Chapter 4

Compare the cell structure of prokaryotes and eukaryotes.
 Prokaryotic and eukaryotic cells are similar in their chemical composition and chemical
reactions.
 Prokaryotic cells typically lack membrane-enclosed organelles (including a nucleus).
 Peptidoglycan is found in prokaryotic cell walls but not in eukaryotic cell walls.
 Eukaryotic cells have a membrane-bound nucleus and other organelles.
The Prokaryotic Cell
• Bacteria are unicellular, and most of them multiply by binary fission.
 Bacterial species are differentiated by morphology, chemical composition, nutritional
requirements, biochemical activities, and source of energy.
The Size, Shape, and Arrangement of Bacterial Cells
• Identify the three basic shapes of bacteria.
 Most bacteria are 0.2 to 2.0 μm in diameter and 2 to 8 μm in length.
 The three basic bacterial shapes are coccus (spherical), bacillus (rod-shaped), and spiral
(twisted).
 Pleomorphic bacteria can assume several shapes.
Structures External to the Cell Wall
• Describe the structure and function of the glycocalyx.
• Differentiate flagella, axial filaments, fimbriae, and pili.
Glycocalyx
 The glycocalyx (capsule, slime layer, or extracellular polysaccharide) is a gelatinous
polysaccharide and/or polypeptide covering.
 Capsules may protect pathogens from phagocytosis.

 Capsules enable adherence to surfaces, prevent desiccation, and may provide nutrients.
Flagella and Archaella
 Bacterial flagella and archaeal archaella rotate to push the cell.
 Flagella are relatively long filamentous appendages consisting of a filament, hook, and
basal body.
 Motile bacteria exhibit taxis; positive taxis is movement toward an attractant, and
negative taxis is movement away from a repellent.
Axial Filaments
 Spiral cells that move by means of an axial filament (endoflagellum) are called
spirochetes.
 Axial filaments are similar to flagella, except that they wrap around the cell.
Fimbriae and Pili
 Fimbriae help cells adhere to surfaces.
 Pili are involved in twitching motility and DNA transfer.
The Cell Wall
• Compare and contrast the cell walls of gram-positive bacteria, gram-negative
bacteria, acid-fast bacteria, archaea, and mycoplasmas.
• Compare and contrast archaea and mycoplasmas.
• Differentiate protoplast, spheroplast, and L form.
Composition and Characteristics
 The cell wall surrounds the plasma membrane and protects the cell from changes in
water pressure.
 The bacterial cell wall consists of peptidoglycan, a polymer consisting of NAG and NAM
and short chains of amino acids.
 Gram-positive cell walls consist of many layers of peptidoglycan and also contain
teichoic acids.
 Gram-negative bacteria have a lipopolysaccharide-lipoprotein-phospholipid outer
membrane surrounding a thin peptidoglycan layer.
 The outer membrane protects the cell from phagocytosis and from penicillin, lysozyme,
and other chemicals.
 Porins are proteins that permit small molecules to pass through the outer membrane;
specific channel proteins allow other molecules to move through the outer membrane.

 The lipopolysaccharide component of the outer membrane consists of sugars (O
polysaccharides), which function as antigens, and lipid A, which is an endotoxin.
Cell Walls and the Gram Stain Mechanism
 The crystal violet–iodine complex combines with peptidoglycan.
 The decolorizer removes the lipid outer membrane of gram-negative bacteria and
washes out the crystal violet.
 Atypical Cell Walls
 Mycoplasma is a bacterial genus that naturally lacks cell walls.
 Archaea have pseudomurein; they lack peptidoglycan.
 Acid-fast cell walls have a layer of mycolic acid outside a thin peptidoglycan layer.
Damage to the Cell Wall
 In the presence of lysozyme, gram-positive cell walls are destroyed, and the remaining
cellular contents are referred to as a protoplast.
 In the presence of lysozyme, gram-negative cell walls are not completely destroyed, and
the remaining cellular contents are referred to as a spheroplast.
 L forms are gram-positive or gram-negative bacteria that do not make a cell wall.
 Antibiotics such as penicillin interfere with cell wall synthesis.
Structures Internal to the Cell Wall
• Describe the structure, chemistry, and functions of the prokaryotic plasma
membrane.
• Define simple diffusion, facilitated diffusion, osmosis, active transport, and group
translocation.
• Identify the functions of the nucleoid and ribosomes.
• Identify the functions of four inclusions.
• Describe the functions of endospores, sporulation, and endospore germination.
The Plasma (Cytoplasmic) Membrane
 The plasma membrane encloses the cytoplasm and is a lipid bilayer with peripheral and
integral proteins (the fluid mosaic model).
 The plasma membrane is selectively permeable.
 Plasma membranes contain enzymes for metabolic reactions, such as nutrient
breakdown, energy production, and photosynthesis.
 Mesosomes, irregular infoldings of the plasma membrane, are artifacts, not true cell
structures.
 Plasma membranes can be destroyed by alcohols and polymyxins.

