Cell Structure: Prokaryotic and Eukaryotic Cells

Macromolecules in Cells

• 80-90% of a cell's dry weight is made up of macromolecules.

Cell Types

• Cells are divided into two main classes: prokaryotic and eukaryotic.

Prokaryotic Cells

• Lack a nuclear envelope.

Eukaryotic Cells

• Have a nucleus where genetic material is separated from the cytoplasm.

Prokaryotic vs. Eukaryotic Organisms

• Prokaryotes:
  • Include bacteria, cyanobacteria, and archaebacteria.
• Eukaryotes:
  • Include plants, animals, protists, and fungi.

Cell Size

• Prokaryotes
  • Small (1-10 micrometers).
• Eukaryotes
  • Large (greater than 10-100 micrometers).

Metabolism and Photosynthesis

• Prokaryotes:
  • Anaerobic, facultative anaerobic, or aerobic.
    • Photosynthesis is usually aerobic.
• Eukaryotes:
  • Aerobic.

Motility

• Prokaryotes:
  • Immotile or have flagella.
• Eukaryotes:
  • Cilia and flagella are common.

Cell Walls

• Prokaryotes:
  • Walls contain sugars and peptidoglycans that are characteristic of bacteria.
• Eukaryotes:
  • Walls contain structural polysaccharides, such as cellulose or chitin.

Cell Organelles

• Prokaryotes:
  • Lack membrane-bound organelles but may have membrane-bound pigments.
• Eukaryotes:
  • Contain organelles like mitochondria and chloroplasts.

Genetic Organization

• Prokaryotes:
  • Have circular DNA dispersed in plasmids or a mesosome.
• Eukaryotes:
  • DNA is organized into chromosomes within a nucleus.

Reproduction

• Prokaryotes:
  • Undergo binary fission, budding, and asexual reproduction.
• Eukaryotes:
  • Sexual reproduction occurs through specialized processes like mitosis or meiosis.

Cellular Organization

• Prokaryotes:
  • Principally unicellular.
• Eukaryotes:
  • Principally multicellular.

Domain Archaea

• Also known as Archaebacteria.

Halophiles

• Prokaryotes that thrive in natural environments like the Dead Sea or evaporation ponds with high salt concentrations.
• Require salt for growth, using it to stabilize cell walls, ribosomes, and enzymes via ions.

Methanogens

• Prokaryotes that live in the rumen of cows and ruminants.
• One cow can emit around 50 liters of methane per day through eructation, contributing to greenhouse gas emissions.
• The rapid accumulation of methane gas in the atmosphere is alarming.

Thermophiles

• Prokaryotes that require very high temperatures (80-105 degrees C) to grow.
• Their membranes and enzymes tend to be stable at these temperatures.
• The majority require sulfur to grow, using it as a final electron acceptor instead of oxygen in respiration.
• Thermus aquaticus grows at 40 degrees.

Prokaryotes compared to Eukaryotes

• Prokaryotes are simpler and smaller than eukaryotes.
• Their genetic material is a single large molecule of circular, double-stranded DNA.
• Enclosed by a plasma membrane, cytosol (cytoplasm), and ribosomes.
• They reproduce though binary fission.
• Exist in a variety of habitats.

Prokaryotic Resistance

• Most prokaryotes can exist regardless of circumstances, because their species have adapted to almost all habitats.

Intracellular Organisms

• Chlamydia trachomatis and Rickettsia are intracellular organisms

Biochemical Processes

• Biochemical processes occur in the cytoplasmic membrane, specifically the nucleoid region.

Plasmids

• Small loops of DNA in the bacterial cytoplasm known as plasmids.
• Small in size, and reproduce rapidly.

Prokaryotic Diversity

• Prokaryotes display a great diversity.

Prokaryotic Adaptability

• Prokaryotes show a capability to adapt to changes in their environment.

Prokaryotic Ecological Roles

• Prokaryotes occupy a variety of ecological niches.

Prokaryotic History

• Prokaryotes developed over 3,000 million year ago.

Bacterial Cell Shapes

• Bacillus (rod-shaped)
• Coccus (spherical)
• Diplococcus (pairs of cocci)
• Staphylococcus (clusters of cocci)
• Streptococcus (chains of cocci)
• Vibrio (curved rod)
• Spirillum (spiral-shaped)
• Streptobacillus (chains of rods)

Prokaryotic Cell Wall

• Cell wall is a rigid outermost part of the cell
• Cell wall is located below the capsule

Prokaryotic Genetic Material

• No nucleus is present
• Genetic material is dissolved in cytoplasm
• Made of single chromosome

Prokaryotic Organelles

• NO organelles within cytoplasm
• Metabolic processes occur in the cytoplasm
• Plasma membrane is only membrane present

Ancient Life Forms

• Prokaryotes are thought to be very old.
• First life forms appeared 350 million years ago.

