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Chapter 3:

Cellular Structure

1. Prokaryotic Cell Structure

2. Eukaryotic Cell Structure

1. Prokaryotic Cell Structure

A. Cell Shape

B. External Structures

C. Internal (Cytoplasmic) Structures

A. Cell Shape

Chapter Reading – pp. 322-325

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Prokaryotic Cell Shape

One convenient characteristic with which to

identify and classify prokaryotes is their

size and shape as seen in the microscope.

• the diameter of prokaryotic cells ranges from

~0.2 to 2.0 mm

• prokaryotes are essentially unicellular and more

or less maintain a constant shape (monomorphic)

• most prokaryotes have a spherical, rod-shaped

or spiral appearance though other shapes exist

as well…

Spherical Cells • spherical prokaryotes are

referred to as cocci(singular = coccus)

diplo- = found in pairs

• different kinds of cocci

exhibit characteristic

arrangements:

strepto- = found in chains

staphylo- = irregular clusters

tetrad = group of 4

sarcina = cube structure of 8

“Rod-Shaped”

Cells • rod-shaped prokaryotes

are referred to as bacilli(singular = bacillus)

• also found in various

arrangements:

diplo- = length-wise pairs

strepto- = length-wise chains”

cocco- = “rounded” bacilli

palisade = bacilli “side by side”

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Curved or Spiral Cells

vibrio = “curved rod”

spirillum = “twisted rod”

spirochete = “corkscrew

rod”

B. External Structures

Chapter Reading – pp. 59-71

Prokaryotic Cell Structures

Ribosome

Cytoplasm

Nucleoid

Glycocalyx

Cellwall Cell

membrane

Flagellum

Inclusions

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Head, whichcontainsphosphate (hydrophilic) Phospholipid

Tail (hydrophobic)

Phospholipidbilayer

Integral protein

Peripheralprotein

Integralglycoprotein

Cytoplasm

Integral proteins

true barrier between

“internal” & “external”

• phospholipid content is a bit different compared to eukaryotes

Plasma Membrane

Cytoplasm

Diffusionthrough thephospholipid bilayer

Facilitateddiffusion through a nonspecific channel protein

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

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

Extracellular fluid

Diffusion & Osmosis

Cell exterior (extracellular fluid)

Integralprotein

Protein

Cell interior (cytoplasm)

DNA

Cytoplasmic membrane

Na+

Cl–

Protein

Concentration Gradients

Different concentrations

of ions inside vs outside

the cell are set up &

maintained by :

Creates a net negative

charge inside vs outside.

• protein pumps

• active transport from

low to high conc.

• protein channels &

transport proteins

• facilitated diffusion

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Glucose N-acetylglucosamineNAG

N-acetylmuramic acidNAM

repeating disaccharidebackbone

tetrapeptide(amino acid)crossbridge

connecting chainsof amino acids

Bacterial Cell Wall

The bacterial cell wall provides structure & support:

• main component is a structure called peptidoglycan

• polypeptide-linked

chains of a repeating

disaccharide

(protects cell from

osmotic lysis!)

Cells without a wall

(e.g., mycoplasmas,

animal cells)

Cells with a wall

(e.g., plants, fungal

and bacterial cells)

H2O

H2O

H2O

H2O

H2OH2O

Cell

wall

Cell membrane

Cell

wall

Cell membrane

Isotonic

solution

Hypertonic

solution

Hypotonic

solution

Osmosis & Cell Lysis

Peptidoglycan layer of cell wall

Lipopolysaccharide

(LPS)

Outermembraneof cell wall

Cell membrane

n

O side chain(varies inlength andcomposition)

Gram-negative cell wall

Lipid A(embeddedin outermembrane)

Fatty acid

Porin

(sectioned)

Periplasmic space

Phospholipid layers

Integral

proteins

Corepolysaccharide

Porin

• thin layer of peptidoglycan

Gram-negative Cell Wall

• outer membrane containing

lipopolysaccharide (LPS)

