Cell MembraneCell Membrane

““Keeping it all Together”Keeping it all Together”

Cell MembraneCell Membrane

►When you think about a membrane, imagine When you think about a membrane, imagine it is like a big plastic bag with some tiny it is like a big plastic bag with some tiny holes.holes.

► That bag holds all of the cell pieces and That bag holds all of the cell pieces and fluids inside the cell and keeps any nasty fluids inside the cell and keeps any nasty things outside the cell. The holes are there things outside the cell. The holes are there to let some things move in and out of the to let some things move in and out of the cell. cell.

Cell Membrane cont…Cell Membrane cont…

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

Cell membrane Cell membrane

►

The cell membrane is composed of a The cell membrane is composed of a double layer of fat cells called a double layer of fat cells called a lipid lipid bilayerbilayer in which membrane proteins in which membrane proteins are embedded. are embedded.

►The structure of the lipid bilayer The structure of the lipid bilayer prevents the free passage of most prevents the free passage of most molecules into and out of the cell. molecules into and out of the cell.

Cell MembraneCell Membrane

►Fluid Mosaic Model:Fluid Mosaic Model:

Cell MembraneCell Membrane

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

Lipid bilayer

The Lipid BilayerThe Lipid Bilayer

►The lipid bilayer is a universal The lipid bilayer is a universal component of all cell membranes component of all cell membranes

► Its role is critical because its structural Its role is critical because its structural components provide the barrier that components provide the barrier that marks the boundaries of a cell. marks the boundaries of a cell.

►The structure is called a "lipid bilayer" The structure is called a "lipid bilayer" because it is composed of because it is composed of twotwo layers layers of of fatfat cells organized in two sheets. cells organized in two sheets.

Lipid Bilayer StructureLipid Bilayer Structure

►The structure of the lipid bilayer The structure of the lipid bilayer explains its function as a barrier explains its function as a barrier

►Lipids are fats, like oil, that are Lipids are fats, like oil, that are insoluble in water. There are two insoluble in water. There are two important regions of a lipid that important regions of a lipid that provide the structure of the lipid provide the structure of the lipid bilayer. bilayer.

Lipid Bilayer Structure cont…Lipid Bilayer Structure cont…

►Each lipid molecule contains a Each lipid molecule contains a hydrophilic regionhydrophilic region or polar head or polar head regionregion and a and a hydrophobic region hydrophobic region or or non polar tail region.non polar tail region.

The hydrophilic region is attracted to aqueous water conditions while the hydrophobic region is repelled from such conditions

PhospholipidsPhospholipids

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

Basic Structure!!Basic Structure!!

Properties of Lipid BilayerProperties of Lipid Bilayer

►Most important property is that it is Most important property is that it is highly impermeable.highly impermeable.

► Impermeable means it does not allow Impermeable means it does not allow molecules to pass through it easilymolecules to pass through it easily

►Some molecules require the assistance Some molecules require the assistance of other structures. of other structures.

Another Bilayer Property:Another Bilayer Property:

►Another property of the bilayer is it’s Another property of the bilayer is it’s fluidityfluidity. .

►The bilayer contains lipids and proteinsThe bilayer contains lipids and proteins►The bilayer's fluidity allows these The bilayer's fluidity allows these

structures mobility within the lipid structures mobility within the lipid bilayer bilayer

Quiz Checkpoint:Quiz Checkpoint:

►What is the main function of the lipid What is the main function of the lipid bilayer? bilayer?

Answer to Question #1Answer to Question #1

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

Quiz Question #2Quiz Question #2

►Why is the structure called a Why is the structure called a lipid lipid bilayerbilayer? ?

Answer to Question #2Answer to Question #2

► It is called a It is called a lipid bilayerlipid bilayer because it is because it is composed of composed of twotwo layers of fat, or lipid, layers of fat, or lipid, molecules. molecules.

Quiz Question #3 – Fill in the Quiz Question #3 – Fill in the BlankBlank

►A phospholipid molecule contains two A phospholipid molecule contains two distinct regions. The __________ region distinct regions. The __________ region is attracted to water and the is attracted to water and the ___________ region is repelled from ___________ region is repelled from water. water.

Answers to Question #3Answers to Question #3

►Hydrophilic; HydrophobicHydrophilic; Hydrophobic

Membrane ProteinsMembrane Proteins

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

Membrane Proteins cont…Membrane Proteins cont…

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

Classifying Membrane Classifying Membrane ProteinsProteins

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

Integral ProteinsIntegral Proteins

► Integral proteins are embedded within Integral proteins are embedded within the lipid bilayer. the lipid bilayer.

►They cannot easily be removed from They cannot easily be removed from the cell membrane without the use of the cell membrane without the use of harsh detergents that destroy the lipid harsh detergents that destroy the lipid bilayer. bilayer.

