1. Chapter 5
The Working Cell
1. A cell needs energy to function
2. Enzymes
3. Membrane Function
1. A cell needs ENERGY to
function.
What is ENERGY?
Energy is defined as the capacity to perform
work.
Kinetic energy is the energy of motion.
Potential energy is stored energy.
Energy can be changed from one form to another.
However, it cannot be created or destroyed.
This is the conservation of energy principle.
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2. Entropy:
Is the measure of disorder or randomness.
Heat - Is a type of kinetic energy contained in the
random motion of molecules (fire)
- Is a product of all energy conversions.
Chemical energy:
- Is a form of potential energy.
- Is found in food, gasoline, and other fuels.
Living cells and automobile engines use the
same basic process to make chemical energy
do work.
ENERGY CONVERSION
Chemical
energy or Entropy: Heat energy
potential Kinetic energy of movement
energy
Cellular respiration:
• Is the energy-releasing chemical breakdown of
fuel molecules.
• Provides energy for the cell to do work.
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3. Where does the energy come from?
Food Calories
A calorie is the amount of energy that raises the
temperature of one gram of water by one
degree Celsius.
1 Kilocalorie = 1000 calories.
= 1 food calorie
The unit used to measure the
energy in food.
We can burn off this energy by
doing some activities
So… where does this energy go?
To make a molecule called ATP
Cellular Respiration: process of breaking down
organic molecules from food to release energy.
TAKES PLACE IN THE MITOCHONDRIA
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4. What’s ATP?
ATP for Adenosine TriPhosphate.
• Consists of adenosine plus a tail of 3 phosphate groups.
• Loose one phosphate group to give ADP (Adenosine
DiPhosphate), that is accompanied by the release of
energy.
The transfer of
Phosphate to
other molecules
provides energy
that can be used
to drive cellular
work.
The ATP Cycle
– Cellular work spends ATP.
– ATP is recycled from ADP and phosphate
through cellular respiration.
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5. 2. Enzymes
What are enzymes?
They are proteins that speed up chemical reactions
Metabolism is the sum total of all chemical
reactions that occur in organisms.
Most reactions in the cell occur with the help of
enzymes.
Activation Energy is the energy that triggers a chemical
reaction to proceed.
Enzymes lower the activation energy for chemical
reactions.
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6. CHARACTERISTICS OF ENZYMES
– very selective.
• Only catalyzes specific reactions.
– recognizes a specific substrate.
• The active site fits to the substrate, and the
enzyme changes shape slightly.
• This interaction is called induced fit.
– function over and over again.
Figure 5.9
BUT ENZYMES CAN BE STOPPED
Enzyme Inhibitors can inhibit a metabolic
reaction.
One way inhibitors work is by binding to the
active site, as substrate imposters.
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7. Other inhibitors bind at a remote site,
changing the enzyme’s shape.
3. Membrane Function
Transport of Molecules
Signal Transduction
Working cells must control the flow of materials
to and from the environment.
• Membrane proteins help with this task, they are the
custom agents of the cells.
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8. Here are some functions of protein membranes
CELL 1
CELL 2
Molecules can pass through the
membrane through different mechanisms
A. Passive Transport: Diffusion Across
Membranes
B. Osmosis and Water Balance
C. Active Transport
D. Exocytosis and Endocytosis: Traffic of
Large Molecules
A. Passive Transport:
Diffusion Across Membranes
– Molecules contain heat energy. They vibrate and
move around.
– Diffusion is one result of the movement of
molecules.
• Molecules tend to spread into the available space.
• Diffusion is passive transport; NO energy is needed.
– Another type of passive transport is facilitated
diffusion, the transport of some substances by
specific transport proteins that act as selective
corridors.
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9. B. Osmosis and Water Balance in
Cells
Osmosis is the passive transport of water
across a selectively permeable membrane.
– A hypertonic solution
• Has a higher concentration of
solute.
– A hypotonic solution
• Has a lower concentration of solute.
– An isotonic solution
• Has an equal concentration of
solute.
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10. Water Balance in Animal Cells
– The survival of a cell depends on its ability
to balance water uptake and loss.
– Osmoregulation is the control of water
balance in animals.
Water Balance in Plant Cells
– Water balance in plant cells is different.
• They have rigid cell walls.
• They are at the mercy of the environment.
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11. C. Active Transport:
The Pumping of Molecules Across
Membranes
Active transport requires energy to move
molecules across a membrane.
IN SUMMARY
Passive Active
No energy Energy
Facilitated
Diffusion Osmosis
Diffusion
Inside the cell
Cytoplasm
D. Exocytosis and Endocytosis:
Traffic of Large Molecules
Mechanisms that involve fusion with the plasma membrane and
use of vesicles.
• Exocytosis (Exo ⇒ Exit)
Secretes substances outside of the cell.
• Endocytosis
Takes substances inside of the cell.
Exocytosis Endocytosis
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12. Different endocytosis:
• In phagocytosis (“cellular eating”), a cell
engulfs a particle and packages it within a
food vacuole.
• In pinocytosis (“cellular drinking”), a cell
“gulps” droplets of fluid by forming tiny
vesicles.
• Receptor-mediated
endocytosis is
triggered by the binding
of external molecules to
membrane proteins.
The Role of Membranes in Cell
Signaling
– Cellular communication
• Begins with the reception of an extracellular signal.
– The signal transduction pathway
• Consists of proteins and other molecules that relay
the signal.
Signal Transduction
Pathway
Cellular Response
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13. An uncharged atom of gold has an atomic number
of 79 and an atomic mass of 197. This atom has
_________ protons, _______ neutrons, and
__________electrons.
a. 79 …118 …79
b. 118 …79 …118
c. 276 …118 …79
d. 79 …276 …79
Enzymes increase the rate of a reaction by
________.
a. decreasing activation energy
b. changing the pH
c. increasing the temperature of the
substances
d. contributing water to
the reaction
TRUE or FALSE:
Facilitated diffusion requires energy to drive a
concentration gradient.
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