Cells
Cell theory
 all living things are composed of cells
 all cells arises from pre-existing cells.
 Basic structural, biological , functional unit that comprise
organism.
 Smallest self-replicating life-form.
 Atomsmoleculescellstissuesorganorganorgan
systemorganism.
 Cells carry genetic information in the form of
deoxyribonucleic acid DNA.
Microscopes
Scientists use microscopes to visualize cells too small to be seen
by unaided eye.
Light microscope 
o uses visible light and a series of lenses to magnify images
(how big)
o and a resolution (how clear),
o field of view diameter is 4 mm on scanning and decreases
by a factor of 10 for each increasingly higher power.
Electron microscopes 
o uses a beam of electrons to create an image
o provides higher magnification than that of light
microscopes
o transmission electron microscope: (TEM) can see through
the image ; view internal structures(organelles).
o Scanning electron microscopes: (SEM)can see the surface
of the image
Cell fractionation (centrifugation)
Enables scientists to determine the functions of organelles
How?
 Takes cells apart and separate the major organelles from
one another
 Spins cellular contents(ultracentrifuge) and separates by
density
 Speed must be at 20k gravity to separate the nuclei
Two types of cells
Prokaryotic
Eukaryotic
Both
No nucleus
Presence of nucleus
Chromosomes
DNA is in unbound DNA in a nucleus that
region called nucleoid
is bounded by a
membranous
envelope
No membrane-bound Membrane bound
organelles
organelles
Cytoplasm bound by
the plasma
membrane
bacteria and archaea
only)
Cytoplasm in the
region between the
plasma membrane
and the nucleus
protists, fungi,
animals, plants
Cytosol
Ribosome
Plasma membrane
Carry out life
processes
Plasma membrane
Function 
 Plasma membrane are selectively permeable
 allows communication; import/export ; movement and
expansion
 outermost component of a cell
structure 
 phospholipid bilayer (heads pointing out and
hydrophilic, tails pointing inward and hydrophobic)
 cholesterol
 proteins
 filaments of cytoskeleton
The nucleus (1)
 largest organelle in the cell and is the most inner
compartment of the cell.
 contains genetic information on strands called
chromosomes.
 Contains chromatin (DNA + HISTONE )
 rRNA synthesis site: the nucleolus (rRNA+
proteins=ribosomes)
 Surrounded by the nuclear membrane/envelope.
The nuclear envelope (2)
 A double membrane (inner/outer) that maintains a
nuclear environment separate and distinct from the
cytoplasm. {continuous with the ER}
 Ribosomes bound to the outer nuclear membrane.
 Nuclear pores in the nuclear membrane allow
selective two-way exchange of material between the
cytoplasm and the nucleus.
Ribosomes
I. Ribosomes are made of rRNA + Protein
II. Molecular machines that build up proteins
III. The process conducted by ribosomes that build up
proteins is called TRANSLATION
IV. They can either be
V. “free” {floating in the cytosol} (proteins synthetized by
those ribosomes will stay IN the cell for organelles uses )
VI. Or “bound ” to the RER (rough endoplasmic reticulum)
(continuous with the nucleus ){proteins made by those
ribosomes are destined to be delivered to the cell
membrane then outside the cell}
The endomembrane system
Components ;
1. Nuclear envelope (continuous with the ER)
2. Endoplasmic reticulum
3. Golgi apparatus (connected via vesicles)
4. Lysosomes (connected via vesicles)
5. Vacuoles (connected via vesicles)
6. Plasma membrane (connected via vesicles)
The endoplasmic reticulum (ER)
 The ER is a series of interconnected membranes that are
continuous with the nuclear envelope
 The double membrane of the endoplasmic reticulum is
folded into numerous invaginations ,creating complex
structures with a central lumen
Two distinct regions of the ER ;
L
L
L
L
L
L
The smooth ER
Lacks ribosomes
Synthesizes lipids
Metabolizes carbohydrates
stores calcium
detoxifies alcohol/drugs/toxin (that’s why its more found
in liver cells )
L hydrolyzes glycogen into glucose
M
M
M
M
M
the rough ER
rich in bound ribosomes
continuous with the nuclear membrane
site of protein synthesis (glycoprotein synthesis )
the proteins are packed in transport vesicles for export
from the cell
the golgi apparatus
(have cis face for receiving and trans face for shipping)
y the golgi apparatus consists of stacked membrane-bound
sacs called cisternea.
y materials from the RER are transferred to the golgi
apparatus in vesicles
y manufactures/modifies macromolecules/products .
y after modification cellular products are repackages in
vesicles .
lysosomes
 membrane bound structures containing hydrolytic
enzymes that are capable of breaking down many
different substrates.
