DNA replication is the process by which a cell makes an identical copy of its DNA before cell division. It involves three main steps: initiation, elongation, and termination. During initiation, enzymes unwind and separate the DNA double helix at the origin of replication. In elongation, DNA polymerase adds complementary nucleotides to each single strand of DNA, creating two new double helix DNA molecules. Termination occurs when the primers are removed and fragments are joined by ligase, completing replication of the original DNA.

1. Science
Quarter 3 – Module 4:
Central Dogma of Biology:
Protein Synthesis
Department of Education ● Republic of the Philippines
10

2. SCIENCE - Grade 10
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Quarter 4 - Module 1: Central Dogma of Biology: Protein Synthesis
First Edition, 2020
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3. 1
Lesson
1 Replication of DNA
What’s New
DNA (Deoxyribonucleic Acid) is the genetic material of all organisms on Earth from
microbes to plants and human beings. An organism’s complete set of DNAs, including all of
its genes is called genome. A genome contains a complete set of information which
determines inherited physical characteristics such as height, skin, eye and hair color and many
others. Every cell in a human body nearly has similar DNA and in eukaryotic cells (cells that
contain a nucleus and organelles, and are enclosed by a plasma membrane). The DNA is a
thin long molecule found in the cell’s nucleus which is made up of nucleotides. The basic
structure of nucleotide consists of a phosphate group, sugar and a nitrogenous base which
will be further discussed in the next lessons. The four different type of nucleotides of DNA are
adenine, thymine, guanine and cytosine which are represented by their first letter A, T, G,
C. These four nucleotides are paired as (Adenine-Thymine) and (Guanine-Cytosine) into
billions to organize a double helix structure.
Try to look closely at the given structure of DNA.
Figure 1. Illustration to show the structure of DNA double helix. (1)

4. 2
DNA molecules fold into paired packages called chromosomes that are stored in the
nucleus of the cell. Different species have different numbers of chromosomes, and humans
have 23 pairs. Chromosome contain many genes and on each string of DNA contains the
gene which is the basic unit of heredity and a segment that describes how a certain protein is
made.
Figure 2. Illustration to show that a cell contains the genome, chromosomes, DNA and
genes. (2)
What is It
James Watson and Francis Crick in 1953, worked out that DNA is double helix which
appears like a staircase. The sides of the double helix structure are the sugar phosphate
backbones and the steps or rungs are the base pairs.
DNA Replication is the process of DNA duplication from an existing DNA. The
replication of DNA is important for the growth repair and reproduction of cells of an organism.
This process occurs in the nucleus of eukaryotic cells before a cell divides either by mitosis of
meiosis. When a cell divides, each resulting cell keeps a copy of all of your chromosomes.
The major key players in DNA replication are the enzymes helicase, primase, DNA
polymerase and ligase. Helicase is the unzipping enzyme and unzips the two strands of
DNA in the double helix through the hydrogen bond that holds the two base pairs together.
Primase will initialize the process and directs the DNA polymerase for it to figure out where
it gets to start. This primer is the starting point for DNA synthesis. The primers are made of
RNA (Ribonucleic Acid). Its major role is to act as a messenger carrying instructions from
DNA for controlling the synthesis of proteins. DNA polymerase is the builder enzyme which
replicates DNA molecules in order to build a new strand of DNA. Ligase is the gluer. which
helps glue DNA fragments together to form the new strand of DNA.
Let us now proceed to the three major steps of DNA replication (initiation, elongation and
termination) and see what happens in each stage.

5. 3
Step 1: Initiation
DNA replication starts at the Origin of Replication. The unzipping enzyme Helicase,
causes the DNA strand separation, which leads to the formation of the replication fork. It
breaks the hydrogen bond between the base pairs to separate the strand, thus separating the
DNA into individual strands.
Step 2: Elongation
During elongation, DNA Polymerase III makes the new DNA strand by reading the
nucleotides on the template strand and binding one nucleotide after the other to generate a
whole new complementary strand. It helps in the proofreading and repairing the new strand.
DNA Polymerase is able to identify and back track any mis paired nucleotides and corrects it
immediately. The bases attached to each strand then pair up with the three nucleotides found
in the cytoplasm. If it finds an Adenine (A) on the template, it will only add a Thymine (T). If it
finds a Guanine (G) on the template, it will only add a Cytosine (C).

