The Cell [BIOLOGY]

• Introduction to Cell Biology

  Discovering living organisms in pond water was what occurred with Anton van Leeuwenhoek, a Dutch scientist known for his works with microscopy and considered one of the pillars of microbiology. Although he did numerous microscope work with many microscopic organisms it was only later, when microscopes improved, when cells were first observed by English scientist Robert Hooke who also coined the term due to the appearance of what he saw as being those of a honeycomb shape.
• Cell Theory

  Different microscopes have been developed over the years and the most common you may have used in school laboratories are called light microscopes where light is passed through a specimen and then the microscope glass to magnify the image. The aid from microscopes gave scientists evidence and helped our understanding of cells which piled up and points us to the concept of “cell theory,” the idea that living organisms are composed of basic, structural units called cells.
• Cell Theory

  • All living organisms are composed of one or many cells.
  • Cells are the basic unit of structure and organization in organisms.
  • Cells must come from pre-existing cells.
• Cell Theory

  Advancements in technology and improvement in our understanding of the cell have also added the following additional concepts with regards to the cell theory:

  • DNA is passed between cells during cell division.
  • All cells of organisms have the same basic chemical composition.
  • Energy flow occurs within cells.
• Anatomy of the Cell

  Cells fall into one of two categories: prokaryotic and eukaryotic.

  All cells share four common components:

  • The plasma membrane, which serves as an outer covering that protects the insides of a cell from its surrounding environment. It is usually composed of phospholipids arranged in a bilayer
  • Cytosol, which is a fluid region in the cell where other cell components are found
  • Chromosomes, structures that contain genetic material in the form of DNA
  • Ribosomes, particles that synthesize proteins.
• Parts of a Eukaryotic Cell

  • Plasma Membrane
  • Cytoplasm
  • Nucleus
  • Nuclear Membrane
  • Nucleoplasm
  • Nucleolus
  • Nuclear Pore
  • Mitochondrion
  • Endoplasmic Reticulum (ER)
  • Rough ER
  • Smooth ER
  • Golgi Apparatus
  • Lysosome
  • Peroxisome
  • Ribosomes
  • Vacuoles
  • Centriole
• Plasma Membrane: A semi-permeable layer that separates the insides of a cell from the external environment and is the location of chemical exchanges for many life functions.
• Cytoplasm: The fluid internal environment of the cell where all internal components of the cell (called “organelles”) are suspended.
• Nucleus: Stores the genetic material of the cell. In prokaryotes, this genetic material is located in a region called the nucleoid.
• Nuclear Membrane: Encloses the nucleus and protects the genetic material.
• Nucleoplasm: The environment within the nucleus.
• Nucleolus: An area in the nucleoplasm where the genetic material is highly concentrated.
• Nuclear Pore: Gateway of materials into or out of the nucleus.
• Mitochondrion: Produces energy for the organism, having the moniker “powerhouse of the cell" due to this function.
• Endoplasmic Reticulum (ER): Sites for lipid and protein synthesis
• Rough ER: Contains ribosomes and is the site for protein synthesis. In addition, it also functions as the cell’s membrane-making machine.
• Smooth ER: Contains cell types used in metabolic processes, especially lipid synthesis, as well as storage of calcium ions.
• Golgi Apparatus: Site for modifying, sorting, and storing of compounds synthesized by the ER.
• Lysosome: Contains digestive enzymes that help break down food or damaged organelles.
• Peroxisome: Helps break down fatty acids to be used as cellular fuel.
• Ribosome: Sites of protein synthesis. Can be found attached to the rough ER or free in the cytosol.
• Vacuoles: Storage of food and other chemicals.
• Centriole: Organelle for cell division.
• There are also cellular parts that are present in specific groups of organisms and there are also additional components of a cell that serve special functions in othe
• Prokaryotes

  Prokaryotes refer to organisms with cells that are simple, often single (unicellular), and lack a nucleus, or any other membrane-bound organelle. We will shortly come to see that this is significantly different in eukaryotes. Prokaryotic DNA is found in the central part of the cell: a darkened region called the nucleoid.
• Prokaryotes

