Archaea and Bacteria Cell Structure and Function

Cell Structure and Function - Learning Outcomes

• 3.1: Describe four major processes of living cells.
• 3.2: Compare and contrast prokaryotic and eukaryotic cells.
• 3.3: Describe the composition, function, and relevance to human health of glycocalyces.
• 3.4: Distinguish capsules from slime layers.
• 3.5: Discuss the structure and function of bacterial flagella.
• 3.6: List and describe different bacterial flagellar arrangements.
• 3.7: Compare and contrast the structures and functions of fimbriae, pili, and flagella.
• 3.8: Describe the common shapes and arrangements of bacterial cells.
• 3.9: Describe the sugar and peptide portions of peptidoglycan.
• 3.10: Compare and contrast the cell walls of Gram-positive and Gram-negative bacteria in terms of structure and Gram staining.
• 3.11: Compare and contrast the cell walls of acid-fast bacteria with typical Gram-positive cell walls.
• 3.12: Describe the clinical implications of the structure of the Gram-negative cell wall.
• 3.13: Diagram a phospholipid bilayer, and explain its significance in reference to a cytoplasmic membrane.
• 3.14: Explain the fluid mosaic model of membrane structure.
• 3.15: Describe the functions of a cytoplasmic membrane as they relate to permeability.
• 3.16: Compare and contrast the passive and active processes by which materials cross a cytoplasmic membrane.
• 3.17: Define osmosis, and distinguish between isotonic, hypertonic, and hypotonic solutions.
• 3.18: Define bacterial cytoplasm and its basic contents.
• 3.19: Define inclusion.
• 3.20: Describe the formation and function of endospores.
• 3.21: Describe the structure and function of ribosomes and the cytoskeleton.
• 3.22: Describe the structure and chemistry of archaeal and bacterial glycocalyces.
• 3.23: Describe the structure and formation of archaeal flagella.
• 3.24: Compare and contrast archaeal and bacterial flagella.
• 3.25: Compare the structure and function of archaal and bacterial fimbriae.
• 3.26: Describe the structure and function of hami.
• 3.27: Contrast the types of archaeal cell walls with each other and with bacterial cell walls.
• 3.28: Contrast the archaeal cytoplasmic membrane with that of bacteria.
• 3.29: Compare and contrast the cytoplasm of archaea with that of bacteria.
• 3.30: Describe the composition, function, and importance of eukaryotic glycocalyces.
• 3.31: Compare and contrast prokaryotic and eukaryotic cell walls and cytoplasmic membranes.
• 3.32: Contrast exocytosis and endocytosis.
• 3.33: Describe the role of pseudopods in eukaryotic cells.
• 3.34: Compare and contrast the cytoplasm of prokaryotes and eukaryotes.
• 3.35: Identify nonmembranous and membranous organelles.
• 3.36: Compare and contrast the structure and function of prokaryotic and eukaryotic flagella.
• 3.37: Describe the structure and function of cilia.
• 3.38: Compare and contrast eukaryotic cilia and flagella.
• 3.39: Describe the structure and function of ribosomes, cytoskeletons, and centrioles.
• 3.40: Compare and contrast the ribosomes of prokaryotes and eukaryotes.
• 3.41: List and describe the three main filaments of a eukaryotic cytoskeleton.
• 3.42: Discuss the function of each of the following: nucleus, endoplasmic reticulum, Golgi body, lysosome, peroxisome, vesicle, vacuole, mitochondrion, and chloroplast.
• 3.43: Label the structures associated with each of the membranous organelles.
• 3.44: Describe the endosymbiotic theory of the origin of mitochondria, chloroplasts, and eukaryotic cells.
• 3.45: List evidence for the endosymbiotic theory.

Bacterial Cell Walls

• Most prokaryotes have a cell wall.
• It provides structure and shape, protects from osmotic forces, and aids in attachment to other cells.
• Bacteria are categorized as Gram-positive or Gram-negative based on cell wall composition.

