Presentation is loading. Please wait.

Presentation is loading. Please wait.

Cell Membranes and Signaling

Similar presentations


Presentation on theme: "Cell Membranes and Signaling"— Presentation transcript:

1 Cell Membranes and Signaling
5 Cell Membranes and Signaling

2 Chapter 5 Cell Membranes and Signaling
Key Concepts 5.1 Biological Membranes Have a Common Structure and Are Fluid 5.2 Some Substances Can Cross the Membrane by Diffusion 5.3 Some Substances Require Energy to Cross the Membrane

3 Chapter 5 Cell Membranes and Signaling
5.4 Large Molecules Cross the Membrane via Vesicles 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals 5.6 Signal Transduction Allows the Cell to Respond to Its Environment

4 Chapter 5 Opening Question
What role does the cell membrane play in the body’s response to caffeine?

5 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
A membrane’s structure and functions are determined by its constituents: lipids, proteins, and carbohydrates. The general structure of membranes is known as the fluid mosaic model. Phospholipids form a bilayer which is like a “lake” in which a variety of proteins “float.” VIDEO 5.1 Cell Visualization: Membranes, hormones, and receptors

6 Figure 5.1 Membrane Molecular Structure

7 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Lipids form the hydrophobic core of the membrane. Most lipid molecules are phospholipids with two regions: Hydrophilic regions—electrically charged “heads” that associate with water molecules Hydrophobic regions—nonpolar fatty acid “tails” that do not dissolve in water

8 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
A bilayer is formed when the fatty acid “tails” associate with each other and the polar “heads” face the aqueous environment. Bilayer organization helps membranes fuse during vesicle formation and phagocytosis. LINK Review the properties of phospholipid bilayers in Concept 2.4

9 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Membranes may differ in lipid composition as there are many types of phospholipids. Phospholipids may differ in: Fatty acid chain length Degree of saturation Kinds of polar groups present

10 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Two important factors in membrane fluidity: Lipid composition—types of fatty acids can increase or decrease fluidity Temperature—membrane fluidity decreases in colder conditions APPLY THE CONCEPT Biological membranes have a common structure and are fluid INTERACTIVE TUTORIAL 5.1 Lipid Bilayer: Temperature Effects on Composition

11 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Biological membranes contain proteins, with varying ratios of phospholipids. Peripheral membrane proteins lack hydrophobic groups and are not embedded in the bilayer. Integral membrane proteins are partly embedded in the phospholipid bilayer. See Figure 5.1

12 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Anchored membrane proteins have lipid components that anchor them in the bilayer. Proteins are asymmetrically distributed on the inner and outer membrane surfaces. A transmembrane protein extends through the bilayer on both sides, and may have different functions in its external and transmembrane domains.

13 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Some membrane proteins can move within the phosopholipid bilayer, while others are restricted. Proteins inside the cell can restrict movement of membrane proteins, as can attachments to the cytoskeleton.

14 Figure 5.2 Rapid Diffusion of Membrane Proteins

15 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Plasma membrane carbohydrates are located on the outer membrane and can serve as recognition sites. Glycolipid—a carbohydrate bonded to a lipid Glycoprotein—a carbohydrate bonded to a protein

16 Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Membranes are constantly changing by forming, transforming into other types, fusing, and breaking down. Though membranes appear similar, there are major chemical differences among the membranes of even a single cell.

17 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Biological membranes allow some substances, and not others, to pass. This is known as selective permeability. Two processes of transport: Passive transport does not require metabolic energy. Active transport requires input of metabolic energy.

18 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Passive transport of a substance can occur through two types of diffusion: Simple diffusion through the phospholipid bilayer Facilitated diffusion through channel proteins or aided by carrier proteins

19 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Diffusion is the process of random movement toward equilibrium. Speed of diffusion depends on three factors: Diameter of the molecules—smaller molecules diffuse faster Temperature of the solution—higher temperatures lead to faster diffusion

20 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
The concentration gradient in the system—the greater the concentration gradient in a system, the faster a substance will diffuse A higher concentration inside the cell causes the solute to diffuse out, and a higher concentration outside causes the solute to diffuse in, for many molecules.

21 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Simple diffusion takes place through the phospholipid bilayer. A molecule that is hydrophobic and soluble in lipids can pass through the membrane. Polar molecules do not pass through— they are not soluble in the hydrophilic interior and form bonds instead in the aqueous environment near the membrane.

22 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Osmosis is the diffusion of water across membranes. It depends on the concentration of solute molecules on either side of the membrane. Water passes through special membrane channels.

