Chapter 3: The Cellular Level of Organization Flashcards

Question

Describe **permeable** (in relation to membrane permeability). ## Footnote The Plasma Membrane

Answer 1

Structure permits passage of substances through it. ## Footnote The Plasma Membrane

Answer 2

Structure does not permit passage of substances through it.

Answer 3

* Permits some substances to pass more readily than others. * Permeability of plasma membrane to different substances varies. ## Footnote The Plasma Membrane

Answer 4

* **Highly permeable** to nonpolar molecules such as oxygen (O2), carbon dioxide (CO2), steroids. * **Moderately permeable** to small, uncharged polar molecules such as water, urea (waste product from breakdown of amino acids). * **Impermeable** to ions and large, uncharged polar molecules such as glucose. * Permeability characteristics of plasma membrane is because lipid bilayer has nonpolar, hydrophobic interior. ## Footnote The Plasma Membrane

Answer 5

Unable to pass across plasma membrane except by **endocytosis** or **exocytosis**. ## Footnote The Plasma Membrane

Answer 6

* Difference in concentration of a chemical from one place to another (ex: inside to outside of plasma membrane). * Example: oxygen molecules and sodium ions (Na+) are more concentrated in extracellular fluid than in cytosol. ## Footnote The Plasma Membrane

Answer 7

* Difference in electrical charges between two regions. * Inner surface of plasma membrane is more negatively charged, outer surface is more positively charged. * Occurs across plasma membrane, charge difference is called **membrane potential**. ## Footnote The Plasma Membrane

Answer 8

* Help move substances across the plasma membrane. * Substance will move across plasma membrane *down its concentration gradient*. * Positively charged substance tend to move toward negatively charged area, and vice versa. ## Footnote The Plasma Membrane

Answer 9

Combined influence of concentration gradient and electrical gradient on movement of a particular ion. ## Footnote The Plasma Membrane

Answer 10

* Substance moves down its concentration or electrical gradient to cross membrane using only its own kinetic energy (energy of motion). * **Kinetic energy** is intrinsic to particles that are moving. No input of energy from cell. Example: Simple diffusion. ## Footnote Transport across the Plasma Membrane

Answer 11

* Cellular energy is used to drive substance "uphill" against its concentration or electrical gradient. * Cellular energy used, usually form of **adenosine triphosphate** (ATP). * Another way some substances may enter/leave cells is active process, tiny, spherical membrane sacs (**vesicles**) are used. ## Footnote Transport across the Plasma Membrane

Answer 12

* Passive process, random mixing of particles in solution occurs because of particles' kinetic energy. * Both the **solutes** (dissolved substances) and **solvent** (liquid that does dissolving), undergo diffusion. ## Footnote Transport across the Plasma Membrane

Answer 13

* If particular solute is present in high concentration in one area of solution and in low concentration in another area, solute molecules will diffuse towards area of lower concentration*move down their concentration gradient*. * Particles become evenly distributed throughout solution and solution is at equilibrium. Particles continue to move about randomly due to kinetic energy, but their concentrations do not change. ## Footnote Transport across the Plasma Membrane

Answer 14

1. Steepness of concentration gradient. 2. Temperature. 3. Mass of diffusing substance. 4. Surface area. 5. Diffusion distance. ## Footnote Transport across the Plasma Membrane

Answer 15

* Greater the difference in concentration between the 2 sides of membrane, the higher the rate of diffusion. * When charged particles are diffusing, steepness of electrochemical gradient determines diffusion rate across membrane. ## Footnote Transport across the Plasma Membrane

Answer 16

Higher the temperature, the faster the rate of diffusion. ## Footnote Transport across the Plasma Membrane

Answer 17

The larger the mass of diffusing particle, the slower the diffusion rate. ## Footnote Transport across the Plasma Membrane

Answer 18

* The larger the membrane surface area available for diffusion, the faster the diffusion rate. * Example: air sacs of lungs have large surface area available for diffusion of oxygen from air into blood. ## Footnote Transport across the Plasma Membrane

Answer 19

1. Simple diffusion. 2. Facilitated diffusion. 3. Osmosis. ## Footnote Transport across the Plasma Membrane

Answer 20

* Passive process, substances move freely through lipid bilayer of plasma membranes of cells without help of membrane transport proteins. * Nonpolar, hydrophobic molecules move across lipid bilayer through this process. * Such molecules include: oxygen, carbon dioxide and nitrogen gases; fatty acids; steroids; and fat-soluble vitamins (A, D, E, K). Small uncharged polar molecules such as water, urea and small alcohols. ## Footnote Transport across the Plasma Membrane

Answer 21

* Integral membrane protein assists specific substance across membrane. * Integral membrane protein can be either a membrane channel or carrier. * Moves solutes that are too polar or too highly charged to move through lipid bilayer by simple diffusion. ## Footnote Transport across the Plasma Membrane

Answer 22

* Solute moves down its concentration gradient across lipid bilayer through membrane channel. * Most membrane channels are **ion channels** (integral transmembrane proteins that allow passage of small, inorganic ions that are too hydrophilic to penetrate the nonpolar interior of the lipid bilayer). * Each ion can diffuse across membrane only at certain sites. ## Footnote Transport across the Plasma Membrane

Answer 23

* Most numerous are selective for K+ (potassium ions) or Cl- (chloride ions). * Fewer channels are available for Na+ (sodium ions) or Ca2+ (calcium ions). ## Footnote Transport across the Plasma Membrane

Answer 24

* Slower than free diffusion throughout lipid bilayer because channels occupy smaller fraction of membrane's total surface area than lipids. * Facilitated diffusion through channels is still very fast process. ## Footnote Transport across the Plasma Membrane

Answer 25

* Channel protein acts as "plug" or "gate", change shape in one way to open pore, in another way to close it. * Alternate between open/closed positions. * Others regulated by chemical or electrical changes inside and outside cell. ## Footnote Transport across the Plasma Membrane

Answer 26

* Carrier (transporter) moves solute down its concentration gradient across plasma membrane. * Passive process, no cellular energy required. * Solute binds to specific carrier on one side of membrane and is released on other side after carrier undergoes change in shape. ## Footnote Transport across the Plasma Membrane

