Chapter 4: Inside the Cell PDF

1 Chapter 4: Inside the Cell 2 Outline: Cells Under the Microscope The Plasma Membrane The Two Main Types of Cells Objectives: Recognize the key components of the cell plasma membrane. Distinguish among the types of membrane proteins by function. Identify the characteristics common to all cells. Dis...

1 Chapter 4: Inside the Cell 2 Outline: Cells Under the Microscope The Plasma Membrane The Two Main Types of Cells Objectives: Recognize the key components of the cell plasma membrane. Distinguish among the types of membrane proteins by function. Identify the characteristics common to all cells. Distinguish between prokaryotic and eukaryotic cells. Identify the structures of a prokaryotic cell. Cells and the Cell Theory Cells are the smallest unit of organization that can perform all activities required for life The cell theory states that: o All living organisms are composed of one or more cells. o A cell is the basic structural and functional unit of living organisms. o All cells arise from pre-existing cells. https://www.dreamstime.com/cell-theory-evolution-pre-existing-cells-development-outline-diagram-celltheory-evolution-pre-existing-cells-image236890068 4 Cells Under the Microscope Cells are extremely diverse Each type in our body is specialized for a particular function. Nearly, all require a microscope to be seen. Light microscope Invented in the seventeenth century Electron microscope Invented in 1930s 5 Relative Sizes of Some Living Things and Their Components Biologists use microscopes and biochemistry to study cells Cells are usually too small to be seen by the naked eye It is helpful to understand how cells are studied Types of Microscopes Light microscopes (LMs) Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen Too low to study organelles, the membrane-enclosed structures in eukaryotic cells Electron microscopes (EMs) are used to study subcellular structures magnification (up to 2 million times) Scanning electron microscopes (SEMs) Transmission electron microscopes (TEMs) Three important parameters of microscopy: Magnification, the ratio of an object’s image size to its real size Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points Contrast, visible differences in brightness between parts of the sample 9 The Limit to Cell Size: Why are cells so small? Cell need surface areas large enough for entry and exit of materials Surface-area-to-volume ratio Small cells have more surface area for exchange. Adaptations to increase surface area Microvilli in the small intestine increase surface area for absorption of nutrients 10 Basic features of all cells: All cells have: A plasma membrane to regulate movement of material Cytoplasm where chemical reactions occur Contain ribosomes to make proteins Genetic material for growth and reproduction 1 Chapter 4: Inside the Cell Prokaryotes 2 Prokaryotes are single-celled organisms that make up domains Bacteria and Archaea Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 µm (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) 3 Prokaryotic Cells Generally smaller and simpler in structure than eukaryotic cells Allows them to reproduce very quickly and effectively Extremely successful group of organisms Bacteria Well known because some cause disease Others have roles in the environment Some are used to manufacture chemicals, food, drugs, and so on. ku.ac.ae Adapted to diverse and extreme environments, they are the most abundant organisms on Earth Halophiles—require high salt concentrations to grow Thermoacidophiles—extremely hot, acidic environments like hot springs and submarine thermal vents (80°C ) Why is this lake’s water pink? ku.ac.ae Archaea in the genus Halobacterium 6 The Prokaryotes The prokaryotic genome has less DNA than the eukaryotic genome Most of the genome consists of a circular chromosome No nucleus—single circular chromosome found in nucleoid (region of cell) No membrane-bounded organelles Cytoplasm surrounded by plasma membrane and cell wall Sometimes a capsule—protective layer Cell wall maintains the shape of a cell Far greater metabolic capabilities than more complex organisms Structural and functional adaptations contribute to prokaryotic success 7 Prokaryotic Cell Structure Access the text alternative for slide images. 8 Origin of the First Cells First living cells were prokaryotes. Found in rocks 3.5 billion years old May have existed before that but no fossils found yet Conditions on early Earth very different from today. Temperatures high, little free oxygen Abiotic (without life) synthesis of organic molecules with input from energy sources Lightning, sunlight, meteorite impact, volcanic activity 9 Origin of the First Cells Protocells Cell-like structures complete with outer membrane. May have resulted from self-assembly of macromolecules Gave rise to cellular life Some researchers think the first hereditary molecule was RNA. Over time, the more stable DNA became the long-term solution. 