Chapter
4a: Functional Anatomy of the Cell - Prokaryotes
Really concentrate on this chapter, this terminology will keep returning.
I. Comparing Prokaryotic and Eukaryotic Cells: An Overview
A. Prokaryotes
1. Nucleus is not enclosed within the membrane.
2. No histones are present with the DNA.
3. No membrane bound organelles
4. Cell walls are composed of peptidoglycan.
5. Division is accomplished through binary fission
B. Eukaryotes
1. DNA is bound in a nucleus.
2. DNA is associated with histones.
3. Membrane bound organelles are present (i.e. mitochondria)
4. Cell walls, if present, are chemically simple.
5. Division is accomplished through the process of mitosis.
II. The Size, Shape, and Arrangement of Bacterial Cells
A. Coccus (plural cocci) Spherical shaped bacteria
1. Diplococci spherical bacteria that remain joined in pairs (Neiserria)
2. Streptococci spherical bacteria that divide along one plane and remain connected in a chain (Streptococcus)
3. Tetrad spherical bacteria that divide in two planes and remain connected in an arrangement of four bacteria (Micrococcus)
4. Sarcinae spherical bacteria that divide in three planes and remain connected in a cubic formation (Sacrina)
5. Staphylococci spherical bacteria that in multiple planes and remain grouped in amorphous clusters (Staphylococcus)
B. Bacillus (plural bacilli) Rod shaped bacteria
1. Diplobacilli bacteria that appear connected after division
2. Streptobacilli bacillus that are connected as a chain
3. Coccobacilli bacilli that have a slightly rounded shape
C. Spiral Spiral shaped bacteria
1. Vibrios bacteria that look like curved rods
2. Spirilla helical shaped bacteria that are rigid
3. Spirochetes helical shaped bacteria that are flexible
D. Other Shapes
1. Star-shaped
2. Rectangular
3. Triangular
E. Monomorphic bacteria that have a single genetically determined shape
F. Pleomorphic bacteria that have multiple possible shapes
III. Structures External to the Cell Wall
A. Glycocalyx sugar coat, substances that surround the outside of the bacterial cell wall.
1. Capsule organized and firmly attached to the cell wall
2. Slime Layer unorganized and loosely attached to the cell wall
3. These layers can be composed of carbohydrates and/or polypeptides
4. Glycocalyx serve in many bacteria as a protection device, blocking the immune system from attacking them.
B. Flagella (singular flagellum) long whip-like appendages that propel bacteria
1. Terminology for flagella refers to the number present and their arrangement on the bacteria.
a. Atrichous no flagellum present
b. Monotrichous single polar flagellum
c. Amphitrichous tuft of flagella at each end of the cell
d. Lophotrichous two or more flagella at one or both ends of the cells.
e. Peritrichous flagella distributed over the entire cell
2. The basic structure of a flagellum is in three parts
a. Filament the long outermost portion forms as a helix of flagelin.
b. Hook wider base of the flagellum
c. Basal body the point of connection with the plasma membrane.
3. Motility the movement of bacteria
a. Taxis movement of bacteria towards a stimulus
b. Chemotaxis movement triggered by chemicals
c. Phototaxis movement triggered by light
C. Axial Filaments bundles of fibrils that run from the ends of the cell beneath the outer sheath and spiral around a bacteria (Treponema), that enable a corkscrew-like motion.
D. Fimbriae and Pili
1. Fimbriae (singular fimbria) tube-like structures that grow out of gram-negative bacteria. These occur in clumps or spread across the entire surface that allow for attachment of bacteria.
2. Pili (singular pilus) tube-like structures that occur in low numbers and allow for the transfer of DNA between bacterial cells.
IV. The Cell Wall
A. The cell wall is a semi-rigid structure that is responsible for the structure of a cell.
B. Composition and Characteristics
1. The cell wall is composed of a material called peptidoglycan
2. Peptidoglycan is a macromolecule composed of repeating carbohydrate attached by polypeptides.
Insert figure of peptidoglycan
3. Gram-Positive Cell Walls are composed of multiple layers of peptidoglycan that form thick, rigid structure. The wall has a complex but organized structure based on a number of components.
a. N-acetylglucosamine (NAG), a carbohydrate utilized in the backbone
b. N-acetylmuramic acid (NAM), a carbohydrate utilized in the backbone
c. NAG and NAM are cross-linked with peptide sidechains and crossbridges between NAM subunits.
d. Teichoic acid alcohol and phosphate compound, in two forms.
i. Lipoteichoic acid spans the peptidoglycan layer and links to the plasma membrane.
ii. Wall teichoic acid crosslinks layers of peptidoglycan.
