for posting-cell structure exclusive of envelope 2014

8/11/2019 For Posting-Cell Structure Exclusive of Envelope 2014

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CELL STRUCTURE

Structures exclusive of the cellenvelope

Pages 26-28, 44-51, 327-328


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The relationship between size andcomplexity


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Eukaryotic cells tend to be larger than prokaryotic cells

This is made possible by the greater

structural complexity of eukaryotic

cells compared to prokaryotes.

Chapt 3. Figure 2 Some very large prokaryotes. a)

Epulopiscium fishelsoni, 600um X 75 um. b)

Thiomargarita manibiensis, 400 X 750 um, the largest

known prokaryote.


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Eukaryotic cells are more structurally complex than prokaryotic cells

Page 10 Figures 11 & 12 Internal

structure of cellseukaryotic cell

Eukaryotic cells possess a number of membrane

bound organelles and tend to be larger than

prokaryotes:

nucleus- holds the linear DNA endomembrane system: the

building and transport system

lysosomesthe recyclers

mitochondriaproduce energy

(ATP) byrespiration. Theytransduce energy from one form to

another.

chloroplastsproduce glucose from

sunlight. They transduce energy from

one form to another.

The ribosomes of eukaryotes can be suspended in

the cytoplasm, associated with the cell membrane,

or associated with the endomembrane system.

Eukaryotes possess 80S sized ribosomes (S

stands for Svedburg Unit...it essentially

represents the size of the molecule)

Possess their

own, circular,chromosomeand theirownribosomes


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no(almost) membrane-bound

organelles

all have a nucleoidwhere they

maintain most of their DNA...which is a

circular chromosome. In addition,

sometime cells possess plasmids.

all metabolism occurs in the

cytoplasmor at the cell membrane

They possess 70S ribosomes

Page 10 Figures 11 & 12 Internal

structure of cellsprokaryotic cell

Eukaryotic cells are more structurally complex than prokaryotic cells


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Diffusion

The time required for diffusion to occur is proportional is the square

of the distance travelled.

For example, it takes about 106X longer for oxygen to

diffuse 1mm compare to 1 um.

Therefore it takes far longer for nutrients to diffuse to the

center of a large cell, and far longer for wastes to leave the

center of a large cell.

Dilution

An adequate concentration of critical intracellular materials need to

be maintained, but many important molecules are present only insmall quantities in the environment

Therefore as cell volume increases, so does dilution of

these molecules.

Consequences of size


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Ratio of membrane surface area to

volume of cytoplasm

The volume of cytoplasm dictates

metabolic need. Many important metabolic

enzymes are located on

membranes.

As a spherical cell become larger,

the volume of cytoplasm

(metabolic need) outstrips the

cells membrane surface area

(ability to meet the metabolic

need), in terms of surface area

across which needed metabolites

and wastes can diffuse in and out,

but also in terms of a site for the

attachment of important metabolic

enzymes.

Consequences of size

Page 28 Figure 3 Surface area and volume

relationships in cells. As a cell increases in size, itsS/V ration decreases.

Soin general, the ratio ofmembrane surface area tocytoplasmic volume indicates

the ability of the membrane of

a cell to meet the metabolicdemands of the cytoplasm


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Solutions to issues of size

1. remain small...like the prokaryotes, or

2. Utilize sub-cellular structures:

Membrane bound organelles add surface area for enzymes,

provide and enclosed environment that limits dilution effects and

provide separate compartments where non-compatible reactionscan occur

Possess membrane and cytoskeleton elements that speed the

transport of materials through the cytoplasm


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Many types of inclusions are suspended in the prokaryotic cytoplasm

Inclusionscan be granules of

inorganic or organic

matter....some can be bound by

a single leaflet of phospholipids

Examples of organic

inclusions: glycogen andpoly--hyroxyalkanoates

(PHA). These are used to

store energy.

Examples of inorganic

inclusions: polyphosphate(PO3-PO2-PO2-etc) used to

store energy, and magnetite

(Fe3O4the function of which

is unknown).

Page 44 Figure 26 Poly--hyroxyalkanoates

Page 45 Figure 27 Polyphosphate .


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Planktonic cyanobacteria possess gas vesicles. These are

rigid cylindrical structures made of protein that arepermeable to atmospheric gases.

These vesicles confer buoyancy thus keeping the cells

afloat in the sunlit regions of the water column. Cells

can descend by collapsing the vesicles and then float

upwards when new ones are constructed.