23 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
When comparing two solutions separated by a membrane: A hypertonic solution has a higher solute concentration. Isotonic solutions have equal solute concentrations. A hypotonic solution has a lower solute concentration.

24 Figure 5.3A Osmosis Can Modify the Shapes of Cells

25 Figure 5.3B Osmosis Can Modify the Shapes of Cells

26 Figure 5.3C Osmosis Can Modify the Shapes of Cells

27 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
The concentration of solutes in the environment determines the direction of osmosis in all animal cells. In other organisms, cell walls limit the volume that can be taken up. Turgor pressure is the internal pressure against the cell wall—as it builds up, it prevents more water from entering.

28 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Diffusion may be aided by channel proteins. Channel proteins are integral membrane proteins that form channels across the membrane. Substances can also bind to carrier proteins to speed up diffusion. Both are forms of facilitated diffusion.

29 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Ion channels are a type of channel protein—most are gated, and can be opened or closed to ion passage. A gated channel opens when a stimulus causes the channel to change shape. The stimulus may be a ligand, a chemical signal.

30 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
A ligand-gated channel responds to its ligand. A voltage-gated channel opens or closes in response to a change in the voltage across the membrane.

31 Figure 5.4 A Ligand-Gated Channel Protein Opens in Response to a Stimulus

32 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Water crosses membranes at a faster rate than simple diffusion. It may “hitchhike” with ions such as Na+ as they pass through channels. Aquaporins are specific channels that allow large amounts of water to move along its concentration gradient.

33 Figure 5.5 Aquaporins Increase Membrane Permeability to Water (Part 1)

34 Figure 5.5 Aquaporins Increase Membrane Permeability to Water (Part 2)

35 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Carrier proteins in the membrane facilitate diffusion by binding substances. Glucose transporters are carrier proteins in mammalian cells. Glucose molecules bind to the carrier protein and cause the protein to change shape—it releases glucose on the other side of the membrane.

36 Figure 5.6 A Carrier Protein Facilitates Diffusion (Part 1)

37 Figure 5.6 A Carrier Protein Facilitates Diffusion (Part 2)

38 Concept 5.2 Some Substances Can Cross the Membrane by Diffusion
Transport by carrier proteins differs from simple diffusion, though both are driven by the concentration gradient. The facilitated diffusion system can become saturated—when all of the carrier molecules are bound, the rate of diffusion reaches its maximum. ANIMATED TUTORIAL 5.1 Passive Transport Facilitated difusion by carrier proteins is specific, difusion may not be.

39 Concept 5.3 Some Substances Require Energy to Cross the Membrane
Active transport requires the input of energy to move substances against their concentration gradients. Active transport is used to overcome concentration imbalances that are maintained by proteins in the membrane.

40 Table 5.1 Membrane Transport Mechanisms

41 Concept 5.3 Some Substances Require Energy to Cross the Membrane
The energy source for active transport is often ATP. Active transport is directional and moves a substance against its concentration gradient. A substance moves in the direction of the cell’s needs, usually by means of a specific carrier protein.

42 Concept 5.3 Some Substances Require Energy to Cross the Membrane
Two types of active transport: Primary active transport involves hydrolysis of ATP for energy. Secondary active transport uses the energy from an ion concentration gradient, or an electrical gradient.

43 Concept 5.3 Some Substances Require Energy to Cross the Membrane
The sodium–potassium (Na+–K+) pump is an integral membrane protein that pumps Na+ out of a cell and K+ in. One molecule of ATP moves two K+ and three Na+ ions.

44 Figure 5.7 Primary Active Transport: The Sodium–Potassium Pump
2 K ions imported into cell and 3 Na ions exported. Important to nervous system to maintain an electrical charge differential b/w internal and external environmennts. Cardiac muscle contraction, kidney function

45 Concept 5.3 Some Substances Require Energy to Cross the Membrane
Secondary active transport uses energy that is “regained,” by letting ions move across the membrane with their concentration gradients. Secondary active transport may begin with passive diffusion of a few ions, or may involve a carrier protein that transports both a substance and ions. ANIMATED TUTORIAL 5.2 Active Transport

46 Concept 5.4 Large Molecules Cross the Membrane via Vesicles
Macromolecules are too large or too charged to pass through biological membranes and instead pass through vesicles. To take up or to secrete macromolecules, cells must use endocytosis or exocytosis.

