Chapter 10 Molecular Biology of the Gene Power
Chapter 10 Molecular Biology of the Gene Power. Point Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
Introduction § Viruses infect organisms by – binding to receptors on a host’s target cell, – injecting viral genetic material into the cell, and – hijacking the cell’s own molecules and organelles to produce new copies of the virus. § The host cell is destroyed, and newly replicated viruses are released to continue the infection. © 2012 Pearson Education, Inc.
Introduction § Viruses are not generally considered alive because they – are not cellular and – cannot reproduce on their own. § Because viruses have much less complex structures than cells, they are relatively easy to study at the molecular level. § For this reason, viruses are used to study the functions of DNA. © 2012 Pearson Education, Inc.
Figure 10. 0_1 Chapter 10: Big Ideas The Structure of the Genetic Material DNA Replication The Flow of Genetic Information from DNA to RNA to Protein The Genetics of Viruses and Bacteria
Figure 10. 0_2
THE STRUCTURE OF THE GENETIC MATERIAL © 2012 Pearson Education, Inc.
10. 1 SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material § Until the 1940 s, the case for proteins serving as the genetic material was stronger than the case for DNA. – Proteins are made from 20 different amino acids. – DNA was known to be made from just four kinds of nucleotides. § Studies of bacteria and viruses – ushered in the field of molecular biology, the study of heredity at the molecular level, and – revealed the role of DNA in heredity. © 2012 Pearson Education, Inc.
10. 1 SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material § In 1928, Frederick Griffith discovered that a “transforming factor” could be transferred into a bacterial cell. He found that – when he exposed heat-killed pathogenic bacteria to harmless bacteria, some harmless bacteria were converted to disease-causing bacteria and – the disease-causing characteristic was inherited by descendants of the transformed cells. © 2012 Pearson Education, Inc.
10. 1 SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material § In 1952, Alfred Hershey and Martha Chase used bacteriophages to show that DNA is the genetic material of T 2, a virus that infects the bacterium Escherichia coli (E. coli). – Bacteriophages (or phages for short) are viruses that infect bacterial cells. – Phages were labeled with radioactive sulfur to detect proteins or radioactive phosphorus to detect DNA. – Bacteria were infected with either type of labeled phage to determine which substance was injected into cells and which remained outside the infected cell. © 2012 Pearson Education, Inc.
10. 1 SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material – The sulfur-labeled protein stayed with the phages outside the bacterial cell, while the phosphorus-labeled DNA was detected inside cells. – Cells with phosphorus-labeled DNA produced new bacteriophages with radioactivity in DNA but not in protein. Animation: Hershey-Chase Experiment Animation: Phage T 2 Reproductive Cycle © 2012 Pearson Education, Inc.
Figure 10. 1 A Head Tail fiber DNA
Figure 10. 1 A_1 Head Tail fiber
Figure 10. 1 B Phage Empty protein shell Radioactive protein Bacterium Centrifuge Pellet 1 Batch 2: Radioactive DNA labeled in green Phage DNA Batch 1: Radioactive protein labeled in yellow The radioactivity is in the liquid. 2 3 4 Radioactive DNA Centrifuge Pellet The radioactivity is in the pellet.
Figure 10. 1 B_1 Phage Empty protein shell Radioactive protein Bacterium DNA Batch 1: Radioactive protein labeled in yellow 2 1 Batch 2: Radioactive DNA labeled in green Phage DNA Radioactive DNA
Figure 10. 1 B_2 Empty protein shell The radioactivity is in the liquid. Phage DNA Centrifuge Pellet 3 4 Centrifuge Pellet The radioactivity is in the pellet.
Figure 10. 1 C 1 A phage attaches itself to a bacterial cell. 2 The phage injects 3 The phage DNA directs its DNA into the bacterium. the host cell to make more phage DNA and proteins; new phages assemble. 4 The cell lyses and releases the new phages.
Figure 10. 1 C_1 1 A phage attaches itself to a bacterial cell. 2 The phage injects its DNA into the bacterium.
Figure 10. 1 C_2 3 The phage DNA directs the host cell to make more phage DNA and proteins; new phages assemble. 3 4 The cell lyses and releases the new phages.
