Cell Structure and Function II: Cell membrane and transport systems
Reading
OpenStax book: Ch. 3 - "Cell Structure & Function" sections 3.5 & 3.6
BJU: 3B - "Cells and their environment"
AP students additional reading: Princeton Review "Cell Structure & Function" from Transport to the end
Lab
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes. Some of you want more hands-on than others. We will do what we can do. This is list of options:
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 3.5 & 3.6
BJU: 3B - "Cells and their environment"
AP students additional reading: Princeton Review "Cell Structure & Function" from Transport to the end
Lab
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes. Some of you want more hands-on than others. We will do what we can do. This is list of options:
- Diagnosing Diabetes lab. We have used this successfully for years to illustrate cell transport mechanisms. It will require handing out certain supplies to students to complete at home, and we can assess when we get here based on the Covid-19 situation.
- Diffusion and Osmosis lab (fulfills AP "dirty dozen lab" #4). There are various versions of this lab exercise, using dialysis tubing and different materials, it will require handing out certain materials to students to complete at home, and we can assess when we get here based on the Covid-19 situation.
- There are several good virtual labs to cover this material, including PhET Membrane Channels and others
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.
Lab: The "Diagnosing Diabetes" lab will be an excellent launching pad for understanding the workings of the cell!
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.
Lab: The "Diagnosing Diabetes" lab will be an excellent launching pad for understanding the workings of the cell!
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.
| Lecture slides: Cell Structure & Function |
LABS & HOMEWORK BELOW: There are numerous labs, projects, presentations, and homework exercises posted on this portal. Don't panic. Some of these are current, some are left over from prior years, and some are just "parked" here for future use. DO NOT WORK ON A LAB OR HOMEWORK EXERCISE unless it has been assigned in your weekly class email! Due to the 2020-2021 Covid-19 situation, I will assign labs and homework as we go along based on what we are able to do.
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 |
Diabetes research assignment
| diabetes_research_assignment_instructions_2018.docx |
| Diabetes sample student papers |
| More diabetes student papers |
Homework (refer to class emails for due dates)
| 4._cell_structure_function_homework_questions1.docx |
| 4._membrane_diffusion_lab_instructions.doc |
| PhET: Membrane_channels_simulation.jar |
Other stuff we may decide to look at
| Lecture Slides: Diabetes |
| Diabetes_-_meal_planning_guide_lilly_pharmaceutical.pdf |