes to digest food? Phagocytosis? Greek? What human cells perform phagocytosis?

Lysosomes carry out intracellular digestion in a variety of circumstances. Amoebas and many other protists eat by engulfing smaller organisms or food particles, a process called phagocytosis (from the Greek phagein, to eat, and kytos, vessel, referring here to the cell). The food vacuole formed in this way then fuses with a lysosome, whose enzymes digest the food (Figure 4.12, bottom). Digestion products, including simple sugars, amino acids, and other monomers, pass into the cytosol and become nutrients for the cell. Some human cells also carry out phagocytosis. Among them are macrophages, a type of white blood cell that helps defend the body by engulfing and destroying bacteria and other invaders (see Figure 4.12, top, and Figure 4.28).

What does golgi manufacture?

Manufactures some macromolecules. Many polysaccharides secreted by cells are Golgi products. For example, pectins and certain other noncellulose polysaccharides are made in the Golgi of plant cells and then incorporated along with cellulose into their cell walls.

Endomembrane System: What is within the EM system? Purpose? How are the membranes related?

Many of the different membranes of the eukaryotic cell are part of the endomembrane system, which includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane. This system carries out a variety of tasks in the cell, including synthesis of proteins, transport of proteins into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons. The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane).

What is the purpose of a central vacuole? Name two common items held w/in the central vacuole?

Mature plant cells generally contain a large central vacuole (Figure 4.14), which develops by the coalescence of smaller vacuoles. The solution inside the central vacuole, called cell sap, is the plant cell's main repository of inorganic ions, including potassium and chloride.

What are the implication of cell size have on metabolism?

Metabolic requirements also impose theoretical upper limits on the size that is practical for a single cell. For each square micrometer of membrane, only a limited amount of a particular substance can cross per second, so the ratio of surface area to volume is critical. As a cell (or any other object) increases in size, its volume grows proportionately more than its sur- face area. (Area is proportional to a linear dimension squared, whereas volume is proportional to the linear dimension cubed.) Thus, a smaller object has a greater ratio of surface area to volume (Figure 4.6). The Scientific Skills Exercise for this chapter (on p. 74) gives you a chance to calculate the volumes and surface areas of two actual cells—a mature yeast cell and a cell budding from it.

What are mitochondria sites of? Describe it

Mitochondria (singular, mitochondrion) are the sites of cellular respiration, the metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels.

What is the general structure/contents of mitochondria? Found in what cells? How are mitochondria dynamic?

Mitochondria are generally in the range of 1-10 μm long. Two membranes which form an outer inter membrane space and inner mitochondrial matrix filled with free ribosomes (enzymes that catalyze the first steps of sugar breakdown). The circular DNA molecules are attached to the inner mitochondrial membrane. Found in nearly all euks. # of depends on the usage of mitochondria in the cell (muscle more nerve less) Time-lapse films of living cells reveal mitochondria moving around, changing their shapes, and fusing or dividing in two, unlike the static structures seen in electron micrographs of dead cells.

What IDs things to the golgi? What are the "ships" that dock? and how do they know where to doc to pick up cargo?

Molecular identification tags, such as phosphate groups added to the Golgi products, aid in sorting by acting like ZIP codes on mailing labels. Finally, transport vesicles budded from the Golgi may have external molecules on their membranes that recognize "docking sites" on the surface of specific organelles or on the plasma membrane, thus targeting the vesicles appropriately.

What How are things modified in the golgi? Example?

Products of the endoplasmic reticulum are usually modified during their transit from the cis region to the trans region of the Golgi apparatus. For example, glycoproteins formed in the ER have their carbohydrates modified, first in the ER itself, then as they pass through the Golgi. The Golgi removes some sugar monomers and substitutes others, producing a large variety of carbohydrates. Membrane phospholipids may also be altered in the Golgi.

Ribosomes: What are they made of/purpose? What are the two locals of protein building? Types of ribosomes and their structure, location, funx, produce?

Ribosomes, which are complexes made of ribosomal RNA and protein, are the cellular components that carry out protein synthesis (Figure 4.9). Bound and free ribosomes are structurally identical, and can alternate between the two roles. At any given time, free ribosomes are suspended in the cytosol, while bound ribosomes are attached to the outside of the endoplasmic reticulum or nuclear envelope (see Figure 4.9). Free: examples are enzymes that catalyze the first steps of sugar breakdown. (free people make more free things) Bound ribosomes generally make proteins that are destined for insertion into membranes, for packaging (bound make more bound)

What is the modern view of how the golgi manufactures things?

The Golgi manufactures and refines its products in stages, with different cisternae containing unique teams of enzymes. Until recently, biologists viewed the Golgi as a static structure, with products in various stages of processing transferred from one cisterna to the next by vesicles. While this may occur, recent research has given rise to a new model of the Golgi as a more dynamic structure. According to the cisternal maturation model, the cisternae of the Golgi actually progress forward from the cis to the trans face, carrying and modifying their cargo as they move. Figure 4.11 shows the details of this model.

What is Tay-Sachs disease? How / Why does this occur?

The cells of people with inherited lysosomal storage diseases lack a functioning hydrolytic enzyme normally present in lysosomes. The lysosomes become engorged with indigestible material, which begins to interfere with other cellular activities. In Tay-Sachs disease, for example, a lipid-digesting enzyme is missing or inactive, and the brain becomes impaired by an ac- cumulation of lipids in the cells. Fortunately, lysosomal storage diseases are rare in the general population.

If the cell wall does not move but the cell takes in water where does it go?

The central vacuole plays a major role in the growth of plant cells, which enlarge as the vacuole absorbs water, enabling the cell to become larger with a minimal investment in new cytoplasm.

