Chapter 3: Cell Structures
Prokaryote comes from the Greek words for prenucleus. Eukaryote comes from the Greek words for
true nucleus.
Prokaryote
 One circular chromosome, not in a membrane. No histones. No organelles.
 Peptidoglycan cell walls if Bacteria, Pseudomurein cell walls if Archaea
 Reproduce by binary fission
Eukaryote

Paired chromosomes, in nuclear membrane. Has histones. Has organelles.

Polysaccharide cell walls

Reproduces with the mitotic spindle
Basic Shapes
Bacillus (rod-shaped)
Coccus (spherical)
Spiral: Spirillum, Vibrio, or Spirochete
Arrangements
Pairs: Diplococci, diplobacilli
Clusters: Staphylococci
Chains: Streptococci, streptobacilli
Multicellular Associations
Some types of bacteria live as multicellular associations. When water or nutrients are depleted, cells aggregate to
form a fruiting body. Other types of bacteria live on surfaces in groups called biofilms
The Cell Wall – Prevents lysis and is made of peptidoglycan (in bacteria)
The Nucleoid – a bacterial chromosome
Cytoplasm – The substance inside the plasma membrane. It is a phospholipid bilayer. It has 3 types of proteins: Peripheral
proteins, Integral proteins, and Trans-membrane proteins
Fluid Mosaic Model – Membrane is as viscous as olive oil. Proteins move to function. Phospholipids rotate and move
laterally.
Selective permeability of the membrane allows passage of some molecules. The membrane also allows for: Enzymes for
ATP production, photosynthetic pigments on foldings called chromatophores or thylakoids, and prevents damage to the
membrane by alcohols, quaternary ammonium (detergents), and polymyxin antibiotics causes leakage of cell contents
Movement of Materials across Membranes
 Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration
 Facilitated diffusion: Solute combines with a transporter protein in the membrane
 Osmosis: The movement of water across a selectively permeable membrane from an area of high water to an area of
lower water concentration
 Osmotic pressure: The pressure needed to stop the movement of water across the membrane
 Aquaporins (water channels)
Directed Movement of Materials across Membranes

Nearly all molecules that enter or exit a cell must cross the membrane through the proteins that function as selective
gates.

Mechanisms allowing nutrients and other small molecules to cross are called transport systems.

Cells actively move certain proteins they synthesize out of the cell in a process called secretion.
Transport Systems
 Mechanisms used to transport molecules across membranes use specific proteins called transport proteins,
permeases, or carriers.
 Cells do not produce all of the transport proteins continuously, rather, they use regulatory mechanisms determine
which transport proteins.
Facilitated Diffusion – Also called passive transport. It moves objects from one side of the membrane to the other using a
concentration gradient. Molecules will move until the concentration is equal on both sides.
EX: Glycerol can enter E. coli this way
Active Transport: Requires a transporter protein and ATP to move compounds against a gradient
Peptidoglycan – Polymer of disaccharide. Two forms: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
Gram-Positive Cell Walls
Teichoic acids: Lipoteichoic acid links to plasma membrane. Wall teichoic acid links to peptidoglycan. May regulate
movement of cations. Polysaccharides provide antigenic variation
Gram-Negative Outer Membrane
 Lipopolysaccharides, lipoproteins, phospholipids
 Forms the periplasm between the outer membrane and the plasma membrane
 Protection from phagocytes, complement, and antibiotics
 O-specific polysaccharide antigen, e.g., E. coli O157:H7
 Lipid A is an endotoxin and causes an immune response
 Porins (proteins) form channels through membrane
Gram-positive Cell Walls have thick peptidoglycan and teichoic acids
Gram-Negative Cell Walls have thin peptidoglycan and a periplasmic space
Antibacterial compounds that target peptidoglycan interfere with the synthesis of peptidoglycan or that can weaken its
structural integrity can lead to the cell bursting.

Penicillin - An antibiotic that interferes with the synthesis of peptidoglycan. Penicillin binds proteins that are
involved with cell wall synthesis and prevent cross-linkage of glycan chains. It is far more effective on gram-positive
cells, but it can be modified to pass through porin channels of gram-negative bacteria.

