Chapter 4 General Features of Cells PDF

CHAPTER 4 GENERAL FEATURES OF CELLS 0  Cell theory 1. All living things are composed of one or more cells 2. Cells are the smallest units of living organisms 3. New cells come only from pre-existing cells by cell division...

CHAPTER 4 GENERAL FEATURES OF CELLS 0  Cell theory 1. All living things are composed of one or more cells 2. Cells are the smallest units of living organisms 3. New cells come only from pre-existing cells by cell division 0  Microscopy Most cells are so small that they cannot be seen with naked eye. The microscope is a magnification tool that enables researchers to structure and function of cells. Magnification, resolution and contrast are the three important parameters in microscopy. Magnification Loading… Ratio between the size of an image produced by a microscope and its actual size Resolution Ability to observe two adjacent objects as distinct from one another Contrast Ability to visualize a particular cell structure may depend on how different it looks from an adjacent structure. The contrast can be enhanced using dyes 0  Microscopy Microscope are categorized into two groups based on the source of illumination Light microscope Uses light for illumination Resolution 0.2 µm Electron microscope Uses an electron beam Resolution 2 nm 0  Cell types Based on cell structure, there are two types of cells 1. Prokaryotic Loading… (bacteria and archaea) 2. Eukaryotic 0  Prokaryotic cells Prokaryotes [grk. Pro, before, and karyon, nucleus] Simple cell structure Lack a membrane-enclosed nucleus Much smaller than eukaryotic cells Present in great numbers in the air, in bodies of water, in the soil, and even in the human organs Two categories: bacteria and archaea Both small Bacteria are abundant, most not harmful Archaea are less common, often found in extreme environments 0  Prokaryotic cell structure All prokaryotic Additional in cells contain: some 1. Cell wall 1. Capsule 2. Cell membrane 2. Plasmids 3. Cytoplasm 3. Flagella 4. DNA 4. Pili 5. Ribosomes 5. Membrane infolding 0  Typical bacterial cell Cell envelope Cytoplas Appendage 0 m s Structure of a Prokaryotic Cell: Cell Envelope Cell envelope includes plasma membrane, cell wall and glycocalyx (layer of polysaccharides outside cell wall). Plasma membrane: A phospholipids' bilayer much like the plasma membrane of eukaryotic cells. Has an important role in regulating the entrance and the exit of substances into the cytoplasm. Cell wall: Composed of a complex molecule peptidoglycan (amino disaccharides and peptide fragments). The cell wall maintains the overall shape of a bacterial cell (coccus, bacillus and spiral). Mycoplasma are bacteria that have no cell wall and therefore have no definite shape. It is above plasma membrane. Based on cell wall bacteria are either gram positive or gram negative Glycocalyx: Layer of polysaccharide lying outside the cell wall. Glycocalyx aids against drying out by traping water and help bacteria to resist a host’s immune system. It allows the bacterium to attach itself to inert surfaces (like teeth or rocks), eukaryotes (e.g. streptococcus pneumoniae attaches itself to lung cells), or other bacteria (their glycocalyxes can fuse to envelop the colony). Secreted from inside of the cell and forms a layer outside. It is viscous. Structure of a Prokaryotic Cell: Cell Envelope Glycocalyx or Capsule: 1.When glycocalyx firmly attached then is it called capsule else it is a slime layer 2.Well organized layer of polysaccharide. 3.Protects the bacterial cell and is often associated with pathogenic bacteria because it serves as a barrier against phagocytosis by white blood cells. 4.Made from starch or glycolipid 5.Protect bacteria from drying out which is called desiccation 6.Stop detection from immune system. Protect from viruses. 7.Also has adhesion properties Prokaryotic cell structure… No nucleus Nucleoid floating in cytoplasm One chromosome which is circular. Loading… No histone proteins with DNA. DNA is called naked DNA because there is no histone protein associated with DNA 0 Prokaryotic plasmid Smaller circular DNA Contains resistance genes, which can be transferred to other organisms Non-essential genes Replication is independent of chromosomal DNA. 0 Ribosome in prokaryotes Smaller than eukaryotic ribosome 70 S 30 s and 50 s subunits Make proteins 0 0  Structure of a Prokaryotic Cell: Cytoplasm Cytoplasm is semi-fluid solution encapsulated by the plasma membrane. Contains all sort of enzymes required for bacterial metabolism. Single chromosome located in gel-like region called nucleoid. Thousands of ribosomes involved in protein synthesis. Inclusion Bodies which are Storage granules of various substances. Some are nutrients that can be broken down when needed.  