What is the general structure/contents of Chloroplast? Diff b/w chloroplast & clorophyll?

The membranes of the chloroplast divide the chloroplast space into three compart- ments: the intermembrane space, the stroma, and the thylakoid space. (the thylakoid TRex picked up the green granum inside the storage storm but split the inter membrane space) Chloroplasts contain the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar. These lens-shaped organelles,about 3-6 μm in length, are found in leaves and other green organs of plants and in algae (Figure 4.18). The contents of a chloroplast are partitioned from the cytosol by an envelope consisting of two membranes separated by a very narrow intermembrane space. Inside the chloroplast is another membranous system in the form of flattened, interconnected sacs called thylakoids. In some regions, thylakoids are stacked like poker chips; each stack is called a granum (plural, grana). The fluid outside the thyla- koids is the stroma, which contains the chloroplast DNA and ribosomes as well as many enzymes.

Cytoskeleton: Purpose? Do animal cells have cell walls? Provides for what for the cell? How does it change shape?

The most obvious function of the cytoskeleton is to give me-chanical support to the cell and maintain its shape. This is especially important for animal cells, which lack walls. The remarkable strength and resilience of the cytoskeleton as a whole is based on its architecture. Provides anchorage for many organelles and even cytosolic enzyme molecules. The cytoskeleton is more dynamic than an animal skeleton, however. It can be quickly dismantled in one part of the cell and reassembled in a new location, changing the shape of the cell.

Peroxisomes: Funx/Create/structure? Example/Location? How is a peroxisome structure crucial for its function? How do they grow larger?

The peroxisome is a specialized metabolic compartment bounded by a single membrane (Figure 4.19). Peroxisomes contain enzymes that remove hydrogen atoms from certain molecules and transfer them to oxygen (O2), producing hy- drogen peroxide (H2O2). These reactions have many different functions. For example, peroxisomes in the liver detoxify alcohol and other harmful compounds by transferring hydrogen from the poisons to oxygen. The H2O2 formed by peroxisomes is itself toxic, but the organelle also contains an enzyme that converts H2O2 to water. This is an excellent example of how the cell's compartmental structure is crucial to its functions: The enzymes that produce H2O2 and those that dispose of this toxic compound are sequestered from other cellular components that could be damaged. Peroxisomes grow larger by incorporating proteins made in the cytosol and ER, as well as lipids made in the ER and within the peroxisome itself. But how peroxisomes increase in number and how they arose in evolution are still open questions.

What is the plasma membrane? Where are things located? What are the regions of the membrane? What is located on the outside?

The plasma membrane and the membranes of organelles consist of a double layer (bilayer) of phospholipids with various proteins attached to or embedded in it. The hydrophobic parts, including phospholipid tails and interior portions of membrane proteins, are found in the interior of the membrane. The hydrophilic parts, including phospholipid heads, exterior portions of proteins, and channels of proteins, are in contact with aqueous solution. Carbohydrate side chains may be attached to proteins or lipids on the outer surface of the plasma membrane.

What does the Greek eu, baryon, and pro mean?

The word eukaryotic means "true nucleus" (from the Greek eu, true, and karyon, kernel, here referring to the nucleus), and the word prokaryotic means "before nucleus" (from the Greek pro, before), reflecting the fact that prokaryotic cells evolved before eukaryotic cells.

What are vacuoles derived from? What are they? Whats their purpose?

Vacuoles are large vesicles derived from the endoplasmic reticulum and Golgi apparatus. Thus, vacuoles are an integral part of a cell's endomembrane system. Like all cellular mem- branes, the vacuolar membrane is selective in transporting solutes; as a result, the solution inside a vacuole differs in composition from the cytosol.

Cell Motility: How does it work? Example?

cytoskeleton + motor proteins in order to move the cell along fibers outside the cell or vesicles and organelles use motor protein feet to walk along a track For example, this is how vesicles containing neurotransmitter molecules migrate to the tips of axons, the long extensions of nerve cells that release these molecules as chemical signals to adjacent nerve cells

Smooth ER Why so named? Funx/Produce? How does smooth ER affect detoxification and drug tolerance/other medications? Where does most detoxification occur? Role of _ in muscle contraction?

named because its outer surface lacks ribosomes. The smooth ER functions in diverse metabolic processes, include (4) lipid synthesis (oils, phospho, steroids..sex hormones) carb metabolism, Detox Ca storage. The cells that synthesize and secrete these hormones—in the testes and ovaries, for example— are rich in smooth ER, a structural feature that fits the function of these cells. Other enzymes of the smooth ER help detoxify drugs and poisons, especially in liver cells. Detoxification usually involves adding hydroxyl groups to drug molecules, making them more soluble and easier to flush from the body. The sedative phenobarbital and other barbiturates are examples of drugs metabolized in this manner by smooth ER in liver cells. In fact, barbiturates, alcohol, and many other drugs induce the pro- liferation of smooth ER and its associated detoxification enzymes, thus increasing the rate of detoxification. This, in turn, increases tolerance to the drugs, meaning that higher doses are required to achieve a particular effect, such as sedation. Also, because some of the detoxification enzymes have relatively broad action, the proliferation of smooth ER in response to one drug can increase tolerance to other drugs as well. Barbiturate abuse, for example, can decrease the effectiveness of certain antibiotics and other useful drugs. The smooth ER also stores calcium ions. In muscle cells, for example, the smooth ER membrane pumps calcium ions from the cytosol into the ER lumen. When a muscle cell is stimulated by a nerve impulse, calcium ions rush back across the ER membrane into the cytosol and trigger contraction of the muscle cell.