Cell Structure
and Function
1
Ch. 4 Outline – Cell Structure & Function
Cell Structure
and Function
Cell Theory
A unifying concept in biology
States that:
All organisms are composed of cells
- Matthais Schleiden in 1838
- Theodor Schwann in 1839
All cells come only from preexisting cells
- Rudolph Virchow in 1850’s
Smallest unit of life
2
Organisms and Cells
3
Sizes of Living Things
4
Cell Structure
and Function
Cell Size
Most much smaller than one millimeter (mm)
Some as small as one micrometer (mm)
Size restricted by Surface/Volume (S/V) ratio
Surface is membrane, across which cell
acquires nutrients and expels wastes
Volume is living cytoplasm, which demands
nutrients and produces wastes
As cell grows, volume increases faster than
surface
Cells specialized in absorption modified to
greatly increase surface area per unit volume
5
Surface to Volume Ratio
Total Surface Area
96 cm2
192 cm2
384 cm2
Total Volume
64 cm3
64 cm3
64 cm3
Surface Area Per Cube / Volume Per Cube
1.5 : 1
3:1
6:1
6
7
1. Magnification
a. How much larger the object
appears compared to real size
8
a. Measure of clarity of image
b. Minimum distance two points can
be separated and still be
distinguished as two separate points
  vs

science
focus
Cell Structure
and Function
Microscopy Today:
Compound Light Microscope
Light passed through specimen
Focused by glass lenses
Image formed on human retina
Max magnification about 1000X
Resolves objects separated by 0.2 mm, 500X
better than human eye
9
science
focus
Cell Structure
and Function
Microscopy Today:
Transmission Electron Microscope
Abbreviated T.E.M.
Electrons passed through specimen
Focused by magnetic lenses
Image formed on fluorescent screen
Similar to TV screen
Image is then photographed
Max magnification 1,000,000 X
Resolves objects separated by 0.00002 mm,
100,000X better than human eye
10
science
focus
Cell Structure
and Function
Microscopy Today:
Scanning Electron Microscope
11
Abbreviated S.E.M.
Specimen sprayed with thin coat of metal
Electron beam scanned across surface of
specimen
Metal emits secondary electrons
Emitted electrons focused by magnetic lenses
Image formed on fluorescent screen
Similar to TV screen
Image is then photographed
science
focus
Cell Structure
and Function
12
Microscopy Today:
Immunofluorescence Light Microscope
Antibodies developed against a specific
protein
Fluorescent dye molecule attached to
antibody molecules
Specimen exposed to fluorescent antibodies
Ultra-violet light (black light) passed through
specimen
Fluorescent dye glows in color where antigen
is located
Emitted light is focused by glass lenses
Allows mapping distribution of a specific
protein in cell
science
focus
Microscopy Today:
Confocal Microscopy
Cell Structure
and Function
Narrow laser beam scanned across
transparent specimen
Beam is focused at a very thin plane
Allows microscopist to optically section a
specimen
Sections made at different levels
Allows assembly of 3D image on computer
screen that can be rotated
13
science
focus
Cell Structure
and Function
Microscopy Today:
Video-enhanced Contrast Microscopy
14
Great for specimens with low contrast, like
living cells
Image is captured by TV camera instead of
eye
Image is then “tweaked” by adjusting contrast
Darkest part of image is made black
Lightest part of image is made white
All parts in between made shades of gray
Also allows various shades to be converted to
different colors for more contrast
science
focus
Cell Structure
and Function
Microscopy Today:
Phase Contrast Microscopy
Great for transparent specimens with low
contrast, like living cells
Some organelles have higher density than
others
15
Speed of light is affected by density
Light passes more slowly through high
density than low density
Light waves entering a specimen “in phase”
exit some parts of the specimen out of phase
Microscope shows only light that is slower or
faster
Causes transparent organelles to “glow”
Microscopy and Amoeba proteus
16
Microscopy and Cheek Cells
17
Prokaryotic Cells:
Domains
Lack a membrane-bound nucleus
Structurally simple
Two domains:
Bacteria
- Three Shapes
 Bacillus
(rod)
 Coccus (spherical)
 Spirilla (spiral)
 Archaea
- Live in extreme habitats
Cell Structure
and Function
18
Shapes of Bacterial Cells
19
Prokaryotic Cells: Visual Summary
20
Prokaryotic Cells:
The Envelope
Cell Structure
and Function
Cell Envelopes
Glycocalyx
- Layer of polysaccharides outside cell wall
- May be slimy and easily removed, or
- Well organized and resistant to removal
(capsule)
Cell wall
Plasma membrane
- Like in eukaryotes
- Form internal pouches (mesosomes)
21
Prokaryotic Cells:
Cytoplasm & Appendages
Cell Structure
and Function
22
Cytoplasm
Semifluid solution
- Bounded by plasma membrane
- Contains inclusion bodies – Stored granules of
various substances
Appendages
Flagella – Provide motility
Fimbriae – small, bristle-like fibers that sprout
from the cell surface
Sex pili – rigid tubular structures used to pass
DNA from cell to cell
Cell Structure
and Function
Eukaryotic Cells
Domain Eukarya
Protists
Fungi
Plants
Animals
Cells contain:
Membrane-bound nucleus
Specialized organelles
Plasma membrane
23
Eukaryotic Cells :
Organelles
Cell Structure
and Function
24
Compartmentalization:
Allows eukaryotic cells to be larger than
prokaryotic cells
Isolates reactions from others
Two classes:
Endomembrane system:
- Organelles that communicate with one another
 via
membrane channels
 Via small vesicles
Energy related organelles
- Mitochondria & chloroplasts
- Basically independent & self-sufficient
Plasma Membrane
25
Hypothesized Origin of Eukaryotic Cells 26
Endosymbiosis
science
focus
Cell Fractionation, and
Differential Centrifugation
Cell Structure
and Function
27
Cell fractionation is the breaking apart of
cellular components
Differential centrifugation:
Allows separation of cell parts
Separated out by size & density
Works like spin cycle of washer
The faster the machine spins, the smaller the
parts that settled out
Science
Focus
Cell Fractionation, and
Differential Centrifugation
Grind
cells
Centrifuge
@ 600 g
Sediment
contains
nuclei
Figure 4C
Then
centrifuge
longer
@ 15,000 g
Sediment
contains
mitochondria,
lysosomes
Then
centrifuge
even longer
@ 100,000 g
Sediment
contains
ribosomes,
ER
Soluble
portion of
cytoplasm.
No
sediment
28
Animal Cell Anatomy
29
Plant Cell Anatomy
30
Cell Structure
and Function
31
Nucleus
Command center of cell, usually near center
Separated from cytoplasm by nuclear
envelope
Consists of double layer of membrane
Nuclear pores permit exchange between
nucleoplasm & cytoplasm
Contains chromatin in semifluid nucleoplasm
Chromatin contains DNA of genes
Condenses to form chromosomes
Dark nucleolus composed of rRNA
Produces subunits of ribosomes
Anatomy of the Nucleus
32
Cell Structure
and Function
Ribosomes
Serve in protein synthesis
Composed of rRNA
Consists of a large subunit and a small
subunit
Subunits made in nucleolus
May be located:
On the endoplasmic reticulum (thereby
making it “rough”), or
Free in the cytoplasm, either singly or in
groups called polyribosomes
33
Nucleus, Ribosomes, & ER
Figure 4.9
34
Cell Structure
and Function
Endomembrane System
Restrict enzymatic reactions to specific
compartments within cell
Consists of:
Nuclear envelope
Membranes of endoplasmic reticulum
Golgi apparatus
Vesicles
- Several types
- Transport materials between organelles of
system
35
Endomembrane System: A Visual Summary36
Endomembrane System:
The Endoplasmic Reticulum
Cell Structure
and Function
37
Rough ER
Studded with ribosomes on cytoplasmic side
Protein anabolism
- Synthesizes proteins
- Modifies proteins
 Adds
sugar to protein
 Results in glycoproteins
Smooth ER
No ribosomes
Synthesis of lipids
Endoplasmic Reticulum
38
Endomembrane System:
The Golgi Apparatus
Cell Structure
and Function
39
Golgi Apparatus
Consists of 3-20 flattened, curved saccules
Resembles stack of hollow pancakes
Modifies proteins and lipids
- Packages them in vesicles
- Receives vesicles from ER on cis face
- Prepares for “shipment” in vesicles from trans
face
 Within
cell
 Export
from cell (secretion, exocytosis)
Golgi Apparatus
40
Endomembrane System:
Lysosomes
Cell Structure
and Function
41
Membrane-bound vesicles (not in plants)
Produced by the Golgi apparatus
Low pH
Contain lytic enzymes
- Digestion of large molecules
- Recycling of cellular resources
- Apoptosis (programmed cell death, like tadpole
losing tail)
Some genetic diseases
Caused by defect in lysosomal enzyme
Lysosomal storage diseases (Tay-Sachs)
Lysosomes
42
Cell Structure
and Function
Peroxisomes
Similar to lysosomes
Membrane-bounded vesicles