Answer 27

* Number of carriers available in a plasma membrane places an upper limit on rate of which facilitated diffusion can occur. * Once all carriers are occupied, transport maximum is reached and a further increase in concentration gradient *does not* increase rate of facilitated diffusion. ## Footnote Transport across the Plasma Membrane

Answer 28

Glucose, fructose, galactose and some vitamins. ## Footnote Transport across the Plasma Membrane

Answer 29

Enters many body cells by carrier-mediated facilitated diffusion. 1. Glucose binds to specific type of carrier protein (glucose transporter (GluT)) on outside surface of membrane. 2. As transporter undergoes change in shape, glucose passes through membrane. 3. Transporter releases glucose on other side of membrane. ## Footnote Transport across the Plasma Membrane

Answer 30

* Type of diffusion, net movement of a solvent through selectively permeable membrane. * Passive process. * In living systems, solvent is water, which moves by osmosis across plasma membranes from area of higher water concentration to area of lower water concentration. ## Footnote Transport across the Plasma Membrane

Answer 31

In two ways: 1. Moving between neighboring phospholipid molecules in lipid bilayer via simple diffusion. 2. Moving through aquaporins (or AQPs), which are integral membrane proteins that function as water channels. ## Footnote Transport across the Plasma Membrane

Answer 32

* Integral membrane proteins, function as water channels. * Play critical role in controlling water content of cells. * Responsible for production of cerebrospinal fluid, aqueous humor, tears, sweat, saliva and concentration of urine. ## Footnote Transport across the Plasma Membrane

Answer 33

When a membrane is permeable to water but is *not* permeable to certain solutes. ## Footnote Transport across the Plasma Membrane

Answer 34

Pressure exerted by a fluid at equilibrium at any point in time due to force of gravity. ## Footnote Transport across the Plasma Membrane

Answer 35

* Osmotic pressure of a solution is proportional to concentration of solute particles that cannot cross membrane. * Higher the solute concentration, the higher the solution's osmotic pressure. ## Footnote Transport across the Plasma Membrane

Answer 36

Measure of solution's ability to change the volume of cells by altering their water content. ## Footnote Transport across the Plasma Membrane

Answer 37

* Any solution in which a cell maintains its normal shape and volume. * Shape is maintained as there is no net water movement into or out of cells. ## Footnote Transport across the Plasma Membrane

Answer 38

A solution that has a *lower* concentration of solutes than that inside a cell. ## Footnote Transport across the Plasma Membrane

Answer 39

A solution that has a *higher* concentration of solutes than that inside the cell. ## Footnote Transport across the Plasma Membrane

Answer 40

* RBCs maintain their normal shape and volume. * Concentrations of solutes that cannot cross the plasma membrane are the same on both sides of membrane in this solution. * Example: 0.9% NcCl solution is isotonic for RBCs. Water molecules enter/exit at same rate. ## Footnote Transport across the Plasma Membrane

Answer 41

* Water molecules enter cell faster than they leave, causing RBCs to swell, eventually burst. * Rupture of RBCs in this manner is called **hemolysis**. ## Footnote Transport across the Plasma Membrane

Answer 42

* Water molecules move out of cells faster than they enter, causing cells to shrink. * Shrinkage of cells is called **crenation**. * Example of hypertonic solution: 2% NaCl ## Footnote Transport across the Plasma Membrane

Answer 43

Substance is moved across a plasma against its concentration gradient ("uphill"). Energy is required for carrier proteins to move solutes across membrane against a concentration gradient. Two sources of cellular energy can be used. 1. **Primary active transport**: Obtained from hydrolosis of ATP. 2. **Secondary active transport**: From energy stored in an ionic concentration gradient. ## Footnote Transport across the Plasma Membrane

Answer 44

* Energy derived from hydrolysis of ATP changes shape of carrier protein, "pumps" substance across plasma membrane against its concentration gradient. * Body expends about 40% of ATP it generates on primary active transport. ## Footnote Transport across the Plasma Membrane

Answer 45

* Expels sodium ions (Na+) from cells, brings potassium ions (K+) into cell. * Part of pump acts as an ATPase (enzyme that hydrolyzes ATP), often called **Na+-K+ ATPase**. ## Footnote Transport across the Plasma Membrane

Answer 46

* Maintain low concentration of Na+ in cytosol by pumping these ions into extracellular fluid against Na+ concentration gradient. * Pumps move K+ into cells against K+ concentration gradient. * Maintains low concentration of Na+ and high concentration of K+ in cytosol. ## Footnote Transport across the Plasma Membrane

Answer 47

1. Three Na+ in cytosol bind to pump protein. 2. Binding of Na+ triggers hydrolysis of ATP into ADP, reaction attaches phosphate group to pump protein. Chemical reaction changes shape of pump protein, expelling the 3 Na+ into extracellular fluid. Shape of pump protein favors binding of 2 K+ into extracellular fluid to pump protein. 3. Binding of K+ triggers release of phosphate group from pump protein. Reaction causes shape of pump protein to change. 4. As pump protein reverts to its original shape, releases K+ into cytosol. Pump is ready again to bind 3 Na+, cycle repeats. ## Footnote Transport across the Plasma Membrane

Answer 48

* Energy stored in a Na+ or H+ concentration gradient is used to drive other substances across membrane against their own concentration gradients. * Indirectly uses energy obtained from hydrolysis of ATP. * Carrier protein simultaneously binds to Na+ and another substances, then changes shape so both substances cross membrane at same time. **Symporters**: Moving 2 substances in same direction. **Antiporters**: Moving 2 substances in opposite directions. ## Footnote Transport across the Plasma Membrane

Answer 49

* Small, spherical sac. * Variety of substances are transported from one structure to another within cells. * Import materials from and release materials into extracellular fluid. ## Footnote Transport across the Plasma Membrane

Answer 50

Materials move into a cell in a vesicle formed from plasma membrane. 3 types of endocytosis: 1. Receptor-mediated endocytosis 2. Phagocytosis 3. Bulk-phase endocytosis ## Footnote Transport across the Plasma Membrane

