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Cell Structure and Function

Processes of life

Cell is the basic unit of life

Common to all living organisms to the processes of life is


Prokaryotic and Eukaryotic Cells overview


Prokaryotic characteristics

- Lack nucleus
- Lack organelles
- Are small, 1-10um in diameter
- Have a simple structure

What are 2 examples of Prokaryotes


Eukaryote characteristics

- Have nucleus
- Have internal membrane-bound organelles
- Are larger, 10-100um in diameter
- Have more complex structure

What are 5 examples of Eukaryotes


Prokaryotes (External Features)

- Flagella
- Pili
- Fimbriae
- Glycocalyx
- Cell walls
- Cytoplasmic membrane

Flagella are responsible for


Prokaryotic Cells (Flagella) can have

one,many or no flagella

Monotrichous has

1 flagella

Lophotrichous has

4 flagella

Amphitrichous has

one flagella on each end

Peritrichous has

many flagella

Prokaryotic cells (flagella) are

long structures that extend beyond cell surface

Flagella function for movement is

rotation propells bacerium through environment

Flagella function rotation is

reversible; can be counterclockwise or clockwise rotation at up to 100,000 rpm!

Flagella function bacteria move in a series of runs and tumbles

runs: movement in a single direction
tumbles: abrupt change in direction

Flagella function bacteria move in response to stimuli (taxis)

- phototaxis
- chemotaxis
- Negative taxis
- Positive taxis

phototaxis bacteria move in response to


Chemotaxis bacteria move in response to


Negative taxis bacteria move in response to stimuli


Bacteria move in response to positive taxis


Prokaryotic cells (axial filament)

are found in spirochetes (like Lyme disease)

Prokaryotic cells (axial filament)

is wrapped around the spirochete "internal flagella" which is enclosed between cytoplasmic membrane and cell wall.

Axial filament of prokaryotic cells rotation of axial filaments

causes corkscrew motion

Prokaryotic Cells

fimbriae & pili

Fimbriae is

- sticky, bristle-like projections
- shorter than flagella
- use by bacteria to adhere to one another, to hosts and to surfaces in the environment.
- serve important functions in biolfilms


- rigid, tubular projection
- longer than fimbriae but shorter than flagella
- Bacteria typically only have one or two per cell
- so far only found on Gram negative bacteria
- Mediate the transfer of DNA from one cell to another

Prokaryotic Cells (glycocalyx)

Gelatinous, sticky substance surrounding the outside of the cell, prevent bacteria from drying out

Two type of glycocalyces

1) Capsule
2) Slime Layer

Capsule Glycocalyces

- firmly attached to cell surface
- May prevent bacteria from being recognized by host

Slime layer

- loosely attached to cell surface
- sticky layer allows prokaryotes to attach to surfaces

Bacterial Cell Walls Functions

- Provide structure and shape
- Protect cell from osmotic forces
- Assist some cells in attaching to other cells
- Assist some cells in resisting antimicrobial drugs
- Also, can be target of some antimicrobial drugs
- Key in distinguishing Gram + and Gram - bacteria

Bacterial shapes and arrangements

1) Cocci:
2) Bacillus
3) Spirals
4) Pleomorphic


Spherical shaped






variations in cell shape

Cocci arrangement

can be found in a single cell
1) tetrads (four)
2) chains (streptococci)
3) Group (staphylococci)
4) Sarcina (cuboidal)

Bacilli arrangement

1) single
2) chains (streptobacilli)

Spiral arrangements

curved forms of spirillum/spirochete

Coccus arrangement

diplococci - 2 cocci
tetrad : 4 packets
streptococci: chains
Sarcinae: packets of 8, 16,32 cells
Micrococci and staphylococci : large cocci in irregular clusters


round rods shaped (hard to tell if round or circular)

mycobactria is a


Sporte-forming rods


Streptomycetes (moldlike filamentous bacteria)


Corynebacteria (palisades arrangement)



curved rods


wavy spirillum/spirochete



Bacterial Cell Wall composition is



alternating units of sugar molecules (NAM-NAG)

Two basic types of bacterial cell walls

Gram- positive
Gram - negative

Gram - positive cell walls

- relatively thick layer of peptidoglycan

What contains unique molecules called teichoic and lipotechoic acids

Gram-positive Cell Walls

What does teichoic and lipotechoic acids anchor to the cytoplasmic membrane?


