Lab 7 DNA and Chromosomes

Lab 7 DNA and Chromosomes
Objectives:
At the end of this lab you should be able to:
1. Describe the structure and function of DNA.
2. Know which bases in DNA pair with each other.
3. Define the terms chromatid, chromosome, diploid, and haploid.
4. Explain the composition and location of genes.
5. Be able to examine a cell and identify which stage of mitosis it is in.
DNA
The unique nature of your DNA and your life experiences define who you are.
Indeed this molecule defines the structure and function of every living cell. The
structure of this molecule reveals how it is duplicated. Soon after this structure
was defined, scientists were able to describe how this molecule is used in the
production of proteins. Now we can actually design genes to make specific
proteins. Before you can understand how we make designer genes, you first
need to understand the nature and function of genes; and that means
understanding the nature and function of DNA.
DNA structure
Locate the display (model and pictures) of the DNA molecule. You may also want
to refer to your textbook. DNA forms a double helix that resembles a twisted
ladder.
1. What molecules make up the sides of the ladder
_____________________________________________________________
2. What molecules make up the rungs of the ladder
_____________________________________________________________
3. What keeps the two sides of the ladder paired
_____________________________________________________________
4. DNA replication involves splitting the molecule in half. New base pairing with
each half of the original DNA, produces two new double helix molecules. With
normal base pairing, what sequence of DNA would pair with the following
sequence of DNA
A T T C G C G A A T
_____________________________________
5. Where is DNA located within organisms
_____________________________________________________________
_____________________________________________________________

Naked DNA - What does this molecule look like
Instructions for extracting DNA (adapted from Scientific American, Sept. 1998)
Use a garlic press to mash fruit. Please thoroughly rinse the garlic
press when you are done.
Place 5 ml of mashed fruit into a small beaker.
Add 10 ml of the chilled buffer.
Stir gently for 2 - 3 minutes
Strain the fruit/buffer mixture through a coffee filter into a beaker.
Pour the strained fruit into a clean test tube.
Add 10 ml of chilled ethanol by slowly trickling the alcohol down the
side of the test tube with a Pasteur pipet. The alcohol should sit on the
top of the fruit.
Chill your test tube in ice for 3 minutes. You should see two distinct
layers in the test tube.
Twirl a DNA hook in the bottom section and then pull the hook up into
the alcohol. Repeat this process until you no longer obtain additional
DNA.
Adding one drop of methylene blue to the test tube should help you
see some strands of DNA you might have missed.
6. Why do we mash our raw materials
_____________________________________________________________
_____________________________________________________________
7. The buffer contains 120 ml distilled water, 1/4 tsp salt, 1 tsp baking soda, and
1 tsp Dawn detergent. What does adding the detergent accomplish
_____________________________________________________________
_____________________________________________________________
8. What happens if you shake or vigorously stir the contents of your test tube
_____________________________________________________________
_____________________________________________________________
9. DNA isolated from different organisms has the same appearance to our
unaided eye. So what makes all these different DNA molecules different
_____________________________________________________________
_____________________________________________________________
Additional Questions
10. The total DNA in one cell is called the genome. Approximately how many
base pairs in the human genome ________________________________
11. Comparisons of the DNA of different human beings reveals that about 99.9%
of our DNA is identical. So about 0.1% of our DNA is unique. How many base
pairs in 0.1% of human DNA ________________________________

Chromosome structure
Chromosomes have a very specific structure. The diagram below is of a
duplicated chromosome. Label the following terms on the diagram.
centromere
chromatid
gene
Chromosome number
In organisms that reproduce by sexual reproduction, cells may have either one
complete set of chromosomes (haploid) or two complete sets of chromosomes
(diploid). Complete the following table.
Organism Haploid
Number of
Chromosomes (1N)
Organism Diploid
Number of
Chromosomes (2N)
Yeast (Saccharomyces 16
cerevisiae)
Corn (Zea mays) 20
Horsetail (Equisetum) 108
Fruit fly (Drosophila 4
melanogaster)
Frog (Rana pipiens) 26
Chimpanzee (Pan 24
troglodytes)
Human (Homo sapiens)

Genes
Genes are the basic units of inheritance and consist of a sequence of DNA. The
structural region of a gene is a sequence of DNA that specifies a sequence of
amino acids (i.e., a sequence of DNA base pairs that “code” for a protein. The
control regions of a gene are sequences of DNA that determine whether or not a
gene is turned on or off.
12. Where are the genes located
________________________________________________________________
________________________________________________________________
13. The entire set of genes for one organism is called its genome. Approximately
how many genes in the human genome ___________________
14. Which human chromosome is the biggest _____ the smallest ______
Chromosome Base pairs Genes Chromosome Base pairs Genes
1 245,203,898 2610 13 114,151,656 496
2 243,315,028 1748 14 105,311,216 1173
3 199,411,731 1381 15 100,114,055 906
4 191,610,523 1024 16 89,995,999 1032
5 180,967,295 1190 17 81,691,216 1394
6 170,740,541 1394 18 77,753,510 400
7 158,431,299 1378 19 63,790,860 1592
8 145,908,738 927 20 63,644,868 710
9 134,505,819 1076 21 46,976,537 337
10 135,480.874 983 22 49,476,982 701
11 134,978,784 1692 X 152,634,166 1141
12 133,464,434 1268 Y 50,961,097 255

You will be given a practice sheet with cells in various stages of mitosis. One
side of the sheet is of plant cells (onion root tip), and the other is of animal cells
(a whitefish embryo). Please examine them, and label each cell with its stage.
After we review; you will obtain a prepared slide of both onion root tip and
whitefish embryo. Focus all the way up to high power, and find at least two cells
in each stage. Draw sketches below.
Interphase
Major Events Onion Root Tip Whitefish Embryo
Prophase
Metaphase
Anaphase
Telophase