2017
The Cell: Structure and Functions.
A MAGAZINE WROTEN BY: EMIR GUZMÁN ANDREA CAMARENA DIEGO REYES CARLOS BENAVIDES. SAINT ANTHONY SCHOOL XI° SCIENCES.
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Introduction. Cells perform a huge number of different roles within our body. For example, epithelial cells protect the outside surface of the body as part of the skin and cover the organs and body cavities within. Bone cells build up bones to provide support for the body. Cells of the immune system fight invading bacteria. Blood and blood cells carry nutrients and oxygen throughout the body while removing carbon dioxide. Each of these cell types plays a vital role in the growth, development, and day-to-day maintenance of the body. In spite of their enormous variety, however, cells from all organisms—even ones as diverse as humans, onions, and bacteria, shown from left to right in the pictures below—share certain fundamental characteristics. This magazine will describe every essential aspect you need to know about the cell, because it’s important to know and learn about the smallest unit in our body that makes us living things.
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Cell Appendages, 1st Part. By Diego Reyes.
The Cell Wall. A cell wall is a structural layer surrounding some types of cells, situated outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes (except mycoplasma bacteria), in algae, plants and fungi but rarely in other eukaryotes including animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters.
The composition of cell walls varies between species and may depend on cell type and developmental stage. The primary cell wall of land plants is composed of the polysaccharides cellulose, hemicellulose and pectin. Often, other polymers such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess cell walls made of glycoproteins and polysaccharides such as carrageenan and agar that are absent from land plants. In bacteria, the cell wall is composed of peptidoglycan. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudo peptidoglycan, or polysaccharides. Fungi possess cell walls made of: The glucosamine polymer chitin. Unusually, diatoms have a cell wall composed of biogenic silica.
Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress. In
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multicellular organisms, they permit the organism to build and hold a definite shape (morphogenesis). Cell walls also limit the entry of large molecules that may be toxic to the cell. They further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition, properties, and form may change during the cell cycle and depend on growth conditions.
In the primary (growing) plant cell wall, the major carbohydrates are cellulose, hemi cellulose and pectin. The cellulose micro fibrils are linked via hemi cellulosic tethers to form the cellulosehemicellulose network, which is embedded in the pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan. In grass cell walls, xyloglucan and pectin are reduced in abundance and partially replaced by glucuronoarabinoxylan, another type of hemicellulose. Primary cell walls characteristically extend (grow) by a mechanism called acid growth, which involves turgor-driven movement of the strong cellulose micro fibrils within the weaker hemicellulose/pectin matrix, catalyzed by expansion proteins. The outer part of
the primary cell wall of the plant epidermis is usually impregnated with cutin and wax, forming a permeability barrier known as the plant cuticle. Secondary cell walls contain a wide range of additional compounds that modify their mechanical properties and permeability. The major polymers that make up wood (largely secondary cell walls) include:  Cellulose, 35-50%  Xylan, 20-35%, a type of hemicellulose  Lignin, 10-25%, a complex phenolic polymer that penetrates the spaces in the cell wall between cellulose, hemicellulose and pectin components, driving out water and strengthening the wall. Additionally, structural proteins (1-5%) are found in most plant cell walls; they are classified as hydroxyproline-rich glycoproteins (HRGP), arabinogalactan proteins (AGP), glycine-rich proteins (GRPs), and prolinerich proteins (PRPs). Each class of glycoprotein is defined by a characteristic, highly repetitive protein sequence.
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intracellular cytoskeleton. Cell membranes can be artificially reassembled.