Answer 51

* Imports materials needed by cells. * Highly selective type of endocytosis, cells take up specific ligands (ligands are molecules that bind to specific receptors). * Vesicle forms after receptor protein in plasma membrane recognizes and binds to a particular particle in extracellular fluid. ## Footnote Transport across the Plasma Membrane

Answer 52

1. Binding 2. Vesicle formation 3. Uncoating 4. Fusion within endosome 5. Recycling of receptors to plasma membrane 6. Degradation in lysosomes ## Footnote Transport across the Plasma Membrane

Answer 53

* Extracellular side of plasma membrane, LDL particle that contains cholesterol binds to specific receptor in plasma membrane to form a **receptor-LDL complex**. * Receptors are integral membrane proteins that are concentrated in regions of plasma membrane called **clathrin-coated pits**. * Protein called **clathrin** attaches to membrane on cytoplasmic side. Clathrin molecules come together, forming basketlike structure around receptor-LDL complexes that causes membrane to invaginate (fold inward). ## Footnote Transport across the Plasma Membrane

Answer 54

* Invaginated edges of membrane around clathrin-coated pit fuse, and a small piece of membrane pinches off. * Resulting vesicle (**clathrin-coated vesicle**), contains receptor-LDL complexes. ## Footnote Transport across the Plasma Membrane

Answer 55

* Almost immediately after formed, clathrin-coated vesicle loses it clathrin coat to become an **uncoated vesicle**. * Clathrin molecules either return to inner surface of plasma membrane or help forms coats on other vesicles inside cell. ## Footnote Transport across the Plasma Membrane

Answer 56

* Uncoated vesicle quickly fuses with vesicle known as an **endosome**. * Within an endosome, the LDL particles seperate from their receptors. ## Footnote Transport across the Plasma Membrane

Answer 57

* Receptors accumulate in enlongated protrusions of the endosome. * These pinch off, forming transport vesicles that return the receptors to plasma membrane. * An LDL receptor is returned to plasma membrane about 10 minutes after it enters cell. ## Footnote Transport across the Plasma Membrane

Answer 58

* Transport vesicles, which contain LDL particles, bud off the endosome and fuse with a **lysosome (contain many digestive enzymes)**. * Certain enzymes break down large protein and lipid molecules of LDL particle into amino acids, fatty acids, cholesterol. * Smaller molecules then leave the lysosome. * Cell uses cholesterol for rebuilding membranes and for synthesis of steroids (ex. estrogen). * Fatty acids and amino acids can be used for ATP production or to build other molecules needed by the cell. ## Footnote Transport across the Plasma Membrane

Answer 59

* Form of endocytosis in which cell engulfs large solid particles, such as worn-out cells, whole bacteria, or viruses. * Only few body cells, called **phagocytes**, are able to carry out phagocytosis. * Vital defense mechanism that helps protect the body from disease. ## Footnote Transport across the Plasma Membrane

Answer 60

1. **Macrophages** (located in many body tissues). 2. **Neutrophils** (a type of white blood cell). ## Footnote Transport across the Plasma Membrane

Answer 61

* Particle binds to a plasma membrane receptor on phagocyte, causing it to extend **pseudopods** (projections of its plasma membrane and cytoplasm). * Pseudopods surround particle outside cell, membranes fuse to form vesicle called a **phagosome**, which enters the cytoplasm. * Phagosome fuses with one or more lysosomes, and lysosomal enzymes break down ingested material. * Any undigested materials in the phagosome remain indefinitely in a vesicle called **residual body**. * Residual bodies are then secreted by cell via exocytosis or remain stored in cell as lipofuscin granules. ## Footnote Transport across the Plasma Membrane

Answer 62

* **Pinocytosis** or "cell drinking", form of endocytosis in which tiny droplets of extracellular fluid are taken up. * No receptor proteins are involved; all solutes dissolved in the extracellular fluid are brought into the cell. * Most body cells carry out bulk-phase endocytosis, especially absorptive cells in intestines and kidneys. ## Footnote Transport across the Plasma Membrane

Answer 63

* Plasma membrane folds inward, forms a vesicle containing droplet of extracellular fluid. * Vesicle detaches/pinches off from plasma membrane, enters cytosol. * Within cell, vesicle fuses with a lysome, where enzymes degrade engulfed solutes. * Resulting smaller molecules, such as amino acids and fatty acids, leave lysosome to be used elsewhere in cell. ## Footnote Transport across the Plasma Membrane

Answer 64

Releases materials from cell. Carried out by all cells. Especially important in 2 types of cells. 1. **Secretory cells** (liberate digestive enzymes, hormones, mucus or other secretions). 2. **Nerve cells** (that release substances called neurotransmitters). In some cases, wastes are also released by exocytosis. ## Footnote Transport across the Plasma Membrane

Answer 65

* Membrane-enclosed vesicles called **secretory vesicles** form inside cell, fuse with plasma membrane and release their contents into extracellular fluid. * Segments of plasma membrane lost through endocytosis are recovered/recycled by exocytosis. ## Footnote Transport across the Plasma Membrane

Answer 66

* Balance between endocytosis and exocytosis keeps the surface area of cells plasma membrane relatively constant. * Membrane exchange is quite extensive in certain cells. * In pancreas, cells that secrete digestive enzymes can recycle an amount of plasma membrane equal to cell's entire surface area in 90 minutes. ## Footnote Transport across the Plasma Membrane

Answer 67

Active process, vesicles undergo endocytosis on one side of a cell, move across the cell, and then undergo exocytosis on the opposite side. ## Footnote Transport across the Plasma Membrane

Answer 68

* As vesicles fuse with plasma membrane, vesicular contents are released into extracellular fluid. * Occurs most often across endothelial cells that line blood vessels and is means for materials to move between blood plasma and interstitial fluid. * During pregnancy, some of Moms antibodies crosss the placenta into fetal circulation via transcytosis. ## Footnote Transport across the Plasma Membrane

Answer 69

Consists of all the cellular contents between the plasma membrane and the nucleus, and has 2 components: 1. **Cytosol** 2. **Organelles** ## Footnote Cytoplasm

Answer 70

* Intracellular fluid, the fluid portion of cytoplasm that surrounds organelles, constitutes about 55% of total cell volume. * Varies in composition and consistency from one part of a cell to another. * 75-90% water plus various dissolved and suspended components. * Among are different type of ions, glucose, amino acids, fatty acids, proteins, lipids, ATP and waste products. * The site of many chemical reactions required for a cell's existence. ## Footnote Cytoplasm