 Use digestive enzymes to break down food and worn out
cell parts.
 Formed by the golgi apparatus
 Low ph of about 5
 The break down ;
1. Macromelecules
2. Food vacuoles by fusing with the molecule
{phagocytosis}
3. (degrades ) worn out cells [autophagy]
4. When releasing these enzymes in the cell it results in
apoptosis degration of cellular components
Vacuoles
Large vesicles derived from the ER or golgi apparatus
a Food vacuoles ; formed by phagocytosis(engulfing of food
particles forms internal vesicle)
a Contractile vacuoles pump excess water out of protist cells
a Central vacuole hold reserves of important organic
compounds and water found in plant cells
Energy related organelles
Mitochondria and chloroplasts;
M
M
M
M
M
Do not belong to the endomembrane system
Have a double membrane
Contain their own DNA
Contain proteins synthesized by free ribosomes
Display similarities with bacteria that led to the
endosymbiont theory.(this theory tries to scientifically
explain the symbiotic relationships that led to the
evolution of membrane-bound organelles and eukaryotic
cells from once free living prokaryotic cells
Mitochondria
o
o
o
o
o
o
o
o
Known as the POWER HOUSE OF THE CELL
Have their own DNA (found in the matrix) / ribosomes .
Site of cellular respiration
Sites of changes ,chemical energy (glucose ) into another
form of chemical energy (ATP)
ATP serves as the source of energy for most cell’s process
The outer membrane serves as barrier between the
cytosol and the inner environment of the mitochondrion.
The inner membrane which is arranged into numerous
infoldings called cristae, contains the molecules and the
enzymes of the electron transport chain .
The cristae increase the surface area available for ETC
enzymes.
o the space between the inner and outer membranes is
called intermembrane space
o the space inside the inner membrane is called
mitochondrial matrix
Chloroplasts
L
L
L
L
L
L
L
L
L
site of PHOTOSYNTHESIS in plants and algae
changes light energy to chemical energy (glucose)
is considered a plastid or pigment container
contain chlorophyll
have their own DNA / ribosomes and enzymes(found in
the stroma)
2 membranes separated by a very thin intermembrane
space
The interior of a chloroplast is composed of stacks of sacklike structure known as thylakoids .
The stacks of thylakoids are known as grana
The pigments are embedded within the membrane of the
thylakoid
L The stroma is mostly water space in between the
thylakoids and outer membrane.
Peroxisomes
S Specialized metabolic compartments bounded by a single
membrane
S >50 enzymes that transfer hydrogen from many
compounds to oxygen
S Primary function the breakdown of very long FATTY acids
via oxidation
S Contain hydrogen peroxide and convert it to water ( by
catalase )
S Specialized peroxisome=glyoxysomes found in fat-storing
tissues and plant seeds
S Enzyme initiate the conversion of fatty acids to sugar
S Used as source of energy and carbon by the emerging
seedling until it can produce its own sugar by
photosynthesis.
The CYTOSKELETON
 A network of fibers
 Provides structure to the cell and helps maintain its shape
,anchor.
 Acts as a conduit to the transport of materials(motor
proteins) .
 Extends throughout the cytoplasm giving mechanical
support to the cell to maintain shape
 Very dynamic can quickly change the shape of the cell
 The components are 3;
microfilaments/microtubules/intermediate filaments .
Microtubules
Hallow tube made up of alpha and beta tubulin
molecules (dimers of tubulin)
(functions)
They maintain cell shape (compressing-resisting)
They helps with cell motility(cilia/flagella)
They aids in mitosis (chromosome movement)
They guide the movements of organelles
Centrioles
Found only in animal cells
Located near the nucleus
Found in a region of the cell called centrosome
Comprises a pair of centrioles
Structures as nine triplets of microtubules with a
hallow center .
Microtubules control the beating of cilia and flagella
,locomotor appendages of some cells .
