ASAM Nukleat

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

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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