Structure and Function of DNA
1. DNA stands for
deoxyribonucleic acid.
2. Watson and Crick were
the first scientists to
construct a working
model of DNA in 1953.
3. DNA is found in the nucleus
of the cell.
4. Genetic material of living
things is made of DNA.
5. Composed of 2 strands, or
chains. (double-stranded)
6. Double helix shape (twisted,
coiled)
7. DNA is a very long molecule
that is made up of smaller
subunits called nucleotides
which consist of three parts:
a. Simple sugar (sugar in
DNA is deoxyribose)
b. Phosphate group
c. Nitrogen base
8. DNA contains four
nitrogen bases:
a. Adenine (A)
A-T
b. Thymine (T)
c. Cytosine (C)
C-G
d. Guanine (G)
9. Adenine and Guanine
are double-ring bases
called purines. (HINT:
purines have nine sides
and hence are noted by
adenine and guanine)
Adenine
Guanine
10. Cytosine and Thymine
are smaller, single-ring
bases called pyrimidines.
(HINT: pYrimidines
(cytosine and thymine)
contain the letter Y)
Cytosine
Thymine
11. The two chains of
nucleotides are joined by
hydrogen bonds.
12.Sides of DNA are made
up of a sugar and
phosphate.
13. In each chain of
nucleotides, sugar of one
nucleotide is joined to the
phosphate group of the
next nucleotide by a
covalent bond.
14.Rungs of DNA are the
nitrogen base pairs.
15. Base pair – 2 bases on the
same rung
16. In DNA, cytosine always
bonds with guanine and
adenine always bonds with
thymine.
17.Organisms are different
from each other, even
though their genetic
material is made up of the
same molecules, because
the order of nucleotides in
their DNA is different.
DNA: Double Helix WS
Notes:
1. Building block is the
nucleotide:
Phosphate group
5-C sugar deoxyribose
nitrogen base
1. Adenine (A)
2. Thymine (T)
3. Cytosine (C)
4. Guanine (G)
2. Double helix structure held
together by weak hydrogen
bonds.
3. Which nitrogen bases
always pair?
cytosine with guanine
adenine with thymine
Genes determine your traits or
characteristics. (At least one
gene per trait.)
How many chromosomes in
humans? 46
How many genes? Thousands
(100,000)
A chromosome is just one long
strand of a DNA molecule.
Answers to picture:
1. Cell(cytoplasm)
2. Nucleus
3. Chromosome
4. Gene
DNA and Genes Worksheet
Study the Diagram:
When the DNA ladder replicates, or
copies itself, the ladder breaks
apart. You can think of the ladder
breaking a part as a zipper
unzipping. When the two sides of
the ladder are apart, free nucleotides
attach to the nucleotides already on
the sides of the ladder, and two
copies of the DNA are formed. The
copies are the same as the original
because adenine (A) usually pairs with
thymine (T). Cytosine (C) usually pairs
with guanine (G).
The diagram below shows an unzipped
strand of DNA. Write the letters
(A,T,C, or G) of the bases that will pair
with the bases on the strand. Some of
the bases have been paired for you.
C-G
T-A
A-T
G-C
G-C
T-A
C-G
A-T
A-T
1. True or False? Nucleotide
bases already attached to
proteins form the copied side
of the DNA ladder. False
2. True or False? The process of
DNA replication results in a
copy of the original strand of
DNA. True
3. True or False? Sugar and
phosphates provide the energy
for DNA replication. False
4. True or False? The final result
of DNA replication is two
copies of the original DNA
strand. True
DNA Replication
1. Replication is the process
by which DNA copies itself
before mitosis or meiosis, so
that each daughter cell will
have an exact copy of the
genetic code.
2. Occurs in the nucleus.
3. Steps of replication:
a. Two strands of DNA
separate at their base pairs
by breaking, or unzipping,
the hydrogen bonds.
b. Each strand builds its
opposite strand by base
pairing with free-floating
nucleotides. Each guanine
(G) pairs with cytosine (C),
while each thymine (T) pairs
with an adenine (A).
c. Each original strand
serves as a template or
pattern for the creation
of a new strand.
d. Each new DNA molecule
will have one strand of
nucleotides from the original,
or parent, strand and one
strand of nucleotides from
the free-floating nucleotides.
e. Results in the formation
of two DNA molecules each
of which is identical to the
original DNA molecule.
