CH 7.2 & 7.4

Biology

LABEL THE MEMBRANE… Phospholipids Cholesterol Peripheral proteins Integral proteins Cytoskeleton Cytoplasm Extracellular fluid

Most of the membrane A phospholipid bi-layer makes up most of the

membrane.

Polar heads

2 Non-polar tails

Fluid Mosaic Model

“Fluid” because the components are in constant motion, moving laterally (from side-to-side).

“Mosaic” because of the embedded proteins viewed from above.

Selectively Permeable

The phospholipid bilayer of the cell membrane allows hydrophobic molecules to pass through easily, but hydrophilic do NOT.

Materials soluble in lipids can pass easily through the cell membrane.

Selectively Permeable

Because the membrane is selectively permeable, only small molecules and larger hydrophobic molecules can pass through easily.

Examples: O2, CO2, and H2O (small)

Selectively Permeable

Ions, hydrophilic molecules larger than water, and large molecules such as proteins do NOT move through the membrane on their own.

Simple Diffusion

Requires NO energy

Molecules move from an area of HIGH concentration to an area of LOW concentration.

Diffusion Diffusion is a passive

process, which means that no energy is used to cause the molecules to move. The do so because of their own natural kinetic energy, or energy of motion.

Plasma Membrane

Osmosis

Osmosis is the diffusion of water across a semipermeable membrane.

Moves from HIGH water potential (low solute) to LOW water potential (high solute)

Osmosis Water diffuses through the pores called aquaporins of

the cell membrane.

These aquaporins are specialized proteins embedded in the plasma membrane.

Movement through these protein channels DOES NOT require energy.

Cell in Isotonic Solution

CELL

10% NaCL 90% H2O

10% NaCL 90% H2O

What is the direction of water movement?

The cell is at _______________. equilibrium

ENVIRONMENT

NO NET MOVEMENT

Cell in Hypotonic Solution

CELL

10% NaCL 90% H2O

20% NaCL 80% H2O

What is the direction of water movement?

Cell in Hypertonic Solution

CELL

15% NaCL 85% H2O

5% NaCL 95% H2O

What is the direction of water movement?

ENVIRONMENT

Cells in Solutions

Isotonic Solution

NO NET MOVEMENT OF H2O (equal amounts entering & leaving)

Hypotonic Solution

CYTOLYSIS

Hypertonic Solution

PLASMOLYSIS

Cytolysis & Plasmolysis

Cytolysis Plasmolysis

24

Osmosis in Red Blood Cells

Isotonic Hypotonic Hypertonic

What Happens to Blood Cells?

26

hypotonic hypertonic isotonic

hypertonic isotonic hypotonic

Which environment is best?

Plants prefer hypotonic environments, while animal cells do best in isotonic environments.

28

Three Forms of Transport Across the Membrane

Passive Transport Simple Diffusion

•Does NOT require energy

• Moves high to low concentration •Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.

Passive Transport Facilitated diffusion

•Does NOT require energy

•Uses transport proteins to move high to low concentration •Examples: Glucose or amino acids moving from blood into a cell.

Types of Transport Proteins

• Channel proteins are embedded in the cell membrane & have a pore for materials to cross by facilitated diffusion.

• Carrier proteins can change shape to move material from one side of the membrane to the other

Facilitated Diffusion

Molecules will randomly move through the pores in Channel Proteins.

copyright cmassengale

Facilitated Diffusion Some Carrier proteins do

not extend through the membrane.

They bond and drag molecules through the lipid bilayer and release them on the opposite side.

Carrier Proteins

Other carrier proteins change shape to move materials across the cell membrane.

Active Transport

•Requires energy or ATP

•Moves materials from LOW to HIGH concentration

•AGAINST concentration gradient

Active Transport • Examples: Pumping Na+

(sodium ions) out and K+ (potassium ions) in against strong concentration gradients.

• Called the Sodium/Potassium Pump

Sodium-Potassium Pump

3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

Moving the “Big Stuff”

Molecules are moved out of the cell in vesicles that fuse with the plasma membrane.

Exocytosis- moving

things out.

This is how many hormones are secreted and how nerve cells communicate with one another.

Endocytosis Large molecules move materials into the cell by one of three

forms of endocytosis.

Pinocytosis

Most common form of endocytosis.

Takes in dissolved molecules as a vesicle.

Pinocytosis • Cell forms an

invagination

• Materials dissolve in water to be brought into cell

• Called “Cell Drinking”

Example of Pinocytosis

pinocytic vesicles forming mature transport vesicle

Receptor-Mediated Endocytosis

Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.

Receptor-Mediated Endocytosis

Phagocytosis

Used to engulf large particles such as food, bacteria, etc. into vesicles

Called “Cell Eating”

50

Phagocytosis About to Occur

51

Phagocytosis in action - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)