New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here

Bio Ch. 4

by: Makenzie Strand

Bio Ch. 4 BIOL 113

Makenzie Strand
GPA 3.2

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

Plasma Membrane and function
Ross, J
Class Notes
25 ?





Popular in Biology

This 6 page Class Notes was uploaded by Makenzie Strand on Monday February 15, 2016. The Class Notes belongs to BIOL 113 at Western Kentucky University taught by Ross, J in Fall 2015. Since its upload, it has received 36 views. For similar materials see GENERAL BIOLOGY in Biology at Western Kentucky University.


Reviews for Bio Ch. 4


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 02/15/16
Ch.4 Bio Plasma Membrane Structure and Function -separates the internal environment of the cell from its external environment. - regulates the entrance and exit of molecules into and out of the cell. -Homeostasis: steady internal environment maintained -The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others **Phospholipid bilayer with embedded proteins – Hydrophilic (water-loving) polar heads • Face inside and outside of cell (water present) – Hydrophobic (water-fearing) nonpolar tails • Face each other, away from water – Cholesterol (animal cells) controls excess fluidity -Cellular membranes are fluid mosaics of lipids and proteins -most abundant lipid in the plasma membrane -amphipathic molecules (hydrophobic and hydrophilic regions) -Fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it The Fluidity of Membranes -Move within the bilayer -Drift laterally -Never flip-flop transversely across the membrane -Temperatures cools: membranes switch from a fluid state to a solid state -Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids -Warm Temps: cholesterol restrains movement of phospholipids -Cool Temps: maintains fluidity by preventing tight packing Membrane Proteins and Their Functions -collage of different proteins embedded in the fluid matrix of the lipid bilayer -Proteins determine most of the membrane’s specific functions Membrane proteins throughout membrane may be: – Peripheral proteins – associated with only one side of membrane – Integral proteins – span the membrane • Can protrude from one or both sides • Embedded within the membrane • Able to move laterally -Both phospholipids and protein can have attached carbohydrate chains. -Glycolipids are lipids attached to carbohydrates. -Glycoproteins are proteins attached to carbohydrates. Functions of Membrane Proteins -Channel proteins are involved in the passage of solutes through the membrane. – Substances simply move across the membrane. – Some may contain a gate that must be opened in response to a signal. – Carrier proteins allow the passage of a solute by combing with it and help it move across the membrane. • Functions of Membrane Proteins • Cell recognition proteins are glycoproteins. – These proteins help the body recognize when it is being invaded by pathogens. – Receptor proteins have a shape that allows a specific molecule to bind. – The binding causes the receptor to change shape to initiate a cellular response. • Functions of Membrane Proteins • Enzymatic proteins carry out metabolic reactions directly. – Example: the proteins of the electron transport chain, which carry out the final steps of aerobic respiration ***Permeability of the Plasma Membrane • The plasma membrane can regulate the passage of molecules into and out of the cell because it is selectively permeable. • Which molecules can freely cross the membrane and which may require carrier proteins and/or energy depends on – Size – Nature of molecule – polarity, charge • Small, uncharged molecules freely cross membrane – Examples: CO , 2 , 2lycerol, and alcohol – Slip in between the hydrophilic heads and pass through hydrophobic tails – Driven by the concentration gradient Concentration gradient – More of a substance on one side of the membrane – Going “down” a concentration gradient • From an area of higher to lower concentration – Going “up” a concentration gradient • From an area of lower to higher concentration • Requires input of energy • Water which is polar would not be expected to readily cross the membrane. – Aquaporin’s are special channels that allow water to cross the membrane. – Aquaporin’s are present in the majority of cells. • Large molecules, ions, and charged molecules are unable to freely cross the membrane, but can cross the membrane via – Channel proteins forming a pore through the membrane – Carrier proteins that are specific for substance they transport – Vesicle formation in endocytosis or exocytosis Diffusion and Osmosis Diffusion – Movement of molecules from an area of higher to lower concentration • Down a concentration gradient • Occurs until equilibrium is reached • For example, when a crystal of dye is placed in water the dye and water molecules move about until equilibrium occurs – Solution contains a solute (solid) and a solvent (liquid) -Once the solute and solvent are evenly distributed, their molecules continue to move about, but there is no net movement of either one in any direction -Gases can diffuse through a membrane -Oxygen and carbon dioxide enter and exit this way • Several factors influence the rate of diffusion – Temperature • As temperature increases, the rate of diffusion increases. – Pressure – Electrical currents – Molecular size Osmosis • diffusion of water across a differentially permeable membrane – Diffusion always occurs from higher to lower concentration. – Osmotic pressure is the pressure that develops in a system due to osmosis. • The greater the possible osmotic pressure, the more likely it is that water will diffuse in that direction. – Membrane is not permeable to solute • Isotonic: the solute concentration is equal inside and