Answer 71

A network of protein filaments that extends throughout cytosol. 3 types of filaments contrubute to cytoskeleton's structure (as well as structure of other organelles). 1. **Microfilaments** 2. **Intermediate filaments** 3. **Microtubules** ## Footnote Cytoplasm

Answer 72

* Thinnest elements of the cytoskeleton. * Composed of the proteins actin and myosin and are most prevalent at edge of a cell. Two general functions: 1. Help generate movement 2. Provide mechanial support. ## Footnote Cytoplasm

Answer 73

* Involved in muscle contraction, cell division, cell locomotion. * Provide much of mechanical support responsible for basic strength and shapes of cells. * Anchor cytoskeleton to integral proteins in plasma membrane. * Provide mechanical support for cell extensions called **microvilli**. ## Footnote Cytoplasm

Answer 74

* Nonmotile, microscopic fingerlike projections of plasma membrane. * Within each microvillus is a core of parallel microfilaments that supports it. * Greatly increase surface area of the cell, are abundant on cells involved in absorption, such as epithelial cells that line small intestine. ## Footnote Cytoplasm

Answer 75

* Thicker than microfilaments, thinner than microtubules. * Are exceptionally strong, composted of several different proteins. * Found in parts of cells subject to mechanic stress. ## Footnote Cytoplasm

Answer 76

Help stabilize the position of organelles such as the nucleus and help attach cells to one another. ## Footnote Cytoplasm

Answer 77

* Largest of cytoskeletal components. * Long, unbranches hollow tubes composed mainly of protein **tubulin**. * Assembly begins in an organelle called the centrosome. * Microtubules grow outward from centrosome toward periphery of cell. ## Footnote Cytoplasm

Answer 78

* Help determine cell shape. * Function in the movement of organelles such as secretory vesicles, of chromosomes during cell division, and of specialized cell projections, such as cilia and flagella. ## Footnote Cytoplasm

Answer 79

1. Serves as a scaffold that helps determine cell's shape and organize cellular contents. 2. Aids movement of organelles within cell, of chromosomes during cell division, and of whole cells such as phagocytes. ## Footnote Cytoplasm

Answer 80

* Specialized structures within cell that have characteristic shapes, and perform specific functions in cellular growth, maintenance, and reproduction. * Is little interference among chemical reactions in a cell as they are confined to different organelles. ## Footnote Cytoplasm

Answer 81

* Each type of organelle has its own set of enzymes that carry out specific reactions. * Serves as functional compartment for specific biochemical processes. * Cooperate to maintain homeostasis. * The nucleus is a large organelle. ## Footnote Cytoplasm

Answer 82

Also called microtubule organizing center, located near the nucleus, consists of 2 components. 1. A pair of centrioles 2. The pericentriolar matrix * During cell division, centrosomes replicate so succeeding generations of cells have capacity for cell division. ## Footnote Cytoplasm

Answer 83

* The 2 centrioles are cylindrical structures, each composed of nine clisters of three microtubules (triplets) arranged in a circular pattern. * Long axis of one centriole is at a right angle to the long axis of the other. ## Footnote Cytoplasm

Answer 84

* Surrounds the centrioles. * Contains hundreds of ring-shaped complexes composed of protein **tubulin**. * Tubulin complexes are organizing centers for growth of mitotic spindle, which plays critical role in cell division, and for microtubule formation in nondividing cells. ## Footnote Cytoplasm

Answer 85

1. The perocentriolar matrix of centrosome contains tubulins that build microtubules into nondividing cells. 2. The pericentriolar matrix of centrosome forms the mitotic spindle during cell division. ## Footnote Cytoplasm

Answer 86

* Motile projections of the cell surface. * Numerous, short, hairlike projections, extend from surface of the cell. * Each cilium contains a core of 20 microtubules surrounded by plasma membrane. * Anchored to basal body just below surface of the plasma membrane. ## Footnote Cytoplasm

Answer 87

* Displays oarlike pattern of beating, relatively stiff during power stroke, more flexible during recovery stroke. * Coordinated movement of many cilia on surface of a cell causes steady movement of fluid along cell surface. * Cells of respiratory tract have hundreds of cilia that sweep foreign particles trapped in mucus away from lungs. ## Footnote Cytoplasm

Answer 88

* Used to move an entire cell. * Generates forward motion along its axis by rapidly wiggling in wavelike patern. * Only example in human body is a sperm cell tail. ## Footnote Cytoplasm

Answer 89

1. Cilia moves fluids along a cell's surface. 2. A flagellum moves an entire cell. ## Footnote Cytoplasm

Answer 90

* The sites of protein synthesis. * High content of one type of ribonucleic acid (ribosomal RNA, or rRNA), but each ribosome includes more than 50 proteins. * Structurally, consists of 2 subunits, large and small subunits. * Also located within mitochondria, where they synthesize mitochondrial proteins. ## Footnote Cytoplasm

Answer 91

* Made separately in the nucleolus, a spherical body inside the nucleus. * Once produced, large and small subunits exit the nucleus separately, then come together in cytoplasm. ## Footnote Cytoplasm

Answer 92

1. Ribosomes associated with endoplasmic reticulum synthesize proteins destined for insertion in the plasma membrane or secretion from the cell. 2. Free ribosomes synthesize proteins used in the cytosol. ## Footnote Cytoplasm

Answer 93

* Network of membranes in form of flattened sacs or tubules. * Extends from nuclear envelope, to which it is connected and projects throughout the cytoplasm. * Extensive, constitutes more than half of membranous surfaces within cytoplasm of most cells. ## Footnote Cytoplasm

Answer 94

1. Rough endoplasmic reticulum 2. Smooth endoplasmic reticulum ## Footnote Cytoplasm

Answer 95

* Continuous with nuclear membrane and usually is folded into series of flattened sacs. * Outer surface is studded with ribosomes (sites of protein synthesis). ## Footnote Cytoplasm

