Chapter 7-3 Cell Boundaries

Chapter 7-3 Cell Boundaries

The Plasma Membrane: Cell Membrane Regulates what enters and leaves the cell. Provides protection and support. Highly selective barrier!!!!

What the plasma membrane is made out of. Outside of cell Hydrophilic head Hydrophobic tail Phospholipid Cytoplasm (inside of cell) phospholipid bilayer of membrane semi permeable

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins Most membranes have specific proteins and cholesterol embedded in the phospholipid bilayer. Two main types of proteins help regulate traffic across the membrane and perform other functions. Integral and peripheral.

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins Surface Carbohydrates function in cell recognition, cell signaling and cell adhesion. Cholesterol helps keep the phospholipids spaced apart.

Figure 4.UN12 Outside of cell Phospholipid Hydrophilic Protein Hydrophobic Hydrophilic Cytoplasm (inside of cell)

Figure 4.6b Hydrophilic region of protein Outside of cell Proteins Hydrophilic head Hydrophobic tail Hydrophobic regions of protein Cytoplasm (inside of cell) Fluid mosaic model of membrane

Membrane Protein Functions Cells must control the flow of materials in and out of the cell. Membrane proteins perform many functions. Cell signaling = relays messages to inside of cell Cytoskeletal attachment = cell shape Transport = a tunnel that substances pass through Intercellular joining = linking adjacent cells Cell-cell recognition = sugar (carbohydrate) ID tags Enzymatic activity = assembly line of chemical pathway

Figure 5.11 Cell signaling Enzymatic activity Cytoplasm Fibers of extracellular matrix Cytoskeleton Attachment to the cytoskeleton and extracellular matrix Transport Intercellular joining Cell-cell recognition Cytoplasm

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins The plasma membrane is a fluid mosaic. Fluid because molecules can move freely past one another. A mosaic because of the diversity of proteins in the membrane.

Cell Walls ONLY IN PLANTS!! Plant cells have rigid cell walls surrounding the membrane. Plant cell walls made of cellulose protect the cells porous enough to allow water, oxygen and carbon dioxide to pass through easily. maintain cell shape keep cells from absorbing too much water.

Diffusion Through Cell Boundaries Living cells exists in a liquid environment in order to survive. The plasma membrane plays a crucial role in regulating the movement of dissolved molecules from one side of the membrane to the liquid of the other side.

Diffusion Through Cell Boundaries Measuring Concentration The cytoplasm of a cell contains a solution of many different substances in water. The plasma membrane is semi-permeable, which means the membrane regulates what can go into and out of the cell.

Diffusion In a solution particles are constantly moving! The particles collide with one another and spread out randomly. As a result of this movement, particles tend to move from areas where they are more concentrated to areas where they are less concentrated.

Diffusion Movement of molecules from areas of high concentration to areas of low concentration

Diffusion no energy required!!!! Molecules of dye Membrane Net diffusion Net diffusion Equilibrium

Diffusion across Membranes Some substances do not cross membranes without the help from channel proteins embedded in the plasma membrane. These substances cross the plasma membrane by a process called facilitated diffusion through protein channels. No energy input is needed, the molecules diffuse from areas of higher concentration to areas of lower concentration through the channel protein. high concentration low concentration

Osmosis and Water Balance The diffusion of water across a selectively permeable membrane is osmosis. Water is moving from where it is more concentrated to where it is less concentrated.

Osmosis and Water Balance When we compare two solutions we say that a hypertonic solution has a greater concentration of solutes a hypotonic solution has a lesser concentration of solutes an isotonic solution has an equal concentration of solutes Remember that when we make a solution the solvent is the liquid and the solute is the solid.

Osmosis and Water Balance Hypotonic solution Hypertonic solution Sugar molecule Selectively permeable membrane Osmosis

Osmosis and Water Balance Hypotonic solution Hypertonic solution Isotonic solutions Sugar molecule Osmosis Selectively permeable membrane Osmosis

Water Balance in Cells Osmoregulation is the control of water balance within a cell or organism. Organisms must have a way to balance the water that exits and enters their cells. The cells in our body are not in danger of swelling because our cells are bathed in fluids like blood that are isotonic.

Animal cell H 2 O H 2 O H 2 O H 2 O Normal Lysing Shriveled Plant cell H 2 O H 2 O H 2 O Plasma membrane H 2 O Flaccid (wilts) (a) Isotonic solution Turgid (normal) (b) Hypotonic solution Shriveled (c) Hypertonic solution

Animal cell H 2 O H 2 O A cell in an isotonic solution in which the concentration of solutes is the same inside and outside the cell. The cell is balanced and behaves normally. Normal Plant cell H 2 O H 2 O Flaccid (wilts) Isotonic solution

A cell in a hypotonic solution such as fresh water. Because the cell has a higher concentration of solutes than the fresh water, water rushes into the cell and the cell swells. H 2 O Bursting H 2 O Turgid (normal) Hypotonic solution Animal cells don t have cell walls and will eventually burst!! The cell wall of the plant cell prevents the plant cell from bursting!

A cell in a hypertonic solution in which the concentration of solutes in the solution is higher than the concentration of solutes inside the cell, which results in the movement of water out of the cell and the cell shrinking. Shriveled Plasma membrane Shriveled Hypertonic solution H 2 O H 2 O The plasma membrane pulls away from the cell wall in the process of plasmolysis, which usually kills the cell.

When plant cells lose water the plasma membrane pulls away from the cell wall and the plant cell shrivels resulting in the plant wilting.

Active Transport: The Pumping of Molecules across Membranes Active transport requires that a cell expend energy to move molecules across a membrane against a concentration difference, meaning, from areas of low solute concentration to areas of high solute concentration. This is done by proteins embedded in the plasma membrane called protein pumps.

Figure 5.16-2 Lower solute concentration Solute ATP Higher solute concentration Active transport

Solute Solute Water Solute Membrane Transport Summary MEMBRANE TRANSPORT Passive Transport (requires no energy) Diffusion Facilitated diffusion Osmosis Higher solute concentration Higher water concentration (lower solute concentration) Active Transport (requires energy) Higher solute concentration Solute Lower solute concentration Lower water concentration (higher solute concentration) ATP Lower solute concentration

Exocytosis and Endocytosis: Traffic of Large Molecules That Requires Energy Endocytosis process of taking materials into the cell by means of infoldings, or pockets of the plasma membrane that form into vesicles once inside the cell. Large molecules, clumps of food or even whole cells can be taken into the cell this way. Phagocytosis cell eating example = ameobas Pinocytosis cell drinking

Endocytosis outside of the cell plasma membrane cytoplasm vesicle

Exocytosis and Endocytosis: Traffic of Large Molecules That Requires Energy Exocytosis is the secretion of large molecules within transport vesicles to the outside of the cell.

Exocytosis Outside of cell Plasma membrane Cytoplasm vesicle