Download Anatomy of a Cell

PROKARYOTES
ARCHAEA
Cells that lack peptidoglycan, tend to live in
harsh environments. Extremophiles:
a) Methanogens: produce methane as a result
of respiration
b) Halophiles: live in areas of extreme salinity
c) Thermophiles: live in extremely hot water
d) Others can survive in extremes of pH
Bacterial Cell Structure
Structure
• Cell wall
• Relative functions
• Protect cells against
osmotic shock (most
important) and physical
damage
• Cytoplasmic membrane
• Regulation of substance
transport into and out of
cells.
• Chromosome
• Contain genome.
Structure
• Plasmid
• Relative functions
• Contain supplemental
genetic information
such as resistance to
antibiotics, production
of toxins and tolerance
to toxic environment.
• Ribosome
• Take part in protein
synthesis.
• Flagella
• Movement of cells.
Structures
• Inclusion body
Relative functions
• Mineral storage of cells.
• Pili
• Attachment to host,
bacterial exchange of
genetic material.
• Endospore
• Tough, heat resistance
structure that help
bacteria survive
in adverse conditions.
Cell Wall
The cell wall of bacteria protects the cell from osmostic shock and physical
damage. In addition, it also confers rigiditiy and shape of bacterial cells.
Gram Negative:
consist of a thin layer of peptidoglycan surrounded by an outer
membrane composed of lipids, lipoproteins, and a large
molecule known as lipopolysaccharide (LPS). LPS can play a
protective role and can also act as an endotoxin, causing some
of the symptoms characteristic of gram-negative bacterial
infections; there are no teichoic acids in gram-negative cell
walls.
Gram Positive:
consist of a thick layer of peptidoglycan and large amounts of
teichoic acids
Plasma Membrane
Cytoplasmic membrane
• The cytoplasmic membrane encloses the cytoplasm. It
regulates the specific transport of substance between the
cell and the environment. The cytoplasmic membrane
contains 2 main components: lipid and protein.
• The lipid component of the bacterial cell is phospholipid
bilayer.
• Thickness: 6-8nm.
• Unit: amphipathic phospholipid, consisting of 1 phosphate
group (hydrophilic ) and unbranched fatty acid chains
(hydrophobic).
• Distribution of 2 portions: hydrophilic heads are exposed
to the external environment or the cytoplasm. The fatty
acid chains point inward, facing each other due to
hydrophobic effects (staying away from water).
Plasma Membrane
• Membrane proteins are located in various positions within
the membrane, through specific interactions with
phospholipid molecules. These proteins consist of 3 main
groups: integral proteins, outer-surface proteins and innersurface proteins. They play distinctive roles in cellular
activities.
• Integral proteins: firmly embedded in the membrane,
transport substance across the cytoplasmic membrane in 3
main mechanisms known as uniport, symport and antiport.
• Outer-surface proteins: usually in Gram-negative bacteria,
interact with periplasmic proteins in the transport of large
molecules into the cells.
• Inner-surface proteins: cooperate with other proteins in
enery yeilding reactions and also other important
cellular functions.
How Do Bacteria Store Genetic
Information?
• Genetic information in bacteria is stored in the
sequence of DNA in two forms, that is
bacterial chromosome and plasmid.
How Do Bacteria Attach To Surfaces?
Glycocalyx:
• Structure: Polysaccharide layers; can be thick and
stable like capsule or loosely attached to cell wall
like slime layer.
• Function: Assist cells in adhesion to solid surface,
and also protect pathogenic bacteria from the
attack of the host's immune system.
Encapsulated streptococci

How Do Bacteria Attach To Surfaces?
Pili:
• Structure: Short, thin,
straight, hairlike projections
form surface of some
bacteria. Composed of
protein pilin, carbohydrate
and phosphate. Pili are
usually few.
• Function: Take part in
adhesion of pathogen to
specific host tissues. Sex pili
are involved in genetic
material exchange between
mating bacterial cells.
How Do Bacteria Attach To Surfaces?
Fimbriae:
• Structure: Similar to pili, but shorter and more
abundant on the cell surface.
• Function: Adhesion of cells to surface and
formation of pellicles (biofilms) containing thin
sheets of cells on a liquid surface.
Movement of Bacteria
Motility of most bacteria is away from or toward
a stimulus.
• Chemotaxis – chemical stimuli
• Phototaxis – light stimuli
• Magnetotaxis – movement along the Earth’s
magnetic field. Occurs in bacteria that contain
magnetosomes including iron.
Structure of flagella
• Long filamentous appendages containing a filament, hook and basal
body.
• Filament: consists of protein flagellin.
• Hook: single type of protein, connects filament to the basal body.
• Basal body: contains a rod and several rings in gram-negative
bacteria. ( Gram-positive bacteria only have the inner pair of rings).
This contributes to rotation of flagella, using energy from
the activity of proton pumps.
Most bacteria can locomote to different parts of their
environment, which helps them to find new resources to
survive. This process is due to flagellum (plural, flagella)
pushing or pulling the cell through a liquid medium.
Types of Flagella distribution
• Monotrichous flagella: one flagellum, if it originates
from one end of the cell, it is called polar flagellum.
Rapid swimming caused by the rotation of flagella.
• Peritrichous flagella: flagella surround the cell.
Bundled peritrichous flagella give rise to slower
forward motion than polar flagella.
• Amphitrichous flagella: groups of flagellum at each
end of the cell.
• Lophotrichous flagella: two or more at one end.
The SLEEPING Bacteria
An endospore, a heat-resistant and non-growing
structure, can retain its viability over long periods of
time under adverse environmental conditions.
When the environment becomes more favourable,
the endospore then germinates to a vegetative cell.
The SLEEPING Bacteria
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Endospore structure
Exosporium: Outer-most layer consisting of protein.
Spore coat: Several layers of spore-specific proteins.
Cortex:
Loosely cross-linked peptidoglycan.
Core:
Core wall, cytoplasmic membrane, cytoplasm,
nucleoid, ribosomes and other cellular compartments. Additionally.
dipicolinic acid-calcium complex maintains dehydrated conditions
inside the spore and helps to stablise DNA against heat
denaturation.
Anatomy of a Cell
The differences and similarities of prokaryotic and
eukaryotic cells.
Genetic Material
Prokaryotic –
Genetic material not
enclosed within a
membrane, generally a
singular circular
chromosome
Eukaryotic –
Genetic material (DNA)
found in the nucleus as
multiple chromosomes
DNA
Prokaryotic –
Eukaryotic –
DNA is not associated with DNA is associated with
histones
chromosomal proteins
called histones and nonhistones. Histones help
coil and shorten
chromosomes
Organelles
Prokaryotic –
Lack membrane enclosed
organelles
Eukaryotic –
Most organelles are
membrane enclosed
Cell Walls
Prokaryotic –
Contain complex
polysaccharide
peptidoglycan
Eukaryotic –
Chemically simple (if
present)
Cell Division
Prokaryotic –
Generally divide by binary
fission
Eukaryotic –
Generally divide by
mitosis
(Sexual reproduction
involves meiosis)
Cell Size
Prokaryotic –
0.2 to 2.0 µm diameter
Eukaryotic –
10 to 100 µm diameter
Flagellum
Prokaryotic –
Consist of two protein
building blocks
Eukaryotic –
Are complex consisting of
multiple microtubiles
Plasma Membrane
Prokaryotic –
No carbohydrates, few
sterols
Eukaryotic –
Includes carbohydrates
and sterols as receptors