► Integral proteins float rather freely Integral proteins float rather freely within the bilayer, much like oceans in within the bilayer, much like oceans in the sea.the sea.

Peripheral ProteinsPeripheral Proteins

►Peripheral proteins are attached to the Peripheral proteins are attached to the exterior of the lipid bilayer. exterior of the lipid bilayer.

►They are easily separable from the They are easily separable from the lipid bilayer, able to be removed lipid bilayer, able to be removed without harming the bilayer in any without harming the bilayer in any way. way.

►Peripheral proteins are less mobile Peripheral proteins are less mobile within the lipid bilayer within the lipid bilayer

Transmembrane Proteins Transmembrane Proteins

►Lipid-bound proteins are located Lipid-bound proteins are located entirely within the boundaries of the entirely within the boundaries of the lipid bilayer lipid bilayer

►Often act as “channels” for molecules Often act as “channels” for molecules to pass through the membrane!to pass through the membrane!

The Cell MembraneThe Cell Membrane

Membrane TransportMembrane Transport

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

Membrane TransportMembrane Transport

►There are a number of different ways There are a number of different ways that molecules can pass from one side that molecules can pass from one side of a cell membrane to the otherof a cell membrane to the other

► Some such means, like Some such means, like diffusiondiffusion and and osmosisosmosis, are natural processes that , are natural processes that require require no expenditure of energy no expenditure of energy from the cellfrom the cell and are called and are called passive transportpassive transport. .

Passive Transport – Passive Transport – Written notes Written notes

Diffusion is the natural phenomenon in Diffusion is the natural phenomenon in which nonpolar molecules naturally flow which nonpolar molecules naturally flow from an area of HIGH concentration to an from an area of HIGH concentration to an area of LOW concentration.area of LOW concentration.

Diffusion DOES NOT require energyDiffusion DOES NOT require energy

Figure 7-14 in textFigure 7-14 in text

OSMOSIS is a similar process, but refers OSMOSIS is a similar process, but refers specifically to water moleculesspecifically to water molecules

Figure 7-16 in textFigure 7-16 in text

Transport across the Transport across the membrane:membrane:

►http://biologycorner.com/bio1/diffusion.htm

►l

Draw this: Draw this: Cytolysis & PlasmolysisCytolysis & Plasmolysis

Cytolysis/

HYPOTONIC

Plasmolysis/

HYPERTONIC

Written Notes: Active Written Notes: Active TransportTransport

►Other methods of transport do Other methods of transport do require require energyenergy and are called and are called ACTIVE transport.ACTIVE transport.

► In addition to these two forms of transport, In addition to these two forms of transport, there exist other forms of transport such as there exist other forms of transport such as exocytosisexocytosis and and endocytosisendocytosis which will be which will be discussed later.discussed later.

►Moves materials Moves materials from LOW to HIGH from LOW to HIGH concentration gradient.concentration gradient.

Checkpoint QuizCheckpoint Quiz

►QUESTION 1: QUESTION 1: The cell membrane is made up of a The cell membrane is made up of a _____ bilayer._____ bilayer.

Carbohydrate Lipid Protein None of the Above

QuizQuiz

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

True False

Quiz Quiz

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

Hydrophilic Hydrophobic

QuizQuiz

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

Hydrophilic Hydrophobic

QuizQuiz

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

True False

QuizQuiz

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

True False False

QuizQuiz

►Question #7Question #7

When something can move through a When something can move through a cell membrane without using any cell membrane without using any energy (like diffusion) it is called energy (like diffusion) it is called ___________ ___________ transport.transport.

With energy (like larger molecules) it is With energy (like larger molecules) it is called called ________________________ transport. transport.

Summary of TransportSummary of Transport

► Passive: (NO ENERGY)Passive: (NO ENERGY)1.1. DiffusionDiffusion

2.2. OsmosisOsmosis

3.3. Facilitated DiffusionFacilitated Diffusion

► http://www.youtube.com/watch?http://www.youtube.com/watch?v=s0p1ztrbXPY&feature=related (clip on v=s0p1ztrbXPY&feature=related (clip on facilitated diffusion)facilitated diffusion)

Summary of TransportSummary of Transport

► ACTIVE (Needs energy)ACTIVE (Needs energy)1.1. Endocytosis: (in)Endocytosis: (in)► Phagocytosis (food) Phagocytosis (food)

http://www.youtube.com/watch?http://www.youtube.com/watch?v=hacbn_xcZdUv=hacbn_xcZdU

► Pinocytosis (water)Pinocytosis (water)

2.2. Exocytosis: (out)Exocytosis: (out)► WasteWaste

►http://www.youtube.com/watch?v=STzOiRqzzL4&feature=relatedhttp://www.youtube.com/watch?v=STzOiRqzzL4&feature=related

http://www.youtube.com/watch?v=dPKvHrD1eS4 – CRASH COURSE – SUMMARY!!!!!