10 Prokaryotes Bacteria Most diverse and prevalent organisms on Earth Tens of thousands of different bacteria identified Likely many more exist but not yet identified What are the 5 criterion to identify a bacteria ? 1. 2. 3. 4. 5. Shape Membrane Type Oxygen Needs Energy and Carbon Sources Nitrogen Metabolism 1. Shape Some form chains or bunches. Most are unicellular, but some species form colonies Most common three shapes—rods (bacilli), spheres (cocci), and spirals (spirilla or spirochetes) Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells Plasmids—extrachromosomal DNA in some Bacteria have ribosomes but no membrane-bounded organelles. Motile bacteria generally have flagella but never cilia—not like eukaryotic flagella. 1. Shape Streptococci E. coli Treponema palladium 2. Membrane Type (Gram-Staining) Outer cell wall is strengthened by peptidoglycan. Prevents bursting or collapsing Some have additional capsule outside the cell wall Note: Archea don’t have peptidoglycan 2. Membrane Type (Gram-Staining) Eukaryote cell walls are made of cellulose or chitin Most bacterial cell walls instead contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides Archaeal walls contain a variety of polysaccharides and proteins, but lack peptidoglycan 2. Membrane Type (Gram-Staining) Scientists use the Gram stain to classify bacteria by cell wall composition Gram-positive bacteria have simpler walls with a large amount of peptidoglycan The walls of gram-negative bacteria have less peptidoglycan and are more complex with an outer membrane that contains lipopolysaccharides 3. Oxygen Needs Obligate aerobes : must use oxygen Obligate anaerobe: are poisoned by oxygen, uses fermentation or anaerobic respiration Facultative anaerobe: uses oxygen when available and fermentation or anaerobic respiration if not 4-Bacterial Nutrition Autotrophs require CO2 as a carbon source (e.g. plants) Heterotrophs require an organic nutrient to make organic compounds (e.g. animals) Phototrophs obtain energy from light (plants) Chemotrophs obtain energy from chemicals 19 4- Bacterial Nutrition (autotrophs) Photoautotrophs (Like plants) Cyanobacteria (Photosynthetic bacteria) Use solar energy and carbon dioxide to make food Chemoautotrophs Don’t use solar energy to reduce carbon dioxide Like deep sea vent bacteria living inside tube worms Chemoheterotrophs (Like animals) Most bacteria are chemoheterotrophs Take in organic molecules as a source of energy and carbon 5. Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids in all organisms Nitrogen fixation Plants are unable to fix atmospheric nitrogen (N₂ gas). Bacteria converts N₂ into a form that plants use ammonia (NH3) N2 N2 ATMOSPHERE SOIL Nitrogen-fixing bacteria Denitrifying bacteria H+ (from soil) NH3 NH4+ Ammonifying (ammonia) (ammonium) bacteria Organic material (humus) Nitrate and nitrogenous organic compounds exported in xylem to shoot system NH4+ Nitrifying bacteria NO3(nitrate) Root 21 Nitrogen fixation: Nodules of a Legume Mutualistic bacteria live inside root nodules. Appendeges in prokayotes: Fimbriae Stick to substrates Flagellum Motility Flagella—propulsion Fimbriae—attachment to surfaces Conjugation pili—DNA transfer Pilus To exchange DNA Internal Organization and DNA 1 µm 0.2 µm Lack of complex compartmentalization but specialized membranes (metabolic functions) Respiratory membrane Circular chromosome (nucleoid) Sometimes some small DNA molecules called plasmids DNA replication, transcription and Translation similar to eukaryotes (smaller ribosomes, protein complex involved …) Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote Chromosome Plasmids 1 µm Endospores Bacteria can produce a “sleeping” structure able to survive to harsh conditions Dehydrate and collapse inside three heavy spore coats Can survive harshest environments Survive for very long periods of time Coat Endospore 0.3 µm 25 Bacteria Reproduce Asexually Bacteria (and archaea) reproduce asexually by binary fission. Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes Key features of prokaryotic reproduction: 1. They are small 2. They reproduce by binary fission (every 1–3 hours) 3. They have short generation times https://simple.wikipedia.org/wiki/Binary_fission Genetic recombination Genetic diversity is due to Genetic recombination through three processes. Transformation: taking up and incorporating foreign DNA from the surrounding environment. Transduction: the movement of genes between bacteria by phages (from “bacteriophages,” viruses that infect bacteria) Conjugation: the process where genetic material is transferred between prokaryotic cells Genetic recombination Transformation Transduction Conjugation Phage 1 µm A+ B+ Donor cell Sex pilus A+ B+ A+ Recombination A+ A- B- A+ B- Recipient cell Recombinant cell 29 Prokaryotes play crucial roles in