What appears purple following Gram staining procedure

Gram - positive cell walls

Gram- Negative Cell Walls have a _____ layer of ___________.

thin ; peptidoglycan

What has a bilayer membrane outside the peptidoglycan?

Gram-Negative Cell Walls

What layer is closest to peptidoglycan that contains phospholipids, and proteins

Gram-Negative cell wall bilayer membrane outside the peptidoglycan.




lipopolysaccharide is protective against harsh conditions
and it offers protection against some antimicrobials

What happened if there are excess of of the LPS

dead cells release lipid A, an endotoxin which may cause fever, inflammation and shock

Gram - Negative Cell Walls appear

red/pink following Gram staining procedure

Bacterial Cytoplasmic Membranes structure

- referred to as phospholipid bilayer

phospholipid bilayer is composed of

lipids and associated proteins

Bacterial cytoplasic Membranes structure

fluid mosaic model describes current understanding of membrane structure

Bacterial Cytoplasmic membranes functions

1) Selectively permeable
2) Energy storage
3) Maintain concentration and electrical gradient
4) Passive process (move along natural concentration gradient, do not require energy)

Selectively permeable

- naturally impermeable to most substances
- protein allow substances to cross membrane

Energy storage

- Cellular respiration
- Photosynthesis

Maintain concentration and electrical gradient of bacterial cytoplasmic membranes function

- chemical gradient: maintain different concentrations of chemicals inside and outside cell
- Electrical gradient: Interior of cell negatively charged

Passive process function of bacterial cytoplasmic membranes

1) Diffusion
2) Facilitated diffusion
3) Osmosis

Diffusion is a passive process

movement of molecules from areas of high concentration to low concentration

Facilitated diffusion is a passive process

diffusion, but requires the aid of proteins to cross the phospholipid bilayer

Osmosis is a passive process of bacterial cytoplasmic membranes function

diffusion of water across a selectively permeable membrane


through the phospholipid bilayer

faciliated diffusion

through a nonspecific channell protein

Facilitated diffusion

through a permease specific for one chemical; binding of substrate causes shape change in channel protein


the diffusion of water through a specific channel protein or through a phospholipid bilayer


semipermeable membrane allows movement of water, but not of solutes

Osmosis Tonicity:

comparison of the concentrations of two solutions on either side of selectively permeable membrane

Tonicity can be



when uneven, the solution with the higher concentration


when uneven, the solution with the lower concentration


same concentration on the both sides of a membrane

Effects of solutions on cells

cells without a wall (e.g., mycoplasmas, animal cells)

Effects of solutions on cells with a wall

e.g., plants, fungal and bacterial cells

Prokaryotic Cytoplasmic Membranes Function of Active processes

Active transport
Group translocation

Active transport:

movement of molecules against the concentration gradient, requires membrane proteins and energy

Group translocation

substance chemically modified during transport, modified substance is trapped inside cell, occurs only in bacteria

Internal Structures of Prokaryotes

1) cytoplasm
2) Nucleoid
3) inclusions (granules)

cytoplasm of prokaryotes internal structures

- mostly water (70 - 80%)

Cytoplasm of prokaryotes internal structures

sugars, amino acids, salts

cytoplasm of prokaryotes internal structures

DNA, ribosomes, granules, actin

Nucleoid internal structures of Prokaryotes

Region in cytoplasm containing DNA

Inclusions (granules) internal structures of Prokaryotes

Diagnostic for several pathogenic bacteria (Chlamydia)
May include reserve deposits of lipids, starch and other chemicals

Endospores are

uniques structures produced by some bacteria that are a defensive strategy against unfavorable conditions

Endospores are extremely resistant to

drying, heat, radiation, boiling, chemicals (bleach & alcohol)

Examples of endospores

Clostridium, Anthrax, Tetanus

Endospores vegetative cell

bacteria capable of replicating, one vegetative cell becomes one endospore

Internal structures of Prokaryotes are

nonmembranous organelles suchas ribosomes & cytoskeleton

Ribosome are internal structures of prokaryotes cells that are nonmembranous organelles