The Cell Membrane: The cell membrane (also known as the plasma membrane or cytoplasmic membrane) is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. The basic function of the cell membrane is to protect the cell from its surroundings. It consists of the lipid bilayer with embedded proteins. Cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for several extracellular structures, including the cell wall, glycocalyx, and
The cell membrane (or plasma membrane or plasma lemma) surrounds the cytoplasm of living cells, physically separating the intracellular components from the extracellular environment. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix and other cells to hold them together to form tissues. Fungi, bacteria, most archaea, and plants also have a cell wall, which provides a mechanical support to the cell and precludes the passage of larger molecules. Cell membranes contain a variety of biological molecules, notably lipids and proteins. Material is incorporated into the membrane, or deleted from it, by a variety of mechanisms:  Fusion of intracellular vesicles with the membrane (exocytosis) not only excretes the contents of the vesicle but also incorporates the vesicle membrane's components into the cell membrane. The membrane may form blebs around extracellular material that
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pinch off to become vesicles (endocytosis).  If a membrane is continuous with a tubular structure made of membrane material, then material from the tube can be drawn into the membrane continuously.  Although the concentration of membrane components in the aqueous phase is low (stable membrane components have low solubility in water), there is an exchange of molecules between the lipid and aqueous phases.
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Cell Appendages, 2nd Part. By Andrea Camarena.
It is usually a projecting part of an animal or plant body that is typically smaller and less functional than the main part to which it is attached. There are two common types of appendages:
Peritrichous flagella are a series of flagella that appear around the cell in all directions.
Flagella:
Flagella have hair-like structure that acts primarily as an organelle of locomotion in the cells of many living organisms. This also occurs on the gametes of algae, fungi, mosses, slime molds, and animals. Flagellar motion causes water currents necessary for respiration and circulation in sponges. Flagella have three types:
Lophotrichious flagella are a group of flagella that are bundled together on one side of the cell.
Monotrichous flagella have only one flagellum attached to one side of the cell.
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Cilia:
Cilia are slender, microscopic, hair-like structures that extend from the surface of nearly all mammalian cells. The length of a single cilium is 1-10 micrometers and width is less than 1 micrometer.
Motile cilia: Larger eukaryotes, such as mammals, have motile cilia as well. Motile cilia are usually present on a cell's surface in large numbers and beat in coordinated waves.
Cytoplasm:
Cilia are broadly divided into two types. They function separately and sometimes together, just like:
Immotile cilia: In animals, primary cilia are found on nearly every cell. Cilia usually occur one per cell; nearly all mammalian cells have a single nonmotile primary cilium.
It consists of all of the contents outside of the nucleus and enclosed within the cell membrane of a cell. The cytoplasm is composed mainly of water and also contains enzymes, salts, organelles, and various organic molecules. His main functions are to support and suspend organelles and cellular molecules. It also helps to move
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materials, such as hormones, around the cell and also dissolves cellular waste.
Microfilaments:
Cytoskeleton:
It’s a structure that help the cells maintain their shape and internal organization. This provides mechanical support that let cells carry out functions like division and movement. Several different components work together to form the structure, unlike having separated functions. The cytoskeleton is made of filamentous proteins and it provides mechanical support to the cell and its cytoplasmic constituents. The Cytoskeleton has three primary fibers:
These are fine, thread-like protein fibers composed predominantly of a contractile protein called actin. They carry out cellular movements including gliding, contraction, and cytokinesis. Microtubules:
They are cylindrical tubes, composed of subunits of the protein tubulin (these subunits are termed alpha and beta). The microtubules provide a set of "tracks" for cell organelles and vesicles to move on and when they are arranged in geometric patterns inside flagella and cilia, it’s used for locomotion.
Intermediate Filaments:
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Those are who provide tensile strength for the cell.
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Types of Cells: By Carlos Benavides.
Eukaryotic Cells: Overview of eukaryotic cells and how they differ from prokaryotic cells (nucleus, organelles, and linear chromosomes).
•Multiple linear chromosomes, as opposed to the single circular chromosome of a prokaryote. Eukaryotic cells are much more complicated than those of prokaryotes. They are packed with a fascinating array of subcellular structures that play important roles in energy balance, metabolism, and gene expression.
What would it be like to live in a oneroom cabin? Well, things would probably be pretty simple. You would eat, sleep, work, and relax in a single room—which might be a bit cramped, but would certainly make cleaning the house a snap! What are the key features of eukaryotic cells? Unlike prokaryotic cells, eukaryotic cells have: •A membrane-bound nucleus, a central cavity surrounded by membrane that houses the cell’s genetic material.
