Structure and Function of the Mitochondria

outline of structure and function

Structure of Mitochondria


  • Inner and outer membrane (creates an envelope)
  • Outer membrane is smooth and inner membrane is folded into cristae, giving it a large surface area.
  • Between the membranes is the intermembranal space
  • The matrix is enclosed by the inner membrane.

Shape, Size, Distribution:

  • Rod-shaped or thread-like
  • 2-5 um long, 0.5 - 1 um in diameter
  • metabolically active cells may have more mitochondria, which may have more densely packed cristae or more ATP synthase enzymes.
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How does their structure relate to their function?

The Matrix:

  • Where the link reaction and krebs cycle take place.
  • Contain specific enzymes
  • Molecules of NAD
  • Oxaloacetate - accepts acetate
  • Mitochondrial DNA (for proteins/ enzymes)
  • Mitochondrial ribosomes for protein assembly

Outer Membrane:

  • Phospholipid composition- contains proteins which form channels or carriers that allow passage of molecules such as pyruvate.


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Structure and Function continued

Inner Membrane:

  • Impermeable to small ions
  • Folded into cristae for large surface area (has embedded electron carriers and ATP synthase enzymes, so more oxidative phosphorylation can take place)
  • Electron transport chains are protein complexes arranged in electron transport chains
  • Each electron carrier is an enzyme associated with a cofactor (haem groups with an iron atom)
  • Cofactors accept and donate electrons...oxidoreductase enzymes.
  • Some electron carriers have a coenzyme that pumps protons from the matrix into the intermembranal space.
  • The inner membrane is impermeable to small ions so protons accumulate forming a gradient- a source of potential energy.
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Inner Membrane Continued

ATP synthase enzymes:

  • protrude from inner membrane into matrix
  • known as stalked particles
  • allow protons to pass through them.
  • protons flow down the proton gradient through ATP synthase enzymes from the intermembranal space into the matrix. This is called chemiosmosis. This flow allows ADP and Pi to join making ATP.
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Why do we need to respire?

All living organisms need energy to drive their metabolic processes.

Metabolism - Catabolic and Anabolic reactions.

Metabolic processes include:

  • active transport
  • endocytosis
  • movement
  • replication of DNA
  • synthesis of large molecules from small ones.

ATP is a phosphorylated nucleotide, consisting of adenine, ribose and three phosphate groups.

ATP is an immediate energy source available in small manageable amounts.It is known as a universal energy currency.

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During glycolysis, link reaction and krebs cycle hydrogen atoms are removed from substrate molecules in oxidation reactions. These reactions are catalysed by dehydrogenase enzymes, but they are not very goo at catalysing oxidation and reduction reactions. Coenzymes are needed to aid the reactions of respiration.


  • Coenzyme A
  • FAD
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