4. Gram-Negative Cells Walls are composed of only a few layers of peptidoglycan that is covered by a second plasma membrane (outer membrane).
a. The peptidoglycan layer is bonded to lipoproteins in the outer layer.
b. The periplasm is the gel-like substance between the outer and inner membranes.
c. Gram-negative bacteria do not contain teichoic acids.
d. The outer membrane contains a number of modified proteins and lipids, especially lipopolysaccharides, which can be toxic.
C. Cell Walls and the Gram Stain Reaction
D. Atypical Cell Walls
1. Mycoplasma small wall-less bacteria whose membranes contain sterols.
2. Acid-Fast Cell Walls Mycobacterium and some Nocardia contain high concentrations of a waxy hydrophobic material called mycolic acid. This helps to prevent uptake by immune cells.
E. Damage to the Cell Wall
1. Cell walls are a popular target for antimicrobials, since the structure has no analogies in eukaryotes.
2. An enzyme that is naturally produced by some eukaryotic cells, lysozyme, can digest peptidogylcan.
3. Gram-positive bacterial cells without their cell wall are referred to as protoplast. Protoplasts are typically spherical and capable of continuing their metabolism.
4. Gram-negative bacterial cells have to be exposed to something to disrupt their outer membranes before they can be attacked by lysozyme, the resulting form is called a spheroplast.
5. Both protoplasts and spheroplasts are sensitive to disruption by osmotic lysis (rupturing of cells by osmotic pressure).
V. The Plasma Membrane
A. The Plasma Membrane a thin lipid bilayer than encases the cytoplasm of the cell.
B. The plasma membrane is composed of phospholipids in a lipid bilayer arrangement, where the hydrophilic heads point out and the hydrophobic tails are sequestered to the center.
C. Proteins are also part of the plasma membrane.
D. The plasma membrane is a dynamic material in which all components are capable of movement laterally through the surface; this dynamic arrangement is called the fluid mosaic model.
E. Functions
1. Selective Permeability (semipermeability) The property of allowing certain ions and molecules to pass while blocking others.
2. Nutrient breakdown
3. Energy production
F. Plasma Membranes can be disrupted by some antibiotics, especially
polymyxins.
G. Movement of Materials across Membranes
1. Passive Process does not require energy to occur
a. Simple Diffusion the net overall movement of ions or molecules from a location of high concentration to low concentration.
b. Facilitated Diffusion Diffusion that occurs through a protein called a transporter.
c. Osmosis the net movement of solvent molecules across a semipermeable membrane from an area of high concentration to that of low concentration.
i. Osmotic pressure the pressure required to prevent the movement of pure water across a semipermeable membrane.
ii. Isotonic solutes concentration is equal inside and outside a membrane
iii. Hypotonic solutes are at a lower concentration outside the cell than inside
iv. Hypertonic solutes are at a higher concentration outside the cell than inside
2. Active Processes movement across a membrane that requires energy.
a. Active Transport The cell uses ATP to pump materials against the gradient.
b. Prokaryotes possess a special type of active transport called group translocation, in which the transported substance is chemically altered so that the membrane is impermeable to the new material.
VI. Cytoplasm the substance that makes up the interior of the cell. It is mainly a gel-like material made of approximately 80% water.
VII. The Nuclear Area (Nucleoid)
A. The nucleoid of the bacterial contains a nonsequestered bacterial chromosome.
B. Bacteria also contain independent circular DNA fragments called plasmids.
VIII. Ribosomes
A. Ribosomes are the site of protein synthesis
B. Ribosomes are significantly different between eukaryotic and prokaryotic cells, allowing for selective inhibition with antibiotics.
IIX. Inclusions reserve deposits of material in the cytoplasm
A. Metachromatic Granules (Volutin) inorganic stores of phosphate present in cells that live in phosphate-rich regions.
B. Polysaccharide Granules Typically consist of glycogen or starch
C. Lipid Inclusions composed of a unique polymer in bacteria called poly-β-hydroxybutyric acid
D. Sulfur Granules Inclusions of sulfur that serve as energy reserves for sulfur bacteria.
E. Carboxysomes Inclusions that contain the enzyme ribulose 1,5- diphosphate carboxylase, a necessary enzyme for photosynthesis.
F. Gas Vacuoles inclusions made of several hundred cylindrical gas vesicles that are utilized for buoyancy.
G. Magnetosomes inclusions composed of iron oxide
IX. Endospores
A. Endospores are the dormant state that some bacteria can produce in response the adverse environmental conditions. (notably Bacillus and Clostridium)
B. Almost exclusive to gram-positive bacteria, but one gram-negative species, Coxiella burnetti, does produce a similar structure.
