Both the mitochondria and chloroplasts are energy-generating organelles. Explain how the
structure of their membrane systems is critical for their functions, emphasizing their similarities
and differences.
Solution
Answer:
Cloroplasts and mitochondria share similarities in many aspects.
Chloroplasts are large organelles that, like mitochondria, are bounded by a double membrane. In
addition to the inner and outer membranes of the envelope, chloroplasts have a third internal
membrane system, called the thylakoid membrane. The thylakoid membrane forms a network of
flattened discs called thylakoids, which are frequently arranged in stacks called grana.
The internal organization of chloroplasts is more complex than that of mitochondria. In
particular, their three membranes divide chloroplasts into three distinct internal compartments:
(1) the intermembrane space between the two membranes of the chloroplast envelope
(2) the stroma, which lies inside the envelope but outside the thylakoid membrane
(3) the thylakoid lumen
Mitochondria are surrounded by a double-membrane system- inner and outer mitochondrial
membranes separated by an intermembrane space. The inner membrane forms numerous folds
(cristae) which extend into the interior of the organelle. Each of these components plays distinct
functional roles, with the matrix and inner membrane representing the major working
compartments of mitochondria.
The membranes of chloroplasts have functional similarities with those of mitochondria and the
role of both organelles in the chemiosmotic generation of ATP. The outer membrane of the
chloroplast envelope, like that of mitochondria, contains porins and is therefore freely permeable
to small molecules. In contrast, the inner membrane is impermeable to ions and metabolites,
which are able to enter chloroplasts only via specific membrane transporters.
These properties of the inner and outer membranes of the chloroplast envelope are similar to the
inner and outer membranes of mitochondria. In both cases the inner membrane restricts the
passage of molecules between the cytosol and the interior of the organelle. The chloroplast
stroma is also equivalent in function to the mitochondrial matrix. It contains the chloroplast
genetic system and a variety of metabolic enzymes, including those responsible for the critical
conversion of CO2 to carbohydrates during photosynthesis.
The major difference between chloroplasts and mitochondria, in terms of both structure and
function, is the thylakoid membrane. This membrane is of central importance in chloroplasts,
where it fills the role of the inner mitochondrial membrane in electron transport and the
chemiosmotic generation of ATP.
The inner membrane of the chloroplast envelope (which is not folded into cristae) does not
function in photosynthesis. In contrast, he chloroplast electron transport system is located in the
thylakoid membrane, and protons are pumped across this membrane from the stroma to the
thylakoid lumen.
Both the mitochondria and chloroplasts are energy-generating organel.pdf
1. Both the mitochondria and chloroplasts are energy-generating organelles. Explain how the
structure of their membrane systems is critical for their functions, emphasizing their similarities
and differences.
Solution
Answer:
Cloroplasts and mitochondria share similarities in many aspects.
Chloroplasts are large organelles that, like mitochondria, are bounded by a double membrane. In
addition to the inner and outer membranes of the envelope, chloroplasts have a third internal
membrane system, called the thylakoid membrane. The thylakoid membrane forms a network of
flattened discs called thylakoids, which are frequently arranged in stacks called grana.
The internal organization of chloroplasts is more complex than that of mitochondria. In
particular, their three membranes divide chloroplasts into three distinct internal compartments:
(1) the intermembrane space between the two membranes of the chloroplast envelope
(2) the stroma, which lies inside the envelope but outside the thylakoid membrane
(3) the thylakoid lumen
Mitochondria are surrounded by a double-membrane system- inner and outer mitochondrial
membranes separated by an intermembrane space. The inner membrane forms numerous folds
(cristae) which extend into the interior of the organelle. Each of these components plays distinct
functional roles, with the matrix and inner membrane representing the major working
compartments of mitochondria.
The membranes of chloroplasts have functional similarities with those of mitochondria and the
role of both organelles in the chemiosmotic generation of ATP. The outer membrane of the
chloroplast envelope, like that of mitochondria, contains porins and is therefore freely permeable
to small molecules. In contrast, the inner membrane is impermeable to ions and metabolites,
which are able to enter chloroplasts only via specific membrane transporters.
These properties of the inner and outer membranes of the chloroplast envelope are similar to the
inner and outer membranes of mitochondria. In both cases the inner membrane restricts the
passage of molecules between the cytosol and the interior of the organelle. The chloroplast
stroma is also equivalent in function to the mitochondrial matrix. It contains the chloroplast
genetic system and a variety of metabolic enzymes, including those responsible for the critical
conversion of CO2 to carbohydrates during photosynthesis.
The major difference between chloroplasts and mitochondria, in terms of both structure and
function, is the thylakoid membrane. This membrane is of central importance in chloroplasts,
2. where it fills the role of the inner mitochondrial membrane in electron transport and the
chemiosmotic generation of ATP.
The inner membrane of the chloroplast envelope (which is not folded into cristae) does not
function in photosynthesis. In contrast, he chloroplast electron transport system is located in the
thylakoid membrane, and protons are pumped across this membrane from the stroma to the
thylakoid lumen. The resulting electrochemical gradient then drives ATP synthesis as protons
cross back into the stroma.
In terms of its role in generation of metabolic energy, the thylakoid membrane of chloroplasts is
thus equivalent to the inner membrane of mitochondria.