Prokaryotic Size

• Prokaryotes an measure 10x smaller than eukaryotic cells
• Size varies between 0.5 to 5 micrometers
• Length varies between 10 to 100 micrometers

Prokaryotic Cellularity

• Prokaryotes always form single cells
• Grouped to form colonies, never form complex organization

Prokaryotic Reproduction

• Asexual reproduction
• Divides through mechanisms of:
  • Bipartition
  • Fission

Bacterial Structure: Obligatory Elements

• Cell wall
• Cytoplasmic membrane
• Cytoplasm
• Ribosomes
• Mesosomes
• Inclusions
• Periplasmic spaces

Bacterial Structure: Facultative Elements

• Glycocalyx
• Flagellum
• Fimbriae
• Capsule
• Sporas
• Plasmids

Cell Wall Properties and Functions

• Provides protection and resistance.
• Provides rigidity to the cell structure.
• Acts as a filter with its pores.
• Participates in bacterial division.
• Confers shape and prevents lysis due to osmotic pressure.

Cytoplasmic Membrane

• Lipid bilayer containing proteins and phospholipids.
• Serves as an active and selective osmotic barrier.
• Site for synthesis of substances for the cell wall and capsule.
• Involved in generation of ATP.
• Facilitates cell division (septum formation).

Functions of the Plasma Membrane

• Acts as an osmotic barrier.
• Facilitates transport of substances.
• Biosynthesis of biomolecules.
• Transduction of energy (respiration).
• Site of DNA replication and nucleoid.
• Anchoring point for flagella, cilia, fimbriae, and pili.

Bacterial Cytoplasm

• Characterized as a colloidal system.
• Composed of 85% water, minerals, and ferments.
• Does not contain membranous systems (organelles).
• Appears granular due to the presence of ribosomes, plasmids, and the nucleoid (DNA).

Ribosomes

• Have a sedimentation coefficient of 70S.
• Consist of two subunits.
• Rich in RNA and proteins.
• Involved in protein synthesis.

Nucleoid

• A region within the cytoplasm where the bacterial DNA is found in a condensed state.
• Contains bacterial DNA that follows the Watson and Crick model, consisting of two antiparallel strands in a double helix.
• Bacteria are haploid organisms, possessing a single chromosome.

Nucleoid Characteristics

• Lacks a nuclear membrane.
• Single Chromosome.
• Measures 1mm.
• Involved in mechanisms of hereditary transfer.
• Regulates protein synthesis.
• Induces changes that lead to cell division.

Cytoplasmic Inclusions

• Granules of polysaccharides
• Lipid inclusions
• Granules of sulfur
• Cyanophycin
• Carboxysomes
• Magnetosomes
• Gas vacuoles

Granules

• Contain glycogen and amyloplast
• Stains with iodine
• Includes Lipids
• Can be colored

Sulfur Granules

• Oxidizes Hydrogen Sulfide
• Sulfur is oxidized to sulfate and energy disappears

Carboxysomes

• Consists of cyanobacteria
• Also consists of nitrogen
• Consists of magnetic iron
• Contains a membrane to transfer gylcolipids

Vacuoles

• Contains gasses to maintain buoyancy

Structure of Prokaryotes

• Contains the different parts
• Can be shown through illustrations

Glycocalyx Properties

• The outermost layer is delicate and flexible
• Made of polysaccharides and glycoproteins
• Facilitates adherence by bacterial cells
• Acts as an antigen

Flagella Features

• Filamentous appendices of a helical structure.
• Organelles for moving bacteria
• Consists of a singular filament and basal body
• Demonstrates taxi

Types of Flagella

• Monotrichous
• Lophotrichous
• Amphitrichous
• Peritrichous

Pili Structure

• Protein based stricture which is long

Pili Sex

• Responsible for DNA manipulation

Fimbriaes

• Protein component, acts as connection in the Mc and passes through cellular pore
• Microscopic element

Fimbriae Roles

• A connection component
• Abundant
• Common in gram staining

Capsule Qualities

• Complicated mucus layer component
• Outside cellular surface
• Contains cellular protein

Capsule Properties

• Present in gram staining
• Protects from phagocytes and toxic materials

Characteristics of Sporas

• Rigid and unbreakable cytoplasm
• Contains genetic components
• Mainly bacillus, resists degradation by chemical agents

Spores Characteristics

• Can be dormant for long periods
• Activation of dormant cells leads to germination

Plasmids

• Circular DNA
• Extra chromosomal
• Independent to other acids
• Resistance to other toxics
• Evolves to be resistant

Asexual Reproduction of Bacteria

• Involves fission, bineria or bipartition
• Conjugations

Sexual and Parasexual bacterial reproduction

• Includes:
  • Transformation
  • Transduction

Fission

• Circular and includes mesonas and ADN

Recombination or Recombination

• DNA fragments are combined with normal cells

Transduction

• After a cell is infected the DNA fragments inject themselves into the bacteria cell

Conjugation

• The conjugative cell (F+) has a sex pilus, while the non-conjugative cell (F-) does not.
• Contact is established between the two cells through the sexual pilus. -Synthesis of the chains of conjugative DNA occurs continuously in the donor cell and discontinuously in the receptor, sealing the pores and separating the cells.
• Each has one copy of the F factor

Bacterial Metabolism Types:

• Autotrophs: Generate cellular carbon from carbon dioxide
• Heterotrophs: use organic compounds.
• Lithotrophs: harness energy via oxidation of substances, such as ammonia.

Role of Bacteria

• Nitrogen recycling
• Biotechnology
• Genetic modification
• Engineering

Explore the fundamental differences between prokaryotic and eukaryotic cells. Understand their unique characteristics, including cell size, metabolism, motility, and cell wall composition. This comparison highlights the key distinctions between these two major cell types.