DNA its Discovery Who Discovered DNA? Credit for who first identified DNA is often mistakenly given to James Watson and Francis Crick, who just furthered Miescher’s discovery with their own groundbreaking research nearly 100 years later. Watson and Crick contributed largely to our understanding of DNA in terms of genetic inheritance, but much like Miescher, long before their work, others also made great advancements in and contributions to the field. In 1866, before many significant discoveries and findings, Gregor Mendel was the first to suggest that characteristics are passed down from generation to generation. Mendel coined the terms as recessive and dominant. In 1869, Friedrich Miescher identified the “nuclein” by isolating a molecule from a cell nucleus that would later become known as DNA. In 1881, Nobel Prize winner and German biochemist Albrecht Kossel, who is credited with naming DNA, identified nuclein as a nucleic acid. He also isolated those five nitrogen bases that are now considered to be the basic building blocks of DNA and RNA: adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U) in case of RNA). In 1882, Walther Fleming devoted research and time to cytology, which is the study of chromosomes. He discovered mitosis in 1882 when he was the first biologist to execute a wholly systematic study of the division of chromosomes. His observations that chromosomes double is significant to the later discovered theory of inheritance. In Early 1900s, Theodor Boveri and Walter Sutton were independently working on what’s now known as the Boveri-Sutton chromosome theory, or the chromosomal theory of inheritance. Their findings are fundamental in our understanding of how chromosomes carry genetic material and pass it down from one generation to the next. In 1902, Mendel’s theories were finally associated with a human disease by Sir Archibald Edward Garrod, who published the first findings from a study on recessive inheritance in human beings in 1902. Garrod opened the door for our understanding of genetic disorders resulting from errors in chemical pathways in the body. In 1944, Oswald Avery first outlined DNA as the transforming principle, which essentially means that DNA transform cell properties.

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SUBMITTED TO: Dr. SARDAR AZHAR MAHMOOD
SUBMITTED BY: GURMEET SINGH
ASSIGNMENT TOPIC NUCLEUS, DNA AND CENTRAL
DOGMA OF MOLECULAR BIOLOGY
ROLL NUMBER: 2032-211003
STUDY LEVEL: MPHIL
DEPARTMENT: DEPARTMENT OF ZOOLOGY
DATE OF SUBMISSION: 10-01-2022

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Nucleus
In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning
kernel or seed) is a membrane-bound organelle found in eukaryotic cells. Eukaryotes
usually have a single nucleus, but a few cell types, such as mammalian red blood
cells, have no nuclei, and a few others including osteoclasts have many. The main
structures making up the nucleus are the nuclear envelope, a double membrane that
encloses the entire organelle and isolates its contents from the cellular cytoplasm;
and the nuclear matrix (which includes the nuclear lamina), a network within the
nucleus that adds mechanical support, much like the cytoskeleton supports the cell.
The cell nucleus contains all the cell's genome, except for the small amount of
mitochondrial DNA and, in plant cells, plastid DNA. Nuclear DNA is organized as
multiple long linear molecules in a complex with a large variety of proteins, such as
histones, to form chromosomes. The genes within these chromosomes are structured
in such a way to promote cell function. The nucleus maintains the integrity of genes
and controls the activities of the cell by regulating gene expression—the nucleus is,
therefore, the control center of the cell.
Nuclear envelope and pores
A cross section of a nuclear pore on the surface of the nuclear envelope (1) the outer
ring, (2) spokes, (3) basket, and (4) filaments.
The nuclear envelope consists of two membranes, an inner and an outer nuclear
membrane. Together, these membranes serve to separate the cell's genetic material
from the rest of the cell contents and allow the nucleus to maintain an environment
distinct from the rest of the cell. Despite their close apposition around much of the
nucleus, the two membranes differ substantially in shape and contents. The inner
membrane surrounds the nuclear content, providing its defining edge Embedded
within the inner membrane, various proteins bind the intermediate filaments that
give the nucleus its structure. The outer membrane encloses the inner membrane and
is continuous with the adjacent endoplasmic reticulum membraneAs part of the
endoplasmic reticulum membrane, the outer nuclear membrane is studded with
ribosomes that are actively translating proteins across membrane. The space between
the two membranes, called the "perinuclear space", is continuous with the
endoplasmic reticulum lumen
Nuclear pore
Nuclear pores, which provide aqueous channels through the envelope, are
composed of multiple proteins, collectively referred to as nucleoporins. The pores
are about 60–80 million Daltons in molecular weight and consist of around 50 (in