C. The process of endospore production is called sporulation.
D. Endospores do not undergo metabolism and have very little water.
E. The water in endospores is replaced with Calcium ions and Dipicolinic acid.
F. The process of endospores coming out of dormancy is called germination.
Chapter
4b: Functional Anatomy of the Cell - Eukaryotes
Sorry not much help here, you just have to memorize the structures and link them to their functions.
I. Structures that have analogous homologies between prokaryotes and eukaryotes.
A. Flagella and cilia
1. Unlike the prokaryotic versions, these projections are surrounded by plasma membrane and filled with cytoplasm.
2. The internal structure of the flagella and cilia are identical, the distinction is based on size and number.
a. Flagella few and longer
b. Cilia numerous and shorter
B. The cell wall and glycocalyx
1. Cell walls in eukaryotes tend to be chemically simpler than those of bacteria.
2. The glycocalyx of eukaryotic cells is composed of carbohydrates and is used for protection, cellular recognition, and attachment
C. The plasma membrane
1. Eukaryotic cells contain sterols, to increase there resistance to osmotic pressure.
2. Eukaryotes do not group translocate, instead they undergo the processes called endocytosis (the ingestion of material).
a. Phagocytosis physical engulfment of a large target with cytoplasmic extensions.
b. Pinocytosis invagination of the plasma membrane in order to take in an amount of the extracellular milieu.
c. Receptor Mediated Endocytosis congregation of receptors for specific molecules on the surface of the cell, with resultant invagination of bound receptors into coated vesicles.
D. Cytoplasm
1. The major difference between the eukaryotic and prokaryotic cytoplasm is that the eukaryotic cytoplasm contains a number of organelles that sequester functions in the cells.
2. Eukaryotic cells possess a cytoskeleton composed of protein filaments of various width and purpose.
a. The cytoskeleton maneuvers the cytoplasm through out the cell, a process called cytoplasmic streaming.
b. The three components of the cytoskeleton are the microfilaments, intermediate filaments, and microtubules.
E. Ribosomes
1. The eukaryotic ribosome is somewhat larger and denser than the prokaryotic variety.
2. Eukaryotic ribosomes come in three varieties.
a. Free ribosomes unattached to any structure.
b. Membrane bound ribosomes attached to either the endoplasmic reticulum or the nuclear membrane.
c. Polyribosome strings of 10-20 ribosomes joined together.
II. Organelles
A. Organelles Membrane bound structures of specific shape and function that are a characteristic of eukaryotic cells.
B. These structures do not have direct homologous structures in the prokaryotes.
C. Nucleus The organelle that contains almost all of the hereditary information in the cell.
1. The nucleus is surrounded by a double membrane called the nuclear membrane.
2. Transport of materials in an out of the nucleus is controlled by nuclear pores in the nuclear membrane.
3. Condensed areas of nuclear material where ribosomal RNA is being produced are called nucleoli.
4. The DNA of a cell is packaged around a number of proteins.
D. Endoplasmic Reticulum (ER) An extensive network of flattened membrane sacs called cisterns that are contiguous with the nuclear membrane.
1. Rough ER continuous with the nucleus and covered in ribosomes, this is the site of protein synthesis for secretory proteins and membrane molecules.
2. Smooth ER The site of many lipid synthesis reactions.
E. Golgi Complex The location of protein processing after the rough ER
F. Lysosomes Single membrane bound spheres that contain digestive enzymes, produced by the Golgi Complex.
G. Vacuoles A membrane bound storage space in the cytoplasm
H. Mitochondria A double membrane bound organelle responsible for cellular energy production.
1. Mitochondria replicate independent of cellular replication
2. Mitochondria possess independent circular DNA and 70S ribosomes.
I. Chloroplasts A double membrane bound organelle responsible for photosynthesis.
1. Like mitochodria, the chloroplasts replicate independent of the cell and have their own DNA and ribosomes.
2. The photosynthesis reactions are accomplished in membrane sacs called thylakoids.
J. Peroxisomes Small sacs that contain enzymes to oxidize a variety of compounds, they are produced by the division of other peroxisomes.
K. Centrosome Small organelles that serve as the base of flagella and cilia. In addition, they serve as the point of origin for the mitotic spindle.
III. The evolution of the eukaryotes
A. Endosymbiotic Theory The current theory for the evolution of eukaryotes that states that eukaryotic cells are due to large bacteria losing their cell walls and engulfing smaller bacteria that became the mitochodria and cholorplast.
B. Evidence for the Endosymbiotic Theory
1. Independent replication of Mitochondria and Chloroplasts
2. DNA studies of mitochondrial and chloroplast DNA links closer to bacteria than eukaryotes.