The prokaryotic cytoplasmic matrix may also contain gas vesicles

Page 46 Figure 30 Gas vesicles of

the cyanobacteriaAnabaena and

Microcystis.


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Flagella are used for motility

Some prokaryotes possess flagella

Page 51 Figure 38 Bacterial flagella. (a) peritrichous (b) polar (c) lophotrichous


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Archaeal flagella are about half the diameter of

Bacterial flagella.

The filament itself is a hollow rigid tube. In

Bacteria, it is composed of a single type of

protein called flagellin, whereas in Archaea

there are several types of protein involved.

eukaryotic flagellum

The structure of the prokaryotic flagellum is different than theeukaryotic flagellum

Page 53 Figure 41 Structure of a

bacterial flagellum in Gram - bacteria

l d l l ll d f l h d


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Capsules and slime layers are usually composed of polysaccharides

Capsules are very compact structures surrounding

the cell whereas slime layers arent as compact and

are less tightly attached to the cell surface

Capsules help resist phagocytosis (as seen

in Streptococcus pneumoniae), dessication,

and provide resistance to bacteriophage and

most hydrophobic toxic materials such as

detergents.

A slime layer attaches a cell to another cell or

a solid object.

In the human body they form on teeth.

They are often instrumental in the

formation of biofilms. Cells in biofilmsare often more resistant to antibiotics

than in their non-attached form.

Page 43. Figure 23 Bacterial

capsules

Fi b i d ili h i lik i f


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Fimbriaeare thin hair like processes arising from the cell that are used for

attachment, including attachment to animal tissues.

Pili are thick hollow processes that attach a bacterium to other cells.

transfer of plasmids(_____________________) between bacterial cells.

adhesion of pathogens to host tissues and the infection of the host (for

example, in the pathogens Neisseria(which causes gonorrhea and

meningitis) and Streptococcus pyogenes (which causes strep throat andscarlet fever).

Fimbriae and pili are hair-like processes serve a variety of processes,but not movement

Page 43. Figure 24 Fimbriae

Page 43. Figure 25 Pili. The pilus of anE. coli cell that is

undergoing conjugation (a form of genetic transfer) with a second

cell is better resolved because viruses have adhered to it.


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Spores


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E d t t i l


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Endospores structure is complex

Thecortexis made of.peptidoglycan. It

is thought to provide some protection

against heat and radiation

The spore coat is made of protein and it

provides much of the protection. It is

resistant to dessication, radiation, extreme

temperatures, pH, salinity and high

pressures.

The corecontains nucleic acids,

ribosomes and maybe some cytoplasm.

Also it has dipicolinic acid + Ca2+and

small acid soluble proteins (SASPS) which

is thought to stabilize the nucleic acids.SASPS are also thought to be an energy

source during the outgrowth of the spore to

a new vegetative cell. Dipicolinic acid and

SASPS comprises about 15% of the

spores weight and are not found in

vegetative cells.

Page 48 Figure 35. Structure of the

bacterial endospore. In (b) the green is a

dye that specifically stains the proteins in

the spore coat.

S f ti i i il b t i


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Spore formation is common in soil bacteria

Spore formation is common in soil bacteria such as Baci l lus and Clostr idium.

Why?

Page 50 Figure 37. Stages in endospore formation.

Endospo es ge minate to p od ce a ne egetati e cell


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Endospores can remain viable for

many, many yearsperhaps

indefinately (see the Microbial

Sidebar article on page 49 of your

text).

Endospore germination is initiated in

response to a return to appropriate

environmental conditions (e.g. sub-lethal temperatures) in the presence

of nutrients.

Calcium dipicolinate is lost from

the core and the cortex breaks

down. The core visibly swells due to

water uptake.

Germination can happen within

a matter of minutes

Vegetative cell emerging from spore coat

Endospores germinate to produce a new vegetative cell


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Prokaryotes and the evolution ofeukaryotic cells

It is thought that all cells evolved from a primitive prokaryotic cell


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What is the evidence?

It comes from the fossil record and from the actual structure of prokaryotic and

eukaryotic cells.

It is thought that all cells evolved from a primitive prokaryotic cell

Pgs. 327-328


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Cells: Eukaryotic structural highpoints


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Cells: Eukaryotic structural highpoints

Do mitochondria and chloroplasts possess

these properties?

for posting-cell structure exclusive of envelope 2014

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