4. Draw the newly formed
strands on this “unzipped”
DNA molecule to show
replication occurring:
Original New
A----------T
T----------A
C----------G
G----------C
C----------G
A----------T
T----------A
New Original
A----------T
T---------A
C---------G
G---------C
C---------G
A---------T
T---------A
DNA Code
1. The message of the DNA
code is information for
building proteins.
2. Proteins become important
structures, such as
filaments in muscle tissue,
walls of blood vessels, and
transport proteins in
membranes.
3. Other proteins, such as
enzymes, control all the
chemical reactions of an
organism.
4. Proteins are built from
chains of amino acids.
5. A codon is a set of three
nitrogen bases representing
an amino acid.
a. 64 are in the genetic
code.
b. 61 code for amino acids.
c. 3 are stop signals
(terminator codons) for
the chain synthesis.
(Terminator codons do
not code for an amino
acid)
d. More than one codon
can code for the same
amino acid; however,
for any one codon, there
is only one amino acid.
6. The sequence of nucleotides
in each gene contains
information for assembling
the string of amino acids that
make up a single protein.
7. It is estimated that each
human cell contains about
80,000 genes.
8. Genetic code is universal
because the codons
represent the same amino
acids in all organisms.
RNA
9. RNA stands for ribonucleic
acid.
10.Single-stranded
11.Contains the sugar, ribose
12. Contains four nitrogen
bases:
a. Adenine (A)
A-U
b. Uracil (U)**
**Uracil takes the place of
thymine in RNA
c. Cytosine (C) C-G
d. Guanine (G)
13.
Three types of RNA:
a. mRNA (messenger
RNA) – brings
information from the
DNA in the nucleus to
the cell’s factory floor,
the cytoplasm
b. tRNA (transfer RNA) –
transports amino acids to
the ribosomes for protein
synthesis
c. rRNA (ribosomal RNA)–
makes up the ribosomes
Transcription of DNA
1. Occurs in the nucleus.
2. Transcription – process of
making RNA from DNA
3. Begins as enzymes unzip
the DNA molecule. (This
results in only one singlestranded RNA molecule.)
4. Free RNA nucleotides (with
uracil) pair with complementary
bases on one unzipped strand of
DNA. (**Uracil(U) pairs with
adenine(A), cytosine(C) pairs
with guanine(G), & thymine(T)
pairs with adenine(A).
5. When base pairing is
completed, mRNA leaves the
nucleus and enters the
cytoplasm.
6. Suppose the following strand
from a segment of DNA is being
copied during transcription to
make mRNA. Complete the
structure for mRNA before it
unattaches from the DNA strand.
DNA
mRNA
A----------U
T----------A
G----------C
G----------C
C----------G
A----------U
G----------C
T----------A
C----------G
Difference between DNA & RNA
Translation: From mRNA to
Protein
1. Translation-process in
which DNA’s code is
translated from mRNA into
a sequence of amino acids
that make up protein.
2. Occurs at the ribosomes in
the cytoplasm.
3. Begins as the first codon of
mRNA attaches to a
ribosome. (AUG is the start
codon which signals the
start of protein synthesiscodes for the amino acid
methionine)
4. tRNA brings amino acids
to the ribosomes.
5. tRNA’s anticodon pairs
with mRNA’s codons
Ex. mRNA strand: AUG
tRNA strand: UAC
6. Amino acids bond together
to form a protein. A peptide
bond joins these amino acids.
7. As translation continues, a
chain of amino acids is
formed until the ribosome
reaches a stop codon on the
mRNA strand. At this point,
a protein is formed, and the
mRNA falls off the ribosome
to the cytoplasm.
8. What amino acid is coded
for by the mRNA base pair
sequence? (see the mRNA
code)
a.
b.
c.
d.
e.
f.
