Cell Structure and Function

Module 3: Cell Structure and Taxonomy

• This module covers cell structure and taxonomy.
• It explains the cell theory.
• It explains the taxonomical classifications of microorganisms.
• It states the contributions of different scientists to cell studies.
• It describes and differentiates prokaryotic and eukaryotic cell structures.

How Animals are Classified (Taxonomy)

• Domain: Broadest classification, grouping organisms with similar basic characteristics.
• Kingdom: Further divides organisms based on general traits and evolutionary relationships.
• Phylum: Groups organisms with a specific body plan or organization.
• Class: Subdivides phyla based on shared characteristics.
• Order: Groups of closely related families.
• Family: Collection of similar genera.
• Genus: Group of closely related species.
• Species: Most specific level, organisms that can interbreed and produce fertile offspring.

Robert Hooke

• Robert Hooke (English physicist) wrote Micrographia.
• Micrographia described observations with a microscope.
• Hooke was the first to use the word "cell".
• “Cell” identified microscopic structures.
• He described box-like cells, resembling monastery cells, in cork.

Cell Theory

• The cell theory is a basic biology principle.
• All living organisms are composed of cells.
• The cell is the basic unit of life.
• Cells arise from pre-existing cells.

Scientists Who Contributed: Theodor Schwann

• "All animals are made of cells."
• He developed the cell doctrine.
• All living things are composed of cells.
• He established the cell as the basic unit of all living things.

Scientists Who Contributed: Matthias Schleiden

• Studied cells as the common element among all plants and animals.

Scientists Who Contributed: Rudolph Virchow

• Rudolph Virchow is the Father of Pathology.
• He introduced the third dictum that all cells come from cells.
• "Omnis cellula e cellula."
• He contributed to the Cell Theory of Biogenesis.

Virchow's Cellular Pathology

• The cell, the smallest living unit of the normal human body, is the basis of all disease.
• Cells encounter many stresses due to environmental changes.

Abiogenesis vs. Biogenesis

• Abiogenesis, or spontaneous generation, says that living organisms arise from non-living matter; a vital force forms life.
• Biogenesis describes living organisms that arise from pre-existing life.

Cell Fundamentals

• The cell is the fundamental living unit of any living organism.
• Cells exhibit basic characteristics of life.
• Metabolism: chemical reactions occurring within a cell
• Growth
• Reproduction
• Response to stimuli in its environment
• Mutation

Major Categories of Microbes

• Acellular infectious particles.
• Cellular microorganisms.

Taxonomy

• Taxonomy is the science of classifying living organisms.
• Functions:
  • Nomenclature
  • Classification
  • Taxa: kingdom or domains, divisions or phyla, classes, orders, families, genera, species
  • Identification

Taxonomy: Carolus Linnaeus

• Carolus Linnaeus is the Father of Taxonomy.
• He devised the binomial nomenclature
• Genus is the first name.
• Specific Epithet: second name.
• Species: 1st and 2nd name
• Example: Escherichia coli
• Devised the hierarchical classification system.
• Published Systema Naturae.

Taxonomy: Earnst Haeckel

• Earnst proposed the 3 kingdom classification of organisms.

Taxonomy: Herbert Copeland

• Proposed the four kingdom classification of organisms.
• Added the kingdom Monera.

Taxonomy: Robert Whittaker

• Proposed the five kingdom classification which is the most common system used today.
• Classification is based on structural similarities and differences.
• Classification is based on how organisms obtain nutrition.

Taxonomy: Carl Woese

• Classified organisms into three domains and six kingdoms.
• Domains: Archaea, Bacteria, Eukarya
• Kingdoms: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia

Origin of Cells

• Cells are divided into two main classes.
• Classes are based on whether they contain a nucleus.
• Prokaryotic cells: Bacteria, Archaea
• Eukaryotic cells: Algae, Protozoa, Fungi, Plants, Animals, Humans

Origin of Cells: Charles Darwin

• Evolution: changes in populations over time
• Darwin first proposed a feasible mechanism for evolution called Natural Selection.
• Darwin proposed the theory of universal descent.
• Universal descent occurs through an evolutionary process.
• Theory detailed in "On The Origin of Species".
• All species descended from a common ancestor.

Origin of Cells: Last Universal Common Ancestor

• The most recent population of organisms.
• All organisms now living on earth have a common descent from this population.
• The organism existed 3.5 to 3.9 billion years ago.

