Movement Through the Cell Membrane

Cell Membrane The thin flexible barrier around the cell that controls what enters/exits. Selectively (semi) permeable- some substances can pass and others cannot

Cell membrane is made up of: Lipid bi-layer- two layers of fat (Fence) Protein channels- that move materials across. (Gates) Carbohydrates- act as chemical identification cards so other cells to identify one another. (Security) Watch

Cell Membrane Functions The Plasma Membrane 12/31/2018 Cell Membrane Functions 1. Protective barrier 2. Regulate transport in & out of cell (selectively permeable) 3.Allow cell recognition 4. Provide anchoring sites for cytoskeleton copyright cmassengale G. Podgorski, Biol. 1010

Overview Cell membrane separates living cell from nonliving surroundings thin barrier = 8nm thick Controls traffic in & out of the cell selectively permeable allows some substances to cross more easily than others hydrophobic vs hydrophilic Made of phospholipids, proteins & other macromolecules

Phospholipids Fatty acid tails Phosphate group head hydrophobic Phosphate group head hydrophilic Arranged as a bilayer Fatty acid Aaaah, one of those structure–function examples

Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

More than lipids… It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model!

Membrane fat composition varies Fat composition affects flexibility membrane must be fluid & flexible about as fluid as thick salad oil % unsaturated fatty acids in phospholipids keep membrane less viscous cold-adapted organisms, like winter wheat increase % in autumn cholesterol in membrane

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Glycoprotein Carbohydrate Glycolipid Phospholipids Transmembrane proteins The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins. Filaments of cytoskeleton Cholesterol Phospholipids Peripheral protein Cytoplasm

Summarize the structure of the plasma membrane. Write your answer in box #1

Membrane Proteins Proteins determine membrane’s specific functions cell membrane & organelle membranes each have unique collections of proteins Membrane proteins: peripheral proteins loosely bound to surface of membrane cell surface identity marker (antigens) integral proteins penetrate lipid bilayer, usually across whole membrane transport proteins channels, permeases (pumps)

Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Enzyme activity Cell surface receptor Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made. Cell surface identity marker Cell adhesion Attachment to the cytoskeleton

In box #2, write down the functions of membrane proteins, and why some go all the way through the membrane

3 Types of Cell transport 1. Diffusion (includes osmosis) 2. Facilitated Diffusion 3. Active Transport (VOCAB NOTE-concentration gradient is the difference in concentration of a substance across a membrane)

1A.Diffusion Movement of molecules(across concentration gradient) from an area of high concentration to an area of low concentration. Require no energy (because molecules randomly move on their own) Does this until equilibrium (equal concentration on both sides of the membrane) Watch

Diffusion

Diffusion Animation http://www.phschool.com/atschool/phbio/active_art/diffusion/index.html

1B. Osmosis Osmosis animation Diffusion of WATER across a semi-permeable membrane from an area of high concentration to an area of low concentration Water moves freely through pores. Solute (green) to large to move across.

Osmosis http://www.phschool.com/atschool/phbio/active_art/osmosis/index.html

Diffusion across cell membrane Cell membrane is the boundary between inside & outside… separates cell from its environment Can it be an impenetrable boundary? NO! OUT waste ammonia salts CO2 H2O products IN food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O OUT IN cell needs materials in & products or waste out

Diffusion through phospholipid bilayer What molecules can get through directly? fats & other lipids What molecules can NOT get through directly? polar molecules H2O ions salts, ammonia large molecules starches, proteins lipid inside cell outside cell salt NH3 sugar aa H2O

Summarize what can and cannot cross through the membrane in box #4.

What’s wrong with this poster? (tell your face partner)

Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) 2. Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane Transport Proteins are specific – they “select” only certain molecules to cross the membrane Transports larger or charged molecules Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Carrier Protein http://bio.winona.edu/berg/Free.htm

2. Facilitated Diffusion(continued) Glucose molecules Cellular Transport From a- High High Concentration Channel Proteins animations Cell Membrane Low Concentration Protein channel Low Transport Protein Through a  Go to Section:

2. Facilitated Diffusion The Plasma Membrane 12/31/2018 2. Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. copyright cmassengale G. Podgorski, Biol. 1010

Facilitated Diffusion Animation https://highered.mheducation.com/sites/9834092339/student_view0/chapter5/how_facilitated_diffusion_works.html

2. Facilitated Diffusion The Plasma Membrane 2. Facilitated Diffusion 12/31/2018 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. copyright cmassengale G. Podgorski, Biol. 1010

Protein changes shape to move molecules: this requires energy! Active Transport Sodium Potassium Pumps (Active Transport using proteins) 1. Protein Pumps -transport proteins that require energy to do work Protein changes shape to move molecules: this requires energy!

Types of Active Transport 2. Endocytosis: taking bulky material into a cell Moves AGAINST concentration gradient Uses energy Cell membrane in-folds around food particle forms food vacuole & digests food

Active Transports http://www.phschool.com/atschool/phbio/active_art/active_transport/index.html

copyright cmassengale The Plasma Membrane Moving the “Big Stuff” 12/31/2018 Large molecules move materials into the cell by one of three forms of endocytosis. copyright cmassengale G. Podgorski, Biol. 1010

Types of Active Transport 3. Exocytosis: Forces material out of cell in bulk membrane surrounding the material fuses with cell membrane Cell changes shape – requires energy EX: Hormones or wastes released from cell in vesicles Endocytosis & Exocytosis animations

Moving the “Big Stuff” Exocytosis- moving things out. The Plasma Membrane Moving the “Big Stuff” 12/31/2018 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. copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale The Plasma Membrane Exocytosis 12/31/2018 Exocytic vesicle immediately after fusion with plasma membrane. copyright cmassengale G. Podgorski, Biol. 1010

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water) Result: Water moves from the solution to inside the cell. Cell Swells and bursts open (cytolysis)!

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypertonic Solution Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water) shrinks Result: Water moves out of cell the cell into the solution: Cell shrinks (Plasmolysis)!

Plasmolysis Video https://www.youtube.com/watch?v=4JyT__Dea8Q https://www.youtube.com/watch?v=VK-_YHakvho

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Isotonic Solution Isotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)