Molecular (cell) transport Material Exchange and Osmosis

Material exchange Cell transport: movement of particles across membrane Takes place because cells are trying to maintain homeostasis

Exchanged Materials What materials are exchanged? WATER – MOST IMPORTANT Oxygen, Carbon Dioxide Ions – Na+, Mg+, Ca+, H+, Cl-, K+ Hormones (to transmit messages) Nutrients enter (sugars & amino acids) Wastes must exit (Ammonium)

Cell Membrane Membrane composed of a Phospholipid bilayer with proteins & carbohydrates interspersed Lipids & proteins cause membrane to be fluid, not rigid

The fluid mosaic model Fluid = all the parts move around Mosaic = made of many different parts

Components of cell membrane Lipid: Main component of cell membrane

Carbohydrates (Sugars) Act as ID tags Attached to phospholipids and proteins

Membrane Proteins Signaling Receptors – receiving signals Transport – move molecules across the membrane Channels – act as doorways Glycoproteins – act as ID tags Enzymes - biological catalysts Attachment - sticks to other cells

Cell membrane: Phospholipid bilayer Phosphate heads: polar, hydrophilic Fatty acid tails: nonpolar, hydrophobic Heads arrange themselves on the outside & tails arrange themselves on the inside

Cell membrane as a barrier Causes membrane to be Selectively permeable: only certain molecules are allowed to pass through Small, nonpolar molecules like nitrogen & oxygen gas pass through easily. Ions (like H+ and Ca2+) are repelled by nonpolar tail and cannot cross membrane Nonpolar O2 Larger ions Polar molecules You shall not pass

2 types of cell transport Passive transport Active transport

Passive transport Molecules move across the cell membrane from an area of higher concentration to an area of lower concentration Does not require cells to expend energy Three types: Diffusion Facilitated Diffusion Osmosis

Diffusion The movement of molecules from an area of HIGHER concentration to an area of LOWER concentration until it reaches EQUILIBRIUM Molecules move down a concentration gradient (from high to low) Concentration: amount of molecules in a given area Concentration gradient: difference in the amount of molecules in a given area

Facilitated diffusion Movement of small molecules across a membrane with the help of proteins Channel Proteins Carrier Proteins

OSMOSIS Diffusion of water molecules Water does this to balance relative concentration of molecules Therefore depends on solutions on both sides of membrane Cell membranes are completely permeable to water with the help of aquaporins

Direction of osmosis is due to the concentration of the solutions Tonicity Direction of osmosis is due to the concentration of the solutions Amount of solutes = tonicity

Isotonic Isotonic Solution: concentration of solute inside and outside the cell are equal No NET movement of water

hypertonic Hypertonic Solution: concentration of solute outside the cell is higher than concentration inside the cell. HYPER = MORE STUFF Water will flow out of cell

hypotonic Hypotonic Solution: concentration of solute outside the cell is lower than the concentration in the cytoplasm. HYPO = NO STUFF Water will flow into cell “In Hypo, cell will be Hippo”

Isotonic: Cell will retain its normal shape!

Hypertonic: Cell will SHRINK!

Hypotonic: Cell will SWELL!

Movement of Materials Through the Cell Membrane

Active Transport Molecules move across the membrane from an area of lower concentration to an area of higher concentration Requires cells to expend energy Three types: Transport Proteins Exocytosis Endocytosis

Transport Proteins Actively pump small molecules and ions across the cell membrane

Exocytosis removal of waste materials from cell Larger molecules Vesicles made by the cell fuse with the cell membrane releasing their contents into the external environment

Exocytosis

Endocytosis Taking material into the cell by formation of a pocket of the cell membrane to make a vesicle Pinocytosis: vesicle contains fluids (cell drinking) Phagocytosis: vesicle contain large particles (cell eating)

Endocytosis

Active transport