Cell Wall Composition

• Bacterial cell walls are made of peptidoglycan, a combination of protein and sugar.
• The sugar component is a polymer with two regularly alternating molecules: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
• Chains of NAG and NAM are connected to other NAG and NAM chains by crossbridges of four amino acids (tetrapeptide). The tetrapeptides are held together by short connecting chains of amino acids.

Gram-Positive Cell Walls

• Thick layer of peptidoglycan.
• Contains teichoic acid.
• Some teichoic acids are linked to lipids, forming lipoteichoic acids.
• Lipoteichoic acids anchor peptidoglycan to the cytoplasmic membrane.

Gram-Negative Cell Walls

• Thin layer of peptidoglycan.
• Has an outer membrane.
• Note the absence of teichoic and lipoteichoic acids.
• Braun lipoprotein links the thin peptidoglycan layer with the outer membrane.

Outer Membrane (Gram-Negative)

• Composed of phospholipids and proteins
• Outer leaflet: Contains lipopolysaccharide (LPS)
• Proteins called porins form channels and allow some solutes to enter and exit the cell.
• LPS has two sugar components (O-specific polysaccharide and core polysaccharide) and a lipid component called lipid A.

Periplasmic Space (Gram-Negative)

• The space between the cytoplasmic membrane and the outer membrane.
• Composed of water, nutrients, enzymes, and substances secreted by the cell.

Bacterial Flagella

• Responsible for bacterial movement
• Similar structure in bacteria that have it
• Not all bacteria have one.
• Three parts:
  • Filament: Hollow shaft. Made of the protein flagellin.
  • Hook: Connects filament to the basal body
  • Basal body: Anchors hook and filament to the cell wall and cytoplasmic membrane. Structure depends on if it is Gram + or -.
• Grows from the tip of the flagella
• Each part has a different protein composition

Microbial Flagellar Arrangement

• Peritrichous: cover the surface
• Amphitrichous: both ends
• Monotrichous: one end
• Lophotrichous: several extending from one or both ends

Endoflagella

• Spiral tightly around the cell
• Can form an axial filament that wraps around the cell between the cytoplasmic membrane and outer membrane
• Rotation causes corkscrew motion of the bacteria

Bacterial Fimbriae

• Sticky projections that adhere to one another and to other substances.
• Typically shorter than flagella.
• Can be used as a rope to pull bacteria towards objects.

Biofilms

• 3D slimy masses of microbes adhering to a substrate and one another by means of fimbriae and glycocalyces.
• Most bacteria in nature exist in biofilms.
• Biofilms can form on many surfaces.

Pilus

• Special fimbriae
• Can transfer DNA from one cell to another
• Typically longer than other fimbriae, but shorter than flagella

Cytoplasm of Bacteria

• Cytoplasm: gelatinous material in the cell
• Cytosol: liquid portion of the cytoplasm
• Nucleoid: DNA containing region.
• Most bacteria have a single circular chromosome

Inclusions

• Deposits of a substance stored in the cytosol of the cell.
• Examples include lipids, starch, and nitrogen, phosphate- or sulfur-containing compounds
• Polyhydroxybutyrate (PHB): a lipid polymer used to store energy

Endospores

• Environmentally resistant structures.
• Formed by Gram + genera Bacillus or Clostridium.
• Extremely resistant to drying, heat, radiation, and lethal chemicals
• Formed from one cell, so it is not a reproductive structure

Eukaryotic Cell Walls

• Plants use cellulose
• Fungi use cellulose, chitin or glucomannan
• Algae use cellulose, proteins, agar, carrageenan, silicates, algin, calcium carbonate, or a combination of the above.

Eukaryotic Cytoplasmic Membranes

• Contain sterols (like cholesterol) to maintain membrane fluidity.
• Possess membrane rafts (lipid rafts) – distinct assemblages of lipids and proteins that remain together.
• Often attach sugars to the outer surface of lipids and proteins.
• Do not perform group translocation.

Active Transport Processes in Eukaryotes

• Endocytosis: uptake of material forming vesicles at the plasma membrane
• Phagocytosis: uptake of large substances (involves the formation of pseudopods that surround substances).
• Pinocytosis: indiscriminate uptake of fluid and dissolved solutes.
• Exocytosis:delivers lipids and proteins to the PM, but this is balanced by removal from endocytosis.

