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___________________________________ Chapter 5 – The Plasma Membrane and Transport

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State Standard • Standard 1.a.

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Membrane Function 1. Forms a boundary between living cells and their surroundings. 2. Controls the movement of molecules into and out of the cell - Selective permeability –

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Membrane Function

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3.

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4. Membranes can contain enzymes that function in various chemical reactions.

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Membrane Structure

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• The plasma membrane is 8 nm thick. • It is mainly made up of

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Membrane Structure

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Membrane phospholipids • Phospholipids have a hydrophilic head and two hydrophilic tails.

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Membrane phospholipids • The phospholipids - The hydrophilic heads face outward and the hydrophobic tails face inward

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Hydrophobic tails

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Membrane Proteins • Membrane proteins are found within the phospholipid bilayer Phospholipid bilayer Integral Protein

Peripheral protein

– integral proteins • They can be found embedded on either surface – peripheral proteins

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Functions of Membrane Proteins

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___________________________________ • Some proteins transport substances across the membrane by forming channels or by

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Membrane Proteins Functions of membrane proteins include: • Transport of substances across the membrane • Join cells to one another • Bind to chemical messengers from other cells • Act as identification tags so • Attach to cytoskeleton and the extracellular matrix

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Membrane cholesterol and carbohydrates Cholesterol • Cholesterol is found within the phospholipid bilayer • It helps

Carbohydrates • Located on outer layer of membrane only • Bound to proteins (glycoproteins) or phopholipids (glycolipids) • Act as identification tags for

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Fluid Mosaic Model

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Fluid Mosaic Model • The membrane is a fluid mosaic • Fluid – the phospholipids and the proteins drift within the membrane • Mosaic – the diversity of proteins found within the membrane and the

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Transport Across the Membrane

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Diffusion • The tendency of particles of any kind to spread from regions of

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Transport Across the Membrane Passive Transport

- They spread from areas of high concentration to areas of lower concentration - At equilibrium the molecules continue to move but there is no net change in the concentration on either side of the membrane

Molecule of dye

Membrane

EQUILIBRIUM

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Transport Across the Membrane

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• Osmosis is

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• Water travels from an area of lower solute concentration to an area of higher solute concentration

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Transport Across the Membrane • Hypertonic - the solution with the higher solute concentration • Hypotonic - the solution with the lower solute concentration • Water moves from the

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Transport Across the Membrane • Water continues to cross the membrane until the solute concentrations are equal on both sides of the membrane • Isotonic - solutions with equal solute concentrations • Water molecules continue to move across the membrane but

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Osmosis Problems – Draw a diagram illustrating the problem, identify the solutions as hyper, hypo or isotonic, and show the direction osmosis will occur

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1. A cell containing 2% solute is placed in a solution containing 10% solute.

4. A candy containing 10% water is placed in a solution containing 90% water.

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2. A candy containing 15% solute is placed in a solution containing 12% solute.

5. A fish contains 95% water lives in freshwater that contains 68% water.

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3. A cell containing 7% solute is placed in a solution containing 9% solute.

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How Does Osmosis Affect Cells? Distilled Water

3x Saline

Induces turgor in cells

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Induces turgor in animal cells Makes plant cell pull away from cell wall

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Makes plant cell lyse Makes animal cell lyse Makes animal cell shrivel

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How Does Osmosis Affect Cells? 1. Explain the different outcomes of adding distilled water to the plant and animal cells. 2. Which conditions best model the effects of drought on plant cells? Explain your answer. 3. Hypothesize why plants grow better when the water surrounding their cells is slightly hypotonic to the cell.

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Water balance between cells and their surroundings is crucial to organisms

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• Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution.

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Transport Across the Membrane

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• Small non-polar molecules diffuse freely through the phospholipid bilayer

Solute molecule

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Transport protein

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Transport Across the Membrane Active Transport

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Transport Across the Membrane

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• Transport proteins can move solutes across the membrane

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- This is called active transport • Active transport requires ATP – cells use energy to move the molecule across the membrane. • The solute is moved from

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Transport Across the Membrane • To move large molecules or particles across the membrane a vesicle may fuse with the membrane and expel its contents –

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Transport Across the Membrane • Or the membrane may fold inward, trapping material from the outside, and form a vesicle that carries the material into the cell –

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Transport Across the Membrane

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• There are 3 kinds of endocytosis Pseudopod of the amoeba

Food being ingested

Plasma membrane

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Material bound to receptor proteins

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Transport Across the Membrane

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There are 3 kinds of endocytosis: 1. Phagocytosis – a cell brings in

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2. Pinocytosis – the cell takes in

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3. Receptor-mediated endocytosis – specific molecules bind to receptors on the membrane that signal to the cell to take the molecule in

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___________________________________ • Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors

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How Does Osmosis Affect Cells? Distilled Water

3x Saline

Induces turgor in plant cell Induces turgor in animal cell Makes plant cell pull away from cell wall Makes plant cell lyse Makes animal cell lyse Makes animal cell shrivel •

Explain the different outcomes of adding distilled water to the plant and animal cells.

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Which conditions best model the effects of drought on plant cells? Explain your answer.

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Hypothesize why plants grow better when the water surrounding their cells is slightly hypotonic to the cell.