47 Figure 5.8 Endocytosis and Exocytosis (Part 1)

48 Figure 5.8 Endocytosis and Exocytosis (Part 2)

49 Concept 5.4 Large Molecules Cross the Membrane via Vesicles
Three types of endocytosis brings molecules into the cell: phagocytosis, pinocytosis, and receptor–mediated endocytosis. In all three, the membrane invaginates, or folds around the molecules and forms a vesicle. The vesicle then separates from the membrane.

50 Concept 5.4 Large Molecules Cross the Membrane via Vesicles
In phagocytosis (“cellular eating”), part of the membrane engulfs a large particle or cell. A food vacuole (phagosome) forms and usually fuses with a lysosome, where contents are digested. LINK Review the discussion of phagocytosis in Concept 4.3

51 Concept 5.4 Large Molecules Cross the Membrane via Vesicles
In pinocytosis (“cellular drinking”), vesicles also form. The vesicles are smaller and bring in fluids and dissolved substances, as in the endothelium near blood vessels. VIDEO 5.2 Pinocytosis and membrane ruffling in a mouse epithelial cell

52 Concept 5.4 Large Molecules Cross the Membrane via Vesicles
Receptor–mediated endocytosis depends on receptors to bind to specific molecules (their ligands). The receptors are integral membrane proteins located in regions called coated pits. The cytoplasmic surface is coated by another protein (often clathrin).

53 Concept 5.4 Large Molecules Cross the Membrane via Vesicles
When receptors bind to their ligands, the coated pit invaginates and forms a coated vesicle. The clathrin stabilizes the vesicle as it carries the macromolecules into the cytoplasm. Once inside, the vesicle loses its clathrin coat and the substance is digested. APPLY THE CONCEPT Some substances require energy to cross the membrane VIDEO 5.3 Cell Visualization: Endocytosis

54 Figure 5.9 Receptor-Mediated Endocytosis (Part 1)

55 Concept 5.4 Large Molecules Cross the Membrane via Vesicles
Exocytosis moves materials out of the cell in vesicles. The vesicle membrane fuses with the plasma membrane and the contents are released into the cellular environment. Exocytosis is important in the secretion of substances made in the cell. ANIMATED TUTORIAL 5.3 Endocytosis and Exocytosis VIDEO 5.4 Exocytosis of coccoliths in a marine golden alga, Pleurochrysis

56 Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals
Cells can respond to many signals if they have a specific receptor for that signal. A signal transduction pathway is a sequence of molecular events and chemical reactions that lead to a cellular response, following the receptor’s activation by a signal.

57 Cells are exposed to many signals and may have different responses:
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals Cells are exposed to many signals and may have different responses: Autocrine signals affect the same cells that release them. Paracrine signals diffuse to and affect nearby cells. Juxtacrine signals require direct contact b/w 2 cells Hormones travel to distant cells. Autocrine: tumor cells selfstimulate cell division by making their own signals. Paracrine: neurotransmitters that are created to cross the synapse between neurons, carrying a signal ie. Pain. Juxtacrine. Signals passing through the plasmodesmata of neighboring cells. Estrogen,testosterone: travel through circulatory or vascular systems.

58 Figure 5.10 Chemical Signaling Concepts
Target cells must be capable of receiving the signal in order to respond to it.

59 Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals
Only cells with the necessary receptors can respond to a signal—the target cell must be able to sense it and respond to it. A signal transduction pathway involves a signal, a receptor, and a response.

60 A common mechanism of signal transduction is allosteric regulation.
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals A common mechanism of signal transduction is allosteric regulation. This involves an alteration in a protein’s shape as a result of a molecule binding to it. A signal transduction pathway may produce short or long term responses. See Figure 5.6

61 The change in shape initiates a cellular response.
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals A signal molecule, or ligand, fits into a three-dimensional site on the receptor protein. Binding of the ligand causes the receptor to change its three-dimensional shape. The change in shape initiates a cellular response.

62 Figure 5.11 Signal Transduction Concepts
A common mechanism of signal transduction is allosteric regulation. This involves an alteration in a protein’s shape as a result of a molecule binding to it.

63 See next slide. Note the similar shapes of the 2 molecules.

64 An inhibitor, or antagonist, can bind in place of the normal ligand.
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals Ligands are generally not metabolized further, but their binding may expose an active site on the receptor. Binding is reversible and the ligand can be released, to end stimulation. An inhibitor, or antagonist, can bind in place of the normal ligand. See Figure 5.6 INHIBITORS aka antagonist can bind to the receptor protein without activating the receptor. This prevents the normal ligand from binding. Caffeine acts as an antagonist, binding to receptors on neorons in the brain, blocking the normal ligand, adenosine. When adenosine binds the neurons, brain activity slows down causing tiredness. By blocking the adenosine binding site, caffeine prevents adenosine from slowing brain activity, keeping us awake.

