Chapter 1 Prokaryote vs eukaryote updated 2.pdf

BIOFS 01 EUKARYOTE & BIOLOGY PROKARYOTE CELLS 1 2  Cells can generally be categorized into two major groups: Prokaryotic Cells: These are cells that lack a distinct nucleus and other membrane-bound organelles. Prokaryotic cells are typically simpler in s...

BIOFS 01 EUKARYOTE & BIOLOGY PROKARYOTE CELLS 1 2  Cells can generally be categorized into two major groups: Prokaryotic Cells: These are cells that lack a distinct nucleus and other membrane-bound organelles. Prokaryotic cells are typically simpler in structure compared to eukaryotic cells. Examples include bacteria and archaea. Eukaryotic Cells: Eukaryotic cells possess a true nucleus enclosed within a nuclear membrane, as well as other membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. Eukaryotic cells are found in organisms belonging to the domain Eukarya, which includes animals, plants, fungi, and protists. 4  PROKARYOTIC CELLS GENERAL DESCRIPTIONS The term "prokaryote" is derived from Greek, meaning "before a nucleus." These cells lack a distinct nucleus and other membrane-bound organelles. Their genetic material is typically organized in a single circular chromosome located in the nucleoid region. Prokaryotic cells are usually smaller and simpler in structure compared to eukaryotic cells. They consist of a single compartment, the cytoplasm, surrounded by a plasma membrane. While both prokaryotes and eukaryotes have DNA, it is organized differently PROKARYOTIC CELLS GENERAL DESCRIPTIONS No internal membrane-bound organelles are present, only ribosomes for protein synthesis. Prokaryotic cells are typically unicellular organisms, although some species can form simple colonies. They exhibit diverse metabolic capabilities and may or may not require oxygen for survival. Prokaryotic cells include all bacteria and Archaea, two of the three domains of life. These organisms are among the earliest forms of life on Earth and are found in various environments, ranging from extreme conditions like hot springs and deep- sea vents to more moderate habitats such as soil and the human body. 6  TYPES OF PROKARYOTES Bacteria: 1.Found Everywhere: Bacteria are incredibly diverse and can be found in virtually every habitat on Earth, including soil, water, air, and living organisms. 2.Unique Cell Wall: Bacteria have cell walls containing peptidoglycan, a distinctive feature that helps differentiate them from other organisms. 3.Varied Shapes and Species: Bacteria come in various shapes, including spheres (cocci), rods (bacilli), and spirals. They encompass a vast array of species, such as Escherichia coli, Streptococcus pneumoniae, and Staphylococcus aureus. 7  TYPES OF PROKARYOTES Archaea: 1.Extreme Environments: Archaea are often found in extreme environments like hot springs, acidic or alkaline environments, deep-sea hydrothermal vents, and salt flats, but they also inhabit more moderate habitats. 2.Unique Cell Structures: Archaea have distinct membrane lipids and cell walls made of different materials compared to bacteria, such as pseudopeptidoglycan or other substances. 3.Diverse Metabolisms: Archaea exhibit diverse metabolic pathways and can be autotrophic (producing their own food) or heterotrophic (relying on external sources of organic carbon). Well-known examples include Methanogens, which produce methane, and Halophiles, which thrive in high-salt environments. 8 MORPHOLOGY OF PROKARYOTES  MORPHOLOGY OF PROKARYOTES 1.Size: 1. Prokaryotic cells are generally smaller than eukaryotic cells, typically ranging from about 0.2 to 2 micrometers in diameter. 2. Some prokaryotes, like certain species of Mycoplasma, are among the smallest cells known, while others, such as Epulopiscium fishelsoni, can be relatively large for prokaryotes. 2.Cellular Arrangement: 1. Prokaryotic cells may occur singly or in groups, depending on their mode of reproduction and environmental conditions. 2. Some bacteria form pairs (diplo), chains (strepto), clusters (staphylo), or packets (sarcinae) based on how they divide and remain attached after division.  MORPHOLOGY OF PROKARYOTES 1.Plasma Membrane:  The plasma membrane is a vital structure surrounding the cell, composed of a lipid bilayer embedded with proteins.  It serves as a selective barrier, controlling the entry and exit of substances into and out of the cell.  Additionally, the plasma membrane plays a role in cell signaling and communication with the environment. 2.Cell Wall:  The cell wall provides structural support and shape to the cell, protecting it from osmotic changes and mechanical stress.  In bacteria, the cell wall typically contains peptidoglycan, a complex polymer made of sugars and amino acids.  