-sites of protein synthesis
-target of antimicrobials

Cytoskeleton internal structure of prokaryotes of nonmembranous organelle

plays a role in forming the cell's basic shape

Classification systems in prokaryotes

Taxonomic scheme
Diagnostic scheme

Taxonomic Scheme classification system in prokaryotes

Bergey's Manual of Determinative Bacteriology divides prokaryotes into 4 groups

What are Bergey's Manual of Determinative Bacteriology divides prokaryotes:

1) Firmicutes
2) Gracilicutes
3) Tenericutes
4) Mendosicutes


Gram postitive


Gram negative


No cell wall



Diagnostic Scheme

more informal, based on easily accessibley morphology and physiology

What are the Diagnostic Scheme physiology

Gram stain
oxygen usage

Pathogenic Prokaryotes

human pathogeic prokaryotes with be addressed in section 4

Free-living Non Pathogenic bacteria

photosynthetic bacteria

photosynthetic bacteria

independent cells that can use energy from sunlight to convert inorganic molecules to necessary nutrients

Two major groupos of free-living Non Pathogenic Bacteria

Grenn and purple sulfur bacteria

Cyanobacteria (previously known as

blue-grenn algae


- internal membrane adaptations resemble thylakoids
- contain gas inclusions, allows them to float on surface of water
- provide oxygen to environment
- nitrogen fixators

Green and purple sulfur bacteria

-anaerobic, found deeper in water supplies
- Use sulfur compounds in metabolism, do not give off oxygen

Free-living Non Pathogenic bacteria

nitrogen fixing bacteria

nitrogen fixing bacteria

- most are soil-dwelling microbes with a synergistic relationship with plants

nitrogen fixing bacteria

capable of converting atmospheric nitrogen into compounds usable by plants

Nitrogen fixing bacteria of free-living non-pathogenic bacteria

fixed nitrogen compounds then can be used by other organisms or recycled into soil by dying plants (green fertilizer)

Survey of Archaes


What is the most primitive of all life forms

Mendosicutes (Archaea)


require extreme conditons to survive (Mendosicutes)

Fetures unique to Archaea

- lack true peptidoglycan
- cell membrane lipids have branced hydrocarbon chains
- different rRNA sequence

Reproduce by binary fission, budding or fragmentation


Most are cocci, bacilli or spiral forms

Archaea (Mendosicutes)

Are Archaea known to cause disease


Thermophiles, halophiles, and methanogens

Archaea (Mendosicutes)


Thrive at hotter temperatures

Thermophiles (Survey of Archaea)

DNA<RNA, cytoplasmic membranes, and proteins do not function properly below 45 degress ( 113F)


require temperatures over 80C

Hot acidic spirings in deep ocean, volcanic habitats

thermophiles (Survey of Archaea)


- thrive at cooler temperature
- Make up 1/3 of prokaryotic biomass of Antarctic waters

Halophiles (survey of Archaea)

- Inhabit extremely salty habitats
- Depend on greater than 9% NaCl to maintain cell walls (some grow in 36% salt!)

What contain red or orange pigments used to synthesize ATP in presence of light?

Halophiles (Survey of Archaea)

Dead Sea, salted fish, solar evaporation ponds

halophiles (Survey of Archaea)

Methanogens (Survey of Archaea)

largest group of archaea


convert coarbon dioxide, hydrogen gas, and organic acids to methane gas

Methanogens (survey of Archaea)

convert orgainc wastes in pond, lake, ocean sediments and sewage treatment plants to methane

Some live in colons of animals


Primary source of environmental methane

colons of animales (methanogens)

Have produced ~10 trillion tons of methane (twice that of oil, natural gas and coal combined) which

is buried in mud on ocean floor

Methan is a

green-house gas (methanogens) - Survey of Archaea


A protkaryote ingested some aerobic baceria.
The aerobes were prtected and produced energy for the prokaryote (aerobic bacteria)


over a long time, the aerobes become mitochondria, no longer able to live on their own ( mitochondria)

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