Untitled Flashcards Set

What is a Plasma Membrane

• Separates Living cytoplasm from non-living environment 

• Is a selectively permeable barrier 

 Fluid-Mosaic Model

• Model composed of lipids with proteins and carbohydrates embedded in them

• Membrane lipids are mostly phospholipids in a biliary

  • Lipids are in a fluid state

  • Fatty acids are mostly unsaturated (cis)

• Membrane proteins free to float in lipids 

What does it mean when we say lipids and proteins are Amphipathic? 

• Have both hydrophilic and hydrophobic  regions 

What are the two predictions that lead to the fluid mosaic model? 

• Prediction 1: Fluidity 

  • If the membrane is fluid → proteins should be able to move in the plane of the membrane 

  • Experiment: Have two different cells (human and mouse), and label the different species of dyes. Fuse the cells and you should see them moving around 

  • Conclusion: Proteins can move laterally in the plane membrane 

• Prediction 2: Independent Movement

  • Membrane proteins are discrete particles → should be able to move independently of each other 

  • Experiment: Combine e-microscopy with freeze-fracture to image membrane proteins 

What affects Membrane fluidity? 

• Varies with temperature 

  • Colder=less fluid 

What is a transition temperature (T_m): 

• The temperature at which the membrane undergoes fluid-to-solid phase change

• T_m is affected by the lipid content of the membrane 

Saturation level of Lipids 

• More kinks mean = Unsaturated 

  • More fluid membrane

  • Lower T_m  

Cholesterol in Membrane: What does it do? 

• Cholesterol reduces membrane fluidity at moderate temperatures, but at low temperatures hinder solidification 

• It interacts with hydrophobic tails and alters interactions with adjacent fatty acids 

• Has one polar region that faces out and core hydrophobic embedded within the membrane bilayer

Integral Membrane Proteins: What are they?

• Penetrate the hydrophobic core of the membrane 

• Can be removed ONLY by dissociating the membrane 

• Can either by partially embedded in the bilayer

• Or can span the entire membrane → Transmembrane 

Define Transmembrane Proteins: 

• Proteins that pass all the way through the membrane 

• Amphipathic

Anchored Membrane Proteins 

• Ex. GPI-anchored proteins: a way for lipid attachment to a protein 

• Covalently attached to lipids that insert into membrane 

• No Hydrophobic transmembrane domains

What does a GPI-anchored protein do? 

• A type of anchored membrane protein that is a way of attachment to a protein 

Peripheral Membrane Proteins: 

• Loosely binds (noncovalently) to integral proteins or lipids 

• Attach to either membrane surface

• Can be removed w/o destroying the membrane 

• Different on each side of the membrane 

• Function on only one side of the membrane 

Glycosylation:

• Monosaccharides or polysaccharide added covalently to membrane proteins or lipid in rough ER and Golgi 

Glycosylated polypeptide

• Glycoprotein 

Glycolipid

• Glycolipid

What is the function of Membrane Carbohydrates? 

• Defense: recognition of self from nonself 

  • Immune 

• Protection: Cell lining of GI, Respiratory, and Reproductive tracts 

• Cell Sorting during embryogenesis

Functions of Membrane Proteins: 

• Transport

• Enzymatic activity 

• Signal transduction 

• Cell-cell recognition 

• Intercellular joining 

• Attachment to the cytoskeleton and extracellular matrix

Membrane Transport

• Selective Permeability and regulated transport create and maintain different environments across a cell membrane. 

When does membrane transport Stop? 

• At equilibrium: point at which forward and backwards rxns occur at same time 

What is Selective Permeability? 

• Membrane lipids allow passage to some but also limit passage to others

Selective permeability: Hydrophobic Molecules: 

• O2, CO2, N2, Benzene

• Pass through the membrane 

Selective permeability: Small Uncharged Polar Molecules: 

• H2O, urea, glycerol 

• Have limited diffusion, do so slower 

Selective permeability: Large Uncharged Polar Molecules: 

• Glucose and sucrose

• Very limited and cannot easily pass through the membrane 

Selective permeability: Ions 

• H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+ 

• Not able to pass through due to their charged nature 

Protein channels 

• Hydrophilic pores 

• Have some specificity but no stable binding to individual solute molecules 

• Allow rapid movement of ions and water

• Millions or billions of transported per second 

Protein Carrier

• Specific binding of solute 

• Requires a conformational change 

• Hundreds or thousands of transported per second 

What Determines Direction of Transport? 

