Biochemistry Unit

 Cells need to import needed materials into the cell and to eliminate waste materials from the cell.  Nutrients like glucose, water, minerals, amino acids, etc., need to be available for cellular processes like cellular respiration, photosynthesis, and protein synthesis.  In addition, the products of these cellular processes like ATP, proteins, and sucrose need to leave the cell.  Very small molecules and non polar molecules are able to pass through the cell membrane.  Large molecules, polar molecules or charged ions will require some assistance in passing through the cell membrane.  Remember, the cell membrane is selectively permeable.

 Passive transport does not require energy to move materials through the cell membrane.  There are three types of passive transport:  1. diffusion  2. osmosis  3. facilitated diffusion

 Diffusion is the net movement of molecules (or ions) from a region of their high concentration to a region of their lower concentration.  The molecules move down a concentration gradient.  Molecules have kinetic energy, which makes them move about randomly.  As a result of diffusion molecules reach an equilibrium where they are evenly spread out. This is when there is no net movement of molecules from either side.

 Diffusion of bromide gas:

1. The steepness of the concentration gradient. The bigger the difference between the two sides of the membrane the quicker the rate of diffusion. 2. Temperature. Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster. 3. The surface area. The greater the surface area the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any one moment. 4. The type of molecule or ion diffusing. Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.

1. Oxygen – Non- polar so diffuses very quickly. 1. Carbon dioxide – Polar but very small so diffuses quickly. 2. Water – Polar but also very small so diffuses quickly.

 Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also ions such as Na + or Cl - cannot pass.  These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION.  Molecules will randomly move through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low conc.

 Protein channels and protein carrier molecules are very specific to the type of molecule each will allow to pass through the membrane.  These protein molecules work to bring molecules into the cell and out of the cell depending on the concentration gradient.  Glucose is a molecule that requires a protein carrier to enter the cell due to its large size and polarity. Without the protein carrier, glucose would not be able to diffuse into the cell.

 Osmosis is a form of diffusion that is specific to water. With osmosis, water molecules move from an area of high concentration (not volume!)to an area of low concentration through a selectively permeable membrane.

 You can clearly see that the volume of the two liquids changed dramatically. The side with the high concentration of water lost volume as the molecules moved to the side with the lower concentration of water molecules. The unequal movement of water molecules will cease once the water concentration levels are equal on both sides of the membrane.

 The movement of water in and out of cells is extremely important to all cellular processes. Maintaining equal water concentration in the interior and exterior of the cell is critical for cell survival. When the concentration of water is equal on both sides of the cell membrane, the cell is in an isotonic solution. In isotonic solutions, the rate of movement of water molecules into the cell equals the rate of movement of water molecules out of the cell. This steady state is ideal for all cells and part of the function of blood is to keep cells in an isotonic solution.  When a cell is placed in a hypotonic solution, there is a higher concentration of water molecules outside of the cell. As a result, water moves into the cell and the cell starts to swell and eventually can burst.  When a cell is placed in a hypertonic solution, there is a higher concentration of water inside the cell. As a result, water moves out of the cell and the cell starts to shrink.

 Cookies are great out of the oven, but biting into a hard crumbly mass later in the week is no fun. That's why you need to understand the science of cookie osmosis, to keep them fresh!  The trick is simple: place a slice of fresh bread in with your cookies a day or two after you've baked them, or whenever you find their texture has deteriorated. The moisture from the fresh bread will migrate to your cookies (through cookie osmosis, see diagram above), rendering them soft and chewable again.

 Active transport requires a cell to expend energy to move materials across the cell membrane against the concentration gradient.  Materials are moving from an area of low concentration to an area of high concentration.

 Do not extend through the membrane, rather bond and drag the molecule through it

 Used in intercellular communication. A hormone binds to the protein receptor, which responds by releasing a signal molecule to perform a particular action.

 online.com/objects/ViewObject.aspx?ID= AP online.com/objects/ViewObject.aspx?ID= AP11203  OLOGY1111/animations/active1.swf OLOGY1111/animations/active1.swf

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 Proteins, lipids, and other materials synthesized within the cell need to leave the cell. Since they are too large to pass through the cell membrane, they exit through the membrane with the help of vesicles.  The vesicles hold the contents within their fluid filled membrane and attach themselves to the cell membrane. Once attached, the vesicles release its contents into the external environment.  Waste materials that need to be removed from the intercellular space also exit the cell using this process. Add this graphic to your notes:

 The inability to metabolize lactose, because of a lack of the required enzyme lactase in the digestive system Lactose