Medical Microbiology: Chapter 3 Cell Structure and Function
I. Processes of Life
A. Growth
B. Reproduction
1. asexual
2. sexual
C. Responsiveness to environment
1. change internal/external properties
2. taxis – ability to move toward/away from environmental stimuli
D. Metabolism
1. take in nutrients
2. nutrients used for energy/structures needed to grow, reproduce, and be responsive
3. metabolic energy store in chemical bonds of ATP
E. organisms do all of these as long as conditions are suitable
II. Prokaryotic and Eukaryotic Cells: An Overview
A. Cell Theory - . Schwann, Schleiden and Virchow
1. all living things are composed of cells
2. cells are basic unit of structure and function in all living things
3. all cells come from existing cells
B. Taxa- groups of organisms based on shared characteristics
1. prokaryotes
a. characteristics
-no nucleus
-no membrane bound organelles (specialized structures that act like tiny organs to
carry on the various functions cell)
-are smaller – under 10 µm
-only bacteria
-are older (3.5 byo)
-have DNA
-have cell membrane
-have ribosomes
-have biomolecules
b. 2 domains (taxa):
-Domain Archaea
-Domain Bacteria
2. eukaryotes
a. characteristics
-nucleus
-membrane bound organelles
-larger – 100 µm
-everything but bacteria (algae, protozoa, fungi, plants, animals)
-are younger (1.5 byo)
-have DNA
-have cell membrane
-have ribosomes
-have biomolecules
b. 1 domain – Domain Eukarya
III. External Structures of Bacterial Cells
A. Function
1. response to other cells
2. response to environment
B. Glycocalyx (glycocalyces)
1. gelatinous, sticky substance – surrounds cell
2. composed of polysaccharides, polypeptides, or both
3. feature of pathogenic bacteria – makes them more virulent
4. two types
a. capsule
-firmly attached to cell surface
-thick
-bacterial colonies appear smooth, glistening, mucoid
-may prevent recognition by host
-may prevent phagocytosis by defensive cells of host
b. slime layer
-water soluble
-thinner
-more easily removed
-loosely attached
-allows attachment to surfaces
5. nonencapsulated
a. colonies appear rough
b. quickly engulfed/destroyed by wbc
c. not as virulent
C. Flagella – made of protein flagellin
1. for bacterial movement
2. structure
a. filament
-long/hollow – extends beyond cell surface/glycocalyx
-senses external wetness
-inhibits growth in dry habitats
b. hook
c. basal body
anchors filament and hook to cell wall
d. rotates
3. arrangement
a. monotrichous - one
b. peritrichous – cover surface of cell
c. polar – only at the ends
4. not present on all bacteria
5. taxis
a. receptors for light/chemicals on cell surface send signals to flagella – adjust speed and direction of rotation
b. phototaxis – response to light
c. chemotaxis – response to chemicals
d. positive/negative taxis
D. Fimbriae and Pili
1. fimbriae
a. sticky bristlelike projections
b. shorter than flagella
c. adhesion to one another/substances in environment/host
d. helps in movement
e. important function in biofilms
-slimy masses of microbes adhering to a substrate
-glycocalyces used too
2. pilus (pili)
a. special type of fimbriae
b. longer than fimbriae but shorter than flagella
c. only 1-2 per cell
d also called conjugation pilus
e. conjugation - transfer of DNA from one cell to another
IV. Bacterial Cell Walls
A. Function
1. provides structure/shape
2. protection from osmotic pressure
3. helps cells attach to other cells
4. helps with resistance to antimicrobial drugs
B. Three shapes
1. coccus - round
2. bacillus - rod
3. spiral
C. Structure of cell wall
1. peptidoglycan
a. polysaccharide
b. composed of alternating sugar molecules
-NAG (N-acetylglucosamine)
-NAM (N-acetylmuramic acid)
c. chains of NAG and NAM bonded to other chains by peptide bonds
D. Two types of bacterial cell walls
1. gram positive
2. gram negative
E. Gram positive bacterial cell walls
1. cell wall is thick layer of peptidoglycan outside of cell membrane
2. contains teichoic acids
3. negatively charged
4. periplasmic space between peptidoglycan (cell wall) and cm
a. contains water, nutrients, substances secreted by cell
b. digestive enzymes
c. proteins for transport
