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Chapter 3 part 2: Cell dynamics
Membrane transport: Diffusion,
osmosis, active transport
Cellular respiration
Lecture outline
• ATP and cell energy
• Cell membrane dynamics
– Diffusion
– Osmosis
– Active transport
• Cell respiration
ATP
The Energy Currency of the Cell
(Text review: Chapter 2, pg. 34)
ATP is the energy currency of all living things
Adenine
Phosphate groups
Ribose
ATP: Adenosine Triphosphate
ATP belongs in which category of
molecule?
1.
2.
3.
4.
5.
Carbohydrates
Lipids
Proteins
Nucleic Acids
None of these
How ATP works
• ATP  ADP + P + energy
• Energy from ATP can do
work in the cell
• When we eat food, we
use its energy to reconvert:
• ADP + P + energy ATP
• Humans use food to
make ATP by the process
of Aerobic Respiration
LE 8-9
P
P
P
Adenosine triphosphate (ATP)
H2O
Pi
Inorganic phosphate
+
P
P
Adenosine diphosphate (ADP)
+
Energy
How ATP Performs Work
• When ATP breaks, the P can be added to a protein
• The recipient protein then changes shape, and behaves
differently
When
proteins
change
shape,
work can
get done
Energy from food Regenerates ATP
ATP
Energy for cellular work
(endergonic, energyconsuming processes)
Energy from catabolism
(exergonic, energyyielding processes)
ADP +
P
i
Your body breaks down and re-builds
your own weight in ATP each day
Cell membranes
Cell Membrane review
• What is the cell membrane made out of?
• What is the purpose of the cell membrane?
One way in, one way out
Everything which enters or exits a cell must pass through the cell
membrane
The cell membrane must therefore:
-Keep things the cell needs
-Get things it wants from its environment
-Get rid of wastes without losing desirable substances
-All parts of the cell membrane work to these tasks
Parts of the cell membrane
•
•
•
•
Phospholipid bilayer
Cholesterol (animal cells only)
Membrane proteins
Some carbohydrates
Cell membranes are made of a phosphlipid
bilayer
Phospholipids are amphipathic
• Similar in structure to
triglycerides
• Phosphate is polar
• Lipids are nonpolar
• Degree of saturation
influences shape and
fluidity
Fatty acid saturation influences fluidity
of cell membranes
Saturated fatty acids pack into
membranes more easily, making
membranes tighter (and less fluid)
Cholesterol can stabilize the fluidity of
animal cell membranes
• Higher temperature
also influences fluidity
of membranes
Proteins comprise ~50% of cell
membranes
The membrane is a fluid mosaic
The membrane is Selectively permeable
Proteins assist in allowing things to pass in
and out
Transmembrane proteins serve a
variety of functions
Some things can pass through easily, others
require help
• Substances which can
pass without help:
– Water
– Small nonpolar
molecules
• Substances that require
help:
– Ions
– Polar small molecules
– Large molecules
Membrane dynamics:
Ways things can enter or leave the
cell
Diffusion, Osmosis, and Active
Transport
Things can enter the cell in three ways
• Diffusion (Can be
Passive or facilitated)
• Osmosis
• Active transport
Diffusion: the movement of a substance from a
high concentration to a low concentration
• Simple diffusion
• Facilitated diffusion
Diffusion is the movement of a
substance from a high concentration
to a low concentration
What happens next?
Membranes can change the way
diffusion works
What determines the rate of diffusion here?
On what properties of the dye and membrane
does the diffusion depend?
Figure 5.12
The cell membrane
can’t control simple
diffusion
Small, nonpolar
molecules can pass easily
through the phospholipid
bilayer:
-Oxygen
-Carbon dioxide
-Alcohol
-Steroids
-gasoline
(Water is polar but very
small- it can pass the
membrane at low rates )
Facilitated diffusion allows passage of
desirable molecules
Membrane proteins allow ions and small polar molecules to pass in and out
-Potassium ions (K+), other things
-Sugars and other nutrients
Diffusion
• Diffusion is the
movement of
substances from a
high concentration
to a low
concentration
• Liquids and gasses
diffuse
spontaneously
Osmosis: the diffusion of water across
a selectively permeable membrane
Osmosis is the diffusion of water
What can we infer about the
permeability of this membrane?
