Cytoskeleton and Cell Membrane I

Question 1

Basic chracteristics of a cell membrane

Answer 1

• Basic strucutre found in both the cell membrane(plasmalemma) and the membranes of the individual organelles
• Basic structure of the unit membrane consists of a phospholipid bilayer in which are embedded or attached a wide variety of proteins and glycoproteins
• defines the boundary of the cell and separates it from the environment
• cell membrane is selective and determines the composition of hte intracellular environment
• Cell membrane mediates interactions between the cell and its envrionment

Question 2

Phospholipid bilayer

Answer 2

• Formed from a neutral fat in which one fo the fatty acid groups on the glycerol moiety is replaced by a phosphate group
• Each phospholipid consist of a hydrophillic end(phosphate group) anda hydrophobic end(fatty acid moieties)
• Each phospholipid has a hydrophilic head and two hydrophobic tails
• In the cell membrane , two laeyrs of phospholipids are arranged so that their hydrophobic tails face each other
• Basic function is to sepearte two aqueous compartments

Question 3

Outer leaflet in the cell membrane strucutre

Answer 3

• Cholesterol-second most common membrane lipid hydrophobic
  
  • major membrane component but it does not form the membrane by itself
  • Has an effect on membrane fluidity by modulating the movement of the fatty acid chains of phospholipids in a temperature-dependent manner
• Phosphatidycholine
• Phosphatidylethanolamine
• Sphingomyelin-a phospholipid in which glycerol is repalced by sphingosine
• consists mainly of phosphatidylcholine, sphingomyelin , and phosphatidylethanoolamine
  
  • Glycolipids are found only in the otuer leaflet , with their carbohydrate portion exposed to the extracellular space

Question 4

• Inner leaflet of hte cell membrane structure

Answer 4

• Cholesterol
• phosphatidylethanolamine
• phosphatidylserine
  
  • Negatively charged
• Phosphatidylionsitol:
  
  • Negatively charged
  • importnat in cell signaling
• Consists mainly of phosphatidylserine,phosphatidylinositol, and phosphatidylethanolamine
  
  • Head groups of phosphatidylserine and phosatidylinositol are negatively cahrged , so the cytosolic face of the plasma membrane ahs a net negative charge

Question 5

Glycolipids

Answer 5

• Found only in the otuer leaflet with carbohydrate portion facing the extracellular environment
• fatty acid tail is coupled via sphingosine to a carbohydrate head group
• Create a cell coat involved in cell-to-cell interactions and converys antigenicity

Question 6

Cholesterol

Answer 6

• Located within phospholipid bilayer
• Moderates membrane fluidity:
  
  • At high temperatures it interferes with FA chain movemnt, makes the outer part of the membranes less fluid, and reduces permeability to small molecules
  • At low tempreatures it prevents membranes from freezing and maintains membrane fluidity

Question 7

Glycocalyx

Answer 7

• Not an integral part of the membrane
• Carbohydrate coat on the extracellular surface of the cell membrane composed of carbohydrate portions of glycolipids and glycoproteins

Question 8

Lipid rafts

Answer 8

• Small patches of:
  
  • Cholesterol
  • Sphingolipids(sphingomyelin and glycolipids)
• serve as landign sites and often the site of phagocytosis

Question 9

Fluid mosaic cell membrane model

Answer 9

• Developed in 1972 by Singer and Nicolson
• Generally accepted paradigm for orgnization of all biological membranes
• Model consists of a phospholipid bilyaer forming a thin layer of oily fluid
• Two classes of proteins are associated with this lipid bilayer:
  
  • Membrane proteins:
    
    • associated with membranes through protein-protein interactions typically involving ionic bonds that can easily be dissociated from the membrane
  • Integral proteins:
    
    • Proteins that are inserted into the membrane and that cna only be dissociated by reagents that disrupt hydrophobic interactions

Question 10

Peripheral proteins

Answer 10

• Found on both the outer and inner leaflets of the cell membrane facing either the extracellular or the intracellular fluid
• Can be removed with detergents
• Linked indrectly to the plasma membrane by protein-protein interactions
• Extracellular portion of integral and peripehral membrane proteins are genrally glycosylated
• Intracellular portion of membrane proteins are bound to cytoskeletal components

Question 11

Integral proteins

Answer 11

• Embedded within the phospholipid bilayer
• Extracellular portion is typically glycolsylated

Question 12

Transmembrane Proteins

Answer 12

• Pass completely through both phospholipid layers
• Typically serve as channel and transporter proteins
• Most integral membrane proteins are transmembrane proteins spanning the membrane through a-helical regions

Question 13

Types of movement mechanisms

Answer 13

• Diffusion
  
  • Movement of particles from high to low concentrations
  • Does not require energy or transport molecules
• Osmosis
  
  • Diffusion of solvent(water) across a semipermeable membrane
  • Does not require energy or transport molecules
• Facilitated diffusion
  
  • A type of diffusion(high to low concentrations)
  • Requires transport molecules but not energy
• Active transport
  
  • Movement against a concentration
  • Requires energy and transport molecules

Question 14

Transport proteins:

Answer 14

• Unitransporters
  
  • Carrier single molecule or ion unidirectionally
• Symporters:
  
  • Co-transporter
  • Carries 2 molecules or ions simultaneously or sequentially in same direction
• Antiporters
  
  • Co-transporter
  • Carriers 2 moleculs or ions simultaneously or sequenitally in opposite directions