Origin Of Cells: Early life

• Life first emerged at least 3.8 billion years ago, 750 million years after Earth was formed.
• The very first cells to appear on Earth were a type of Archaea.
• The first eukaryotic cells appeared on Earth 1.6 to 2.7 billion years ago.
• Eukaryotic cells evolved from prokaryotic organisms by intracellular symbiosis.
• First primitive eukaryotic cells were single-celled and independent.
• Complex multicellular organisms evolved through evolution.

Origin of Cells: Endosymbiosis

• Eukaryotic cells arose when a larger prokaryotic cell engulfed smaller bacterial cells.
• Bacterial cells began to live and reproduce inside the prokaryotic cell.

Viruses

• Viruses are a result of regressive or reverse evolution.
• Composed of few genes protected by a protein coat.
• They depend on the metabolic machinery of a host cell to reproduce.
• Viruses are acellular.

Eukaryotes

• EU stands for true.
• KARYO stands for nut or nucleus.
• Eukaryotes are microorganisms with a true nucleus.
• The true nucleus is enclosed by a nuclear membrane.

Eukaryotic Cells features

• Large complex cells divided into separate compartments by membrane-bound organelles.
• Each organelle serves an essential function.
• Includes Fungi, protozoa, algae, plants, animals.
• Ranges 10-30um in diameter

Eukaryotes: Cell Membrane

• Plasma membrane is also known as the cytoplasmic or cellular membrane.
• The cell membrane surrounds the cell.
• Composed of a phospholipid bilayer with embedded proteins.
• Separates internal contents from the surrounding environment of the cell.
• Selectively permeable.

Eukaryotes: Nucleus

• The nucleus is the command center of the cell.
• It is enclosed by membranes.
• Contains the cell's DNA.
• Directs the synthesis of proteins and ribosomes.

Eukaryotes: Nucleus Details

• Nucleoplasm: gelatinous matrix.
• Chromosomes.
• DNA: linear, beads on a string.
• Histones
• Nuclear membrane.
• Nucleolus: site of rRNA synthesis.

Eukaryotes: Genes

• Located along DNA molecules.
• Each gene contains the genetic information that enables the cell to produce gene products.
• Includes proteins, rRNA, IRNA.
• Genotype.
• Organism's complete collection of genes.

Eukaryotes: Cytoplasm

• Semifluid, gelatinous, nutrient matrix.
• Majority of the volume of the cell.
• Contains cytosol, organelles, and granules or particles called cytoplasmic inclusions.
• Site of metabolic reactions.
• CYTOSOL is the semifluid portion.

Eukaryotes: Endoplasmic Reticulum

• Responsible for the synthesis, folding, modification, and transport of proteins.

Eukaryotes: Ribosomes

• Protein factories.
• Consist mainly of rRNA and proteins.
• Polyribosomes.
• Two sub-units.
• Large: 60s
• Small: 40s
• 40s + 60s = 80s
• Produced in the nucleolus.
• Transported to the cytoplasm.
• Produce proteins, when joined with mRNA.

Eukaryotes: Golgi Complex

• Packaging plants of the cell.
• Completes transformation of newly synthesized proteins into mature, functional ones.
• Packages proteins into small membrane-enclosed vesicles.
• Vesicles are transported within or outside the cell.

Eukaryotes: Lysosomes

• Garbage disposal/ digestive system of the cell.
• Digest macromolecules, old cell parts, and microorganisms.
• Contain acid hydrolases that break down macromolecules.

Eukaryotes: Peroxisomes

• Carry out oxidation reaction to produce hydrogen peroxide.
• Catalyze conversion of hydrogen peroxide to oxygen and water.
• Contain oxidases and catalases.
• Synthesized in the free ribosomes.
• Numerous in hepatocytes.

Eukaryotes: Mitochondria

• Generates chemical energy for biochemical reactions.
• Abundant in cells with high energy requirement.
• Those include: Stomach parietal cells, kidney tubule cells, adrenal cortex, and hepatocytes.
• Other functions.
• Accumulation of calcium
• Synthesis of sodium and proteins
• Oxidation of fatty acids

Eukaryotes: Cytoskeleton

• Made up of filamentous proteins to strengthen, support, stiffen, and give shape to the cell.