• Lipid A (endotoxin) + polysaccharide

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Peptidoglycan layer(cell wall)

Cell membrane

Teichoic acid

Integralprotein

Lipoteichoic acid

Gram-positive cell wall

Gram-positive Cell Wall

• thick-layered peptidoglycan cell wall w/teichoic acids

• NO outer membrane

Bacterial Glycocalyx (“sugar cup”)

Outermost layer that surrounds the bacterium

• called a slime layer if loosely attached, water soluble

• called a capsule if compact, tightly attached to cell wall

• mediates

adhesion,

biofilm

formation

• protects from

dessication,

phagocytosis

Bacterial Flagellum

• basal body,

hook &

filament

• basal body

anchors

flagellum in

PM, cell wall,

rotates hook

& filament to

propel

bacterium

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Tumble

Run

Tumble

Run attractant

Flagella & Bacterial Motility Bacteria undergo taxis, i.e. movement in response to

something.

e.g., chemotaxis (movement in response to a chemical substance)

Involves random “runs” & “tumbles”:

• longer runs, less tumbles in direction of “good stuff”

(RUN = flagella rotate

counterclockwise)

(TUMBLE = clockwise)

Axial

Filament

Bundle of

endoflagella

found in

spirochetes

• anchored at one

end of cell and

rotate in unison

• rotates cell like

a “corkscrew” to

propel it forward

Fimbriae & Pili

FlagellumFimbria Conjugation pilus

Non-motile appendages that are chemically and

functionally different than flagella.

Fimbriae

• involved in adhesion

Pili (singular = pilus)

• used in conjugation

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C. Internal (Cytoplasmic) Structures

Chapter Reading – pp. 71-76

Prokaryotic Ribosomes

Ribosomes consist of 1 large and 1 small subunit.

Carry out protein synthesis (i.e., translation of mRNA).

• both subunits are made of rRNA & ribosomal proteins

• smaller, somewhat different from eukaryotic ribosomes

• specifically targeted by some antibiotics

Firstmembrane

Forespore

Vegetative cell

Cell wall

DNA aligns along

the cell’s long axis.

Cytoplasmic membrane

invaginates to form

forespore.

Cytoplasmic membrane

grows and engulfs

forespore within a

second membrane.

Vegetative cell’s DNA

disintegrates.

DNA is replicated.1

3

2

4

Cytoplasmic

membrane

DNA

Secondmembrane

Endospores When conditions

are bad, some

Gram+ bacteria

can form

endospores:

• inactive, dormant

cells enclosed in a

highly resistant

spore coat

• remain dormant until

conditions are good

(even 1000’s of yrs!)

• very resistant to

heating, freezing,

dessication

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Spore coat

Outerspore cost

Spore coat forms

around endospore.

Maturation of endospore;

completion of spore coat

and increase in resistance

to heat and chemicals by

unknown process.

Endospore released from

original cell.

A cortex of calcium and

dipicolinic acid is

deposited between

the membranes.

5

7

6

8

Cortex

Outerspore cost

Endospore

Completion of Endospore Formation

The Genetic MaterialA region called the nucleoid contains the circular

bacterial chromosome (DNA + non-histone proteins):

• usually several million

base pairs (bp) in size

e.g.the E. coli genome is

~4 mega-bp’s (4 Mbp)

• contains all bacterial

genes plus an origin

of replication (Ori)

• Ori is where DNA

replication starts,

essential to copy

the chromosome

PlasmidsSome bacteria have >1

extrachromosomal,

non-essential circular

DNA molecules called

plasmids:

• much smaller than

bacterial chromosome

• have own Ori so it is

copied when cell divides

• several kilo-base pairs

(usu. 3-6 Kb)

plasmid

map

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What’s the Role of Plasmids?Plasmids generally contain genes that confer

some sort of advantage for survival and

reproduction:

1) genes providing protection from toxic substances

2) genes enabling the metabolism of additional

sources of energy

3) genes for toxins to kill microbial competitors,

enhance pathogenicity

4) genes involved in gene transfer by conjugation

• including antibiotic resistance

Inclusions & Chromatophores

Inclusions are deposits of various materials found in

certain types of bacteria (e.g., magnetosomes).

