Chapter 3: Exchanging Materials with the Environment. Cellular Transport Transport across the Membrane

Transcription

1 Chapter 3: Exchanging Materials with the Environment Cellular Transport Transport across the Membrane

2 Transport? Cells need things water, oxygen, balance of ions, nutrients (amino acids, sugars..building blocks), nucleotides, hormones Cells need to get rid of things waste (carbon dioxide, ammonia, any material that has been broken down) Transport allows these materials into a cell and allows these materials to leave the cell across the cell membrane.

3 The Cell Membrane

4 ALL cells have a cell membrane (also called the plasma membrane, phospholipid bilayer, fluid mosaic model).

5 Why is it called the FLUID MOSAIC MODEL? FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. 5

6 Functions of the Cell Membrane Selectively Permeable allows certain things to enter and leave the cell (transport). Acts as a protective barrier. Recognizes other cells/things nearby.

7 Parts to the Cell Membrane proteins proteins

8 Contains 2 fatty acid chains Make that up the are cell nonpolar membrane (repel charged particles but let fat-soluble molecules to pass) Phospholipids Head is polar & contains a Phosphate group & glycerol 8

9 Membrane transport properties: The structure of the lipid bilayer dictates that most polar compounds are unable to pass through it unless assisted by some transport mechanism. Large molecules (macromolecules) cannot freely cross the membrane. Small non-charged molecules, particularly if they are lipid soluble, have no difficulty crossing the membrane. Gases can also diffuse through the lipid bilayer (ex. Lungs). Water passes into and out of cells with relative ease.

10 Polar heads (phosphate heads) are hydrophilic (water loving) Nonpolar tails (fatty acid tails) are hydrophobic (water fearing) This makes the cell membrane selective in what crosses.

11 Cell Membrane The cell membrane is made of 2 layers of phospholipids called the lipid bilayer Hydrophobic molecules pass easily; hydrophilic DO NOT 11

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13 Another Look at the CM proteins proteins

14 Parts of Cell membrane Proteins Embedded throughout the cell membrane Receptor proteins Communication proteins Act as channels that allow materials through Hold glycoproteins that allow for cell recognition Glycoproteins Carbohydrate chains attached to the proteins embedded in the cell membrane Act as antennae that detect cells and materials nearby

15 Importance of Protein Channels

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17 Cholesterol? Major membrane lipid Similar to phospholipids-one end is hydrophilic and one end is hydrophobic Makes the membrane less permeable to most biological molecules Lowers the temperature that a membrane solidifies and it decreases fluidity at higher temperatures

18 Importance of Glycoproteins & Glycolipids Embedded in cell membrane Sometimes have sugar chains attached to the proteins or sugar chains attached to the phospholipids Function: act as antennae that receive chemical messages from other cells and function in cell recognition

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20 Getting through the Cell Membrane Can pass easily Small hydrophobic nonpolar molecules move through easily. e.g. O 2, CO 2, N 2, Small uncharged polar molecules that are soluble in lipids (fat-soluble) can pass easily e.g. ethanol, glycerol, H2O Cannot pass easily Ions (charged particles), hydrophilic molecules larger than water, and larger uncharged polar molecules do not move through the membrane on their own. e.g. H+ ions, Ca+ ions, Na+ ions, Cl- ions, amino acids, glucose, nucleotides

21 So what determines if material can cross write this down! Polarity In general, nonpolar molecules do not interact with polar molecules (oil-nonpolar, water-polar) Polar molecules interact with polar molecules (salt ion, water-polar) Hydrophobicity- lipid bilayer is hydrophobic so would repel hydrophilic molecules. Hydrophobic molecules can pass Charge- the hydrophobic tails will not allow charged particles to cross...they need special transport proteins

22 Review Questions 1. What materials need to be exchanged across a cell membrane? 2. In what way is an organism a protected compartment? 3. What is the significance of a membrane being selectively permeable?

23 Answers to Review Questions 1. CM must control the exchange of nutrients, waste, water, and communication signals 2. An organism is a protected compartment in the sense that whether it is made of a single cell or many, each cell is completely surrounded by a protective membrane 3. A cell membrane must be selectively permeable so that the cell can exert some level of control over which types of molecules can pass through the membrane

24 3.3 Diffusion and Osmosis

25 Movement of molecules from high concentration to low concentration (down the concentration gradient like balls rolling down a hill).