Structure of a Prokaryotic Cell: Appendages Bacteria may have the following appendages: Flagella: Responsible for most types of bacterial motility. Flagella are long appendages which rotate by means of a "motor" located just under the plasma membrane. Bacteria may have one, a few, or many flagella in different positions on the cell. Fimbriae: Small fibers that sprout from the cell surface. Not involved in the motility. Help bacteria to attach to a surface. Sex Pili: Rigid tubular structure used by bacteria to pass DNA from a cell to cell. Bacteria reproduce asexually by binary fission, but they can exchange DNA through the sex pili. 0  Eukaryotic cells DNA housed inside nucleus Eukaryotic cells exhibit compartmentalization into organelles: Organelle is subcellular structure or membrane-bounded compartment with its own unique structure and function Shape, size, and organization of cells vary considerably among different species and even among different cell types of the same species 0  The Proteome Determines the Characteristics of a Cell How does a single organism produce different types of cells? Identical DNA in different cells but different proteomes The proteome of a cell determines its structure and function Gene regulation, amount of protein, amino acid sequence of a particular protein and protein modification can influence a cell’s proteome Proteomes in healthy cells are different from the proteomes of cancerous cells Proteome is a set of expressed proteins in a given type of cell or organism, at a given time, under defined conditions. Cytosol Region of a eukaryotic cell that is outside the cell organelles but inside the plasma membrane Cytoplasm includes everything inside the plasma membrane.Cytosol, the endomembrane system and the semiautonomous organelles Metabolism Cytosol is central coordinating region for many metabolic activities of eukaryotic cells Catabolism: breakdown of a molecule into smaller components Anabolism: synthesis of cellular molecules and macromolecules 0  Cytoskeleton Serves as internal skeleton that maintains cell shape (construction and organization) and assists in movement of its parts. Strengthen cell. Holds organelles in place. Contains three types of elements: Microtubules: -Long cylindrical structures composed of polymers of alpha and beta tubulin. -Alpha and beta form dimer and they pair with each other to form a sheet like structure which is further folded into a cylinder shape structure. - They have polar structure with a plus end and minus end. - A single microtubule can oscillate between growing and shortening phases: Dynamic instability. - They play key roles in:. Intracellular transport (associated with dyneins and kinesins, they transport organelles like mitochondria or vesicle). E these 2 made up are of microtubules.. The axoneme of cilia and flagella. - -. The mitotic spindle.. Synthesis of the cell wall in plants. Intermediate filaments: -Tend to be more stable than microtubules and actin filaments, which readily polymerize and depolymerize -Function in the maintenance of cell-shape and rigidity by bearing tension -Found in cytoplasm, in nucleus and also outside cell so binding cells together. -Keratin family proteins Actin filaments (also known microfilaments): -composed of two intertwined actin chains -actin filament - Actin filaments support the plasma membrane and provide strength and shape to the cell. - Participate in some cell-to-cell or cell-to- matrix junctions. - Phagocytosis - Tensile strength 0 Cytoskeleton function Maintaining cell shape Microfilament: cytoplasmic streaming. Circulating cytosol so that all organelles receive cytoplasm. Cytokinesis of animal cells. Helps in cell division. Microtubule Segregation of chromosome during cell division anaphase Interact with centromere for separating sister chromatid Helps in motility. Are part of flagella, cilia. Intermediate filament: Helps in forming stable tissues. As it also appear outside the cell, it helps in cell to cell interaction 0  Motor Proteins Category of cellular proteins that use ATP as a source of energy to promote movement Consist of three domains called the head, hinge, and tail Walking analogy Ground is a cytoskeletal filament, your leg is the head of the motor protein, and your hip is the hinge Three different kinds of movements:. Motor protein moves the cargo from one location to another (kinesin). Motor protein can remain in place and cause the filament to move (myosin). Motor protein attempting to walk (both the motor protein and filament restricted in their movement) exerts a force that causes the filament to bend (dynein) Convert chemical energy into mechanical energy by hydrolysis of ATP https://www.youtube.com/watch?v=y-uuk4Pr2i8 0  Motor Proteins: Flagella and cilia. Flagella usually longer than cilia and present singly or in pairs. Cilia are often shorter than flagella and tend to cover all or part of the surface of a cell. Share the same internal structure. Microtubules, dynein, and axoneme. Microtubules form an arrangement called a 9 + 2 array. Movement involves the propagation of a bend, which begins at the base of the structure and proceeds toward the tip 0  Nucleus Contains chromatin in semi-fluid called nucleoplasm. Chromatin undergo condensation to form chromosomes just before the cell divides Chromatin contains DNA, diverse proteins and some RNA. -Separated from cytoplasm by double-membrane (outer and inner membrane) called nuclear envelope. - Pores in nuclear membrane allows transport of protein, RNA to cytoplasm -Primary function involves the protection, organization, and expression of the genetic material -Ribosome assembly occurs in the nucleolus -Nucleoplasm which is fluid inside nucleus 0  Endomembrane system Network of membranes enclosing the nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles Also includes plasma membrane May be directly connected to each other or pass materials via vesicles Restrict enzymatic reactions to specific compartments within cell. 0 Endomembrane system:Nuclear envelope -Double-membrane structure enclosing nucleus -Outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum membrane - Nuclear pores provide passageways permitting passage in and out of the nucleus - Materials within the nucleus are not part of the endomembrane system 0  Endoplasmic reticulum Protein Network of membranes that form flattened, fluid-filled tubules or cisternae synthesis in ER happens ER membrane encloses a single compartment called the ER lumen Physically continuous with the outer membrane of the nuclear envelope. Rough endoplasmic reticulum (rough ER) Is studded with ribosomes on the side of the membrane that faces the cytoplasm. Involved in protein synthesis and sorting. Rough ER modifies proteins after they have entered the ER lumen. ER enzymes add carbohydrates chain to protein. Other enzymes assist the folding process that result in the final shape of the protein. Smooth endoplasmic reticulum (smooth ER). Is continuous with rough ER. No attached ribosomes.. Detoxification, carbohydrate metabolism, calcium balance, synthesis and modification of lipids & 0 Endoplasmic reticulum ribosomeeug de Loading… 5 o a 0  Golgi apparatus Also called the Golgi body, Golgi complex, or simply Golgi Stack of flattened, membrane-bounded compartments, which are not continuous with the ER. Roles in post translational modification In animal cells, the inner face is directed toward the ER, and the outer face is directed toward the plasma membrane. Modifies proteins and lipids and packages them in vesicles. Vesicles transport materials between stacks Three overlapping functions: Secretion, processing, and protein sorting O 0  Lysosomes. Membrane-bounded vesicles produced by the Golgi apparatus.. They have a very low pH and contain a powerful hydrolytic digestive enzymes (acid hydrolases) to break down proteins, carbohydrates, nucleic acids and lipids.. They digest food particles, and engulfed viruses or bacteria through endocytosis.. They digest excess or worn out organelles througn endocytosis “autophagy”.. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell. Involved in autophagy (self death) 0  Vacuoles Functions of vacuoles are extremely varied, and they differ among cell types and even environmental conditions Central vacuoles in plants for storage and support Contractile vacuoles in protists for expelling excess water Phagocytic vacuoles in protists and white blood cells for degradation 0  Peroxisomes Relatively small organelles found in all eukaryotic cells General function to catalyze certain chemical reactions, typically those that break down molecules by removing hydrogen or adding oxygen Long fatty acid chains β-oxidation Reaction by-product is hydrogen peroxide (H2O2): Short & medium fatty acid chains [RH2 + O2 R + H2O2] Hydrogen peroxide is immediately broken Mitochondria down to water and oxygen by another peroxysomal enzyme called catalase. Enzymes in peroxisome are cell-specific. CO2 + H2O In liver peroxisome produce bile salts from cholesterol and others break down fats 0  Plasma membrane - Boundary between the cell and the extracellular environment - Membrane transport in and out of cell. Selectively permeable - Cell signaling using receptors - Cell adhesion 0  Semiautonomous organelles Semiautonomous because they divide by fission to produce more of themselves Somewhat independent Genetic material, synthesize some proteins, divide independently of cell Not entirely autonomous. Do depend on the cell for raw materials and most of their proteins Mitochondria, chloroplasts, 0 Involved in cellular respiration. Mitochondria Carbohydrate + oxygen carbon dioxide + water + energy (ATP)Adenosine triphosphate (ATP) is used for all energy-requiring processes in cells. Mitochondria produce most of ATP utilized by the cell. Mitochondria have two membranes, the outer and the inner membrane. The inner membrane that encloses matrix is called Cristae. The Matrix contains enzymes that break down carbohydrates and other nutrient molecules. Also involved in the synthesis, modification, and breakdown of several types of cellular molecules 0  Mitochondria and chloroplasts Two traits similar to bacteria 1. Contain DNA separate from the nuclear genome Mitochondrial and chloroplast genome. Single small circular double stranded chromosome.. Similar to bacterial chromosomes 2. Reproduce via binary fission (splitting in two) Like bacteria 0  Chloroplasts Photosynthesis: capture light energy and use some of that energy to synthesize organic molecules such as glucose: Solar energy + Carbon dioxide + water carbohydrate + oxygen Found in nearly all species of plants and algae. Chloroplasts are green due to the green pigment chlorophyll. Chloroplast have an outer and an inner membrane separated by a small space. The material within the chloroplast is called the stroma which contains a concentrated mixture of enzymes. Within the stroma are stacks of thylakoids, the sub-organelles which are the site of photosynthesis. The thylakoids are arranged in stacks called grana (singular: granum). 0