Presentation on theme: "Functions and Transport"— Presentation transcript:
1 Functions and Transport The Cell MembraneFunctions and Transport
2 Cell (Plasma) membrane- Introduction A basic principle in biology is that all living things are made of cells. While they come in a wide variety of shapes and sizes, all cells have a fluid inside (called cytoplasm) surrounded by a protective layer.
3 Cell (Plasma) membrane- Introduction The cell membrane, also called plasma membrane, is the boundary that separates all living cells from their nonliving surroundings. This membrane: 1. Controls what enters and leaves the cell 2. Maintains homeostasis 3. Protects the cell from the outside environment 4. Is selectively permeable, meaning it allows some substances to cross more easily than others.
4 Cell (Plasma) membrane- Components The cell membrane is made up of three types of organic compoundsLipids (phospholipids and steroids)CarbohydratesProteinsThe membrane is flexible and made of lipid molecules. It is mixed with large protein molecules that act as channels through which other molecules enter and exit the cell.
5 Components of cell Membrane- Lipids Phospholipids- make up the majority of the cell membraneThe heads are polar (hydrophilic- “water loving”)The tails are nonpolar (hydrophobic- “water fearing”)By forming a bilayer, the hydrophobic tails are shelteredfrom the water that surrounds the cell inside and out.
6 Components of cell Membrane- Lipids 2. Steroids (or sterols)- a second, less abundant type of lipid found in the cell membrane.The function is to regulate the fluidity of the cell membrane.At high temperatures, steroids help hold the cell membrane together.At low temperatures, steroids keep the bilayer from packing too tightly together.Cholesterol is the main membrane steroid found in animal cells.Cholesterol is made by all animals and is found in varying quantities in the food you eat.HDL= Good cholesterol (Healthy)LDL= Bad Cholesterol (want Less of this)
7 Components of cell membrane- proteins Membrane proteins- used to transport material in to the cell (things that cannot easily pass through the membrane itself)There are 2 types of membrane proteins:Peripheral proteins- located on the surface of the cell membrane (inside and outside)Integral proteins- pass through the lipid bilayer
8 Components of cell membrane- carbohydrates Carbohydrates are usually attached to the outer surface of the cell membrane.They act as “antenna” and are used by the cells to identify each other.There are 2 types, depending on what they are attached to:Glycolipids- a carbohydrate attached to a lipidGlycoprotein- a carbohydrate attached to a protein
9 Maintaining homeostasis- buffers How do cells use buffers?Carbonic Acid SystemMaintains blood pH at 7.4Controlled by respiration (breathing)Carbonic acid is converted to carbon dioxideIllnesses can result from too much carbonic acid or from the blood becoming too basicDihydrogen Phosphate SystemOperates in the cytoplasmCytoplasm has a pH range of 6.9 to 7.4The ions work to maintain this
10 Movement of material across a membrane Passive Transport
11 Passive TransportThe movement of material across the cell membrane without using energy. There are 2 types you need to know.Diffusion and Osmosis
12 Passive transport-diffusion Diffusion- The process by which molecules of a substance (not water) move from an area of high concentration to an area of low concentration Equilibrium is reached when the concentration is the same throughout.
13 Passive transport-diffusion Dynamic Equilibrium-Movement into the cell is at the same rate as the movement out of the cellThe cell has achieved a “steady state”…HOMEOSTASISRate of water entering = Rate of water leaving Hence the level of water is constant
14 Passive transport-diffusion What does it all mean?HIGH Concentration: lots of soluteLOW Concentration: little soluteThe goal: To reach EQUILIBRIUMCONCENTRATION GRADIENT: difference in concentration on each side of a membrane, the larger the difference, the greater the gradientFactors that influence rate of diffusion:1. temperature2. pressure3. concentration
15 OTHER EXAMPLES OF DIFFUSION The diffusion of solute particles through solvent particles.The diffusion gas particles through the air.
16 Passive transport- facilitative diffusion Facilitate= “to help”Facilitative diffusion- molecules are moved across the membrane from an area of higher to lower concentration with the help of a carrier proteinDoes not require energyNeeded when the solute particle is too large to pass throughThe carrier protein opens up a larger hole in the membrane to allow the solute to pass through.
17 Passive transport- osmosis The movement of water molecules across a selectively permeable membrane.Movement is from high to low concentrationThe goal is to create equilibriumSince water is a small molecule, it can move quicklyWater will move to the area of higher solute concentration to dilute it
18 Passive transport- osmosis How does osmosis affect solutions?Hypertonic- a solution with a higher concentration than another solutionHypotonic- a solution with a lower concentration than another solutionIsotonic- a solution with an equal concentration to another solution
19 Passive transport- osmosis How does osmosis affect cells?Cytolysis- the bursting of an animal cell when placed in a hypotonic solutionPlasmolysis- the shrinking of a plant or animal cell when placed in a hypertonic solutionTurgor pressure- the force that pushes out on a plant’s cell wall when placed in a hypotonic solution
20 Movement of material across a membrane Active transport
21 Active transportRequires energy to get material across the cell membrane against a concentration gradient (think paddling against a current)Substances are forced to move from an area of lower concentration to an area of higher concentrationThere are 3 different types you should knowPumpsEndocytosisExocytosis
22 Active transport- pumps Pump- a special type of carrier protein that is used to push molecules from lower to higher concentrationEx. Sodium (Na+) and Potassium (K+) pumpsEnergy is required for pumpsThe carrier will take three Na+ ions out of the cell and pick up two K+ to pump into the cell.This unequal exchange of ions creates a charge on the cell. The cell uses this charge to send signals to other cells.
23 Active transport- endocytosis Endocytosis- taking material into a cell by forming a pocket around it (the cell membrane folds around something in the external environment)Phagocytosis- intake of large particles or cells (solid particles) through the cell membrane within a vesiclePinocytosis- using a vesicle or pocket to take in liquid or dissolved substances (solutes)
24 Active transport- exocytosis Exocytosis- a vesicle made by the cell fuses with the cell membrane, releasing its contents outside of the cellProteins made by ribosomes in the cell are packaged into transport vesiclesThese transport vesicles fuse with the cell membrane and then the proteins are secreted out of the cell (e.g. insulin) to help maintain glucose levels