4. gram staining procedure
a. stain with crystal violet
b. wash with ethanol
b. cells purple
5. some bacterial cell walls have mycolic acid
a. waxy lipid
b. acid fast stain used
c. cells called acid fast bacteria
F. Gram negative bacterial cell walls
1. cell wall has 2 parts
a. inner thin layer of peptidoglycan
b. outer membrane of cell wall
-is a bilayer
-contains phospholipids, proteins, lipopolysaccharides (LPS)
-LPS has sugars and lipid A
-if lipid A accumulates in blood – could cause shock, fever, blood clotting
-is protective
-has integral proteins – porins – allows substances to move across membrane
2. periplasmic space between peptidoglycan (cell wall) and cm
3. gram staining procedure
a. stain with crystal violet
b. wash with ethanol – breaks down thin cell wall of gram negative bacteria
c. counter stain with safranin
d. cells pink
4. may be impediment to treatment of disease
V. Bacterial Cytoplasmic Membranes (plasma membrane, cell membrane)
A. Beneath glycocalyx and cell wall
B. Composition
1. phospholipids
2. associated proteins
C. Structure
1. phospholipid bilayer
a. phosphate heads – polar – hydrophilic
b. fatty acid (hydrocarbon) tails – nonpolar - hydrophobic
2. proteins in bilayer
a. integral proteins
-some penetrate both sides of bilayer
- some only half way in bilayer
b. peripheral proteins
-loosely attached to surface of bilayer on either side
c. used for recognition, enzymes, receptors, carriers, or channels
3. fluid mosaic model
D. Function
1. separates internal from external environment
2. controls movement of substances into/out of cell
a. selectively permeable
b. substances that can’ t cross
-large molecules
-ions
-molecules with electrical charge
-hydrophilic substances
c. proteins in bilayer function as pores, channels, or carriers - allow substances to cross
d. movement – passive or active
-passive – no cell energy used to move molecules across membrane
-active – uses cellular energy
3. produces molecules for energy storage
4. captures light energy in photosynthetic bacteria
5. maintains concentration gradient
a. aka chemical gradient
b. difference in concentration of a substance (chemical) on the 2 sides of a membrane
6. has electrical gradient
a. many substances with concentration gradient across cm are electrically
charged
b. creates voltage or electrical gradient across cm
c. outside of cm positive; inside of cm negative
d. negatively charged substances repelled
e. positively charged substances attracted into cells
E. Passive processes – no cell energy used
1. diffusion, facilitated diffusion, osmosis
2. diffusion
a. consider solution in terms of solutes (dissolved substances) it contains
- solutes move in/out of cell
b. movement of molecules from high to low concentration – said to move down
concentration gradient
c. no cell energy used
d. small molecules, lipid soluble molecules can move across
-O2, CO2, alcohol fatty acids can
-glucose, proteins can’t
e. size of molecule and concentration determine rate of diffusion
3. facilitated diffusion
a. consider solution in terms of solutes (dissolved substances) it contains
- solutes move in/out of cell
b. molecules move down concentration gradient
c. no cell energy used
d. electrochemical gradient provides energy
b. integral proteins act as channels or carriers
-proteins provide pathway for diffusion
-size or charge determines if can move through proteins
-some are permeases
– specific - carry only certain substrates
-have binding site – substance must fit
4. osmosis
a. consider solution in terms of solvent - water
b. diffusion of wateracross selectively permeable membrane
-cm not permeable to solutes
-only water moves down concentration
c. osmosis continues until equilibrium reached or pressure of water = to force of
osmosis
5. solutions classified according to concentration of solutes
a. isotonic, hypertonic, hypotonic
-used relative to the interior of cells (cytoplasm)
b. isotonic
– solutions on both sides of cm have same concentration of solutes
-no net gain or loss of water
c. hypertonic
– concentrations of solutions not equal
-solution on one side of cm has higher concentration of solutes - less water