26 Concentration Gradient Refers to a change in solute concentration, either from a low concentration to a high one or the opposite. Diffusion moves molecules down a concentration gradient, but it cannot transport molecules against a concentration gradient.

27 Diffusion Diffusion is a PASSIVE process requires no energy from the cell Molecules will diffuse until the concentration is the same throughout Does diffusion increase or decrease entropy of a system?

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29 Osmosis Diffusion of water across the cell membrane Water moves from high to low concentration Water will always move to where there is more solute! Does not require energy from the cell (passive)

30 Water will always move to where there is more solute! low solute high solute

31 Osmotic States of a Cell Isotonic state solute concentration inside the cell and outside the cell is equal. No movement of water Hypotonic state the solute concentration inside the cell is lower than outside the cell. Water will move out of the cell. The cell will shrink Hypertonic state the solute concentration inside the cell is higher than outside the cell. Water will move into the cell. The cell will swell/expand

32 Cell in Isotonic Solution 10% NaCL 90% H 2 O ENVIRONMENT CELL 10% NaCL 90% H 2 O NO NET MOVEMENT What is the direction of water movement? The cell is at. 32

33 Cell in Hypotonic Solution 10% NaCL 90% H 2 O CELL 20% NaCL 80% H 2 O What is the direction of water movement? 33

34 Cell in Hypertonic Solution 15% NaCL 85% H 2 O ENVIRONMENT CELL 5% NaCL 95% H 2 O What is the direction of water movement? 34

35 Cells in Solutions copyright cmassengale 35

36 Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Cell bursts (CYTOLYSIS) Cell shrinks & shrivels (PLASMOLYSIS) 36

37 Cytolysis & Plasmolysis Cytolysis copyright cmassengale Plasmolysis 37

38 Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic copyright cmassengale 38

39 Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells. These channels are widely distributed in all kingdoms of life, including bacteria, plants, and mammals. Aquaporins

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41 What happens in plant cells? Plant cells have a cell wall (which means extra protection from bursting) animal cells do not. Turgor is the outward pressure of a cell against its cell wall. Flaccid- opposite. Lacking firmness or turgor

42 Plasmolysis- when the cell membrane of a plant cell pulls away from the cell wall due to the loss of water through osmosis

43 Plasmolysis

44 hypotonic hypertonic isotonic hypertonic isotonic hypotonic copyright cmassengale 44

45 3.4 Passive & Active Transport

46 Passive Transport Simple Diffusion Doesn t require energy Moves high to low concentration Example: Oxygen diffusing into a cell and carbon dioxide diffusing out. 46

47 Passive Transport Facilitated diffusion Doesn t require energy Uses transport proteins to move molecules from a high to low concentration Examples: Glucose or amino acids moving from blood into a cell. 47

48 Types of Transport Proteins Channel proteins are embedded in the cell membrane & have a pore for materials to cross Carrier proteins can change shape to move material from one side of the membrane to the other copyright cmassengale 48

49 Active Transport Requires energy or hydrolysis of ATP Moves materials from LOW to HIGH concentration AGAINST concentration gradient 49

50 Active transport Examples: Pumping Na + (sodium ions) out and K + (potassium ions) in against strong concentration gradients. This is called Na+-K+ Pump copyright cmassengale 50

51 Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; 51 creates a membrane potential

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53 More Active Transport requires energy! EXOCYTOSIS getting things out of the cell Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. Example: This is how many hormones are secreted and how nerve cells communicate with one another. 53

54 Exocytosis vesicle immediately after fusion with plasma membrane. copyright cmassengale 54

55 Exocytosis Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell copyright cmassengale Cell environment 55

56 ENDOCYTOSIS getting things INTO the cell copyright cmassengale 56

57 2 types: Pinocytosis and Phagocytosis 57

58 Pinocytosis Most common form of endocytosis. Taking in dissolved (LIQUID) molecules-cell drinking - think pino colada!