Archaeal cell walls may lack peptidoglycan and instead contain other substances like pseudopeptidoglycan, S-layer proteins, or glycoproteins. 3.Surface Structures:  Prokaryotic cells may have additional structures on their surface:  Capsule: A gelatinous layer outside the cell wall that provides additional protection and aids in adherence to surfaces.  Pili (or Fimbriae): Hair-like appendages that protrude from the cell surface, assisting in adherence to surfaces and facilitating the transfer of DNA between cells (conjugation).  Flagella: Whip-like structures extending from the cell surface that enable movement by rotating like propellers.  MORPHOLOGY OF PROKARYOTES 4. Cytoplasm:  The cytoplasm is the gel-like substance filling the interior of the cell.  It contains various organelles and cellular structures and is the site of many metabolic reactions, including protein synthesis and nutrient metabolism. 5. Nucleoid Region:  Prokaryotic cells lack a true nucleus found in eukaryotic cells. Instead, their genetic material is concentrated in a region called the nucleoid.  The nucleoid region contains a single, circular chromosome made of DNA, along with proteins that help organize and maintain the DNA. 6. Ribosomes:  Ribosomes are cellular structures responsible for protein synthesis.  In prokaryotic cells, ribosomes are found free-floating in the cytoplasm or attached to the cell membrane.  They consist of ribosomal RNA (rRNA) and protein molecules and function by reading mRNA transcripts and synthesizing proteins accordingly. 7. Plasmid:  Plasmids are small, circular DNA molecules found in some prokaryotes.  They can carry extra genes that provide advantages like antibiotic resistance or the ability to metabolize certain compounds.  Plasmids can be transferred between cells through processes like conjugation, allowing for the spread of genetic material among bacterial populations. 12 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane- enclosed organelles of the eukaryotic cell. 13 SHAPES OF PROKARYOTES 1.Coccus (plural: cocci): 1. Spherical or round-shaped bacteria. 2. Examples include Streptococcus pneumoniae and Staphylococcus aureus. 2.Bacillus (plural: bacilli): 1. Rod-shaped bacteria. 2. They may be short or long, and sometimes slightly curved. 3. Examples include Escherichia coli and Bacillus anthracis. 3.Spirillum (plural: spirilla): 1. Spiral-shaped bacteria with a rigid helical shape. 2. They may have one or more twists. 3. Examples include Spirillum volutans. 4.Vibrio: 1. Curved or comma-shaped bacteria. 2. They resemble a curved rod. 3. Examples include Vibrio cholerae, the bacterium responsible for cholera. 5.Filamentous: 1. Long, thin, and filament-like bacteria. 2. They may form branching structures. 3. Examples include Actinomycetes, which are important decomposers in soil. 14 CHARACTERISTICS OF EUKARYOTES Eukaryotic cells appeared approximately one billion years ago Eukaryotes: Eu = true karyot = nucleus. Plant and animals have real nucleus, surrounded with nuclear membrane. Eukaryotes are generally more advanced than prokaryotes Nuclear membrane surrounds linear genetic material (DNA) CHARACTERISTICS OF EUKARYOTES In eukaryote cells, the chromosomes are contained within a membranous nuclear envelope. The region between the nucleus and the plasma membrane is the cytoplasm. Within the cytoplasm of a eukaryotic cell is a variety of membrane-bounded organelles of specialized form and function.  CHARACTERISTICS OF EUKARYOTES Eukaryotic cells are generally much bigger than prokaryotic cells. The logistics of carrying out metabolism set limits on cell size. At the lower limit, the smallest bacteria, mycoplasmas, are between 0.1 to 1.0 micron. Most bacteria are 1-10 microns in diameter. Eukaryotic cells are typically 10-100 microns in diameter. 18 WHAT DO EUKARYOTIC CELLS LOOK LIKE? Fig. 7.8 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 20 Differences Between Prokaryotic And Eukaryotic Cells: Characteristic Prokaryotic Cells Eukaryotic Cells Nucleus Absent Present Genetic Material Circular DNA (nucleoid region) Linear DNA (enclosed in nucleus) Membrane-bound Present (e.g., mitochondria, Generally absent Organelles endoplasmic reticulum) Size Generally smaller (0.1-5 µm) Generally larger (10-100 µm) Often contains peptidoglycan (bacteria), Cell wall composition varies (e.g., Cell Wall Composition pseudopeptidoglycan or other substances cellulose in plants, chitin in fungi) (archaea) Larger (80S in cytoplasm, 70S in Ribosomes Smaller (70S) organelles) Various modes including mitosis Reproduction Binary fission (asexual) and meiosis (sexual) Numerous membrane-bound Organelles