  Bacteria are considered prokaryotes. They have a cell wall made of peptidoglycan, composed of sugars and amino acids, and many have a polysaccharide capsule. This cell wall acts as an extra layer of protection, helping the cell maintain its shape, and prevents dehydration. The capsule allows the cell to attach to surfaces in its environment. Other prokaryotes have flagella, pili, or fimbriae. Flagella are used for locomotion, while most pili are used to exchange genetic material during a type of reproduction called conjugation.
• Eukaryotes

  A eukaryote, meanwhile, is composed of cells that have a membrane-bound nucleus and other membrane-bound compartments, called organelles, with specialized functions. The word eukaryotic means “true nucleus,” due to the presence of a membrane-bound nucleus in these cells. The word “organelle” means “little organ,” and organelles have specialized functions, similar to how our organs have specific functions.
• Eukaryotes

  In nature, form and function are apparent at all levels, including the level of the cell, and this will become clear as we explore eukaryotic cells. The principle “form follows function” is found in many contexts. It means that, in general, one can deduce the function of a structure by looking at its form because the two are related. For example, birds and fish have streamlined bodies that allow them to move quickly through where they live, be it air or water.
• Animal Cell

  The most obvious mark of a eukaryotic cell is its nucleus. Other functions:

  • Genetic control, through the nucleus and ribosomes.
  • Manufacture, distribution, and breakdown of molecules which include the endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes.
  • Energy processing which includes the mitochondria in all cells and chloroplasts in plants.
  • Structural support, movement, and communication between cells performed by the cytoskeleton, plasma membrane, and plant cell wall.

  
• Plant Cell

  Among structures that are present in plant cells that animal cells lack are the rigid, and a rather thick cell wall. This cell wall is made of cellulose which makes it chemically different from the cell wall of a prokaryotic cell. Unique structures called plasmodesmata (singular plasmodesma) connect adjacent plant cells. Another key difference present in plant cells is the chloroplast, where photosynthesis occurs. Plant cells also have a large, central compartment called a vacuole that stores water and a variety of chemicals.
• Both plant cell and animal cell: lysosomes (which is not commonly found in plant cells) and centrosomes (organelles containing the centrioles), the organelles in animal cells are also found in plant cells
• Plant Cell and Animal Cell

  Eukaryotic cells also contain non-membranous structures as well, of particular note is the cytoskeleton which is composed of different protein fibers that extend throughout the cell. Another example is ribosomes which can be found free in the cytosol as well as attached to certain membranes
• Cell Surfaces

  Networks of protein fibers extend throughout the cell. Collectively called the cytoskeleton, these fibers provide structural support as well as movement.
• Cytoskeleton (thickest to thinnest)

  • Microtubules
  • Intermediate filaments
  • Microfilaments
• Cell Surfaces

  Microtubules - straight and hollow tubes composed of proteins called tubulins. In animal cells, microtubules grow from the centrosome while plant cells have other means of synthesizing as they lack centrosomes.
• Cell Surfaces

  Intermediate filaments - found in cells of most animals, these reinforce cell shape and anchor some organelles. For example, the outer layer of our skin is made of dead skin cells composed of intermediate filaments.
• Cell Surfaces

  Microfilaments - also called actin filaments, these help support the cell’s shape particularly in animal cells that lack cell walls. Microfilaments are also involved in cell movements.
• Cell Surfaces

  The role of the cytoskeleton in movement is clearly observed in motile appendages that rise from certain cells. For example, short and numerous appendages called “cilia” propel the protist Paramecium (see image above). Other protists move using a flagellum, which is longer than the cilia but present in fewer numbers or as a sole structure per cell.
• Cell Junctions

  Animal cells produce an extracellular matrix (ECM) that helps hold cells together and protects and supports the plasma membrane. The main components of the ECM are glycoproteins, proteins bonded with carbohydrates. The ECM may attach to the cell through other glycoproteins that bind to membrane proteins called integrins. As their name implies, they function in integration, i.e., transmit signals between the ECM and cytoskeleton; communicating changes occurring within and outside of the cell.
• Cell Junctions

  Neighboring animal cells often interact and communicate through specialized junctions between them. 3 types:

  • Tight junction
  • Gap junction
  • Anchoring junction