My AP Biology Thoughts  Unit 2 Cell Structure and Function

Welcome to My AP Biology Thoughts podcast, my name is Morgan Bernstein and I am your host for episode #59 Unit 2: Active Transport: Endocytosis, Exocytosis, and Protein Pumps.

Segment 1: Introduction to Active Transport

First, we have to know that within any cell, things are always moving. Proteins need to get places, waste has to be excreted, and food is consumed. 

• Two umbrella terms of movement- Passive Transport and Active Transport
• Passive Transport=no energy required, almost like a habit
• Active transport = within a vesicle, does require energy 

Active transport is what we will be discussing in this episode, but be sure to check out episode 58 to learn about passive transport as well!

Why does active transport require energy? 

• Goes against the concentration gradient
• Things are moving from low concentration to high concentration (disrupts equilibrium and requires extra energy) 
• Can happen across a cell membrane or within the cell itself

Segment 2: Examples of Active Transport: Endo/Exocytosis and Pumps

The first type of active transport is one that does cross a cell-membrane barrier, and it is known as the sodium-potassium pump. 

• Two potassium ions into the cell and takes three sodium ions out
• Works because of the protein pump in the plasma membrane. 
• Three sodium ions bind to the carrier protein pump inside the cell, and are transported out using the energy available from ATP. 
• Protein then changes shape to allow for the potassium ions to bind to it as well, and pumps those inside of the cell membrane where they are transported for use in the cell before the process repeats. 
• Higher concentration of potassium ions inside the cell than outside, and a higher concentration of sodium ions outside the cell, so this sodium-potassium pump is going against the concentration gradient and is therefore a form of ACTIVE transport
• Requires energy.

Another form of active transport comes in endocytosis and exocytosis

• First, cytosis means cell, which is present in all three terms
• Endo = enter, + cytosis = cell, so endocytosis = into the cell
• Exo = exit, + cytosis = cell, so exocytosis = exiting the cell. 

Endocytosis 

• Things brought into the cell across the membrane, but not through a pump 
• Requires energy
• Happens inside a vesicle (small cellular bubble that holds and transports other molecules and ions)
• Molecules or ions outside of the cell are enclosed by a part of the plasma membrane, forming the vesicle, and vesicle brings the contents through the membrane into the cell for transport 

Exocytosis 

• export proteins or excrete waste products
• Requires energy

Necessary protein or waste products inside of a transport vesicle, vesicle connects with plasma membrane and contents released into outside environment. 

Segment 3: Connection to the Course

Active transport has many connections to our Unit 2 about Cells and to biology in general. 

• Goes against the rules used for any other cellular movement ex. osmosis or...