Chapter 7 3 Cell Membrane Structure Membrane Transport
Chapter 7 -3 Cell Membrane Structure & Membrane Transport
Homeostasis • Maintaining constant or stable internal conditions • How does your body regulate (aka maintain) homeostasis? • Much of homeostasis is maintained by the cell membrane controlling movement of things in & out of the cell • Needed materials must move into cells ex. O 2 & glucose for cell. resp. • Waste must move out ex. CO 2 from cell. resp.
The Cell Membrane • Gatekeeper • Semipermeable/ selectively permeable- some substances can pass directly through the membrane & others cannot • Main components: proteins & phospholipids
Fluid Mosaic Model • Phospholipid bilayer: made up of 2 rows of phospholipids, * heads (hydrophilic- “waterloving) outside * tails (hydrophobic-”waterhating”) on the inside • Cholesterol molecules that provide strength & fluidity to the cell • Proteins: act as channels & also act as support in cytoskeleton • Carbohydrates: act as ID tags
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 5 membrane is viewed from above.
https: //www. youtube. com/watch? v=Pfu 1 DE 9 PK 2 w
Movement through the Cell Membrane • Passive transport- movement of a substance from an area of high concentration to an area of low concentration. • Does NOT require cellular energy Over time…
Passive Transport • Dependent upon the permeability of the cell membrane • 3 main types: – Diffusion – Facilitated diffusion – Osmosis • Ex: – Gas exchange (O 2 into a cell, CO 2 out of a cell)
Diffusion • Spreading of molecules from areas of high concentration areas of lower concentration • Can happen with or w/out a membrane • With membrane: Molecules move from one side of the membrane to the other- directly through the membrane (w/out need of membrane protein) • Molecules tend to “spread out” • Along the concentration gradient- difference in conc. • Requires no energy
Equilibrium • When molecules are evenly spread throughout a space
Facilitated Diffusion • A transport protein acts as a protein channel to help (facilitate) the diffusion of molecules that normally couldn‘t pass through the cell membrane (large molecules & polar molecules) • Molecules move down a concentration gradient, from high conc. to an area of low conc. – Ex. Glucose/sugar, sodium/salt Over time…
Osmosis • The diffusion of water across a membrane • The cell membrane is selectively permeable • Aquaporins- channel proteins that allow water to pass through them • Watch the animation Over time…
Osmosis v Water flows from an area with a higher water conc. to an area of lower water conc. in an attempt to “even out” the conc. on each side of the membrane. v. Tries to “water down” the side with more solute
• Ex: Osmosis – Large intestine reabsorbs water by osmosis which keeps the body’s systems from dehydrating
Rule for Osmosis: …the water toward it. • If the area outside the cell has more salt – then water will be sucked out of the cell
Solutions • • Mixtures of substances Ex. Salt + water; sugar + water Solute Solvent
Cells In Different Solutions * If cells are placed in solutions very different in concentration from itself, the cell may be damaged & shrivel or lyse (burst)
Hypotonic Solution • Hypo = less • Cell may burst, or organelles called “contractile vacuoles” remove excess water • Lower solute outside, higher solute inside
Hypertonic Solution • Hyper = more • Cell will shrink or die, plants wilt • Higher solute outside, lower solute inside Why is it dangerous to drink sea water? Why does pouring salt on a slug kill it?
Isotonic Solution • Iso = same • Water conc. same inside & out • No net movement of water (water moves in & out of cell at a constant rate
What happens to the cell in each solution? Blood in Isotonic Solution Blood in Hypertonic Solution Blood in Hypotonic Solution
Passive Transport: Osmosis Hypertonic H 2 O Cell shrivels Hypotonic Isotonic H 2 O Cell swells H 2 O Cell stays the same
Practice Time! ENVIRONMENT CELL 20% Na. Cl 80% H 2 O The cell is in a 10% Na. Cl 90% H 2 O HYPOTONIC solution and will SWELL.
Practice Time! ENVIRONMENT CELL 5% Na. Cl 95% H 2 O 15% Na. Cl 85% H 2 O The cell is in a HYPERTONICsolution and will SHRIVEL.
Practice Time! ENVIRONMENT CELL 10% Na. Cl 90% H 2 O The cell is in a ISOTONIC 10% Na. Cl 90% H 2 O solution and will STAY THE SAME.
ACTIVE TRANSPORT • Requires the cell to use energy ATP • Against concentration gradient (low to high conc. )- “uphill” 2 Types: 1. Pumps 2. Movement of the Cell Membrane
1. ) Molecular Pumps • When a cell uses energy to change shape & pump molecules across the membrane through a transport protein/ pump. • This allows a cell to concentrate key molecules within the cell, or remove waste quickly from the cell. – Ex. Calcium (Ca 2+), potassium (K+), chlorine (Cl-) & sodium (Na+) = ions (charged particles) ENERGY Over time…
2. ) Movement of the Cell Membrane: 2 Types: 1. ) Endocytosis • A cell uses energy to import materials INTO the cell using a vesicle • Ex. White blood cells engulf bacteria to fight infection
http: //academic. brooklyn. cuny. edu/biology/bio 4 fv/page/phago. htm http: //academic. brooklyn. cuny. edu/biology/bio 4 fv/page/endocytb. htm
Endocytosis- 2 Types: 1. Phagocytosis • Cell “eating” • Cell engulfs solids into vesicle & “digests” them 2. Pinocytosis (think “pineapple juice”) • Cell “drinking” • Cell engulfs liquids into vesicle & “digests” them http: //highered. mheducation. com/olcweb/cgi/pluginpop. cgi? it=swf: : 535: : /sites/dl/free /0072437316/120068/bio 02. swf: : Endocytosis%20 and%20 Exocytosis
Movement of the Cell Membrane: 2 Types: 2. ) Exocytosis • A cell uses energy to export materials OUT OF the cell using a vesicle • Ex. Nerve cells release neurotransmitters to pass signals to the brain
• Examples: Wastes, Secretions, Digestive Enzymes, Hormones, Insulin
• Removing large particles (waste) from the cell • Stuff “exits” the cell • Watch video at • Mc. Graw Hill Site
Passive Transport vs. Active Transport
https: //www. youtube. com/watch? v=Hq. Kl. Lm 2 Mjk. I
Add to Word List • • • Active Transport Endocytosis Phagocytosis Pinocytosis Exocytosis Protein Pump
2. ) Movement of the Cell Membrane 2 Types: 1. ) Endocytosis • Taking “in” large molecules by the cell • Phagocytosis = taking in food particles • Pinocytosis = liquid substances
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