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Chapter 5: Eukaryotic Cells
3. Endomembrane System: It’s all integrated!
Chapter 5: Eukaryotic Cells
4. Vacuoles
ii. Large Central Vacuole (Plants)
Fills up most of plant cell
Membrane bound (tonoplast)
Helps cell’s water balance
Dump site for hazardous
wastes
! Vacuole fills with water &
gives “Turgor Pressure”
!
!
!
!
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Chapter 5: Eukaryotic Cells
5. Energy Related Organelles
i. Mitochondria
! “Powerhouses” in
eukaryotic cells
! Animals and Plants
! 100-10,000 per cell;
highest numbers in
muscle, brain, and eye
cells
! Surrounded with 2
membranes
! inner membrane forms cristae (folds)
Chapter 5: Eukaryotic Cells
5. Energy Related Organelles
i. Mitochondria
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Chapter 5: Eukaryotic Cells
5. Energy Related Organelles
i. Mitochondria
!Semi-autonomous
– own DNA, circular, codes for ~15 genes
– own ribosomes
– however, dependent on
proteins coded in the
nucleus
! Function: ATP (energy)
synthesis through aerobic
respiration; converts the
energy stored in sugar to ATP
Chapter 5: Eukaryotic Cells
ii. Chloroplasts
! Site of photosynthesis
! Larger than mitochondria
– uses the energy in sunlight to
drive the production of ATP
and simple sugars
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Chapter 5: Eukaryotic Cells
ii. Chloroplasts
!Contain Thylakoids
! Plants and some protists
– organized into grana
! Surrounded by 2 membranes
– chlorophyll (in membranes)
! 1 – 100’s per cell
– Transfer Light E ! ATP
Chapter 5: Eukaryotic Cells
ii. Chloroplasts
! contains DNA (circular)
! codes for ~130 genes
! however, like the mitochondria, dependent on
proteins coded in the nucleus
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Chapter 5: Eukaryotic Cells
iii. Endosymbiosis: living in close association
!Endosymbiotic theory: some modern organelles are the
result of engulfed prokaryotes that provided their hosts
with advantages associated with specialized metabolic
activities.
!Origin of the Mitochondria and Chloroplast
!Supported by a wealth of information
– number and structure of membranes
– size of structures is similar
– ribosomal makeup
– DNA: circular
– DNA: replicates in the
same way
Chapter 5: Eukaryotic Cells
6. Cytoskeleton
! Network of protein fibers that
crisscrosses the cytoplasm of
eukaryotic cells
!supports cell shape,
movement, and anchors
organelles
! It is a dynamic system,
constantly forming and
disassembling
! Polymerization: the
construction of long chains by
the addition of identical protein
subunits
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Chapter 5: Eukaryotic Cells
i. Components
Actin
Filaments:
Intermediate
Filaments:
Supports
cell shape,
movement
reinforce cell,
anchor organelles
Microtubules:
cell rigidity, anchor &
tracks for organelles,
major role in mitosis
Chapter 5: Eukaryotic Cells
i. Components
a. Actin Filaments
! composed of two protein
chains twined together
! the subunits of the actin
filament are the globular protein
Actin
! concentrated just inside the
plasma membrane
! rapid polymerization and
depolymerization
! contraction, crawling,
pinching during cell division,
cellular extensions
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Chapter 5: Eukaryotic Cells
i. Components
b. Microtubles
! hollow tube
! subunits are globular proteins
that consist of dimers of alpha
and beta tubulin
! rapid polymerization and
depolymerization
[CLIP]
! cellular movement, internal
cellular movement, during cell
division they move chromosomes
Cilia
Chapter 5: Eukaryotic Cells
i. Components
c. Intermediate filaments
! fibrous protein molecules
twined together
Rat epithelial cell
! subunits are fibers
! tremendous strength
! once formed they are stable
! structural stability,
constituents of hair and
fingernails (Keratin)
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Chapter 5: Eukaryotic Cells
7. Cilia and flagella: made of microtubules in Eukaryotes
i. Cilia: Short, numerous “oars”
ii. Flagella Longer, fewer, with whip-like/ wave like motion
Chapter 5: Eukaryotic Cells
7. Cilia and flagella: made of microtubules
microtubules
LM 600!
Plasma
membrane
TEM 206,500!
SEM 4,100!
TEM 206,500!
Flagellum
9 + 2 Arrangement: More
complex than Prokaryotes
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Chapter 5: Eukaryotic Cells
8. Cell Walls
! plants, fungi, and most
protists
! prokaryotic !
eukaryotic cell wall
!protection & support
!fungi: chitin
! plants: cellulose
! in plants it is thick, strong,
and rigid
! plants have a primary wall, a
middle lamella, and may have a
secondary cell wall
Chapter 5: Eukaryotic Cells
8. Cell Walls
! plants, fungi, and most
protists
! prokaryotic !
eukaryotic cell wall
!protection & support
!fungi: chitin
! plants: cellulose
! in plants it is thick, strong,
and rigid
! plants have a primary wall, a
middle lamella, and may have a
secondary cell wall
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Chapter 5: Eukaryotic Cells
9. Extracellular Matrix—Animal cells
! Animal cells lack cell walls.
