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Chapter 7
Cell Structure &
Function
Scientists &
Discoveries
• Early 1600’s (Holland): 1st
microscope was constructed
• Anton van Leeuwenhoek (1600’s) used
single lens as a microscope to study and very
carefully draw tiny living organisms
• (1665) English physicist Robert Hooke used
light microscope to study thin slices of plantssaw cork had many tiny chambers he called
“cells” like monastery cells
• cells= the basic units for all
forms of life
• (1838) Matthias Schleiden concluded all plants made of
cells
• (1839) Theodor Schwann animals made of cells
• (1855) Rudolf Virchow -studied
cell reproduction; 5yrs research
concluded with: “Where a cell
exists, there must have been a
preexisting cell…”
The Cell Theory
• All living things are
composed of cells
• Cells are the basic
units of structure
and function in
living things
• New cells are
created from
existing cells.
Basic Cell Structures
• Cells usually measure 5-50 micrometers
• Smallest: measures 0.2 micrometers
• Largest: (amoeba Chaos chaos) 1000
micrometers
• All cells have a cell membrane and
cytoplasm
• Cell membrane: thin flexible barrier
around a cell
• Cytoplasm: material inside the cell
membrane
• Many cells also have cell wall (strong layer
around cell membrane)
• Cell membranes & cell walls support &
protect cells while allowing them to interact
with their environment
• Some cells also have a nucleus (a large
structure that stores the cells genetic
information & controls the cells activities)
Prokaryotes vs. Eukaryotes
• Cells are divided into 2 categories:
1. Prokaryotes
2. Eukaryotes
*divided into these 2 categories to separate
cells that contain a nucleus and
organelles (eukaryotes) and those that
do not (prokaryotes)
Prokaryotes
• Usually smaller & simpler
than eukaryotes
• Contain cell membranes
& cytoplasm
• DO NOT have nuclei
• All bacteria are prokaryotes
- examples: Escherichia coli (intestines),
Staphylococcus aureus (skin infections)
Prokaryotes
• Carry out all
activities that
define life
(grow,
reproduce,
respond to
their
environment, &
some even
move)
Eukaryotes
• CONTAIN nuclei, cell membrane,
cytoplasm, & dozens of other specialized
structures that perform special functions
(organelles)
• Some are single celled organisms, but
most make up multicellular organisms
• All plants, animals, fungi, and many
microorganisms are eukaryotes
Eukaryotes
Section 2: Cell Structures
• A. Cytoplasm- refers to
the region outside the
nucleus but inside the cell
membrane
B. Cell Membrane
• Also called the plasma
membrane
• Bi-layer phospholipids
that regulates what enters
and leaves the cell
C. Cell Wall
*main function=provide support & protection
for the cell
*located outside cell membrane
*found in plants and algae & nearly all
eukaryotes (not animal cells)
• In plants the cell wall is
composed of cellulose
• In fungi the cell wall contains
chitin
• In bacteria it contains peptidoglycan
C. Nucleus
*controls most of the cell
processes & contains
hereditary information
of DNA
*chromatin-granular
material in the nucleus
that consists of DNA
bound to protein
*chromosomescondensed chromatin
that consists of genetic
information that is to
be passed on during
cell division
(Nucleus contd.)