Osmosis
• The diffusion of water
• Requires no energy
• Water moves from a
high concentration to a
low concentration
• Water can pass through
membranes
Osmosis can do work
When only
water can
pass,
Osmosis
can cause a
cell to
shrivel, or
to swell
The bag gains and
loses the same amount
of water and maintains
its shape.
The bag loses
more water than
it gains and shrivels.
(a) Hypertonic
Solution
(90% water
10% sugar)
98% water
2% sugar
(b) Isotonic
solution
(98% water
2% sugar)
The bag gains
more water than
it loses and swells.
(c) Hypotonic
solution
(100% water,
distilled)
Figure 5.14
Isotonic- equal concentrations of solutes
inside and out
• Water flows equally into
and out of cells
• Necessary for animal
cells
• A wilted state in plant
cells
Hypotonic- A low concentration of solutes
outside the cell
• Water flows in
• This keeps plants in
proper shape
• This can lyse an animal
cell
Hypertonic- A greater concentration of
solutes outside the cell
• Water flows from a high
concentration (inside
the cell) to a low
concentration (outside
the cell)
What kind of solution are these plants in?
Active Transport
• Substances are moved by the cell from low
concentration to high
• Spending cellular energy to move substances
against a concentration gradient
Membrane proteins can do Active Transport to
bring needed items into the cell
What kind of substances might a cell wish to bring
into the cell in this way?
Figure 3.10
ATP can be used to power Active Transport
Active transport for very large things
• When substances are too big to be brought in
through a channel, the cell can do endocytosis
• Substances can be shipped out of the cell by
exocytosis
• Both are forms of active transport
Endocytosis and Exocytosis
• When things are too big to fit through the
membrane, they can be brought in by
endocytosis
• …or released by exocytosis
Endocytosis
• The vesicle then travels into the cell and
through the cytoplasm
• Two types
– Phagocytosis (cell eating) – large particles or
bacteria
– Pinocytosis (cell drinking) – droplets of fluid
Endocytosis
Figure 3.11a
Endocytosis
Figure 3.11b
Exocytosis- a
vesicle fuses
with the
membrane,
freeing the
contents
Figure 3.12
Figure 5.17
Figure 5.18
Membrane transport review
The “powerhouse of the cell” is
the_________.
1.
2.
3.
4.
5.
Nucleus.
Mitochondrion.
Golgi complex.
Ribosome.
None of these
Mitochondrial structure review
Cellular respiration provides us with
the energy we use
Slow-twitch muscles have more mitochondria than fast-twitch
Cellular Respiration
All Living Things Require and Consume
Energy
• Ultimate source of
energy for all life on
earth is the sun
• We get our energy from
food
Aerobic respiration of glucose is the most
basic means for cells to acquire energy
C6H12O6(s) + 6O2(g)  6CO2(g)+ 6H2O(l)
This is a combustion reaction
Respiration at the cellular level
necessitates our breathing
The more our cells respire, the more
oxygen (& food) we need
The Stages of Cellular Respiration
• Cellular respiration has three stages:
– Glycolysis
– The citric acid cycle (a.k.a. the Krebs cycle)
– The electron transport chain
LE 9-6_1
Glycolysis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Substrate-level
phosphorylation
LE 9-6_2
Glycolysis
Citric
acid
cycle
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Substrate-level
phosphorylation
ATP
Substrate-level
phosphorylation
LE 9-6_3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Citric
acid
cycle
Pyruvate
Glucose
Cytosol
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
ATP
Substrate-level
phosphorylation
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
Overview of respiration
• Glycolysis: Glucose is split, 2 pyruvates are
formed, a little ATP is gained ( 2 ATP/ glucose)
• The Citric Acid Cycle: Pyruvates are brokent into
CO2, Redox molecules NAD+ and FAD are charged
up, a little ATP is gained (2 ATP/ glucose)
• Electron transport: Lots of ATP is made by ATP
synthase (~32 ATP/ glucose)
Step 1: Glycolysis
In: 1 glucose, 2 NAD+
Out: 2 ATP (net), 2NADH,
pyruvate
2
Glycolysis converts glucose to
pyruvate
• Glycolysis (“breaking of sugar”) breaks down
glucose into two molecules of pyruvate
• Glycolysis occurs in the cytoplasm and has two
major phases:
– Energy investment phase
– Energy payoff phase
Overview of Glycolysis
•
•
•
•
Actually a 10- step process
Glucose (6C)  2 Pyruvate ( 3 C ea.)
