CELLS AND THEIR ENVIRONMENT

Types of cell transport I.Passive transport Movement of molecules of a solute from areas of high to low concentration without the use of energy

Types of Passive Transport 1.diffusion: - movement of molecules of a solute from areas of high to low concentration (down a concentration gradient) until equilibrium is reached - equilibrium: steady state where equal numbers of molecules move in each direction - concentration gradient: differences in concentration of a substance across a space animation

Diffusion through gated ion channels ion channel: transport protein that span the thickness of the membrane with a polar pore through which ions can pass - ions can’t move through non polar interior of lipid bilayer - allows ion to move thru membrane without touching non polar lipid interior - form of passive transport: ions move down concentration gradient - influenced by ions charge – the more negative the charge, more likely to move out and vice versa - some gates always open - some gates stimulated by : electrical charge stretching of membrane binding of specific molecules

2. Osmosis movement of water from areas of high to low concentration until equilibrium is reached - direction of movement depends on CONCENTRATION OF WATER on either side of the concentration gradient animation

Types of osmotic solutions -hyptonic -hypertonic -isotonic -indicates relative concentration of two solutions being compared Osmotic pressure force caused by osmosis

Results of water transport in and out of cells: Animal Cells Hypertonic: crenation Hypotonic: cytolysis Plant cells Hypertonic: plasmolysis Hypotonic: turgor pressure Plant cell adaptations: Cell wall: limits amount of water into cell Contractile vacuole: rhythmically pumps water out of cell (unicellular org.) Osmosis interactive animation

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3.facilitated diffusion - movement of a substance from areas of high to low concentration with the aid of a carrier protein (driven by diffusion) -type of passive transport ex: glucose or amino acids into a RBC

Steps of Facilitated Diffusion 1.carrier protein binds a specific molecule on one side of membrane 2.change in shape of carrier protein exposes one molecule to other 3.carrier protein shields the molecule from interior of lipid bilayer 4.molecule is released from carrier protein which goes back to original shape

II. Active transport movement of substances through a membrane against (up) a concentration gradient requires energy (from ATP)

2 types active transport 1. membrane pumps - involves carrier proteins which act as pumps - ions in lower concentration bind to carrier protein and are released to areas of higher concentration (Ca+, K+, Na+, others)

Sodium Potassium Pump 1. three Na+ INSIDE cell bind to Na/K pump (phosphate group is broken off ATP and binds to pump to give pump energy) 2.pump changes shape and transports three Na across cell membrane and releases them OUTSIDE cell

Sodium Potassium Pump 3.pump now exposed on the surface of cell so two K+ which are on OUTSIDE bind to pump (phosphate group released changing shape of pump) 4. pump again exposed to inside of cell so two K+ are transported across membrane and are released INSIDE cell ion_pump/ionpump.html

-this process creates and electrical gradient across cell membrane Outside ( like + and - terminals on battery) membrane___________________________ Inside Why important: -animal cells must have higher concentration of Na OUTSIDE cell, and higher concentration K inside cell in order to function properly (nerve impulse conduction) - prevents accumulation of Na+ inside cell which would cause water to move in and expand or burst cell

2. endocytosis/exocytosis Endocytosis process where cells engulf substances too large to enter by passing through membrane Types - phagocytosis: cells engulf solid particles too large to pass thru membrane - pinocytosis: cells engulf liquid substances

Exocytosis process of removing large substances out of cell (opposite mechanism of endocytosis) Ex: cells manufacture proteins – vesicles fuse with cell membrane and dump contents out of cell - removal of cell debris, bacteria/viruses, old organelles animation

Cellular communication Cells must communicate with each other to coordinate your growth, metabolism, and other activities Ex: hormones – made in one part of the body and carried to other parts where they perform their function Involves signal molecules that are bound by receptor proteins on receiving cells Receptor protein: membrane protein (embedded in lipid layer) that binds to a specific signal molecule - enables cell to respond to signal molecule Function: changes receiving cell’s activity

Results of cell communication 1. enables specific ions to cross cell membrane - by changing permeability in receiving cell ion channels open allowing specific molecules to pass Ex: this type receptor protein found in nervous system

2. causes formation of a second messenger - amplifies signal of first messenger (original signal molecule) - results: activates enzyme, changes permeability of membrane opening ion channels 3. speeds up chemical reactions inside cell - receptor protein acts as enzyme - may activate other enzymes located inside cell or membrane Ex: some drugs affect binding of signal molecules to receptor proteins - heroin - beta blockers

CELL COMMUNICATION SIGNAL TRANSDUCTION Signal transduction video

HIV and Receptor Proteins -initially HIV will only affect macrophages because a second receptor protein is needed to bring it into cell - lympohcytes lack this second receptor protein -as HIV grows and spreads to other macrophages, it undergoes genetic changes and no longer needs second protein receptor -will then attack to lymphocytes (WBC, immune) eventually will destroy body’s lymphocytes and ultimately cause death because body can no longer fight off infections

Study for the test !!!!