The Cell Membrane The Cell Membrane The chemistry of living organisms involves the study of solutions. ◦ A large portion of our body is water, and the chemical reactions of life occur in aqueous (watery) solutions. ◦ Nutrients move through the watery matrix of your blood to deliver the nutrients to cells. Cell membranes help organisms by controlling what substances may enter or leave the cells. ◦ Known as Selectively Permeable or Semipermeable ◦ Some substances can cross the cell membrane without any input of energy, whereas other materials need ATP to help cross through the membrane.
The Cell Membrane It’s Selectively Permeable… HOW DOES IT DO THAT? ◦ Because of the membrane’s structure ◦ Cell membrane is a PHOSPHOLIPID BILAYER BILAYER - 2 LAYERS PHOSPHOLIPID - 2 PARTS 1. Phosphate head 2. Lipid tail
1. Phosphate head - Outer part of the bilayer ◦ HYDROPHILIC - "Water loving” 2. Lipid Tail - Middle part of the bilayer ◦ HYDROPHOBIC - "Water hating"
The phospholipids are not attached to one another, enabling the membrane to have “fluid” like properties Because of the lipid bilayer’s chemical properties, not all types of molecules can cross through the membrane Some substances can cross through on their own ◦ Small, uncharged particles can squeeze between phospholipids and can cross though the lipid layer Some substances need assistance to cross through the membrane ◦ Large molecules cannot fit between phospholipids ◦ Charged particles (ions) cannot cross through the lipid layer
Other Parts of the Cell Membrane 1. CHOLESTEROL (type of lipid) ◦ Function: Helps to make the membrane "fluid", not rigid ◦ Location: Part of the the bilayer 2. PERIPHERAL PROTEINS ◦ Function: Helps to keep the shape of the cell ◦ Location: Inner layer of cell membrane, connected to fibers of the cytoskeleton
Other Parts of the Cell Membrane 3. INTEGRAL PROTEINS ◦ Function: Channel for molecules to come into the cell ◦ Location: Embedded in the membrane (goes through membrane, from one side to the other) ◦ Some integral proteins have carbohydrates attached Known as Glycoprotein
Other Parts of the Cell Membrane 4. GLYCOPROTEINS ◦ Location: Integral protein with a carbohydrate attached Carbohydrate (glycogen) sticks out of the cell, on outside of cell membrane ◦ Functions: Used in cell recognition Different cell types have different shaped glycoproteins attached Used as a cell receptor Glycoprotein accepts proteins/substances meant for that specific cell type
Unit 5: Lecture 2 Topics: ◦ Transport across membranes ◦ Passive Transport (Diffusion, Osmosis) Covers: ◦ Chapter 5, pages 95 – 99
Transport Across Cell Membrane Many materials cross through the cell membrane (enter cell or leave cell) The types of transport are grouped into two categories: ◦ Passive Transport ◦ Active Transport The type of transport used to move the material depends on the concentration gradient as well as the type of molecule being transported
CONCENTRATION GRADIENT – when the solutions on either side of the membrane do not have the same concentration of solutes (one more concentrated than the other) When the concentration is equal throughout the space/solution, the solution is said to be in EQUILIBRIUM Due to kinetic energy, molecules are in constant motion, even when the solution is in a state of equilibrium In the cell, molecules will diffuse in & out of the cell even when the cell is in equilibrium with its surroundings
Types of Transport: Passive Passive Transport occurs naturally due to kinetic energy, so it does not require any additional energy from the cell. ◦ In passive transport, the molecules are said to be moving "down the concentration gradient" because the molecules are moving to an area with a lower concentration.
Types of Passive Transport: ◦ Diffusion ◦ Osmosis ◦ Facilitated Diffusion ◦ Ion Channel DIFFUSION: Movement of molecules from an area of high concentration to an area of lower concentration EXAMPLES : Food coloring in water, Solute added to a solvent
Types of Passive Transport: ◦ Diffusion ◦ Osmosis ◦ Facilitated Diffusion ◦ Ion Channel OSMOSIS Type of Passive Transport driven by kinetic energy OSMOSIS is the diffusion of water! ◦ Water molecules are moving from an area of high concentration (of water) to an area of low concentration (of water) ◦ If water is diffusing into or out of a cell, the water molecules will be crossing through the cell membrane Cell is trying to reach EQULIBRIUM with its surrounding environment
HYPOTONIC SOLUTION External solution has higher concentration of water than inside the cell Water moves into the cell Cell can burst! HYPERTONIC SOLUTION External solution has a lower concentration of water than inside the cell Water moves out of the cell Cell shrivels up! ISOTONIC SOLUTION Concentration of water inside and outside the cell is and inside the cell are equal Cell is in equilibrium with its surrounding environment!
