Journal Entry:
What is DNA? What are the subunits of DNA?
Objectives:
1. List 3 important events that led to understanding the
structure of DNA.
2. Describe the basic structure of a DNA molecule.
3. Explain how DNA molecules can be copied.
 DNA stands for deoxyribonucleic acid.
 DNA is the genetic material that determines inherited
characteristics.
 Nucleotides: The Subunits of DNA
 DNA is made of subunits called nucleotides.
 A nucleotide consists of a sugar, a phosphate, and a base.
 Chargaff’s Rule
 Erwin Chargaff found that the amount of adenine in
DNA always equals the amount of thymine, and the
amount of guanine always equals the amount of
cytosine. (A = T, C= G)
 Franklin’s Discovery
 Chemist Rosalind Franklin was able to make images of
DNA molecules by using X-ray diffraction.
 X-ray diffraction: X rays of a DNA molecule projected on film.
 Showed that DNA has a spiral shape.
 Watson and Crick’s Model
 James Watson and Francis Crick used Chargaff’s and
Franklin’s research to build a model of DNA.
 The model, which looked like a long, twisted ladder,
eventually helped explain how DNA is copied and how
it functions in the cell.
 The Double Helix
 The shape of DNA is
known as a double helix.
 The two sides of the ladder
are made of alternating
sugar parts and phosphate
parts.
 The rungs of the ladder are
made of a pair of bases.
 How Copies Are Made
 During replication, a DNA molecule is split down the
middle, where the bases meet.
 The bases on each side of the molecule are used as a
pattern for a new strand.
 When Copies Are Made
 DNA is copied every time a cell divides.
 Each new cell gets a complete copy of all the DNA.
 1. Unwinding: Old strands that make
up the parental DNA molecule are
unwound and “unzipped”. A special
enzyme called helicase unwinds the
molecule.
 2. Complementary base pairing:
New complementary nucleotides are
paired together.
 3. Joining: The complementary
nucleotides join to form new
strands.
 In a cell that has a nucleus,
the strands of DNA
(chromatin) and proteins are
bundled into chromosomes.
 A gene consists of a string of
nucleotides that give the cell
information about how to
make a specific trait.
 Groups of 3 bases form the code for an amino acid.
 Many amino acids strung together form a protein.
 Proteins and Traits
 Proteins act as chemical triggers for many of the
processes within cells.
 Proteins help determine traits.
 A gene is a segment of DNA that specifies the amino
acid sequence of a protein.
 Help from RNA
 Another type of molecule that helps make proteins is
called RNA, or ribonucleic acid.
 RNA is so similar to DNA that RNA can serve as a
temporary copy of a DNA sequence.
 Genes pass genetic information onto RNA molecules
which are more directly involved in protein synthesis.
 The nucleotides in RNA, however, contain the sugar
ribose and the bases adenine, cytosine, guanine, and
uracil (which replace thymine).
 There are 3 major classes of RNA.
 Messenger RNA (mRNA): Takes a message from DNA in
the nucleus to the ribosomes in the cytoplasm.
 Transfer RNA (tRNA): Transfers amino acids to the
ribosomes.
 Ribosomal RNA (rRNA): Makes up the ribosomes,
where amino acids are collected to form proteins (many
amino acids form a protein).
Journal Entry:
Unscramble the following words:
tpsoneir
neesg
Now think of 3 words you associate with each of the
above words and use them all in a paragraph that
highlights what you know about DNA.
Objectives:
1. Explain the relationship between DNA, genes, and
proteins.
2. Outline the basic steps in making a protein.
3. Describe three types of mutations, and provide an
example of a gene mutation.
4. Describe two examples of uses of genetic knowledge.
 The Making of a Protein
 The first step in making a protein is to copy one side of
the segment of DNA containing a gene.
 This copy is called messenger RNA (mRNA).
 A ribosome is a cell organelle composed of RNA and
protein.
 A ribosome uses mRNA, transfer RNA (tRNA), and
amino acids to make proteins.
 Mutations
 Changes in the number,
type, or order of bases on
a piece of DNA are
known as mutations.
 Do Mutations Matter?
 There are three possible consequences to changes in
DNA: an improved trait, no change, or a harmful trait.
 How Do Mutations Happen?
 Mutations happen regularly because of random errors
when DNA is copied.
 Any physical or chemical agent that can cause a
mutation in DNA is called a mutagen.
 A mutation, such as a substitution, can be harmful
because it may cause a gene to produce the wrong
protein.
 A simple change in an amino acid can cause a disease
such as sickle cell anemia.
 Genetic Engineering
 Scientists can manipulate individual genes within
organisms.
 This kind of manipulation is called genetic engineering.
 Genetic Identification
 Your DNA is unique, so it can be used like a fingerprint
to identify you.
 DNA fingerprinting identifies the unique patterns in an
individual’s DNA.