Answer 96

* Synthesizes glycoproteins and phospholipids. * Produces secretory proteins, membrane proteins, and many organellar proteins. * Proteins synthesized by ribosomes attached to rough ER enter spaces within ER for processing, sorting. Some cases, enzymes attach proteins to carbohydrates, form glycoproteins. ## Footnote Cytoplasm

Answer 97

* Extends from rough ER to form network of membrane tubules. * Does not have ribosomes on outer surfaces of its membrane. * Contains unique enzymes that make it functionally more diverse. * Does not synthesize proteins. ## Footnote Cytoplasm

Answer 98

* Synthesize fatty acids and steroids (ex. estrogen and testosterone). * Liver cells: enzymes of smooth ER help release glucose into blood, inactivate/detoxify lipid-soluble drugs or harmful substances. * Liver, kidney, intestinal cells: enzyme removes phosphate group from glucose-6 phosphate, allows free glucose to enter blood. Releases calcium ions that trigger contraction in muscle cells. ## Footnote Cytoplasm

Answer 99

* An organelle. * Consists of 3-20 **cisterns**, small, flattened membranous sacs with bulging edges. * Cisterns are often curved, giving a cuplike shape. * Most cells have several Golgi complexes, more extensive in cells that secrete proteins. ## Footnote Cytoplasm

Answer 100

1. Modifies, sorts, packages, and transports proteins received from rough ER. 2. Forms secretory vesicles that discharge processed proteins via exocytosis into extracellular fluid. 3. Forms membrane vesicles that ferry new molecules to plasma membrane. 4. Forms transport vesicles that carry molecules to other organelles, such as lysosomes. ## Footnote Cytoplasm

Answer 101

* Cisterns at opposite ends of Golgi complex differ in size, shape, enzyme activity. * Convex **entry (cis) face** is a cistern that faces rough ER. * Concave **exit (trans) face** is a cistern that faces plasma membrane. * Sacs between entry and exit faces are called **medial cisterns**. * Transport vesicles from ER merge to form entry face. From entry face, cisterns are thought to mature, in turn becoming medial and then exit cisterns. ## Footnote Cytoplasm

Answer 102

1. Entry face received and modifies proteins produced by rough ER. 2. Medial cisterns add carbohydrates to proteins to form glycoproteins and lipids to proteins to form lipoproteins. 3. Exit face modifies molecules further and then sorts and packages them for transport to destinations. ## Footnote Cytoplasm

Answer 103

1. Proteins synthesized by ribosomes on rough ER are surrounded by a piece of ER membrane, buds from membrane surface to form transport vesicles. 2. Transport vesicles move toward entry face of Golgi complex. 3. Fusion of several transport vesicles creates entry face of Golgi complex, releases proteins into its lumen. 4. Proteins move from entry face into one or more medial cisterns. Enzymes in medial cisterns modify proteins to form glycoproteins, glycolipids, and lipoproteins. Transfer vesicles that bud from edges of cisterns move specific enzymes back toward the entry face and move some partially modified proteins toward exit face. 5. Products of medial cisterns move into lumen of exit face. 6. Within exit face cistern, products are further modified, sorted and packaged. 7. Some of processed proteins leave exit face, are stored in secretory vesicles. These vesicles deliver proteins to plasma membrane, where they are discharged by exocytosis into extracellular fluid. 8. Other processed proteins leave exit face in membrane vesicles, deliver contents to plasma membrane for incorporation into membrane. Golgi complex adds new segments of plasma membrane as existing segments are lost and modifies number and distribution of membrane molecules. 9. Some processed proteins leave exit face in transport vesicles that will carry proteins to another cellular destination. ## Footnote Cytoplasm

Answer 104

1. Lysosomes 2. Plasma membrane 3. Secretion ## Footnote Cytoplasm

Answer 105

* Membrane-enclosed vesicles that form from Golgi complex. * Contain as many as 60 kinds of powerful digestive and hydrolytic enzymes, can break down variety of molecules once lysosomes fuse with vesicles formed from endocytosis. * Work best at an acidic pH, lysosomal membrane includes active transport pumps that import hydrogen ions, thus, lysosomal interior has pH of 5. ## Footnote Cytoplasm

Answer 106

1. Digest substances that enter cell via endocytosis and transport final products of digestion into cytosol. 2. Carry out autophagy (digestion of worn-out organelles). 3. Implement autolysis (digestion of entire cell). 4. Accomplish extracellular digestion. ## Footnote Cytoplasm

Answer 107

* Organelle to be digested is enclosed by membrane derived from the ER to create a vesicle called **autophagosme**. * Vesicle then fuses with a lysosome. Lysosomal enzymes help recycle worn-out cell structures. * Can engulf another organelle, digest it and return digested components to the cytosol for reuse. * Enzymes may destroy entire cell that contains them, called **autolysis**. ## Footnote Cytoplasm

Answer 108

* Group of organelles, smaller than lysosomes. * Also called microbodies. * Contain several oxidases, enzymes that can oxidize various organic substances. * Amino acids and fatty acids are oxidized in peroxisomes as part of normal metabolism. * Enzymes in peroxisomes oxidize toxic substances. * Abundant in the liver. ## Footnote Cytoplasm

Answer 109

* Peroxisomes contain the enzyme catalase, which decomposes H2O2 (hydrogen peroxide). * Production and degradation of H2O2 occur within the same organelle, peroxisomes protect other parts of cell from toxic effects of H2O2. * Peroxisomes also contain enzymes that destroy superoxide. ## Footnote Cytoplasm

Answer 110

* Tiny barrel-shaped structures consisting of four stacked rings of proteins around a central core. * Provide continuous destruction of unneeded, damaged or faulty proteins. * Typical body cell contains thousands of proteasomes, in cytosol and nucleus. * Contain myriad **proteases** (enzymes that cut proteins into small peptides). * Once enzymes of proteasome have chopped up protein into smaller chunks, other enzymes break down the peptides into amino acids, which can be recycled into new proteins. ## Footnote Cytoplasm

Answer 111

* "Powerhouses" of the cell. * Generate most of the ATP through aerobic respiration. * Cell can have hundreds or thousands of mitochondria, depending on its activity. * Active cells that use ATP at high rates (muscles, liver, kidneys) have large number of mitochondria. * Usually located within cell where oxygen enters the cell or where the ATP is used. ## Footnote Cytoplasm

