Chapter 3. Section 3.3 Transport Across Membranes Pages 63-66

Transcription

1 Chapter 3 Section 3.3 Transport Across Membranes Pages 63-66

2 Membrane Transport The plasma membrane is a phospholipid bilayer. The inside of the bilayer is hydrophobic and the outside of the bilayer is hydrophilic. Hydrophobic substances can dissolve in the membrane and pass through it more easily than hydrophilic substances. H 2 O, CO 2, and O 2 move freely across the membrane. Large molecules, charged molecules and ions need protein channels to move through the membrane.

3 Diffusion The movement of molecules from an area of high concentration to an area of low concentration is diffusion. The net movement of molecules is down a concentration gradient. This movement does not need energy. This is called passive transport. Diffusion occurs until equilibrium. Simple diffusion involves very small hydrophobic molecules.

4 Facilitated Diffusion Hydrophilic molecules and charged molecules, such as ions, move through the plasma membrane using facilitated diffusion. This is also passive transport because no energy is needed. Facilitated diffusion is the diffusion of molecules helped by substrate-specific membrane proteins. Molecules move from high to low concentration gradient.

5 Water Movement Water can move through proteins in the membrane, called aquaporins. Or water can move using osmosis.

6 Osmosis is a special type of diffusion that involves water moving from high to low concentration. Water moves towards an area that has more dissolved solute. Higher concentration of solute outside the cell: Water leaves the animal cell. The cell shrinks. Example: when an animal cell is put in salt water. Higher concentration of solute inside the cell: Water enters the animal cell. The cell will expand and may burst. Osmosis

7 Osmosis Higher concentration of solute outside the cell: Water leaves a plant cell. The plant wilts, instead of shrinks, because plant cells have a cell wall. Example: When a plant is overfertilized or exposed to road salt: Higher concentration of solute inside the cell: Water enters the plant cell. The plant cell becomes turgid.

8 Active Transport Active Transport uses proteins. Active Transport needs energy (ATP). Substances are moved up a concentration gradient. They move from a low concentration to a high concentration. Example: nerve cells

9 Exocytosis Exocytosis is the movement of substances out of the cell. A vesicle, containing a substance, fuses with the membrane of the cell and releases the substance out of the cell.

10 Endocytosis Endocytosis is the movement of substances into the cell. A substance is brought into the cell by a vesicle pinching inward, bringing the substance with it.

11 Questions 1 1. What substances can move freely across the plasma membrane? 2. What substances cannot move freely across the plasma membrane? 3. What is diffusion? 4. Why is diffusion passive transport? 5. What is facilitated diffusion? 6. What are 2 ways water can move out of a cell or into a cell? 7. What happens to an animal cell, where there is higher solute outside the cell? 8. What happens to a plant cell, where there is higher solute outside the cell? 9. What does Active Transport need? 10. In active transport: substances are moved down a concentration gradient. Yes or No? 11. What is exocytosis? 12. What is endocytosis?

12 Enzymes & Metabolism Section 4.1 Pages 72-74

13 Metabolism Metabolism describes all the chemical reactions in your body.

14 Enzymes 1. Enzymes are special proteins that speed up, or catalyze, the rate of reactions. 2. Enzymes can help break down or build up substances, or build more complex substances from simpler ones. 3. Enzymes help break down food in your body to get the energy from it. Enzymes are named for the reaction that they catalyze and end in the suffix -ase. Example: sucrase is needed to break down sucrose.

15 Activation Energy Enzymes lower the activation energy for a chemical reaction so that the reaction can occur quickly.

16 The chemicals that are metabolized by an enzyme catalyzed reaction are the enzyme's substrate. The place the enzyme binds to the substrate is the enzyme's active site. The shape change by the enzyme in response to substrate binding is called induced fit. Enzymes have specificity. Induced Fit

17 Metabolism A person s metabolic rate is how much energy he or she uses. This rate changes with the person s activity level. For example: we need less energy when asleep versus when we are awake. The basal metabolic rate is the energy use of a person who is awake. The average basal metabolic rate is 70 calories per hour or 1680 calories per day. This rate can change because it depends on exercise habits, gender, and genetics.

18 Factors that affect Metabolic Rate Exercise Intensity of exercise can affect the length of time the metabolic rate is high. Gender (males versus females) Males need more calories per day than females. Testosterone, in males, increases the rate of fat breaking down. Men also have more muscle than women, which needs more energy to maintain. Genetics Some people were born with lower metabolic rates.

19 Questions 2 1. What is metabolism? 2. What do enzymes do? 3. What enzyme breaks down sucrose? 4. What 2 products are made after sucrose splits? 5. What is a substrate? 6. What is an active site? 7. What is induced fit? 8. What is a person s metabolic rate? 9. What is the basal metabolic rate? 10. What is a person s average basal metabolic rate? 11. What are 3 factors that affect metabolic rate? 12. What are the 3 gender differences that affect metabolic rate?