10. 2 DNA and RNA are polymers of nucleotides § DNA and RNA are nucleic acids. § One of the two strands of DNA is a DNA polynucleotide, a nucleotide polymer (chain). § A nucleotide is composed of a – nitrogenous base, – five-carbon sugar, and – phosphate group. § The nucleotides are joined to one another by a sugar-phosphate backbone. © 2012 Pearson Education, Inc.
10. 2 DNA and RNA are polymers of nucleotides § Each type of DNA nucleotide has a different nitrogen-containing base: – adenine (A), – cytosine (C), – thymine (T), and – guanine (G). Animation: DNA and RNA Structure © 2012 Pearson Education, Inc.
Figure 10. 2 A T A C T G Sugar-phosphate backbone A C G T A C G A G T T Covalent bond joining nucleotides T C A C A A G Phosphate group Nitrogenous base Sugar Nitrogenous base (can be A, G, C, or T) C G T A A DNA double helix DNA nucleotide T Thymine (T) T Phosphate group G G Two representations of a DNA polynucleotide Sugar (deoxyribose) DNA nucleotide
Figure 10. 2 A_1 A G C T T A C G G A C G T T T A A C G T A A DNA double helix
Figure 10. 2 A_2 Sugar-phosphate backbone A A Covalent bond joining nucleotides C DNA nucleotide T Nitrogenous base Sugar C T G G Two representations of a DNA polynucleotide Phosphate group
Figure 10. 2 A_3 Nitrogenous base (can be A, G, C, or T) Thymine (T) Phosphate group Sugar (deoxyribose) DNA nucleotide
Figure 10. 2 B Thymine (T) Cytosine (C) Pyrimidines Guanine (G) Adenine (A) Purines
Figure 10. 2 B_1 Thymine (T) Cytosine (C) Pyrimidines
Figure 10. 2 B_2 Guanine (G) Adenine (A) Purines
10. 2 DNA and RNA are Polymers of Nucleotides § RNA (ribonucleic acid) is unlike DNA in that it – uses the sugar ribose (instead of deoxyribose in DNA) and – RNA has the nitrogenous base uracil (U) instead of thymine. © 2012 Pearson Education, Inc.
Figure 10. 2 C Nitrogenous base (can be A, G, C, or U) Phosphate group Uracil (U) Sugar (ribose)
Figure 10. 2 D Cytosine Uracil Adenine Guanine Ribose Phosphate
10. 3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix § In 1952, after the Hershey-Chase experiment demonstrated that the genetic material was most likely DNA, a race was on to – describe the structure of DNA and – explain how the structure and properties of DNA can account for its role in heredity. © 2012 Pearson Education, Inc.
Figure 10. 3 A
Figure 10. 3 A_1
Figure 10. 3 A_2
10. 3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix § In 1953, James D. Watson and Francis Crick deduced the secondary structure of DNA, using – X-ray crystallography data of DNA from the work of Rosalind Franklin and Maurice Wilkins and – Chargaff’s observation that in DNA, – the amount of adenine was equal to the amount of thymine and – the amount of guanine was equal to that of cytosine. © 2012 Pearson Education, Inc.
10. 3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix § Watson and Crick reported that DNA consisted of two polynucleotide strands wrapped into a double helix. – The sugar-phosphate backbone is on the outside. – The nitrogenous bases are perpendicular to the backbone in the interior. – Specific pairs of bases give the helix a uniform shape. – A pairs with T, forming two hydrogen bonds, and – G pairs with C, forming three hydrogen bonds. Animation: DNA Double Helix © 2012 Pearson Education, Inc.
Figure 10. 3 B
Figure 10. 3 C Twist
Figure 10. 3 D Hydrogen bond Base pair Ribbon model Partial chemical structure Computer model
Figure 10. 3 D_1 C C G G C C T Base pair A A T C G A T T C G C A G C G A A T T T Ribbon model A
Figure 10. 3 D_2 Hydrogen bond G T C A A C T G Partial chemical structure
Figure 10. 3 D_3 Computer model
10. 3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix § In 1962, the Nobel Prize was awarded to – James D. Watson, Francis Crick, and Maurice Wilkins. – Rosalind Franklin probably would have received the prize as well but for her death from cancer in 1958. Nobel Prizes are never awarded posthumously. § The Watson-Crick model gave new meaning to the words genes and chromosomes. The genetic information in a chromosome is encoded in the nucleotide sequence of DNA. © 2012 Pearson Education, Inc.
