Origin And Evolution Of Cells PDF

1 ORIGIN AND EVOLUTION OF CELLS Fluorescence Micrograph of a Cell. This image of a bovine pulmonary arterial endothelial cell shows Copyright © 2022 Pearson Education Ltd. All Rights Reserved. DNA in the nucleus (blue), mitochondria (green), and the actin...

1 ORIGIN AND EVOLUTION OF CELLS Fluorescence Micrograph of a Cell. This image of a bovine pulmonary arterial endothelial cell shows Copyright © 2022 Pearson Education Ltd. All Rights Reserved. DNA in the nucleus (blue), mitochondria (green), and the actin cytoskeleton (purple).  2 Cells and Organelles Two questions to consider – Where did the first cells come from? – How do today’s cells function? Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  3 The Origins of the First Cells The appearance of cells involved four phases: 1. Abiotic (nonliving) synthesis of simple organic compounds 2. Abiotic polymerization of these into macromolecules 3. Emergence of a macromolecule capable of replication and storing genetic information 4. Encapsulation of the first living molecule within a simple membrane Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  4 Simple Organic Molecules May Have Formed Abiotically in the Young Earth In a classic experiment, Stanley Miller (1953) tested the hypothesis that energy from lightning could have powered production of simple organic compounds from atmospheric gases. The early atmosphere was thought to consist largely of reduced gases such as hydrogen (H2), methane (CH4), ammonia (NH3), and water vapor (H2O). Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  5 Results of the Experiment After a week of continuous exposure of gases to electrical discharge, Miller checked the flask. He detected two simple amino acids (alanine and glycine) in the flask. This suggested that some organic compounds could be produced under abiotic conditions. Alanine Glycine Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  6 Miller’s Apparatus for Abiotic Synthesis of Simple Organic Compounds Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  7 Additional Experiments Other researchers have tested different proposed atmospheres exposed to electrical discharge. They have detected a variety of simple organic compounds produced in this way. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  8 Models for Formation of Organic Compounds Formation in the atmosphere, precipitation into the oceans, and concentration into ―primordial soup‖ as simulated by Miller’s experiments Deep-sea hydrothermal vents provided a catalytic environment for combining dissolved gases into organic molecules. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. https://doi.org/10.1038/nchem.2219  9 RNA May Have Been the First Informational Molecule Deoxyribonucleic acids, used to form DNA, are derived enzymatically from the corresponding ribonucleotides. RNAs called ribozymes are capable of performing certain enzymatic reactions; for example, the formation of the peptide bonds during translation. This suggests that an ―RNA world‖ existed before the appearance of DNA and proteins. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. https://doi.org/10.1016/j.bpc.2022.106914  10 Liposomes May Have Defined the First Primitive Protocells Using lipids, scientists have produced hollow, membrane- bound vesicles called liposomes. Under some circumstances, these can carry out simple metabolic reactions. Primordial lipids may have come together in an early ocean, trapping RNAs and forming the first ―protocells.‖ Liposome Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  11 Artificial Liposomes Image ―a‖ of liposomes shows two smaller vesicles within a bigger one and another vesicle on the circumference of the bigger vesicle. A small vesicle is also found next to the bigger one. Both these vesicles along with liposome are enclosed by lipid bilayer. It shows a measurement of 20 micrometer at the left end. Image ―b‖ shows a measurement of 1 micrometer at the left end and shows liposomes enclosed in a circular body. The R N A is shown in yellow coloured round shaped bodies inside liposomes. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  12 Basic Properties of Cells Several general characteristics of cells – Organizational complexity – Molecular components – Sizes and shapes – Specialization Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  13 The Three Domains of Life Are Bacteria, Archaea, and Eukaryotes Biologists recognized two types of cells. The simpler type is characteristic of bacteria and archaea (prokaryotes), and the more complex type is characteristic of plants, animals, fungi, algae, and protozoa (eukaryotes). The main distinction between the two cell types is the membrane-bounded nucleus of eukaryotic cells. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  14 A Changing View of Prokaryotes Recently, the term prokaryote has become unsatisfactory in describing the non-nucleated cells. Sharing of a gross structural feature is not necessarily evidence of relatedness. Based on rRNA sequence analysis, prokaryotic cells can be divided into the widely divergent bacteria and archaea. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  15 Three Domains Bacteria and archaea are as divergent from one another as humans and bacteria are. Biologists now recognize three domains, the Archaea, Bacteria, and Eukarya (eukaryotes). Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  16 The Three Domains of Life The composition of each domain is as below: 1.Bacteria: The components are green nonsulfur bacteria with mitochondria, spirochetes, chlamydia, green sulfur bacteria, and cyanobacteria with plastids, including chloroplasts. 2.Eukarya: The main components are land plants, animals, and fungi. The other parts shown as branches are dinoflagellates, diatoms, ciliates, euglena, trypanosomes, leishmania, cellular slime molds, amoebae, green algae, red algae, and forams. 3.Archaea: The components are sulfolobus, thermophiles, halophiles, and methanobacterium. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  17 Bacteria These include most of the commonly encountered single- celled, non-nucleated organisms that were traditionally called bacteria. Examples include – Escherichia coli – Pseudomonas aeruginosa – Streptococcus lactis Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  18 Archaea (1 of 2) Archaea were originally called archaebacteria before they were discovered to be so different from bacteria. They include many species that live in extreme habitats and have diverse metabolic strategies. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  19 Archaea (2 of 2) Types of archaea include – Methanogens—obtain energy from hydrogen and convert CO2 into methane – Halophiles—occupy extremely salty environments – Thermacidophiles—thrive in acidic hot springs They are considered to have descended from a common ancestor that also gave rise to eukaryotes long after diverging from bacteria. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  20 The Common Ancestor of Bacteria, Archaea, and Eukarya Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  21 There Are Several Limitations on Cell Size Cells come in various sizes and shapes. Some of the smallest bacteria are about 0.2–0.3 μm in diameter. Some highly elongated nerve cells may extend a meter or more. Despite the extremes, cells in general fall into predictable size ranges. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Map%3A_Raven_Biology_12th_Edition/04%3A_Cell_Structure/4.01%3A_Cell_Theory/ 4.1D%3A_Cell_Size  22 Size Ranges Bacteria cells normally range from 1 to 5 μm in diameter. Animal cells have dimensions in the range of 10–100 μm. Cells are usually very small. There are three main limitations on cell size. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  23 Limitations on Cell Size Cell size is limited by: – The requirement for adequate surface area relative to volume – The rates at which molecules can diffuse – The need to maintain adequate local concentrations of substances required for necessary cellular functions Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  24 Surface Area/Volume Ratio In most cases, the major limit on cell size is set by the need to maintain an adequate surface area/volume ratio. Surface area is important because exchanges between the cell and its surroundings take place at the cell surface. The cell’s volume determines the amount of exchange that must take place across the available surface area. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  25 Maintaining Adequate Surface Area/Volume Ratio The volume of a cell increases with the cube of its length. But the surface area of the cell increases with the square of its length, so larger cells have proportionately smaller surface areas. Beyond a certain threshold, a large cell would not have a large enough surface area to allow for sufficient intake of nutrients and release of wastes. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  26 The Effect of Cell Size on the Surface Area/Volume Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  27 Cells Specialized for Absorption Cells that are specialized for absorption have characteristics to maximize their surface area. For example, cells lining the small intestine have microvilli— fingerlike projections that increase the surface area. The Microvilli of Intestinal Mucosal Cells Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  28 Diffusion Rates of Molecules The internal volume of the cell, not including the nucleus, is the cytoplasm. Cytoplasm contains organelles, cytoskeletal fibers, and the semifluid cytosol in which they are suspended. Many molecules move through this liquid-based environment by diffusion, the unassisted movement of a substance from a region of high concentration to a region of low concentration. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  29 Limitation on Rates of Diffusion The rate of diffusion of molecules decreases as the size of the molecule increases. This limits diffusion for macromolecules such as proteins and nucleic acids. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. https://studymind.co.uk/notes/transport-across-membranes-diffusion/  30 Avoiding Limitations of Rates of Diffusion Eukaryotic cells can avoid the problem of slow diffusion rates by using carrier proteins to actively transport materials through the cytoplasm. Some cells use cytoplasmic streaming (cyclosis in plants) to actively move cytoplasmic contents. Other cells move molecules through the cell in vesicles that are transported along protein fibers. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  31 The Need for Adequate Concentrations of Reactants and Catalysts For a reaction to occur, the reactants must collide with and bind to a particular enzyme. The frequency of such collisions is greatly increased by higher concentrations of enzymes and reactants. As cell size increases, the number of molecules increases proportionately with volume. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  32 Compartmentalization of Cellular Activities A solution to the concentration problem is the compartmentalization of activities within specific regions of the cell. Most eukaryotic cells have a variety of organelles, membrane- bounded compartments that are specialized for specific functions. For example, cells in a plant leaf have most of the materials needed for photosynthesis compartmentalized into structures called chloroplasts. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  33 Bacteria, Archaea, and Eukaryotes Differ from Each Other in Many Ways There are shared characteristics among cells of each of the domains, Bacteria, Archaea, and Eukarya. However, each type of cell has a unique set of distinguishing properties. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  34 Presence of a Membrane-Bounded Nucleus A eukaryotic cell has a true, membrane-bounded nucleus. The genetic information of a bacterial or archaeal cell is folded into a compact structure called the nucleoid and is attached to the cell membrane. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  35 Structure of a Rod-Shaped Bacterial Cell Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  36 Use of Internal Membranes to Segregate Function Bacterial and archaeal cells do not usually contain internal membranes. A group of photosynthetic bacteria (cyanobacteria) have extensive internal membranes upon which photosynthetic reactions are carried out. Some bacteria have membrane-bound or protein-lined structures that serve as (or resemble) organelles. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  37 Internal Membranes in Eukaryotes Nearly all eukaryotes make extensive use of internal membranes to compartmentalize specific functions and have numerous organelles. Examples: endoplasmic reticulum, Golgi complex, mitochondria, chloroplasts, lysosomes, peroxisomes, and various types of vacuoles and vesicles. Each organelle contains the materials and molecular machinery needed to carry out the functions for which the structure is specialized. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  38 An Animal Cell The parts of an animal cell are lysosome, peroxisome, mitochondrion, nucleus, ribosome, rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, centrosome, microtubule, and actin filaments. The nucleus comprises of an inner nucleolus and an outer nuclear envelope. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  39 A Plant Cell The different parts that are labeled are a large part of vacuole, chloroplast, granum or stack of thylakoids, mitochondrion, peroxisome, Golgi apparatus, smooth endoplasmic reticulum, rough endoplasmic reticulum, nucleus, and ribosome. The nucleus comprises of nucleolus and nuclear envelope. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  40 Exocytosis and Endocytosis Eukaryotic cells can exchange materials between compartments within the cell and the exterior of the cell. This is possible through exocytosis and endocytosis, processes involving membrane fusion events unique to eukaryotic cells. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  41 Vesicle Transport Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  42 Organization of DNA Bacterial DNA is present in the cell as a circular molecule, called a chromosome, associated with few proteins. Eukaryotic DNA is organized into linear molecules (chromosomes) complexed with large amounts of proteins called histones. Archaeal DNA is circular and complexed with proteins similar to eukaryotic histone proteins. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  43 DNA Packaging The circular DNA of bacteria or archaea is much longer than the cell itself and so must be folded and packed tightly, equivalent to packing about 60 feet of thread into a thimble. Eukaryotic cells have about 1000 times more DNA than bacteria. The problem of DNA packaging is solved among eukaryotes by organizing the DNA into chromosomes. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  44 A Pair of Eukaryotic Chromosomes Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  45 Segregation of Genetic Information Prokaryotes and eukaryotes differ in how genetic information is allocated to daughter cells upon division. Bacterial and archaeal cells replicate their DNA and divide by binary fission, with one molecule of the replicated DNA and the cytoplasm going into each daughter cell. Eukaryotic cells replicate DNA and then distribute their chromosomes into daughter cells by mitosis and meiosis, followed by cytokinesis, division of the cytoplasm. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  46 Expression of DNA Eukaryotic cells transcribe genetic information in the nucleus into large RNA molecules that are processed and transported into the cytoplasm for protein synthesis. Each mature RNA molecule typically encodes one polypeptide. Bacteria transcribe genetic information into RNA, and the RNA molecules produced may contain information for several polypeptides. There is very little RNA processing in bacteria. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. https://www.youtube.com/watch?v=URUJD5NEXC8 47