d. hypotonic
-concentrations of solutions not equal
-solution on one side of cm has lower concentration of solutes - more water
e. hypotonic/hypertonic refer to concentration of solute
f. osmosis refers to movement of solvent
g. water moves from hypotonic solution to a hypertonic solution
h. cell in hypotonic solution – water moves into cell – cell swells – if cell bursts - cytolysis
i. cell in hypertonic solution – water moves out of cell – cell shrivels - crenates
j. cell in isotonic solution – water moves in/out of cell at same rate – cell maintains
its shape
F. Active processes
1. ATP (cell energy) used directly or indirectly to move molecules across cm
2. molecules moved against concentration gradient
3. active processes in bacteria
a. active transport
-integral transmembrane permease proteins used
-some are gated channels or ports – open or close as needed
-uniport protein– one substance moved across cm
-antiport protein – 2 substances moved at same time in opposite directions by same protein
-symport protein – 2 substances moved at same time in same direction by same
Protein
b. coupled transport
c. group translocation
-only in some bacteria
-substance moved across cm physically changed during transport
-cm is impermeable to altered substance
-substance either locked out or trapped inside cell
-very efficient
VI. Cytoplasm of Bacteria
A. General information
1. gelatinous material inside cell
2. fluid, elastic, aqueous
3. composed of cytosol, inclusions, ribosomes, cytoskeleton
B. Cytosol
1. composition
a. water
b. ions
c. carbohydrates
d. proteins (mostly enzymes)
e. lipids
f. minerals
g. salts
h. waste
2. prokaryotes
a. nucleoid area – where DNA found
b DNA circular
3. site of some chemical reactions
C. Inclusions
1. deposits of lipids, starch, glycogen, or cpds. containing nitrogen, phosphate, or sulfur
2. type of inclusion diagnostic for pathogenic bacteria
D. Endospores
1. spore formed within cell
a. thick membrane surrounds cell’s DNA
b. has small amt. of cytoplasm
c. very little water
2. function
a. defense against unfavorable conditions
b. resistant to drying, heat, radiation, lethal chemicals
-can withstand boiling for hours, bleach, alcohol, peroxide, 400 rad radiation (5X’s humanlethal limit)
3. barely undergo metabolism
4. germinate when conditions improve
5. can remain viable for thousands of years
6. bacteria with endospores produce deadly toxins
a. anthrax
b. tetanus
c. gangrene
d. botulism
E. Nonmembranous organelles
1. ribosomes
a. site of protein synthesis
b. made of rRNA and polypeptides
2. cytoskeleton
a. internal network of fibers
b. help with cell shape
VII. External Structures of Archaea
A. Glycocalyces
1. gelatinous/sticky
2. made of polysaccharides, polypeptides, or both
3. aid in formation of biofilms
4. function
a. helps cells adhere to one another, other types of cells, and inanimate surfaces
b. receptor and communication functions
c. protection
B. Flagella – for movement
C. Fimbriae and Hami
1. fimbriae
a. nonmotile, rodlike, sticky projections
b. anchor cells to each other and environment
2. hami – looks like grappling hook – attaches bacteria to things
VIII. Archaeal Cell Walls and Cytoplasmic Membranes
A. Cell Wall
1. composed of proteins or polysaccharides
2. no peptidoglycan
3. rod shaped or spherical
4. gram positive (purple) or gram negative (pink)
B. Cell membrane
1. lipids – no phosphate groups
2. linked to glycerol by ether linkages – strong
3. allows archaea to live in extreme environments
4. has electrochemical gradients
5. controls substances moving in/out of cell
C. Cytoplasm of Archaea
1. gel like substance
2. ribosomes
3. cytoskeleton
4. circular DNA
5. no membrane bound organelles
IX. External Structure of Eukaryotic Cells
A. Glycocalyces
1. anchor cells to each other
2. strengthens cell surface
3. protection against dehydration
4. aids in cell to cell recognition and communication
5. not in eukaryotic cells with cell walls
B. Eukaryotic Cell Walls and Cytoplasmic Membranes
1. cell wall present in fungi, algae, plants, some protozoa
2. cell wall function
a. protection
b. shape/support