*Nucleolus-small ,
dense region where
assembly of
ribosomes begins
*Nuclear envelopedouble-membrane
layer that surrounds
the nucleus. It
contains many
nuclear pores that
allow material to
move in/out of the
nucleus
D. Cytoskeleton
*network of protein
filaments that help
the cell to maintain
its shape, also
involved in cell
movement
*microtubules-hollow tubes of protein, can serve
as “tracks” along which organelles move
*microfilaments-long, thin fibers that function in
the movement & support of cells
E. Organelles in the cytoplasm
Ribosomes -small particles made of RNA &
protein
-produce proteins following coded
instructions from the nucleus
Endoplasmic Reticulum (ER)- organelle in
which components of the cell membrane
are assembled & some proteins
are modified (rough
E.R.-have ribosomes
attached to the surface)
Golgi Apparatus-enzymes in the
Golgi Apparatus attach
carbohydrates & lipids to proteins
Lysosomes-small organelles filled
with enzymes that break down lipids,
carbohydrates, & proteins
from food into particles
that can be used by the
rest of the cell (also break
down organelles)
Vacuoles- sac-like structures that store
materials like water, salts, proteins &
carbohydrates
Chloroplast-found in plants
-use energy from sunlight to make
energy rich molecules in a process
known as photosynthesis
-have a double membrane
Mitochondria- use energy from food to make
high energy compounds that the cell can
use to power growth, development, &
movement
-have a double
membrane
-found in nearly all
eukaryotic cells
F. Organelle DNA
• Chloroplasts and mitochondria contain
some of their own genetic information in
the form of DNA
• These small DNA molecules contain
information that is essential for them to
function
• Could be prokaryotic cells that were
engulfed by eukaryotic cells & formed a
symbiotic relationship
CENTRIOLES
Appear during cell
division to guide
chromosomes apart
Made up of microtubules
Only seen in animal cells
CENTRIOLES/MITOTIC SPINDLE
Made of MICROTUBULES (Tubulin)
Image from: http://www.coleharbourhigh.ednet.ns.ca/library/organelle_worksheet.htm
FLAGELLA & CILIA
Made of
PROTEINS
called
MICROTUBULES
(9 + 2 arrangement)
Image from: http://www.stchs.org/science/courses/sbioa/metenergy/flagella.jpg
FLAGELLA
Help in cell
movement
Very few
and long in
length
CILIA
Animation from: http://web.jjay.cuny.edu/~acarpi/NSC/13-cells.htm
Move cell itself
And substances
past the cell.
Very many and
short in length
Section 3: Movement through the
Membrane
• The cell membrane regulates what enters &
leaves the cell & also provides protection &
support (figure 7-15)
-lipid bilayer–a double layered membrane formed
when certain kinds of lipids are dissolved in
water
-embedded proteins-forms channels & pumps that
help move materials across the membrane
-carbohydrate chains-attach to proteins & aids in
chemical identification to allow cells to ID one
another
Cell Membrane
Diffusion: tendency of molecules to move
from an area of high concentration to an
area of lower concentration to reach
equilibrium (figure 7-16)
-causes many substances to move across
the cell membrane but does not require
the cell to use energy
-concentration=mass of solute/volume of
solution
Osmosis: diffusion of water through a
selectively permeable membrane (fig 7-17)
-selectively permeable= some substances
can pass through but others cannot
-isotonic-same strength solution on both
sides
-hypertonic-above strength inside (water
leaves)
-hypotonic-below strength inside (water
enters)
• Osmosis exerts pressure known as
osmotic pressure on the hypertonic side of
the selectively permeable membrane.
-osmotic pressure can cause a cell to shrink
or burst (figure 7-18)
Facilitated Diffusion: the process of
protein channels allowing a pathway for
certain molecules to cross the membrane
(figure 7-19)
-100’s of different protein channels have
been found that allow ions, sugars & salts
to cross the membrane
Active Transport: requires energy to
move molecules across a cell membrane
against a concentration difference. The
materials move from an area of lower
concentration to an area of higher
concentration (figure 7-20)-often
compared to a pump
Endocytosis: the
process of taking large
particles into the cell by
means of infoldings or
pockets of the cell
membrane that form
vacuoles
Phagocytosis: process of taking large
particles into the cell by endocytosis.
Extensions of the cytoplasm surround &
engulf the large particles.
Exocytosis:
membrane of the
vacuole surrounding
material fuses with
the cell membrane,
forcing the contents
out of the cell
Review
1. What processes are made possible by
the cell membrane?
2. How does diffusion affect cells?
3. Describe how water moves during
osmosis.
4. What is the basic structure of a cell
membrane?
5. How does active transport differ from
diffusion?