Enzyme Kinetics
The following simulation is designed to give you the opportunity to test a hypothesis related to the enzyme kinetics of three enzymes. You may test a hypothesis related to problems associated with the effects of pH and temperature on enzyme reactions. An example of a problem might be: What are the effects of changes in pH on the enzyme-substrate reaction of three different enzymes? Your first task would be to develop a hypothesis (a guess) such as: Each enzyme will work better as you increase the pH. You will be able to use this program to simulate a test of your hypothesis. Your second task would be to design a way to test your hypothesis. This program will let you test your hypothesis, by changing the pH around the enzyme-substrate reaction, have the computer run the and you will then be able to analyze the results of the experiment which will include the amount of enzyme concentration, substrate concentration and/or product produced over time. On the experiment screen you will see an "? " button, click on this button to get instructions on running the experiments. To start, your instructor will present you with a problem and/or hypothesis to test. First click on the Prediction button (picture of the clip board above the word prediction to the right) to write about your experimental design and what you predict will happen. Next - come back to this screen and click on the enzyme you would like to study (right side of the screen) to perform your simulated experiments. Then - come back to this screen, click on the clip board, above the Proof button to write about the results of your experiment(s).
Osmosis
This is an experimental setup, which will allow you to simulate experiments involving diffusion and osmosis. You will be experimenting with an "artificial cell", which is surrounded by a semi-permeable membrane (made of dialysis tubing), and is placed in a beaker of water. The cell may contain a certain amount of sucrose, determined by you, dissolved in water. You may set up the experiments by adjusting the amount of sucrose that you want in the cell, and the degree of membrane permeability to sucrose and/or water., and test the affect of these variables on the flow of water into and out of the cell. You may set up these parameters by clicking on the button below called "Osmosis Experiment" below and then using the sliding buttons provided. You may run the experiment from there and view the simulated measurements of the water concentration inside the cell, water concentration outside the cell, the volume inside the cell or the volume outside the cell all over time. You may graph the data sets yourself and then you can view a graphical representation of this data on the same card. This will indicate if your graph was correct. For instructions on how to work this simulated experiment click on the help "?" button at any time
Cell Growth
The number of cells in a population will increase exponentially with time, however, different populations of cells will grow at different rates. These different rates might be dictated by the species of organism or the growth conditions such as temperature and pH. The growth of a random culture of cells is described by the differential equation dN/dt=kN, Here, N is the number of cells present at time t, dN/dt is the change in the cell number with time and k is the growth constant which is specific for each species of cell or growth condition. The above equation may be solved by integration and is expressed as 2.3 log 10(N2/N1)=k(t2-t1). A conventional value that expresses the specific rate of growth of a population of cells under a specified set of conditions is the doubling time. The doubling time is the time required for the number of cells in a population to double during exponential growth. The relationship between the growth constant (k) and the doubling time (T) can be expressed as T=0.693/k. This simulation of experiments will allow you to investigate exponential cell growth of any cell population over time. To begin, click the button below titled Cell Growth Experiment. You may then adjust the t1 (initial time the cells were counted), t2 (the next time the cells were counted), the t1cells (the initial number of cells counted) and the t2 cells (the number of cells counted at t2), using the slide bars provided, run the experiment, then observe the data collected over time and the graphical relationship between the time and cell concentration. Observe the growth constant (k) and doubling time (T) as it relates to your cell counts over time. The data that you observe represents a simulated growth of cells, starting with a cell population of 1000, over a period of time (days). The growth dynamics of this group of cells is based on the data that you determined when you Set up the Experiment. Problem 1: Suppose that at t1, the number of cells in a population is 29,703 and at t2, 18 hours later, there are 362,745 cells. What will be the doubling time of this population. Problem 2: Can you find a relationship between K and the doubling time. Problem 3: In a population of cells growing exponentially, as the growth rate increases, what happens to the doubling time? Click on the Prediction button to write what you predict the answers to be.
