The central dogma of molecular biology describes the flow of genetic information from DNA to RNA to protein. DNA contains the genetic code in nucleotide base pairs. During transcription, a complementary mRNA copy of a DNA sequence is generated. The mRNA is then modified before undergoing translation, where ribosomes read the mRNA codons to assemble amino acids into proteins according to the genetic code. This process allows genetic information stored in DNA to be converted into functional proteins.

1. MODULE 4:
THE CENTRAL DOGMA
OF MOLECULAR BIOLOGY

3. COMPONONENT OF THE
CENTRAL DOGMA OF
MOLECULAR BIOLOGY

4. DEOXYRIBONUCLEIC ACID
(DNA)

5. Deoxyribonucleic acid of DNA is the genetic
material passed on from parents to offspring. It
contains instructions necessary for the survival
of every organism. Most of the cells in the
body of an organism contains DNA, but its
locations vary. In prokaryotes, DNA is located
in the nucleoid region in the cytoplasm. In
eukaryotes, DNA is often located in the
membrane-bound nucleus, but some may be
found in the mitochondria.

7. JAMES WATSON FRANCIS CRICK

8. The DNA model, proposed by biologists
Francis Crick and James Watson in 1953,
is a double helix structure that twists
spirally, similar to a twisted ladder or a
spiral staircase. The two helices may coil
either clockwise or counterclockwise. Its
backbone or building block, called the
nucleotide, is composed of a phosphate
group, a sugar, and nitrogenous bases.

11. The phosphate group in the DNA is
composed of a phosphorus atom
surrounded by four oxygen atoms. By
itself, the nucleotide may have three
phosphates. However, when joined to
the growing strand of DNA, two of its
phosphates are lost, and the remaining
one attaches to another nucleotide’s
sugar.

13. The sugar group in DNA is called deoxyribose.
The prefix deoxy- in “deoxyribose” means
that ribose has lost an oxygen atom. The
five-carbon structure of ribose in the DNA
molecule is numbered, based on its carbon
atom. The carbon atom on the right side is
assigned as number 1, second carbon in
deoxyribose sugar helps distinguish DNA from
RNA. This also makes DNA a relatively stable
molecules, as it is less likely to get involved in
chemical reactions.

15. The last carbon in the ribose sugar is
numbered as 5’ (read as “five-prime”).
The small mark in the numbering
distinguishes it from any of the numbers
given to atoms in the other rings.

16. The nitrogenous bases in the nucleotide
can be classified according to the number
of rings in their structure. Purines, which
are adenine and guanine, have double-
ringed structure, and the pyramidines,
which as cytosine, thymine, and uracil,
contain only one ring on their structure.
Uracil is usually found in RNA and serves
as the counterpart of thymine in DNA.

18. The nitrogenous bases undergo
complementary base pairing, wherein
each pair should contain a purine and
pyrimidine. Each nucleotide is paired
together by forming hydrogen bonds. In
DNA, adenine (A) is paired with thymine
(T), and guanine (G) is paired with
cytosine (C). Uracil replaces thymine in
RNA.

20. The amount and sequence of the nitrogenous
base pairs may vary with each species.
Keep in mind, however, that both amount and
sequence needs to be accurate and precise
depending on the species. This is important
because the genetic information is stored in
these base pairs. The specific instructions for
several biological processes depend on the
sequence of nitrogenous base pairs in the
genetic material.

21. DNA molecules are very long. An
Escherichia coli bacterium found inside
the large intestine of humans may contain
DNA that has close to five million base
pairs. Surprisingly, E.coli can measure only
at least 1.6 micrometers (µm), but the
length of its DNA molecule is roughly 1.6
millimeters (mm). This means that the DNA
molecules are folded into a space in only
0.001 of its length.

22. RIBONUCLEIC ACID
(RNA)

23. Ribonucleic acid, or RNA, is a single-
stranded molecule that is also composed
of nucleotides, with a few modifications.
The sugar backbone of RNA is ribose.
Uracil replaces thymine of the
nitrogenous bases in RNA.

25. When the cell needs to get
information that codes specific
protein, RNA will copy the
information, which stored in DNA.
This helps the cell get the
instructions needed to produce the
protein while keeping the DNA
information intact.

27. TYPES OF RNA AND ITS
DESCRIPTIONS

28. TYPE FUNCTION LOCATION IN
THE CELL
STRUCTURE
Messenger RNA
(mRNA)
Translates the
genetic code into
proteins with help
of ribosomes.
Nucleus and
cytoplasm
Transfer RNA
(tRNA)
Helps in
transferring amino
acids to the correct
sequence in the
mRNA.
Cytoplasm

30. Ribosomal RNA
(rRNA)
Structural
component of ribose
Ribosome

31. FUNCTIONS OF RNA
- creating proteins
- acts as enzyme
- helps in regulating various cell processes,
ranging from cell division, diffusion, and
growth, to cell aging and death.
RNA defects can result in human diseases.
myotonic dystrophy type 1 (DM1), fragile X-
associated tremor ataxia syndrome (FXTAS), and
spinocerebellar ataxia 8 (SCA8).