• No energy needed → passive transport

• If energy need → Active transport

What is Passive Transport? 

• Spontaneous and increases entropy

• Solute moves from higher concentration to lower concentration 

• Towards opposite charge 

What is Active transport:

• Non-spontaneous

• Used to concentrate solutes by pumping them from lower to higher concentration

• OR forcing ions to be near others of the same charge

Electrochemical Gradient

• Combined effects of concentration and charge

Osmosis 

• Passive movement of water across a membrane is called osmosis 

• To balance different solute concentrations, water moves across the membrane 

What are the special water uses? 

• Aquaporins

Isotonic

• The solution around cell has the same solute concentration as the inside the cell 

• Equilibrium 

Hypotonic

• Solution around cell has a lower solute concentration than inside the cell

• Net movement of H2O is INTO the cell 

Hypertonic:

• The solution around cell has a higher solute concentrtaiton than inside the cell 

• Net movement OUT of the cell 

Facilitated Diffusion 

• Passive transport aided by proteins 

• Both channels and carriers 

• Passive no energy, increases entroypy, spontaneous, has almost zero activation energy Ea

• When channels maybe “Gated” to control transport 

  • Ligand Gated

  • Electrically gated 

  • Mechanically gated 

Types of gated Channgels for facilitated Diffusion

• Ligand Gated

  • Can change the proteins shape to activate it

• Electrically gates

• Mechanically gated 

Cotransport 

• Some transport protein move more than one substance at a time 

• Can be Passive or Active 

• Type 1: Symport 

  • Multiple solutes in same direction

• Type 2: Antiport 

  • Multiple solutes in different directions

What type of transport proteins do Active Transport?

• Only: carriers or pumps

• Never: Channels 

Channel Protiens 

• Routs for passive diffusion along a gradient, not pumps 

Primary Active Transport: 

• Energy usually from ATP hydrolysis, is used to pump something across a membrane to a region of  [higher] (concentration)

• Primary = that protein doingt the transport 

Primary Active Cotransport: 

• ATP hydrolysis can provide teh energy to actively more TWO Substances

• Can be in same or different directions

• Can be symporters or Antiports 

Na+/ K+ ATPase Pump

• Sodium potassium pump that is feuled my ATP

• One pump actively sends Na+ to outside, K+ inside 

• 3 Na+ for every two 2 K+

• Type of Antiporter 

Secondary Active Cotransport 

• Uses ATP hydrolysis to transport one ion into an ion gradient 

• Stores portiential energy cna drive the active transport of another solute with a separate contransport protein 

• Central ot both mitochondrial respiration and photosynthesis

Example of Secondary Active Cotransport

• Common mechanism for transporting sugars and Amino Acids into cells

• Without Na+/K+ pump, Na+/glucose cotransporter couldn’t work.

Difference between Transport of small and large molecules

• Large: Bulk transport 

• Small: Diffusion or transporters 

Bulk Transport 

• Larger molecules such as proteins and polysaccharides move by Bulk Tranport 

• Types: Exocytosis or Endocystosis 

Exocytosis: 

• Secretion

• Release of material out of the sell 

Endocytosis 

• Mechanism for bringing material into the cell (Uptake of Material)

• “Reverse of exocytosis” 

• Three types 

  • Phagocytosis 

  • Pinocytosis

  • Receptor-meditated endocytosis   

Phagocytosis

• Type of Endocytosis

• Cellular Eating 

• Cells engulf a particle into a vesicle 

  • Surround particals with the membrane and bring into cell → food vacuole

Pinocytosis 

• Type of Endoxytosis

• Cellular drinkimg 

• Gulp of fluid is takin into vesicles 

• nonspecific uptake of soluble materials (not visible/not obvious)

  • Anyhting dissolved outside of the cell; such as water or ions the cells may need

Receptor-meditated endocytosis 

• Type of endoxytosis 

• Used to bring in specific molecules 

• Ligands bind to specific receptors 

• Causes a coated vesivle with a coated pit of specidc ligand bound to receptor 

• Trasnderred to lysosome for digestion 

• Ex, Hormones