59 Phagocytosis The cell engulfs large particles such as food, bacteria, etc. into vesicles cell eating (foodphago) 59

60 Phagocytosis About to Occur copyright cmassengale 60

61 Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) copyright cmassengale 61

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63 Three Forms of Transport Across the Membrane 63

64 Cystic Fibrosis why protein channels are important!

65 Review Summary Questions 1. What is a concentration gradient? How does it affect diffusion? 2. Explain the differences between active & passive transport. Why is it important to a cell? 3. In what way is a cell membrane selective? 4. Would you expect osmosis and diffusion to stop when substances are evenly distributed? 5. What type of evidence demonstrates active transport? 6. How do membranes regulate the movement of molecules into and out of the cell?

66 Answers to Review Questions 1. Refers to a change in solute concentration, from a high to low concentration, or from low to high. 2. Active transport uses energy to move molecules against their concentration gradient. Passive transport describes transport of molecules down their concentration gradient & is accomplished without the input of energy.

67 Answers cont. 3. The cell membrane allows small molecules to pass through but restricts the movement of large molecules. It uses a variety of transport proteins to help move certain large molecules wither with or against their concentration gradients. It also contains transport proteins that help transport ions across the membrane. 4. When substances attain equal distribution over an area, there is no longer any net movement of the substance, and diffusion (or osmosis) stops.

68 Answers cont. 5. Since substances cannot move against their concentration gradients, the observation that some substances do move into areas of higher concentration suggests that some energyrequiring process must be involved in this movement. 6. Membranes regulate movement of molecules by providing barriers to certain larger molecules. Other molecules are regulated by specific transport proteins or by coupling the movement of one type of molecule to the movement of another type of molecule.

69 Notes Gas Exchange (O 2 and CO 2 ) in Aquatic Organisms

70 How do Fish Breathe?

71 Countercurrent flow gas exchange in fish The gills of fish utilize countercurrent flow, a very effective mechanism for removing the maximum amount of oxygen from the water flowing over them During countercurrent flow, two types of fluids (in this case blood and water) flow in opposite directions past one another. These fluids are separated by thin membranes. Countercurrent flow promotes diffusion of oxygen down its concentration gradient from water into the blood.

72 Gas Exchange in the Land Dwellers In order for oxygen and carbon dioxide to enter or leave the cell, they must be dissolved in water SO that happens across a membrane. Exchange surfaces are in an interior space. It protects the surface from excess evaporation caused by contact with outside air.

73 Gas Exchange- Grasshopper Small branched air ducts. The ducts branch into smaller and smaller tubes providing a large surface area relative to volume.

74 Gas Exchange - Human Alveoli-air sacs that make up the lungs. One cell thin Capillaries surround alveoli. Capillaries are also one cell thin Gas exchange occurs between alveoli & capillary walls

75 Human Respiratory System

76 Alveoli with surfactant Surfactant chemical that prevents alveoli from closing

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79 Surfactant secreting cells

80 O 2 = transported by the hemoglobin molecule in the red blood cells. Each hemoglobin molecule carries 4 molecules of O 2. Each polypeptide chain contains: Hemoglobin

81 Bohr Shift-in muscle cells At rest, PO 2 is lower, ph Is normal, O 2 is released from hemoglobin During exercise, muscle Releases more CO 2, decreasing ph, and PO 2 is higher so hemoglobin releases MORE O 2 (Bohr shift)

82 Bohr Shift When the blood is fully saturated all the erythrocytes are in the form of oxyhemoglobin. As the erythrocytes travel to tissues deprived of oxygen the partial pressure of oxygen will decrease. Consequently, the hemoglobin releases the oxygen to form hemoglobin

83 Breathing rate varies with exercise. Changes in carbon dioxide concentration leads to a lowering of blood ph. This is detected by chemosensors in the aorta and carotid arteries that send impulses to the breathing center of the brain. Nerve impulses are then sent to the diaphragm and the intercostal muscles to increase contraction or relaxation rates.

84 Asthma

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86 Human Urinary System/Excretory System MAINTAINS HOMEOSTASIS. Important for eliminating metabolic waste (waste produced from metabolism) Maintains the appropriate water-salt balance in the blood Maintains blood pressure Maintains Acid-base balance of blood Secretes hormones

87 Organs of the Urinary System Kidneys 2 Ureters 2 Urinary bladder -1 Urethra 1 Lump of glandular tissue on each kidney these are the adrenal glands.