65 Receptors can be classified by their location in the cell.
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals Receptors can be classified by their location in the cell. This is determined by whether or not their ligand can diffuse through the membrane. VIDEO 5.5 Cell Visualization: Signals and calcium

66 Figure 5.12 A Signal Binds to Its Receptor
Transmembrane proteins such as this HGH receptor span tne membrane (Human growth hormone)

67 Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals
Cytoplasmic receptors have ligands, such as estrogen, that are small or nonpolar and can diffuse across the membrane. Membrane receptors have large or polar ligands, such as insulin, that cannot diffuse and must bind to a transmembrane receptor at an extracellular site.

68 Receptors are also classified by their activity: Ion channel receptors
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals Receptors are also classified by their activity: Ion channel receptors Protein kinase receptors G protein–linked receptors VIDEO 5.5 Cell Visualization: Signals and calcium

69 https://youtu.be/FkkK5lTmBYQ

70 Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals
Ion channel receptors, or gated ion channels, change their three- dimensional shape when a ligand binds. The acetylcholine receptor, a ligand- gated sodium channel, binds acetylcholine to open the channel and allow Na+ to diffuse into the cell. See Figure 5.4 LINK Nerve cells communicate with muscle cells at neuromuscular junctions, which are described in Concept 36.1 The Na+ initiates a series of events that result in muscle contractions.

71 Protein kinase receptors change their shape when a ligand binds.
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals Protein kinase receptors change their shape when a ligand binds. The new shape exposes or activates a cytoplasmic domain that has catalytic (protein kinase) activity. Protein kinase activity means that target proteins in the cell have Phosphate groups added to them. ATP + Protein--P. Kinase----> ADP + phosphorylated protein Protien kinase is an enzyme that adds phosphates to other proteins, phosphorylating them. The phosphorylated protein usually undergoes some functional. change

72 Figure 5.13 A Protein Kinase Receptor
In this case, the ligand is insulin. The phosphorylated Receptor protein then phosphorylates target proteinsthat will in turn initiate the cells response. In this case, the cell would responsd by generating and inserting glucose transport proteins into the cell membrane, allowing glucose to enter the cell.

73 Protein kinases catalyze the following reaction:
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals Protein kinases catalyze the following reaction: ATP + protein  ADP + phosphorylated protein Each protein kinase has a specific target protein, whose activity is changed when it is phosphorylated.

74 G Protein linked receptors
Put your headfs down and relax. Yell. Epinephrine aka adrenalne is a hormone , the ligand that triggers the fight or flight response in animals. Here is how 1 molecule of epinephrine can instantly result in the release and mobilization of 10,000 glucose to be metabolized to power the fight or flight response.

75 Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals
Ligands binding to G protein–linked receptors expose a site that can bind to a membrane protein, a G protein. The G protein is partially inserted in the lipid bilayer, and partially exposed on the cytoplasmic surface.

76 Many G proteins have three subunits and can bind three molecules:
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals Many G proteins have three subunits and can bind three molecules: The receptor GDP and GTP, used for energy transfer An effector protein to cause an effect in the cell

77 Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals
The activated G protein–linked receptor exchanges a GDP nucleotide bound to the G protein for a higher energy GTP. The activated G protein activates the effector protein, leading to signal amplification. ANIMATED TUTORIAL 5.4 G Protein–Linked Signal Transduction and Cancer

78 Figure 5.14 A G Protein–Linked Receptor
We will see this slide again in a couple of slides Identify the 4 major components of the pathway: ligand, Gprotein linked receptor, Inactive G protein, inactive effector protein.

79 Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
Signal activation of a specific receptor leads to a cellular response, which is mediated by a signal transduction pathway. Signaling can initiate a cascade of protein interactions—the signal can then be amplified and distributed to cause different responses. VIDEO 5.6 Chemotaxis of human neutrophils

80 Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
A second messenger is an intermediary between the receptor and the cascade of responses. In the fight-or-flight response, epinephrine (adrenaline) activates the liver enzyme glycogen phosphorylase. The enzyme catalyzes the breakdown of glycogen, yielding vast amounts of glucose to provide quick energy.

81 Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
Researchers discovered that another molecule delivered the message from the “first messenger,” epinephrine, to the enzyme.

