Lecture 3: Movement into Cells

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Questions and Answers

What is the primary function of the phospholipid bilayer in the plasma membrane?

To regulate the movement of water and small molecules (correct)

To provide structural support to the cell

To facilitate the passage of ions and macromolecules

To recognize and respond to external signals

What is the term for the movement of molecules from an area of higher concentration to an area of lower concentration?

Active transport

Osmosis

Diffusion (correct)

Passive transport

What type of molecules can pass through the phospholipid bilayer?

Sugars, salts, and ions

Water, oxygen, and carbon dioxide (correct)

Glucose, proteins, and RNA

Ions, proteins, and RNA

What is the term for the bulk flow of water through a semipermeable membrane from an area of higher water concentration to an area of lower water concentration?

Osmosis Signup and view all the answers

Why does water flow from an area of higher concentration to an area of lower concentration?

To eliminate concentration gradients Signup and view all the answers

What is the term for the characteristic of the plasma membrane that allows certain molecules to pass through while restricting others?

Semipermeability Signup and view all the answers

What is the role of the Sodium-Potassium Pump in the cell?

To move ions against their concentration gradient Signup and view all the answers

What is the consequence of Na-K ATPase action in the cell?

Unequal movement of key ions, resulting in a negative membrane potential Signup and view all the answers

What is the purpose of patch-clamping in single ion channel recording?

To record the activity of single ion channels Signup and view all the answers

What is the concentration of sodium ions outside the cell?

140 mM Signup and view all the answers

What is the osmotic pressure gradient of a solution with 1 M glucose compared to a solution with 0.1 M glucose?

Hypertonic Signup and view all the answers

What is the role of aquaporins in the cell?

To form water channels Signup and view all the answers

What is the result of the unequal movement of charge due to the Na-K ATPase?

A negative membrane potential Signup and view all the answers

What type of transport does a transmembrane protein that forms a pore in the cell membrane facilitate?

Facilitated diffusion Signup and view all the answers

What is the term for the movement of water molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane?

Osmosis Signup and view all the answers

What is the main function of transporters in the cell membrane?

To facilitate active transport of ions and nutrients Signup and view all the answers

What is the term for a solution that has the same osmotic pressure as red blood cells?

Isotonic Signup and view all the answers

What is the primary function of integral membrane proteins?

To facilitate the transport of ions and nutrients Signup and view all the answers

What determines the relative contribution of an ion across the plasma membrane?

Both concentration gradient and relative membrane permeability Signup and view all the answers

What type of movement is facilitated by Na+ gradient as a driving force?

Facilitated diffusion Signup and view all the answers

What is the primary function of Clathrin-mediated endocytosis?

Nutrient uptake and signal transduction Signup and view all the answers

What is the term for the process of engulfing particles?

Phagocytosis Signup and view all the answers

What is the main function of cell membranes in terms of compartmentalization?

To regulate the flow of substances into and out of cells Signup and view all the answers

What is the primary outcome of a cell's ability to survive and function in isolation?

Homeostasis Signup and view all the answers

Study Notes

Cell Membrane Structure and Function

The cell membrane is a phospholipid bilayer that is semi-permeable, allowing certain molecules to pass through while keeping others out.
The lipid bilayer is impermeable to most essential molecules and ions, but permeable to water molecules and a few small, uncharged molecules like oxygen and carbon dioxide.

Diffusion and Osmosis

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, resulting in equal distribution.
Osmosis is the bulk flow of water through a semi-permeable membrane into another aqueous compartment containing a higher concentration of solute.
Water molecules move to equalize the concentration of solute, resulting in equilibrium.

Tonicity and Osmotic Pressure

Tonicity refers to the osmotic pressure gradient across a membrane.
Isotonic solutions have the same concentration of solute as the cell, while hypotonic solutions have a lower concentration and hypertonic solutions have a higher concentration.
Water molecules move into or out of the cell to equalize the concentration of solute, resulting in changes to the cell's shape and volume.

Ion Transport

Ion transport occurs through transmembrane proteins, which form pores through the membrane.
There are two broad categories of ion transport: channels (facilitated diffusion) and transporters (facilitated diffusion or active transport).
Ion channels can be specific to particular ions, such as the glycine receptor chloride channel.
Aquaporins are water channels that facilitate the movement of water across the membrane.

Active Transport

Active transport involves the movement of molecules against their concentration gradient, requiring energy from ATP.
The sodium-potassium pump is an example of active transport, where Na+ ions are pumped out of the cell and K+ ions are pumped in.
The sodium-potassium pump creates an electrochemical potential difference across the membrane, resulting in a negative membrane potential.

Facilitated Diffusion

Facilitated diffusion is the movement of molecules down their concentration gradient, facilitated by transport proteins.
Facilitated diffusion can be regulated, and often uses the Na+ gradient as a driving force.

Cell Movement and Transport

Endocytosis is the movement of molecules into the cell through the formation of vesicles.
Exocytosis is the movement of molecules out of the cell through the fusion of vesicles with the membrane.
Clathrin-mediated endocytosis is a specific type of endocytosis that involves the use of clathrin proteins to form vesicles.

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