Ch 4
Tour of the Cell
Microscopic Worlds
• Microscopes led to the
discovery of the cell
– Light microscopes
–
–
–
–
Cell membrane - yes
Large macromolecules - no
Microtubules - no
Mitochondria - maybe just
barely
– Many bacteria - yes
Microscopic Worlds
• Electron scanning microscope
• Scanning electron microscope
• Transmission electron microscope
Cell Size
• House DNA, protein molecules and internal
structures
• Obtain nutrients and diffuse nutrients and O2
• Smaller cells have a greater surface area to
volume ratio than do larger cells
– Surface area is significant for diffusion and
osmosis
Surface area : Volume
10 m
30 m
30 m
Surface area
of one large cube
 5,400 m2
10 m
Total surface area
of 27 small cubes
 16,200 m2
• Volume= 30 um *30 um* 30 um=27000um
• SA (large)= 6*(30um*30um)=5,400 um
• SA (small)=(6*(10um*10um))*27=16,200 um
Domains of Life
• The 3 domains of life
– Bacteria (prokaryotic cells)
– Archaea (prokaryotic cells)
– Eukarya (all other life forms)
Cells
• Prokaryotic
• Eukaryotic
– Protists, fungi,
plants, animals
Colorized TEM 15,000 
– Bacteria & Archaea
Prokaryotic cell
Nucleoid
region
Nucleus
Eukaryotic cell
Organelles
Prokaryotic cells are simpler & usually smaller than
Eukaryotic cells
In Common
•
•
•
•
Bounded by plasma membrane
Ribosomes
Cytoplasm
DNA as genetic material
Prokaryote
• Do not have membrane
bound nucleus
• Have a cell wall outside
their plasma membrane
• Circular DNA strands
• No membrane bound
organelles
Prokaryotic
flagella
Ribosomes
Capsule
Cell wall
Plasma
membrane
Nucleoid region (DNA)
Pili
Eukaryote
Rough
endoplasmic
reticulum
Smooth endoplasmic
reticulum
Nucleus
Flagellum
Not in most
plant cells Lysosome
Centriole
Peroxisome
Microtubule
Intermediate
Cytoskeleton filament
Microfilament
Ribosomes
• Membrane
bound nucleus
• Linear DNA
• Membrane
bound organelles
Golgi
apparatus
Plasma membrane
Mitochondrion
Size of cell
Smaller
Larger
Nucleus
No nuclear membrane
True nucleus, consisting of
nuclear membrane &
nucleoli
Membrane-enclosed
organelles
Absent
Present
Cell wall
Usually present;
chemically complex
When present, chemically
simple
Plasma membrane
Present
Present
Cytoplasm
Present
Present
Ribosomes
Present
Present
Chromosome (DNA)
arrangement
Single circular
chromosome; lacks
histones
Multiple linear chromosomes
with histones
Sexual reproduction
No meiosis; transfer of
DNA fragments
through cell-to-cell
contact
Involves meiosis
Eukaryotic Cells
• A typical animal cell:
• Contains a variety of membranous organelles (underlined)
Rough
endoplasmic
reticulum
Smooth endoplasmic
reticulum
Nucleus
Flagellum
Not in most
plant cells
Lysosome
Ribosomes
Centriole
Golgi
apparatus
Peroxisome
Microtubule
Cytoskeleton
Plasma membrane
Intermediate
filament
Mitochondrion
Figure 4.4A
Microfilament
Categories of Organelles
• Manufacturing
– Nucleus, ribosomes, endoplasmic reticulum, Golgi
apparatus
• Hydrolysis
– Lysosomes (animals), vacuoles (plants),
peroxisomes
• Energy processing
– Mitochondria (animal), chloroplasts (plants)
• Structural support, movement, communication
– Cytoskeleton, plasma membrane, cell wall (plants)
Plasma Membrane
• Forms boundary
around cell
• Controls and
regulates material
transport
• Phospholipid bilayer
Nucleus
Chromatin
Nucleolus
Nucleus
Two membranes
of nuclear
envelope
Pore
Rough
endoplasmic
reticulum
Ribosomes
• Contains most of the
cells DNA
• Nucleus enclosed by
nuclear envelope
• rRNA synthesized in the
nucleolus
Ribosomes
• Synthesize proteins
• Free and bound ribosomes
• Composed of 2 subunits
Endoplasmic Reticulum
• Smooth lacks attached
ribosomes
– Processes toxins and drugs
in liver cells
– Stores and releases
calcium ions in muscle cells
Figure 4.7
Smooth ER
