1) The structure of DNA was determined in the 1950s by Watson and Crick to be a double helix with complementary base pairing between adenine and thymine and between guanine and cytosine. 2) DNA replication occurs through unwinding of the DNA double helix, followed by synthesis of new strands using the old strands as templates. 3) Gene expression involves transcription of DNA into mRNA in the nucleus, followed by translation of mRNA into proteins with the help of tRNA and rRNA in the cytoplasm.

1. DNA Structure and
Replication
Submitted by:
Esguerra, Joanna Marie
Evaristo, Roselle
AAPD2G
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2.  In the early 1900s, scientists knew that
chromosomes are made up of DNA
(deoxyribonucleic acid) and proteins,
contained genetic information.
 However, they did not know whether the DNA or
the proteins was the actual genetic material.
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3.  In the 1940s, various researchers
showed that DNA was the genetic
material
 In the 1950s, the structure of DNA was
determined.
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4. Structure of DNA
The structure of DNA was determined by
James Watson and Francis Crick in
the early 1950s.
DNA is a polynucleotide; nucleotides are
composed of a phosphate, a sugar, and a
nitrogen-containing base. 4

5.  The sugar in DNA is deoxyribose
 The four different bases in DNA are:
adenine (A), thymine (T), guanine
(G), and cytosine (C).
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6. A nucleotide
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7. Watson and Crick showed that DNA is a double
helix in which
A is paired with T
G is paired with C
This is called complementary base pairing
because a purine is always paired with a
pyrimidine.
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9. When the DNA double helix unwinds, it resembles a
ladder.
The sides of the ladder are the sugar-phosphate
backbones, and the rungs of the ladder are the
complementary paired bases.
The two DNA strands are anti-parallel – they run
in opposite directions.
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10. DNA
double
helix
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11. Replication of DNA
DNA replication occurs during chromosome
duplication.
An exact copy of the DNA is produced with the aid of
DNA polymerase.
Hydrogen bonds between bases break and enzymes
“unzip” the molecule.
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12.  Each old strand of nucleotides serves
as a template for each new strand.
 New nucleotides move into
complementary positions are joined by
DNA polymerase.
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13. DNA replication
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14. Ladder configuration and DNA replication
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15. Gene Expression
A gene is a segment of DNA that specifies the amino
acid sequence of a protein.
Gene expression occurs when gene activity leads to
a protein product in the cell.
A gene does not directly control protein synthesis;
instead, it passes its genetic information on to RNA,
which is more directly involved in protein synthesis.
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16. RNA (ribonucleic acid ) is a single-
stranded nucleic acid in which
(adenine) A pairs with U (uracil )
(guanine) G pairs with C. (cytosine)
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17.  messenger RNA (mRNA) carries genetic
information to the ribosomes,
 ribosomal RNA (rRNA) is found in the ribosomes,
 transferRNA (tRNA) transfers amino acids to the
ribosomes, where the protein product is
synthesized.
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18. Structure of RNA
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19. Two processes are involved in the synthesis of
proteins in the cell:
Transcription makes an RNA molecule
complementary to a portion of DNA.
Translation occurs when the sequence of
bases of mRNA directs the sequence of
amino acids in a polypeptide.
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20. The Genetic Code
DNA specifies the synthesis of proteins
because it contains a triplet code: every
three bases stand for one amino acid.
Each three-letter unit of an mRNA
molecule is called a codon.
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21.  Most amino acids have more than one
codon; there are 20 amino acids with a
possible 64 different triplets.
 The code is nearly universal among
living organisms.
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23. Central Concept or " The Central Dogma"
The central concept of genetics involves the DNA-
to-protein sequence involving transcription and
translation.
DNA has a sequence of bases that is transcribed into
a sequence of bases in mRNA.
Every three bases is a codon that stands for a
particular amino acid.
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24. Overview
of gene
expression
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25.  During transcription in the nucleus, a segment
of DNA unwinds and unzips, and the DNA serves as
a template for mRNA formation.
 RNA polymerase joins the RNA nucleotides so
that the codons in mRNA are complementary to
the triplet code in DNA.
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26. Transcription and mRNA synthesis
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27. Translation
Translation is the second step by which gene
expression leads to protein synthesis.
During translation, the sequence of codons in mRNA
specifies the order of amino acids in a protein.
Translation requires several enzymes and two other
types of RNA: transfer RNA and ribosomal RNA.
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28. Review of Gene Expression
DNA in the nucleus contains a triplet
code; each group of three bases stands
for one amino acid.
During transcription, an mRNA copy of
the DNA template is made.
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29.  The mRNA is processed before leaving the
nucleus.
 The mRNA joins with a ribosome, where
tRNA carries the amino acids into position
during translation.
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