Cuarto de secundaria, microscopio y células

Microorganisms: The First Inhabitants of Earth

Introduction to Microorganisms

• Microorganisms are believed to have inhabited Earth for over 3.5 billion years, making them the first forms of life.

• In contrast, terrestrial plants emerged only 530 million years ago, and mammals appeared around 220 million years ago; humans have existed for approximately 250,000 years.

Overview of the Class

• The lesson is led by Heriberto Cordero, focusing on microorganisms and their significance in nature.

• Previous discussions included the COVID-19 virus as a microorganism and an introduction to microscopes invented by Zacharias Janssen in 1590.

Understanding Cells

• Today's focus will be on cell structures and viruses, particularly the COVID-19 virus.

• The discovery of cells began two centuries after the microscope's invention; it was established that all living beings are composed of cells.

Cell Theory Development

• In 1839, scientists Theodor Schwann and Matthias Schleiden proposed that cells are the basic structural and functional units of life.

• Rudolf Virchow later stated that all cells arise from pre-existing cells, forming what is known as cell theory.

Importance of Cells in Living Organisms

• Humans consist of over 37 trillion cells that form organs and tissues necessary for physiological functions like nutrition, reproduction, and response to stimuli.

• All living organisms are made up of at least one cell; some organisms are unicellular while others are multicellular.

Diversity of Life: Prokaryotic vs. Eukaryotic Cells

Characteristics of Prokaryotic Cells

• Prokaryotic cells contain genetic material dispersed in cytoplasm without a nucleus; they include bacteria and archaea.

• Key structures include a plasma membrane made up of phospholipids and proteins which retain compounds within the cell.

Functions Within Prokaryotic Cells

• Cytoplasm houses ribosomes essential for protein synthesis; genetic material consists of a single circular DNA molecule located in a region called nucleoid.

Protective Structures in Prokaryotes

• The cell wall provides structural rigidity while preventing dehydration; some prokaryotes also possess a capsule made from polysaccharides for additional protection.

Mobility Features

• Flagella enable movement in prokaryotic cells; examples include Staphylococcus aureus found on human skin which can cause infections if not properly managed.

Eukaryotic Cells: Complexity and Diversity

Overview of Eukaryotic Cells

• Eukaryotic cells are larger and more complex than prokaryotes. They can exist independently (unicellular organisms like amoebas or yeasts).

This structured approach captures key insights from the transcript while providing timestamps for easy reference.

Understanding Eukaryotic Cells and Zoonotic Viruses

Structure of Eukaryotic Cells

• All eukaryotic cells, including plants, animals, and fungi, contain a nucleus which houses chromosomes that carry genetic information (DNA).

• The cell membrane acts as a barrier allowing selective entry and exit of substances; plant and fungal cells have a rigid cell wall made of cellulose or chitin for added support.

• The cytoplasm consists of water and various organelles separated by membranes, each fulfilling specialized functions within the cell.

• Organelles such as lysosomes aid in digestion within the cell, while mitochondria are responsible for energy production through metabolic processes like respiration or photosynthesis.

• Chloroplasts found in plant cells contain chlorophyll, giving them their green color and enabling photosynthesis.

Zoonotic Origins of Coronaviruses

• All coronaviruses are zoonotic in origin; they can jump from animals to humans. For instance, SARS-CoV originated from bats via an intermediate host (civets), similar to COVID-19's likely origins involving pangolins.

• Seven types of coronaviruses infect humans; four common strains contribute to colds while three recent strains include COVID-19.

• A significant portion of the population has developed immunity against these common coronaviruses due to prior exposure.

Historical Context of Human Coronaviruses

• The first human coronavirus was identified in the 1960s; it was named 229E after being discovered by researchers studying cold symptoms.

• Until the 21st century, five additional coronaviruses were identified. Their structures vary widely in form and chemical composition.

Virus Structure and Infection Mechanism

• Viruses consist of nucleic acid encased in a protective protein coat called a capsid; some also possess an outer lipid membrane akin to packaging that enhances stability.

• When viruses invade host cells (known as infected cells), they act as parasites requiring cellular machinery for replication. This invasion often leads to disease symptoms or destruction of host cells.

Effects on Host Cells

• Viral infections can result in various outcomes: complete destruction of host cells or prolonged infection where viruses replicate without immediate symptoms appearing.

Understanding Viral Genomes and COVID-19

The Nature of Viral Genomes

• Viruses possess a genome that contains instructions for replication and characteristics such as species they can infect, modes of transmission, and interactions with cellular defense mechanisms.

• Viral genomes can be composed of DNA or RNA; while most genetic information is stored in DNA, many challenging viruses have RNA genomes.

Mutations and Their Implications

• Errors known as mutations occur during the replication of viral genomes, influencing virus behavior within cellular environments.

• RNA viruses like influenza, HIV, Ebola, and coronaviruses (e.g., SARS-CoV-2) exhibit high mutation rates due to the lack of error-correcting mechanisms found in DNA viruses.

Transmission and Infection Mechanisms

• SARS-CoV-2 likely originated from bat viruses through an intermediate animal host that allowed it to interact with human cell receptors, leading to the COVID-19 epidemic.

• Once inside the body, SARS-CoV-2 rapidly replicates within initial host cells, producing thousands of new viral particles ready to infect more cells. Unlike SARS (2002), which primarily infected lungs, COVID-19 spreads through respiratory pathways including the nose and throat.

Symptoms and Public Health Measures

• Initial symptoms of COVID-19 often include fever and dry cough rather than common cold-like symptoms such as sore throat or nasal discharge; loss of taste or smell is particularly notable.

• To mitigate spread, maintaining physical distance (at least one meter) and wearing masks are crucial public health measures during infection periods.

Microorganisms' Role in Life on Earth

• Microorganisms contribute significantly to life on Earth by forming various kingdoms including animals, plants, fungi, parasites, and bacteria; these organisms consist of specialized eukaryotic cells or prokaryotic cells without nuclei.

Cellular Functions in Humans

• Human bodies comprise trillions of cells performing essential functions; for instance, mitochondria facilitate respiration at a microscopic level akin to how humans breathe through their respiratory systems.

Conclusion: Understanding Virus Behavior

• The study highlights how understanding viral behavior aids in comprehending disease transmission dynamics like those seen with COVID-19; further exploration into microorganisms is encouraged for deeper insights into their roles in health and disease management.