Rough ER
Nuclear
envelope
Smooth ER
Ribosomes
Rough ER
TEM 45,000
– Synthesis of lipids, oils,
phospholipids, and
steroids
ER
• Makes more membrane & proteins
• Rough ER has attached ribosome
– Produce proteins that are secreted,
inserted into membranes, or transport ed in
vesicles to other organelles
Fig. 4-9b
Transport vesicle
buds off
4
Ribosome
Secretory
protein
inside transport vesicle
3
Sugar
chain
1
2 Glycoprotein
Polypeptide
Rough ER
Golgi Apparatus
• Finishes, sorts, and ships cell products
– Stacks of membranous sacs receive and modify ER
products then ship them to other organelles or the
cell surface
“Receiving” side of
Golgi apparatus
Golgi apparatus
Golgi
apparatus
New vesicle
forming
“Shipping” side
of Golgi apparatus
Figure 4.9
Transport
vesicle from
the Golgi
TEM 130,000
Transport
vesicle
from ER
Lysosomes
• Digestive functions in many single celled
organisms
• In white blood cells, they destroy ingested
bacteria
• Also recycle damaged organelles
Lysosomes
Rough ER
1
Transport vesicle
(containing inactive
hydrolytic enzymes)
Golgi
apparatus
Plasma
membrane
2
Engulfment
of particle
“Food”
Lysosomes
Lysosome
engulfing
damaged
organelle
3
5
4
Food
vacuole
Figure 4.10A
Digestion
Vacuoles
• Function in the general maintenance of the cell
– Plant cells contain a large central vacuole, which has
lysosomal and storage functions
Nucleus
Chloroplast
Figure 4.12A
Colorized TEM 8,700
Central
vacuole
Endomembrane System
• Interconnected structurally and functionally
Rough ER
Transport vesicle
from ER to Golgi
Transport vesicle from
Golgi to plasma membrane
Plasma
membrane
Nucleus
Vacuole
Lysosome
Smooth ER
Nuclear envelope
Golgi apparatus
Mitochondria
• Cellular respiration
Outer
membrane
Inner
membrane
Cristae
Matrix
TEM 44,880
– Converts chemical energy
to ATP
– Phospholipid bilayer
Mitochondrion
membrane
– Has own DNA and
Intermembrane
ribosomes
space
Chloroplasts
• Convert solar energy to chemical energy (photosynthesis)
• Stroma
– Contains DNA, ribosomes and enzymes
• Thylakoids
– Interconnected sacs that form stacks called granum
Endosymbosis
• Hypothesis of endosymbosis
– Mitochondria and chloroplasts were once small
prokaryotes living independently
– At some point, began living within larger cells
The Cytoskeleton and Related Structures
The cell’s internal skeleton helps organize its
structure and activities
– A network of protein fibers make up the cytoskeleton
Tubulin subunit
Actin subunit
Fibrous subunits
25 nm
7 nm
Microfilament
10 nm
Intermediate filament
Microtubule
– Microfilaments (actin filiments)
• Enable cells to change shape and move
– Intermediate filaments
• Reinforce the cell and anchor certain organelles
– Microtubules give the cell rigidity
• And provide anchors for organelles and act as tracks for
organelle movement
Tubulin subunit
Actin subunit
Fibrous subunits
25 nm
7 nm
Microfilament
10 nm
Intermediate filament
Microtubule
Movement
Cilia and flagella move when microtubules bend
Figure 4.17A
LM 600
Colorized SEM 4,100
– Eukaryotic cilia and flagella are locomotor appendages
that protrude from certain cells
Figure 4.17B
Cell Junctions
•Tight junctions can bind cells together into leakproof sheets
•Anchoring junctions link animal cells into strong tissues
•Gap junctions allow substances to flow from cell to cell
Tight junctions
Anchoring junction
Gap junctions
Extracellular matrix
Space between cells
Figure 4.18B
Plasma membranes of adjacent cells
Plants and Cell Walls
•Supported by rigid cell walls made largely of cellulose
•Connect by plasmodesmata
•Connecting channels
Walls of two
adjacent plant
cells
Vacuole
Plasmodesmata
Layers of one
plant cell wall
Cytoplasm
Plasma membrane
Figure 4.18A
Fig. 4-23