Cellular Structures: Nucleus, Golgi, Lysosomes, Mitochondria, and Chloroplasts

Posted on Jan 24, 2025 in Biology

Core Structure and Composition of the Interphase Nucleus

  • Nuclear envelope
  • Chromatin
  • Nucleolus
  • Nucleoplasm

Note: The term “Nucleo ///////// mitotic” seems out of context and may be a typo or error.

Golgi Complex Functions

  • Modifies proteins synthesized in the Rough Endoplasmic Reticulum (RER).
  • Involved in the transport and secretion of proteins and lipids.
  • Participates in the formation of the plant cell wall and glycocalyx in animal cells.
  • Related to the transit of lipids in the sweat glands.
  • Plays a role in the genesis of lysosomes.

Two Types of Lysosomes

  • Primary lysosomes: Recently formed by the Golgi apparatus and contain hydrolytic enzymes.
  • Secondary lysosomes: Formed after the merger of several primary lysosomes with an endocytic or phagocytic vesicle, where cellular digestion takes place.

Functions of Lysosomes

Due to their hydrolytic enzymes, lysosomes are involved in cellular digestion. Depending on the process they participate in, they are classified as:

  • Phagolysosomes: Organelles formed from the union of a vacuole with primary lysosomes.
  • Autophagolysosomes: Lysosomes fuse with autophagic vacuoles to remove cellular debris.
  • Multivesicular bodies: Lysosomes that contain various vesicles inside.

Vacuoles

Functions of Vacuoles

  • Maintenance of turgor and cell surface increases, allowing for exchange with the exterior.
  • Serve as a reserve stock for ions, carbohydrates, amino acids, proteins, toxins, and waste.

Structure and Composition of Mitochondria

  • External mitochondrial membrane
  • Intermembrane space or perimitochondrial space
  • Internal mitochondrial membrane
  • Matrix

Function of Mitochondria

Mitochondria are responsible for obtaining energy for the cell.

In the mitochondrial matrix, the following processes occur:

  • Beta-oxidation of fatty acids.
  • Oxidative decarboxylation of pyruvic acid from glycolysis.
  • Tricarboxylic acid cycle (Krebs cycle). In these reactions, acetyl-CoA derived from pyruvate is completely oxidized to CO2, generating reduced intermediates.
  • Mitochondrial protein synthesis machinery at the expense of mitochondrial DNA replication.

In the inner mitochondrial membrane, electron transport is carried out through the respiratory chain to oxygen, and ATP synthesis occurs via oxidative phosphorylation. Mitochondria divide independently within the cell through mechanisms such as:

  • Bipartition
  • Strangulation
  • Budding

Chloroplast Structure

  • Envelope: The outer and inner plastid membranes have a continuous structure and are separated by the intermembrane space.
  • Stroma: The matrix of the chloroplast, defined by the inner plastid membrane, contains grana, thylakoids, plastid DNA, and 70S ribosomal proteins.
  • Thylakoids and grana: Inside, you can see stromal thylakoids (membrane vesicles arranged parallel to the axis of the chloroplast). Some are stacked in groups called grana.

Function of Chloroplasts

This is where photosynthesis takes place (the cell uses light as an energy source and CO2 as a carbon source). Photosynthesis has two phases:

  • Light-dependent phase: In the thylakoid membrane, reactions occur to convert light energy into chemical energy.
  • Light-independent phase (Dark phase): In the stroma, CO2 fixation into organic molecules and their storage in the form of reserve polysaccharides occurs.

Chloroplasts can originate from other pre-existing chloroplasts in the cell by binary fission.