A cell is chemical system that is able to
maintain its structure and reproduce.
Cells are the fundamental unit of life. All
living things are cells or composed of cells.
The interior contents of cells is the
cytoplasm. The cytoplasm is isolated from
the surrounding environment by the
plasma membrane g y p.
There are two fundamentally different
forms of cells.
Prokaryotic cells - relatively simple cells -
lack nuclear membrane and many
organelles -bacteria and their relatives are
Eukaryotic cells - more complex cells - have a nucleus and many organelles - all cells of plants, animals, fungi, and protists.
Most cells are small
Prokaryotic: 1-10 µm
Eukaryotic: 10 - 100 µm
(1 µm = .001 mm)
What are the types of cells?
Blood and immune system cells
Erythrocyte (red blood cell)
Megakaryocyte (platelet precursor)
Monocyte (white blood cell )
Connective tissue macrophage (various types)
Epidermal Langerhans cell.
Osteoclast (in bone)
Dendritic cell (in lymphoid tissues)
Microglial cell (in central nervous system)
Cells and organelles.
Organelles, Macromolecules, & Atoms .
Why are cells small?
As cell size increases the volume increases much faster than the surface area.
Cells obtain nutrients, gain information
and rid waste through their plasma
As cell size increases, a cell’s ability to
exchange with its environment becomes
limited by the amount of membrane
area that is available for exchange.
Robert Hooke - 1665 - using an early
microscope viewed cork and saw many
repeating box-like structures and called
What he saw were spaces surrounded by walls that once contained living cells. Since Hooke’s first observations what is known about cells has increased greatly.
• Cells are the fundamental unit of life -
nothing less than a cell is alive.
• All organisms are constructed of and by cells.
• All cells arise from preexisting cells.
Cells contain the information necessary
for their own reproduction. No new cells
are originating spontaneously on earth today.
• Cells are the functional units of life. All
biochemical processes are carried out by cells.
• Groups of cells can be organized and
function as multicellular organisms
• Cells of multicellular organisms can
become specialized in form and function
to carry out sub-processes of the multicellular
Prokaryotic cell structure
small, with a plasma membrane surrounded by a rigid cell wall
- in many the cell wall is made of _____________ - a carbohydrate
cross-linked with polypeptides cell wall may be covered with a capsule made of polysaccharides few or no membrane enclosed spaces within the cytoplasm no nucleus - DNA is in a region called the nucleoid.
DNA is circular and naked (has no protein associated with it)
Bacteria often have flagella with a single protein core (flagellin)
that they can use to move in a rotary corkscrew like fashion.
The rotary motor of prokaryotic flagella is powered by proton flow
through the cell membrane.
Rotating structures are rare in nature.
Membrane enclosed spaces allow cell
functions to be compartmentalized
and isolated from other functions.
Prokaryotes lack membrane enclosed
spaces in their cytoplasm.
Some prokaryotes are photosynthetic.
The biochemical machinery for
trapping light energy is contained
within a highly folded plasma membrane.
Eukaryotic cell structure larger, with a typical plasma membrane - some with a cell wall.
Many _________________________ and
other interior spaces enclosed by membranes:
Nucleus, Endoplasmic reticulum, Golgi apparatus,
Mitochondria, Chloroplasts, Lysosomes,Vacuoles, Vesicles.
Cytoplasm with a cytoskeleton - protein tubules and fibers
cell wall found in plants (cellulose), fungi (chitin), some protists.
Nucleus - the largest and most obvious
membrane bound compartment -
controls cell activities contains the
nucleolus - a darkened region where
ribosomal RNA is synthesized contains
chromosomes - consist of DNA
wrapped around proteins.
Nucleus is surrounded by the nuclear
envelope - a double membrane.
Nuclear membrane has nuclear pores
that control entry and exit of materials.
Chromosome - “colored body” consists of
both DNA and protein - seen as
chromosomes when highly condensed in
preparation for cell division. At other
times the DNA and protein are threadlike
and called __________.
The most common proteins are histones.
DNA is coiled around histones in a
regular pattern that produces structures
Endoplasmic reticulum (ER) - a web-like
series of membranes within the cytoplasm
in the form of flattened sheets, sacs, tubes,
creates many membrane enclosed spaces -
spreads throughout the cytoplasm - has
connections with the outer membrane of
the nucleus and the plasma membrane
interior space is called the ______
-circulation and transport
-storage of proteins and minerals
-synthesis of lipids, carbohydrates, and proteins
-A large surface area for enzyme action.
Two types of ER - rough and smooth:
rough ER - studded with ribosomes site of synthesis of many proteins all ribosomes on rER are actively involved in protein synthesis -
smooth ER - site for synthesis of steroids
and other lipids Ca++ storage in muscles
detoxification of drugs, toxins, alcohol
(especially in liver).
The highly convoluted surface provides a
large surface area for enzymatic activities.
Many enzymes are imbedded in the
Ribosomes - protein synthetic machinery
• two subunits - large and small - each made of protein and ribosomal RNA (rRNA)
• subunits associate when they are synthesizing proteins
• protein synthesis occurs on ribosomes that are free-floating in the
cytoplasm and on ribosomes attached to ER
• rRNA is synthesized in the nucleolus
Golgi Apparatus -
a collection of membranes associated with
the ER composed of flatten sacs called ___
______concentrates and packages proteins
synthesized on the ER
The Golgi is functionally associated with the ER.
Proteins synthesized on the ER are concentrated internally and transport vesicles are budded off.
Transport vesicles fuse with the Golgi, dump their contents into the Golgi.
Golgi packages proteins in vesicles so that they may be excreted from the cell, or used within the cell.