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yeast) to several hundred proteins (in vertebrates). The pores are 100 nm in total
diameter; however, the gap through which molecules freely diffuse is only about 9
nm wide, due to the presence of regulatory systems within the center of the pore.
This size selectively allows the passage of small water-soluble molecules while
preventing larger molecules, such as nucleic acids and larger proteins, from
inappropriately entering or exiting the nucleus. These large molecules must be
actively transported into the nucleus instead.
Structure of Nucleus
Function of Nucleus
The nucleus provides a site for genetic transcription that is segregated from the
location of translation in the cytoplasm, allowing levels of gene regulation that are
not available to prokaryotes. The main function of the cell nucleus is to control gene
expression and mediate the replication of DNA during the cell cycle.
Cell compartmentalization
The nuclear envelope allows the nucleus to control its contents and separate them
from the rest of the cytoplasm where necessary. This is important for controlling
processes on either side of the nuclear membrane. In most cases where a cytoplasmic
process needs to be restricted, a key participant is removed to the nucleus, where it

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interacts with transcription factors to downregulate the production of certain
enzymes in the pathway. This regulatory mechanism occurs in the case of glycolysis,
a cellular pathway for breaking down glucose to produce energy.
Replication
The main function of the cell nucleus is to control gene expression and mediate the
replication of DNA during the cell cycle. It has been found that replication happens
in a localized way in the cell nucleus.
Gene expression
A generic transcription factory during transcription, highlighting the possibility of
transcribing more than one gene at a time. The diagram includes 8 RNA polymerases
however the number can vary depending on cell type. The image also includes
transcription factors and a porous, protein core.
Gene expression first involves transcription, in which DNA is used as a template to
produce RNA. In the case of genes encoding proteins, that RNA produced from this
process is messenger RNA (mRNA), which then needs to be translated by ribosomes
to form a protein. As ribosomes are located outside the nucleus, mRNA produced
needs to be exported.
Since the nucleus is the site of transcription, it also contains a variety of proteins that
either directly mediate transcription or are involved in regulating the process. These
proteins include helicases, which unwind the double-stranded DNA molecule to
facilitate access to it, RNA polymerases, which bind to the DNA promoter to
synthesize the growing RNA molecule, topoisomerases, which change the amount
of supercoiling in DNA, helping it wind and unwind, as well as a large variety of
transcription factors that regulate expression
RNA Polymerase
RNA Polymerase I is a workhorse, producing nearly fifty percent of the RNA
transcribed in the cell. It exclusively polymerizes ribosomal RNA, which forms a
large component of ribosomes, the molecular machines that synthesize proteins.
RNA Polymerase II is extensively studied because it is involved in the transcription
of mRNA precursors. It also catalyzes the formation of small nuclear RNAs and
micro RNAs.
RNA Polymerase III transcribes transfer RNA, some ribosomal RNA and a few other
small RNAs and is important since many of its targets are necessary for normal
functioning of the cell. RNA polymerases IV and V are found exclusively in plants,

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and together are crucial for the formation of small interfering RNA and
heterochromatin in the nucleus.
DNA DISCOVERY
Many people believe that American biologist James Watson and English physicist
Francis Crick discovered DNA in the 1950s. That is not the case, but DNA was first
identified in the late 1860s by Swiss chemist Friedrich Miescher. 1869 was the year
in which Swiss physiological chemist Friedrich Miescher first identified DNA what
he called as "Nuclein" inside the nuclei of human white blood cells. The term nuclein
was later changed to "nucleic acid" and eventually to deoxyribonucleic acid or DNA.
In the early 1950s, American biologist James Watson and British physicist Francis
Crick came up with their famous model of the DNA double helix. They were the
first to cross the finish line in this scientific race with others such as Linus Pauling
(who discovered protein secondary structure) also trying to find the correct model.
Franklin was an expert in a powerful technique for determining the structure of
molecules, known as X-ray crystallography. When the crystallized form of a
molecule such as DNA is exposed to X-rays, some of the rays are deflected by the
atoms in the crystal, forming a diffraction pattern that gives clues about the
molecule's structure.
Who Discovered DNA?
Credit for who first identified DNA is often mistakenly given to James Watson and
Francis Crick, who just furthered Miescher’s discovery with their own
groundbreaking research nearly 100 years later. Watson and Crick contributed
largely to our understanding of DNA in terms of genetic inheritance, but much like
Miescher, long before their work, others also made great advancements in and
contributions to the field.

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In 1866, before many significant discoveries and findings, Gregor Mendel was the
first to suggest that characteristics are passed down from generation to generation.
Mendel coined the terms as recessive and dominant.
In 1869, Friedrich Miescher identified the “nuclein” by isolating a molecule from a
cell nucleus that would later become known as DNA.
In 1881, Nobel Prize winner and German biochemist Albrecht Kossel, who is
credited with naming DNA, identified nuclein as a nucleic acid. He also isolated
those five nitrogen bases that are now considered to be the basic building blocks of
DNA and RNA: adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U)
in case of RNA).
In 1882, Walther Fleming devoted research and time to cytology, which is the study
of chromosomes. He discovered mitosis in 1882 when he was the first biologist to
execute a wholly systematic study of the division of chromosomes. His observations
that chromosomes double is significant to the later discovered theory of inheritance.
In Early 1900s, Theodor Boveri and Walter Sutton were independently working on
what’s now known as the Boveri-Sutton chromosome theory, or the chromosomal
theory of inheritance. Their findings are fundamental in our understanding of how
chromosomes carry genetic material and pass it down from one generation to the
next.
In 1902, Mendel’s theories were finally associated with a human disease by Sir
Archibald Edward Garrod, who published the first findings from a study on recessive
inheritance in human beings in 1902. Garrod opened the door for our understanding
of genetic disorders resulting from errors in chemical pathways in the body.
In 1944, Oswald Avery first outlined DNA as the transforming principle, which
essentially means that DNA transform cell properties.

