7-1 Life is Cellular
A. The Cell Theory
The History of the Cell
1600s – Anton vonLeeuwenhoek
- the first person to use a microscope with a single, powerful lens
- observed tiny organisms in pond water (animacules)
1665 – Robert Hooke
- Observed plant tissue
- - looked at slices of cork (dead cells)
Cross Section through cork
1838 – Matthias Schleiden
- concluded that all plants are made of cells
1839 – Theodor Schwann
- concluded that all animals are made up of cells
1855 - Rudolph Virchow
- studied cell reproduction
- stated all cells come from pre-existing cells
***These discoveries were the basis for the Cell Theory
which states the following:
1.
All living things are made up of cells
2.
Cells are the basic units of structure and function
in living things.
3.
New cells come from pre-existing cells
B.
Basic Cell Structures
cells come in all sizes and shapes
range in size from 0.2 microns (bacteria) to 1000
microns (giant amoeba); most typically range between 5-50
microns (1000 micrometers = 1 mm)
- Cells have certain structures in common:
1. Cell membrane
- thin, flexible barrier around the cell
- some cells (plants) have a cell wall that
surrounds the cell membrane
- both support and protect cells while allowing them
to interact with their environment
2. nucleus
- contains the cell’s genetic material and controls
cellular activity
3. cytoplasm
- the material that lies between the nucleus and cell
membrane
- contains the organelles
C. Prokaryotes and Eukaryotes
Cells are divided into two categories:
1. Prokaryotes
- small and simple
- cell membrane and cytoplasm, but no nucleus
Ex. bacteria such as E. coli and
Staphylococcus aureus
- they grow, reproduce, and respond to changes in
their environment
- some have motility
2. Eukaryotes
- contain a membrane-bound nucleus, cell
membrane, and cytoplasm
- contain many organelles (perform special functions
in the cell)
- may be single-celled organisms or multicellular
Ex. plants, animals, fungi
7-2 Cell Structure
A.
Cell Wall
- found in plants, fungi, and all prokaryotes
(bacteria)
- lies outside the cell membrane
- provides support and protection for the cell
- allows passage of water, O2, CO2, and other
substances
- made of the carbohydrate cellulose and protein
B. Nucleus
- controls most cell processes
- contains DNA (deoxyribonucleic acid), our
hereditary material
- found in all eukaryotes (plant and animal cells)
- The DNA in the nucleus contains coded
instructions for making proteins and other important
molecules
INSIDE NUCLEUS:
1. chromatin
- DNA bound to proteins
- appears granular in the nucleus
- chromosomes are the coiled form that
chromatin takes when a cell divides
- these threadlike structures contain the genetic
information passed from one generation to
the next
2. nucleolus
- small, dense region in the nucleus
- site where ribosomes are assembled
SURROUNDING THE NUCLEUS
3. nuclear envelope (nuclear membrane)
- a double-membraned layer surrounding the
nucleus
- dotted with pores which allow movement of
materials in/out of the nucleus (RNA, ribosomes, etc.)
C. Cytoskeleton
- network of protein filaments called microtubules
and microfilaments that help maintain cell shape and that
are involved in cell movement
microtubules
- hollow tubes of protein
- maintain cell shape and serve as “tracks” along which
organelles are moved
- some form cilia (hair-like projections) and flagella on
the cell surface which produce enough force to move cells
microfilaments
- long, thin fibers (narrower than microtubules)
- produce tough, flexible network that supports the
cell
- they also move organelles within the cell
D. Organelles in the Cytoplasm
1. ribosomes
- assemble proteins from coded instructions in the
nucleus
- small particles of RNA and protein
2. endoplasmic reticulum
- internal membrane system
Two types:
a. Rough endoplasmic reticulum (RER)
- called “rough” because ribosomes coat its
surface; they chemically change the proteins as they
move from the ribosomes into the RER
- also modifies many cell membrane proteins
b. Smooth endoplasmic reticulum (SER)
- contains enzymes involved with the synthesis of
lipids
3. Golgi apparatus
- a stack of membranes that accepts proteins
made in the RER
- contains enzymes that attach carbohydrates and
lipids to newly-made proteins
4. lysosomes
- small organelles filled with enzymes
- function: breaks down lipids, carbohydrates, and
proteins from food into particles that can be used by the cell
- breaks down worn-out organelles
- removes debris from the cell
5. vacuoles
- sac-like structures that store water, salts, proteins, and
carbohydrates
- plants have 1 large, central vacuole which when filled,
help plants support its leaves and flowers
- animal cells contain smaller vacuoles some of which
are involved with transport and are called vesicles
6. chloroplasts
- found only in plants or other cells that use the
energy from sunlight to make food in the process of
photosynthesis
- not found in animal or fungal cells
- contain the green pigment called chlorophyll
7. mitochondria
- organelles that release energy from stored food
molecules and convert it to high energy compounds that
the cell can use for growth, development, movement,
etc.
