CH 7.2 & 7.4 Biology

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: O 2, CO 2, and H 2 O (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 10% NaCL 90% H 2 O ENVIRONMENT CELL 10% NaCL 90% H 2 O NO NET MOVEMENT What is the direction of water movement? The cell is at. equilibrium

Cell in Hypotonic Solution 10% NaCL 90% H 2 O CELL 20% NaCL 80% H 2 O What is the direction of water movement?

Cell in Hypertonic Solution 15% NaCL 85% H 2 O ENVIRONMENT CELL 5% NaCL 95% H 2 O What is the direction of water movement?

Cells in Solutions

Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) CYTOLYSIS PLASMOLYSIS

Cytolysis & Plasmolysis Cytolysis Plasmolysis

Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic 24

What Happens to Blood Cells?

hypotonic hypertonic isotonic hypertonic isotonic hypotonic 26

Which environment is best? Plants prefer hypotonic environments, while animal cells do best in isotonic environments.

Three Forms of Transport Across the Membrane 28

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 Exocytosis - moving things out. Molecules are moved out of the cell in vesicles that fuse with the plasma membrane. 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

Phagocytosis About to Occur 50

Phagocytosis in action - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) 51