Cilia
o Structure – membrane bound cylinders enclosing a matrix
of 9 microtubules doublets arranged in a circle around 2
central microtubules (9+2 pattern){core}; moves when
these doublets slide past one another using molecules
called dynein.
o Cilium grows from a Basal body in the cytoplasm
(9+0)arrangement
o it is covered by the plasma membrane
o function helps with locomotion of organisms or molecules
with back-and-forth motion
flagella
 structure same as cilia
 function helps with locomotion of organisms with an
undulating and (wave like propulsion )motion
 longer than cilium
how dynein “walking ”moves flagella and cilia
 dynein arms alternately grab,move,release the outer
microtubules
 protein cross-links limit sliding
 forces exerted by dynein arms cause doublets to curve
,bending the cilium or flagellum
Microtubules grows and shrinks rapidly back toward the
centrosome
o may shrink partially then recommence growing ,or may
disappear completely
o continual polymerisation and depolymerization is called
dynamic instability
o GTP hydrolysis is involved in microtubules dynamics
o GTP tightly bound to beta-tubulin, that has ability to
hydrolyse to GDP shortly after a dimer is added to growing
microtubules
o
Microfilaments
 structure/function two intertwined stands of actin and
myosin
 maintains and changes cell-shape (tension-resisting
elements )
 aids with muscle contraction -thousands of actin filaments
are arranged parallel to one another
 involved in cytoplasmic streaming (chloroplast movement)
 cell motility (pseudopodia)-cellular extension extend and
contract
 through the reversible assembly and contraction of actin
subunits into microfilaments called amoeboid movement
 cell division (cleavage furrow formation )
 microfilaments that function in cellular motility contain
the protein myosin in addition to actin
 actin utilises ATP for actin polymerisation , similar to GTP
hydrolysis in tubulin polymerisation
 ATP hydrolysis weakens the bonds in the polymer, causing
depolymerization
 Microvilli: use actin filaments to lengthen and shorten
themselves(used to move molecules in small intestine )

Intermediate filaments
Structure fibrous proteins supercoiled into thicker cables (size
between small microfilaments and large microtubules)
Function
o
o
o
o
Maintain cell shape (tension-resisting elements )
Anchors nucleus and other organelles
Aids in formation of nuclear lamina
Have different jobs depending on cell type
 Most diverse IF are the keratin filaments found in
epithelial cells
 Keratin filaments are bound to desmosomes
 Nuclear lamina is a meshwork of IF that lines the inside of
nuclear envelope
 Phosphorylation weakens bonds between Lamins to cause
disassembly
 Dephosphorylation leads to re-assembly

Extracellular matrix
The extracellular matrix consists of molecules that are secreted
by a cell into the space out of the cell membrane .
Many types of ECM : cell walls of plants / ECM of animal cells
Cell walls in plants
 ECM structure that distinguish plant cells from animal cells
 Protect the cell and maintain its shape and prevents
excessive uptake of water
 Made of cellulose fibers embedded in other
polysaccharides and proteins .
Plant cell walls may have multiple layers
o Primary cell wall: relatively thin and flexible
o Middle lamella : thin layer between primary walls of
adjacent cells that absorbs water and primary cell to
another made of pectin
o Secondary cell wall: located between the plasma
membrane and the primary cell wall in order to make it
thicker
Plasmodesmata are channels between adjacent plant cell that
permit intercellular communication
The ECM of Animal cells
Animals cells lack cell walls but are covered by a rich ecm
The ECM is made up of glycoproteins such as collagen and
fibronectin, imbedded in a network of proteoglycans
ECM proteins bind to receptor proteins in the plasma
membrane called integrins
Function of ECM :
o
o
o
o
Support
Adhesion
Movement
Regulation
Cell junction
Neighboring cells in tissues, organ or organ systems often
adhere interact and communicate through direct physical
contact
ICJ facilitate this contact
There are several types of ICJ
o
o
o
o
Plasmodesmata in plant cells
Tight junction
Desmosomes
Gap junction
Plasmodesmata in plant cells
 Channels that perforate plant cell walls
 Allow water and small solutes to pass from cell to cell
Animal cell junction
 Tight junction membrane of neighboring cells are pressed
together preventing leakage of ECM fluid
 Desmosomes anchoring junction fasten cells together into
strong sheets
 Gap junction communicating junction provide cytoplasmic
channels between adjacent cells .
The cell; a living unit greater than the sum of its parts
 Cells rely on the integration of structures and organelles in
order to function