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In 1944-1950, Erwin Chargaff discovered that DNA is responsible for heredity and
that it varies between species. His discoveries, known as Chargaff’s Rules, proved
that guanine and cytosine units as well as adenine and thymine units were the same
in double-stranded DNA, and he also discovered that DNA varies among species.
In Late 1940s, Barbara McClintock discovered the mobility of genes, and her
discovery is known as “jumping gene,” or the idea that genes can move on a
chromosome.
In 1951, Roslind Franklin’s work in X-ray crystallography began when she started
taking X-ray diffraction photographs of DNA. Her images showed the helical form,
which was confirmed by Watson and Crick nearly two years later.
In 1953, Watson and Crick published on DNA’s double helix structure that twists to
form the ladder like structure which they called as DNA.
When Was DNA Discovered?
What we know about DNA today can be largely credited to James Watson and
Francis Crick, who discovered the structure of DNA in 1953. This is the year they
discovered DNA’s double helix, or spiraling, intertwined structure which is
fundamental to our current understanding of DNA.
DNA CONCEPT
DNA has a regular structure. It's orientation, width, width between nucleotides,
length, and number of nucleotides per helical turn is constant. All these features were
described by Watson and Crick. Adenine is always opposite thymine, and cytosine
is always opposite guanine. The two strands are held together by hydrogen bonds.
There are two bonds between adenine and thymine and three bonds between guanine
and cytosine.

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DNA is a string of deoxyribonucleotides. These consist of three different
components. These are the deoxyribose sugar, a phosphate group, and a nitrogen
base. These nitrogen bases are further broken down into four types, including
Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
What is DNA Made of?
DNA is made up of molecules known as nucleotides. Each nucleotide contains a
sugar and phosphate group as well as nitrogen bases.
1. Deoxyribose sugar
This is the basic building block which is distinguished because it contains a
hydrogen (H) atom at the number 2' carbon.
2. Triphosphate group
It attached to the 5' carbon. This group is important because in a DNA chain
it undergoes a reaction with the 3' OH group to produce polydeoxynucleotide.
3. Nitrogen base
This is final component of DNA which is attached to the 1' carbon. There are
mainly Four bases are possible in DNA i.e. Two pyrimidines which are
thymine and cytosine while two purines which are adenine and guanine.

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The double stranded DNA molecule is held together by hydrogen bonds. Pairing
involves specific atoms in each base. Adenine pairs with the thymine, and guanine
pairs with cytosine. Each strand of the double-stranded DNA molecule has the same
basic structure. It is a series of series of deoxyribonucleotides linked together by
phosphodiester bonds. This bond joins a phosphate group to the 3' carbon of the
deoxyribose sugar. Each strand is complementary to the opposite strand. If one
strand has an adenine at a position, its anti-parallel strand would have a thymine at
the corresponding position. Likewise, guanine and cytosine would be
complementary according to Chargaff’s rule.

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a. Structure of DNA
CENTRAL DOGMA
The process of converting DNA into RNA and then RNA in a specific
Polypeptide, this whole process is known as central dogma.
Transcription
DNA RNA POLYPEPTIDE
Transcription Translation
CENTRAL DOGMA

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Transcription is the process of making an RNA copy of a gene sequence. It takes
place in cell nucleus.
✓ This copy is called a messenger RNA (mRNA) molecule, leaves the cell
nucleus, and enters the cytoplasm.
✓ It directs the synthesis of the protein in cytoplasm which it encodes.
Translation
The process of translating the sequence of a messenger RNA (mRNA) molecule to
a sequence of amino acids during protein synthesis. It takes place in the cytoplasm
of the cell.
➢ Genetic code describes the relationship between the sequence of base pairs in
a gene and the corresponding amino acid sequence that it encodes.
➢ In the cell cytoplasm, the ribosome reads the sequence of the mRNA in groups
of three bases to assemble the protein.

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References
1. Pauling, L., and Corey, R. B., Nature, 171, 346 (1953); Proc. U.S. Nat.
Acad. Sci., 39, 84 (1953).
2. Chargaff, E., for references see Zamenhof, S., Brawerman, G., and Chargaff,
E., Biochim. et Biophys. Acta, 9, 402 (1952).
3. Astbury, W. T., Symp. Soc. Exp. Boil. 1, Nucleic Acid, 66 (Camb. Univ.
Press, 1947).
4. Wyatt, G. R., J. Gen. Physiol., 36, 201 (1952).