1

Chapter 26 Nucleic Acids and Protein Synthesis

2

Nucleic AcidsNucleic acids are:

Molecules that store information for cellular growth and reproduction.Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).Large molecules consisting of long chains of monomers called nucleotides.

3

Nucleic Acids

Nucleic acids are:Made from NucleotidesNucleotides are made from NucleosidesNucleosides are made from Nitrogen bases and pentose (five-carbon) sugar.

4

Nucleosides and nucleotides

HO

NucleotideNucleoside

5

The nucleotides adenosine 5´-monophosphate (AMP) and deoxycytidine 5´-monophosphate (dCMP) are shown below. Nucleotides are formed from nucleosides by

1. addition of a heterocyclic nitrogen base to a sugar.2. changing the heterocyclic nitrogen base.3. changing the monsaccharide.4. conversion of an alcohol functional group on the

monosaccharide to a phosphate ester.

6

The nucleotides adenosine 5´-monophosphate (AMP) and deoxycytidine 5´-monophosphate (dCMP) are shown below. Nucleotides are formed from nucleosides by

1. addition of a heterocyclic nitrogen base to a sugar.2. changing the heterocyclic nitrogen base.3. changing the monsaccharide.4. conversion of an alcohol functional group on the

monosaccharide to a phosphate ester.

7

Nitrogen BasesThe nitrogen bases in nucleic acids consist of the: Pyrimidines C, T, and U And purines A and G.

8

The hetereocyclic nitrogen base in the nucleotide shown below is the

1. purine base adenine.2. purine base cytosine.3. pyrimidine base

adenine.4. pyrimidine base

cytosine.

9

The hetereocyclic nitrogen base in the nucleotide shown below is the

1. purine base adenine.2. purine base cytosine.3. pyrimidine base

adenine.4. pyrimidine base

cytosine.

10

Pentose Sugars

The pentose (five-carbon) sugar:In RNA is ribose.In DNA is deoxyribose. Has carbon atoms numbered with primes to distinguish them from the nitrogen bases.

11

HO

A nucleoside:Has a nitrogen base linked by a glycosidicbond to C1’ of a ribose or deoxyribose.Is named by changing the nitrogen base ending to -osine for purines and –idine for pyrimidines

Nucleosides

12

A nucleotide:Is a nucleoside that forms a phosphate ester with the C5’ OH group of ribose or deoxyribose.Is named using the name of the nucleoside followed by 5’-monophosphate.

Nucleotides

13

Nucleic acids are polynucleotides. Nucleic acids are classified as either DNA or RNA. The nucleotide shown below might be found in

1. either DNA or RNA.2. neither DNA nor

RNA.3. only DNA.4. only RNA.

14

Nucleic acids are polynucleotides. Nucleic acids are classified as either DNA or RNA. The nucleotide shown below might be found in

1. either DNA or RNA.2. neither DNA nor

RNA.3. only DNA.4. only RNA.

15

Names of Nucleosides and Nucleotides

16

DNA and RNA differ in the nature of the monsaccharide unit and the nature of the heterocyclic base. In a nucleic acid, which heterocyclic base is never combined with the sugar shown below?

1. Adenine2. Guanine3. Thymine4. Uracil

17

DNA and RNA differ in the nature of the monsaccharide unit and the nature of the heterocyclic base. In a nucleic acid, which heterocyclic base is never combined with the sugar shown below?

1. Adenine2. Guanine3. Thymine4. Uracil

18

Nucleosides and Nucleotides with Purines

19

Nucleosides and Nucleotides with Pyrimidines

20

AMP, ADP, and ATPAdding phosphate groups to AMP forms the diphosphateADP and the triphosphateATP.

21

Learning CheckGive the name and abbreviation for the following and list its nitrogen base and sugar:

22

Solution

Guanosine 5’-monophosphate; GMPnitrogen base: guanine sugar: ribose

23

Primary Structure of Nucleic Acids

In the primary structure of nucleic acids:Nucleotides are joined by phosphodiesterbonds.The 3’-OH group of the sugar in one nucleotide forms an ester bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide.