82 The second messenger was later discovered to be cyclic AMP (cAMP).
Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment The second messenger was later discovered to be cyclic AMP (cAMP). Second messengers allow the cell to respond to a single membrane event with many events inside the cell—they distribute the signal. They amplify the signal by activating more than one enzyme target. LINK Review enzyme regulation in Concept 3.4

83 Figure 5.14 A G Protein–Linked Receptor
Identify the 4 major components of the pathway: ligand, Gprotein linked receptor, Inactive G protein, inactive effector protein. 1 ligand binds 1 G protein linked receptor which has kinase activity in the intracellular side, which activates the G protein. The G protein has an GDP which it exchanges for a GTP. This causes the G protein to change shape, releasing one of its subunits, as shown in diagram 3. The change in shape allows part of the G protein to activate the effector protein which in this case is called Adenylyl cyclase. The Adenylyl cyclase converts ATP to cAMP, a second messenger which then distributes the signal to protein kinases which will activate enzymes.. We will see this in more detail in a little bit.

84 Figure 5.16 The Formation of Cyclic AMP
CyclicAMP (cAMP) is the primary second messanger involved in many sensory responses in animals.

85 Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
Signal transduction pathways involve multiple steps—enzymes may be either activated or inhibited by other enzymes. In liver cells, a signal cascade begins when epinephrine stimulates a G protein–mediated protein kinase pathway.

86 Epinephrine binds to its receptor and activates a G protein.
Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment Epinephrine binds to its receptor and activates a G protein. cAMP is produced and activates protein kinase A—it phosphorylates two other enzymes, with opposite effects: Inhibition Activation

87 Figure 5.17 A Cascade of Reactions Leads to Altered Enzyme Activity (Part 1)
Here is where the cascade part comes in. 1 molecule of epinephrine, activates 1 G protein, which activates 1Adenylyl cyclase. This in turn causes ATP molecules to drop 2 phosphates and be converted into 20 molecules of cAMP, which can activate 100 protein kinase A molecules. This step also inactivates another enzyme called glycogen synthase. Glycogen synthase stores glucose molecules as glycogen.

88 Figure 5.17 A Cascade of Reactions Leads to Altered Enzyme Activity (Part 2)
The activated Protein kinase A enzymes will then activate 1000 glycogen phosphorylase enzymes which break down glycogen, liberating 10,000 molecules of glucose, to power muscle contraction in the heart and throughout the body. The

89 Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
Inhibition—protein kinase A inactivates glycogen synthase through phosphorylation, and prevents glucose storage. Activation—Phosphorylase kinase is activated when phosphorylated and is part of a cascade that results in the liberation of glucose molecules. See Figure 5.17, step 1 See Figure 5.17, steps 2 and 3 ANIMATED TUTORIAL 5.5 Signal Transduction Pathway

90 We just saw how this signal transduction pathway when occuring in liver and cardiac muscle cells liberates 10,000 molecules of glucose ready to power fight or flight muscle contractions and increase the heart rate to deliver blood faster.. Interestingly, the same pathway in cells in smooth muscle cells lining the intestines have a very different result. Here, the same pathway with the same players, inhibit enzymes. The result is that smooth muscle relaxes, increasing the diameter of blood vessels, allowing more nutrients to be carried form the digestive tract to the rest of the body.

91 Resources/Animated Tutorials/pol2e_at_0506_Signal_Transduction_Pathway/pol2e_at_0506_Signal_Transduction_Pathway.html

92 Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
Signal transduction ends after the cell responds—enzymes convert each transducer back to its inactive precursor. The balance between the regulating enzymes and the signal enzymes determines the cell’s response.

93 BOZEMAN

94 Cells can alter the balance of enzymes in two ways:
Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment Cells can alter the balance of enzymes in two ways: Synthesis or breakdown of the enzyme Activation or inhibition of the enzymes by other molecules

95 Cell functions change in response to environmental signals:
Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment Cell functions change in response to environmental signals: Opening of ion channels Alterations in gene expression Alteration of enzyme activities See Figure 5.4 See Figure 5.17 VIDEO 5.7 Calcium waves in brain glial cells

96 Answer to Opening Question
Caffeine is a large, polar molecule that binds to receptors on nerve cells in the brain. Its structure is similar to adenosine, which binds to receptors after activity or stress and results in drowsiness. Caffeine binds to the same receptor, but does not activate it—the result is that the person remains alert.

97 Figure 5.19 Caffeine and the Cell Membrane (Part 1)
Red is caffeine or adenosine, fitting into the receptor binding site. Adenosine causes drowsiness, caffeine prevents the binding of adenosine, resulting in alert feeling.

98 Figure 5.19 Caffeine and the Cell Membrane (Part 2)


Download ppt "Cell Membranes and Signaling"

Similar presentations


Ads by Google