Curso EXANI II 2026 Biología La célula: Organelos celulares Parte 1 #4

Introduction to Cellular Organelles

Overview of Cellular Organelles

• The course focuses on cellular organelles, which are structures within cells that perform specific functions.

• Organelles are primarily found in eukaryotic cells but also exist in prokaryotic cells, albeit to a lesser extent.

• Eukaryotic cells have defined nuclei and internal membranes separating various cellular components.

Types of Cells

• There are two main types of cells: prokaryotic (simpler structure) and eukaryotic (more complex).

• Both cell types contain ribosomes, genetic material (DNA and RNA), cytoplasm, and a plasma membrane.

• Eukaryotic cells have more organelles compared to prokaryotes due to their complexity.

Differences Between Plant and Animal Cells

Structural Similarities and Differences

• Eukaryotic cells can be divided into plant and animal cells, which share many structural similarities.

• Key organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes.

• Significant differences between plant and animal cells include the presence of chloroplasts, cell walls, and vacuoles in plant cells.

The Nucleus: The Control Center

Functions of the Nucleus

• The nucleus is a membranous structure at the center of eukaryotic cells containing most genetic material as DNA.

• It protects genetic material with a nuclear membrane that prevents damage or degradation.

• The nucleus is responsible for DNA replication/transcription into RNA for protein production.

Regulation Roles

• It regulates the cell cycle ensuring proper division so daughter cells receive complete genetic copies.

• Additionally, it controls gene expression based on cellular needs.

Mitochondria: Powerhouses of the Cell

Energy Production

• Mitochondria generate most of the energy required by the cell through ATP production via cellular respiration.

• They possess a complex membranous structure with an outer membrane and an inner membrane where ATP synthesis occurs.

Unique Characteristics

• Mitochondria contain their own mitochondrial DNA allowing them to replicate independently within the cell.

Regulatory Functions

Cellular Organelles and Their Functions

Ribosomes: Structure and Function

• Ribosomes are complex membranous structures that replicate themselves and play a crucial role in cellular regulation.

• They are responsible for protein synthesis from genetic information, specifically mRNA, found in both eukaryotic and prokaryotic cells.

• Composed of two subunits (large and small), ribosomes read the genetic code from mRNA to assemble amino acids into protein chains.

• Each triplet of nucleotides on the mRNA corresponds to one amino acid, forming proteins or enzymes with catalytic activity.

• Free ribosomes synthesize proteins for the cell itself, while those attached to rough endoplasmic reticulum (RER) produce proteins for export or membrane incorporation.

Regulation of Protein Synthesis

• The synthesis process is regulated by various factors such as nutrient availability and hormonal signals.

• An example illustrates how inadequate protein intake affects muscle growth despite proper training.

Endoplasmic Reticulum: Types and Functions

Rough Endoplasmic Reticulum (RER)

• The RER is an organelle connected to the nuclear membrane, characterized by its rough appearance due to ribosome attachment.

• It plays a significant role in synthesizing and modifying proteins destined for secretion or incorporation into membranes.

• Proteins synthesized here undergo folding within the RER after being produced by ribosomes.

Smooth Endoplasmic Reticulum (SER)

• The SER lacks ribosomes, giving it a smooth appearance; it is primarily involved in lipid synthesis including phospholipids and steroids.

• It also participates in detoxifying substances within the cell and metabolizing hormones, along with storing calcium ions essential for muscle contraction.

Golgi Apparatus: Processing Center

• The Golgi apparatus processes and packages proteins and lipids produced in the RER before distributing them inside or outside the cell.

Overview of Cellular Organelles and Their Functions

Golgi Apparatus

• The Golgi apparatus processes and packages proteins and lipids from the rough and smooth endoplasmic reticulum for transport within the cell.

• It modifies proteins by adding sugars to form glycoproteins, with a structure divided into cis (near ER) and trans (near plasma membrane) parts for efficient processing.

• The Golgi is likened to Amazon in its role of distributing modified proteins and lipids to their final destinations, highlighting its complex structure with defined polarity.

Cell Membrane

• The cell membrane surrounds the cell, protecting it while regulating substance passage in and out due to its phospholipid bilayer composition.

• It maintains cellular integrity, allowing small molecules like oxygen and carbon dioxide to pass while blocking larger ones such as proteins.

• The dynamic structure of the membrane adapts to cellular needs, containing various proteins and carbohydrates for functions like cell identification and communication.

Cytoplasm

• Cytoplasm is the gel-like space between the cell membrane and nucleus, composed mainly of water, proteins, carbohydrates, lipids, salts, and organelles.

• Its primary function is serving as a medium for biochemical reactions; it houses most organelles including mitochondria and ribosomes.

• The cytoplasm's viscous nature supports organelles while enabling movement for cellular locomotion and substance transport.

Lysosomes

• Lysosomes are spherical structures containing hydrolytic enzymes that degrade complex organic molecules like proteins, lipids, carbohydrates, and nucleic acids.

• They play a crucial role in intracellular digestion by breaking down foreign particles such as bacteria or viruses along with damaged cellular material.

The Role of Cellular Organelles in Degradation and Homeostasis

Lysosomes: Key Functions

• Lysosomes play a crucial role in programmed cell death by releasing enzymes that degrade cellular content, leading to cell death.

• They are essential organelles involved in the degradation and recycling of molecules and cellular materials, contributing to homeostasis regulation.

Peroxisomes: Characteristics and Functions

• Peroxisomes are spherical organelles found in animal, plant cells, and microorganisms; they contain enzymes that oxidize organic molecules using oxygen.

• These organelles are involved in detoxification processes, neutralizing toxic substances like hydrogen peroxide through specific enzymes.

• Additionally, peroxisomes participate in lipid synthesis (e.g., phospholipids and bile acids) and help maintain cellular homeostasis by degrading and recycling cellular materials.

Comparison of Lysosomes and Peroxisomes

• A table comparing various organelles highlights similarities between lysosomes and peroxisomes, emphasizing their overlapping functions which may be relevant for exam questions regarding their differences.

Upcoming Topics on Plant Cells

• Future discussions will cover additional organelles specific to plant cells such as chloroplasts, vacuoles, and cell walls, as well as prokaryotic cell structures.

Exam Question Review

• An example exam question asks about the organelle responsible for substance degradation via enzymes. Possible answers include lysosome, rough endoplasmic reticulum, or centrioles.