24

Primary Structure of Nucleic Acids

25

A nucleic acid polymer:Has a free 5’-phosphate group at one end and a free 3’-OH group at the other end.Is read from the free 5’-end using the letters of the bases. This example reads 5’—A—C—G—T—3’.

Structure of Nucleic Acids

26

Example of RNA

In RNA, A, C, G, and U are linked by 3’-5’ester bonds between ribose and phosphate.

27

Example of DNA

In DNA, A, C, G, and T are linked by 3’-5’ester bonds between deoxyriboseand phosphate.

28

DNA Double HelixIn DNA:

There are two strands of nucleotides that wind together in a double helix.Two hydrogen bonds form between the complementary base pairs A-T.Three hydrogen bonds form between the complementary base pairs G-C.

29

DNA Double Helix Structure

30

How many hydrogen bonds link the two complementary strands of DNA shown below?

1. 102. 113. 124. 13

31

How many hydrogen bonds link the two complementary strands of DNA shown below?

1. 102. 113. 124. 13

32

Write the complementary base sequence for the matching strand in the following DNA section:

5’—A—G—T—C—C —A—A—T—C— 3’

Learning Check

33

Write the complementary base sequence for the matching strand in the following DNA section:

5’—A—G—T—C—C—A—A—T—C—3’

Solution

3’—T—C—A—G—G—T—T—A—G—5’

34

What is the sequence of the DNA strand on the right-side of the picture below?

1. A–G–T–C2. C–T–G–A3. G–A–C–T4. T–C–A–G

35

What is the sequence of the DNA strand on the right-side of the picture below?

1. A–G–T–C2. C–T–G–A3. G–A–C–T4. T–C–A–G

36

DNA replication involves:Unwinding the DNAPairing the bases in each strand with new bases to form new complementary strands.Producing two new DNA strands that exactly duplicate the original DNA.

DNA Replication

Animation_26.1

37

Hydrolysis Energy

Energy from the hydrolysis of each nucleoside triphosphateadding to the complementary strand is used to form the phosphodiesterbond.

38

Direction of Replication

During replication, helicase unwinds the parent DNA at several sections.At each open DNA section called a replication fork,DNA polymerase catalyzes the formation of5’-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 ligaseto give a single 3’-5’ DNA strand.

39

Direction of Replication

40

Learning Check

Match the following: 1) helicase 2) DNA polymerase3) replication fork 4) Okazaki fragmentsA. Short segments formed by the lagging strand.B. The starting point for synthesis in unwound

DNA sections.C. The enzyme the unwinds the DNA double helix.D. The enzyme the catalyzes the formation of

phosphodiester bonds of complementary bases.

41

Solution

Match the following:1) helicase 2) DNA polymerase3) replication fork 4) Okazaki fragmentsA. 4 Short segments formed by the lagging strand.B. 3 The starting point for synthesis in unwound

DNA sections.C. 1 The enzyme the unwinds the DNA double helix.D. 2 The enzyme the catalyzes the formation of

phosphodiester bonds of complementary bases.

42

26.7 DNA and RNAThe three differences in structure between DNA and RNA are

DNA bases are A, G, C, and TT; the RNA bases are A, G, C, and UUthe sugar in DNA is 22--deoxydeoxy--DD--riboseribose; in RNA it is DD--riboseriboseDNA is always double strandeddouble stranded; there are several kinds of RNA, all of which are singlesingle--strandedstranded

43

Transfer RNA and Protein Synthesis

The following two processes are involved in transfer, and use of genetic information:

Transcription: The process by which the genetic messages contained in DNA are read and copied.

Translation: The process by which the genetic messages carried by RNA are decoded and used to build proteins.

