Membranes

1
Membranes

• Structure and Function

2
Membrane Structure

• Phospholipid Bi-layer
• Contains Different Types of Proteins
• Channel proteins
• Protein Pumps proteins
• Adhesion proteins
• Cell-to-Cell Communication proteins
• Hormone Receptor proteins
• Immobilized Enzymes
• Fluid Mosaic Model

3
Phospholipid Bi-layer

• Contains
• Glycoproteins
• Integral Proteins
• Peripheral Proteins
• Cholesterol

4
Channel proteins

• Integral protein embedded across bi-layer
• Allows for movement of molecules across cell
  membrane

5
Protein Pumps

• Integral protein
• Transports molecules across membranes by changing
  shape

6
(No Transcript)
7
Adhesion proteins

• Connects internal cytoskeleton to external points
  of attachment
• Secures cells of multi-cellular organisms in place

8
Cell-to-Cell Communication proteins

• Cells within the same organism use membrane
  proteins to recognize each other
• Often use glycoproteins
• Major importance to immune system

9
Hormone Receptor proteins

• Hormones bind to cell surface proteins
• Initiates a series of reactions within cell
• Results in cellular response such gene expression
  (making more or less of a protein)

10
Immobilized Enzymes

• Many enzymes used by cells are embedded within
  membranes
• Useful in keeping certain reactions in specific
  parts of the cell

11
(No Transcript)
12
(No Transcript)
13
Membrane Function

• Boundary Separates Two Environments
• Selectively Permeable
• Passive Transport
• Simple Diffusion
• Facilitated Diffusion
• Active Transport
• Protein Pumps
• Endocytosis / Exocytosis

14
Selectively Permeable

• Membranes and their proteins allow only certain
  molecules to cross
• Diffusion movement of a substance from an area
  of high concentration to low concentration
• Osmosis movement of water from an area of low
  solute concentration to high

15
Diffusion
16
Osmosis
17
Passive Transport

• The movement of a molecule across a membrane from
  high to low concentration
• Molecules move with the concentration gradient
• Simple Diffusion
• No proteins needed
• Facilitated Diffusion
• Membrane proteins required

18
Simple Diffusion

• Small, uncharged molecules can move directly
  across membrane
• Includes gases (CO2 and 02 ) and water

19
Facilitated Diffusion

• Uses either protein channels or transporters
  (change shape)
• Channel Transporter

20
Passive Transport
21
Active Transport

• Movement of molecules across a membrane from low
  concentrations to high
• Molecules move against the concentration gradient
• Requires a protein transporter (pump) and energy
  supplied by ATP
• Ex. sodium/potassium pump

22
Active Transport
23
Active Transport
24
Passive Vs. Active Transport
25
Endocytosis

• Cell membrane surrounds and engulfs food particle
  or extra-cellular fluid
• Results in vesicle inside cell
• Phagocytosis engulfing large particles like
  bacteria
• Pinocytosis engulfing extra-cellular fluid and
  whatever it might contain

26
(No Transcript)
27
(No Transcript)
28
Exocytosis

• Opposite of endocytosis
• Vesicle containing secretory proteins or wastes
  joins with plasma membrane
• Molecules inside vesicle are then released
  outside of the cell

29
(No Transcript)
30
Summary
31
Review Questions

• Name 5 types of membrane proteins and describe
  their functions
• What is the most significant difference between
  passive and active transport?
• Why are transport proteins necessary in
  facilitated diffusion?
• Why does active transport require energy?

32
Problems

• 1
• The internal cell concentration of sucrose is
  1M, the external concentration is .1M, how might
  a cell raise the internal concentration to 2M
  without using a metabolic pathway?

• 2
• What might happen if a cell continually secreted
  enzymes, but never participated in endocytosis?