outside of a cell • Hypotonic: a solution has a lower solute concentration than the inside of a cell • Hypertonic: a solution has a higher solute concentration than the inside of a cell Isotonic – No net gain or loss of water – 0.9% NaCl – No net gains or loss of water Hypotonic – Cell gains water – Cytolysis – hemolysis – Turgor pressure keeps plants erect (cell wall) Hypertonic – Cell loses water – Crenation – Plasmolysis Transport by Carrier Proteins -The plasma membrane impedes the passage of all but few substances. -Substances enter or exit cells because of carrier proteins. • Carrier proteins are specific. – Combine with a molecule or ion to be transported across the membrane – Change shape to move molecules across membranes • Transport by Carrier Proteins • Carrier proteins are required for – Facilitated Transport – Active Transport Facilitated Transport -Explains the passage of molecules such as glucose or amino acids. – Neither molecule is lipid-soluble. – Reversible combination and transport occurs. – Like diffusion, ATP is not required because molecules are transported down their concentration gradient. • Small molecules that are not lipid-soluble • Molecules follow the concentration gradient • Energy not required Active Transport – Molecules or ions combine with carrier proteins. • Often called pumps – Molecules move against the concentration gradient • Entering or leaving cell • Accumulate either inside or outside the cell – Energy and carrier proteins are required. • Usually ATP is used -Referred to as pumps. • Proteins use energy to move molecules against the concentration gradient. + + + • Na /K pump+is especially important for nerve and muscle cells –it moves Na out and K into cells. • The carrier changes shape after phosphate attaches, and then again after it detaches. Bulk Transport • Macromolecules are transported into or out of cells by vesicle formation. – Macromolecules are too large to be transported by carrier proteins. – Energy is required to form vesicles. – Vesicle formation is called membrane-assisted transport. • Exocytosis – exit from cell • Endocytosis – enter into cell •     Exocytosis – The vesicle fuses with plasma membrane as secretion occurs. – The vesicle membrane becomes part of plasma membrane. – Cells of particular organs are specialized to produce and export molecules. • Pancreatic cells release insulin or enzymes. • Anterior pituitary cells release growth hormone. • Endocytosis – Cells take in substances by vesicle formation. • Part of the plasma membrane invaginates to envelop the substance. • The membrane then pinches off to form an intracellular vesicle. – Three types of endocytosis • Phagocytosis • Pinocytosis • Receptor-mediated endocytosis • Phagocytosis: large, particulate matter such as “food” molecules or viruses or whole cells – Amoeba and macrophages • Pinocytosis: liquids and small particles dissolved in liquid – Certain blood cells or plant root cells • Receptor Mediated Endocytosis: a type of pinocytosis that involves a coated pit – Certain placental cells Modifications of Cell Surfaces • Interact with external environment. • Extracellular environment is made of large molecules produced by nearby cells. • Materials are deposited by secretion. -Plants, prokaryotes, fungi are surrounded by cell walls. -Animals have more varied extracellular environments that can change. Cell Surfaces in Animals • Animal cells have two different types of cell surfaces. – Extracellular matrix outside of cells – Junctions that occur between cells – Both can associate with the cytoskeleton and contribute to cell-to-cell communication – Extracellular Matrix • A meshwork of proteins and polysaccharides closely associated with cells that produced them • Common structural proteins in ECM – Collagen resists stretching – Elastin provide resilience to ECM – Fibronectin is an adhesive protein that links integrin Extracellular Matrix • Polysaccharides made of amino sugars in ECM attach to proteins called proteoglycans – Proteoglycans attach to a long, centrally placed polysaccharide. • Resist compression of ECM • Assist cell signaling by regulating the passage of molecules through ECM to plasma membrane – Junctions Between Cells • Cell surfaces in certain tissues of animals – Junctions Between Cells • Adhesion Junctions – Intercellular filaments between cells • Tight Junctions – Form impermeable barriers between cells • Gap Junctions – Plasma membrane channels are joined (allows communication) Plant Cell Walls • All plant cells have a cell wall. – It contains cellulose as the main component. – Pectin’s allow the walls to stretch as cells grow. – No cellulose polysaccharides harden the wall as the cell matures. – Pectin is abundant in the middle lamella, a layer of adhesive substances that holds cells together. • Plasmodesmata are narrow channels that penetrate the cell wall to connect adjacent cells. • Each channel contains a strand of cytoplasm. • Cytoplasm allows exchange of materials between cells. – Only water and small solutes pass freely. • Cytoplasm connects all the cells within a plant.


Buy Material

Are you sure you want to buy this material for

25 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."

Jennifer McGill UCSF Med School

"Selling my MCAT study guides and notes has been a great source of side revenue while I'm in school. Some months I'm making over $500! Plus, it makes me happy knowing that I'm helping future med students with their MCAT."

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."

Parker Thompson 500 Startups

"It's a great way for students to improve their educational experience and it seemed like a product that everybody wants, so all the people participating are winning."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.