Enclose enzymes
However
Enzymes synthesized by free ribosomes in
cytoplasm (instead of ER)
Active in lipid metabolism
Catalyze reactions that produce hydrogen
peroxide H2O2
- Toxic
- Broken down to water & O2 by catalase
43
Peroxisomes
44
Cell Structure
and Function
45
Vacuoles
Membranous sacs that are larger than
vesicles
Store materials that occur in excess
Others very specialized (contractile vacuole)
Plants cells typically have a central vacuole
Up to 90% volume of some cells
Functions in:
- Storage of water, nutrients, pigments, and
waste products
- Development of turgor pressure
- Some functions performed by lysosomes in
other eukaryotes
Vacuoles
46
Endomembrane System: A Visual Summary47
Energy-Related Organelles:
Chloroplast Structure
Cell Structure
and Function
48
Bounded by double membrane
Inner membrane not folded
Disc-like thylakoids are stacked to form grana
Suspended in semi-fluid stroma
Green due to chlorophyll
Green photosynthetic pigment
Found ONLY in membranes of thylakoids of
chloroplast
Energy-Related Organelles:
Chloroplasts
Cell Structure
and Function
49
Captures light energy to drive cellular
machinery
Photosynthesis
Synthesizes carbohydrates from CO2 & H2O
Makes own food using CO2 as only carbon
source
Energy-poor compounds converted to energy
rich compounds
Energy-Related Organelles:
Chloroplast Structure
50
Energy-Related Organelles:
Mitochondria
Cell Structure
and Function
51
Bounded by double membrane
Cristae – Infoldings of inner membrane that
encloses matrix
Matrix – Inner semifluid containing respiratory
enzymes
Involved in cellular respiration
Produce most of ATP utilized by the cell
Energy-Related Organelles:
Mitochondrial Structure
52
Cell Structure
and Function
The Cytoskeleton
Maintains cell shape
Assists in movement of cell and organelles
Three types of macromolecular fibers
Actin Filaments
Intermediate Filaments
Microtubules
Assemble and disassemble as needed
53
Cell Structure 54
The Cytoskeleton:
and Function
Actin Filaments
Extremely thin filaments like twisted pearl
necklace
Dense web just under plasma membrane
maintains cell shape
Support for microvilli in intestinal cells
Intracellular traffic control
For moving stuff around within cell
Cytoplasmic streaming
Function in pseudopods of amoeboid cells
Pinch mother cell in two after animal mitosis
Important component in muscle contraction
(other is myosin)
The Cytoskeleton:
Actin Filament Operation
55
Cell Structure 56
The Cytoskeleton:
and Function
Intermediate Filaments
Intermediate in size between actin filaments
and microtubules
Rope-like assembly of fibrous polypeptides
Vary in nature
From tissue to tissue
From time to time
Functions:
Support nuclear envelope
Cell-cell junctions, like those holding skin
cells tightly together
The Cytoskeleton:
Microtubules
Cell Structure
and Function
57
Hollow cylinders made of two globular
proteins called a and b tubulin
Spontaneous pairing of a and b tubulin
molecules form structures called dimers
Dimers then arrange themselves into tubular
spirals of 13 dimers around
Assembly:
Under control of Microtubule Organizing
Center (MTOC)
Most important MTOC is centrosome
Interacts with proteins kinesin and dynein to
cause movement of organelles
The Cytoskeleton:
Microtubule Operation
58
Microtubular Arrays:
Centrioles
Cell Structure
and Function
59
Short, hollow cylinders
Composed of 27 microtubules
Microtubules arranged into 9 overlapping
triplets
One pair per animal cell
Located in centrosome of animal cells
Oriented at right angles to each other
Separate during mitosis to determine plane of
division
May give rise to basal bodies of cilia and
flagella
Cytoskeleton:
Centrioles
60
Cell Structure 61
Microtubular arrays:
and Function
Cilia and Flagella
Hair-like projections from cell surface that aid
in cell movement
Very different from prokaryote flagella
Outer covering of plasma membrane
Inside this is a cylinder of 18 microtubules
arranged in 9 pairs
In center are two single microtubules
This 9 + 2 pattern used by all cilia & flagella
In eukaryotes, cilia are much shorter than
flagella
Cilia move in coordinated waves like oars
Flagella move like a propeller or cork screw
Structure of a Flagellum
62
63
Video: The Inner Life of a Cell
http://multimedia.mcb.harvard.edu/a
nim_innerlife_Hi.html