Slide 1
Earlier in the course, we attempted to define life. We
cannot come up with one simple perfect definition but we do know that all
living things are highly ordered and living things grow, reproduce, respond to
the environment, and regulate their internal environments.
All of these processes require energy so all living things require a constant supply of energy.
In the context of energy, organisms are open systems. This means that they take in energy from the environment and also return energy to the environment.
If the organism we are talking about is an animal - the energy comes in the form of food. If the organism is a plant - the energy comes from sunlight.
Slide 2
To discuss the energy requirements of organisms, we must define
energy. We can't see energy but we can observe what energy does to
matter. When matter moves - energy is acting upon that matter.
Energy occurs in two basic classes. One class is potential energy. This is energy that matter has due to its position or location so it is stored energy.
For example, when this ball is at the top of a hill - it has stored energy. As we will talk about (and as you obviously know from your observations of the world) - it is likely that this ball will roll down hill.
Slide 3
As the ball rolls down hill, the potential energy is converted to
kinetic energy. Kinetic energy is the energy of moving matter.
Slide 4
Our analysis of energy is going to focus on the energy of chemical
bonds. Our model molecule will be the sugar glucose - because glucose is
a common energy source for organisms.
Glucose is a 6-carbon sugar that has a lot of energy stored in its chemical bonds. When we use glucose for energy - there needs to be a small input of energy to break these bonds. However, when the bonds reform to create the breakdown products of glucose metabolism - more energy is released than was invested.
Slide 5
Let's look at a sample problem from the practice tutorial
questions to illustrate this idea.
Organisms like ourselves use glucose as an energy source but we need oxygen to fully breakdown glucose. When the bonds reform they reform to produce carbon dioxide and water. We will be learning more about this in the next tutorial.
The breakdown of glucose requires breaking all of the Carbon-Carbon bonds and all of the Carbon-Hydrogen bonds.
This image of glucose is a typical representation of an organic molecule. To understand this representation you need to know that there is a Carbon atom at each corner of the molecule.
Pause this recording and see if you can count all of the carbon-carbon bonds and all of the carbon-hydrogen bonds. Once you have counted them all - hit play again.
Slide 6
You should have counted 5 carbon-carbon bonds and 7
carbon-hydrogen bonds. Remember, there is a carbon at each corner of the
molecule.
Now - calculate the total amount of energy that must be invested to break these bonds. Pause the recording and hit play when you have calculated the answer.
Slide 7
The answer is C - 1017 kcal/mole. This means it takes 1017 kcal of
energy to break the bonds in a glucose molecule. This is the energy
investment phase.
Slide 8
But the goal of breaking down a glucose molecule is to gain
energy to do cell work. So next let's think about how much energy is
gained. This question tells you that 1703 kcal of energy are gained when
the broken bonds reform around oxygen. So how much energy is
gained?
Pause the recording to calculate the energy gain from metabolizing a molecule of glucose.
Slide 9
The answer is B - 686 kcal/mole. This means that when we
metabolize a molecule of glucose - we get an energy gain of 686 kcals of
energy.
Slide 10
This is why we eat. We need energy to do cell work and that
energy come from our food. We will focus on glucose as our food source
but we also get energy from eating proteins and fats.
When we study the energy uses of organisms - we are talking about thermodynamics. Thermodynamics is the study of energy transformations within a system.
Organisms are open systems - we take in energy from our environments but we also return energy to our environments.
All of these energy transformations within our cells are collectively referred to as our metabolism.
Our metabolism is made up of anabolic reactions and catabolic reactions. Recall from our earlier discussions that anabolic reactions are energy requiring reactions that build macromolecules. It should make intuitive sense that it takes energy to build a large complex molecule. Catabolic reactions are energy releasing reactions that result in the breakdown of a macromolecule. When an energy rich molecule like glucose is broken down - energy is released.
We will be looking at these ideas in more detail in the next several tutorials.