33. PROTEINS

34. Proteins are the final products in the central
dogma of molecular biology. They are called the
building blocks of life because they have diverse
functions in the body.
FUNCTIONS OF PROTEINS:
- serve as structural support.
- aid in transporting molecules around your body.
- act as enzymes
- act as a passageway of molecules and
substances into and out of the cell.

35. Proteins are the key to many
physiological processes,
including metabolism, DNA
replications, and molecule
transport.
BIG IDEA:

36. Proteins are composed of polymers of numerous
amino acids known as polypeptides. The three-
dimensional structure of a protein not only defines
its size and shape, but also its function. The
folding in a protein structure allows for interactions
between amino acids that are distant to each other.
Scientist have identified 20 amino acids. These
amino acids can potentially be configured into more
unique information- carryings structures of proteins
are determined by the order of the amino acids in
polypeptide .

39. There is a system by which the
particular order of nitrogenous bases
in DNA and RNA can be translated
into specific amino acids in
polypeptide. The language of
instructions in the mRNA is called
the genetic code.

41. How can a code with just three letters carry
instructions for 20 amino acids?
The secret is that the genetic code is read using
a combination of only three letters at a time.
Thus, each word of the coded message is three
bases long. The three-letter combination in the
mRNA is known as a codon. Amino acids can
be formed by 64 possible codons of the
genetic code.

45. Some of the amino acids can be specified
by more than one codon. However, few
codons can specify only one amino acid.
Also, three codons are referred to as
STOP codons- UAG, UGA, and UAA.

46. DNA code for proteins. This process involves
transcription and translation. DNA
transcription is the first process wherein the
important information in the DNA strand is
copied into the mRNA. The next step is DNA
translation, wherein the information sent by the
mRNA is analyzed with the help of ribosomes.
The ribosomes translate the mRNA code into
the proper protein format.

48. MODULE 4:
REPLICATION,
TRANSCRIPTION, AND
TRANSLATION

49. DNA REPLICATION

51. Ensures that each cell has the complete set
of DNA molecules during cell division.
During the replication, the DNA are
separated into two complimentary strands.
DNA replication on prokaryotes is easier
because the replication usually begins at a
single point in the chromosome. However,
eukaryotes have its own challenge because
the DNA replication occurs on hundreds of
sites in the cell.

52. Different enzymes are important for carrying out
DNA replication. They have different purposes
such as to brake down the hydrogen bond
between the base pairs. After the bonds are
unwind or separated, they then begin to attach
complementary bases like ACGTTA paired with
TGCAAT. The complementary strand is
identical to the original strand thus the
replication produces one original strand and
one new strand.

53. THREE MAJOR STEPS
OF DNA REPLICATION

54. 1. INITIATION
This is the first major step in the process of DNA
replication where the DNA strands start to unwind.
The enzyme called helicase separates the DNA in
to two single strands by dissolving the hydrogen
bond, this is the origin of replication usually
starting from adenine and thymine for they have
only two hydrogen bonds in between them, unlike
guanine and cytosine which have three hydrogen
bonds between them. The structure formed on this
process is called the replication fork.

55. The RNA primase then binds the RNA
nucleotides to the initiation point of the 3’-
5’ parent strand. The RNA nucleotides act
as a primer or the starting point for DNA
synthesis. Once all the nucleotides are
attached to the template DNAs the RNA
primase exits in preparation for
elongation.

56. 2. ELONGATION
The DNA polymerase adds DNA nucleotides to
the 3’ end of the newly synthesized strand. The
addition of nucleotides is specified by the
nitrogenous bases in the template strand,
wherein only those that are complementary in
the template nucleotides are added to the new
strand. This process is repeated until the DNA
polymerase reaches the end of the template
strand.

57. During the elongation the strands separated
into two with different arrangements of carbon
atoms forms two version, the leading strand and
the lagging strand. The leading strand is where
the nucleotides are continuously replicated in the
5’-3’ template strand by the DNA polymerase, while
the lagging strand has a discontinuous version of
the replication due to the DNA polymerase being
unable to continuously read its strand, thus forming
different chunks of DNA known as Okazaki
fragments which later on are joined together.

59. 3. TERMINATION
The last step in DNA replication wherein the
DNA polymerase halts when it reaches a
section in the DNA template that has already
been replicated. However, this event does not
end the whole replication process. In the
lagging strand, there are gaps where the
primers were present, these primers have been
removed by the enzyme exonuclease, these
RNA primers need to be replaced with DNA.

61. As soon as the RNA primers are removed, a
free-floating polymerase will attach to the 3’ end
of the DNA fragment, finally, an enzyme called
ligase seals up the sequence into two
continuous double strands, resulting in two
DNA molecules. The DNA replication process is
usually described as semi conservative
because half of the DNA is composed of the old
template strand and the other half is composed
of the newly synthesized strand.

