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The Cell
Chapter 4
Cells
Marks the boundary between the “living
and the dead”
 Structural and functional unit of an
organism
 Smallest structure capable of performing
all of the functions necessary for life

What is a cell?

Why do we care?
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We have TRILLIONS of them!! (@65)
Every organism is composed of
one or more cells
Basic unit of structure and
function in organisms
All come from pre-existing cells
Cell Theory
Why are Cells so Small????
Large cells have far less surface for each unit of volume than do small cells
All cells…….
Have an outer plasma membrane
 Contain DNA



Enclosed within the cell somewhere
Contain cytoplasm
Plasma Membrane

All cells surrounded by a
plasma membrane
 Phospholipid bilayer
 forms spontaneously
whenever a collection
of phospholipids is
placed in water
Cytoplasm

material inside a cell
is the cytoplasm
 Everything between
the plasma
membrane and the
region of DNA
 Gives cells their
shape
 Assist in movement
of cell and
organelles
Microscopes

Compound light
microscope

Multiple lenses increase
magnifying power
Two basic kinds of cells

Prokaryotic


Nothing separates the
DNA from
internal cell parts
Eukaryotic


Contain organelle sacs
Nucleus – contains the
DNA
Eukaryotic Cells
Examples of Eukaryotic Cells:
Animal
 Plant
 Fungi
 Protozoa

Organelles

Organelles act as their own separate
“organs”

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They physically isolate chemical reactions
inside cells
Animals and plants will differ in their
organelles
Nucleus



Encloses the DNA of a
eukaryotic cell
Contains chromosomes
Functions:
 Prevents DNA from
getting entangled with
structures in the
cytoplasm
 Outer membranes act as
a boundary
Components of the nucleus
Nuclear pores
 Nuclear envelope
 Nucleolus
 Nucleoplasm
 DNA

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Chromosomes
Chromatin
Nuclear envelope

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
Double-membrane
system composed of lipid
bilayer (with pores)
Bilayers surround the
fluid part of nucleus
(nucleoplasm)
Continuous with the
endoplasmic reticulum
Nucleolus


Dense mass located
within the nucleus
Produces ribosomes
Ribosomes

Site of protein
synthesis



Occurs in the cytoplasm
Attached to the
endoplasmic reticulum
Differ between
prokaryotes and
eukaryotes

Why is this important
from a health aspect?
Endomembrane System

Helps modify proteins into final form

Lipids are assembled
Compartmentalizes the cell
 Main components:
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1.
2.
3.
4.
Nuclear envelope
Endoplasmic reticulum (ER)
Golgi body
Various vesicles (transport)
1. Nuclear envelope


Merges with the
membrane of the ER
Consists of
membranous channels
and saccules
2. Endoplasmic Reticulum



Channel that snakes
through the cytoplasm
Lipids assembled and
polypeptide chains modified
into final proteins
Can be rough or smooth


Dependant on the
attachments of ribosomes
Rough ER


Processing and
modification of proteins
Smooth ER

Synthesizes phospholipids
3. Golgi Body (Apparatus)



Series of flattened
sacs
Collects, sorts,
packages, and
distributes materials
such as proteins and
lipids
Contain enzymes
that put the finishing
touches on proteins
and lipids
4. Vesicles

Enzymes from golgi apparatus sort and
package the molecules into vesicles
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Tiny sac that moves through cytoplasm
Function in transport, storage, or digestion of
substances
Two main types:

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Lysosomes
Peroxisomes
Lysosome

A lysosome is a
membrane-enclosed sac

contains digestive
enzymes to break down:


Macromolecules
damaged organelles
Put it all together……
Organelles That Contain DNA

Eukaryotic cells contain cell-like organelles
that, besides the nucleus, also contain
DNA

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these organelles appear to have been derived
from ancient bacteria that were then
assimilated by the eukaryotic cell
they include the following organelles:

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Mitochondria
Chloroplasts
Energy-Related Organelles

organelles specialize in
converting energy to a
form that can be used
by the cell
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Chloroplasts
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Requires solar energy
Dissipates as heat
Use solar energy to
synthesize carbohydrates
Carbohydrates then
broken down in the…..
Mitochondria

Produce ATP molecules
Energy-Related Organelles

Photosynthesis

Cellular Respiration

The chemical energy of
carbohydrates is
converted at ATP
DNA in mitochondria??

mtDNA

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Inherited solely from
mother
First set of DNA to be
sequenced
Endosymbiotic theory
Helps in evolutionary
inheritance
Organelles That Contain DNA

The theory of
“endosymbiosis”

states that some
organelles evolved
from a symbiosis

one cell of a prokaryotic
species was engulfed by
and lived inside of a cell
of another species of
prokaryote
Organelles That Contain DNA

Other evidence supporting endosymbiotic theory:
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Mitochondria are about the same size as modern
bacteria
The cristae in mitochondria resemble folded membranes
in modern bacteria
Mitochondrial ribosomes are similar to modern, bacterial
ribosomes in size and structure
Mitochondria divide by fission, just like modern bacteria
Cytoskeleton – Cytoplasm



System of
interconnected fibers,
threads, and lattices in
the cytosol
Extend from nucleus to
the plasma membrane
Gives cells their shape

Assists in movement of
cell and organelles

Assemble and
disassemble as needed
The three protein fibers of the
cytoskeleton
The Cytoskeleton: Interior Framework
of the Cell

Centrioles

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complex structures
that assemble
microtubules in
animal cells and the
cells of most protists
anchor locomotory
structures

such as flagella or
cilia
The Cytoskeleton: Interior Framework
of the Cell

vacuoles

membrane-bound
storage centers

central vacuole

filled with water and
dissolved substances
Outside the Plasma Membrane

Cell walls

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
found in plants, fungi,
and many protists
comprised of different
components than
prokaryotic cell walls
function in providing
protection, maintaining
cell shape, and
preventing excessive
water loss/uptake
Outside the Plasma Membrane

Extracellular matrix (ECM)


takes the place of the cell wall
in animal cells and is
comprised by a mixture of
proteins secreted by the cell
collagen and elastin
proteins


fibronectin protein


Form a protective layer over
the cell surface
Connects the ECM to the
plasma membrane
integrins


Connected to fibronectin
Proteins that extend into the
cytoplasm of the cell
Plant Cells
Cell wall
 Central vacuole
 Chloroplasts

Fungal Cells
Mold or yeast
 Spores
 Cell wall
 Unicellular or
multicellular

Protozoa Cells
No cell wall
 Unicellular
 Motility

Prokaryotes
Archae
Bacteria
“Micro”organisms
Characteristics of Cells
Prokaryotic cells
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~1.0 µm in diameter
All are microorganisms
Unicellular
Bacteria and Archaea
no nucleus
no membrane-bound
organelles
Prokaryotes – General cell structure
Nucleoid
 Pili
 Fimbriae
 Flagella
 Cell wall
 Glycocalyx
 Ribosomes
