Chapter 7, Problem 29A

Summary Introduction

To analyze: Comparison between the structure and functions of the chloroplast and mitochondria.

Introduction:Cell is the basic structural and functional unit of life. All living organisms are composed of cells. Cells can be classified as eukaryotic or prokaryotic.

Prokaryotic are unicellular organisms that lack internal membrane-bound structures. Eukaryotic cell possesses a clearly well-defined nucleus. The eukaryotic cell has a nuclear membrane that surrounds the nucleus, in which the well-defined chromosomes are located, and these cells also possess membrane bound cell organelles.

Explanation of Solution

Chloroplast: Chloroplasts are cell organelle found in most of the plants and few organisms. It contains double-stranded circular DNA. The chloroplast has an inner and outer membrane with an empty intermediate space in between. Inside the chloroplast are stacks of thylakoids, called grana, as well as stroma, the dense fluid inside of the chloroplast. These thylakoids contain the chlorophyll that is necessary for the plant to go through photosynthesis.

Mitochondria: Mitochondria are double membrane-bound cell organelle and they also contain double stranded circular DNA. They are found in most mammalian cells, except mature erythrocytes.They are known as the ‘powerhouse of the cell’, and they are the site of the majority of ATP synthesis.

Mitochondria have inner and outer membrane with inter-membrane space between them. The outer membrane contains proteins called porins which allow movements of ions into and out of mitochondria, and it also contains some enzymes.

The inter-membrane space contains fluid called matrix also contains enzymes involved in Kreb-cycle. The inner membrane contains variety of enzymes and contains ATP synthetase which generates ATP in the matrix and transport proteins that regulate the movement of metabolites into and out of matrix. The inner membrane is arranged into cristae which increases the surface area for energy production via oxidative phosphorylation.

Function of chloroplast and mitochondria:

The chloroplasts are the site of photosynthesis, which is the process by which energy from the Sun is converted into chemical energy for growth. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant. Chloroplasts capture light energy from the sun to produce the free energy stored in ATP and NADPH through a process called photosynthesis.

The mitochondrion is the site of ATP synthesis for the cell. The numbers of mitochondria found in a cell are therefore a good indicator of the cell’s rate of metabolic activity. Cells which are very metabolically active, such as hepatocytes, will have many mitochondria.

Mitochondria also have a role to help maintain the intracellular environment.

1. They store caspases responsible for triggering apoptosis.
2. They are also able to transiently store calcium contributing to calcium homeostasis.

Conclusion

The chloroplast performs photosynthesis while mitochondria involves in respiration. They both contain double stranded circular DNA which resembles prokaryotic origin.