Hyperchromic Effect
Renaturing (reannealing) of DNA can be accomplished by lowering
the temperature. By following changes in UVL absorption one can
assess the size of an organisms genome and the complexity of the
DNA.
DNA is easily denatured (called melting) by extremes of temperature
and pH (hydrogen bonds between complementary bases are disrupted).
When the temperature of a native solution of DNA is elevated,
the resulting melting is accompanied by an increase in ultraviolet
light (UVL) absorption. This HYPERCHROMIC EFFECT occurs because
the pyrimidines and purines can absorb more light than when they
are part of a double helix. A quantitative measure of the change
in UVL absorption as the temperature of the DNA solution is slowly
elevated and is called the melting curve. The point in the melting
curve at which the change from double to single stranded DNA is
half complete is called the Tm value and is characteristic of
a particular source of DNA.
Problem 1: What are the effects of changes in temperature on the
configuration of DNA? What is the Tm value for this DNA? Click
on the Prediction button below and write what you think will be
the answers to these questions and why. After you have done this,
click on the Hyperchromic Effect Experiment button below to experiment
and test your hypothesis.
Hardy/Weinberg
This model will give you the opportunity to study the effects
of natural selection on allele frequencies. You are a scientist
who is studying peppered moths in England. The moths rest on trees
during the days and may be eaten by birds. In years past, air
pollution was less severe and the moths were protected, as their
color was similar to the tree bark. They were mottled grey.
Occasionally, the recessive gene (g) for grey color would mutate
to the dominant gene (G) for black.
The black moths were easily seen and eaten by the birds. They
usually did not survive long enough to reproduce and pass on this
dominant gene to their offspring.
With the increase in industry, and thus polluted air, the tree
bark became darker. Black moths became harder to see and the birds
began eating more of the grey colored moths. This caused a change
in the frequencies of these genes among the moth population. Problem
1: Ten years ago you counted 72 black moths and 22 white on
the trees in England. Today you measured 51 black and 42 white.
What has happened to the gene frequencies and why? What do you
expect to happen to the phenotypes of these moths over the next
6 generations? Why? Problem 2: Ten years from now you anticipate
the burning of more and more fossil fuels in England. What do
you expect to happen to the phenotypes and genotypes of the moths
over this period of time and why?
Predator/Prey
The Year is 1992. The place is the Catoctin Mountain National Park Region, Thurmont, Maryland . You have been given the responsibility of managing the wildlife in the Park in a manner that satisfies the major interest groups of the area. There are many groups whose concerns you will need to balance as you play the game.
ooo Local Farmers and Ranchers:
The farmers and ranchers of the region are concerned about the
large number of predators that exist in the Park Region. The
predators feed primarily on the rodents and deer, but are beginning
to make raids on cattle herds and local crops. The economic losses
to ranchers and farmers are growing. To combat the problem, ranchers
encourage you to set a high bounty on predators. A high bounty,
they argue, will encourage hunting of predators and thereby keep
cattle and crop losses to a minimum. Ranchers are also beginning
to graze their cattle on the fields. Ranchers want you to ensure
that the forage on the range remains healthy. Because ranchers
and farmers in this area exert political clout, you have been
counseled to heed their advice.
ooo Hunters:
Deer hunting is growing in popularity in this region. Pressure
is now growing for you to increase the annual deer tag allotment.
Deer tags, of course, are the major source of funding for your
management department.
ooo Conservationists:
Conservationists are concerned about the "purity"
of this very popular camping and hunting region. They have told
you that they think you can be a good manager for the Mountain
Park Region. They have also warned you not to let the system
get "out of control."
ooooo To Play the Game ooooo
First, click on the "Play" button. Doing so
will allow you to set the major characteristics of the Catoctin
Mountain Park region. (Use the help "?" button
for instructions.) Once you're satisfied that you like the initial
setup for the environment, click on the "Play!"
button. While playing the game, you will have the opportunity
to set predator bounties, establish deer tag quotas, and truck
in food for deer -- should they for some reason run short on food.
There will be 5000 deer, initially, in the region. When you are
done playing, you can examine in detail what happened, and why.