The Movement of Materials across Membranes
 Movement across the membrane may be by passive processes, in which materials move
from areas of higher to lower concentration and no energy is expended by the cell.
 In simple diffusion, molecules and ions move until equilibrium is reached.
 In facilitated diffusion, substances are transported by transporter proteins across
membranes from areas of high to low concentration.
 Osmosis is the movement of water from areas of high to low concentration across a
selectively permeable membrane until equilibrium is reached.
 In active transport, materials move from areas of low to high concentration by
transporter proteins, and the cell must expend energy.
 In group translocation, energy is expended to modify chemicals and transport them
across the membrane.
Cytoplasm
 Cytoplasm is the fluid component inside the plasma membrane.
 The cytoplasm is mostly water, with inorganic and organic molecules, DNA, ribosomes,
inclusions, and cytoskeleton proteins.
The Nucleoid
 The nucleoid contains the DNA of the bacterial chromosome.
 Bacteria can also contain plasmids, which are circular, extrachromosomal DNA
molecules.
Ribosomes
 The cytoplasm of a prokaryote contains numerous 70S ribosomes; ribosomes consist of
rRNA and protein.
 Protein synthesis occurs at ribosomes; it can be inhibited by certain antibiotics.
Inclusions
 Inclusions are reserve deposits found in prokaryotic and eukaryotic cells.
Endospores
 Endospores are resting structures formed by some bacteria; they allow survival during
adverse environmental conditions.
The Eukaryotic Cell
• Define organelle.

• Describe the functions of the nucleus, endoplasmic reticulum, Golgi complex,
mitochondria, chloroplasts, peroxisomes.
Flagella and Cilia
 Flagella are few and long in relation to cell size; cilia are numerous and short.
 Flagella and cilia are used for motility, and cilia also move substances along the surface
of the cells. Different from prokaryotic flagella
The Cell Wall and Glycocalyx
 Plant cells have cell wall.
 Animal cells are surrounded by a glycocalyx, which strengthens the cell and provides a
means of attachment to other cells.
The Plasma (Cytoplasmic) Membrane
 Like the prokaryotic plasma membrane, the eukaryotic plasma membrane is a
phospholipid bilayer containing proteins.
 Eukaryotic cells can move materials across the plasma membrane by the passive
processes and by active transport used by prokaryotes and endocytosis (phagocytosis,
pinocytosis, and receptor-mediated endocytosis).
Cytoplasm
 The chemical characteristics of the cytoplasm of eukaryotic cells resemble those of the
cytoplasm of prokaryotic cells.
Ribosomes
 80S ribosomes are found in the cytoplasm or attached to the rough endoplasmic
reticulum.
Organelles
 Organelles are specialized membrane-enclosed structures in the cytoplasm of
eukaryotic cells.
 The nucleus, which contains DNA in the form of chromosomes, is the most characteristic
eukaryotic organelle.
 The nuclear envelope is connected to a system of membranes in the cytoplasm called
the endoplasmic reticulum (ER).

 The ER provides a surface for chemical reactions and serves as a transport network.
Protein synthesis and transport occur on the rough ER; lipid synthesis occurs on the
smooth ER.
 The Golgi complex consists of flattened sacs called cisternae. It functions in membrane
formation and protein secretion.
 Lysosomes are formed from Golgi complexes. They store digestive enzymes.
 Vacuoles are membrane-enclosed cavities derived from the Golgi complex or
endocytosis. They are usually found in plant cells that store various substances and
provide rigidity to leaves and stems.
 Mitochondria are the primary sites of ATP production. They contain 70S ribosomes and
DNA, and they multiply by binary fission.
 Chloroplasts contain chlorophyll and enzymes for photosynthesis. Like mitochondria,
they contain 70S ribosomes and DNA and multiply by binary fission.
 A variety of organic compounds are oxidized in peroxisomes. Catalase in peroxisomes
destroys H2O2.
 The centrosome consists of the pericentriolar material and centrioles. Centrioles are 9
triplet microtubules involved in formation of the mitotic spindle and microtubules.
The Evolution of Eukaryotes
• According to the endosymbiotic theory, eukaryotic cells evolved from symbiotic
prokaryotes living inside other prokaryotic cells.