Chapter 3
Cell Transport-Active,
Cytoplasm, Cytoskeleton
Slide 185-226
Cell Transport
REVIEW
2
Membrane Proteins
Movement of molecules
Cell membranes only allow some molecules across w/out help:
• Small, non-polar molecules OK
ex. steroids, O2, CO2
• No charged, polar, or large molecules
ex. sugars, ions, water*
Transport Across Membranes
Types of transport:
A. Passive transport
- Simple diffusion
- Facilitated diffusion
- Osmosis
B. Active transport
C. Bulk transport
• Energy Required?
• Directionality?
Passive Transport - Simple Diffusion
• NO ENERGY required
• DOWN concentration gradient
• molecules
equally distribute
across available
area by type
- non-polar molecules
(steroids, O2, CO2)
Passive Transport – Facilitated Diffusion
• NO ENERGY required
• DOWN concentration gradient
• molecules equally distribute but cross membrane
with the help of a channel (a) or carrier (b) protein.
Passive Transport - Osmosis
• osmosis – movement
of water across cell
membrane
• water crosses cell
membranes via
special channels
called aquaporins
• moves into/out of cell until
solute concentration is balanced
Passive Transport - Osmosis
In each situation below, does water have net
movement, and which direction:
fewer solutes in
solution, than in cell
equal solutes in
solution as in cell
more solutes in
solution, than in cell
Passive Transport - Osmosis
• tonicity – # solutes in solution in relation to cell
- hypotonic – fewer
solutes in solution
- isotonic – equal
solutes in solution
animal cell
- hypertonic – more
solutes in solution
plant cell
Passive Transport - Osmosis
Paramecium example
• regulate water balance
• pond water hypotonic
• water into contractile
vacuole
– water
expelled
Passive Transport - Osmosis
Scenario: in movie theater, watching a long movie.
You are: drinking water
What happens to your
blood?
You are: eating popcorn
What happens to your
blood?
Active Transport
• ENERGY IS required
• UP/AGAINST
concentration gradient
• Ex. Na-K ion pump
- Na+ ions: inside to out
- K+ ions: outside to in
• transport proteins
a. ion pumps
(uniporters)
b. symporter/antiporter
c. coupled transport
• antiporter: two molecules move
opposite directions (UP gradient)
Active Transport - uniporter
• Ex. proton (H+) pump
• ATP used pump H+ ions out
• uniporter:
ONE molecule
UP gradient
• against concentration and charge gradients
*gradients – used by cell for energy potential
Active Transport – coupled transport
• Ex. Active glucose transporter
• coupled transport: one molecule
UP gradient & other DOWN
gradient (opposite directions)
• Na+ diffusion used for
glucose active transport
• Na+ moving DOWN
concentration gradient
• Glucose moving UP
concentration gradient
Bulk Transport
• ENERGY IS required
• Several or large molecules
• Molecules moved IN
- endocytosis
• phagocytosis
– “food” in
• pinocytosis
– water in
Bulk Transport
• receptor-mediated endocytosis
– proteins bind molecules, vesicles inside
• Molecules
moved OUT
- exocytosis
18
Cell Membrane
http://www.youtube.com/watch?v=r1AkcotMSuQ
19
Cell Wall (only in plant cells)

a strong wall outside the cell membrane
that provides

–support for plant cells since they do not have
a skeleton
20
Cell Fractionation and Differential
Centrifugation

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 are settled out
21
21
Cytoplasm

Viscous fluid
containing
organelles

components of
cytoplasm




Interconnected
filaments & fibers
Fluid = cytosol
Organelles (not
nucleus)
storage substances
22
Cytoskeleton

Filaments & fibers

Made of 3 fiber types




Microfilaments
Microtubules
Intermediate filaments
3 functions:



mechanical support
anchor organelles
help move
substances
23
The Cytoskeleton

Maintains cell shape (mechanical support)

Assists in movement of cell and organelles Anchor
organelles

Three types of macromolecular fibers


Actin Filaments (Microfilaments)

Intermediate Filaments

Microtubules
Assemble and disassemble as needed
24
The Cytoskeleton: 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)
25
A = actin, IF = intermediate filament, MT = microtubule
26
The Cytoskeleton: Actin Filament Operation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
actin filament
ADP +
ATP
tail
myosin
molecules
P
head
membrane
27
The Cytoskeleton: 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
28
The Cytoskeleton: Microtubules

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
29
The Cytoskeleton: Microtubule Operation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ATP
vesicle
kinesin
kinesin
receptor
vesicle moves, not microtubule
30
The Cytoskeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
actin
subunit
Chara
a. Actin filaments
fibrous
subunits
peacock
b. Intermediate filaments
tubulin
dimer
chameleon
c. Microtubules
a(Actin): © M. Schliwa/Visuals Unlimited; b, c(Intermediate, Microtubules): © K.G. Murti/Visuals Unlimited; a(Chara): The McGraw-Hill Companies, Inc./photo by
Dennis Strete and Darrell Vodopich; b(Peacock): © Vol. 86/Corbis; c(Chameleon): © Photodisc/Vol. 6/Getty Images
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Microtubular Arrays: Centrioles



