- Slides: 60
Cell Membrane • • Boundary that separates the living cell from it’s non-living surroundings. Phospholipid bilayer Amphipathic - having both: hydrophilic heads hydrophobic tails Phospholipid ~8 nm thick
Cell Membrane - cont. • Controls traffic into and out of the cell with phospholipids and transport proteins. • Selectively permeable Transport protein
Selective Permeability • The property of biological membranes which allows some substances to cross more easily than others.
Fluid Mosaic Model • 1972 - Singer and Nicolson called the membrane a “Fluid Mosaic Model”. • Mosaic: different proteins embedded in the phospholipids. • Fluid: proteins and phospholipids can move freely in the membrane.
Fluid Mosaic Model- cont. • Components of a phospholipid bilayer. 1. phospholipids 2. proteins - enzymes, receptors, transport. 3. glycolipids 4. glycoproteins 5. carbohydrates 6. cholesterol
Animal Cell’s Cell Membrane
What are typical roles of proteins in the cell membrane?
Some Functions of Membrane Proteins
What is Diffusion?
Diffusion • The net movement of a substance (molecules) down a concentration gradient from an area of high concentration to an area of low concentration • passive transport: NO energy is expended. • facilitated diffusion: type of passive transport which uses transport proteins.
• What is osmosis?
Osmosis • The movement of water across selectively permeable membranes • The water moves from a high concentration to low concentration
Question: What’s in a Solution? Answer: • solute + • Na. Cl + H 20 solvent solution saltwater
Hypertonic • A solution with a greater solute concentration compared to another solution 3% Na. Cl 97% H 2 O Red Blood Cell solution 5% Na. Cl 95% H 2 O
Hypotonic • A solution with a lower solute concentration compared to another solution 3% Na. Cl 97% H 2 O Red Blood Cell solution 1% Na. Cl 99% H 2 O
The contractile vacuole of Paramecium: an evolutionary adaptation for osmoregulation
Movement of H 2 O • Water will “ALWAYS” diffuses down a concentration gradient from a HYPOTONIC solution to a HYPERTONIC solution “ALWAYS REMEMBER” • HYPOTONIC HYPERTONIC • Water flows towards the solutes!!
Isotonic • A solution with an equal solute concentration compared to another solution 3%Na. Cl 97% H 2 O Red Blood Cell solution 3%Na. Cl 97% H 2 O
Do Water Molecules Stop Moving in Isotonic Conditions? • No. • They continue to diffuse, however there is no net movement! • In general, which way does water move? • From hypotonic to hypertonic!
Elodea in Distilled Water
Elodea in Salt Water
Which way will the water move?
Plant Cells • When the plasma membrane pulls away from the cell wall (vacuole empty) in a hypertonic environment (loss of water) is called PLASMOLYSIS. Water plasma membrane Cell Water
Plant Cells • Firmness or tension (vacuole full) that is found in plant cells (cell wall) that are in a hypotonic environment is called TURGID. • This process is called TURGOR PRESSURE. Water Cell Water Central Vacuole Water
Water Balance in Cells
A watered tomato plant regains its turgor
Animal Cells • Animal cells placed into a hypotonic solution will HEMOLYSIS (EXPLODE). • Animal cells placed into a hypertonic solution will CRENATE (SHRIVEL). Hemolysis Crenation Red Blood Cells
Facilitated Diffusion • Diffusion of solutes with the help of transport proteins. (passive transport) • Example: How glucose enters cells • Why do these solutes need a protein to facilitate their diffusion?
That’s right! Because they are too polar or too large to pass through the lipid bilayer Facilitated Diffusion: http: //highered. mheducation. com/sites/0072495855/stud ent_view 0/chapter 2/animation__how_facilitated_diffusi on_works. html
Two Models for Facilitated Diffusion Channel Protein Carrier Protein
Active Transport • The movement of molecules (small or large) across the plasma membrane in which energy (ATP) is required • Examples: 1. 2. 3. Sodium (Na) - Potassium (K) Pump Exocytosis Endocytosis
Review of Passive and Active Transport:
• A transport protein that generates voltage across a membrane is called an electrogenic pump. • One example is the sodium potassium pump
The Sodium-Potassium Pump: a Specific Case of Active Transport
Active Transport Animations: http: //www. biologyalive. com/life/classes/apbiology/documents/Unit%204/07_Le ctures_PPT/media/07_16 Active. Transport_A. swf Sodium-Potassium Pump: http: //highered. mheducation. com/sites/9834092339/student_view 0/chapter 5/so dium-potassium_exchange_pump. html http: //highered. mheducation. com/sites/0072495855/student_view 0/chapter 2/an imation__how_the_sodium_potassium_pump_works. html Proton Pumps: http: //highered. mheducation. com/olc/dl/120068/bio 05. swf http: //highered. mheducation. com/sites/9834092339/student_view 0/chapter 5/pr oton_pump. html Endocytosis and Exocytosis: http: //highered. mheducation. com/olc/dl/120068/bio 02. swf
Proton pumps are the main electrogenic pumps of bacteria, fungi and plants.
Transport Proteins • Transports molecules or ions across biological membranes using active transport. • 3 types of transport proteins: proteins 1. uniport 2. symport 3. antiport
Uniport Transport Protein • Carries a single solute across the membrane. extracellular fluid intracellular fluid
Symport Transport Protein • Translocates 2 different solutes simultaneously in same direction. • Ex: amino acids that enter the intestine require simultaneous binding of Na and an amino acid to the same transport protein. extracellular fluid intracellular fluid
Antiport Transport Protein • Exchanges 2 solutes by transporting them in opposite directions extracellular fluid intracellular fluid
Sodium-Potassium Pump • This antiport uses energy (active transport) released from splitting ATP to transport Sodium (Na+) out of and Potassium (K+) into cells. extracellular fluid intracellular fluid K+ K+ Na+
What is cotransport ?
Question: • How are large molecules transported into and out of the plasma membranes?
Answer: • Endocytosis and Exocytosis
Endocytosis • The energy requiring movement of particles (foreign or natural) into the cell. • 3 types of endocytosis: A. Phagocytosis B. Pinocytosis C. Receptor-mediated endocytosis
A. Phagocytosis • Cell eating: cells engulf particles • Example: White Blood Cells Bacteria White Blood Cell
B. Pinocytosis • “Cell drinking”: droplets of extracellular fluid are absorbed into the cell by small vesicles. • Examples: 1. How mammalian embryonic cells take in nutrients from surrounding cells. 2. How endothelial cells take in nutrients from blood capillaries and move them into surrounding tissues
Exocytosis • Cell secretes macromolecules (proteins and other biochemicals) out of cell. Examples: • Part of the Endomembrane System: the fusion of transport vesicles with plasma membrane. • Nervous System: How neurotransmitters are secreted into the synapse between neurons
C. Receptor-Mediated Endocytosis • Importing specific macromolecules (hormones) into the cell by the inward budding of vesicles formed from coated pits (receptors). Liver Cell Hormones Receptors
The Three Types of Endocytosis in Animal Cells
1)Describe how facilitated diffusion differs from “regular” diffusion and osmosis. 2) Give one similarity between the two 3) Describe how active transport differs from passive transport and give an example of active transport.
3) Describe how active transport differs from passive transport and give an example of active transport.
4) Why did you calculate percent changes in mass during the lab yesterday? 5) What condition results in plants as a result of them being placed in a hypotonic solution? (this was in the video)
How is osmosis different than diffusion? If the solution on the outside of the cell has more solute than the solution inside the cell the outer solution is said to be _____ to the cell.
Why don’t cells in large organisms burst?