Cell Communication and Transport

What is the main function of the plasma membrane?

Protects the inside of the cell from the environment and controls what enters and leaves the cell.

What is meant by the term "selectively permeable"?

Allows only certain molecules to enter or leave the cell.

What are the two main molecules that make up the plasma membrane?

Phospholipids:

Head- charged and hydrophyllic

Tail- non-charged and hydrophobic

Why do we call the plasma membrane a lipid bi-layer?

Because it is two layers of lipid molecules, one layer that faces the outside of the cell and one that faces the inside of the cell.

Which part of the phospholipid is hydrophobic?

Tail

Which part of the phospholipid is hydrophillic?

Head

What is meant by "fluid mosaic model"?

A model that describes the structure of cell membranes. In this model, a flexible layer made of lipid molecules is interspersed with large protein molecules that act as channels through which other molecules enter and leave the cell.

What is active transport?

Movement of ions or molecules across cell membrane that requires energy because they are moving against the concentration gradient.

What is passive transport?

Movement of material across cell membranes without need of energy input as in osmosis, diffusion and facilitated diffusion. Moving with the gradient from area of high concentration to low.

What is diffusion?

Movement of molecules or atoms down a concentration gradient. It is passive transport because it does not require energy.

What is a concentration gradient?

A measure of how the concentration of something changes from one place to another.

What is osmosis?

Movement of solvent (water) from area of high concentration to low. It is passive transport.

Define hypertonic, hypotonic, and isotonic.

Hypertonic solution is one with a higher concentration of solutes outside the cell than inside the cell. Water leaves the cell;

Hypotonic has a lower concentration of solutes outside of the cell than inside the cell. Water leaves the cell.

Isotonic has equal concentration inside and outside the cell. Equilibrium

What is facilitated diffusion?

A process by which substances that are too large or charged are transported across cell membranes by protein molecules. "Getting a little help from my friends."

Is it active or passive? Passive

What is endocytocis?

When a cell absorbs molecules, such as proteins, from outside the cell by engulfing it with the cell membrane.

What are the 2 types?

Pinocytosis, (cell drinking) Cell membrane brings molecules into the cell and pinches off, enclosing the molecule.

Phagocytosis (cell eating) Cell membrane extends outward and surrounds the molecule bringing it into the cell.

What is exocytosis?

A form of active transport in which a cell transports molecules (such as proteins) out of the cell (exo- + cytosis) by expelling them in an energy- using process.

List and give an example of three types of signaling that occur between cells.

Direct contact; cell membranes of different cells touch and message is passed from one cell to another cell. (post it notes) Ex: Cell brings in an antigen from a virus and destroys it.

Local Regulators; (messenger molecules) that influence nearby cells without touching them. Communication is still one cell to another cell. (EMAIL) Ex: Neurotransmitters sent across a synapse to indicate pain signal to brain.

Long Distance - One cell communicates with many cells (facebook) said to influence many cells.

Ex; Hormones used to send massages to cells to target growth especially during puberty.

What are the 3 steps to a Signal Transduction Pathway?

Reception- A receptor protein outside the cell detects chemical signals.

Transduction- Ligand docs on receptor protein and sends signal intro the cell.

Response- Cell activity (target cells)

What does a ligand do?

It docs with the receptor protein and sends a signal.

Where does it attach?

To a protein.

What happens when it attaches?

It docs with the receptor protein and sends a signal which causes the protein subunit inside to change shape. This in turn causes secondary messengers to activate protein kinase and the process of phosphorylation begins.

What is the most common pathway used by cells?

G-protein pathway

Phosphorylation vs. Dephosphorylating

Phosphorylation:

ATP adds a phosphate group to a protein which turns the enzyme on or off.

Dephosphorylation:

Removes phosphate group and activates or deactivates the enzyme (does opposite of phosphorylation)