Eukaryotes: Plastids

• Membrane-bound structures contain photosynthetic pigments.
• Chloroplasts.
  • Contains chlorophyll.
  • Found in plant cells and algae.
• Photosynthesis.
• Light energy converts carbon dioxide and water into carbohydrates and oxygen.
• This involves the conversion of light energy into chemical energy.

Eukaryotes: Cell Wall

• External structure that provides rigidity, shape, and protection to the cell.
• Cellulose: Algae and plants.
• Chitin: Fungi and the exoskeleton of beetles & crabs.
• Lignin
• Pectin
• Mineral salts

Eukaryotes: Presence of Cell Wall

• Cell wall is Present in:
• Plants
• Algae
• Fungi
• Bacteria
• Cell Wall is Absent in:
• Animals
• Protozoa
• Mycoplasma sp.

Eukaryotes: Organelles of Locomotion: Flagella

• Enable cells to swim through liquid environment.
• Present in spermatozoa, protozoa, algae.
• The motion is a whipping motion.

Eukaryotes: Organelles of Locomotion: Cilia

• Beat with a coordinated rhythmic movement.
• Cilia are thinner, shorter, and more numerous.
• Present in protozoa and human body.

Prokaryotes: Cell Membrane

• Similar to eukaryotic cell membrane.
• Consists of phospholipids and proteins.
• Contains enzymes to catalyze metabolic reactions.
• Selectively permeable.

Prokaryotes: Cell Membrane and More

• Cell membrane.
• Mesosomes-Invaginated structures formed by the localized infoldings of the plasma membrane.
• Site of cellular respiration.
• Chlorophyll and Other Pigments
• Found within the infoldings of the cell membrane in cyanobacteria.

Prokaryotes: Chromosomes

• Consist of a single long, supercoiled, circular DNA molecule.
• Control center of the cell.
• Suspended in the cytoplasm.
• Bacterial Nucleoid is the DNA-occupied space within a bacterial cell.
• Plasmids are extrachromosomal DNA.

Prokaryotes: Cytoplasm Features

• Semiliquid.
• Contains enzymes, oxygen, waste products, nutrients, proteins, carbohydrates, lipids.
• Exhibits Cytoplasmic granules.
• Cytoplasmic granules contain starch, lipids, sulfur, and iron.

Prokaryotes: Cytoplasmic particles

• Site of protein synthesis.
• 30S + 50S = 70S

Prokaryotes: Bacterial Cell Wall

• Peptidoglycan (Murein).
• Most important bacterial structure.
• Polysaccharide chains linked by small peptide chains.
• Its thickness and exact composition varies with the species of bacteria.
  • Basis for classifying bacteria as Gram Positive or Gram Negative.

Prokaryotes: Glycocalyx

• Slimy, gelatinous material produced by the cell membrane.
• Secreted outside of the cell wall.
• Slimy Layer.
• Not highly organized.
• Not firmly attached to the cell wall.
• Easily detaches from the cell wall and drifts away. Pseudomonas aeruginosa.
• Produce R COLONIES when cultured.

Prokaryotes: Glycocalyx: Capsule

• Highly organized.
• Firmly attached.
• Anti-phagocytic.
• Produce S COLONIES.
• H. influenzae, Neisseria meningitides, Streptococcus pneumoniae.

Prokaryotes: Capsule Stain

• Capsules are stained using India Ink: negative staining

Prokaryotes: Flagella

• Thread-like protein appendages for movement.
• Flagellin is made of protein threads.
• Do not contain microtubules.
• Not membrane-bound.

Prokaryotes: Axial Filaments

• Flagella-like fibrils of spirochetes.
• Allow spirochetes to move in a spiral or helical manner.

Prokaryotes: Pili / Fimbriae

• Hair-like structures arising from the cytoplasm of Gram negative bacteria.
• Pilin: protein components arranged helically to form a cylinder.
• Types.
• For attachment to surfaces
• Causes urethritis
• Sex Pilus: For transference of genetic material

Prokaryotes: Endospores

• Dormant stage of some bacteria to survive extreme conditions.
• Conditions include:e.g. drought or extreme heat
• Commonly found in soil and water.
• Resistance to UV and gamma radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants.
• Sporulation is the process of spore formation.

Test your knowledge of cell theory, microbial structures, and their functions, including the contributions of key scientists like Virchow, Hooke, Schleiden, and Schwann. Explore bacterial virulence factors, endospores, and staining techniques.