C-C-C
A-A-A
G-C-U
A-G-U
U-U-A
C-A-C
proline
lysine
alanine
serine
leucine
histidine
9. Identify the amino acid
sequence coded for by this
short strand of mRNA:
A-U-G U-U-C U-C-G G-U-U
met
phe
ser
val
A-A-A G-G-G U-G-A
lys
gly
stop
SUMMARY REVIEW:
10. Which molecule contains
the genetic code for making
all proteins in your body?
DNA
11. Which type of RNA has the
code for making a specific
protein? mRNA
12. Which type of RNA picks
up the amino acids in the
cytoplasm from the digestion
of foods and delivers them to
the ribosomes for assembly
into proteins? tRNA
CODON CHART
Chemical Basis of Genetics
(Translation) Worksheet
The sequence of bases of a DNA
molecule directs the formation
of proteins. Genes usually make
either a single protein or a
polypeptide, a sequence of
amino acids that make up a large
part of the protein molecule.
Study the diagrams below. On
the right is the genetic code,
showing the codons for each
amino acid. On the left is the
sequence of bases in the gene
that makes beef insulin, a
protein that breaks down sugar
in cow’s blood. Use these two
Diagrams to fill in the correct
sequence of amino acids in the
beef insulin molecule shown
below.
1.
2.
3.
4.
5.
6.
7.
UUU
GUC
AAU
CAG
CAU
CUG
UGU
phe
val
asn
gln
his
leu
cys
8. GGG
9. AGU
10.CAC
11.CUA
12.GUC
13.CAG
14.GCC
gly
ser
his
leu
val
gln
ala
15.CUA
16.UAU
17.UUG
18.GUU
19.UGC
20.GGC
21.GAG
leu
tyr
leu
val
cys
gly
glu
22.AGA
23.GGG
24.UUC
25.UUU
26.UAC
27.UAC
28.CCC
arg
gly
phe
phe
tyr
tyr
pro
29.AAA
30.GCA
31.GGU
32.AUU
33.GUG
34.GAA
35.CAG
lys
ala
gly
ile
val
glu
gln
36.UGU
37.UGU
38.CGU
39.UCU
40.GUU
41.UGU
42.UCG
cys
cys
arg
ser
val
cys
ser
43.UUG
44.UAC
45.CAA
46.UUG
47.GAG
48.AAU
49.UAU
leu
tyr
gln
leu
glu
asn
tyr
50.UGU cys
51.AAC asn
52.UAG term (stop codon)
Protein Synthesis WS
1. mRNA is made from one
strand of DNA.
2. mRNA is made in the nucleus
of cells.
3. After mRNA is made, it leaves
the nucleus through nuclear
pores and goes to a ribosome
in the cytoplasm.
4. Ribosomes are the site of
protein synthesis.
RNA Transcription:
5. An enzyme called RNA
polymerase unzips DNA so
that one strand of DNA serves
as a pattern.
6. mRNA will “read” DNA’s
code for protein synthesis.
7. This occurs when mRNA
nucleotides attach to
complementary bases on
DNA’s strand.
8. Example:
DNA: TAC CTA AAC CCA
mRNA:AUG GAU UUG GGU
DNA: TCT CAT TGA
mRNA: AGA GUA ACU
RNA Translation:
9. In a process called
translation, DNA’s code on
making proteins will be
translated from mRNA to
amino acids.
10. mRNA is attached to
ribosomes in the cytoplasm.
11. tRNA anticodons will
attach to mRNA’s codons.
12. tRNA is bringing amino
acids to the ribosome.
13. When 20 amino acids bond
together, a protein is made.
14. Peptide bonds hold the
amino acids together.
15. Example:
DNA: TAC CTA AAC CCA
mRNA:AUG GAU UUG GGU
Amino: met
acid
asp
leu
gly
tRNA:UAC CUA AAC CCA
DNA: TCT CAT TGA
mRNA: AGA GUA ACU
Amino: arg
val
thr
acid
tRNA: UCU CAU UGA
Mutation: Genetic Changes
Notes
I.
Mutation – any change in the
DNA sequence that also
changes the protein it codes
for
A. A wrong base in DNA
gives the cell the wrong
message; the result is the
wrong type of protein is made
and the change may cause
different traits to appear.
B. Occurs in the nucleus of the
cell during the replication
process of cell division.