Lysozyme - An enzyme found in the body fluids, mainly tears and saliva. Breaks the bonds that link two molecules of
the peptidoglycan. This destroys the structural integrity of the glycan chain.
Cell walls of the Domain Archae
Because their habitats are so diverse, and in some cases extreme, they have a wide variety of cell walls. They have not
been studied as extensively as the Bacteria, so less is known about their cell wall structure. None contain peptidoglycan,
but they do have a similar molecule, pseudopeptidoglycan.
Capsules and slime layers - A gel-like layer that functions in protection or attachment
 If the layer is distinct and gelatinous, it is a capsule (The bacteria, Streptococcus mutans, uses a capsule to adhere to
teeth)
 If it is diffuse and irregular, it is a slime layer
Glycocalyx - Outside cell wall. Usually sticky
 Capsule: neatly organized. Capsules prevent phagocytosis
 Slime layer: unorganized and loose. Extracellular polysaccharide allows cell to attach
Flagella - Outside cell wall. Made of chains of flagellin. Attached to a protein hook and anchored to the wall and membrane
by the basal body
Fimbriae and Pili
Pili are structurally similar to the flagella and have distinct functions. Pili that enable attachment are called fimbriae
 Conjugation allows transfer of DNA from one cell to another (A sex pilus is used to join the cells)
 Pili - Facilitate transfer of DNA from one cell to another
Gliding or Twitching motility
Internal Structures
The Chromosome of prokaryotes is an irregular mass within the cytoplasm, forming a region called the nucleoid. It is a
single, circular double-stranded DNA molecule that contains all of the genetic material. Chromosomal DNA is tightly
packed and supercoiled.
 Plasmids are circular, supercoiled double-stranded DNA that carry a few to several hundred genes. Many plasmids
can be found in a single cell and may convey different information to the cell. Some may code for antibiotic resistance
Endospores - Resting cells that are resistant to desiccation, heat, chemicals
 Sporulation: Endospore formation
 Germination: Return to vegetative state
The Eukaryotic cell
Cell wall - Plants, algae, fungi. Made of carbohydrates (Cellulose, chitin, glucan, mannan)
Glycocalyx - Carbohydrates extending from animal plasma membrane. Bonded to proteins and lipids in membrane
The Plasma Membrane - selective permeability allows passage of some molecules. (Simple diffusion, Facilitative diffusion,
Osmosis)
 Active transport includes Endocytosis
Phagocytosis: Pseudopods extend and engulf particles
Pinocytosis: Membrane folds inward, bringing in fluid and dissolved substances
Transport proteins - Carriers of eukaryotes are the same as those of prokaryotes and mediate facilitated diffusion and
active transport. Channels are pores in the membrane that only allow the diffusion of specific ions with the concentration
gradient.
Endocytosis - Allows eukaryotes to take up materials from the surrounding environment
 Pinocytosis allows the uptake of liquids
 Receptor-mediated endocytosis allows cells to internalize external materials that fuse with the membrane
 Phagocytosis allows the uptake of large debris
Exocytosis - Allows for the removal of substances from the cell
Cytoplasm
 Cytoplasm membrane: Substance inside plasma and outside nucleus
 Cytosol: Fluid portion of cytoplasm
 Cytoskeleton: Microfilaments, intermediate filaments, microtubules
 Cytoplasmic streaming: Movement of cytoplasm throughout cells
Flagella and Cilia
 Microtubules of Tubulin in a 9 pairs + 2 array
Organelles
 Nucleus: Contains chromosomes
 Mitochondrion: Cellular respiration
 Chloroplast: Photosynthesis
 ER: Transport network
Rough – intracellular transport
Smooth – lipid synthesis and calcium storage
 Golgi complex: Membrane formation and secretion
 Lysosome: Digestive enzymes
 Peroxisome: Oxidation of fatty acids; destroys H2O2
 Vacuole: Brings food into cells and provides support
 Centrosome: Consists of protein fibers and centrioles