Unit 4: Cell Structure and Function II: Cell membrane and transport systems
Reading (weeks 8 & 9)
Homework
Homework handouts are posted near the bottom. See class emails for instructions and due dates.
Labs
Pancreas below: Studying diabetes and the pancreas is a really good way to learn about cell transport systems!
- OpenStax book: Ch. 3 - "Cell Structure & Function" sections 3.4 through 3.6
- BJU: 3B - "Cells and Their Environment"
- AP: Green book Ch. 5 "Structure and Function of Plasma Membranes"
Homework
Homework handouts are posted near the bottom. See class emails for instructions and due dates.
Labs
- Diagnosing Diabetes lab. This is an excellent platform for learning cell structure and function.
- Enzyme Activity lab (fulfills AP lab #13). Looks at the enzyme 'Catalase' and the effects of concentration and pH.
Pancreas below: Studying diabetes and the pancreas is a really good way to learn about cell transport systems!
Introduction
You are made of trillions of cells. Each of your cells is a complex factory: for example, your muscle cells must contract-and-release using a biochemical-ratcheting mechanism, your nerve cells must pass electrical signals to each other, your pancreas cells must manufacture a protein called 'insulin', your red blood cells must manufacture a molecule called 'hemoglobin' so they can carry oxygen, and so on.
Cells must 'communicate' with other cells and with their environment. For example, the cell membrane (plasma membrane) must be able to allow-in certain molecules - while preventing others from entering, and it must pump-out certain molecules - while preventing others from leaving. As a simple example, all animal cells need to let-in glucose and oxygen for fuel purposes, and then let-out carbon dioxide (CO2) and water as waste products. In addition, cells in an organism are always surrounded by water and minerals. The minerals are things like sodium, calcium, potassium, chloride, and so on. A cell must be able to pump certain minerals in-and-out of its plasma membrane in order to maintain the proper concentration inside the cell. Think: every nerve cell in your body is constantly pumping sodium and potassium in-and-out to generate the electrical impulses needed to blink your eyes and keep your heart pumping. Other cells are simply trying to maintain the proper concentration of minerals in order to function.
You are made of trillions of cells. Each of your cells is a complex factory: for example, your muscle cells must contract-and-release using a biochemical-ratcheting mechanism, your nerve cells must pass electrical signals to each other, your pancreas cells must manufacture a protein called 'insulin', your red blood cells must manufacture a molecule called 'hemoglobin' so they can carry oxygen, and so on.
Cells must 'communicate' with other cells and with their environment. For example, the cell membrane (plasma membrane) must be able to allow-in certain molecules - while preventing others from entering, and it must pump-out certain molecules - while preventing others from leaving. As a simple example, all animal cells need to let-in glucose and oxygen for fuel purposes, and then let-out carbon dioxide (CO2) and water as waste products. In addition, cells in an organism are always surrounded by water and minerals. The minerals are things like sodium, calcium, potassium, chloride, and so on. A cell must be able to pump certain minerals in-and-out of its plasma membrane in order to maintain the proper concentration inside the cell. Think: every nerve cell in your body is constantly pumping sodium and potassium in-and-out to generate the electrical impulses needed to blink your eyes and keep your heart pumping. Other cells are simply trying to maintain the proper concentration of minerals in order to function.
| Lecture slides: Cell Structure & Function |
Lecture outline
- Homeostasis means "steady-state". All cells - and organisms - have feedback mechanisms to maintain the proper chemical balance within their environment. A simple example is tonicity - a cell will strive to maintain the proper balance of minerals, by passing or pumping minerals through its cell membrane.
- Cells are bathed in a solution of water and minerals. Water will diffuse in and out of the cell, depending on the surrounding concentration of minerals. The movement of water across a membrane due to concentration differences is known as osmosis.
- If a cell is placed in too-salty water, the situation is called hypertonic. (hyper = excessive). Water will then diffuse out of the cell, leaving a shriveled-up cell.
- If a cell is placed in too-pure water, the situation is called hypotonic. (hypo = less than normal). Water will then diffuse into the cell, resulting in a burst cell.
- When the salt concentration is the same inside and outside the cell, the situation is called isotonic. (iso = equal). Since there is no concentration gradient, there will be no net change in water in or out of the cell.
- In addition - food, waste products, and gases must continually pass through - or be pumped through - the cell membrane.
- Passive transport requires no energy expenditure and is driven simply by the concentration gradient inside and outside. Important gases (O2, CO2, N2) will simply diffuse across the cell membrane in this way.
- Facilitated diffusion requires the help of transport proteins embedded in the cell membrane. Larger molecules like water, amino acids, and sugars require this method to get across the cell membrane. Ionic salts also cross over using transport proteins - also called "channel proteins". These transport proteins actually carry the molecules across the cell membrane by binding to them, changing shape, and releasing them on the other side of the membrane. It's a type of pumping mechanism, and the energy input comes from the concentration gradient itself.
- Active transport can go against the concentration gradient, and is carried out by transport proteins which function as pumps mounted in the cell membrane. Since these proteins actively pump molecules against their concentration gradient (pumping the molecules "uphill"), they require energy input usually supplied by ATP. The sodium/potassium (Na/K) pumps in your nerve cells are a good example.
- Bulk transport: larger molecules such as proteins and carbohydrates are transported across cell membranes by endocytosis (in) and exocytosis (out).
- Endocytosis (transport in) is where the cell membrane - or a vacuole membrane - surrounds and traps molecules-of-interest, and encapsulates them. Then it can move them around and digest them or do whatever it's going to do with them.
- Exocytosis (transport out) is where the cell builds a membrane-bound vesicle around molecules-of-interest, and transports the whole 'package' out to the plasma membrane where it is emptied out onto the surface of the cell.
Diagnosing Diabetes lab
Diabetes serves as an excellent launching pad for understanding cells & membranes, signaling molecules, and membrane transport mechanisms.
Diabetes serves as an excellent launching pad for understanding cells & membranes, signaling molecules, and membrane transport mechanisms.
| Diagnosing_diabetes_complete_lab_handout.pdf |
Catalase Enzyme Activity Lab
The lab handout with instructions is posted below. Print and bring to the lab!
The lab handout with instructions is posted below. Print and bring to the lab!
- Read the introductory sections (important!)
- Fill out Tables 1 & 2
- Complete Graphs 1 & 2
- Respond to the lab report questions
- Upload your completed work to Canvas
| catalase_enzyme_activity_lab_handout.docx |
Virtual lab instructions:
- Open the "Enzyme Catalysis" virtual lab here www.phschool.com/science/biology_place/labbench/index.html.
- Carefully read the "Key Concepts" and "Design of the Experiment"
- Take the "Lab Quiz" and turn in a screen shot of it.
- Turn in a lab report with all 5 required elements. The "lab report requirements" are posted on the Policies/Handouts page, and there are several student examples posted next to it.
- Upload your lab report and lab quiz screen-shot to Canvas.
Homework (see class emails for due dates)
| 4._cell_structure_function_homework_questions_2020.docx |
| 4._ap_free_response_questions_on_biol_macromolecules.docx |
| cell_structure_function_questions_-_student_exemplar.pdf |
| 4._membrane_channels_weblab.doc |
Other stuff we may decide to look at
| Lecture Slides: Diabetes |
| Diabetes_-_meal_planning_guide_lilly_pharmaceutical.pdf |
Diabetes research assignment (old assgmt)
| diabetes_research_assignment_instructions_2018.docx |
| Diabetes sample student papers |
| More diabetes student papers |
Cell Membrane Transport videos