- found in all eukaryotes, including plants and
algae
E. organelle DNA
- found in chloroplasts and mitochondria; they
contain their own DNA (small)
- contains information that controls the function of
both organelles
- chloroplasts and mitochondria are believed to be
ancestors of ancient prokaryotes
F. The Cell as a Factory
factory
- the way in which proteins are made in a cell is similar to the way products are made in a
Factory
Cell
Supported by concrete or
steel beams and columns
cytoskeleton
transportation system to
move parts and machines
cytoskeleton
main office to control
factory by sending out
instructions to the floor
nucleus sends out
RNA and other
information-carrying molecules
customization shop puts
finishing touches on
products before shipping
Golgi apparatus
adds CHOs and
lipids to proteins
Energy source (furnace or
solar power)
mitochondria and
chloroplasts
G.
Comparing Cells
See Fig. 7-14 pg. 183
7-3 Movement Through the
Membrane
A. Cell Membrane
Function:
regulates what enters and leaves the cell
provides support and protection
Structure:
lipid bilayer (double layered) which forms a strong barrier
between the cell and its surroundings with proteins running
through it
many proteins have attached carbohydrate chains attached
to their outer surface See Fig.7-15
Some of the proteins have channels (move substances
across cell membrane) and some have identification sites (allow
cells to identify one another)
Cell Membrane
B. Diffusion
- occurs when molecules in solution (solute) move
from an area where they are more concentrated to an
area where they are less concentrated until they reach
equilibrium
- no energy required
C. Osmosis
- the diffusion of water molecules through a
selectively permeable membrane
- water moves from an area that is highly
concentrated to an area that is less concentrated until
equilibrium is reached with concentrations on both
sides of the membrane being the same (isotonic)
hypertonic solution: one where there is more
concentrated solute than water molecules in solution
hypotonic solution: one where there is less concentrated
solute than water molecules in solution
osmotic pressure
- the pressure exerted on the hypertonic side of a
selectively permeable membrane as the result of osmosis
D. Facilitated Diffusion
- the movement of molecules across the cell
membrane but not by passing through the lipid bilayer
- they move across through protein channels of a
protein that spans the membrane
- hundreds of different membrane channels are
known that allow ions, sugars, and salts to cross
- very fast and specific
- does not require energy and is subject to the
concentration gradient of the solute at the membrane
E. Active Transport
- movement of materials from an area of low
concentration to an area of higher concentration
(against the concentration gradient)
- requires energy (ATP)
Ex. a. Na+-K+ pump
- a membrane protein that pumps Na+ ions
out of the cell and K+ ions in
b. endocytosis (receptor mediated)
- the taking of materials into the cell by enclosing
them in small pockets or inward folding of the cell
membrane
- the pockets break loose from the cell membrane
inside the cell and form vacuoles
- this method can take up cells, clumps of food, or
large molecules
Ex. Phagocytosis - the taking in of solid particles
pinocytosis – the taking in of liquid materials
c. exocytosis
- the removal of material from cells
- the opposite of endocytosis
7-4 The diversity of Cellular Life
Cells are specialized to perform certain tasks, either
alone or working with other parts of an organism
A. Unicellular organisms
- single-celled organisms that perform all of life’s
activities such as grow, respond, and reproduce
- includes both prokaryotes and eukaryotes
a. prokaryotes (bacteria)
- very adaptable living in soil, leaves, oceans, air,
and within the human body
Prokaryote (bacterial cell)
b. eukaryotes
- some types of algae (found in oceans, lakes and
streams)
- yeasts (break down complex nutrients making
them available for other organisms)
- some are colonial living in groups attached to one
another (Volvox)
B. Multicellular Organisms
- cells do not live on their own, but are
interdependent with each cell having a function that
benefits the whole organism
- cells are specialized performing particular
functions within the organism
Ex.: movement (muscle cell)
Reacts to environment (nerve cell)
– transmits information
Produces products (pancreatic cells)
Transport (red blood cells)
Specialized cells
C.
Levels of Organization
Cellstissuesorgansorgan systemorganism
1.
body
and
Cells
there is a division of labor amongst the cells of the
some cells exist because other cells obtain the food
oxygen they need
2. Tissues
- a group of similar cells that perform a particular
function
- there are 4 types of tissues:
a. muscle (smooth, cardiac, skeletal)
b. epithelial (skin, glands)
c. nervous (brain, spinal cord)
d. connective (bone, blood, cartilage, ligaments and
tendons, fat)
3. Organs
- two or more tissues working together toward a
specific goal
Ex. heart: cardiac muscle
Connective tissue
4. Organ Systems
- a group of organs working together to perform a
particular task to maintain the living organism
- there are 11 major organ systems, all
interdependent
muscular
skeletal
endocrine
integumentary
reproductive
excretory
digestive
respiratory
cardiovascular
lymphatic
nervous
Levels of Organization