Understanding Mitochondria and Chloroplasts - High School Biology

Chloroplasts are an organelle that harbors large amounts of the green pigment chlorophyll. The chloroplast converts the energy of sunlight into chemical energy through a process called photosynthesis. This takes place inside a system of membranous sacs called thylakoids within the chloroplast.

Plants, algae, and cyanobacteria all produce energy via photosynthesis. Plants and algae use chloroplasts, but cyanobacteria are prokaryotes and do not contain membrane-bound organelles. Cyanobacteria use internal thylakoid structures to perform photosynthesis.

Plasmids are circular pieces of DNA found in prokaryotes, and are not linked to photosynthesis. Guard cells are responsible for opening and closing stomata on the surface of plant leaves, and are also not involved in photosynthesis.

Mitochondria are unique organelles because they contain their own double-stranded DNA. The genes on these DNA molecules are always transmitted to the offspring from the mother. During development, the mitochondrial DNA from the sperm (the gamete from father) is destroyed in the embryo. Since all genes in the mitochondria are only inherited from the mother, we can conclude that this disease is maternally inherited. We also know that the genes must be found on double-stranded DNA. There are very small amounts of double-stranded RNA molecules inside mitochondria, but they don’t code for any known diseases.

Mitochondria are the site of Krebs cycle and oxidative phosphorylation; however, they are not the site of glycolysis. Glycolysis occurs in the cytosol. Mitochondria have two membranes: the inner and the outer membrane. The space between these two membranes is termed the intermembrane space. The mitochondrial matrix is inside the inner membrane and is the site of Krebs cycle. Scientists theorize that mitochondria and chloroplasts (from plants) were initially prokaryotic organisms that joined with another cell to form a symbiotic relationship, not a parasitic relationship. This theory is called the endosymbiotic theory and it explains the reasons why mitochondria contain DNA.

Mitochondria do have their own ribosomes, which produce unique mitochondrial proteins. Remember, however, that the mitochondria still utilize the normal proteins produced by the ribosomes in the rough endoplasmic reticulum and cytosol.

The cristae increase the surface area available within the cell. In order for oxidative phosphorylation of occur, certain proteins must be embedded in the inner mitochondrial membrane. The fold in the membrane allow for a larger surface area, which in turn allows more of these proteins to be embedded. More proteins to create energy means more energy (ATP) for the cell.

Mitochondria and chloroplasts are plastids, and are thought to have arisen in eukaryotic cells via endosymbiosis. All the other options are true of mitochondria and chloroplasts.

The mitochondria are responsible for synthesis of the majority of the cell's ATP. This is why mitochondria are commonly referred to as the powerhouse of the cell. The rough endoplasmic reticulum and Golgi apparatus are involved in protein synthesis and delivery. The nucleus houses the DNA and is the site of transcription and ribosome assembly (nucleolus). The lysosome contains hydrolytic enzymes that are used for degradation of certain materials.

All of the listed organelles contain DNA. Scientists have identified nuclear DNA, mitochondrial DNA and chloroplast DNA that are exclusive to these cellular structures.

Mitochondria is the organelle involved in ATP production. Specifically, the Krebs cycle and electron transport chain occurs in the mitochondria. Smooth ER synthesizes lipids and detoxifies harmful substances. Rough ER and ribosomes are involved in protein synthesis.

Chloroplasts are the organelles found in plant cells that contain chlorophyll pigments which conduct photosynthesis in plants , some bacteria, and some protists. They form glucose molecules, which can be connected to form polysaccharides of starch. Animal cells do not have chloroplasts. Rather, animals need to eat their food, they cannot produce their own food from the sun.

Mitochondria produces most of the energy of the cell. The nucleus stores genetic information and is the site of transcription. The rough endoplasmic reticulum is the site of translation of proteins that have destinations other than in the cytoplasm. These proteins made in the rough endoplasmic reticulum are subsequently transported to the Golgi apparatus, where they are modified, packaged, and sent to their final destinations. Lysosomes have an acidic environment in which digestive enzymes break down polymers that will eventually be recycled.

Mitochondrial DNA is much smaller and simpler than nuclear DNA, meaning it does not need histones or introns. Mitochondrial DNA is also circular, like bacterial DNA, rather than linear like nuclear DNA. As the ovum is the only contributor of mitochondria to an offspring, all mDNA must therefore be inherited from the mother.

The mitochondria is responsible for making the energy for the cell by cellular respiration. It does this by taking the major breakdown products of glucose (pyruvate and NADH) and converting them into ATP by the citric acid cycle and electron transport chain. This is an oxygen-dependent process.