6. 4
Step 3. Termination
In the previous steps of DNA replication, at the Origin, a Primer helps the DNA
Polymerase to initiate the process. As the strand is created, the primer has to be removed.
This is when DNA Polymerase I comes into the picture to replace the RNA nucleotides from
the Primer with DNA nucleotides to make sure it is DNA all the way through. When DNA
Polymerase III adds nucleotides to the lagging strand and forms Okazaki fragments, it leaves
a gap or two between the fragments. These gaps are filled by the enzyme ligase and makes
sure that everything else is connected.
Now, try to examine the two figures below for you to see and understand the complete process
of DNA Replication.
Figure 3. DNA replication process. (5)

7. 5
Figure 4. DNA Replication process. (6)
The Replication process is considered complete once all the Primers are removed and Ligase
has filled in all the remaining gaps between the Okazaki Fragments. This process gives us
two identical copies of the original DNA molecule. This whole replication process is happening
in billions of cells in your body even at this very moment. The original DNA is called the
template DNA, while the replicate DNA is called the complement DNA, both templates
IDENTICAL as shown in Figure 4!
Now, you might ask this question; ‘Why is it important for DNA TO UNDERGO
REPLICATION?” Well, it is important for DNA present in the nucleus to be replicated so that
every new cell receives the appropriate number of chromosomes. This process is necessary
for cell repair and growth and reproduction in living organisms.
What’s More
Activity 1.1 Word Shuffle
Word shuffle is an activity which helps strengthen your speed in processing learned
information. To understand the words better, a definition or a clue is given on the right side of
the sheet. One way of getting the word correctly is by looking at the definition and the shuffled
letters and align them both to arrive at the correct answer.
Learning the Skill: Identifying Words in Context
1. First, read the definition or clue on Column C.
2. If the word is not defined directly, read several sentences beyond the one in which the
word first appears. These sentences may provide information about the definition of
the word.
3. Next, identify the word based on what we have discussed earlier.
4. Write the correct term on Column A.

8. 6
Identify the correct term using the shuffled letters in Column B using the given
definition or clue on Column C.
A. Correct Word B. Shuffled Word C. Definition or Clue
1 UOEBLD XHILE Structure of a DNA.
2 OTSYINEC The nucleotide pair of Guanine.
3
XOEDCIELCUNOYBIR
CADI
Contains the genomes.
4 RPCATILEOIN
Process of DNA duplication from an
existing DNA
5 ELIHCSAE
Enzyme that unzips the DNA strand
during replication.
6 BSEA
What do you call the Adenine-
Thymine pair?
7 OKAKIZA
Fragments of DNA that are produced
during the process of DNA replication
8 YDRGOHNE
The type of bond which breaks down
when helicase starts to unzip the DNA
strand.
9 ENGE
Basic unit of heredity which carries
the characteristic of parents to
children.
10 OLAIONTNEG
This is the step of DNA replication
where the DNA Polymerase creates
new strands of nucleotide specifically
paired to another nucleotide.
What I Have Learned (Lesson Summary)
1. What do you call the process which converts the instructions in the DNA into a
functional biological product called Protein? (3 points)
2. What is the genetic material of all organisms on Earth from microbes to plants and
human beings? (3 points)
3. What do you call the process of DNA duplication from an existing DNA and is also
considered important for the growth repair and reproduction of cells of an organism?
(3 points)
4. What are the three major steps in DNA Replication? (3 points)
5. What are the major key players in DNA replication? (3 points)
Lesson 1: Assessment
Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper.

9. 7
1. Which of the following enzymes is used to join strands of DNA?
A. DNA Ligase
B. Primase
C. Nucleic Acid
D. DNA Polymerase
2. According to the central dogma, which of the following represents the flow of genetic
information in cells?
A. protein to DNA to RNA
B. DNA to RNA to protein
C. RNA to DNA to protein
D. DNA to protein to RNA
3. What happens during the start of DNA replication?
A. The bonds between nitrogen base and deoxyribose sugar break.
B. The leading strands produce the Ozaraki fragments.
C. The hydrogen bonds between the nucleotides of two strands break.
D. The phosphodiester bonds between the nucleotides break.
4. Unwinding of the DNA is done by which enzyme?
A. Ligase
B. Helicase
C. Hexonuclease
D. DNA Polymerase
5. By the end of DNA replication, a new DNA is formed with what structure?
A. Hexagonal
B. Linear
C. Double Helix
D. Planar
6. DNA replication is possible due to:
A. Hydrogen bond.
B. Complementary base pairing
C. Phosphate backbone
D. Nucleotides
7. Proofreading and repair of a DNA strand occurs during:
A. Initiation
B. Elongation
C. Termination
D. Polymerization
8. The synthesis of DNA by DNA polymerase occurs in the
A. 3' to 5' direction
B. 5' to 5' direction
C. 5' to 3' direction
D. 3' to 3' direction
9. During which of the following process a new copy of a DNA molecule is precisely
synthesized?
A. Transformation
B. Transcription

10. 8
C. Translation
D. Replication
10. What is the purpose of a DNA primer?
A. To build the daughter strand of DNA.
B. To unwind the double helix.
C. To terminate the process of DNA replication.
D. To initiate the process of DNA replication.
11. Protein synthesis refers to the:
A. process of formation of amino acids from mRNA
B. process of formation of amino acids directly from a DNA template
C. process of formation of mRNA from DNA template
D. process of duplicating DNA required for protein synthesis
12. When DNA replication starts,
A. The phosphodiester bonds between the adjacent nucleotides break
B. The bonds between the nitrogen base and deoxyribose sugar break
C. The leading strand produces Okazaki fragments
D. The hydrogen bonds between the nucleotides of two strand break
13. During DNA replication, the synthesis of DNA on the laggings strand takes place in
segments, these segments are called.
A. Satellite segments
B. Double helix segments
C. Kornberg segments
D. Okazaki segments
14. True replication of DNA is possible due to:
A. Hydrogen bonding
B. Phosphate backbone
C. Complementary base pairs
D. None of the above
15. Eukaryotes differ from prokaryote in the mechanism of DNA replication due to:
A. Different enzyme for synthesis of leading and lagging strand
B. Use of DNA primer rather than RNA primer
C. Unidirectional rather than bidirectional replication
D. Discontinuous rather than semi discontinuous replication

11. 9
Lesson
2
Transcription of DNA
to RNA
What’s New
RNA (Ribonucleic Acid), unlike the double stranded DNA, is a nucleic acid polymer
with a single strand. It is composed of the four nucleotides adenine, uracil (replaced thymine
in DNA), guanine and cytosine which are represented by their first letter A, U, G, C. (The
only difference with DNA is the Uracil). RNA is the first intermediate in converting the
information from the DNA into proteins which is important for proper cellular function. Below
is a short summary of the difference between DNA and RNA.
DNA RNA
Contains the sugar deoxyribose
Contains the sugar ribose (ribose has one more -
OH group than deoxyribose)
Double-stranded molecule Single-stranded molecule
Stable under alkaline conditions Not stable under alkaline conditions
Storing and transferring genetic
information
Acts as a messenger between DNA and
ribosomes to make proteins.
Uses the bases adenine, thymine,
cytosine, and guanine
Uses adenine, uracil, cytosine, and guanine
Figure 5. Structure of DNA and RNA. (8)
RNA falls into three major categories: Messenger RNA (mRNA), Transfer RNA
(tRNA) and Ribosomal RNA (rRNA). mRNA copies the genetic code from the DNA into a
form that can be read and used to make proteins. mRNA transmits genetic information from

12. 10
the nucleus to the cell’s cytoplasm. rRNA is situated in the cytoplasm of a cell, where we can
find the ribosomes. rRNA leads the translation of mRNA into proteins. tRNA transfers amino
acids to the ribosome that matches to each three-nucleotide codon of rRNA. The amino acids
then can be combined together and processed to make polypeptides and proteins.
Transcription in protein synthesis is the process where RNA is made from the DNA
by copying the base sequence of the double stranded DNA into a piece of a single stranded
nucleic acid. This transcription process is catalyzed by the enzyme RNA Polymerase.
What is It
Transcription of DNA to form RNA takes place in the cell’s nucleus. This process uses DNA
as a model to make an RNA (mRNA) molecule. During transcription, a strand of mRNA is
made that corresponds to a strand of DNA. Just like DNA replication, transcription also occurs
in three major steps: initiation, elongation and termination.
Figure 6. Transcription process in eukaryotic cells. (9)
1. Initiation
Initiation is the start of transcription. It transpires when the enzyme RNA polymerase binds to
a specific region of a gene which is called the promoter with the help of proteins called
‘transcription factors’. This signals the DNA double strand to unwind and open so the RNA
polymerase enzyme can ‘‘read’’ the bases found in one of the DNA strands. With the open

13. 11
strands, one is considered as the template strand (anti-sense strand) and this will be used to
generate the mRNA. The other is called the non-template strand (sense strand). After reading
the bases, the RNA polymerase enzyme is now ready to make a strand of mRNA with a
complementary sequence of bases.
2. Elongation
Elongation is the adding of nucleotides to the mRNA strand. RNA polymerase reads the
opened DNA strand and forms the mRNA molecule with the use of complementary base pairs.
There is a short time during this process when the newly formed RNA is bound to the opened
DNA. During this process of elongation, an adenine (A) in the DNA binds to an uracil (U) in
the RNA. RNA polymerase does not need a primer during this process. It simply initiates the
mRNA synthesis from the starting point and then moves downstream reading the anti-sense
strand from 3’ to 5’ and generating the mRNA from the 5’ to 3’ end as it goes. Unlike helicase
enzyme in DNA replication, RNA polymerase zips DNA back up as it goes keeping only 10-
20 bases exposed one at a time.
3. Termination
Termination is the last step of the transcription process. This happens when RNA polymerase
enzyme reaches a stop or termination sequence in the gene. When the stop sequence or stop
codon is reached, the enzyme detaches from the gene. The mRNA strand is now produced
and it detaches from DNA. It carries with it the information encoded in the gene.
By the end of transcription, the DNA segment is transcribed to form the mRNA molecule. The
template strand shown below with the sequence T-A-C-T-A-G-A-G-C-A-T-T transcribes to
form the mRNA A-U-G-A-U-C-U-C-G-U-A-A.
Figure 7. Transcription of DNA to mRNA. (10)
Remember to take note of the transcription pattern: Thymine to Adenine, Adenine to Uracil,
Cytosine to Guanine, Guanine to Cytosine. Uracil is being synthesized instead of Thymine as
compared during DNA replication.
What’s More
Activity 2.1 Transcribe your DNA to RNA.
Imagine you are a scientist in a laboratory. To safeguard the integrity and accuracy of your
synthesized protein, your job is to transcribe the identified DNA sequences to mRNA. To

14. 12
perform the task better, create a summary of the nucleotide pairs during the translation
process.
Learning the Skill: Identifying the mRNA Product of DNA Transcription.
1. First, identify the nucleotides in the given DNA sequence.
2. Next, transcribe the mRNA nucleotide from the given DNA template.
3. Write the transcription using the code of each nucleotide.
Identify the correct mRNA sequence from the given DNA template sequence.
1. DNA Coding ATG ACT AGC TGG GGG TAT TAC TTT TAG
DNA Template TAC TGA TCG ACC CCC ATA ATG AAA ATC
mRNA
2. DNA Coding ATG GCG AGG CGG CAG CTG TTA TGG TGA
DNA Template TAC CGC TCC GCC GTC GAC AAT ACC ACT
mRNA
3. DNA Coding ATG GTG GGG GCA TAC CGA CCC TTA TAG
DNA Template TAC CAC CCC CGT ATG GCT GGG AAT ATC
mRNA
4. DNA Coding ATG AGA GGG TTT TTT ATG GTG GGG TAG
DNA Template TAC TCT CCC AAA AAA TAC CAC CCC ATC
mRNA
5. DNA Coding ATG GAG TGT GAT GCG TAC AAC CCC TAA
DNA Template TAC CTC ACA CTA CGC ATG TTG GGG ATT
mRNA
What I Have Learned (Lesson Summary)
1. What do you call a nucleic acid polymer with a single strand?

15. 13
2. What are the four nucleotides in the nucleic acid Item 1?
3. What are the three major categories of RNA? (3 pts.)
4. What are the three major steps of transcription? (3 pts.)
5. What is this step of transcription transpires when the enzyme RNA polymerase binds to a
specific region of a gene which is called the promoter with the help of proteins called
‘transcription factors’? (3 pts.)
5. What do you call the transcription step where nucleotides are added to the mRNA strand?
(2 pts.)
6. What is the transcription step that happens when RNA polymerase enzyme reaches a stop
or termination sequence in the gene when the stop codon is reached? (2 pts.)
Lesson 2: Assessment
Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper.
1. Which molecule contains the genetic code?
A. rRNA
B. tRNA
C. DNA
D. mRNA
2. The transcribing enzyme is called.
A. Amino acid t-amylase
B. RNA polymerase
C. DNA polymerase
D. Ligase
3. Transcription occurs along a ____ template forming an mRNA in the ____ direction.
A. 5' to 3'; 5' to 3'
B. 5' to 3'; 3' to 5'
C. 3' to 5'; 5' to 3'
D. 3' to 5'; 3' to 5’
4. RNA contains which bases?
A. adenine, thymine, guanine, cytosine, uracil
B. adenine, thymine, guanine, cytosine
C. thymine, guanine, cytosine, uracil
D. adenine, guanine, cytosine, uracil
5. If the DNA template reads “ATA”, then which of the following would be the corresponding
sequence on the mRNA?
A. UAU
B. ATA
C. TUT
D. UCU
6. Which mode of information transfer usually does not occur?
A. DNA to DNA
B. DNA to RNA
C. DNA to Protein
D. All occur in a working cell

16. 14
7. One similarity between DNA and messenger RNA molecules is that they both contain:
A. The same sugar.
B. Genetic code based on base sequence.
C. Nitrogenous base known as Uracil.
D. Double stranded polymers.
8. The specific site of RNA transcription from DNA is the:
A. Mitochondria
B. Cytoplasm
C. Nucleus
D. Chromosome
9. RNA is stable under alkaline conditions.
A. True
B. False
C. Depends on the condition
D. Depends on the DNA sequence
10. What is the complementary messenger-RNA sequence for the DNA template sequence
shown below?
C-A-A-G-G-T
A. GTTCCA
B. CAAGGU
C. GUUCCA
D. CAAGGT
11. A promoter site on DNA:
A. Initiates transcription
B. Regulates termination
C. Codes for RNA
D. Transcribes repressor
12. The DNA chain acting as a template for RNA synthesis has the following order of bases,
AGCTTCGA. What will be the order of bases in the mRNA?
A. TCGAAGCT
B. UGCUAGCT
C. TCGAUCGU
D. UCGAAGCU
13. What is the main function of tRNA in relation to protein synthesis?
A. Inhibits protein synthesis
B. Proof reading
C. Identifies amino acids and transport them to ribosomes
D. All of the above

17. 15
14. Which site of tRNA molecule hydrogen bonds to an mRNA molecule?
A. Codon
B. Anticodon
C. 5’ ends of the tRNA
D. 3’ ends of the tRNA
15. Sigma factor is a component of:
A. DNA ligase
B. DNA polymerase
C. RNA polymerase
D. Endonuclease
Lesson
3
Translation of RNA to Protein
What’s New
Translation is the final process of protein synthesis that takes place in the cytoplasm.
The genetic information of the DNA is used as the origin to form messenger RNA (mRNA) by
the transcription process. The single stranded mRNA then serves as a template during
translation. Ribosomes are the facilitators of the translation process in the cytoplasm.
Ribosomes induce the binding of complimentary transfer RNA (tRNA) anticodon sequences
to the mRNA. The tRNAs contain particular amino acids linked together by the ribosome.
During translation, the mRNA sequence is decoded to produce a specific amino acid chain
called the polypeptide. Folding of the polypeptide produces an active protein which is able to
perform important functions within the cell.
What is It
Protein Structure. Proteins may generally have globular or fibrous
structure depending on its particular role in the bodily functions. Globular proteins are
spherical, compact and soluble. Fibrous proteins are elongated and insoluble. However, these
two structure types may exhibit one or more types of protein structures.

18. 16
Figure 7. An illustration of fibrous and globular protein. (11)
The protein building block is the amino acid. Amino acids combine through a dehydration
link called a peptide bond. When several groups of amino acids are joined together, a protein
macromolecule is formed. This is why proteins are considered as polymers of amino acids.
Proteins are typically made of a chain of 20 amino acids. The human body makes any protein
it needs by using a combination of these 20 amino acids. Most amino acids have a structural
template where an alpha carbon is bonded to the following forms:
*A hydrogen atom (H) *A carboxyl group (-COOH)
*An amino group (-NH2) *A “variable” group
The “variable” group is most responsible for difference as all of them have hydrogen, carboxyl
group, and amino group bonds. Amino acids are linked through dehydration synthesis peptide
bonds are formed. Amino acids linked together by polypeptide bonds forms a polypeptide
chain. When polypeptide chains are twisted, a 3-D shape forms a protein.
Figure 8. A guide to 20 common amino acids. (12)

19. 17
These amino acids are grouped as: essential and non-essential. Non-essential amino
acids are those which the human body is capable of synthesizing, whereas essential amino
acids must be obtained from the diet.
Essential
Amino Acids
Symbol
Non-Essential
Amino Acids
Symbol
histidine His alanine Ala
isoleucine Ile arginine Arg
leucine Leu asparagine Asn
lysine Lys aspartic acid Asp
methionine Met cysteine Cys
phenylalanine Phe glutamic acid Glu
threonine Thr glutamine Gln
tryptophan Trp glycine Gly
valine Val proline Pro
serine Ser
tyrosine Tyr
Since the proteins formed by amino acids are incredibly huge and bulky molecules, it is
very time consuming and difficult to draw out their chemical structure in similar way we draw
smaller molecules. The common amino acids that make up proteins are given codes that
represent them as shown in the table above. This makes describing the molecules so much
easier.
Proteins are synthesized in the human body through a process called translation.
Translation occurs in the cytoplasm and involves converting genetic codes into proteins.
Genetic codes are assembled during DNA transcription, where DNA is decoded into RNA.
Cell structures called ribosomes then help transcribe RNA into polypeptide chains that need
to be modified to become functioning proteins. (13)
Figure 9. Translation of mRNA to form a polypeptide chain of protein. (10)

20. 18
The key components required for translation are mRNA, tRNA, ribosomes, and
aminoacyl tRNA synthetases. These four structures are briefly explained below: (14)
*Ribosome
The ribosome is a complex organelle, present in the cytoplasm, which serves as the site
of action for protein synthesis. It provides the enzymes needed for peptide bond formation.
The nucleotide sequence in mRNA is recognized in triplets, called codons. The ribosome
moves along the single strand mRNA, and when a complimentary codon sequence belonging
to amino acid bearing tRNA bonds with the mRNA, the amino acid is added to the chain.
The mRNA possesses a stop codon, a sequence of three nucleotides that indicates that
translation is complete. Upon reaching the stop codon, the ribosome ceases translation and
releases the mRNA and newly generated polypeptide.
*Messenger RNA (mRNA)
mRNA is used to convey information from DNA to the ribosome. It is a single strand molecule,
complimentary to the DNA template, and is generated through transcription. Strands of mRNA
are made up of codons, each of which signifies a particular amino acid to be added to the
polypeptide in a certain order. mRNA must interact with ribosomal RNA (rRNA), the central
component of ribosomal machinery that recognizes the start and stop codons of mRNA, and
transfer RNA (tRNA), which provides the amino acid once bound with a complimentary mRNA
codon.
*Transfer RNA (tRNA)
This is a single strand of RNA composed of approximately 80 ribonucleotides. Each tRNA is
read as a ribonucleotide triplet called an anticodon that is complementary to an mRNA codon.
tRNA carry a particular amino acid, which is added to the growing polypeptide chain if
complimentary codons bond.
*Aminoacyl tRNA synthetases
These are enzymes that link each amino acid to their corresponding tRNA with the help of a
two-step process. Each amino acid has a unique synthetase and the active site of each
enzyme fits only one specific combination of the amino acid and tRNA. (14)
There are three major steps in translation: initiation, elongation, and termination.
These steps are briefly discussed below: (14)
1. Initiation
After mRNA is formed in the nucleus, it leaves and moves to the cytoplasm where it finds the
ribosome. Small ribosomal subunits then bind to mRNA. The initiator tRNA which is equipped
with the anticodon (UAC) also binds to the start codon (AUG) of the mRNA. Let us say we
have the mRNA codon AUG-UGC-AAG-UCC-GGA-CAG, the tRNA anticodon would be UAC-
ACG-UUC-AGG-CCU-GUC. The resulting large complex forms a complete ribosome and
initiates protein synthesis. Each different tRNA is covalently linked to a particular amino acid.

21. 19
2. Elongation
Following initiation, a new tRNA-amino acid complex enters the codon next to the AUG
codon. If the anticodon of the new tRNA matches the mRNA codon, base pairing occurs and
the two amino acids are linked by the ribosome through a peptide bond.
If the anticodon does not match the codon, base pairing cannot happen and the tRNA
is rejected. Then, the ribosome moves one codon forward making space for a new tRNA-
amino acid complex to enter. This process is repeated several times until the entire
polypeptide has been translated.
3. Termination
As the ribosome moves along the mRNA, it encounters one of the three stop codons
for which there is no corresponding tRNA. Terminator proteins present at the stop codon bind
to the ribosome and trigger the release of the newly synthesized polypeptide chain. The
ribosome then disengages from the mRNA. On release from the mRNA, the small and large
subunits of the ribosome dissociate and prepare for the next round of translation. The
polypeptide chains produced during translation undergo some post-translational
modifications, such as folding, before becoming a fully active protein. (14)
Figure 10. A diagram showing the translation process for eukaryotic cells. (15)
Below is a chart of all the mRNA codons and the amino acids they code for. Decoding
codons is a task made simple because of the codon chart. Just start at the center of the chart
for the first letter. Move to the outside next ring for the second letter and finally, find the final
letter among the smallest set of letters in the third ring. Then you can read the amino acid in
that sector.
Figure 11. Codon Chart. (16)

22. 20
To decode the codon for CAC, find the first letter C in the set of bases at the center of
the circle. Then find the letter A in the second ring, then C in the third ring. There, you will read
the amino acid in this sector as Histidine. Some of these codons are special. AUG is the start
codon which initiates translation by coding for Methionine. And these three are stop codons:
UAA, UAG and UGA. These are the ones that terminate translation.
What’s More
Activity 3.1 Translate your mRNA to Protein.
In Activity 2.1, you have transcribed your mRNA from the given DNA template sequence.
In this activity, it’s time to translate your mRNA to amino acids. To perform the task, you need
to use the codon chart in Figure 11. Also take note of the start and stop codons.
Identify the correct tRNA sequence and amino acid from your identified mRNA
sequence from Activity 2.1
1. DNA Coding ATG ACT AGC TGG GGG TAT TAC TTT TAG
DNA Template TAC TGA TCG ACC CCC ATA ATG AAA ATC
mRNA
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
tRNA
Amino Acid
2. DNA Coding ATG GCG AGG CGG CAG CTG TTA TGG TGA
DNA Template TAC CGC TCC GCC GTC GAC AAT ACC ACT
mRNA
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
tRNA
Amino Acid
3. DNA Coding ATG GTG GGG GCA TAC CGA CCC TTA TAG
DNA Template TAC CAC CCC CGT ATG GCT GGG AAT ATC
mRNA
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
tRNA

