Understanding Mitochondria and Chloroplasts in Cells
– Mitochondrial Matrix: Contains a semi-liquid material with the consistency of gel. It contains:
1. Mitochondrial DNA molecules, which in most mammalian cells is circular, double-stranded DNA, different from nuclear DNA.
2. Molecules for mitochondrial function.
3. Enzymes for RNA replication, transcription, and translation of mitochondrial DNA.
4. Enzymes involved in the Krebs cycle and the beta-oxidation of fatty acids.
5. Ions of Ca, P, and ribonucleoproteins.
– Intermembrane Space: Located between the outer and inner membranes, containing enzymes that use ATP to phosphorylate AMP or other nucleotides.
– Inner Mitochondrial Membrane: It has folds into the intermembrane space called cristae. It contains 20% lipids and 80% proteins.
– Outer Mitochondrial Membrane: The mitochondria’s outer membrane is a double-layer structure made of lipids and associated proteins. It contains 40% lipids (cholesterol, etc.) and 60% proteins.
– Elemental F1 Particles: On the outer side of the cristae, oriented towards the matrix. They consist of a spherical head or F1 complex, which is a globular protein, a stalk, and a hydrophilic base.
__The reason mitochondria have different enzyme complexes is that each performs different functions.
– Krebs Cycle: It takes place in the mitochondrial matrix and is a process of great importance for cellular catabolism.
– Respiratory Chain: In the Krebs cycle, electrons are transported through three complexes organized in the inner mitochondrial membrane.
– Oxidative Phosphorylation: This process occurs on particles in the cristae. The F1 head of this particle can phosphorylate ADP to ATP.
– Beta-Oxidation of Fatty Acids: Enzymes for this process are located in the mitochondrial matrix.
– Concentration of Substances in the Internal Chamber: Includes proteins, iron, dyes, lipids, etc.
Plastids: They are organelles unique to plant cells, possessing pigments (chlorophylls and carotenoids) and synthesizing and accumulating reserve substances (starch, oil, etc.). They are classified into two groups:
1. Leucoplasts: Lack pigments and store substances such as starch and fats, found in plant stem cells and parts of the roots.
2. Chromoplasts: Contain pigments that give color. Those that contain chlorophyll are green and are called chloroplasts, while those containing phycoerythrin are red and are called rhodoplasts.
Chloroplasts: These plastids are biologically important because they are responsible for photosynthesis, transforming light into chemical energy. Their morphology is varied. In higher plants, they are usually oval-shaped, but in some algae, they have different forms: helical, cup-shaped, etc. Each cell usually contains 20 to 40 chloroplasts, with extreme cases having up to 400,000 per mm² (as seen in Ricinus cells). The size varies from species to species. They are located in the cytoplasm, with no fixed position, and can move like amoebae due to cyclosis.
They are formed by a double membrane, an intermembrane space, and stroma, within which are the thylakoids—flattened sacs that can be isolated or superimposed over others.
– Inner and Outer Membrane: Similar in structure to other external membranes. The outer membrane has more permeability, while the inner membrane is almost impermeable.
– Thylakoids: They are flattened sacs stacked on top of each other, forming a membranous network. Each stack is called a granum, and the space between two granum stacks is called intergranum. Here, the process of photosynthesis requires light.
– Stroma: It contains a circular DNA molecule, double-stranded, and plastid ribosomes. The dark phase of photosynthesis occurs here.
– Photosynthesis: Chloroplasts are responsible for this process, producing ATP and NADPH.
– Biosynthesis of Fatty Acids: This process uses carbohydrates, NADPH, and ATP.
– Reduction of Nitrate to Nitrite: This process involves ammonia, which is the source of nitrogen for forming amino acids and nucleotides.