This document discusses cells and their role in living organisms. It begins by explaining that organisms need to exchange nutrients through their surface area, and keeping cells small helps maintain a high surface area to volume ratio to allow for efficient nutrient exchange. It then discusses the key characteristics of prokaryotic cells, the simplest type of cell, including their lack of internal compartmentalization, circular DNA structure, rapid reproduction through binary fission, and ability to transfer genes through plasmids. The document concludes by contrasting prokaryotic and eukaryotic cells, noting key differences like prokaryotes lacking nuclei and organelles while eukaryotes have internal membrane-bound structures.

1. 16/09/2012
Cells: “Little rooms”
Cells, Prokaryotes and
Eukaryotes
A sense of Scale Why are large living things
made of small cells?
Living things (organisms) need to
exchange nutrients with the
outside world
Surface area to volume ratio is
important
Too little surface area for the
volume
Means that exchange cannot
happen fast enough to support
the whole volume.
Various mechanisms keep the
surface area to volume ratio high.
One mechanism is keeping
distinct cells in multicellular Fig 6.7
Fig. 6.2 organisms.
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The simplest organisms are of course Internal Organization and DNA
single cells
• Prokaryotic cells usually lack complex
compartmentalization
– Limited internal organization
And the simplest
Single celled organisms • Some prokaryotes do have specialized membranes
Are Prokaryotes
that perform metabolic functions
• These are usually infoldings of the plasma
membrane
– Which of course serve to increase the surface area.
Fig 6.5
© 2011 Pearson Education, Inc.
Prokaryote DNA
• Prokaryotes have
relatively few genes
• Relatively little DNA
• Usually one circular
loop
• May have a few small
extra loops called
plasmids.
Fig. 6.5
Fig 27.8
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Prokaryote reproduction Plasmids can be copied from one cell
Copy the DNA, then divide in two. to another, transfering information
Figure 27.13a-3
Bacterial
F plasmid chromosome
F cell
F cell
(donor)
Mating
bridge
F cell
(recipient)
F cell
Bacterial
chromosome
Fig 12.12
(a) Conjugation and transfer of an F plasmid
Rapid Reproduction and Mutation
• Prokaryotes reproduce by binary fission, and offspring R Plasmids and Antibiotic Resistance
cells are generally identical
• R plasmids carry genes for antibiotic resistance
• Mutation rates during binary fission are low, but because
of rapid reproduction, mutations can accumulate rapidly
• Antibiotics kill sensitive bacteria, but not bacteria
in a population with specific R plasmids
• High diversity from mutations allows for rapid evolution • Through natural selection, the fraction of bacteria
• Prokaryotes can also absorb ‘naked’ DNA from their with genes for resistance increases in a population
environment exposed to antibiotics
– Usually nothing much happens • Antibiotic‐resistant strains of bacteria are becoming
– Occasionally acquire new capabilities (e.g. Drug resistance) more common
© 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc.
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Prokaryotes vs Eukaryotes
• Their short generation time allows prokaryotes to
evolve quickly Prokaryotes Eukaryotes
– For example, adaptive evolution in a bacterial • No Nucleus • Chromosomes contained in
• Circular DNA a nucleus.
colony was documented in a lab over 8 years
• Little internal structure • Extensive internal structure
• Prokaryotes are not “primitive” but are highly
• No organelles • Specialized organelles
evolved – Mitochondrion, Chloroplast
etc
• Always unicellular, binary
• All multicellular organisms
fission
are eukaryotes.
• Hugely abundant and
• Visible, but actually make
diverse, but invisible
up only a small portion of
life on earth
© 2011 Pearson Education, Inc.
What do I mean prokaryotes are
“Life on Earth is microscopic”
diverse?
Genetically Metabolically
Fig 26.21 • Genes taken from two • All Eukaryotes have pretty
random prokaryotes will be similar metabolism
much more different than compared to prokaryotes.
• Comparable genes taken • Plants:
– Photo,Autotrophs
from two random animals.
– Generate their energy from
light, carbon from CO2
• Animals
– Heterotrophs
– Get their energy and carbon
from food.
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There are prokaryotes that...
• Get their energy from • Aerobic (use Oxygen)
inorganic chemicals • Anaerobic (cannot use
• “Breath” iron oxygen)
– Use iron as a final electron • E.g., Methanogens
acceptor in respiration “exhale” methane
– What we do with oxygen – What we do with CO2
• “Burn” iron
– Use iron as an original
electron donor in
respiration
– What we do with food.
Prokaryotes in the living world Exploring diversity of prokaryotes
• “The major biogeochemical • “Our view of the natural world [is
cycles on which we depend were changing] as radically as did our
in place three billion years ago, view of the cosmos when we
long before the appearance of began looking at it with
visible life, and are today technologies that allowed us to
maintained by the ‘invisibles’ and see more than can be seen with
their vast range of metabolisms.” the naked eye.”
• “Neglect of the invisible world is
• “The contribution of visible life to no longer any more acceptable
biodiversity is very small indeed.” than, say, teaching astronomy but
ignoring the existence of galaxies
beyond the Milky Way, or
teaching physics while refusing to
discuss anything smaller than a
Nee, 2004
pin head.”
Fig 27.15
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Until Recently Prokaryote diversity was
Gram Positive vs Gram Negative
hard to study
Fig 27.3
Fig 27.2
Categorized
By Shape..
More susceptible to those Antibiotics
More likely to be antibiotic resistant
That target the cell wall
Outer shell involved is in attachment
Exploring Prokaryotes
to other cells
• “Genetic Prospecting”
• Take a sample of (e.g.)
