Chapter 3A Cell Membranes Cell Structure Chapter 3A Cell Membranes

Objectives I will be able to describe the characteristics of a cell membrane. I will be able to distinguish between passive transport and active transport. I will be able to compare the processes of diffusion and osmosis.

Cytology The study of cells

Cell Boundaries The cell membrane is the outer boundary of most cells. Found in all cells. A cell wall is a stiff structure outside the cell membrane that protects a cell from attack by viruses and other harmful organisms. Found in plant cells.

Cell membrane

Cell Membrane Functions Senses and responds to changes in the environment Protects cell from harmful substances Allows needed materials into the cell

Cell Membranes Fluid mosaic model Phospholipids Lipid bilayer Hydrophilic (point towards outside) Hydrophobic (point towards middle) Lipid bilayer

Fluid Mosaic Model

Selectively Permeable A selectively permeable membrane allows certain molecules to pass through the membranes and others to not pass through

Selectively Permeable Not all membranes are permeable to the same molecules. However water, oxygen, and carbon dioxide are small and easily passes through most membranes.

How does a substance pass through a unit membrane? Passive Transport Active Transport

Passive Transport Passive transport moves substances through a membrane without the use of the cell’s own energy.

PASSIVE TRANSPORT This is the main way. Small molecules, such as oxygen and carbon dioxide, pass through membranes via passive transport. Passive transport depends on the amount of substance on each side of a membrane. This is the main way.

main forms of passive transport Diffusion Osmosis Facilitated Diffusion

diffusion the movement of molecules from an area of higher concentration to an area of lower concentration diffusion from Latin diffusionem, means “scatter, pour out”

diffusion diffusion can be speeded up by such things as heat, movement, and pressure

Diffusion Diffusion continues until the concentration of a substance is the same on both sides of the membrane. The substance is then in equilibrium.

The diffusion of water through a selectively permeable membrane Osmosis The diffusion of water through a selectively permeable membrane

Facilitated Diffusion Facilitated diffusion occurs when molecules pass through a cell membrane using special proteins called transport proteins. Carrier proteins are transport proteins that carry large molecules through the cell membrane. Channel proteins are transport proteins that form pores through the cell membrane.

Facilitated Diffusion The Plasma Membrane 11/12/2018 Facilitated Diffusion *Is a type of passive transport Doesn’t require energy Uses transport proteins to move molecules from high to low concentration Facilitated Diffusion- is the movement of larger molecules like glucose through the cell membrane  larger molecules must be “helped” Examples: Glucose or amino acids moving from blood into a cell. G. Podgorski, Biol. 1010

Facilitated Diffusion

ACTIVE TRANSPORT Active transport requires the cell to use its own energy to move substances through a membrane. (sometimes because of the size of the molecule being so large, or going against gradient)

This is going to be hard work!! Active Transport Requires Energy. ATP (form of energy made by mitochondria). Moves against the concentration gradient. High low This is going to be hard work!!

Sodium Potassium Pump Active transport goes AGAINST the concentration gradient Low solute concentration to high solute concentration The cell uses energy (ATP) to actively transport Na+ out of the cell and K+ into the cell against the concentration gradient

Sodium Potassium Pump

Endocytosis and Exocytosis Endocytosis and Exocytosis is the mechanism by which very large molecules (such as food and wastes) get into and out of the cell **ENERGY IS REQUIRED

Endocytosis Think endo- Think enter Transporting material into a cell by the in folding of a membrane. Think endo- Think enter To take inside of the cell

2 Types of Endocytosis Phagocytosis- Solid particles are ingested into the cell. Pinocytosis – liquids and very small molecules are taken into the cell.

Endocytosis

Exocytosis Moves materials out of the cell Think exo- Think exit

Exocytosis- moving things out. The Plasma Membrane Moving the “Big Stuff” 11/12/2018 Exocytosis- moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another. G. Podgorski, Biol. 1010