Cell Membrane “Keeping it all Together”

Cell Membrane ► When you think about a membrane, imagine it is like a big plastic bag with some tiny holes. ► That bag holds all of the cell pieces and fluids inside the cell and keeps any nasty things outside the cell. The holes are there to let some things move in and out of the cell.

Cell Membrane cont… ► The cell membrane is what defines the cell and keeps its components separate from outside cells or organisms.

Cell membrane ► The cell membrane is composed of a double layer of fat cells called a lipid bilayer in which membrane proteins are embedded. ► The structure of the lipid bilayer prevents the free passage of most molecules into and out of the cell.

Cell Membrane ► Fluid Mosaic Model:

Cell Membrane ► The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer. Lipid bilayer

The Lipid Bilayer ► The lipid bilayer is a universal component of all cell membranes ► Its role is critical because its structural components provide the barrier that marks the boundaries of a cell. ► The structure is called a "lipid bilayer" because it is composed of two layers of fat cells organized in two sheets.

Lipid Bilayer Structure ► The structure of the lipid bilayer explains its function as a barrier ► Lipids are fats, like oil, that are insoluble in water. There are two important regions of a lipid that provide the structure of the lipid bilayer.

Lipid Bilayer Structure cont… ► Each lipid molecule contains a hydrophilic region or polar head region and a hydrophobic region or non polar tail region. The hydrophilic region is attracted to aqueous water conditions while the hydrophobic region is repelled from such conditions

Phospholipids ► The most abundant class of lipid molecule found in cell membranes is the phospholipid.

Properties of Lipid Bilayer ► Most important property is that it is highly impermeable. ► Impermeable means it does not allow molecules to pass through it easily ► Some molecules require the assistance of other structures.

Another Bilayer Property: ► Another property of the bilayer is it’s fluidity. ► The bilayer contains lipids and proteins ► The bilayer's fluidity allows these structures mobility within the lipid bilayer

Quiz Checkpoint: ► What is the main function of the lipid bilayer?

Answer to Question #1 ► The lipid bilayer acts as a barrier between the inside and outside of the cell. It is highly impermeable and does not allow most molecules to freely pass through it into or out of the cell.

Quiz Question #2 ► Why is the structure called a lipid bilayer?

Answer to Question #2 ► It is called a lipid bilayer because it is composed of two layers of fat, or lipid, molecules.

Quiz Question #3 – Fill in the Blank ► A phospholipid molecule contains two distinct regions. The __________ region is attracted to water and the ___________ region is repelled from water.

Answers to Question #3 ► Hydrophilic; Hydrophobic

Membrane Proteins ► While the lipid bilayer provides the structure for the cell membrane, membrane proteins allow for many of the interactions that occur between cells.

Membrane Proteins cont… ► Membrane proteins perform various functions, and this diversity is reflected in the significantly different types of proteins associated with the lipid bilayer.

Classifying Membrane Proteins ► Proteins are generally broken down into the smaller classifications of integral proteins, peripheral proteins, and transmembrane proteins…(type of integral)

Integral Proteins ► Integral proteins are embedded within the lipid bilayer. ► They cannot easily be removed from the cell membrane without the use of harsh detergents that destroy the lipid bilayer. ► Integral proteins float rather freely within the bilayer, much like islands in the sea.

Peripheral Proteins ► Peripheral proteins are attached to the exterior of the lipid bilayer. ► They are easily separable from the lipid bilayer, able to be removed without harming the bilayer in any way. ► Peripheral proteins are less mobile within the lipid bilayer

Transmembrane Proteins ► Lipid-bound proteins are located entirely within the boundaries of the lipid bilayer ► Often act as “channels” for molecules to pass through the membrane

The Cell Membrane

Membrane Transport ► We have discussed how the lipid bilayer acts as an efficient barrier by only allowing a very small number of non-polar molecules to freely enter or exit a cell. While for the most part this selectivity is a valuable function and allows the cell to maintain its integrity, cells do need to move certain large, polar molecules such as amino acids, sugars, and nucleotides across their membranes. As a result, cell membranes require specific structures that allow for the transport of certain molecules.

Membrane Transport ► There are a number of different ways that molecules can pass from one side of a cell membrane to the other ► Some such means, like diffusion and osmosis, are natural processes that require no expenditure of energy from the cell and are called passive transport.

Membrane Transport ► Other methods of transport do require cellular energy and are called active transport ► In addition to these two forms of transport, there exist other forms of transport such as endocytosis and exocytosis, which will be discuss later.

Transport across the membrane: ►

Cytolysis & Plasmolysis Cytolysis/ HYPOTONIC Plasmolysis/ HYPERTONIC

Checkpoint Quiz ► QUESTION 1: The cell membrane is made up of a _____ bilayer. Carbohydrate Lipid Protein None of the Above Carbohydrate Lipid Protein None of the Above Carbohydrate Lipid Protein None of the Above

Quiz ► QUESTION 2: All eukaryotic cells are surrounded by a cell membrane. True False True False True False

Quiz ► QUESTION 3: The lipids in the bilayer have tails that are... Hydrophilic Hydrophobic Hydrophilic Hydrophobic Hydrophilic Hydrophobic

Quiz ► Question 4: The heads of the lipids in the cell membrane are... Hydrophilic Hydrophobic Hydrophilic Hydrophobic Hydrophilic Hydrophobic

Quiz ► QUESTION 5: Some molecules can pass through a cell membrane without help. True False True False True False

Quiz ► QUESTION 6: You will also find proteins in the lipid bilayer. True False True False True False

Quiz ► Question #7 When something can move through a cell membrane without using any energy (like diffusion) it is called ___________ transport. With energy (like larger molecules) it is called ____________ transport.

Summary of Transport ► Passive: (NO ENERGY) 1. Diffusion 2. Osmosis 3. Facilitated Diffusion ► &feature=related &feature=related &feature=related ►

Summary of Transport ► ACTIVE (Needs energy) 1. Endocytosis: (in) ► Phagocytosis (food) ► Pinocytosis (water) 2. Exocytosis: (out) ► Waste ►