88 Kidneys Main organs of the Urinary System Bean shaped/reddish brown and fist sized Covered by a tough capsule of connective tissue called the renal capsule Renal arteries bring blood to the kidneys Renal veins carry blood away from the kidneys Anytime you see the word renal think kidneys

89 Extend from kidneys to bladder Peristalsis of ureters cause urine to enter the bladder Ureters

90 UrinaryBladder Recieves urine from the ureters Stores urine until it is expelled from the body Urine enters the bladder in spurts 1-5 spurts per minute.

91 Urethra Small tube that extends from the bladder to an external opening When the urinary bladder fills to about 250 ml of urine, stretch receptors and nerve impulses cause the urinary bladder to contract, sphincters to relax - and you pee.

92 Cortex- outer layer Anatomy of the Kidney Medulla middle that consists of tissue masses Pelvis central space that is continuous with the ureter Each kidney is composed of over one million nephrons

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94 Nephrons (kidney tubules) Each kidney is composed of over one million microscopic nephrons Long, coiled tube with one cuplike end that fits over a mass of capillaries, the other end opens into a duct that collects urine. Cup of nephron Glomerulus capsule or Bowman s capsule Ball of capillaries within the cup - Glomerulus

95 3 Functions of the nephron Filtration Reabsorbtion Secretion

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101 Filtration Filtration: fluid portion of the blood is forced into the glomerular capsule (filtrate) Happens in the glomerulus capsule Water, salts, nutrients (glucose, amino acids, small proteins), nitrogenous waste (urea) Blood cells and large blood proteins are NOT filtered

102 Reabsorption Reabsorption absorbing again (into blood) Cells of tubules reabsorb substances needed by the body from the filtrate. happens in the proximal (close to the capsule) kidney tubules of nephron Nutrients (glucose, amino acids) and salt molecules

103 Secretion Secretion: Process of secreting a substance from the blood into the kidney tubules Happens between the nephron capillaries and the distal (far away from capsule) kidney tubules of the nephron (countercurrent exchange) Anything that wasn t filtered at the glomerulus capsule or anything that was reabsorbed that shouldn t have been H+ ions, K+ ions, creatinine and drugs

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105 Urea comes from the breakdown of amino acids. So Urine Contains: 1. Substances that have undergone filtration but have not been reabsorbed 2. Substances that have undergone secretion

106 Urea: CH 4 N 2 O is the primary Nitrogenous end product of metabolism. Amino acids broken down in the liver causing the liver to release ammonia- toxic to cells. The liver combines the ammonia with carbon dioxide to make urea not toxic to cells and can be released in urine. Creatinine: C 4 H 9 N 3 O 2 High energy phosphate reserve molecule in muscles Uric Acid: C 5 H 4 N 4 O 3 From the breakdown of nucleic acids

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108 Blood pressure regulation ADH and aldosterone are two of the most important hormones needed in the regulation of blood pressure. When blood pressure (BP) goes down, the body will automatically counter it by starting a systemic change to increase the BP. When the person is severely dehydrated, the body has no other option but to limit urine output and conserve more water for the body cells to use. These processes can be carried out by two hormones aldosterone and ADH (Anti-diuretic hormone) Although both hormones have the same ultimate goal of water preservation or retention, they do it differently.

109 Aldosterone & ADH Aldosterone Adrenal cortex ADH- Hypothalamus

110 ADH ADH regulates the rate or amount of water reabsorption at the distant tubules of the kidney s nephrons ADH also has the ability to reabsorb urea which, in turn, reabsorbs water through osmosis

111 Aldosterone Aldosterone, like ADH also acts on the distant tubules, but also at the kidney s collecting ducts. Water retention with the aid of aldosterone is more complex because it has to undergo the Sodium-Potassium exchange channels. In this setup, potassium is excreted while sodium is retained

112 ADH vs. Aldosterone ADH is synthesized in the hypothalamus while aldosterone is made in the adrenal cortex of the adrenal glands on top of the kidneys. ADH conserves water directly through its reabsorption while aldosterone conserves water indirectly through the reabsorption of sodium.

113 Transpiration in Plants Gases leave through openings in leaves- called Stomates Leaves covered with waxy cuticle to prevent water loss

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