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DNA
Pre-Lesson Reading:
1.
What is cell?
a. Cells are the basic building blocks of all living things.
b. Human body is composed of trillions of cells.
c. Cells provide structure for a body, take in nutrients from food, convert
nutrients into energy, and carry out specialised functions.
2.
What is DNA?
a.
In a cell, DNA (deoxyribonucleic acid) molecules are packaged in
chromosomes within the nucleus.
b.
In a human body cell, there are 23 pairs of chromosomes.
c.
DNA (deoxyribonucleic acid) is a large, polymeric molecule. A gene is a
segment of DNA molecule of a chromosome. It is the basic unit of
heredity. Genes determine the body characteristics of an organism. Each
inherited characteristic is controlled by one or several genes.
d.
DNA (deoxyribonucleic acid) is found in nearly every cell in the body.
One significant exception is red blood cells (lack nuclei).
e.
Nearly every cell in a person’s body has the same DNA.
f.
As shown in Figure 1, DNA looks like an incredibly long twisted ladder.
This shape is called a double helix. The sides of the ladder are a linked
chain of alternating sugar and phosphate molecules (called the backbone).
The rungs connected to the sugar molecules are known as bases.
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Figure 1 A representation of DNA model
g.
The DNA backbone is exactly the same in all people. On the other hand,
the rungs are different in people.
h.
Each rung is made up of two bases that link together. There are four bases
- adenine (A), thymine (T), guanine (G) and cytosine (C). Because of their
chemical nature, A will only link with T and G will only link with C (i.e.
A-T; G-C). No base can join with itself (i.e. No A-A / T-T / G-G / C-C).
i.
The order of the bases of DNA determines the information available for
building and maintaining an organism. This order is referred to as genetic
code.
j.
Human DNA consists of about 3 billion bases, and more than 99 % of the
base sequence in DNA is the same in all people. Less than 1 % is unique
to each individual (except identical twins).
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Lesson 8
DNA Fingerprinting
Worksheet 8.1
1.
What is DNA?
Decide whether the following statements are TRUE or FALSE.
a.
b.
c.
d.
e.
There are 46 pairs of chromosomes in the cell nucleus.
Chromosomes are made of DNA and proteins.
DNA determines the body characteristics of an organism.
DNA is extracted from red blood cells found in a blood sample.
The hair and teeth of the same person are composed of same DNA
f.
g.
molecules.
Identical twins have different base sequences of DNA.
In the DNA structure, adenine (A) will only link with cytosine (C) and
guanine (G) will only link with thymine (T).
Answers:
a.
b.
c.
d.
e.
f.
g.
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Follow-up Activity
Extended Reading– O. J. Simpson murder case
1. Download the article (O. J. Simpson murder case ) from the following websites:
a. O. J. Simpson Trial Homepage,
http://www.law.umkc.edu/faculty/projects/ftrials/Simpson/simpson.htm
b. http://phobos.ramapo.edu/~jweiss/laws131/unit3/simpson.htm
2. Read the article and answer the following questions:
a.
b.
c.
“If you are the lawyer of the defendant, what type of questions you would
focus to challenge the DNA evidence provided by the prosecutor? Why?”
Is it possible for criminals to erase traces of DNA evidence? Explain your
answers?
May refer to O. J. Simpson murder case to ask students more questions on
the use of DNA evidence in court case.
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