Prokaryotic Cells:
•A number of membrane-bound organelles, compartments with specialized functions that float in the cytosol. (Organelle means “little organ,” and this name reflects that the organelles, like the organs of our body, have unique functions as part of a larger system.)
Prokaryotes are unicellular organisms that lack organelles or other internal membrane-bound structures. Therefore, they do not have a nucleus, but, instead, generally have a single chromosome: a piece of circular, double-stranded DNA located in an area of the cell called the nucleoid. Take a moment and look at yourself. How many organisms do you see? Your first thought might be that there's just
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one: yourself. However, if you were to look closer, at the surface of your skin or inside your digestive tract, you would see that there are actually many organisms living there. That’s right! You are home to around 100 trillion bacterial cells. This means that your body is actually an ecosystem. It also means that you—for some definition of the word you— actually consist of both of the major types of cells: prokaryotic and eukaryotic. All cells fall into one of these two broad categories. Only the single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes— pro means before and kary means nucleus. Animals, plants, fungi, and protists are all eukaryotes—eu means true—and are made up of eukaryotic cells.
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Cell Organelles. By Emir GuzmĂĄn.
Organelles are eukaryotic cell structures with specific functions, as they enable cells to carry out different functions at the same time. For example, cells can obtain energy from food, store information, make macromolecules, and get rid of waste materials all at the same time because different organelles performing the different tasks. Below you’ll find a more detailed explanation of this organelles and tasks.
The Nucleus:
organized into structures called chromosomes, and the number of them in a nucleus is different from other species of organisms, as most human cells contain 23 pairs of chromosomes.
In addition to chromosomes, the nucleus contains proteins and an organelle called nucleolus, which is seen as a large dark spot in the nucleus of a cell. Its function is to make ribosomes, organelles that are involved in the production of proteins. Surrounding the nucleus are two membranes that form a structure called the nuclear envelope, and they contain many pores. Certain molecules move into and out of the nucleus through these pores.
Ribosomes; Manufacturing Molecules: The nucleus is the most important part of a eukaryotic cell. It directs cell activities and contains genetic information stored in DNA. DNA is
Proteins are important molecules in the cells. Proteins are made on small structures called ribosomes. Unlike other organelles, ribosome is not surrounded by a membrane. They also can be attached to a web-like organelle
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called endoplasmic reticulum (abbreviated ER). The ER spreads from the nucleus throughout most of the cytoplasm. ER with ribosomes on its surface is called rough ER, and it is the site of protein production. ER without ribosomes is called smooth ER, and it makes lipids such as cholesterol and it helps removing harmful substances from a cell.
Mitochondria and Chloroplasts; Processing Energy: It’s a fact that all living things need energy to survive. Cells process some energy in specialized organelles, and most eukaryotic cells contain hundreds of organelles called mitochondria.
and outer as shown in Figure 1). Energy is released during chemical reactions that occur in the mitochondria. This energy is stored in a high-energy molecules called ATP (Adenosine triphosphate) and it is the fuel for cellular processes such as growth, cell division and material transport. Plant cells and some protists, such as algae, also contain organelles called chloroplasts, that are membrane-bound organelles that use light energy and make food and a sugar called glucose from water and carbon dioxide in a process known as photosynthesis. The sugar contains stored chemical energy that can be released when a cell needs it.
Processing, Transporting and Storing Molecules:
Like a nucleus, a mitochondria is surrounded by two membranes (inner
Near the ER is an organelle called Golgi apparatus, that prepares proteins for their specific functions, then it packages
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the proteins into tiny, ball-like structures called vesicles, which are organelles that transports substances from one area of a cell to another area. Some vesicles in an animal are called lysosomes.
Some cells also have saclike structures called vacuoles, these are organelles that store food, water and waste material. A typical plant cell usually has one large vacuole that stores water and other substances. Some animal cells have many small vacuoles.