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
32
Cytoskeleton: Centrioles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
empty center
of centriole
one microtubule
triplet
one centrosome: one pair of centrioles
two centrosomes: two pairs of centrioles
200 nm
(Middle): Courtesy Kent McDonald, University of Colorado Boulder; (Bottom): Journal of Structural Biology, Online by Manley McGill et al. Copyright 1976 by Elsevier
Science & Technology Journals. Reproduced with permission of Elsevier Science & Technology Journals in the format Textbook via Copyright Clearance Center
33
Microtubular Arrays: Cilia and Flagella

Hair-like projections from cell surface that aid in
cell movement (Provide motility)
 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
34
Cilia & Flagella

Provide motility
 Cilia



Flagella



Short
Used to move substances
outside human cells
Whip-like extensions
Found on sperm cells
Basal bodies like
centrioles
35
Cilia & Flagella Structure
Bundles of microtubules
 With plasma membrane

36
Structure of a Flagellum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
outer
microtubule
doublet
Flagellum
radial
spoke
central
microtubules
The shaft of the
flagellum has a ring
of nine microtubule
doublets anchored
to a central pair of
microtubules.
shaft
dynein
side arm
Flagellum cross section
Sperm
plasma
membrane
triplets
25 nm
The side arms
of each doublet
are composed
of dynein, a
motor molecule.
dynein
side arms
Basal body
ATP
Basal body cross section
100 nm
The basal body of a flagellum has
a ring of nine microtubule triplets
with no central microtubules.
In the presence of
ATP, the dynein side
arms reach out to
their neighbors,
and bending occurs.
(Flagellum, Basal body): © William L. Dentler/Biological Photo Service
37
Centrioles
Pairs of microtubular structures
 Play a role in cell division

38
Cell Fractionation and Differential
Centrifugation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Grind cells
speed of 600 g
for 10 min
Centrifuge cells at
different speeds
speed of 15,000 g
for 5 min
nuclei
in sediment
speed of 100,000 g
for 60 min
mitochondria and lysosomes
in sediment
soluble portion
of cytoplasm
ribosomes and endoplasmic
reticulum in sediment
39
Animal Cell Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Plasma membrane:
outer surface that
regulates entrance and
exit of molecules
protein
phospholipid
Nucleus: command center of cell
Cytoskeleton: maintains
cell shape and assists movement
of cell parts:
Microtubules: protein
cylinders that move
organelles
Intermediate filaments:
protein fibers that provide
stability of shape
Nuclear envelope: double
membrane with nuclear pores
that encloses nucleus
Chromatin: diffuse threads
containing DNA and protein
Nucleolus: region that produces
subunits of ribosomes
Endoplasmic reticulum:
protein and lipid metabolism
Rough ER: studded with
ribosomes that synthesize
proteins
Actin filaments: protein
fibers that play a role in
change of shape
Smooth ER: lacks
ribosomes, synthesizes
lipid molecules
Peroxisome: vesicle
that is involved in
fatty acid metabolism
Centrioles*: short
cylinders of microtubules
of unknown function
Centrosome: microtubule
organizing center that
contains a pair of centrioles
Ribosomes:
particles that carry
out protein synthesis
Lysosome*: vesicle that
digests macromolecules
and even cell parts
Polyribosome: string of
ribosomes simultaneously
synthesizing same protein
Vesicle: small membranebounded sac that stores
and transports substances
Cytoplasm: semifluid
matrix outside nucleus
that contains organelles
*not in plant cells
Mitochondrion: organelle
that carries out cellular respiration,
producing ATP molecules
Golgi apparatus: processes, packages,
and secretes modified proteins
40
Representative Animal Cell
41
Plant Cell Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nucleus: command center of cell
Nuclear envelope: double membrane with
nuclear pores that encloses nucleus
Nucleolus: produces subunits of ribosomes
Central vacuole*: large, fluid-filled
sac that stores metabolites and
helps maintain turgor pressure
Cell wall of adjacent cell
Chromatin: diffuse threads containing
DNA and protein
Middle lamella:
cements together the
primary cell walls of
adjacent plant cells
Nuclear pore: permits passage of
proteins into nucleus and ribosomal
subunits out of nucleus
Ribosomes: carry
out protein synthesis
Chloroplast*: carries
out photosynthesis,
producing sugars
Centrosome:
microtubule organizing
center (lacks centrioles)
Endoplasmic
reticulum: protein
and lipid metabolism
Granum*: a stack
of chlorophyll-containing
thylakoids
in a chloroplast
Rough ER: studded
with ribosomes that
synthesize proteins
Mitochondrion: organelle
that carries out cellular
respiration, producing
ATP molecules
Smooth ER: lacks
ribosomes, synthesizes
lipid molecules
Peroxisome: vesicle that
is involved in fatty acid
metabolism
Golgi apparatus: processes,
packages, and secretes
modified proteins
Cytoplasm: semifluid matrix outside
nucleus that contains organelles
Microtubules: protein cylinders
that aid movement of organelles
Actin filaments: protein fibers
that play a role in movement of
cell and organelles
Plasma membrane: surrounds
cytoplasm, and regulates entrance
and exit of molecules
Cell wall*: outer surface that shapes,
supports, and protects cell
*not in animal cells
42
Representative Plant Cell
43