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 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.

10 Cell Membrane The cell membrane is made of 2 layers of phospholipids called the lipid bilayer Hydrophobic molecules pass easily; hydrophilic DO NOT 10

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12 Another Look at the CM proteins proteins

13 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

14 Importance of Protein Channels

15 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

16 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. H 2 O, ethanol, glycerol 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

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18 So what determines if material can cross? 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

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20 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?

21 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

22 3.3 Diffusion and Osmosis

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

24 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.

25 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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27 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)

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

29 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

30 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. 30

31 Cell in Hypotonic Solution 10% NaCL 90% H 2 O CELL 20% NaCL 80% H 2 O What is the direction of water movement? 31

32 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? 32

33 Cells in Solutions copyright cmassengale 33

34 Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Cell bursts (CYTOLYSIS) Cell shrinks & shrivels (PLASMOLYSIS) 34

35 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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37 Cytolysis & Plasmolysis Cytolysis copyright cmassengale Plasmolysis 37

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

39 What Happens to Blood Cells? copyright cmassengale 39

40 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

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

42 Plasmolysis

43 hypotonic hypertonic isotonic hypertonic isotonic hypotonic copyright cmassengale 43