– form extracellular matrix
• support
• strength
• resilience
• binds cells together
! Composed of an elaborate
mixture of sticky
glycoproteins (=proteins
with short chains of sugars
attached to them)
Chapter 5: Eukaryotic Cells
REVIEW
Eukaryotic organelles fall into 4 functional groups
1. Manufacture and transport – dependent on network of membranes
• Nucleus
• Ribosomes
• Rough, smooth ER
• Golgi apparatus
2. Breakdown – all single-membrane sacs
• Lysosomes (plants, animals, some protists)
• Peroxisomes
• Vacuoles (plants)
3. Energy Processing – involves extensive membranes embedded with enzymes
•
•
Chloroplasts
Mitochondria
4. Support, Movement, Communication
• Cytoskeleton – includes cilia, flagella, filaments, microtubules
• Cell walls
• Extracellular matrix
• Cell junctions
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Chapter 5: Cell Membrane Structure and Function
I.
II.
III.
IV.
Phospholipid Bilayer & Fluid Mosaic Model
Membrane Components
Transport Mechanisms
Cell-Cell Interactions
Fig.
6.3 (TEArt)
I. Phospholipid
Bilayer & Fluid Mosaic Model
Polar
hydrophilic
heads
Nonpolar
hydrophobic
tails
Polar
hydrophilic
heads
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Membrane structure is related to membrane function
A. Membrane Structure= “Fluid Mosaic”
• “Fluid” = Membrane = phospholipid bilayer
• “Mosaic” = Proteins embedded in membrane
• Membrane is flexible,
“fluid”
• Not rigid
• Proteins are embedded
in the bilayer, but are free
to move laterally
I. Phospholipid Bilayer & Fluid Mosaic Model
Membrane structure is related to membrane function
A. Membrane Structure= “Fluid Mosaic”
B. Function: Plasma membrane = gatekeeper
Functions (For Cell):
• selective from environment
1. Isolation• exchange of essential substances
2. Regulation• with other cells
3. Communication-
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Membrane structure is related to membrane function
A. Membrane Structure= “Fluid Mosaic”
• “Fluid” = Membrane = phospholipid bilayer
• “Mosaic” = Proteins embedded in membrane
– Transport proteins: channels and carriers
– Receptor proteins: triggers and gates
– Recognition proteins: ID tags
• Membrane is flexible,
“fluid”
• Not rigid
• Proteins are embedded
in the bilayer, but may
move laterally
B. Transmembrane Proteins
Anchoring Proteins in the Bilayer
Nonpolar areas
of
protein
i. Single-Pass
Anchors
Single non-polar
segment anchored into
the membrane
Polar areas
of protein
ii. Multi-Pass Channels
& Carriers
iii. Pores
Several non-polar !helices form a channel in
the membrane
Several non-polar "pleated sheets form a pore
in the membrane
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B. Transmembrane Proteins
Anchoring Proteins in the Bilayer
i. Single-Pass
Anchors
Single non-polar
segment anchored into
the membrane
ii. Multi-Pass Channels
& Carriers
iii. Pores
Several non-polar !helices form a channel in
the membrane
Several non-polar "pleated sheets form a pore
in the membrane
Membrane proteins have a variety of functions:
Transporter
Enzyme
Cell Surface Receptor
Cell Surface Identity
Marker
Cell-to-Cell Adhesion
Attachment to the
Cytoskeleton
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III. Transport Mechanisms
• How particles get across cell membranes.
Background: Two factors influence transport:
1) Hydrophilic/hydrophobic interactions
2) Concentration gradients
• a physical difference between 2 areas
– concentration (# molecules/unit volume)
• Molecules tend to move down a concentration
gradient:
High concentration
Low concentration
III. Transport Mechanisms
Lipid bilayers are selectively permeable
! some substances can readily pass from one side to
the other, others only with great difficulty, and others
not at all
– small hydrophobic substances pass through with ease
– some small hydrophyllic substances can pass (prob. negligible)
– large hydrophobic substances show minimal potential for
crossing
– membranes are generally impermeable to proteins, amino
acids, nucleic acids, & carbohydrates
– but permeable to lipids, lipid-like substances, and gasses
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III. Transport Mechanisms
Which molecules can cross the plasma membrane?
Due to its polarity,
water cannot cross the
membrane freely.
However, water flow is
facilitated by
Aquaporins (channel
proteins).