Answer 112

1. Generate ATP through reactions of aerobic cellular respiration. 2. Play an important early role in apoptosis. ## Footnote Cytoplasm

Answer 113

* Mitochondrion consists of external mitochondrial membrane and internal mitochondrial membrane with small fluid-filled space between. * Both membranes are similar in structure to plasma membrane. * Internal mitochondrial membrane contains series of folds called **mitochondrial cristae**. * Central fluid-filled cavity of a mitochondrion, enclosed by internal mitochonrial membrane, the **mitochondrial matrix**. * Elaborate folds of the cristae provide enormous surface afea for chemical reactions that are part of the aerobic phase of cellular respiration (the reactions that produce most of a cell's ATP). ## Footnote Cytoplasm

Answer 114

Is the orderly, genetically progreammed death of a cell. ## Footnote Cytoplasm

Answer 115

* Response to stimuli, certain chemicals are released from mitochondria following formation of pore in outer mitochondrial membrane. * One of chemicals released into cytosol of cell is cytochrome c, which while inside mitochondria, is involved in aerobic cellular respiration. * In cytosol, cytochrome c and other substances initiate a cascade of activation of protein-digesting enzymes that bring about apoptosis. ## Footnote Cytoplasm

Answer 116

* Mitrochondria have their own DNA, in form of multiple copies of a circular DNA molecule that contains 37 genes. * Mitochondrial genes control synthesis of 2 ribosomal RNAs, 22 transfer RNAs, and 13 proteins that build mitochondrial components. * Mitochondrial genes are inherited only from mother. ## Footnote Cytoplasm

Answer 117

* Spherical or oval-shaped structure, usually most prominent feature of a cell. * Most cells have a single nucleus, although some, such as mature red blood cells, have none. * Skeletal muscle cells and other types of cells have multiple nuclei. ## Footnote Nucleus

Answer 118

* Double membrane that separates nucleus from cytoplasm. * Both layers of nuclear envelope are lipid bilayers similar to plasma membrane. * Outer membrane of nuclear envelope is continuous with rough ER and resembles it in structure. ## Footnote Nucleus

Answer 119

* Many openings that extend through the nuclear envelope. * Each nuclear pore consists of circular arrangement of proteins surrounding large central opening that is about 10 times wider than the pore of a channel protein in plasma membrane. ## Footnote Nucleus

Answer 120

* Control the movement of substances between nucleus and cytoplasm. * Small molecules and ions move through pores passively by diffusion. * Most lage molecules, such as RNAs and proteins, cannot pass through nuclear pores by diffusion. Instead, involves active transport process, molecules are recognized and selectively transported through nuclear pore into or out of nucleus. ## Footnote Nucleus

Answer 121

* Spherocal bodies inside the nucleus that function in producing ribosomes. * Each nucleolus is a cluster of protein, DNA and RNA; it is **not** enclosed by a membrane. ## Footnote Nucleus

Answer 122

* Sites of synthesis of rRNA and assembly of rRNA and proteins into ribosomal subunits. * Are prominent in cells that synthesize large amounts of protein (muscle and liver cells). * Nucleoli disperse and disappear during cell division and reorganize once new cells are formed. ## Footnote Nucleus

Answer 123

* Cell's hereditary units, control cellular structure and direct cellular activities. * Arranged along chromosomes. * Human somatic (body) cells have 46 chromosomes, 23 inherited from each parent. * Each chromosome is a long molecule of DNA that is coiled together with several proteins. ## Footnote Nucleus

Answer 124

The total genetic information carried in a cell or an organism. ## Footnote Nucleus

Answer 125

* A complex of nucleic acids (DNA or RNA) and proteins (e.g. histones). * In cells that are not dividing, chromatin appears as a diffuse, granular mass. * Has a beads-on-a-string structure. ## Footnote Nucleus

Answer 126

* The basic repeating subunit of chromatin packaged inside the cell’s nucleus. * Each bead of chromatin string structure is a neuleosome that consists of double-stranded DNA wrapped twice around a core of eight proteins called histones, which help organize the coiling and folding of DNA. ## Footnote Nucleus

Answer 127

1. Controls cellular structure. 2. Direct cellular activities. 3. Produces ribsomes in nucleoli. ## Footnote Nucleus

Answer 128

Refers to all of an organism's proteins. ## Footnote Protein Synthesis

Answer 129

* Gene's DNA is used as template for synthesis of a specific protein. * First, information encoded in a specific region of DNA is transcribed to produce a specific mole of RNA (transcription). * Second, RNA attaches to ribosome, where information contained in RNA is translated into corresponding sequence of amino acids to form a new protein molecule (translation). ## Footnote Protein Synthesis

Answer 130

* Sequence of three nucleotides in DNA, where genertic information is stored in sets of three nucleotides. * Each DNA base triplet is transcribed as a complementary sequence of three nucleotides, called a codon. * A given codon specifies a particular amino acid. ## Footnote Protein Synthesis

Answer 131

Set of rules that relate the base triplet sequence of DNA to corresponding condons of RNA and amino acids they specify. ## Footnote Protein Synthesis

Answer 132

Occurs in nucleus, genetic information represented by the sequence of base triplets in DNA serves as template for copying information into a complementary sequence of codons. Genetic information in DNA is copied to RNA. 3 types of RNA are made from DNA template: 1. **Messenger RNA** (mRNA). 2. **Ribosomal RNA** (rRNA). 3. **Transfer RNA** (tRNA). ## Footnote Protein Synthesis

Answer 133

Directs the synthesis of a protein. ## Footnote Protein Synthesis

Answer 134

Joins with ribosomal proteins to make ribosomes. ## Footnote Protein Synthesis

Answer 135

* Binds to amino acid, holds it in place on ribosome unit, incorporated into a protein during translation. * One end of tRNA carries a specific amino acid, and the opposide end consists of a triplet of nucleotides called anticodon. * By pairing between complementary bases, tRNA anticodon attaches to mRNA codon. ## Footnote Protein Synthesis

Answer 136

* Enzyme that catalyzes transcription of DNA. * Enzyme must be instructed where to start transcription process and where to end it. * Only one of two DNA strands serves as a template for RNA synthesis. ## Footnote Protein Synthesis

