Bio Chapter 5

What does the Fluid Mosaic Model describe?

A cell membrane's structure as a mosaic of various proteins embedded in or attached to a fluid lipid bilayer.

Why is the plasma membrane referred to as 'selectively permeable'?

It regulates what substances can enter or exit the cell.

Define passive transport.

The movement of molecules across a cell membrane without the use of energy.

What is diffusion?

The movement of molecules from an area of higher concentration to an area of lower concentration.

What is osmosis?

The diffusion of water across a semipermeable membrane.

What is tonicity?

The ability of a surrounding solution to cause a cell to gain or lose water.

What happens to a cell placed in a hypertonic solution?

The cell shrinks as water moves out of the cell.

Define facilitated diffusion.

A process by which molecules diffuse across the membrane with the help of transport proteins.

What is active transport?

The movement of molecules against their concentration gradient, requiring energy.

What is the Na/K pump?

A mechanism that pumps sodium ions out of the cell and potassium ions into the cell, against their gradients.

What is exocytosis?

The process by which a cell expels large molecules by engulfing them in a vesicle that fuses with the plasma membrane.

What is endocytosis?

The process by which a cell takes in large molecules by engulfing them in a vesicle.

What are exergonic reactions?

Chemical reactions that release energy.

What are endergonic reactions?

Chemical reactions that require an input of energy to proceed.

What is ATP?

A molecule that carries energy within cells for metabolism.

Compare ADP and ATP.

ADP (adenosine diphosphate) has two phosphate groups, while ATP (adenosine triphosphate) has three; ATP is energy-rich, ADP is lower in energy.

What is a catalyst?

A substance that speeds up a chemical reaction without being consumed.

How do enzymes lower energy barriers?

By providing an alternative pathway for a reaction with a lower activation energy.

What is the catalytic cycle of an enzyme?

The series of steps in which an enzyme binds to substrate, catalyzes the reaction, and releases products.

What is feedback inhibition?

A regulatory mechanism whereby the end product of a metabolic pathway inhibits an enzyme involved in its production.

Name an example of an enzyme inhibitor.

Drugs like aspirin, which inhibit cyclooxygenase enzymes involved in inflammation.