Journal Compare/Contrast the structures of PROKKARYOTES and EUKARYOTES

Structure and Function of the Cell Membrane Chapter 7.2 & 7.4

Cell membrane In order to funciton, living things must maintain a biological balance with their immediate environment. This balance is called homeostasis

Cell membrane The cell membrane forms a selective barrier around the cell and monitors the movements of molecules into and out of the cell. It is selectively permeable. The cell membrane is therefore largely responsible for maintaining homeostasis.

Fluid Mosaic Model of the Cell Membrane 1. The cell membrane is composed of two layers (bilayer) of phospholipids with proteins interspersed throughout. 2. The phospholipids have 2 definite ends: Hydrophilic—Dissolves in water (water loving)-focusing to the outside and inside of the membrane.Hydrophilic—Dissolves in water (water loving)-focusing to the outside and inside of the membrane. Hydrophobic—Does not dissolve in water (water fearing)-forming the center of the membraneHydrophobic—Does not dissolve in water (water fearing)-forming the center of the membrane

Draw the structure of the cell membrane into your notes Tails Head Peripherial protein Integral protien Phospholipid Bilayer

Fluid Mosaic Model of the Cell Membrane 3. The transport proteins are of two types: IntegralIntegral -provide a tunnel to allow material to flow through PeripheralPeripheral -Many molecules extend from these proteins and serve as receptors, which are baseball mitt-like structures that capture specific molecules outside. ~ Triggering a specific activity within ~ Enabling cells to stick together ~ Binding to the substance and physically move it

Integral Receptor

Fluid Mosaic Model of the Cell Membrane 4. Cholesterol molecules are found in animal membranes to help add support to its structure.

Traffic of molecules across the membrane: How do chemicals get across? Hydrophobic molecules (Hydrocarbons and Oxygen) can cross with ease because they can dissolve in the lipid bilayer. Small uncharged molecules will pass (water and carbon dioxide). Large uncharged molecules will not pass (sugar). Ions will not readily pass ( H+, Na+, Cl-).

Traffic of molecules across the membrane:

Movement Across a Membrane 1. Diffusion of water or other substance, from an area of high concentration to an area of low concentration. Diffusion is a passive type of transport, it requires no additional energy to make it work. Diffusion is a passive type of transport, it requires no additional energy to make it work. Osmosis is diffusion of water across a biological membrane. Osmosis is diffusion of water across a biological membrane. 2. Facilitated Transport or the movement of material by a carrier protein without the use of energy. 3. Active transport or the movement of material by a transport protein with the use of energy.

Traffic of molecules across the membrane: Passive Transport—no energy needed Facilitated Transport— no energy; need proteins Active Transport— extra energy needed ATP

14 Movements Into and Out of the Cell Passive (Physical) Processes require no cellular energy simple diffusion facilitated diffusion osmosis filtration Active (Physiological) Processes require cellular energy active transport endocytosis exocytosis transcytosis

Warm-Up Draw and label the structure of the cell membrane. –Must have: Phospholipid bilayer Integral protein Peripheral protein

16 Simple Diffusion movement of substances from regions of higher concentration to regions of lower concentration oxygen, carbon dioxide and lipid-soluble substances

17 Osmosis movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration water moves toward a higher concentration of solutes

18 Osmosis Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water Osmotic pressure increases as the concentration of nonpermeable solutes increases hypertonic – higher osmotic pressure hypotonic – lower osmotic pressure isotonic – same osmotic pressure

19 Facilitated Diffusion diffusion across a membrane with the help of a channel or carrier molecule glucose & amino acids

20 Filtration smaller molecules are forced through porous membranes hydrostatic pressure important in the body molecules leaving blood capillaries

21 Active Transport carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration sugars, amino acids, sodium ions, potassium ions, etc.

22 Endocytosis cell engulfs a substance by forming a vesicle around the substance three types pinocytosis – substance is mostly water phagocytosis – substance is a solid receptor-mediated endocytosis – requires the substance to bind to a membrane-bound receptor

23 Exocytosis reverse of endocytosis substances in a vesicle fuse with cell membrane contents released outside the cell release of neurotransmitters from nerve cells

Types of Solutions 1. Hypotonic (hypo- lower): concentration of solute molecules outside the cell is lower than that inside the cell - the solution outside the cell is hypotonic. Example: H2O Water enters cell Cell size swells

Types of Solutions 2. Hypertonic (hyper-higher): concentration of solute molecules outside the cell is higher than that inside the cell the solution outside the cell is hypertonic. Example: H2O Water leaves cell Cell size shrinks

Types of Solutions 3. Isotonic (iso – equal): concentrations of solute molecules are equal inside and outside a cell. Water moves equally in both directions H2O Water moves into & out of cell Cell stays the same

Water balance in a living cell 1. Cells placed in a hypertonic environment (salt-water) animal cells crenate (shrivel). Plant cells plasmolyze (shrivel). 2. Cells placed in a hypotonic environment (fresh water) animal cells lyse (explode) and plant cells become turgid (firm). 3. Cells placed in an isotonic solution: animal cells are normal, plant cells are flaccid (limp).

Types of Movement DIFFUSION/ OSMOSIS FACILITED DIFFUSION ACTIVE TRANSPORT