active transport Flashcards
(8 cards)
Active Processes
When a cell uses ATP to move substances across the membrane, the process is active. Substances moved actively are usually unable to pass in the desired direction by diffusion. They may be too large to pass through membrane channels, the membrane may lack special protein carriers for their transport, they may not be able to dissolve in the fat core, or they may have to move “uphill” against their concentration gradients. The two most important active processes are active transport and vesicular transport.
Happens when the cell must use energy (ATP) to move substances across the membrane.
Used when passive transport won’t work, because:
Molecules are too large to fit through membrane channels.
The membrane doesn’t have the right carrier proteins.
The molecules can’t dissolve in the lipid layer of the membrane.
They need to go “uphill” — meaning against their concentration gradient (from low to high).
🔁 Two Main Types of Active Transport:
Active Transport
Sometimes called solute pumping, active transport is similar to facilitated diffusion in that both processes require protein carriers that interact specifically and reversibly with the substances to be transported across the membrane. However, facilitated diffusion is driven by the kinetic energy of the diffusing molecules, whereas active transport uses ATP to energize its protein carriers, which are called solute pumps. Amino acids, some sugars, and most ions are transported by solute pumps, and in most cases these substances move against concentration (or electrical) gradients. This is opposite to the direction in which substances would naturally flow by diffusion, which explains the need for energy in the form of ATP; they are essentially moving “uphill”. solute pumps are the protien carriers
sodium-potassium pump, the sodium-potassium pump is a type of solute pump!
What is the Sodium-Potassium Pump?
It’s a protein in the cell membrane that uses ATP (energy) to move:
Sodium (Na⁺) out of the cell
Potassium (K⁺) into the cell
This movement goes against their natural direction, so it requires energy.
🔁 Why does the cell need this?
Normally, there’s more sodium outside the cell, and more potassium inside the cell.
But some sodium leaks in, and some potassium leaks out all the time.
The cell uses this pump to restore the correct balance, especially for things like nerve impulses.
🧠 How the Pump Works:
ATP is used for energy. It breaks into:
ADP (adenosine diphosphate)
Phosphate (P) — which is temporarily added to the pump (phosphorylation)
This phosphate powers the pump to change shape and:
Push 3 sodium ions (Na⁺) out of the cell
Pull 2 potassium ions (K⁺) into the cell
The pump resets and repeats this process.
🔒 Important Fact:
The pump is very specific — it only moves sodium and potassium. If the pump is missing or broken, no transport happens for those ions.
💬 In simple terms:
The sodium-potassium pump is like a battery charger for your cells. It uses energy (ATP) to keep the right ions in the right place — which is vital for nerve function and muscle movement.
Would a visual diagram help you see the steps more clearly?
The Sodium-Potassium Pump Helps Maintain Cell Balance (Equilibrium)
More sodium (Na⁺) naturally stays outside the cell.
More potassium (K⁺) naturally stays inside the cell.
But because ions can leak in and out, the balance gets thrown off.
🔄 So, the pump:
Pushes 3 sodium ions out of the cell
Pulls 2 potassium ions in to the cell
Uses ATP (energy) to do this because it’s moving ions against their natural gradient.
⚡ Why it’s important:
It keeps the inside of the cell more negative than the outside — needed for:
Nerve impulses
Muscle contractions
Cell homeostasis
The **sodium-potassium pump does NOT move sodium into the cell during a nerve impulse.
✅ It moves sodium out of the cell — after the impulse, to reset things.
Vesicular Transport Overview
Vesicular transport is a process where cells move large amounts of substances (like solids, liquids, or proteins) in bulk into or out of the cell using vesicles (small membrane-bound sacs). These substances don’t actually pass through the cell membrane directly — they’re transported by vesicles that fuse with or separate from the cell membrane.
It uses ATP to do the job, because it requires energy to move big quantities of substances in or out.
The Two Types of Vesicular Transport:
1. Exocytosis (Out of the cell):
This is when the cell sends out large molecules (like hormones, waste, or proteins).
The vesicle containing the substance fuses with the plasma membrane, and then the contents are released outside the cell.
Example:
Neurotransmitter release — nerve cells release neurotransmitters to send signals to other cells.
- Endocytosis (Into the cell):
This is when the cell takes in substances from the outside.
The plasma membrane wraps around the substance and forms a vesicle to bring it into the cell.
There are 3 types of endocytosis:
Phagocytosis (“cell eating”) — When the cell engulfs large particles or debris (like bacteria).
Pinocytosis (“cell drinking”) — When the cell takes in fluids or small molecules.
Receptor-mediated endocytosis — When the cell takes in specific molecules that bind to receptors on the cell membrane.
Example:
White blood cells use phagocytosis to engulf bacteria and other foreign particles.
In Simple Terms:
Exocytosis: The cell exports large substances.
Endocytosis: The cell imports large substances.
Both types use vesicles and ATP to transport things in bulk without them directly crossing the plasma membrane.
In Endocytosis (Toy going inside):
You have a toy (a substance) outside the slime (plasma membrane).
The slime wraps around the toy, pulling it inside.
Once the slime has fully wrapped around the toy, it forms a bubble (vesicle) and pulls the toy inside the slime (cell).