How cells deal with osmosis... HYPOTONIC SOLUTION In plants - vacuole fills with water creating turgor pressure ◦ Helps to support plant cell In unicellular freshwater organisms - water constantly entering cell, these organisms must continuously pump the water out of the cell ◦ Contractile Vacuole - Organelle that removes water In Red Blood Cells – water fills up the RBC & the cell can burst! ◦ Known as CYTOLYSIS HYPERTONIC SOLUTION In plants - when water leaves cell, turgor pressure reduced and plants become wilted, Known as PLASMOLYSIS In Red Blood Cells - cells can't compensate for extreme changes in concentration, so cells would shrivel ◦ Known as CRENATION
Unit 5 Lecture 3 Topics: ◦ Transport across membranes Passive Transport (Facilitated Diffusion, Ion Channel) Active Transport Covers: ◦ Chapter 5, pages 99 – 104
Types of Passive Transport: ◦ Diffusion ◦ Osmosis ◦ Facilitated Diffusion ◦ Ion Channel FACILITATED DIFFUSION Type of passive transport that is driven by kinetic energy ◦ Moving molecules from high to low concentration (“Down the gradient”) Transports molecules that can not diffuse on their own ◦ EX. - too big, not soluble in lipids, glucose, polysaccharides These molecules are assisted across the membrane by a type of integral protein known as a CARRIER PROTEIN Many types of carrier proteins because each carrier protein can only assist ONE type of molecule * REMEMBER - Form Fits Function! *
Types of Passive Transport: ◦ Diffusion ◦ Osmosis ◦ Facilitated Diffusion ◦ Ion Channel ION CHANNEL * REMEMBER - An ION is an atom or molecule with a charge Type of passive transport that is driven by kinetic energy ◦ Moving molecules from high to low concentration (“Down the gradient”) Ions are not soluble in lipids, so ions cannot cross through the lipid bilayer (cell membrane) on their own Ions cross through the cell membrane by traveling through a type of integral protein known as an ION CHANNEL Many types of ion channels because each ion channel can only assist ONE kind of ion across the membrane Sodium (Na+)- Potassium (K+) Calcium (Ca++)- Chlorine (Cl-)
ACTIVE TRANSPORT Unlike passive transport, ACTIVE TRANSPORT requires the cell to use energy to move the molecules across the membrane ◦ Energy supplied by the cell's mitochondria in the form of ATP Active transport moves molecules from an area of lower concentration to an area of higher concentration ◦ Molecules moving "up the gradient” or “against the gradient”, solution moving away from equilibrium
Types of Active Transport: ◦ Membrane Pumps (Sodium-Potassium) ◦ Endocytosis ◦ Exocytosis SODIUM - POTASSIUM PUMP Type of Active Transport, requires ATP to occur Membrane Pumps require a special type of carrier proteins (a type of integral protein) Membrane Pumps transport molecules from an area of low concentration to an area of high concentration In the Sodium-Potassium Pump, sodium ions (Na+) are pumped out of the cell and potassium ions (K+) are pumped into the cell ◦ 3 sodium leave cell for every 2 potassium that enter Cell needs to have a high concentration of Na+ outside the cell and a high concentration of K+ inside the cell
Types of Active Transport: ◦ Membrane Pumps ◦ Endocytosis ◦ Exocytosis ENDOCYTOSIS Type of Active Transport, requires ATP to occur ◦ Requires additional energy because the cell is making major structural changes Endocytosis is how: ◦ Cells ingest large particles ◦ Unicellular organisms ingest their food ◦ Our body begins to get rid of bacteria and viruses 2 Types of Endocytosis: ◦ PINOCYTOSIS - transport of fluids ◦ PHAGOCYTOSIS - movement of large particles or whole cells
Endocytosis: The Process 1. Cell membrane folds in and begins to form a pouch 2. Cell membrane encloses the external materials in a pouch 3. Pouch pinches off to form a VESICLE ◦ Vesicle - membrane bound organelle used to transport molecules. Often combines with lysosomes to break down ingested materials
Types of Active Transport: ◦ Membrane Pumps ◦ Endocytosis ◦ Exocytosis EXOCYTOSIS Type of Active Transport, requires ATP to occur ◦ Requires additional energy because the cell is making major structural changes Exocytosis is how: ◦ Cells release proteins after protein leaves the Golgi ◦ Cells release waste products
Exocytosis: The Process 1. Vesicle moves to the cell membrane 2. Vesicle fuses with the cell membrane 3. Contents gets released to the outside of the cell