Few; no membrane-bound organelles organelles Generally simpler in structure and More complex in structure and Complexity organization organization Examples Bacteria, Archaea Animals, plants, fungi, protists 21 HOW DO THE SIMILARITIES LINE UP? Lets See!!! Both types of cells have cell membranes (outer covering of the cell) Both types of cells have ribosomes Both types of cells have DNA Both types of cells have a liquid environment known as the cytoplasm Endosymbiosis theory: Endosymbiosis, as described by Lynn Margulis, is a theory proposing that certain organelles found in eukaryotic cells, such as mitochondria and chloroplasts, originated from symbiotic relationships between primitive prokaryotic cells. According to this theory, ancestral prokaryotes were engulfed by early eukaryotic cells through endocytosis. Instead of being digested, these prokaryotes established a mutually beneficial relationship with the host cell, eventually evolving into organelles. Margulis, an American biologist, proposed this theory in the 1960s to explain the origin of these organelles and their unique characteristics. 23 ENDOSYMBIOTIC THEORY According to Margulis's endosymbiotic theory: 1.Mitochondria and chloroplasts were once free-living prokaryotic organisms, possibly related to modern-day bacteria. 2.These ancestral prokaryotes were engulfed by larger host cells through a process called endocytosis, where one cell engulfs another. 3.Instead of being digested, the engulfed prokaryotes established a symbiotic relationship with the host cell, providing beneficial services such as energy production (mitochondria) or photosynthesis (chloroplasts). 4.Over time, the engulfed prokaryotes evolved into organelles, losing some of their original features and becoming dependent on the host cell for survival. 5.This symbiotic relationship between the host cell and the engulfed prokaryotes eventually led to the formation of eukaryotic cells with membrane-bound organelles. ENDOSYMBIOTIC THEORY  ENDOSYMBIOTIC THEORY The origin of the nucleus and plasma membrane through infoldings of the plasma membrane is a hypothesis regarding the evolutionary development of eukaryotic cells. This hypothesis suggests that the nucleus and the internal membrane systems of eukaryotic cells, such as the endoplasmic reticulum and the Golgi apparatus, originated from infoldings of the plasma membrane of ancestral prokaryotic cells. 26  Here's how the process might have occurred: 1.Infoldings of the Plasma Membrane: The early stages of eukaryotic cell evolution likely involved infoldings or invaginations of the plasma membrane of primitive prokaryotic cells. These invaginations would have increased the surface area of the cell, providing more space for cellular processes. 2.Formation of Internal Membrane Systems: Over time, these invaginations of the plasma membrane may have become more elaborate and compartmentalized, giving rise to internal membrane systems within the cell. These internal membranes would have separated various cellular processes and allowed for greater complexity and specialization. 3.Origin of the Nucleus: One of these internal compartments eventually enclosed the genetic material, forming the nucleus. The nucleus would have initially been an enclosed region within the cell, formed by invaginations of the plasma membrane that surrounded the genetic material. 4.Evolution of the Endomembrane System: Alongside the development of the nucleus, other internal membrane systems, such as the endoplasmic reticulum and the Golgi apparatus, may have evolved from further infoldings and compartmentalization of the plasma membrane. These systems would have facilitated the synthesis, modification, and transport of proteins and other molecules within the cell. 5.Specialization and Complexity: As these internal membrane systems became more elaborate, eukaryotic cells gained the ability to carry out a wider range of cellular functions. The specialization and compartmentalization provided by the nucleus and internal membranes allowed for increased efficiency and regulation of cellular processes. 27 FROM PROKARYOTES TO EUKARYOTES EVIDENCE FOR THE ENDOSYMBIOTIC THEORY 1) Mitochondria/Chloroplast have their own DNA similar to prokaryotic DNA 2) Mitochondria/Chloroplast divide like prokaryotes independent of the rest of the cell 3) Mitochondria/Chloroplast have double membranes and inner structures resembling bacteria. 4) Mitochondria/Chloroplast have simple ribosomes that are the same size and structure as in prokaryotes 5) Fossil records indicate the presence of ancient cells with structures resembling mitochondria and chloroplasts, supporting the idea of their bacterial origin. 30