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Transport
Use the magnet board to illustrate a plasma membrane. Use the magnets to represent
solutes and show the processes of passive, active, and facilitated diffusion—you need to
draw the appropriate proteins in the membrane if they are required. Make sure the
students understand which way the gradient is going and which processes require ATP.
Points:
• Channel proteins
• Cotransport (symporters)—H+ / sucrose, anti-porters—Na+/H+
o Symport=same direction of diffusion, antiport=opposite
• Gradients—chemical, electrochemical
o Chemical=solute concentration, electrical=ion/charge gradient
Make the students draw in the plasma membrane and the proteins correctly, the transport
proteins will be integrins.
Now show osmosis by adding a representation of water and changing the tonicity of one
side. Insist on the fact that water follows solute concentrations—not changing water
gradients. Assume for this representation that the membrane is only permeable to water
and that the solute is impermeable to a plasma membrane (sucrose).
What would happen if you put a red blood cell in a hypotonic solution (i.e. what would
happen if you gave someone an IV with pure water instead of a saline solution)?
Energy and Enzymes (Orr Version) - Key
Discuss this activity as a class. An overhead is provided.
The following graph is a representation of a typical enzymatic reaction. Using the
following words, label the numbered items on the graph:
-
Reactants 3
Products 4
Transition state without enzyme present 7
Transition state with enzyme present 8
free energy 1
activation energy without enzyme 5
activation energy with enzyme 6
time of reaction. 2
7
8
5
6
1
3
4
2
Peer Teaching on Enzymes (Orr Version) - Key
Materials: Cut out the topics at the end of this document
There is no better way to learn something than to have to explain it to someone else.
Thus, in this section, the students will teach each other. Have the students find partners
and select one topic. Each pair will “teach” the topic they select to the other students.
Make sure you emphasize the different types of inhibition.
Topic 1: What an enzyme is;
Key words: protein, catalyst, rate of reaction, consumed
An enzyme is a protein catalyst that speeds up the rate of biological reactions without
being consumed.
Topic 2: Enzyme function;
Key words: substrates, products, active site, energy of activation, transition state
The substrates fit into the active site of the enzyme, which lowers the energy of activation
by stabilizing the transition state and speeds the reaction. The products are released
from the active site.
Topic 3: Coupled reactions;
Key words: exergonic, endergonic, ATP, phosphorylation
Exergonic reactions are ‘coupled’ or combined with endergonic reactions that the cell
needs to perform. This way, the energy from the exergonic reaction can make the
endergonic reaction go. ATP is a common source of energy for such reactions.
Breakdown of ATP (exergonic) is coupled to another reaction when one of the phosphate
groups on ATP is put onto one of the substrates of the other reaction. This is called
‘phosphorylation’ of that substrate, and adds energy to it.
Topic 4: Enzyme inhibitors;
Key words: competitive, noncompetitive, active site, feedback
Competitive inhibitors bind in the active site and block it, while noncompetitive (or
allosteric) inhibitors bind at a site distant from the active site, but cause the active site to
take on a less functional shape. Feedback inhibition is when the products of the reaction
block the enzyme active in that reaction.
Topic 5: Factors affecting enzyme function;
Key words: temperature, pH, tertiary structure, optimum
Temperature and pH change the tertiary structure of proteins and alter the way they
function. The temperature or pH at which the enzyme functions best is called the
optimum temperature or pH.
Demonstrate.
Do the short activity we discussed in the meeting. Have students pair up to make
‘sucrose’ molecules, and another student who is the ‘sucrase’ enzyme break them apart.
Ask them which parts of the student enzyme are the active sites? Hands
Also ask another student to act as a competitive inhibitor or a noncompetitive inhibitor.
Review Questions
Metabolism:
The totality of an organism’s chemical processes,
consisting of catabolic and anabolic pathways.
Anabolic reactions:
(1) Reactions characterized by the build up in the
body of complex chemical compounds from smaller
simpler compounds (e.g., proteins from amino acids),
usually with the use of energy.
Catabolic reactions:
(pathways)
A metabolic pathway that releases energy by
breaking down complex molecules into simpler
compounds.
Kinetic energy:
The energy of motion, energy in the process of doing
work.
Potential energy:
The energy stored by matter as a result of its location
or spatial arrangement, chemical bonds provide
potential energy.
Adenosine triphosphate:
(ATP)
A molecule composed of ribose sugar, adenine, and
three phosphate groups. ‘High-energy bonds,’ that
require considerable energy to form and release that
energy again when broken; attach the last two
phosphate groups. ATP serves as the major energy
carrier in cells.
Free energy:
A quantity of energy that interrelates entropy (S) and
the system’s total energy (H); symbolized by G. The
change in free energy of a system is calculated by the
equation
Δ G = Δ H – T Δ S, where T is absolute temperature.
Exergonic reaction:
A spontaneous chemical reaction in which there is a
net release of free energy.
Endergonic reaction:
A nonspontaneous chemical reaction in which free
energy is absorbed from the surroundings.
Enzyme:
A class of proteins serving as catalysts, chemical
agents that change the rate off a reaction without
being consumed by the reaction.
Substrate:
The substance on which an enzyme works.