Chapter 4: Membrane Structure & Function

What does the plasma membrane do?

regulates what enters and exits the cell

What makes up the phospholipid bilayer?

hydrophilic polar heads & hydrophobic non polar tails made up of two fatty acids

hydrophobic nonpolar tails are made of

two fatty acids

What does cholesterol do in plasma membrane?

stabilizes the interactions between the phospholipids and prevents the membrane from getting too fluid or too flexible

What does hydrophilic mean?

water-loving

What does hydrophobic mean?

water-fearing

What are two types of membrane proteins?

peripheral and integral

Where are peripheral proteins found?

only on one side of the membrane

Where are integral proteins found?

found on one or both sides of the membrane

Which membrane protein can move laterally?

integral proteins

How is it possible for molecules to get through the phospholipid bilayer?

membrane is semipermeable

What are 3 factors that determine how a substance will be transported across the membrane?

size, polarity, charge

What is a concentration gradient?

the region along which the density of a substance increases or decreases

What does "going down" a concentration gradient mean?

going from an area of high to low concentration

What does "going up" a concentration gradient mean?

going from an area of low to high concentration

Does going up (low to high) a concentration gradient require energy?

yes

What types of molecules move freely across the membrane?

water

small molecules

noncharged molecules

What other method will water use to cross the membrane?

aquaporins

Other molecules use what 3 methods to cross the membrane?

channel proteins, carrier proteins, vesicles

What two specific methods to vesicles use?

endocytosis and exocytosis

What is diffusion?

movement of molecules from area of higher to lower concentration

In a solution what two things are present?

a solute (solid) and a solvent (liquid)

Can gases also diffuse across a membrane?

yes

Give an example of diffusion of gases in the body.

oxygen and carbon dioxide exchange in the lungs

List four factors that influence the rate of diffusion.

concentration gradient, membrane permeability, temperature, and pressure

Electrical currents

movements of ions across cell membrane that are driven by electrochemical gradients

Molecular size

As temperature increases does the rate of diffusion increase or decrease?

increase

What is osmosis?

diffusion of water across a semipermeable membrane

In diffusion what is always the direction the concentration will go?

from higher to lower concentration

What is osmotic pressure?

pressure that develops in a system due to osmosis

The greater the osmotic pressure the more likely or less likely water will diffuse in that direction?

more likely

What is an isotonic solution?

solute concentration equal inside and out cell

What is a hypotonic solution?

a solution that has lower solute concentration than inside the cell

What is a hypertonic solution?

a solution that has a higher solute concentration inside the cell

In a hypotonic solution a cell may ____?

lysis (burst)

In a hypertonic solution a cell may _____?

crenate (shrivel)

Are carrier proteins specific or nonspecific?

specific

How do carrier proteins transport a molecule across the membrane?

carrier proteins combine with a molecule

What two methods are carrier proteins required for?

facilitated transport and active transport

What types of molecules are associated with facilitated transport?

small molecules that are not lipid-soluble

What is a concentration gradient?

the region along which the density of a substance increases or decreases

Is energy required in facilitated transport?

no

What happens in active transport?

molecules combine with carrier protein which uses energy to move against their concentration gradient

What are these carrier proteins called in active transport?

pumps

What is the function of vesicle formation?

membrane-assisted transport

Why is a vesicle required to transport macromolecules?

to keep it contained

What do vesicles transport?

macromolecules

Does vesicle formation require energy?

yes

What are two types of vesicle transport?

exocytosis and endocytosis

What happens in exocytosis?

vesicle fuses with plasma membrane and secretion occurs

What happens in endocytosis?

a process by which cells take in substances from outside the cell, such as macromolecules, particles, and other cells, to inside the cell

What happens to the membrane of the vesicle when it fuses with the plasma membrane?

it becomes part of the plasma membrane

What are there types of endocytosis?

phagocytosis, pinocytosis, and receptor mediated endocytosis

When is phagocytosis used?

when you have large separate matter

When is pinocytosis used?

when you have liquids or small particles dissolved in liquid

What is receptor mediated endocytosis?

a form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule