Department of Education
National Capital Region
Schools Division of Paranaque City
Self-Learning Modules
Science 10 Quarter 3 Week 4
DNA STRUCTURE and CHROMOSOMAL MUTATION
Learning Competencies:
1. Explain how protein is made using information from DNA. (S10LT-llld-37)
2. Explain how mutations may cause changes in the structure and function of
a protein. (S10LT-llle-38)
Objectives:
At the end of this module, the learners should be able to:
1. Explain the role of DNA and RNA in protein synthesis.
2. Explain how mutation occurs by identifying the amino acids codon using the
genetic code table.
3. Explain how mutation may cause changes in the structure and function of a
protein using models/illustration.
4. Explain how mutation may affect the growth and development of organisms
using video clips/illustrations.
Let’s Understand (Study the Concept)
Protein synthesis is the process of making protein molecules, in the cells,
proteins are produced involving transcription and translation processes. In translation, each
set of three nucleotides in an mRNA molecule codes for one amino acid in a protein. A codon
is a sequence of three DNA or RNA that corresponds with specific amino acids and a full set
of codons is called genetic code. This explains why each set of three nucleotides in the mRNA
is called a codon. Each codon specifies a particular amino acid. For example, the first codon
which is, cytosine-guanine, uracil (CGU), instructs the ribosome to put the amino acid arg
(arginine) in the protein. The sequence of codons in the mRNA determines the sequence of
amino acids in the protein.
The following events can help you understand the process of transcription:
•
Step 1. Ribonucleic Acid polymerase enzyme binds and opens the DNA molecule that
will be transcribed.
•
Step 2. As the DNA molecule opens, the RNA polymerase slides along the DNA strand
and links free RNA nucleotides that pair with the nitrogenous bases of the complementary
DNA strand. Hence, if the sequence of bases on the DNA strand were CCG TTA CAT, the
sequence of bases on the RNA strand would be GGC AAU GUA.
•
Step 3. When the process of base-pairing is completed, the RNA molecule breaks
away as the DNA strands rejoin. The RNA leaves the nucleus and goes to the cytoplasm.
Figure 6 shows the transcription process.
1
But how are the right amino acids added in the right sequence to match the sequence of
codons in the mRNA? The following events in translation can help you understand the
process:
•
•
•
•
Step 1. As translation begins, mRNA binds to a ribosome. Then, tRNA molecules,
each carrying a specific amino acid, approach the ribosome. The tRNA anticodon
pairs with the first mRNA (start) codon arginine-uracil-guanine (AUG), to form the
initiation complex. The two molecules temporarily join together.
Step 2. Usually, the first codon on mRNA is AUG, which codes for the amino acid
methionine. AUG signals the start of protein synthesis. Then, the ribosome slides
along the mRNA to the next codon.
Step 3. A new tRNA molecule carrying an amino acid pair with the second mRNA
codon.
Step 4. When the first and second amino acids are in place, an enzyme joins them
by forming a peptide bond between them.
Source: www. Scq.ubc.ca
Translation
•
Step 5. As the process continues, a chain of amino acids is formed until the
ribosome reaches a stop codon (e.g., UAA, UAG, UGA) on the mRNA strand. The
polypeptide chain is released. Protein synthesis is complete.
Source: education-portal.com
2
Chromosomal Mutation
●
A mutation is a change in the base sequence of DNA. Mutations may affect only
one gene, or they may affect whole chromosomes.
Mutations in eggs or sperm affect future generations by transmitting these
changes to their offspring’s.
Mutations in body cells affect only the individual and are not passed on to the
offspring.
When DNA from two different species is joined together, it is called recombinant
DNA. This process uses restriction enzymes to cleave one organism’s DNA into
fragments and other enzymes to splice the DNA fragment into a plasmid or viral
DNA.
●
●
●
MUTATION: Changes in the Genetic Code
Chromosomal Mutations
● Alterations of chromosome number or structure cause some genetic
disorders.
● Large-scale chromosomal alterations often lead to spontaneous abortions
or cause a variety of developmental disorders, or even cancers.
● Breakage of a chromosome can lead to four types of changes in
chromosome structure.
Let’s Apply
Directions: Use your codon chart to determine the amino acid sequence. Remember to read
through the strand and ONLY start on AUG and STOP when it tells you to stop. Follow
example below:
DNA
TAC
CTC
CGG
TGG
GTG
CTT
GTC
TGT
ATC
mRNA
AUG
GAG
GCC
ACC
CAC
GAA
CAG
ACA
UAG
tRNA
UAC
CUC
CAA
TGG
GTG
CUU
GUC
UGU
AUC
Glu
ala
thre
hist
asp
glu
threo
stop
Protein Start/met
3
1. DNA = TAA ACT CGG TAC CTA GCT TAG ATC TAA TTA CCC ATC
mRNA=_______________________________________________
t-RNA= _______________________________________________
protein_________________________________________________
2. DNA = CTA TTA CGA TAC TAG AGC GAA TAG AAA CTT ATC ATC
mRNA=__________________________________________________
tRNA=___________________________________________________
protein=__________________________________________________
2. Transcribe and Translate this DNA sequence
DNA
AUG
CCC
CUC
GGG
GAA
UGU
AAU
CGG
UGA
mRNA
Protein
Let’s Analyze
A. Answer the given question.
1. How are the right amino acids added in the right sequence to match the codon in the
mRNA?
2.In transcription and translation process where is mRNA synthesized?
3.How chromosomal mutation be prevented?
4
Let’s Try
Directions: Choose the letter of the best answer. Write the letter only.
1. Alteration of chromosomes number or structure may lead to:
a. Normal genetic code
c. Genetic disorder
b. Normal individual
d. None of these
2. A mutation is change in the base sequence of ___________
a. tRNA
b. DNA
c. RNA
d. mRNA
3. Uses a strand of DNA as a template to build a molecule called DNA.
a. Translation
b. Transcription
c. Deletion
d. Replication
4. A process where mRNA binds to a ribosome outside the nucleus to produce
specific amino acids.
a. Transcription
b. Translation
c. Deletion
d. Duplication
5. A process in which a cell produces proteins.
a. Mutation
b. DNA Replication
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c. Protein Synthesis
d. Transcription
Let’s Create
Collage Making
Directions: Collect different pictures of mutated organisms from different sources like
newspapers, magazines, old books or any sources you want. Paste them on a one whole
sheet of pad paper or bond paper creating a collage.
RUBRIC for ASSESSMENT
Criteria
Excellent
(4)
Proficient
(3)
Adequate
(2)
Limited
(1)
All the parts of
the presentation
said something
rather important
Most of the parts
of the
presentation said
something
vaguely important
Many parts of
the
presentation
needed
improvement
Unique but not
organized
Not unique but
organized
Not unique
but not
organized
Create a
powerful
image
Create an
interesting
image
Create
an
adequate image
that is moderately
suitable
Create an
adequate
image which
is not suitable
Information
contains
essentially no
errors
Information
contains minor
errors
Information
contains errors
Information
contains many
errors
Details and
Information
All parts of the
presentation
were clear and
interesting
Method of
Presentation
Understandable
, unique, and
Exemplary
Techniques/
Creativity
Accuracy
6