Chromatophores are pigment-containing infoldings of

the plasma membrane in some photosynthetic bacteria.

2. Eukaryotic Cell Structure

Chapter Reading – pp. 77-86

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Eukaryotic Organelles

Nucleolus

Perinuclearspace

Cilia

Ribosomes

CytoskeletonSmooth endoplasmicreticulum

Cell membrane

Rough endoplasmicreticulum

Transportvesicles

Golgi body

Secretoryvesicle

Centriole

Mitochondrion

Lysosome

Nuclear pore

Nuclearenvelope

Nucleolus

Nucleoplasm

Chromatin

Nuclear envelope

Two phospholipidbilayers

Nuclear pores

Rough ER

Rough ER

Nucleus Storage of Genetic Material:

• DNA + histones =

Chromosomes when

condensed in M phase

Chromatin when

uncondensed

Nucleolus

• assembly of

ribosomes from

rRNA & proteins

Membrane-boundribosomes

Mitochondrion

Freeribosomes

Rough endoplasmicreticulum (RER)Smooth

endoplasmicreticulum (SER)

Endoplasmic Reticulum (ER) Rough ER (RER)

• beginning of the secretory pathway

• ribosomes on cytoplasmic face of ER membrane synthesize proteins

across ER membrane into lumen

Smooth ER (SER)

• no ribosomes

• has membrane-

associated

enzymes that

catalyze new lipid

synthesis

(also found in RER)

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Secretory vesicles

Vesiclesarriving from ER

The Golgi Complex

Proteins destined to leave ER next go to the Golgi

• transported in vesicles, next stop in “secretory pathway”

• undergo any

necessary

modifications or

processing

• then sent via vesicles

to various destinations

• e.g., plasma membrane,

exterior of cell, other

organelles

Outer membrane

Crista

Inner membrane

Ribosomes

Matrix

Mitochondrion

ATP production via cellular respiration

• Krebs cycle • e- transport • chemiosmosis

• high [H+] in the

intermembrane

space due to

e- transport

in inner membr.

*H+ gradient

fuels ATP

synthesis*

Granum

Stroma

Thylakoid

Inner bilayermembrane

Outer bilayermembrane

Chloroplast

Organelle of photosynthesis:

• “light” reactions

occur in the

thylakoids

• convert sunlight

to energy in ATP

and NADPH

• “dark” reactions

occur in stroma

• energy from ATP

& NADPH used to

make sugars from

CO2 and H2O

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Flagella & Cilia Microbial structures used for locomotion:

Flagella• long & “few”

• wave-like motion

Cilia• short & “many”

Other OrganellesLysosomes• acidic compartments for the breakdown or

“digestion” of foreign or waste material

Vacuoles• large storage compartments

Peroxisomes• metabolize fats for heat production, degrade toxins

• H2O2 byproduct is “neutralized” by catalase

Centrosomes• region containing centrioles and other proteins

• “organizing center” for mitotic spindle fibers

Key Terms for Chapter 3

• diplo-, strepto-, staphylo-, tetrad, sarcina

• glycocalyx, capsule, fimbriae, pili

• peptidoglycan, teichoic acid, LPS, endotoxin

• coccus, bacillus, vibrio, spirillum, spirochete

• chemotaxis, endospores, plasmids, nucleoid

• inclusions, chromatophores, vegetative

• periplasmic space (periplasm)

Relevant Chapter Questions MC: 1, 5, 7-10, 13-15 Matching: 1, 2

Labeling (both) SA: 1-4, 7-10, 12-16