Catalyst

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Catalyst

• Which of the following choices lists the
  Organization of Life in order of increasing
  complexity?
• Organism ? Organs ? Organ Systems ? Cells ?
  Tissues
• Organs ? Cells ? Tissues ? Organ Systems ?
  Organism
• Cells ? Tissues ? Organs ? Organ Systems ?
  Organisms
• Tissues ? Organs ? Organ Systems ? Cells ?
  Organism
• 2. What is the main difference between
  prokaryotes and Eukaryotes?
• 3. Where do you find the DNA in a Eukaryote? A
  prokaryote?

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The Cell Membrane (Plama membrane)
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Overview

• Cell membrane separates living cell from
  nonliving surroundings
• thin barrier 8nm thick
• Controls traffic in out of the cell
• selectively permeable
• allows some substances to cross more easily than
  others
• hydrophobic vs hydrophilic
• Made of phospholipids, proteins other
  macromolecules

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Phospholipids
Phosphate

• Fatty acid tails
• hydrophobic
• Phosphate group head
• hydrophilic
• Arranged as a bilayer- what is a bilayer?

Fatty acid
Aaaah, one of thosestructurefunction examples
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Phospholipids are the major structural component
of membranes. Heads are made of phosphate group
and alcohol Tails are nonpolar and made of carbon
and hydrogen.
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Phospholipid bilayer
polar hydrophilic heads
nonpolar hydrophobic tails
polar hydrophilic heads
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More than lipids

• In 1972, S.J. Singer G. Nicolson proposed that
  membrane proteins are inserted into the
  phospholipid bilayer

Its like a fluidIts like a mosaic Its the
Fluid Mosaic Model!
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Membrane is a collage of proteins other
molecules embedded in the fluid matrix of the
lipid bilayer
Extracellular fluid
Phospholipids
Cholesterol
Cytoplasm
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Membrane fat composition varies

• Fat composition affects flexibility
• membrane must be fluid flexible
• about as fluid as thick salad oil
• unsaturated fatty acids in phospholipids
• keep membrane less viscous
• cold-adapted organisms, like winter wheat
• increase in autumn
• cholesterol in membrane

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Cholesterol

• What does cholesterol do?
• Helps maintain the integrity of the plasma
  membrane.
• Helps maintains the fluidity of the membrane-
  helps with extremes
• Helps hold integral proteins into the membrane.

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Membrane Proteins

• Proteins determine membranes specific functions
• cell membrane organelle membranes each have
  unique collections of proteins
• Membrane proteins
• peripheral proteins
• loosely bound to surface of membrane
• cell surface identity marker (antigens)
• integral proteins
• penetrate lipid bilayer, usually across whole
  membrane
• transmembrane protein
• transport proteins
• channels, permeases (pumps)

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What do membrane proteins do?

• Plasma membrane proteins function in several
  different ways.
• selective transport of certain substances across
  the phospholipid bilayer, either acting as
  channels or active transport molecules.
• receptors, which bind information-providing
  molecules, such as hormones, and transmit
  signals
• Membrane proteins may also exhibit enzymatic
  activity, catalyzing various reactions related to
  the plasma membrane.

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Many Functions of Membrane Proteins
Outside
Plasma membrane
Inside
Transporter
Enzymeactivity
Cell surfacereceptor
Cell adhesion
Cell surface identity marker
Attachment to thecytoskeleton
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Why areproteins the perfect molecule to build
structures in the cell membrane?
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Membrane carbohydrates

• Play a key role in cell-cell recognition
• ability of a cell to distinguish one cell from
  another
• antigens
• important in organ tissue development
• basis for rejection of foreign cells by immune
  system

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Movement across the Cell Membrane