chapter 3 part 2: cell dynamics membrane transport: diffusion, osmosis, active transport cellular...
TRANSCRIPT
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
ATPThe Energy Currency of the Cell(Text review: Chapter 2, pg. 34)
ATP is the energy currency of all living things
Phosphate groups
Ribose
Adenine
ATP: Adenosine Triphosphate
ATP belongs in which category of molecule?
1. Carbohydrates2. Lipids3. Proteins4. Nucleic Acids5. 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 re-convert:
• ADP + P + energy ATP• Humans use food to
make ATP by the process of Aerobic Respiration
LE 8-9
Adenosine triphosphate (ATP)
Energy
P P P
PPP i
Adenosine diphosphate (ADP)Inorganic phosphate
H2O
+ +
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
Pi
ADP
Energy for cellular work(endergonic, energy-consuming processes)
Energy from catabolism(exergonic, energy-yielding processes)
ATP
+
Energy from food Regenerates ATP
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 membraneThe 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 mosaicThe 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
cellDiffusion, 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 losesmore water thanit gains and shrivels.
The bag gainsmore water thanit loses and swells.
98% water2% sugar
(a) HypertonicSolution
(90% water10% sugar)
(b) Isotonicsolution
(98% water2% sugar)
(c) Hypotonicsolution
(100% water,distilled)
The bag gains andloses the same amountof water and maintainsits shape.
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
Figure 3.10
What kind of substances might a cell wish to bring into the cell in this way?
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. Nucleus.2. Mitochondrion.3. Golgi complex.4. Ribosome.5. 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
C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l)
This is a combustion reaction
Aerobic respiration of glucose is the most basic means for cells to acquire energy
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
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
LE 9-6_2
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
ATP
Substrate-levelphosphorylation
Citricacidcycle
LE 9-6_3
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
ATP
Substrate-levelphosphorylation
Citricacidcycle
ATPOxidative
phosphorylation
Oxidativephosphorylation:
electron transportand
chemiosmosis
Electronscarried
via NADH
Electrons carriedvia NADH and
FADH2
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, 2
pyruvate
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
ADP
Hexokinase
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
Glucose-6-phosphate
Phosphoglucoisomerase
Phosphofructokinase
Fructose-6-phosphate
ATP
ADP
Fructose-1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
LE 9-9b_2
2 NAD+
Triose phosphatedehydrogenase
+ 2 H+
NADH2
1, 3-Bisphosphoglycerate
2 ADP
2 ATPPhosphoglycerokinase
Phosphoglyceromutase
2-Phosphoglycerate
3-Phosphoglycerate
2 ADP
2 ATPPyruvate kinase
2 H2OEnolase
Phosphoenolpyruvate
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
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Proteincomplex Electron
carrier
Electronflow
NADH NAD
FADFADH2
H
H
HH
H2O
H
H
ATPsynthase
2O212
H
PADP ATP
Electron Transport Chain Chemiosmosis
OXIDATIVE PHOSPHORYLATION
H
H
H
H
H
H
H
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+
H+
H+
H+
ATP
MITOCHONDRAL MATRIX
ADP+
P i
A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient.
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.
Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.
ATP BookkeepingCYTOSOL Electron shuttles
span membrane 2 NADHor
2 FADH2
MITOCHONDRION
Oxidativephosphorylation:
electron transportand
chemiosmosis
2 FADH22 NADH 6 NADH
Citricacidcycle
2Acetyl
CoA
2 NADH
Glycolysis
Glucose2
Pyruvate
+ 2 ATP
by substrate-levelphosphorylation
+ 2 ATP
by substrate-levelphosphorylation
+ about 32 or 34 ATP
by oxidation phosphorylation, dependingon which shuttle transports electronsform NADH in cytosol
About36 or 38 ATPMaximum per glucose:
Review of Cellular Respiration
STEP Key Players ATPGlycolysis Glucose, pyruvate 2/glucoseKrebs NAD+/NADH, CO2 2/glucosee- transport e- transport chain,
ATP synthase32-34/glucose
The portion of aerobic respiration which generates the most ATP is
1. Glycolysis2. The Citric Acid/Krebs cycle3. Electron transport4. All of these make the same amount of ATP5. None of these make ATP
Review of Cellular Respiration
Oxygen is the final acceptor in the electron transport chain
Review of Cellular Respiration
STEP Key Players ATPGlycolysis Glucose, pyruvate 2/glucoseKrebs NAD+/NADH, CO2 2/glucosee- transport e- transport chain,
ATP synthase32-34/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