62. In DNA replication all process should be controlled.
The “proofreading” function of the DNA polymerase
helps prevent mistakes in the replication process.
As the DNA polymerase moves along a single
strand of DNA building the complimentary strands,
the base pairing is checked. How are errors in
base pairing detected? If a wrong nitrogenous
base has been inserted into the DNA strand, it
causes an unstable bond that the DNA polymerase
can easily recognize. Once detected, the wrong
nitrogenous base is soon replaced by the DNA
polymerase itself.

63. DNA TRANSCRIPTION

64. The process of synthesizing RNA from DNA.
This process is the first stage in the central
dogma of molecular biology. Transcriptions
happen when a DNA portion is copied to
form its complimentary mRNA sequence.
For prokaryotes transcription happens on its
cytoplasm, while in eukaryotes it occurs on
the nucleus. Transcriptions steps are similar
to the DNA replication.

65. THREE STEPS OF DNA
TRANSCRIPTION

66. 1. INITIATION
Transcription needs an enzyme called RNA
polymerase, which is similar to DNA polymerase.
Transcription happens when RNA polymerase
binds to DNA, separating the DNA strands. RNA
polymerase uses only a single strand of DNA as a
template to create a strand of mRNA. RNA
polymerase binds at specific sequences in the
DNA nucleotides called the promoters, which
serve as initiation sites for the enzyme.

67. 2. ELONGATION
As mentioned in the previous process
only one of the unmounted DNA strands
acts as a template for mRNA synthesis.
Elongation happens when different
nucleotides from the cytoplasm are
added to the growing RNA chain. Similar
to DNA replication, RNA is also
synthesized in the 5’-3’ direction.

68. 3. TERMINATION
This happens when the RNA polymerase reaches the
terminator site. The Terminator site contains a specific
sequence of nucleotides that signals the end of
transcription. When this happens, transcription stops
along with the release of the RNA polymerase and the
transcribed mRNA strand. The terminator consists of a
series of adjacent adenines which is preceded by
nucleotide palindrome that stops the RNA polymerase
from transcribing any further. Then, the DNA double
helix reforms.

70. MODIFICATION

71. Before translating mRNA to proteins, it
undergoes modification by several different
processes, such as RNA splicing, 5’ end
capping, and adding a poly-A tail.

72. RNA SPLICING
To modify RNAs into usable forms, large
pieces of known as introns or intervening
sequences are cut out while they are still in the
nucleus. The remaining portions are then
called exons or expressed sequences are
spliced back together to form the final mRNA.
The reason for this process where actually still
not yet fully understood by the scientists but
they have suggested that it played a vital role
in evolution.

73. 5’ END CAPPING
Aside from RNA splicing, this is another
process to modify the produced mRNA
into functional forms. This process
protects the mRNA from exonuclease
activity that might degrade the mRNA. It
also regulates nuclear transport and
promotes the translation and the excision
of the introns.

74. POLY-A TAIL
is the shortcut for polyadenylation, which
allows the addition of multiple adenosine
monophosphates at the end of the mRNA
molecule. This means that a stretch of adenine
bases is added at the tail end of the mRNA. This
process produces mature mRNA that is ready for
translation. The addition of adenine bases at the
end of mRNA also protects it from enzymatic
degradation in the cytoplasm and aids in the
termination process.

76. TRANSLATION

77. The sequence of nucleotide bases created
in mRNA after transcription serves as a
code for the order of amino acids to be
joined together. There should be a
mechanism that translates this code.
Translation happens when the message
carried by mRNA is decoded into a protein
or a polypeptide chain. The process
involves the ribosomes, which contain
small and large subunits.

78. THREE STEPS OF
TRANSLATION

79. 1. INIATION
This is where the mRNA transcribed inside
the nucleus is released into the cytoplasm. It
starts when the ribosomal subunits, especially
the small subunit, binds to the 5’ strand of the
mRNA until it encounters the start codon
(AUG). note that translation also work works
in the 5’-3’ direction. The presence of the start
codon initiates translation.

80. Each tRNA molecule found freely in the
cytoplasm has an anticodon, which is
composed of a set of three nitrogenous bases
in the tRNA molecule that is complementary
to one of the mRNA codons. The ribosome
positions the start codon AUG at the P site to
attract its anticodon which is part of the
initiator tRNA that binds methionine. The next
tRNA would arrive at the P site of the
ribosome.

82. 2. ELONGATION
As each of the codon moves through the
ribosomes, the proper amino acid is
brought into the ribosome and is attached
to the growing polypeptide chain.
Elongation is simply the formation of the
growing polypeptide chain by bringing in
the proper tRNA to translate the mRNA
into a protein.

84. 3. TERMINATION
Continuous attachment of tRNA to the mRNA allows
the polypeptide chain to elongate until it encounters a
STOP codon (UAA, UAG, or UGA), which terminates
and completes the process of translation. There are
no tRNA molecules with anticodons for STOP
codons. Instead, the stop codon would signify protein
release factors that would release the polypeptide
from the ribosomes. Then, the ribosome splits into its
subunits, which can later be reassembled for another
round of protein synthesis.

86. In summary, gene expression happens when
DNA is transcribed into a molecule of mRNA,
which is then translated into a defined
sequence of amino acids in a protein.