Soil, Mud, Water
– It will contain billions of
prokaryotes
• Purify DNA from the
sample
• Sequence the samples
• Fit them in among other
known samples
Fig 27.15
Fig 27.4
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Extreme environments Eukaryote cells are a lot bigger
• Extremely hot • Extremely salty
– An autoclave 120C and – “The Dead Sea isn’t dead
high pressure sterilizes – it just doesn’t have any
most bacteria fish.”
– “Strain 121” from a sea • Extremely acidic
floor hydrothermal vent
is just starting to get
• Solid Rock.
comfortable in those – Yes, you read that right
conditions. – Some microbes live off
chemical energy in the
pores of solid rock.
Fig 27.17
A single‐celled eukaryote related to A single‐celled Eukaryote related to
plants animals
Fig. 6.8
Fig. 6.8
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A typical cell in an Animal
A typical Plant Cell
• Bounded by a membrane
• No Cell Wall Similarities to Animal Cell:
• Linear Chromosomes in a Nucleus, endoplasmic
Nucleus bounded by reticulum, ribosomes
nuclear membrane Mitochondria
• Nucleus surrounded by
Endoplasmic reticulum Differences:
• Ribosomes
• Cytoskeleton Plasma membrane
• Various other membrane surrounded by a cell wall
bound organelles, esp: ‐ Rigid, made of cellulose
‐Mitochondrion Big central vacuole
‐Golgi Apparatus Chloroplast
‐Peroxisome/Lysosome Fig. 6.8
Fig. 6.8
Endoplasmic Reticulum
The Nucleus
Sort of the defining feature of Endo – within
Eukaryote cells. Plasmic – the cytoplasm
Reticulum – network.
Contains the DNA, which is
packaged into Chromosomes A highly folded membrane,
Keeps large amounts of DNA contiguous in places with
organized nuclear envelope
Bounded by a double Rough ER had many bounded
membrane ribosomes
(sort of like a cell within a cell)
But with pores. Outer edges ‘bleb’ off into
transport vesicles
Outer membrane contiguous
with endoplasmic reticulum
Fig. 6.9 Fig 6.11
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Ribosomes
Made primarily of RNA
Central in protein synthesis
“Read” a transcript of the
DNA code
(Details in genetics section)
Very numerous in the cell
(NB Ribosomes are also
present in prokaryotes, but
not typically bound to Fig 6.10
membranes).
Fig 6.11
E.g. Lysosomes
Golgi Apparatus
Appears to function in a
sorting and transport Lysosomes contain digestive
capacity. enzymes
Proteins synthesized by the
ribosomes in Rough ER Therefore contained in a
Contained within vessicles vessicle where they can’t
which merge with Golgi, digest the cell itself.
May be some additional
processing (e.g. Folding into But allow digestion of food
correct shape) particles
Eventually ‘delivered’ to area Phagocytosis  food vacuole
where they are needed
Lysosome merges with
‐Made into vacuole
lysosomes/peroxisomes
Digestion takes place
‐Merge with cell membrane
Fig 6.15 (single celled eukaryotes) Fig 6.13
‐Etc.
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Two Really Important Mitochondrion
Organelles
Mitochondria – respiration
Outer membrane
Intermembrane space
Chloroplasts – Inner membrane
Photosynthesis. “Matrix” (the inside)
Inner membrane
Highly folded
There is some DNA in mitochondria
Increased surface area
Codes for a few proteins particularly important
In respiration
Some ribosomes
Fig. 6.17
Fig 9.2
Chloroplast somewhat similar Mito’s and Chloro’s as
Endosymbionts.
Surprisingly, the DNA of
mitochondria and chloroplasts is
Outer membrane more similar
Intermembrane space To the DNA of prokaryotes
Inner membrane than it is to Eukaryotes
Stroma
Thylakoid membrane Evidence that mitochondria and
Thylakoid space. chloroplasts are
Prokaryotic symbionts
Ancient symbiosis – many mito
Thylakoid highly folded – surface area and chloro genes have “migrated”
Fig 6.18 to the nucleus
DNA and Ribosomes as in Mito’s
Original symbiosis 2‐3 Billion
years ago.
Fig 6.16
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11. 16/09/2012
Prokaryotes with highly infolded
Cytoskeleton.
plasma membranes.
Actin
Structural protein
Polymer of actin
Subunits
(a polymer of polymers)
Tensive
Fig 27.7 Table 6.1
Recall Muscle Actin is important in cellular movement
Myson pulls on strands of Actin phagocytosis, cytoplasmic streaming
Fig 6.27 Fig 6.27
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Cytoskeleton. Cytoskeletin
Keratin
Microtubules
Also tensive
Rigid, resist compression
Fibrous polypeptides
Coiled together Tubulin dimers
Major anchoring
External protein structures
e.g. Hair
Table 6.1 Table 6.1
Cellular Movement
Motor proteins
A series of motor proteins
connecting two microtubules
One way organelles move
things to the right part of
the cell Move the doublets laterally
Push cellular structures into
Use Atp energy
position
e.g. chromosomes during cell
Pull the vesicle along division.
microtubule
Fig 6.21 Fig 6.25
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If the two proteins are anchored:
waving motion of cilia.
Fig 6.25 Fig 6.23
A flagellum rotates driven by Intercellular connections
a protein ‘motor’ at the base recall membrane proteins bind to things outside the cell
Fig 6.30
Fig 6.6
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Cell Connections ‐ Animals Cell Connections ‐ Plants
Cell walls are connected
Tight junctions: a series of
closely connected proteins Cells are therefore held in
(sort of like a sewn seam) place
Channels between cells Series of pores through cell
walls (technically called
Increased surface area where plasmodesmata)
absorption is important.
Fig 6.32
Fig 6.33
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