The Working Cell - De Anza College

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Transcript The Working Cell - De Anza College

The Working Cell
Chemical Energy
ATP & Cellular Work
Enzymes
Membrane Function
Chemical Energy
Where 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
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?
Can be converted to kinetic energy
Or, muscle activity
More cellular respiration and ATP in Chapter 6
Cell respiration
Food
?
?
?
?
?
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?
~60%
What is the
~60% heat
converted to?
~40%
What percent is captured as ATP?
Food Calories
What is a calorie?
A unit of energy
And, how is it measured?
– is the amount of energy
– that raises the temperature
– of one gram (g) of water
– by one degree (1o) Celsius
How much energy is in this
handful of peanuts?
Enough to boil a quart of water!
(as fuel for energy)
(in kilocalories)
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
(adenosine triphosphate)
What is ATP?
It is a nucleotide that performs
many essential roles in the cell
Why is ATP so important?
It ‘powers’ all cellular work
How?
• It releases ‘free’ energy
• When its phosphate bonds are
hydrolyzed
(or, broken down)
What does the ATP structure look like?
Adenosine
Phosphate
‘tail’
Ribose sugar
+
ADP?
ATP is broken down
Accompanied
to ADPby release of energy
(adenosine
diphosphate)
Where’s the power in ATP?
In the phosphate tail
Unstable. Why?
Repulsion between negatively
charged phosphate groups
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
•
Mech
•
anical
Trans
•
port
Chem
ATP and Mechanical Work?
Phosphate transferred to special
motor proteins
(muscles)
What happens then?
Proteins change shape
Muscle cells contract
Perform 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
Reactants
Products
What happens then?
Amino acids are linked to make a
protein
Via a dehydration reaction
What is the ATP cycle?
Its recyclable!
Our cells need energy (ATP) all the time!
Energy out…
Food
Cellular respiration
Energy in…
To regenerate ATP
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 catalyst
Increases the rate of the reaction
‘lowers the energy barrier’
Reduces activation energy
What are the details?
• Enzyme very selective
• Binds to specific molecules (substrates)
• At the enzymes active site
• Puts them under physical or chemical stress
• Which makes it easier to break bonds
• And start a reaction
Substrate ? Sucrose
Induced fit?
What is this site?
sucrase
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
Inhibits an enzyme required for normal
function of the insect nervous system
Antibiotics
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.
c.
d.
e.
into ... membranous vesicles
into ... a transport protein
out of ... diffusion
out of ... membranous vesicles
2. What name is given to the process by which
water crosses a selectively permeable membrane?
a. diffusion
b.
c.
d.
e.
passive transport
phagocytosis
pinocytosis
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 diseasefighting 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.