NUCLEIC ACIDS
• Nucleic acids are molecules that store information for cellular growth and reproduction
• A nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group:
The pyrimidines and purines found in DNA and RNA
Nucleotides and Nucleic Acids
Structures of the four deoxyribonucleotides
Nucleotides and Nucleic Acids
Structures of the four ribonucleotides
Nucleotides and Nucleic Acids
Pentose Sugars
• There are two related pentose sugars:
- RNA contains ribose- DNA contains deoxyribose
• The sugars have their carbon atoms numbered with primes to distinguish them from the nitrogen bases
Ikatan nukleotida DNA dan RNA
Ikatan Hidrogen pada pasangan basa Watson dan Crick
Base Pairing in the DNA Double Helix
Avery-Macleod-McCarty
Difraksi Sinar XDNA
Watson-Crick model for the structure of DNA
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• Hydrogen bonds between bases hold the strands together: A and T, C and G
Figure 10.3D
Ribbon model Partial chemical structure Computer model
Hydrogen bond
“Central dogma of molecular genetics”• The function of DNA is to store information and pass it to RNA• The function of RNA is to read, decode, and use the information
received from DNA to make proteins• Three fundamental processes take place:
• Replication – process by which identical copies of DNA are made so the information can be preserved and handed down to offspring
• Transcription – the process by which the genetic messages are read and carried out of the cell nucleus to ribosomes, where protein synthesis occurs
• Translation – the process by which the genetic messages are decoded and used to synthesize proteins
Base Pairing in DNA: The Watson-Crick Model
A representation of semiconservative DNA replication
Replication of DNA
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• DNA replication begins at many specific sites
How can entire chromosomes be replicated during S phase?
Figure 10.5A
Parental strandOrigin of replication
Bubble
Two daughter DNA molecules
Daughter strand
Direction of Replication• The enzyme helicase unwinds several sections of parent DNA • At each open DNA section, called a replication fork, DNA
polymerase catalyzes the formation of 5’-3’ester bonds of the leading strand
• The lagging strand, which grows in the 3’-5’ direction, is synthesized in short sections called Okazaki fragments
• The Okazaki fragments are joined by DNA ligase to give a single 3’-5’ DNA strand
What sequence of bases on one strand of DNA is complementary to the sequence TATGCAT on another strand?
Worked Example 24.1
Predicting the Complementary Base Sequence in Double-Stranded DNA
Strategy• Remember that A and G form complementary pairs with T
and C• Go through the sequence replacing A by T, G by C, T by A,
and C by G• Remember that the 5′ end is on the left and the 3′ end is on
the right in the original strand
Worked Example 24.1
Predicting the Complementary Base Sequence in Double-Stranded DNA
Solution
Original: (5′) TATGCAT (3′)
Compliment: (3′) ATACGTA (5′) or
(5′) ATGCATA (3′)
Worked Example 24.1
Predicting the Complementary Base Sequence in Double-Stranded DNA
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– The DNA is transcribed into RNA, which is translated into the polypeptide
Figure 10.6A
DNA
RNA
Protein
TRANSCRIPTION
TRANSLATION
• The information constituting an organism’s genotype is carried in its sequence of bases
DNA TRANSCRIPTION
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• An exercise in translating the genetic code
Figure 10.8B
Startcodon
RNA
Transcribed strand
StopcodonTranslation
Transcription
DNA
Polypeptide
U C A G
U
C
A
G
GACU
GACU
GACU
GACU
UUUUUCUUAUUG
CUUCUCCUACUG
AUUAUCAUAAUG
GUUGUCGUAGUG
phe
leu
leu
ile
met (start)
val
UCUUCCUCAUCG
CCUCCCCCACCG
ACUACCACAACG
GCUGCCGCAGCG
ser
pro
thr
ala
UAUUACUAAUAG
CAUCACCAACAG
AAUAAC
AAGAAA
GAUGACGAAGAG
tyr
stopstop
his
gln
asn
lys
asp
glu
UGUUGCUGAUGG
CGUCGCCGACGG
AGUAGCAGAAGG
GGUGGCGGAGGG
cys
stoptrp
arg
ser
arg
gly
First Base T
hird Base
Second Base
Virtually all organisms share the same genetic code “unity of life”
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• Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other
Figure 10.11B, C
Anticodon
Amino acidattachment site
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Ribosomes build polypeptides
Figure 10.12A-C
Codons
tRNAmolecules
mRNA
Growingpolypeptide
Largesubunit
Smallsubunit
mRNA
mRNAbindingsite
P site A site
P A
Growingpolypeptide
tRNA
Next amino acidto be added topolypeptide
What amino acid sequence is coded by the following segment of a DNA coding strand?
(5′) CTA-ACT-AGC-GGG-TCG-CCG (3′)
Worked Example 24.2
Predicting the Amino Acid Sequence Transcribed from DNA
Strategy• The mRNA produced during translation is a copy of the DNA
coding strand• Each T replaced by U
• The mRNA has the sequence
(5′) CUA-ACU-AGC-GGG-UCG-CCG (3′)
Worked Example 24.2
Predicting the Amino Acid Sequence Transcribed from DNA
Solution • Leu-Thr-Ser-Gly-Ser-Pro
Worked Example 24.2
Predicting the Amino Acid Sequence Transcribed from DNA
DNA Sequencing
Polymerase Chain Reaction
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• Types of mutations
Figure 10.16B
mRNA
NORMAL GENE
BASE SUBSTITUTION
BASE DELETION
Protein Met Lys Phe Gly Ala
Met Lys Phe Ser Ala
Met Lys Leu Ala His
Missing
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11.8 Recombinant DNA Technology, Continued
11.8 Recombinant DNA Technology, Continued
Therapeutic Proteins
• The human insulin gene was the first application of recombinant DNA technology. It was incorporated into a bacteria called Escherichia coli.
• Insulin produced in this manner eliminated many of the side effects that occurred from the use of pig and cow insulin.
• Recombinant technology is used to insert genes into crop and food plants offering many growth advantages.
11.8 Recombinant DNA Technology, Continued
Nuclear Transplantation—Cloning an Organism
• Clone means to make an exact copy.
• Cloning an organism creates a genetic copy of the original organism.
• Cloning involves taking nuclear DNA from an adult cell and transplanting it into an egg whose DNA has been removed.
11.8 Recombinant DNA Technology, Continued