Membrane Structure

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Membrane Structure FunctionSpring 2013 -
Althoff Reference Mader Windelspecht Ch. 5)
Lec 05
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• ____________________ the boundary between
  the cells inside workings and the world outside
  it.
• Keys to consider 1) ____________ for
  exchange between inside and outside the
  cell 2) _________________ are exchanged

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A Little History

• Beginning of 20th century researchers noted
  lipid soluble molecules entered cells more
  rapidly than water soluble molecules
• In ______________________________ determined
  phospholipid content of a cell just enough to
  form a bilayer around the cells
  In ______________________________
  proposed proteins also part of membrane. Model
  they proposed was sandwich-like, further
  enhanced by Robertson in late 1950s.

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A Little History

• Robinsons ______ _________ model. late1950s

BILAYER PHOSPHOLIPID SANDWICH,

• Singer Nicolson __________ model, 1972.

EMBEDDED PROTEIN MOLECULES
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(No Transcript)
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PHOSPHOLIPID
OUTSIDE THE CELL
INSIDE THE CELL
(similar to Mader p86 Fig. 5.1)
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Components of the PLASMA MEMBRANE
Lipids
Proteins

• Phospholipids bilayer (meaning 2 layers)
• Exterior portions are hydrophilic (2 places)
• Interior portion of the bilayer is hydrophobic
• Provides essential structure to this portion of
  the cell

• Protein molecules are embedded in the plasma
  membrane
• Serve to stabilize and shape the plasma membrane
• Various (many) proteins perform specific
  functions 1) channel 2) transport 3) cell
  recognition 4) receptors 5) enzymes 6) form
  junctions

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PLASMA MEMBRANE A matrix of proteins
Proteins

• Some proteins span the entire bilayer distance
  (__________________ proteins)
• Some proteins reach the inside surface only

OUTSIDE
INSIDE
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Fluidity of the Plasma Membrane

• At room temperature, the __________________
  of the plasma membrane has the consistency of
  olive oil
• Result ___________________
• _____________________ those not attached to the
  cytoskeletoncan move within the fluid lipid
  bilayer
• This fluidity is critical to the _________ of
  proteins, particularly enzymes which speed up
  chemical reactions

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Lipid Movement
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Plasma Membrane PROTEINS

• CHANNEL proteins _________________, control
  passage of molecules
• CARRIER proteins ____________ combine with a
  substance and move it across the membrane
• CELL RECOGNITION proteins _________ looking
  for pathogens, alert immune system
• RECEPTOR proteins __________, bind with other
  molecules resulting in shape change that brings
  about cellular response
• ENZYMATIC proteins ________, facilitate/speed
  up metabolic reactions directly
• JUNCTION proteins ___________________ form
  junctions between cells

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CHANNEL
CARRIER
RECOGNITION
JUNCTION
RECEPTOR
ENZYMATIC
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When Function Goes _____

• CHANNEL proteins faulty chloride (Cl-) channel
  results in cystic fibrosis (thick mucus collects
  in airways, pancreatic ducts, liver ducts)
• CARRIER proteins inability to use energy
  transport for sodium potassium (NaK-)transport
  may cause obesity for some
• CELL RECOGNITION proteins can explain rejection
  of organ transplants, liked to MHC (major
  histocompatibility complex) glycoprotein
• RECEPTOR proteins why some are pygmies.
  Membrane receptors faulty and cannot interact
  with growth hormone
• ENZYMATIC proteins diarrhea impact of cholera
  bacteria toxin released on enzyme adenylate
  cyclase, which reduces water Na retention in
  large intestine

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Plasma Membrane Permeability

• _______________________________ the plasma
  membrane is choosy about the passage of
  molecules into and out of the cell.

Energy Not Required
Energy Required

• ACTIVE TRANSPORT
• EXOCYTOSIS
• ENDOCYTOSIS

• DIFFUSION
• FACILITIATED TRANSPORT

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Some sugars, amino acids ions
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Lipid-soluble molecules, H20,
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gases
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Some sugars amino acids
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macromolecules
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macromolecules
(Mader p89 Fig. 5.4)
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Direction of molecule passage
Key process
DIFFUSION

• Toward _______ concentration
• Toward _______ concentration
• Toward _______ concentration
• Toward _______ of cell
• Toward _______ of cell

FACILITATED TRANSPORT
ACTIVE TRANSPORT
EXOCYTOSIS
ENDOCYTOSIS
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Requirement
Key process

• Concentration gradient
• Channels or carrier AND concentration gradient
• Carrier plus energy
• Vesicle fuses with plasma membrane
• Vesicle formation

DIFFUSION
FACILITATED TRANSPORT
ACTIVE TRANSPORT
EXOCYTOSIS
ENDOCYTOSIS
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PROCESS OF DIFFUSION (Mader p91 Fig. 5.5)
DIFFUSION is spontaneous and ___ chemical energy
is required
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PROCESS OF OSMOSIS (Mader p93 Fig. 5.8)
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_______ the Cell EUKARYOTIC CELLS
MULTICELLUAR ORGANISMS

• Must make the ____________ between cells
• Permits ________________ between cells
• Permits _________________ between cells
• Components and construction ______ between plants
  and animals
• We consider these _________________
  structures examples for plants __________
  plasmodesmata examples for animals
  __________________

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PLANTS -- Outside
CELL 1
CELL 2
CYTOPLASMA
PLASMODESMATA
CELL WALL -- PRIMARY
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ANIMAL Extracellular Matrix

• MESHWORK OF _______________________
• Examples structural proteins
  ________________ matrix strength __________
  ______ resilience
• Examples rigid packing gel permits
  ________________ of nutrients, metabolites, and
  hormones between blood and tissue cells

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ANIMAL Extracellular Matrix
INSIDE
OUTSIDE
(Mader p99 Fig. 5.13)
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Extracellular Matrix Rigid or Flexible?

• RIGID ______ is rock solid because the
  extracellular matrix includes mineral salts
  (i.e., calcium salts) deposited outside the cell
• FLEXIBLE _________

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Animal Cell JUNCTIONS
ADHESION JUNCTIONS

• _________ sheet of cells results
• Attach to ____________, within the cell via
  cytoplasmic plaques, intercellular filaments
• Common in heart, stomach, and bladder where
  ___________ must stretch

CELL 1
CELL 2
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Animal Cell JUNCTIONS
TIGHT JUNCTIONS

• ____________ fastening
• Plasma membrane proteins _______ to each other
• Common in kidney where urine passes through
  intestines have this type of lining to __________
  ______________ from entering lining

CELL 1
CELL 2
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Animal Cell JUNCTIONS
GAP JUNCTIONS
CELL 1
CELL 2

• Permits ______________
• __________ plasma membrane channels join
• Common in the ________ muscle _____________
  (stomach)
• Permit _____________ to facilitate synchronous
  contraction

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Know Where You Are Inside or Outside
the Eukaryotic Cell RELATIVE TO THE
_____________________
INSIDE looking out OUTSIDE looking in
COMPONENTS Cell wall (plants) Nucleus Ribosomes
Plasmodesmata (plants) Golgi
apparatus Extracellular matrix
(animals) Adhesion junctions (aniamls) Gap
junctions (animals)
Yes
No
No
Yes
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Know What Requires Energy What Doesnt
Relative to _________________ of the Plasma
Membrane
Energy Required Direction of
passage
Passage type Diffusion Endocytosis Exocytosis
Active Transport Facilitated Transport
No
Yes
Toward outside
Toward lower concentration Toward
outside Toward higher concentration
Toward inside