Cellular Structures: Mitochondria, Chloroplasts & Nucleus
Mitochondria: Structure and Function
Outer membrane: Contains proteins that regulate the exchange of substances with the cytosol. Inner membrane: Consists of ridges and contains mitochondrial proteins. Matrix: The space inside the mitochondria; contains enzymes, DNA (as a double-stranded, closed circular molecule).
Mitochondria Function: Energy production.
Chloroplast: Structure and Function
Found in plant cells and photosynthetic eukaryotes.
- Outer membrane: Fluid mosaic.
- Inner membrane: No crests.
- Stroma: Chloroplast internal cavity, containing DNA, enzymes, ribosomes, and various substances.
- Thylakoid: Contains chlorophyll and carotenoids, electron transport chain, and ATP synthase.
- Thylakoid space: Maintains pH conditions.
Chloroplast Function: Organelles where photosynthesis takes place.
Nuclear Envelope: Structure and Function
Envelope: Structure formed by a double membrane that has continuity with the cellular endoplasmic reticulum (ER). Outer nuclear membrane: Contains cytoplasmic ribosomes and is in contact with the ER. Nuclear space: Connected with the ER lumen. Inner nuclear membrane: In contact with the nucleoplasm.
Nuclear Lamina: Network of protein filaments. Pore: Allows for the exchange of substances.
Envelope Function: The biological importance of DNA necessitates a compartment that separates the chromosomes from the cytoplasm. The nuclear envelope allows the passage of substances through it.
Cytosol
The space between the membranous organelles.
Ingredients: Water constitutes the majority, along with a great variety of substances involved in cellular metabolism.
Cytosol Function: Contains reserve materials suitable for developing reactions.
Cytoskeleton
A network of filaments and tubules formed by the polymerization of several proteins; a dynamic structure.
Microfilaments: Part of the cytoskeleton, made up mainly of intracellular actin fibers attached to the inner surface of the plasma membrane.
Cytoskeleton Functions:
- Maintains and modifies membrane structure.
- Stabilizes structure.
- Facilitates vesicle endocytosis.
- Allows muscle contraction: Inside muscle cells, the sliding between myosin fibers and actin microfilaments causes shortening of the bundles, requiring Ca2+ ions and energy.
Microtubules
Cylindrical structures of variable length. We can distinguish:
- Standing in Mobile: Centrioles: 0.4 microns long by 0.2 microns in diameter, with triplets. Two centrioles form the centrosome, the cell area where the arrangement of microtubules is organized, which participate in cell division.
- Cilia and Flagella: 0.2 microns in diameter and 5-10 microns in length (cilia), or >50 microns (flagella).
- Microtubule Structure: (Axoneme / Transition zone / Basal corpuscle).
- Modify their position: They are deposited radially around the centrioles in the interphase cell, and during cell division, they form the mitotic spindle.
- Intermediate filaments: Form a network that stretches from the nucleus to the periphery; they also form the nuclear lamina.
Ribosomes
Composed of two subunits, one small and one large. Each subunit contains various RNA chains (rRNA) and proteins.
Function: Protein synthesis. The molecules involved attach to the ribosomes:
- mRNA (messenger RNA): Synthesized from DNA, containing the amino acid pattern for the union.
- tRNA (transfer RNA): Carries the amino acids.
The large subunit catalyzes peptide bond formation between the amino acids, forming a peptide according to the required sequence.
Nucleus
- Chromosomes: Long chains of DNA associated with proteins, allowing for the packaging and unpackaging of chromosomes per cell cycle.
- Nucleolus: Between 1 and 7 (micrometers), formed by chromatin from different chromosomes.
Functions:
- Transmits genetic information from generation to generation.
- Controls the activity that takes place in each cell.
These functions are made possible because the chromosomes determine the protein synthesis of the cell. The nucleolus is where rRNA is synthesized, and ribosomal components are assembled: ribosomal proteins are synthesized in the cytosol, enter the nucleus, and are directed to the nucleolus, where they bind to different RNA molecules. Once assembled, the ribosomes exit to the cytosol, where they complete their structure.