DNA REPLICATION © 2012 Pearson Education, Inc.
10. 4 DNA replication depends on specific base pairing § In their description of the structure of DNA, Watson and Crick noted that the structure of DNA suggests a possible copying mechanism. § DNA replication follows a semiconservative model. – The two DNA strands separate. – Each strand is used as a pattern to produce a complementary strand, using specific base pairing. – Each new DNA helix has one old strand with one new strand. Animation: DNA Replication Overview © 2012 Pearson Education, Inc.
Figure 10. 4 A_s 1 A T C G G C A T T A A parental molecule of DNA
Figure 10. 4 A_s 2 A T A C G C G A T A T A parental molecule of DNA T A G C T G C C A Free nucleotides The parental strands separate and serve as templates T A
Figure 10. 4 A_s 3 A T A C G C G A T A T A parental molecule of DNA T A G C C A Free nucleotides The parental strands separate and serve as templates T A T G C G C G C T A T A T A Two identical daughter molecules of DNA are formed
Figure 10. 4 B A T G A A T Parental DNA molecule T A G C Daughter strand T C G T C A C C G G T A C C G T G A T T A C A G A A G C T C C A Parental strand G G T T Daughter DNA molecules
10. 5 DNA replication proceeds in two directions at many sites simultaneously § DNA replication begins at the origins of replication where – DNA unwinds at the origin to produce a “bubble, ” – replication proceeds in both directions from the origin, and – replication ends when products from the bubbles merge with each other. © 2012 Pearson Education, Inc.
10. 5 DNA replication proceeds in two directions at many sites simultaneously § DNA replication occurs in the 5 to 3 direction. – Replication is continuous on the 3 to 5 template. – Replication is discontinuous on the 5 to 3 template, forming short segments. © 2012 Pearson Education, Inc.
10. 5 DNA replication proceeds in two directions at many sites simultaneously § Two key proteins are involved in DNA replication. 1. DNA ligase joins small fragments into a continuous chain. 2. DNA polymerase – adds nucleotides to a growing chain and – proofreads and corrects improper base pairings. Animation: Origins of Replication Animation: Leading Strand Animation: Lagging Strand Animation: DNA Replication Review © 2012 Pearson Education, Inc.
10. 5 DNA replication proceeds in two directions at many sites simultaneously § DNA polymerases and DNA ligase also repair DNA damaged by harmful radiation and toxic chemicals. § DNA replication ensures that all the somatic cells in a multicellular organism carry the same genetic information. © 2012 Pearson Education, Inc.
Figure 10. 5 A Parental DNA molecule Origin of replication “Bubble” Two daughter DNA molecules Parental strand Daughter strand
Figure 10. 5 B 3 end 5 end P 4 3 P 5 2 1 2 A T 5 C P P G C P P T 3 end 3 4 G P OH 1 HO A P 5 end
Figure 10. 5 C DNA polymerase molecule 5 3 Parental DNA Replication fork 5 3 DNA ligase Overall direction of replication 3 5 This daughter strand is synthesized continuously This daughter strand is 3 synthesized 5 in pieces
THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN © 2012 Pearson Education, Inc.
10. 6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits § DNA specifies traits by dictating protein synthesis. § The molecular chain of command is from – DNA in the nucleus to RNA and – RNA in the cytoplasm to protein. § Transcription is the synthesis of RNA under the direction of DNA. § Translation is the synthesis of proteins under the direction of RNA. © 2012 Pearson Education, Inc.
Figure 10. 6 A_s 1 DNA NUCLEUS CYTOPLASM
Figure 10. 6 A_s 2 DNA Transcription RNA NUCLEUS CYTOPLASM
Figure 10. 6 A_s 3 DNA Transcription RNA NUCLEUS Translation Protein CYTOPLASM
10. 6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits § The connections between genes and proteins – The initial one gene–one enzyme hypothesis was based on studies of inherited metabolic diseases. – The one gene–one enzyme hypothesis was expanded to include all proteins. – Most recently, the one gene–one polypeptide hypothesis recognizes that some proteins are composed of multiple polypeptides. © 2012 Pearson Education, Inc.
