Download The Architecture of Cells

The Architecture of Cells
By Keene Folwell
Prokaryotes
-Prokaryotes are ancient, small, and simple organisms.
-Share many essential subcellular structures with eukaryotes
-Also different in numerous structural features.
-Don’t have a nucleus or other membrane–enclosed structures
-Their DNA is clustered in a region called the nucleoid.
-Generally smaller then eukaryotes
-Exist as either single-celled organisms, in chains, or in clusters
-Further grouped into 2 major domains: Eubacteria and Archaebacteria.
Cell Structures of Prokaryotes
Cell Structures of Prokaryotes
-Nucloid Region
-Cell wall
-Surface appendages
-Cytoplasm
-Ribosomes
-Plasmids
-Plasma membrane
Cell Structures of Prokaryotes
-Nucloid Region
• The cell’s DNA is stored in the nucleoid region.
• In prokaryotes, there is only a single circular DNA molecule with a few thousand
genes that are responsible for reproduction and all cellular activities.
-Cell wall
• Rigid wall outside of the plasma membrane that supports and protects the cell
from significant changes in the environment.
• The Prokaryotic cell wall is made out of peptidoglycan (a peptides and
carbohydrates mixture); different from the cellulose (major component of cell
walls in plant cells).
• The Prokaryotic cell wall is comparatively porous to allow nutrients in the
environment to enter the cell.
• Some bacteria have a capsule (a thick layer of polysaccharides firmly attached to
the cell wall).
• The capsule can also trap nutrients from the environment, and it provides
another layer of protection from the host’s immune system.
Cell Structures of Prokaryotes
-Surface Appendages
• Some prokaryotes have a distinct appendages that allow them to move about or
adhere to solid surfaces.
• These appendages consist of delicate strands of proteins and come in 2 main
forms.
1. Flagella – long, thin extensions that allow bacteria to move about freely
in aqueous environments.
2. Pili – shorter, finer appendages that surround the cells of some bacteria;
pili have no role in motility, but permit microbes to adhere to solid
surfaces.
-Cytoplasm
• A fluid-filled space where the majority of cellular activities take place.
• Activities include: Synthesis of biological molecules, Production of energy,
Processing of waste products, and reproduction.
• The fluid portion of the cytoplasm without the subcellular organelles is called
the cytosol.
Cell Structures of Prokaryotes
-Ribosomes
• Complexes of ribosomal RNA and about 3 dozen proteins found in cytoplasm.
• Each of the thousands of ribosomes found in a prokaryotic cell is a self-contained
protein factory.
-Plasmids
• Small, circular, double-stranded DNA pieces that are separate from the
chromosomal DNA found in the nucleoid region.
• Can carry foreign genes and can self replicate independent of the larger
chromosomal DNA.
• Many bacterial plasmids carry genes that benefit the survival of the host and can
move from one bacterium to another, even across species.
-Plasma membrane
• A phospholipid bilayer that serves as the border that separates the cell from it’s
external environment.
• Each layer is lined with an array of individual phospholipids composed of a
hydrophilic phosphate head “head” and two hydrophobic fatty acid “tails.”
• Serves as a semi-impermeable barrier surrounding the cell.
Cell Structures of Prokaryotes
-Plasma membrane (continued)
• Biological membranes in both prokaryotes and eukaryotes are have numerous
species of proteins embedded in the lipid bilayer.
• Serve as gates, tunnels, pumps, receptors, recognition molecules, and enzymes
that control traffic flow and signal transmission into and out of the cell and
perform important metabolic reactions.
• Since the nonpolar fatty acids cannot exist in an aqueous solution such as water,
these phospholipid molecules spontaneously orient themselves into double-layer
with fatty acid tails pointing toward each other in the interior portion of the
bilayer and phosphate heads exposed to the aqueous environment.
• These bilayered phospholipids further self-organize into round-up vesicles in an
aqueous solution and establish an internal environment that is different from the
external environment.
Eukaryotes
-Larger and more complex then Prokaryotic cells.
-Evolved much later in evolutionary history then
Prokaryotes.
-Many membrane-enclosed subcellular organelles
-Can be divided into 3 distinct structures.
1. Outer selective barrier
2. Internal membrane-bound structures
3. A fluid-filled space
Cell Structures of Eukaryotes
-Nucleus
-Golgi apparatus
-Endomembrane system
-Cytoplasm
-Ribosomes
-Rough endoplasmic reticulum
-Plasma membrane
-Lysosome
-Vesicles
-Smooth endoplasmic reticulum
-Cytoskeleton elements
-Centrioles
-Centrosomes
-Cilia & Flagella
-Mitochondria & Chloroplasts
-Central vacuoles
Cell Structures of Eukaryotes
-Mitochondria & Chloroplasts
• structures involved in transforming & harvesting energy (cellular respiration &
photosynthesis)
• Mitochondria
 the powerhouses of the cells.
 The final and most energy-productive step of metabolism take place here
to generate cellular energy in the form of ATP (adenosine triphosphate).
• Chloroplasts
 only found in plants and photosynthetic protists.
 organelles containing the pigment chlorophyll.
 Harness sunlight and turn it into the chemical energy for ATP for the
synthesis of sugar. (photosynthesis)
• Both organelles are self-sufficient and can replicate by themselves.
• Both have their own circular DNA; their own ribosomes (similar to prokaryotic
ribosomes); and they are surrounded by double membranes (2 layers of
phospholipid bilayer with the internal layer structurally similar to prokaryotic
membranes).
Cell Structures of Eukaryotes
-Nucleus
• The main difference between eukaryotes & prokaryotes
• Membrane-bound
• Stores DNA, and spreads information to the rest of the cell
• In Eukaryotes, that information is stored in genes.