3. cell wall made of polysaccharides – no peptidoglycan
a. plants – cellulose
b. fungi – cellulose, chitin, and/or glucomannan
c. algae – variety of polysaccharides/other chemicals
-depends on type of algae
4. cm
a. composition
-phospholipids
-proteins
-recognition molecules
-enzymes
-receptors
-carriers or channels for facilitated diffusion
-anchor cells together
-cholesterol – stabilizes cm
-membrane rafts/lipid rafts
-signaling
-protein sorting
-cell movement
-used by some viruses to enter cell or for viral replication
-glycolipids/glycoproteins
-intercelluar signaling
-attachment to each other
b. controls movement of substances into/out of cell
-passive processes
-diffusion, facilitated diffusion, osmosis
-active transport
-endocytosis
-Phagocytosis – brings in solid
-pinocytosis – brings in liquid
-exocytosis – reverse of endocytosis
c. amoeboid movement
X. Cytoplasm of Eukaryotes
A. Flagella
1. some have flagella
2. may be single or multiple
3. internal structures /push out cytoplasmic membrane around them
4. function
a. movement
b. positive and negative phototaxis and chemotaxis
B. Cilia
1. movement
2. shorthairlike structures
3. numerous
4. no prokaryotic cells have cilia
5. coordinated beating
6. move substances over cell(s)
C. Other nonmembranous organelles
1. ribosomes
a. in cytosol
b. attached to er
c. site of protein synthesis
2. cytoskeleton
a. internal network of fibers and tubules
b. anchors organelles
c. involved with cytoplasmic streaming
d. helps move organelles
e. help basic shape of cell
f. helps with cell contraction, endocytosis, amoeboid action
3. centrioles and centrosome
a. 2 centrioles at right angles
b. found in cytoplasm near nucleus – centrosome
c. plants, algae, most fungi – lack centrioles
d. function during mitosis, cytokinesis, and formation of cilia/flagella
D. Membranous Organelles – sequester chemical reactions within cell
1. surrounded by phospholipid bilayer
2. nucleus
a. largest organelle
b. control center
c. contains DNA
d. nucleoplasm
e. nucleoli – where RNA is made
f. chromatin – threadlike DNA
-during mitosis becomes visible as chromosomes
g. nuclear envelope
-4 phospholipid layers
h. nuclear pores
- controls what goes in/out of nucleus
2. endoplasmic reticulum
a. continuous with nuclear envelope
b. network of hollow tubes
c. transport system
d. 2 types
-rougher – ribosomes attached
-proteins produced by ribosomes inserted into lumen of RER
-proteins transported throughout cell
-smoother – no ribosomes attached
-plays role in lipid synthesis and transport
3. golgi body
a. flattened hollow sacs
b. receives, processes, packages large molecules
c. places them in secretory vesicles
d. releases them to outside
4. vesicle – sac for storage, digestion, transport
5. vacuole – sac for storage
a. plants – one large vacuole
b. animals – many small ones
6. lysosomes – “suicide sacs” of cell
a. in animal cells
b. contains enzymes
c. used during self-destruction of damaged or aged cells
d. digest nutrients
7. peroxisomes
a. contain enzymes oxidase and catalase
b. degrade toxins (free radicals and hydrogen peroxide)
c. prominent in kidney and liver cells
8. mitochondria – powerhouse of cell
a. outer membrane
b. folded inner membrane – cristae
-increases surface area
-where ATP produced
c. has ribosomes
d. has circular DNA
e. semiautonomous
– can divide independently of cell
-depends on cell for most of their proteins
9. chloroplasts
a. captures sunlight to make glucose
b. found in photosynthetic eukaryotes
c. 2 phospholipid bilayers
d. sacs in chloroplast – thylakoids
-increases surface area
e. fluid in chloroplast – stroma
f. has ribosomes
g. has DNA
h. semiautonomous –
-can divide independently of cell
-depends on cell for most of their proteins
E. Endosymbiotic Theory- for formation of eukaryotic cells
1. union between small aerobic and larger anaerobic prokaryotes
2. smaller prokaryotes became internal parasites
3. parasites lost ability to exist independently
4. larger cell became dependent on parasite for aerobic ATP production
5. aerobic prokaryotes became mitochondria
6. similar scenario for origin of chloroplasts
-from phagocytized photosynthetic prokaryotes