Secretory vesicles - used for excretion - leave the Golgi and move to plasma membrane where they fuse and dump their contents outside - seen in many glands.
The Golgi Apparatus also forms lysosomes.
Lysosomes - vesicles filled with digestive
enzymes - used for intracellular digestion.
Particles can be taken into cell by phagocytosis and vesicle fused
The components of organelles can be
recycled after digestion by lysosomes.
Microbodies: Peroxisomes and
Glyoxisomes vesicles that form through
growth and division within the cytoplasm
Glyoxisomes are found in plants - contain
enzymes that convert fats into carbohydrates.
Peroxisomes - used for removing reactive compounds from the
cytoplasm - create H2O2 as a byproduct and degrade it with the enzyme catalase.
Mitochondria - cellular powerhouses - the site of much of the
energy harvest by cells have double membrane structure inner membrane folded into inward projections called cristae two spaces within the mitochondrion - the matrix and the intermembrane space.
• The site of oxygen consumption within cells
• Have their own DNA that is similar to prokaryotic DNA
• Have their own ribosomes that are
similar in construction to prokaryotic ribosomes
• Synthesize many, but not all, of their own proteins
• Mitochondria replicate by binary fission - similar to prokaryotic cell division
Chloroplasts - sites of photosynthesis - in
nearly all plants and some protists trap
light energy and convert it into chemical
energy have double membrane structure -
inner space is the stroma.
Within the stroma have a series of stacks
of flattened membrane structures called
thylakoids - the stacks are called grana.
The light energy trapping molecules of
photosynthesis are found in the membranes of
Chloroplasts have their own DNA, similar to prokaryotic DNA.
Can synthesize many of their own proteins using prokaryote-like ribosomes'
Synthesize many, but not all, of their own proteins.
Replicate through division similar to prokaryotic cell division.
Chloroplasts can take on other functions.
____________ synthesize and store starch in roots and tubers.
____________ have pigments and give fruits ripened color.
Centrioles - are part of specialized region
of the cell called the centrosome (cell
center) found in animals and most protists.
The centrioles are involved in the
production of microtubules.
Microtubules have many functions
including moving chromosomes during
cell division centriole structure - 9 triplets
of microtubules surrounding a hollow core -________________similar to the basal
body of flagella
Cytoskeleton - scaffolding of proteins that
transport materials, position and move
organelles, maintain and change cell shape,
and organize enzymes into functional associations 3 components - actin filaments, microtubules, and intermediate filaments.
All are polymers of smaller protein subunits - lengthen through addition of polymer subunits, shorten through
actin filaments - involved in cell movements and in membrane
deformations - smallest components of the cytoskeleton.
microtubules - hollow tubes made of
proteins called tubulins responsible for cell
movements and movements of organelles
within the cytoplasm, movement of
chromosomes during cell division -
largest components of the cytoskeleton.
intermediate filaments- 8 stranded protein fibers - play a role in
cell structure, anchoring organelles and in transport of materials within the cytoplasm anchor neighboring cells to each other in tissues.
Flagella and Cilia - cellular appendages can propel cells or propel materials over the cell surface cells that have flagella have few (usually 1 or 2) cells that have cilia have many - covering the surface flagella move with whip-like movements to propel the cell
cilia have a more regular stroke and groups of cilia appear to
move in unison, resulting in a wave-like motion flagella 5 to 20x longer than cilia
Structure has basal body with 9 + 0 structure of microtubules
flagellum is membrane bound with pairs of microtubules in a 9+2
Each pair of tubules has short arms of another protein - dynein -
that extend to neighboring tubules movement of the flagellum is produced by sliding of the microtubule pairs
Plant Cells have, in addition to the collection of organelles found
in other groups, a central vacuole for storage and for producing
________ pressure inside the the cell.
The central vacuole is usually filled with water and solutes. A high solute concentration draws water into the vacuole, expanding the vacuole and the cell.
Because plant cells are enclosed by a cell
wall, the expansion of the vacuole can
exert pressure on the cell without causing
the cell to burst.
Plants have cell walls made of cellulose.
During cell division plant cells build
dividing walls between the two new
cells called the cell plate. An adhesive
layer - the middle lamella - is laid down
between the new cell walls.
Cell walls can be thickened through the
addition of materials to the inside of the
primary cell wall.
Where did Eukaryotic Cells come from?
The oldest rocks with evidence of fossil
cells date to 3.5 billion years. The oldest
rocks with cells large and complex enough
to be eukaryotic date to 1.0 billion years.
For 2.5 billion years only prokaryotic cells
existed on earth.
The best hypothesis for the origin of
eukaryotic cells was proposed by Lynn
Margulis in the early 1970s. This
hypothes is now called the ___________
Eukaryotic cells appear to be the product
of a collaboration among different types
of prokaryotic cells. Some prokaryotic
cells became the host for other prokaryotic
cells that lived inside them. Some of the
complex organelles of eukaryotes provide
evidence for this theory.
Mitochondria and chloroplasts appear to
be the direct descendants of energy
producing bacteria. Mitochondria are the
descendants of bacteria that were capable
of oxidative respiration.
Chloroplasts are the descendants of
Both have their own DNA and ribosomes
that are similar to those found in
prokaryotes. Both make many of their
own proteins and both multiply in a
fashion similar to prokaryotic cell division.
Both are double membrane organelles -
the inner membrane descended from the
ancestral guest cell, and the outer
membrane descended from the vacuole
membrane that was formed around the
Other organelles may also be the product
Some centrioles and basal bodies have
naked DNA as part of their structure.
There are many modern examples of
endosymbiosis involving organisms that
can live together or live independently.
The same was probably true of the
ancestors of endosymbiotic organelles
in the distant past.