III. Transport Mechanisms
A) Passive transport
– Follows concentration gradient
– Does not require energy
– Either direct or via channels or carriers
1) Diffusion
2) Osmosis
B) Active Transport
– Against concentration gradient
– Requires energy (ATP)
C) Bulk Transport
– Exocytosis, Endocytosis
ATP
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A. Types of Passive Transport
1.
Diffusion
•
All molecules constantly vibrating/moving
•
Mixtures tend to become uniform
– Molecules move from high concentration ! low
concentration
– “Down” the gradient
– Doesn’t require energy
Time 0
Steep
Concentration
Gradient
Time 1
Reduced
Concentration
Gradient
Time 2
No
Concentration
Gradient
1. Diffusion (Types)
i. Diffusion Across a Membrane:
• Small nonpolar (hydrophobic)
molecules and gasses e.g. hydrocarbons
• Follows concentration gradient
• Does not show saturation
• Does not require energy
Can occur either directly across a membrane (ex., O2), or
through Channel proteins. Channels are very specific for a
particular ion (ex., Ca++, Na+) or molecule (ex., H2O). Channel
proteins DO NOT bind to the solute, they are open passages.
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1. Diffusion (Types)
ii. Facilitated Diffusion:
• Uses Carrier proteins
• A given carrier is specific; it will only transport
certain molecules or ions
• Transports polar (hydrophillic) molecules
e.g. Sugars, amino acids, ions
• PHYSICALLY BINDS TO THE SOLUTE
• Follows concentration gradient, does not use energy
• Can saturate if all carriers are in use
A. Types of Passive Transport
2. Osmosis
• Diffusion of water, but
not solutes, across a
selectively permeable
membrane due to
concentration differences
• EX: Net water movement
toward sugar; Water
follows concentration
gradient, sugar cannot.
Sugar
molecule
Semipermeable
membrane
Water molecules
Net water movement toward
regions of higher solute
concentration!
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2. Osmosis: Water movement across membranes
(other molecules cannot readily cross)
Solution is
HYPOTONIC to cell;
(lower [solute] )
salt
Solution = 5% salt
Solution = 95% H20
Where will
water go?
Cell =45% salt
Cell = 55% H2 0
2. Osmosis: Water movement across membranes
(other molecules cannot readily cross)
Solution is
HYPERTONIC to cell;
(higher [solute] )
salt
Solution = 40% salt
Solution = 60% H20
Where will
water go?
Cell = 5% salt
Cell = 95% H2 0
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A. Types of Passive Transport
2. Osmosis: How animal & plant cells behave in different solutions
Isotonic solution
Hypotonic solution
H2O
H2O
Hypertonic solution
H2O
H2O
Animal
cell
(2) Lysed
(1) Normal
H2O
H2O
(3) Shriveled
Plasma
membrane
H2O
H2O
Plant
cell
(4) Flaccid
(5) Turgid
(6) Plasmolysis
(shriveled)
B. Active Transport
! Requires energy (ATP)
! Moves molecules against concentration gradient
! Pumped by conformational changes in transport protein
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B. Active Transport: The Sodium-Potassium Pump
Extracellular
PP ATP
P
A
Na+
PP
P
ATP A
Intracellular
1. Protein in membrane binds
intracellular sodium.
2. ATP phosphorylates protein
with bound sodium.
K+
P
PP
ADP A
3. Phosphorylation causes
conformational change in
protein, allowing sodium to
leave.
P
PP
A
ADP
4. Extracellular potassium
binds to exposed sites.
P
PP
A
ADP+Pi
5. Binding of potassium causes
dephosphorylation of protein.
PP ATP
P
A
6. Dephosphorylation of
protein triggers change back
to original conformation,
potassium moves into cell,
and the cycle repeats.
B. Active Transport: Coupled Transport
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III. Transport Mechanisms
C) Bulk transport
1) Endocytosis
i. Phagocytosis: particulate matter
ii. Pinocytosis: liquid
iii. Receptor-mediated endocytosis
2) Exocytosis
1. Endocytosis:
Phagocytosis of a bacterium
by a mouse cell
• Processes to move large molecules, groups of molecules, or polar
molecules into the cell. (Uses Vesicles)
i. Phagocytosis
! Macrophage: WBC
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III. Transport Mechanisms
2. Exocytosis
• Secretes unwanted materials, materials for cell wall
formation, hormones, digestive enzymes, etc.
IV. Cell-Cell Interactions
A. Membranes have important
roles in cell signaling and cell-cell
interactions
A. Cells signal one another with chemicals
B. Membrane proteins [and other proteins
inside the cell] receive the signals
C. Membrane proteins mediate cell-cell
interactions
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IV. Cell-Cell Interactions
B. Cell Junctions
1. Gap Junctions:
• in Animal cells
• pairs of channel proteins to
connect cytoplasm of cells
2. Plasmodesmata:
• in Plant cells
• “Cytoplasmic” bridges
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