Cell Membranes ~ Module 2

What are the four major functions of the cell membrane?

• Physical Isolation

• Regulation of exchange with the environment

• Communication between the cell and its environment

• Structural support

What do each of the functions do?

• Acts as a barrier to separate ICF from ECF

• Controls entry, elimination and release

• Contains proteins that allow for responding or interacting with the external environments

• Proteins in the membrane are used to make cell-to-cell connections (tissue) and to anchor the cytoskeleton

What are the main constituents of the cell membrane and why can they vary from cell to cell?

• lipid (3)

• protein (2)

• small amount of carbohydrate (2)

*it varies due to the metabolic activeness, the more active the more protein

What are the two body fluid compartments?

• Extracellular fluid such as blood plasma and interstitial fluid surrounding cells

• Intracellular Fluid, inside the cells

What are the three types of lipids found in the cell membrane?

• phospholipids: major lipids

• sphingolipids: lipid rafts, a bit longer

• cholesterol: increases viscosity (high = honey, low = water), decreases permeability, stiffens the membrane so it can be flexible without breaking

What three shapes can lipids form into?

• phospholipid bilayer

• micelles

• liposomes (have an aqueous center)

What is a monolayer?

• separating the fat from water

  • the tails face up against water

  • the head groups are in contact with water

• if in an aqueous environment with any air water interface then you’ll have a bilayer

What is the fluid mosaic model

• has proteins dispersed throughout

• extracellular surface contains glycoproteins and glycolipids

How much different type of proteins are inserted into the membrane

• 10-15

What are the two types of integral proteins?

• transmembrane proteins: fully immersed

• lipid anchored proteins: doesn’t cross entire membrane

  • directly attached to fatty acid

  • a sugar that hold the protein in place (GPI anchor)

What are the roles of integral proteins?

• membrane receptors senses signals

• cell adhesion molecules, connecting

• transmembrane movement: channels, carries, pores, pumps

• enzymes

• mediators of intracellular signaling

Peripheral proteins

*usually attached to integral proteins

• loosely attached to phospholipid head

• can be on extra or intracellular side

What are the roles of peripheral proteins?

• participate in intracellular signaling

• help link inner cytoskeleton to membrane to give cell its structure

Are there higher or lower cholesterol levels in lipid rafts?

• higher cholesterol content by 3-5 times

What are the two types of lipid rafts?

• Planar

• Caveolae

*attract other integral proteins

Where are glyco proteins and lipids usually positioned?

• on the extracellular side of the cell

• these are both cell membrane carbs chains

What is the function of glycoproteins?

• forms a protective coat (glycocalyx)

• cell to cell recognition and interaction

• immune responses

What is the function of glycolipid?

• cell to cell interactions and immune responses

Explain how the body can be in osmotic equilibrium but in chemical and electrical disequilibrium

• because while the fluid components are fairly equal, there are different components that are either found more in or out of the cell and carry different charges

About how much water do we have in our bodies?

• 60% of the body is water

• avg male back then was 70kg

Where is the water in our bodies found?

• 28L in intra

• 14L in extra (25% plasma, 75% interstitial fluid)

What are Aquaporin channels?

• channels that allow water to go through

• there are 13 different types

Are your cells more negative or positive?

• negative, more negative charges are in them

Why is osmolarity not molarity?

• molarity is the number of dissolved solutes/litre of solution (single molecule and assuming it stays attached)

• osmolarity describes the number of particles in a solution: some molecules separate into smaller particles and in theory those smaller parts would have an impact on osmosis too*multiplying by dissociation constant

What is the normal osmolarity in the human body?

*both intra and extra cellular

• 280-296mOsm

What does Isosmotic mean?

*equal

• solutions have identical osmolarities

What does Hyperosmotic mean?

*greater than

• describes the solution with the higher osmolarity

What does Hypoosmotic mean?

*less than

• describes the solution with the lower osmolarity

What is osmolarity?

• describes number of particles in solution

• the osmotic movement of water can be predicted by knowing the concentrations of each solution

What is tonicity?

• describes a solution based on how the cell reacts to it, and how its volume is affected

  • Hypertonic: cell burst

  • Isotonic: normal

  • Hypertonic: cell shriveled

What are the differences between tonicity and osmolarity?

• osmolarity

  • measurable, quantitative, comparing two solutions, does not tell what happens to cell volume

• Tonicity

  • has no units, only comparable, only based on cell

Why doesn’t osmolarity tell you what happens to the cell when placed in a solution?

• because the tonicity depends on the nature of the solutes, whether or not they can cross the membrane; depends on concentration of non-penetrating solutes

• while osmolarity takes into account all the solutes, both penetrating and non-penetrating

What are each of the categories of cell transport?

• Passive: across, requires no energy, might need a channel protein

• Active: require ATP, uses carrier proteins

What are the properties of simple diffusion?

• the concentration gradient

• the membrane surface area

• the lipid solubility

• molecular size

• composition of lipid layer

*only occur for small uncharged

What are the four functions of membrane proteins?

• membrane transport

• structural

• membrane enzymes

• membrane receptors

What are channel proteins made of?

• made of membrane spanning protein subunits that create a cluster of cylinders with a pore in the center

What determines the allowing of substances to pass through the channels?

• the size of the pore and the charge it allows

• smaller substances such as ions and water

What are gated channels?

• normally closed need a stimulus to open

  • ligand or chemically

  • voltage

  • mechanically

What are some facts about carrier proteins?

• slow

• one side open at a time, no thorough pore

• three types: Uniport, symport, antiport

• usually named by what it carries

Do charged ions follow a concentration gradient or an electrical chemical gradient?

• usually both, charge matters

Why does some facilitated diffusion such as glucose is slow?

• converts it while taking it up so it can be stored

How do the carrier proteins accept the substances?

• by a concentration gradient OR

• binds by affinity, high to accept, low to let go

Compare and contrast movement through channels vs carriers

• Channels: Form open, aqueous pores through the membrane. They are highly selective (size/charge) and allow rapid, passive flow. They do not bind to the substance and do not exhibit saturation.

• Carriers: Function by binding to a specific substance on one side of the membrane, inducing a conformational shape change to release it on the other. They are slower, highly specific, and exhibit saturation and competition.

What is primary active transport?

• energy to move molecule comes directly from hydrolyzing ATP and referred to as ATPase

*common example

• Sodium Potassium ATPase: exchanger, sodium out, potassium in

• 3 binding sites for sodium, 2 binding sites for potassium

What is secondary active transport?

• uses the potential energy stored in the concentration gradient of one molecule to push another molecule against their concentration gradient

• you need the primary first, doesn’t directly use ATP

Apply the principles of specificity, competition and saturation to carrier-mediated transport

• specificity: ability of a transporter to move one specific molecule or a closely related group of molecule

• competition: competition for binding sites and have lower amounts moved (some have preferences, some don’t transfer but just bind and clog)

• Saturation: rate reaching a maximum and saturation point, depends on the number of transporters: all transporters are being used in MAX and if you inc. the concentration it doesn’t change because it’s already using up its max

Compare phagocytosis, endocytosis, and exocytosis

Explain transcellular, paracellular and transcytosis as they apply to epithelial transport?

What does it mean for a cell to have a resting membrane potential difference?

How do changes in ion permeability change membrane potential?

What is Osmosis?

Tonicity

Cell transport

Active transport

Passive transport

Diffusion

Resting Membrane potential