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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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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.

Chemical energy or potential energy

Entropy: Heat energy Kinetic energy of movement

ENERGY CONVERSION

Cellular respiration: •  Is the energy-releasing chemical breakdown of

fuel molecules. •  Provides energy for the cell to do work.

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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.

Where does the energy come from?

We can burn off this energy by doing some activities

So… where does this energy go?

Cellular Respiration: process of breaking down organic molecules from food to release energy.

TAKES PLACE IN THE MITOCHONDRIA

To make a molecule called ATP

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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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2. Enzymes

Metabolism is the sum total of all chemical reactions that occur in organisms. Most reactions in the cell occur with the help of enzymes.

What are enzymes?

They are proteins that speed up chemical reactions

Activation Energy is the energy that triggers a chemical reaction to proceed. Enzymes lower the activation energy for chemical reactions.

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– 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.

CHARACTERISTICS OF ENZYMES

Figure 5.9

Enzyme Inhibitors can inhibit a metabolic reaction. One way inhibitors work is by binding to the active site, as substrate imposters.

BUT ENZYMES CAN BE STOPPED

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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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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

– 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.

– Molecules contain heat energy. They vibrate and move around.

A. Passive Transport: Diffusion Across Membranes

– 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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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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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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C. Active Transport: The Pumping of Molecules Across

Membranes

Active transport requires energy to move molecules across a membrane.

Diffusion Facilitated Diffusion Osmosis

Inside the cell Cytoplasm

Passive No energy

Active Energy

IN SUMMARY

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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•  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.

Different endocytosis:

•  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.

Cellular Response

Signal Transduction Pathway

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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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TRUE or FALSE: Kinetic energy is the energy of movement