Answer 137

* Segment of DNA where transcription begins, a special nucleotide sequence. * Promoter is located near beginning of a gene. * This is where RNA polymerase attaches to the DNA. ## Footnote Protein Synthesis

Answer 138

**DNA Template** / **RNA Strand** Adenine (A) pairs with Uracil (U) Thymine (T) pairs with Adenine (A) Guanine (G) pairs with Cytosine (C) Cytosine (C) pairs with Guanine (G) ## Footnote Protein Synthesis

Answer 139

* Special nucleotide sequence, which specifies the end of the gene. * When RNA ploymerase reaches terminator, enzyme detaches from transcribed RNA molecule and DNA strand. ## Footnote Protein Synthesis

Answer 140

Regions that **do not** code for parts of a protein. ## Footnote Protein Synthesis

Answer 141

Regions that **do** code for segments of a protein. ## Footnote Protein Synthesis

Answer 142

* Nucleotide sequence in an mRNA molecule specifies amino acid sequence of a protein. * Ribosomes in cytoplasm carry out translation. * mRNA molecule binds to a ribosome. Then, mRNA nucleotide sequence specifies the amino acid sequence of a protein. ## Footnote Protein Synthesis

Answer 143

1. mRNA molecule binds to small ribosomal subunit at mRNA binding site. Special tRNA (initiator tRNA) binds to start codon (AUG) on mRNA where translation begins. tRNA anticodon (UAC) attaches to mRNA codon (AUG) by pairing between complementary bases. AUG is also the codon for amino acid methionine, thus methionine is always first amino acid in growing polypeptide. 2. Large ribosomal subunit attaches to small ribosomal subunit-mRNA complex, creating functional ribosome. Initiator tRNA with its amino acid(methionine), fits into P site of ribosome. 3. Anticodon of another tRNA with its attached amino acid pairs with second mRNA codon at A site of ribosome. 4. Component of large ribosomal subunit catalyzes formation of peptide bond between methionine and the amino acid carried by the tRNA at the A site. 5. Following formation of peptide bond, resulting two peptide protein becomes attached to tRNA at A site. 6. After peptide bond formation, ribosome shifts mRNA strand by one codon. tRNA in the P site enters E site and is released from ribosome. tRNA in A site bearing the 2 peptide protein shifts into P site, allowing tRNA with its amino acid to bind to newly exposed codon at A site. Steps 3-6 occur repeatedly and protein legthens progressively. 7. Protein synthesis ends when ribosome reaches stop codon at A site, causes completed protein to detach from final tRNA. Also, tRNA vacates P site and ribosome splits into its large and small subunits. ## Footnote Protein Synthesis

Answer 144

* About 15 peptide bonds per second. * As ribosome moves along mRNA, before it completes synthesis of whole protein, another ribosome may attach behind it and begin translation of same mRNA strand. ## Footnote Protein Synthesis

Answer 145

* Several ribosomes that are attached to same mRNA molecule. * Simultaneous movement of several ribosomes along same mRNA molecule permits translation of one mRNA into several identical proteins at same time. ## Footnote Protein Synthesis

Answer 146

The process by which cells reproduce themselbes. Two types of cell division: 1. **Somatic cell division** 2. **Reproductive cell division** ## Footnote Cell Division

Answer 147

Is any cell of the body other than a germ cell. ## Footnote Cell Division

Answer 148

* Cell undergoes nuclear division called **mitosis** and a cytoplasmic division called **cytokinesis**, to produce two genetically identical cells, each with the same number and kind of chromosomes as original cell. * Replaces dead/injured cells and adds new ones during tissue growth. ## Footnote Cell Division

Answer 149

A gamete (sperm or oocyte) or any precursor cell destined to become a gamete. ## Footnote Cell Division

Answer 150

* Mechanism that produces gametes, cells needed to form next generation of sexually reproducing organisms. * Consists of a special 2-step division called meiosis, in which the number of chromosomes in the nucleus is reduced by half. ## Footnote Cell Division

Answer 151

**Intraphase**: G1 phase, S phase, G2 phase. **Mitotic Phase**: Mitosis, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis. ## Footnote Cell Division

Answer 152

* Orderly sequence of events in which a somatic cell duplicates its contents and divides into two. * Some cells divide more than others. ## Footnote Cell Division

Answer 153

* Two chromosomes that makeup each pair (homologs). * Contain similar genes arranged in the same (or almost the same) order. * Human cells contain 23 pairs of chromosomes, for a total of 46. ## Footnote Cell Division

Answer 154

One pair of chromosomes, designated X and Y. **Females**: homologous pair of sex chromosomes consists of 2 large X chromosomes **Males**: pair consists of an X and a much smaller Y chromosome. ## Footnote Cell Division

Answer 155

Cells that contain two sets of chromosomes. Also called (2n) cells. ## Footnote Cell Division

Answer 156

* Process where cell replicates its DNA. * Produces additional organelles and cytosolic components in anticipation of cell division. * A state of high metabolic activity; it is during this time that cell does most of its growing. * Consists of 3 phases: **G1**, **S** and **G2**. ## Footnote Cell Division

Answer 157

* Interval between mitotic phase and S phase. * Cell is metabolically active; replicates most of its organelles and cytosolic componenets but not DNA. * Replication of centrosomes begins. * For cell with total cell cycle time of 24 hours, G1 lasts 8-10 hours, duration is variable. Very short in embroyonic cells and cancer cells. ## Footnote Cell Division

Answer 158

* Cells that remain in G1 for very long time, perhaps destined never to divide again. * Most nerve cells are in the G0 phase. ## Footnote Cell Division

Answer 159

* DNA replication and centrosome replication occurs. * Interval between G1 and G2, lasts about 8 hours. * Once cell enters S phase, is committed to go through rest of cell cycle. * As result of DNA replication, 2 identical cells formed during cell division later in cell cycle will have the same genetic material. ## Footnote Cell Division

Answer 160

* Interval between S phase and mitotic phase. * Lasts 4-6 hours. * Cell growth continues, enzymes and other proteins are synthesized in preparation for cell division, and replication of centrosomes is completed. ## Footnote Cell Division