(during mitosis or meiosis)
C. Mutations can affect the
reproductive cells of an organism
by changing the sequence of
nucleotides within a gene in a
sperm or egg cell. If these cells
take part in fertilization, the
altered gene would become part
of the genetic makeup of the
offspring. (meiosis)
D. Mutations can affect the
body cells (ex. skin, muscle,
bone). If the cell’s DNA is
changed, this mutation would
not be passed on to offspring.
However, the mutation may
cause problems for the
individual. (mitosis)
II. Two major groups of
mutations:
A. Gene mutation-involves
individual genes on a
chromosome
B. Chromosomal mutationinvolves whole
chromosomes
III. Gene mutations-involve a
single nucleotide or affect
sections of DNA that include
many nucleotides
A. Point mutation-a change in
a single base pair in DNA;
these are less harmful to an
organism because they disrupt
only a single codon
EX. Normal
mRNA: AUG AAG UUU GGC
Protein: met lys phe gly
mRNA: GCA UUG UAA
Protein: ala leu stop
Point Mutation
mRNA: AUG AAG UUU AGC
Protein: met lys
phe ser
mRNA: GCA UUG UAA
Protein: ala leu stop
Example: Sickle-cell anemia:
Substitution of a single base
in the gene for hemoglobin
can produce the gene for
sickle-cell hemoglobin
B. Frameshift mutation-where
a single nitrogen base is
added or deleted from
DNA
1. Addition or deletion
causes the genetic code to
be read out of sequence.
2. Every codon (and amino
acid) after the addition or
deletion is changed or
different.
Normal
mRNA: AUG AAG UUU* GGC
Protein: met lys phe
gly
mRNA: GCA UUG UAA
Protein: ala leu stop
Frameshift Mutation
mRNA: AUG AAG UUG GCG
Protein: met lys leu ala
mRNA: CAU UGU AA……
Protein: his cys……….
IV. Chromosomal Mutations-where
parts of the chromosome are
broken off and lost during
mitosis or meiosis
A. Many chromosomal
mutations result from the
failure of chromosomes to
separate properly during
meiosis.
Nondisjunction is the failure of
homologous chromosomes to
separate properly during meiosis.
(Note: During Meiosis I, 1
chromosome from each
homologous pair moves to each
pole of the cell; occasionally,
error occurs in which both
chromosomes of a homologous
pair move to the same pole.
Effects of nondisjunction are
often seen when gametes fuse
in fertilization – 1 gamete has
an extra chromosome, 1
gamete is missing a
chromosome)
E. Types of chromosomal
mutations:
Deletion-occurs when part
of a chromosome is left out
(most are lethal)
Inversion-occurs when part of
a chromosome breaks off and
is reinserted backwards.
Insertion-occurs when a part
of a chromatid breaks off
and attaches to its sister
chromatid. The result is a
duplication of genes on the
same chromosome.
Translocation-occurs when part
of one chromosome breaks off
and is added to a different
chromosome. (changes the
number)
Chromosomal mutations may
be serious because they affect
the distribution of genes to the
gametes during meiosis.
Few chromosomal mutations
are passed on to the next
generation because the zygote
In cases where the zygote
develops, the mature
organism is sterile and
incapable of producing
offspring.
V. Causes of Mutations:
A. Usually occur at random
(these are called spontaneous
mutations).
B. Many are caused by factors
in the environment. Any agent
that can cause a change in
DNA is called a mutagen.
***Mutagens include: high
energy radiation, chemicals, &
even high temperatures; forms
of radiation, such as X-rays,
cosmic rays, UV light, & nuclear
radiation; chemical mutagens
include dioxides, asbestos,
benzene, cyanide, &
formaldehyde
C. Errors in DNA provide
variation that enable species
to evolve.
D. Mutations result in sterility
or the lack of development in
an organism.
E. If mutations occur in
human gametes (called germ
cell mutations), they can
cause birth defects.
F. If mutations occur in body
cells (called somatic
mutations), they can lead to
cancer.
1. Oncogene-gene hat causes a
cell to become cancerous.
2. Causes of cancer:
a. Some are inherited.
b. Some result from
environmental factors.
c. Some are a combination of
genetic & environmental
factors.