The Working Cell
ATP & Cellular Work
Enzymes
Membrane Function
Chemical Energy
Chemical EnergyWhere do our muscles get energy to perform work?
From food we eat
When body breaks down food molecules what happens?
Energy from food molecules is stored
Potential energy
Can be converted to kinetic energy
Or, muscle activity
When, how is stored energy released?
During the process of cellular respiration
What does cell respiration do?Converts chemical energy (food)
To another form of energy: ATP
What is the significance of ATP?
More cellular respiration and ATP in Chapter 6
Food
Cell respiration
?
? ?
Energy for cellular work
Muscle work
?
?
How much energy do we get to use for cellular work?
The diagram gives us a clue
What percent is given off as heat?
What percent is captured as ATP?
~60%
~40%
What is the ~60% heat converted to?
Food Calories
– is the amount of energy – that raises the temperature – of one gram (g) of water
– by one degree (1) Celsius
What is a calorie? A unit of energy
And, how is it measured?
How much energy is in this
handful of peanuts? Enough to boil a quart of water!
(in kilocalories)(as fuel for energy)
The kilocalorie (Kcal or C) is 1,000 calories• The unit used to measure the energy in food
Pizza!
What would you have to do to burn off the calories from this
pizza?
You’d have to run about 14 miles!
ATP
Why is ATP so important? It ‘powers’ all cellular work
How? • It releases ‘free’ energy
(adenosine triphosphate)
• When its phosphate bonds are hydrolyzed
(or, broken down)
What is ATP? It is a nucleotide that performs many essential roles in the cell
Phosphate ‘tail’
What does the ATP structure look like?
Adenosine
Ribose sugar
ATP is broken down to ADP
+
Accompanied by release of energy
ADP? (adenosine diphosphate)
Where’s the power in ATP?
Unstable. Why?
Repulsion between negatively charged phosphate groups
In the phosphate tail
Release of last P makes energy available
(adenosine diphosphate)
What about that ‘leftover’ phosphate?
Its used to energize other molecules
What do these other molecules do?
Help cells do 3 main types of work
• Mechanical • Transport• Chemical
ATP and Mechanical Work?
Phosphate transferred to special motor proteins
(muscles)
What happens then?Proteins change shape
Muscle cells contractPerform mechanical work
ATP and Transport Work?
Phosphate transferred to brain cells
What happens then?Ions pumped across membranes
ATP and Chemical Work?
Make cell’s giant molecules
What happens then?Amino acids are linked to make a protein
Via a dehydration reaction
Reactants Products
What is the ATP cycle?
Our cells need energy (ATP) all the time!
Its recyclable!
Cellular respiration
Food
Energy in…
To regenerate ATP
Energy out…
For cellular work
The 3rd phosphate
Acts as an energy shuttle
Learning check
1. What is the source of energy for regenerating ATP from ADP?
2. A kilocalorie is equal to _______?
3. Most cellular work is accomplished by _____ energizing molecules by _____ them.
a. enzymes ... activating
b. diffusion ... activating
c. substrates ... transferring a phosphate group to
d. ATP ... transferring a phosphate group to
Enzymes What is the barrier for reactions to occur?
Energy must be added
What is this energy called?
Energy of activation EA
How does the cell overcome the barrier?Uses a specialized protein, an enzyme
What does the enzyme do?Serves as a biological catalystIncreases the rate of the reaction
‘lowers the energy barrier’Reduces activation energy
• Binds to specific molecules (substrates)
• Puts them under physical or chemical stress
• Which makes it easier to break bonds
• And start a reaction
What are the details?
• Enzyme very selective
• At the enzymes active site
Induced fit?
sucrase
Substrate ? Sucrose
What is this site?
What are these molecules?
Identify the steps?1. Enzyme available with empty active site
2. Substrate binds to enzyme
3. Substrate converted to products
4. Products are released
What are enzyme inhibitors?
‘Imposters’ that plug up the active site
Or at some remote site
How do they function?
Binding changes the shape of the enzyme
Active site no longer receptive
Examples of enzyme inhibitors?
Poisons e.g., malathion
Antibiotics
Inhibits an enzyme required for normal function of the insect nervous system
e.g., penicillin
Inhibits an enzyme bacteria use to make cell walls
Membrane Function
1. Endocytosis moves materials _____ a cell via _____.
a. into ... facilitated diffusion
b. into ... membranous vesicles
c. into ... a transport protein
d. out of ... diffusion
e. out of ... membranous vesicles
2. What name is given to the process by which water crosses a selectively permeable membrane?
a. diffusion
b. passive transport
c. phagocytosis
d. pinocytosis
e. osmosis
3. Active transport ______.
a. Can move solutes against their concentration gradient
b. Can involve the transport of ions
c. Requires the cell to expend energy
d. Uses ATP as an energy source
e. All of the above
2. A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mothers milk. These molecules probably enter the cells lining the baby’s digestive tract via ____________?
a. osmosis
b. passive transport
c. exocytosis
d. active transport
e. endocytosis
Hydrolysis Decomposition of a substance by the insertion of water molecules between certain of its bonds. Food is digested by hydrolysis.
protein A three-dimensional biological polymer constructed from a set of 20 different monomers called amino acids.
enzyme A protein serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction.
substrate The reactant on which an enzyme works.
active site The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.