• Unlike prokaryotes, most eukaryotes have more than one DNA molecule inside
their nucleus.
• Inside of the nucleus is the nucleolus, a ribosomal RNA factory.
-Rough endoplasmic reticulum (rough ER)
• Got it’s name from the ribosomes that are studded on it’s membrane and give it
a rough or rugged appearance.
• The first station in the endomembrane system after protein assembly.
-Golgi apparatus
• A.K.A. the Golgi complex, or the Golgi body
• A set of membranous sacs that receive proteins from the rough ER
• Proteins are modified, concentrated, and packaged here, then sent out.
• Highly ordered modification steps take place here.
Cell Structures of Eukaryotes
-Endomembrane system
• A system to ensure that each protein arrives at it’s intended destination
• Consists of:
 Nuclear envelope
 Endoplasmic reticulum
 Golgi apparatus
 Transport vesicles
-Cytoplasm
• The cytoplasm of eukaryotic cells is filled with a large, complex collection of
organelles, many of them enclosed in their own membranes; unlike prokaryotic
cells which have none.
• Located between the plasma membrane & the membrane-enclosed nucleus.
• Cytoskeleton & cytoplasmic streaming
-Plasma membrane
• Basically, the same as the prokaryotes with little differences.
• In eukaryotic cells, the plasma membrane consists of sterols and carbohydrates;
whereas the prokaryotic cells don’t.
• The composition of phospholipids & proteins varies greatly between eukaryotic
and prokaryotic cells
Cell Structures of Eukaryotes
-Lysosome
• The digestive organ of a cell.
• Digests food via endocytosis
• Also responsible for removing old & worn structures (autophagy{self-eating}) in
the cell to recycle molecules.
• Plant cells have the central vacuole instead of the lysosome.
-Smooth endoplasmic reticulum (sER)
• Ribosome-free
• The synthesis of lipids, steroids, & carbohydrates happen in the sER’s membrane
• Detoxifies drugs, alcohol, pesticides, & other toxins takes place.
-Centrioles
• Paired organelles within the centrosomes
• Duplicate before cell division & move to the opposite poles of the cell & serve as
anchors for spindle fibers.
• Usually found around the nucleus in animal cells only.
-Centrosomes
• Serves as the microtubule organizing center & plays an important role in cell
division.
Cell Structures of Eukaryotes
-Central vacuoles
• Found in plant cells & some protists
• Exert pressure (turgor pressure) to help support the plant cell wall & maintains
its rigidity.
• Store pigments, wastes & toxic byproducts.
• In single-celled protists, they serve a function similar to lysosome.
• Contractile vacuoles help eliminate excess water & restore the proper salt
balance in the cytoplasm.
-Ribosomes
• Made up of 70 different types of protein combined with strands of ribosomal
RNA.
• These particles are engaged in the synthesis of proteins under the instruction of
DNA.
• There are 2 types of ribosomes
1. Those free-floating in the cystol.
2. Those attached to the surface of rough endoplasmic reticulum.
Cell Structures of Eukaryotes
-Vesicles
• Small and membrane-enclosed compartments.
• Acts as the cargo trucks of the endomembrane system for the proteins.
-Cilia & Flagella
• Both are external projections of the plasma membrane that participate in cell
locomotion, adhesion, and the movement of materials on the outer surface.
• The internal structure consists of microtubules bundled in a unique fashion.
• The major difference, between cilia & flagella is that cilia has numerous small
projections from cell, while flagella usually exist as 1 or 2 large tails and propel a
cell by undulating movement.
Cell Structures of Eukaryotes
-Cytoskeleton elements
• Comprised of a set of long, thin fibers
• Found in the cytoplasm
• The muscular, skeletal, anchoring, & conveyor belt system of the cells.
• The jobs of the cytoskeletal elements include:
 Supporting & maintaining the cell’s shape.
 Facilitating the cellular movement.
 Anchoring organelles at their needed location.
 Acting as tracks for “motor proteins” that transport cargo within the cell.
 Interacting with extracellular structures that anchor the cell.
• There are 3 major types of cytoskeleton elements:
 Microtubules.
 Intermediate filaments.
 Microfilaments (aka actin filaments).
• Each of these cytoskeletal elements is made of distinct protein building blocks.
• All three cytoskeletal elements play important roles during cell division.
-Cytoskeleton elements (continued)
• Microtubules
 Largest of the 3 major types
 Act as the skeletal system of the cell
 Provides intracellular support for cells
 Serve as “monorail” tracks to transport cargo throughout the cell
 Plays a prominent role as spindle fibers during cell division.
 Other important structures arising from microtubules are the cilia & flagella.
• Intermediate filaments
 Intermediate-sized fibers.
 Responsible for stabilizing & maintaining the position of the nucleus and other
organelles in the cell by forming a “cage” around them.
 Their molecular configuration resembles the steel cables found in suspension
bridges
• Microfilaments
 The thinnest of the 3.
 A strung bead-like structure.
 Generally located around the periphery of a cell.
 Provides shape, strength, and motility to the cell.
 Depending on the cell type, they may play a key role in cell eating, drinking, and
muscle contraction.
 Also responsible for cellular activities such as amoeboid movement.
Subcellular Organelles Involved in Cell Reproduction
-Cells involved in replicating DNA
• Nucleus
• Centrosomes & microtubules
• Cell memebrane & cell wall
Life Cycle of an Organism
-Reproduction
• Necessary to avoid extinction
• Sexual and asexual reproduction
 Asexual
 Binary fission for prokaryotes
 Mitosis for eukaryotes
The Cell Cycle
Most of the time during the cell cycle the cell
prepares for mitosis, this preparation stage is called
Interphase, which can be divided into 3 phases: G1
phase, S phase, & G2 phase in that order.