Figure 10. 6 B
10. 7 Genetic information written in codons is translated into amino acid sequences § The sequence of nucleotides in DNA provides a code for constructing a protein. – Protein construction requires a conversion of a nucleotide sequence to an amino acid sequence. – Transcription rewrites the DNA code into RNA, using the same nucleotide “language. ” © 2012 Pearson Education, Inc.
10. 7 Genetic information written in codons is translated into amino acid sequences – The flow of information from gene to protein is based on a triplet code: the genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of nonoverlapping threebase “words” called codons. – Translation involves switching from the nucleotide “language” to the amino acid “language. ” – Each amino acid is specified by a codon. – 64 codons are possible. – Some amino acids have more than one possible codon. © 2012 Pearson Education, Inc.
Figure 10. 7 DNA molecule Gene 1 Gene 2 Gene 3 DNA A C C G G C A A Transcription RNA Translation U U U G G C Codon Polypeptide Amino acid C G U U
Figure 10. 7_1 DNA A C U U U C G G C A A C G U U U Transcription RNA Translation Codon Polypeptide Amino acid G G C U
10. 8 The genetic code dictates how codons are translated into amino acids § Characteristics of the genetic code – Three nucleotides specify one amino acid. – 61 codons correspond to amino acids. – AUG codes for methionine and signals the start of transcription. – 3 “stop” codons signal the end of translation. © 2012 Pearson Education, Inc.
10. 8 The genetic code dictates how codons are translated into amino acids § The genetic code is – redundant, with more than one codon for some amino acids, – unambiguous in that any codon for one amino acid does not code for any other amino acid, – nearly universal—the genetic code is shared by organisms from the simplest bacteria to the most complex plants and animals, and – without punctuation in that codons are adjacent to each other with no gaps in between. © 2012 Pearson Education, Inc.
Figure 10. 8 A Third base First base Second base
Figure 10. 8 B_s 1 DNA Strand to be transcribed T A C T T C A A T A T G A A G T T T C T A G
Figure 10. 8 B_s 2 Strand to be transcribed DNA T A C T T C A A T A T G A A G T T T C T A G Transcription RNA A U G A A G U U A G
Figure 10. 8 B_s 3 Strand to be transcribed DNA T A C T T C A A T A T G A A G T T T C T A G Transcription RNA A U G A A G U U A G Translation Start codon Polypeptide Met Stop codon Lys Phe
Figure 10. 8 C
10. 9 Transcription produces genetic messages in the form of RNA § Overview of transcription – An RNA molecule is transcribed from a DNA template by a process that resembles the synthesis of a DNA strand during DNA replication. – RNA nucleotides are linked by the transcription enzyme RNA polymerase. – Specific sequences of nucleotides along the DNA mark where transcription begins and ends. – The “start transcribing” signal is a nucleotide sequence called a promoter. © 2012 Pearson Education, Inc.
10. 9 Transcription produces genetic messages in the form of RNA – Transcription begins with initiation, as the RNA polymerase attaches to the promoter. – During the second phase, elongation, the RNA grows longer. – As the RNA peels away, the DNA strands rejoin. – Finally, in the third phase, termination, the RNA polymerase reaches a sequence of bases in the DNA template called a terminator, which signals the end of the gene. – The polymerase molecule now detaches from the RNA molecule and the gene. Animation: Transcription © 2012 Pearson Education, Inc.
Figure 10. 9 A Free RNA nucleotides RNA polymerase A T C C A A T Direction of transcription Newly made RNA A T A G U G T C C A U C C A G T A G G T U T A C C Template strand of DNA
Figure 10. 9 B RNA polymerase DNA of gene Terminator DNA Promoter DNA 1 Initiation 2 Elongation Area shown in Figure 10. 9 A 3 Termination Growing RNA Completed RNA polymerase
Figure 10. 9 B_1 RNA polymerase DNA of gene Promoter DNA 1 Initiation Terminator DNA
Figure 10. 9 B_2 2 Elongation Area shown in Figure 10. 9 A Growing RNA
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