the biosphere Why prokaryotes are important ? Primary producers (base of food chain) Frees oxygen from carbon dioxide Chemoheterotrophic prokaryotes function as decomposers, digest dead organic remains to return inorganic nutrients to producers. Life would halt without decomposers Prokaryotes can increase the availability of nitrogen, phosphorus, and potassium for plant growth Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment Ecological interactions of Prokaryotes Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont - Mutualism, both symbiotic organisms benefit - Commensalism, one organism benefits while neither harming nor helping the other in any significant way - Parasitism, an organism called a parasite harms but does not kill its host Parasites that cause disease are called pathogens Prokaryotes have both beneficial and harmful impacts on humans Some prokaryotes are human pathogens, but many others have positive interactions with humans Beneficial bacteria Bacteria that break down food that is undigested by our intestines Pathogenic bacteria Bacteria cause about half of all human diseases e.g more than 1.5 million people die each year of tuberculosis (Mycobacterium tuberculosis) Salmonella Cholera … Bacteria in Food Science and Biotechnology Wide variety of foods use bacteria. Fermentation produces lactic acid. Pickles cucumbers, curdles milk into cheese, and gives tangy flavor Experiments using prokaryotes have led to important advances in DNA technology For example, E. coli is used in gene (to produce vitamins, antibiotics, and hormones) Insulin, human growth hormone, and vaccines Most antibiotics are discovered in soil bacteria. 34 Applications using bacteria Bacteria can also be used in bioremediation, the use of organisms to remove pollutants from the environment Ability of bacteria to break down pollutants is exploited Some bioengineered Damage from human impact can be lessened if conditions are right (nutrients, such as nitrogen and phosphates). (example Deep Water Horizon spill). 35 Bacterial Diseases in Humans Pathogens are able to produce a toxin and/or adhere to surfaces and sometimes invade organs or cells. Toxins are small organic molecules or pieces of bacteria released when bacteria die. Often, toxins cause more problems than the growth of the microbe itself. Clostridium tetani causes tetanus (lock jaw). Antibiotics generally either inhibit protein synthesis or inhibit cell wall production. Thank You ku.ac.ae 11 The Plasma Membrane Marks boundary between outside and inside of a cell Is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell Phospholipid bilayer with embedded proteins Polar heads (hydrophilic) of phospholipids face into watery medium Nonpolar tails (hydrophobic) face each other The structure of the plasma membrane is also known as the Fluid mosaic model 12 A Model of the Plasma Membrane: Fluid mosaic model ku.ac.ae Membrane Protein Diversity a. Channel proteins :Form tunnel for specific molecules b. Transport proteins: Involved in passage of molecules through the membrane, sometimes requiring input of energy c. Cell recognition proteins: Enable our body to distinguish between our own cells and cells of other organisms d. Receptor proteins: Allow signal molecules to bind, causing a cellular response e. Enzymatic proteins: participate in metabolic reactions f. Junction proteins:Form junctions between cells and Cell-to-cell adhesion and communication 13 Basic Features of all cells: Cytoplasm, Ribosomes and Genetic material Cytoplasm: is the gelatinous liquid that fills the inside of a cell. o composed of water (80%), salts, and various organic molecules. o Medium for chemical reactions within the cell cytoplasm Ribosome is an intercellular structure made of both RNA and protein Ribosome o the site of protein synthesis in the cell Genetic material is the hereditary substance in the cell. o carries all information specific to an organism. DNA 15 There are Two Main Types of Cells Two main types of cells based on organization of genetic material Prokaryotic cells—lack membrane-bounded nucleus Eukaryotic cells—have nucleus housing DNA 16 A Prokaryotic Cell 17 Eukaryotic cell: Typical Animal Cell The Two Main Cell Types Prokaryotes Eukaryotes Small (~5µm) Simple Relatively Large (~40µm) No Nucleus 70s ribosomes Circular DNA in cytoplasm One “un-true” chromosome Unicellular organisms No membrane-bound organelles Cell division by binary fission Plasma Membrane Cytoplasm Ribosomes Genetic material Relatively complex Nucleus present 80s ribosomes DNA packed inside the nucleus More than one chromosome Usually multicellular (some are unicellular) Membrane bound organelles are present Somatic cell division by mitosis, germ cell division by meiosis The Two Main Cell Types Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists, fungi, animals, and plants all consist of eukaryotic cells Thank You ku.ac.ae