Eukaryotic Flagella

• Inside the cell, surrounded by the cytoplasmic membrane
• Composed of microtubules
• Microtubules are in a 9+2 arrangement
• Anchored to a basal body in the cytoplasm in a 9+0 arrangement
• Undulates rather than rotates

Eukaryotic Cilia

• Shorter and more numerous than flagella
• Surrounded by cytoplasmic membrane.
• Same 9+2 arrangement anchored by a 9+0 basal body as flagella.
• Not found in prokaryotes.

Eukaryotic Nonmembranous Organelles

• 80S, larger than prokaryotic ribosomes
• Cytoskeleton: moves organelles within the cytosol, serves as an internal scaffold, maintains basic shape, helps move cytoplasmic membranes for locomotion.
• Made of microtubules, intermediate filaments, and microfilaments.

Centrioles

• Composed of nine microtubule triplets.
• Found in some animal and fungal cells.
• Two centrioles lie at right angles to one another are found in a region of the cytoplasm known as the centrosome.
• Involved in mitosis and cytokinesis, formation of flagella and cilia.

Membranous Organelles

• Contains the genetic material of the cell (multiple linear chromosomes).
• Surrounded by a double membrane called the nuclear envelope.
• Nucleoplasm: the semiliquid matrix of the nucleus
• Nucleoli: specialized regions where RNA is synthesized

Endoplasmic Reticulum

• Categorized as smooth or rough depending on the presence of ribosomes studding the surface.
• Rough: involved in protein synthesis and processing.
• Smooth: lipid synthesis and transport, calcium storage, drug detoxification, and carbohydrate metabolism.

Golgi Body

• Manufactures, receives, modifies and ships proteins throughout the cell.
• Forms vesicles that bud off and fuse with other organelles or to the cytoplasmic membrane

Lysosomes, Peroxisomes, Vacuoles, Vesicles

• Vesicle and vacuoles are sacs that store material (lipids, starch, water, ions, etc.)
• Lysosomes: found in animal cells, contain hydrolytic enzymes that break down old cells, organelles, and phagocytosed material.
• Peroxisomes degrade metabolic wastes.

Mitochondria

• The "powerhouse of the cell." Involved in ATP production
• Possess an inner membrane, outer membrane, and an intermembrane space.
• Inner membrane contains folds called cristae.
• The matrix lies within the inner membrane.

Chloroplasts

• Involved in photosynthesis
• Contains an inner and outer membrane.
• Thylakoids: membranous sacs, where photosynthesis is conducted
• Granum: stack of thylakoids
• Stroma: space outside of grana contained within the inner membrane.

Endosymbiotic Theory

• Early ancestor of eukaryotic cells engulfed nonphotosynthetic prokaryotes and photosynthetic prokaryotes which ultimately became mitochondria and chloroplasts, respectively.
• Accounts for the two membranes, circular DNA, and presence of 70S ribosomes in both organelles.
• Doesn't explain:
  • Why the nuclear envelope has two membranes
  • Why most mitochondrial/chloroplast proteins come from nuclear DNA

Prokaryotes vs Eukaryotes

• Key characteristics distinguishing prokaryotes from eukaryotes include size, nucleus, membrane-bound organelles, cell wall composition, ribosome size, and chromosome structure.

Eukaryotic External Structures

• Some animal and protozoan cells have a glycocalyx anchored to the cytoplasmic membrane.
• Cell-cell recognition and adhesion.
• Protection of the cell surface
• Permeability layer
• Not as organised as bacterial capsules
• Absent in eukaryotes with cell walls

Additional Notes

• Page numbers in the file are shown for reference of the image.

This quiz covers the structural components of archaea and bacteria, including cell walls, cytoplasmic membranes, glycocalyx, and ribosomes. It emphasizes the unique characteristics that enable archaea to thrive in extreme conditions, and the key differences between archaeal and bacterial structures.