Now, the toy is inside the slime, like how substances are brought inside the cell!
In Exocytosis (Toy coming out):
The toy (substance) is already inside the slime (vesicle).
The slime then moves toward the edge of the slime (plasma membrane).
The slime opens up and releases the toy (substance) outside.
The toy comes out and is now outside the slime (cell), just like how exocytosis works!
Exocytosis
Exocytosis (ek″so-si-to′sis; “out of the cell”) (Figure 3.12) is the mechanism that cells use to actively secrete hormones, mucus, and other cell products or to eject certain cellular wastes. The product to be released is first “packaged” (typically by the Golgi apparatus) into a secretory vesicle. The vesicle migrates to the plasma membrane, fuses with it, and then ruptures, spilling its contents out of the cell (also look back at pathway 1 of Figure 3.6). Exocytosis involves a “docking” process in which docking proteins on the vesicles recognize plasma membrane docking proteins and bind with them. This binding causes the membranes to “corkscrew” together and fuse
The Steps of Exocytosis:
Packaging: The substance to be released is packaged inside a vesicle, often by the Golgi apparatus.
Docking: The vesicle moves toward the plasma membrane, and its docking proteins bind with the docking proteins on the plasma membrane.
Fusion: The membranes of the vesicle and plasma membrane fuse together, forming a path for the substance to be released.
Release: The vesicle ruptures, and its contents are spilled out of the cell into the extracellular space.
Endocytosis
Endocytosis is the process by which a cell takes in extracellular substances (substances outside the cell) by engulfing them into the cell. This process requires energy (ATP) because it involves the movement of the cell membrane and the formation of vesicles.
Here’s a breakdown of the process:
Engulfment:
The plasma membrane of the cell folds inward to surround the substance (which could be nutrients, particles, or even pathogens like bacteria).
This results in the formation of a vesicle, a small, membrane-bound pocket that contains the substance.
Vesicle Formation:
The vesicle detaches from the plasma membrane and is pulled into the cytoplasm of the cell.
Fusion with Lysosome:
Once inside the cell, the vesicle fuses with a lysosome. Lysosomes are organelles that contain digestive enzymes.
The enzymes in the lysosome break down the contents of the vesicle (such as nutrients, pathogens, or debris), allowing the cell to process or dispose of the substance.
Release via Exocytosis (optional):
In some cases, after the substance is broken down, the vesicle may travel to the opposite side of the cell and release its contents outside the cell through exocytosis. This happens, for example, in immune responses or when cells secrete certain products.
Types of Endocytosis:
Phagocytosis: The cell engulfs large particles (e.g., bacteria, dead cells) in a process similar to “cell eating.”
Pinocytosis: The cell engulfs fluid and its dissolved solutes (similar to “cell drinking”).
Receptor-mediated endocytosis: The cell selectively engulfs specific molecules by binding them to receptors on the cell surface before internalizing them in vesicles.
Key Point:
Endocytosis is an energy-dependent process (requires ATP), where the cell “engulfs” material from the extracellular environment into vesicles, which then travel into the cell to be processed.
This process is crucial for absorbing nutrients, removing waste, or protecting the cell from harmful substances like bacteria.
Let me know if you’d like more details on any of the specific steps or types! 😊
This section is explaining two types of endocytosis, which is how cells bring substances into themselves using vesicles:
. Phagocytosis – “Cell Eating” 🍽️
What it is: This is when the cell takes in large particles, like bacteria or dead cells.
How it works: The cell extends pseudopods (fake “arms”) around the particle to engulf it.
Once surrounded, the particle is pulled into the cell in a vesicle, and then digested—usually by a lysosome.
Why it happens: This is not for food, but for protection and cleaning. It helps the body get rid of dangerous or useless stuff.
Example: White blood cells like macrophages do this to fight infections.
Pinocytosis – “Cell Drinking” 🥤
What it is: This is when the cell takes in fluid and dissolved substances, like proteins or fats.
How it works: The plasma membrane forms a small indent (cup), which fills with fluid from outside the cell. The cup then closes off, forming a small vesicle inside the cell.
Why it happens: This is a routine process used by most cells to absorb nutrients, especially in areas like the small intestine, where absorption is key.
Receptor-mediated endocytosis
This is a very specific way for cells to take in certain target molecules.
How it works:
The cell membrane has receptor proteins on it—these are like locks.
Only specific molecules (like enzymes, cholesterol, hormones, iron, etc.) that match the receptor can bind—like the right key fitting into a lock.
Once enough of those matching molecules are attached, the membrane folds in, forming a vesicle that brings the molecules inside the cell.
Inside, the cell processes or uses the molecules—or sometimes sends them elsewhere.
🔍 Compared to Other Types:
Phagocytosis = Big particles, not very picky
Pinocytosis = Fluids & nutrients, not very picky
✅ Receptor-Mediated Endocytosis = Highly selective
😷 Bonus Fact:
Some viruses (like the flu) trick the receptors into letting them in—so this system can sometimes be exploited.
So yes, this type of endocytosis is like VIP access—only the “invited guests” (specific molecules) get in.
Would you like a chart comparing all 3 types of endocytosis?