2 ATPs net profit
2 NAD+’s are charged
LE 9-9a_2
Glucose
ATP
Hexokinase
ADP
Glucose-6-phosphate
Phosphoglucoisomerase
Fructose-6-phosphate
ATP
Phosphofructokinase
ADP
Fructose1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
LE 9-9b_2
2 NAD+
Triose phosphate
dehydrogenase
2 NADH
+ 2 H+
1, 3-Bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
2-Phosphoglycerate
2 H 2O
Enolase
Phosphoenolpyruvate
2 ADP
Pyruvate kinase
2 ATP
Pyruvate
Step 2: The Krebs Cycle
Bonds in pyruvate are stripped of
their energy
The Krebs cycle strips all the
electrons off of glucose’s carbon
atoms, forming CO2
The electrons are used to charge up electron
carriers NAD+ ( NADH) and FAD ( FADH2)
Step 3: Electron transport
In which the electron transport chain
generates a proton gradient, and ATP
synthase makes tons of ATP
The electron transport chain uses electrons to
generate a proton gradient
H+
H+
Protein
complex
H+
Intermembrane
space
H+
H+
H+
H+
Electron
carrier
H+
H+
ATP
synthase
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
FADH2
FAD
NAD+
NADH
H+
1
2
O2
+ 2 H+
H+
H+
H2O
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
ADP
+ P
ATP
H+
Chemiosmosis
Some poisons can disrupt e- transport, creating
a lethal e- traffic jam
Oxygen is the final e- resting place in
the chain
• ATP synthase uses the potential energy in the
proton gradient to generate ATP
LE 9-14
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
A rotor within the
membrane spins as
shown when H+
flows past
it down the H+
gradient.
H+
H+
A stator anchored in
the membrane
holds the knob
stationary.
A rod (or “stalk”)
extending into the
knob also spins,
activating catalytic
sites in the knob.
H+
ADP
+
P
ATP
i
MITOCHONDRAL MATRIX
Three catalytic sites
in the stationary
knob join inorganic
phosphate to ADP
to make ATP.
ATP Bookkeeping
Electron shuttles
span membrane
CYTOSOL
2 NADH
Glycolysis
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2
Pyruvate
2
Acetyl
CoA
6 NADH
Citric
acid
cycle
+ 2 ATP
+ 2 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
About
36 or 38 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by oxidation phosphorylation, depending
on which shuttle transports electrons
form NADH in cytosol
Review of Cellular Respiration
STEP
Glycolysis
Krebs
e- transport
Key Players
Glucose, pyruvate
NAD+/NADH, CO2
e- transport chain,
ATP synthase
ATP
2/glucose
2/glucose
32-34/glucose
The portion of aerobic respiration which
generates the most ATP is
1.
2.
3.
4.
5.
Glycolysis
The Citric Acid/Krebs cycle
Electron transport
All of these make the same amount of ATP
None of these make ATP
Review of Cellular Respiration
Oxygen is the final acceptor in the
electron transport chain
Review of Cellular Respiration
STEP
Glycolysis
Krebs
e- transport
Key Players
Glucose, pyruvate
NAD+/NADH, CO2
e- transport chain,
ATP synthase
ATP
2/glucose
2/glucose
32-34/glucose
Human cells can do glycolysis faster
than human lungs can take in oxygen
Q: What happens if there is not
enough oxygen?
A: It depends on what kind of creature
you are…
Without O2, yeast make alcohol, and
CO2 is a waste product
This is alcohol fermentation
Humans make lactic acid instead of
ethanol
This is lactic acid fermentation
Lactic Acid in muscles creates a burning
sensation
• Overworked muscles
can become anoxic
• In low oxygen
environments, pyruvate
is converted to lactate
to regenerate NAD+
• Lactic acid causes great
suffering
Where is
aerobic
respiration
here?
Metabolism can build up, or break
down
The Versatility of Catabolism
• Catabolic pathways funnel electrons from many kinds
of organic molecules into cellular respiration
• Glucose- 4 calories/gram
• Proteins- 4 calories/gram
• Fats- 9 calories/gram
Anabolic
process are
fueled with
ATP
Which of the following produces the
most ATP per glucose?
A) aerobic respiration
B) anaerobic respiration
C) alcoholic fermentation
D) lactic acid fermentation
E) All produce approximately the same amount
of ATP per molecule of glucose