Cell Structure and Function

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Chapter 3

• Cell Structure and Function

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Outline

• Cellular Organization
• Plasma Membrane
• Functions
• Nucleus
• Endomembrane System
• Cytoskeleton
• Cilia and Flagella
• Cellular Respiration
• Fermentation

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Cell Size- Why are cells so small?

• Relatively small cell size is explained by
  surface-to-volume-ratio.
• As cells get larger in volume, proportionate
  amount of surface area decreases.

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Microscopy and Cell Structure

• Three common types of microscopes
• Compound light microscope.
• Light rays are focused by glass lenses.
• Transmission electron microscope.
• Electrons are focused by magnetic lenses.
• Scanning electron microscope.
• 3D View of object coated with metal

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Microscopy and Cell Structure
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• Cellular
• Organization
• Plasma
• membrane
• Nucleus
• Organelles
• Cytoskeleton

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Plasma Membrane

• Plasma membrane is a phospholipid bilayer with
  attached or embedded proteins.
• Polar head and non-polar tails.
• Form spherical bilayer when placed in water.
• Plasma membrane proteins form receptors,
  conductors, or enzymes in metabolic reactions.

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Plasma Membrane Model
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Plasma Membrane Functions

• Plasma membrane is selectively permeable.
• Diffusion
• Osmosis and osmotic pressure
• Tonicity
• degree to which a solutions solute concentration
  causes water to move into or out of cells.

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Plasma Membrane Functions

• Transport by Carriers.
• Facilitated transport
• a molecule is transported across the plasma
  membrane down a concentration gradient
• Active transport
• a molecule is moving against a concentration
  gradient with the input of energy

Active Transport
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Plasma Membrane Functions

• Transport by Carriers.
• Endocytosis occurs when a portion of the plasma
  membrane invaginates to envelop a substance and
  then pinches off to form an intracellular
  vesicle.
• Exocytosis occurs when a vesicle fuses with the
  plasma membrane as secretion occurs.

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Nucleus and Nuclear Membrane
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Ribosomes

• Ribosomes are found singly or in groups
  (polyribosomes) in the cytoplasm.
• Function in protein synthesis.

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Endomembrane System
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Mitochondria

• Mitochondria are double-membrane organelles
  involved in cellular respiration.
• Site of ATP
• production.

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The Cytoskeleton

• The cytoskeleton is formed of several types of
  filamentous structures that give the cell its
  shape and organelles the ability to move about
  the cell.
• Microtubules.
• Actin Filaments.

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Centrioles

• Centrioles are short cylinders composed of
  microtubules that are involved in spindle
  formation during cell division and give rise to
  basal bodies.

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Cilia and Flagella

• Cilia and flagella (cilium, flagellum) are
  projections that move in an undulating or
  whipping fashion.
• Cilia tend to be shorter while flagella tend to
  be longer.

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Cellular Metabolism

• Cellular metabolism includes all the chemical
  reactions that occur in a cell.
• Often organized into metabolic pathways.
• Most regulated by feedback inhibition.

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Enzymes and Coenzymes

• When an enzyme speeds up a reaction, the
  participating reactants are called the enzymes
  substrates.
• Many enzymes require cofactors for assistance.
• Some cofactors may accept or donate atoms to the
  reaction.

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Enzymatic Action
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Cellular Respiration

• Glucose breakdown requires three sub-pathways.
• Glycolysis.
• Citric Acid Cycle.
• Electron Transport System.
• Altogether, the breakdown of one glucose molecule
  results in 36 ATP molecules.

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Cellular Respiration
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Fermentation

• Fermentation is an anaerobic process that results
  in the buildup of lactate.
• Lactate is toxic to cells and causes muscle
  cramps and fatigue.
• Only produces two ATP per glucose molecule.