23. 21
Amino Acid
4. DNA Coding ATG AGA GGG TTT TTT ATG GTG GGG TAG
DNA Template TAC TCT CCC AAA AAA TAC CAC CCC ATC
mRNA
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
tRNA
Amino Acid
5. DNA Coding ATG GAG TGT GAT GCG TAC AAC CCC TAA
DNA Template TAC CTC ACA CTA CGC ATG TTG GGG ATT
mRNA
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
Activity
2.1
tRNA
Amino Acid
Activity 3.2 Decoding DNA Segment
Objective:
Apply the concept of protein synthesis through the amino acids coded for the mRNA
codon using the genetic code.
Materials:
Pen
Crayons
Activity sheet: Decoding DNA segment
Procedure:
1. Study the given scenario (see attached activity) and study the profile of the suspects and
additional information.
2. Using your knowledge about DNA and RNA base-pairing, decode the DNA sample in
order to identify the sequence of amino acids. Use the amino acid identifier chart as your
reference.
3. Compare the sequence of amino acids (proteins) to the profile of the suspects and
additional information given in order to determine the corresponding traits.
4. Name the culprit using the data or information you got. 5. Using the pencil and crayons
make a cartographic sketch of the suspect.
Q1. What amino acids sequences did you get upon decoding the genes?
Q2. What are the traits of the culprit based on your data?
Q3. Who among the suspects matches with the sequence of amino acids (proteins) you got?
Q4. Draw the possible appearance of the culprit.

24. 22
DECODING DNA SEGMENT
An intruder razed the science laboratory of a Junior High School. The school is in
chaos. The school administrators and teachers demanded to know the culprit. They have to
identify the culprit and do it fast. They had three suspects namely Rudy Tee, Von Go and
Rambo Tan. As a forensic expert, your mission is to identify the intruder using the profile of
the suspects and other information taken from the laboratory:
THE PROFILE OF THE SUSPECTS
1. Rudy Tee (Suspect 1)
 Flunked physics class three times
 With long nose hair,
 Oval eyes
 Full lips
 Attached ear lobe
 Straight hair
2. Von Go (Suspect 2)
 His investigative project is about the potential applications of nuclear fusion in
generating energy.
 Short nose hair
 Chinky eyes
 Full lips
 Free earlobe
 Curly hair
3. Rambo Tan (Suspect 3)
 Suspended for a week by the Disciplinary Committee for repeated tardiness.
 Short nose hair
 Oval eyes
 Harelip
 Attached earlobe
 Wavy hair
Additional Information:
Below are the specific amino acid sequences for specific trait.
1. Nose Hair Sequence
Short ----- phe-lys
Long ----- leu-lys
2. Shape of Eyes
Oval ----- val-ala-ala
Chinky ----- val-ala-val
3. Lips
Full Lips ----- phe- glu-ala
Harelip ----- phe-lys-ala
4. Ear Attachment

25. 23
Free Earlobe ----- thre- tyr-ser
Attached ----- leu-arg-gly
5. Type of Hair
Straight ----- lys-glu
Wavy ----- phe-ala
Curly ----- glu-phe
THE DNA CODE OF THE SUSPECT A fresh DNA sample was obtained from the
laboratory; believe to have been left by the suspect. Using the DNA sequences, the following
nucleotide sequence was obtained:
SUSPECT:
TAC-AAA-TTT-ATC-TAC-AAA-CTT-CGT-ATC-TAC-CAT-CGT-CAT-ATT-TAC-TGG-ATA-
TCG-ATC-TAC-CTT-AAA-ATC
Complementary base pairs: DNA is represented by nitrogen bases that are read in
groups of threes. To decode, use the DNA as a blueprint to produce mRNA. Then use the
mRNA as blueprint to produce the linear sequence of tRNA. A specific nitrogen base in the
DNA pairs up with a specific nitrogen base in the mRNA, and a specific nitrogen base in the
mRNA pairs up with a specific nitrogen base in the tRNA. Breaking the Code:
Complete the data table below:
DNA Triplet Code mRNA tRNA Amino Acid
TAC
AAA
TTT
ATC
TAC
AAA
CTT
CGT
ATC
TAC
CAT
CGT
CAT
ATT
TAC
TGG
ATA

26. 24
TCG
ATC
TAC
CTT
AAA
ATC
Characteristics and traits of the suspect based on the DNA code.
1. Nose Hair
2. Eyes
3. Lips
4. Ear Attachment
5. Type of Hair
Name and Draw the cartographic sketch of the suspect:
What I Can Do
1. Describe the importance of the knowledge you learned from this lesson in solving crimes.
(10 pts.)
2. Explain the importance of DNA testing. (5 pts.)
Lesson 3: Assessment
Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper.
1. During translation, proteins are synthesized by ribosomes using the information on:
A. DNA B. mRNA C. tRNA D. rRNA
2. Translation occurs in the:
A. Lysosome
B. Nucleus
C. Cytoplasm
D. Nucleolus

27. 25
3. The enzyme involved in amino acid activation is:
A. ATP synthetase
B. Aminoacyl tRNA synthetase
C. Aminoacyl rRNA synthetase
D. Aminoacyl mRNA synthetase
4. Which of the following is the name of the three-base sequence in the mRNA that binds to
a tRNA molecule?
A. P Site
B. Codon
C. CCA binding site
D. Anti-codon
5. Each codon within the genetic code encodes a different amino acid.
A. True
B. False
C. Depends on the condition of the codon.
D. Depends on the genetic code.
6. During elongation in translation, to which ribosomal site does an incoming charged tRNA
molecule bind?
A. a. A Site
B. b. B Site
C. c. E Site
D. d. P Site
7. Below are types of proteins except one:
A. Keratin B. Contractile protein C. Insulin D.RNA
For items 8-10. Identify the amino acid which results in the codon sequences below:
8. UGU – ACA 9. AAG – UUC 10. CAC - GUG
11. Which is the source of energy for amino acid activation?
A. ATP B.GTP C. CTP D. TTP
12. Which of the following statements is correct?
A. Termination codon has no tRNA
B. Activated amino acid binds to the 5’ end of respective tRNA molecule
C. CTP is required for amino acid activation
D. There is only one amino acid acyl-tRNA synthetase in a cell
13. Which of the following is not a requirement for protein synthesis?
A. Ribosomes
B. Peptidyl transferase
C. Spliceosome
D. Amino acid tRNA synthase
14. Translation occurs in the:
A. Lysosome
B. Nucleus
C. Cytoplasm
D. Nucleolus
15. Peptidyl transferase involved in peptide bond formation is located in the
A. 3’ region of tRNA

28. 26
B. Smaller subunit of ribosome
C. Larger subunit of ribosome
D. Near Shine Dalgarno sequence
Assessment (Unit Test)
Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper.
1. Protein synthesis refers to the:
A. process of formation of amino acids from mRNA
B. process of formation of amino acids directly from a DNA template
C. process of formation of mRNA from DNA template
D. process of duplicating DNA required for protein synthesis
2. When DNA replication starts,
A. The phosphodiester bonds between the adjacent nucleotides break
B. The bonds between the nitrogen base and deoxyribose sugar break
C. The leading strand produces Okazaki fragments
D. The hydrogen bonds between the nucleotides of two strand break
3. During DNA replication, the synthesis of DNA on the laggings strand takes place in
segments, these segments are called.
A. Satellite segments
B. Double helix segments
C. Kornberg segments
D. Okazaki segments
4. True replication of DNA is possible due to:
A. Hydrogen bonding
B. Phosphate backbone
C. Complementary base pairs
D. None of the above
5. Eukaryotes differ from prokaryote in the mechanism of DNA replication due to:
A. Different enzyme for synthesis of leading and lagging strand
B. Use of DNA primer rather than RNA primer
C. Unidirectional rather than bidirectional replication
D. Discontinuous rather than semi discontinuous replication
6. If the DNA template reads “ATA”, then which of the following would be the corresponding
sequence on the mRNA?
A. UAU
B. ATA
C. TUT
D. UCU
7. One similarity between DNA and messenger RNA molecules is that they both contain:
A. The same sugar.
B. Genetic code based on base sequence.
C. Nitrogenous base known as Uracil.
D. Double stranded polymers.

29. 27
8. The specific site of RNA transcription from DNA is the:
A. Mitochondria
B. Cytoplasm
C. Nucleus
D. Chromosome
9. RNA is stable under alkaline conditions.
A. True
B. False
C. Depends on the condition
D. Depends on the DNA sequence
10. What is the complementary messenger-RNA sequence for the DNA template sequence
shown below?
C-A-A-G-G-T
A. GTTCCA
B. CAAGGU
C. GUUCCA
D. CAAGGT
11. Translation occurs in the:
A. Lysosome
B. Nucleus
C. Cytoplasm
D. Nucleolus
12. During translation, proteins are synthesized by ribosomes using the information on:
A. DNA
B. mRNA
C. tRNA
D. rRNA
13. The enzyme involved in amino acid activation is:
A. ATP synthetase
B. Aminoacyl tRNA synthetase
C. Aminoacyl rRNA synthetase
D. Aminoacyl mRNA synthetase
14. Which of the following is the name of the three-base sequence in the mRNA that binds to
a tRNA molecule?
A. P Site B. Codon C. CCA binding site D. Anti-codon
15. During elongation in translation, to which ribosomal site does an incoming charged tRNA
molecule bind?
A. A Site B. B Site C. E Site D. P Site

30. 28
Answer