Answer 161

* Results in formation of two identical cells. * Consists of nuclear division (mitosis) and cytoplasmic division (cytokinesis) to form two identical cells. * These events are visable under microscope. ## Footnote Cell Division

Answer 162

The distribution of two sets of chromosomes into two separate nuclei. Process results in exact partitioning of genetic information. A continuous process; one stage merges seamlessly into the next. Divided into 4 stages: 1. **Prophase** 2. **Metaphase** 3. **Anaphase** 4. **Telophase** ## Footnote Cell Division

Answer 163

* Chromatin fibers condense into paired chromatids. * Nucleolus and nuclear envelope disappear. * Each centrosome moves to an opposite pole of the cell. * Process can be seen under light microscope. ## Footnote Cell Division

Answer 164

* Constricted region which holds chromatid pair together during cell division. * At the outside of each centromere is protein complex known as the **kinetochore**. ## Footnote Cell Division

Answer 165

* Football-shaped assembly of microtubules that attach to the kinetochore. * Responsible for separation of chromatids to opposite poles of the cell. ## Footnote Cell Division

Answer 166

Centromeres of chromatid pairs line up at metaphase plate. ## Footnote Cell Division

Answer 167

* Centromeres split; identical sets of chromosomes move to opposite poles of cell. * When separated, chromatids are termed chromosomes. * Chromosomes appear V-shaped because centromeres lead way, dragging trailing arms of chromosomes toward the pole. ## Footnote Cell Division

Answer 168

* Nuclear envelopes and nucleoli reappear; chromosomes resume chromatin form; mitotic spindle disappears. * Final stage of mitosis. Begins after chromosomal movement stops. * Identical sets of chromosomes uncoil and revert to threadlike chromatin form. * Nuclear envelope forms around each chromatin mass, nucleoli reappear in indentical nuclei and mitotic spindle breaks up. ## Footnote Cell Division

Answer 169

* Division of a cells cytoplasm and organelles into two identical cells. * Usually beings in late anaphase with formation of a cleavage furrow (slight indentation of the plasma membrane) and is completed after telophase. * Cleavage furrow divides cytoplasm into separate and equal portions. * When complete, interphase begins. ## Footnote Cell Division

Answer 170

A cell has 3 possible destinies: 1. Remain alive and functioning without dividing. 2. Grow and divide. 3. To die. Homeostasis is maintained when there is balance between cell proliferation and cell death. ## Footnote Cell Division

Answer 171

A normal type of cell death. ## Footnote Cell Division

Answer 172

* Pathological type of cell death that results from tissue injury. * Adjacent cells swell, burst, and spill their cytoplasm into interstitial fluid. * The cellular debris usually stimulates inflammatory response by immune system, a process that **does not** occur in apoptosis. ## Footnote Cell Division

Answer 173

The reproductive cell division that occurs in the gonads (ovaries and testes), produces gametes in which the number of chromosomes is reduced by **half**. Gametes contain single set of 23 chromosomes, are haploid (n) cells. Fertilization restores the dioloid number of chromosomes. Occurs in two successive stages: 1. **Meiosis I** 2. **Meiosis II** ## Footnote Cell Division

Answer 174

Begins when chromosomal replication complete. Consists of 4 phases: 1. **Prophase I** 2. **Metaphase I** 3. **Anaphase I** 4. **Telophase I** ## Footnote Cell Division

Answer 175

* Extended phase, chromosomes shorten and thicken, nuclear envelope and nucleoli disappear, mitotic spindle forms. * Two sister chromatids of each pair of homologous chromosomes pair off (synapsis). * Resulting 4 chromatids form structure called a tetrad. * Parts of chromatids of 2 homologous chromosomes may be exhanged with one another. * Exchange between parts of nonsister chromatids is crossing over, which resulting cells are genetically unlike eachother and from starting cell. ## Footnote Cell Division

Answer 176

* Results from crossing-over (exchange between parts of nonsister chromatids). * Formation of new combinations of genes-and accounts for part of genetic variation among humans and other organisms that form gametes via meiosis. ## Footnote Cell Division

Answer 177

Tetrads formed by homologous pairs of chromosomes line up along metaphase plate of the cell, with homologous chromosomes side by side. ## Footnote Cell Division

Answer 178

* Members of each homologous pair of chromosomes separate, pulled to opposite poles of cell by microtubules attached to centromeres. * Paired chromatids, held by centromere, remain together. ## Footnote Cell Division

Answer 179

Each cell has one of the replicated chromosomes from each homologoous pair of chromosomes. ## Footnote Cell Division

Answer 180

Is the second stage of meiosis and consists of 4 phases: 1. Prophase II 2. Metaphase II 3. Anaphase II 4. Telophase II Phases similar to those that occur during mitosis; centromeres split, and sister chromatids separate and move toward opposite poles of cell. ## Footnote Cell Division

Answer 181

During anaphase I of meiosis, the paired chromatids are held together by a centromere and do not separate. During anaphase of mitosis, the paired chromatids separate and the centromeres split. ## Footnote Cell Division

Answer 182

The result of crossing-over is that four haploid gametes are genetically unlike each other and genetically unlike the starting cell that produced them. ## Footnote Cell Division

Answer 183

Cytokinesis usually begins in late anaphase. ## Footnote Cell Division

Answer 184

DNA replicates during the S phase of interphase of the cell cycle. ## Footnote Cell Division

Answer 185

DNA replication must occur before cytokinesis so that each of the new cells will have a complete genome. ## Footnote Cell Division

Answer 186

A single set of 23 chromosomes. ## Footnote Cell Division

Answer 187

Measured in units called micrometers. One micrometer is equal to 1 one-millionth of a meter. ## Footnote Cellular Diversity

Answer 188

1. Round 2. Flat 3. Oval 4. Cube-shaped 5. Column-shaped 6. Elongated 7. Star-shaped 8. Cylindrical 9. Disc-shaped ## Footnote Cellular Diversity

Answer 189

* The greater the distance over which diffusion must occur, the longer it takes. * Diffusion across a plasma membrane takes fraction of a second because membrane is thin. ## Footnote Transport across the Plasma Membrane

Chapter 3: The Cellular Level of Organization Flashcards

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