Animation_26.10

Animation_26.10.1

44

26.7 Structure and Function of RNA

RNA is similar to DNA – both are sugar-phosphate polymers and both have nitrogen-containing bases attached – but there are differences between them. DNA has only one kind of function-storing

genetic information. By contrast, the different kinds of RNA perform different functions.

45

The following three RNA make it possible for the encoded information carried by the DNA to be put to use in the synthesis of proteins.Ribosome RNA: The granular organelles in the

cell where protein synthesis takes place. These organelles are composed of protein and ribosomal RNA (rRNA).Messenger RNA (mRNA): The RNA that

carries the code transcribed from DNA and directs protein synthesis.

46

Transfer RNA (tRNA): The smaller RNA that delivers amino acids one by one to protein chains growing at ribosomes. Each tRNA recognizes and carries only one amino acid.

47

26.8 Transcription: RNA SynthesisRNA are synthesized in the cell nucleus. Before leaving the nucleus, all types of RNA are modified in the various ways needed for their various functions. In transcription, a small section of the DNA double helix unwinds, the bases on the two strands are exposed, and one by one the complementary nucleotides are attached.

48

rRNA, tRNA, and mRNA are all synthesized in essentially the same manner. Only one of the two DNA strands is transcribed during RNA synthesis. The DNA strand that is transcribed is the template strand; while the its complementary strand is the informational strand.The messenger RNA produced is a duplicate of the DNA informational strand, but with U base wherever the DNA has a T base.

49

The process of forming mRNA from DNA is called

1. reduction.2. replication.3. transcription.4. translation.

50

The process of forming mRNA from DNA is called

1. reduction.2. replication.3. transcription.4. translation.

51

26.9 The Genetic Code

The ribonucleotide sequence in an mRNA chain is like a coded sentence that species the order in which amino acid residues should be joined to form a protein. Each word, or codon in the mRNA sentence is a series of three ribonucleotidesthat code for a specific amino acid.

52

For example, the series uracil-uracil-guanine(UUG) on an mRNA chain is a codondirecting incorporation of the amino acid leucine into a growing protein chain. Of the 64 possible three-base combinations in RNA, 61 code for specific amino acids and 3 code for chain termination.

53

26.10 Translation: Transfer RNA and Protein Synthesis

The synthesis of proteins occur at ribosomes, which are outside the nucleus and within the cytoplasm of cells.The mRNA connects with the ribosome, and the amino acids attached to transfer RNA (tRNA) are delivered one by one.

54

Three stages in protein Three stages in protein Synthesis are initiation, Synthesis are initiation, elongation, and elongation, and termination. A diagram termination. A diagram of translation is shown of translation is shown in the Fig 26.8.in the Fig 26.8.

55

Chapter SummaryNucleic acids are polymers of nucleotides.Each nucleotide contains a sugar, a base, and a phosphate group.The sugar is D-ribose in ribonucleic acid (RNA) and 2-deoxy-D-ribose in deoxyribonucleic acid (DNA).A nucleoside contains a sugar and a base, but not the phosphate group.The DNA in each chromosome consists of two polynucleotides strands twisted together in a double helix.

56

Chapter Summary Contd.The bases on the two strands are complementary – opposite every thimine is an adenine, opposite every guanine is a cytisine. The base pairs are connected by hydrogen bonds – two between T and A; three between G and C.Messenger RNA (mRNA) carries the genetic information out of the nucleus to the ribosomeswhere protein synthesis occurs.

57

Chapter Summary Contd.Transfer RNA (tRNA) bond to amino acids that they deliver to protein synthesis.Ribosomal RNA (rRNA) are incorporated into ribosomes.In transcription, one strand of the DNA is copied (the template) and the other is the informational strand, and is not copied.The genetic information is read as a sequence of codons-triplets of bases in DNA that give the sequence of amino acids in a protein.

58

End of Chapter 26

59

Animationshttp://207.207.4.198/pub/flash/24/menu.swfhttp://www.lewport.wnyric.org/JWANAMAKER/animations/Protein%20Synthesis%20-%20long.htmlhttp://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html