Properties of Life Figure 1.2 (c) Response to environment (a) Organization (d) Homeostasis (g) Reproduction (f) Growth and development (b) Evolutionary adaptation (e) Energy utilization
What is a cell? Both living and nonliving things are composed of molecules made from atoms. The organization of these molecules into cells is one feature that distinguishes living things from all other matter. The cell is the smallest unit of matter that can carry on all of the processes of life.
The Plasma Membrane Membrane of the Cell Fluid mosaic model, semi-permeable (selectively permeable), double layer of phospholipids with embedded proteins
Cell Membrane Jobs of the cell membrane Isolate the cytoplasm from the external environment Regulate the exchange of substances Communicate with other cells Identification
Phospholipid Bilayer Phospholipids (fats) contain a hydrophilic head and a nonpolar hydrophobic tail, which creates a barrier.
Parts of the Cell Membrane Cholesterol - stiffens the membrane by connecting phospholipids Glycolipids - signal molecules Glycoproteins - have an attached chain of sugar (antibodies)
Proteins in Cell Membrane Proteins embedded in membrane serve different functions Channel Proteins - form small openings for molecules to diffuse through Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell, (gated channels) Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins) Cell Recognition Proteins - ID tags, to identify cells to the body's immune system Enzymatic Proteins - carry out metabolic reactions
Proteins in Cell Membrane
Transport Across Membrane The membrane is selectively permeable (also called semipermeable ) Small particles, or particles with no charge can pass through the bilayer (carbon dioxide and oxygen) Water has a charge, does not easily cross the membrane - a channel protein, aquaporin helps water across
Passive Transport Simple Diffusion - water, oxygen and other molecules move from areas of high concentration to areas of low concentration, down a concentration gradient Facilitation Diffusion - diffusion that is assisted by proteins (channel or carrier proteins) Osmosis - diffusion of water
Solutions A hypertonic solution is a particular type of solution that has a greater concentration of solutes on the outside of a cell when compared with the inside of a cell. A hypotonic solution is any solution that has less solute and more water than another solution. An isotonic solution refers to solutions that have the same osmotic pressure across a semipermeable membrane
Solutions Hypertonic | Isotonic | Hypotonic
Contractile Vacuoles Help pump out excess water in freshwater organisms The central vacuole of plants can store excess water, creating a turgor pressure; plants are less likely to burst due to cell walls
Active Transport involves moving molecules "uphill" against the concentration gradient, which requires energy (ATP) Endocytosis - taking substances into the cell (pinocytosis for water, phagocytosis for solids) Exocytosis - pushing substances out of the cell, such as the removal of waste Sodium-Potassium Pump - pumps out 3 sodiums for ever 2 potassium's taken in against gradient