Chapter 7

What were the ideas concerning the plasma membrane models of Gorter and Grendel?

- Cell membrane was a phospholipid bilayer

What were the ideas concerning the plasma membrane models of Davson and Danielli?

- Sandwich Model - Phospholipid bilayer coated on both sides by hydrophilic proteins

What does selective permeability mean and why is that important to cells?

- Some substance can pass through more easily than others - Cell can seal itself off from environment but still take in nutrients and eliminate wastes

Why is membrane sidedness an important concept in cell biology?

- the two lipid layers have different lipid layers have different lipid composition. Each protein has a directional orientation. - molecules that start on the inside of the ER end up on the outside of the plasma membrane

Why is water balance important for cells that have walls as compared to cells without walls?

-Cell Walls push back on the cell when they become turgid -Cells without walls cannot push back, they can burst.

What is cotransport and why is it an advantage in living systems?

-Cotransport is a substance pumped across a membrane, and does work as it diffuses back across the membrane. - ATP indirectly provides energy for co-transport

What is diffusion and how does a concentration gradient relate to passive transport?

-Diffusion- movement of molecules that spread out in a space. -Diffusion across a semi permeable membrane is passive transport -Substances diffuse down their concentration gradient without using energy.

List the 6 broad functions of membrane proteins.

-Transport - Enzymatic activity - Signal Transduction - Cell-Cell recognition -Intercellular Joining - Attachment to cytoskeleton and ECM

How has our understanding of membrane permeability changed since the discovery of aquaporins?

-aquaporins allow a tremendous amount of water to pass through a hydrophobic membrane at a fast rate. - other ions and polar molecules pass through transport proteins

How do glycolipids and glycoproteins help in cell to cell recognition?

-identifies foreign cells -important in sorting types of cells in embryos - designates type A, B, AB and O in blood groups

Describe the freeze fracture technique and why is it useful in cell biology.

A cell is frozen and fractured with a knife. Fracture plane follows the hydrophobic interior, the membrane proteins go with one of he layers Allows us to see the structure of the membrane.

What is ligand?

A molecule that binds specifically to the receptor sites of another molecule

What is an amphipathic molecule?

A molecule that has a hydrophilic and hydrophobic end. Example: phospholipids

How is ATP specifically used in active transport?

ATP transfers a phosphate group to a transport protein, this powers the change in shape to move the substances against their concentration gradient.

Proton Pump

Actively transporting hydrogen ions. *Inside the cell is negative, therefore cations move in and anions move out*

Pinocytosis

Cell drinking, droplets are engulfed into a vesicle

Receptor-Mediated Endocytosis

Coated pits contain receptors that attach to specific molecules, engulf and put into vesicle.

Electrochemical Gradient

Combination of chemical force and electrical force on an ion.

Phagocytosis

Engulfs solid particles, packaged in vesicles, fuses with a lysosome and digests particles

What is the relationship between ion channels and gated channels and facilitated diffusion?

Facilitated diffusion allows polar molecules and ions to passively diffuse through the membrane channel proteins such as ion channels which function as gated channels allows water or specific solutes to passively diffuse.

What were the ideas concerning the plasma membrane models of Singer and Nicolson?

Phospholipid bilayer with proteins individually inserted into the bilayer with hydrophilic ends protruding.

Why is free water concentration the "driving" force in osmosis?

Some water molecules cluster around and solute molecules and are unable to diffuse. The Free water molecules move from high concentration to low concentration until solute concentration is the same on both sides.

Electrogenic Pump

Transports protein that generates voltage across a membrane.

Membrane Potential

Voltage across a membrane

How is the fluidity of cell membrane's maintained?

movement of phospholipids- lipids move laterally within the rapid membrane. Membrane fludity- unsaturated hydrocarbons have kinked tails so they don't perk together. Cholesterol- Reduces fluidity at moderate temps, hinders solidification at low temps.