DNA Replication, Transcription and Translation DNA Replication, Transcription and Translation DNA Replication, Transcription and Translation DNA Replication,

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  • DNA Replication, Transcription and Translation DNA Replication, Transcription and Translation DNA Replication, Transcription and Translation DNA Replication, Transcription and Translation Chapter 25: Nucleotides, Nucleic Acids, and Heredity
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  • Overview Replication Transcription Translation DNA mRNA Protein AA A A A Francis Crick (1958): Central Dogma of Molecular Biology
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  • DNA Structure Deoxyribonucleic acid (DNA) Structure: Double Helix (Two strands) Function: long-term storage of information
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  • DNA Replication AA Enzymes: 1-Helicase 2-DNA Polymerase 3-Topoisomerase 4-DNA primase 5-DNA Ligase
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  • RNA Structure Ribonucleic acid (RNA) Structure: Single strand Functions: Four bases : (adenine, cytosine, guanine and uracil) o mRNA: information carrier o rRNA: Ribosomes Constituent o tRNA: amino acid transporter
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  • Transcription A A
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  • Protein Structure Polypeptide: amino acids arranged in a linear chain Structure: multiple linear and 3D structures Functions: o Enzymes o Cell signaling (insulin) o Ligand binding (antibodies) o Transport o Structural
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  • Translation A Video Initiation: the small subunit of the ribosome binds to 5' end of the mRNA with the help of initiation factors Elongation: additional amino acid is added to the growing polypeptide chain Termination: one of the three termination codons moves into the A site
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  • 25-9 The Molecules of Heredity Each cell of our bodies contains thousands of different proteins. How do cells know which proteins to synthesize out of the extremely large number of possible amino acid sequences? chromosomes From the end of the 19th century, biologists suspected that the transmission of hereditary information took place in the nucleus, more specifically in structures called chromosomes. genes The hereditary information was thought to reside in genes within the chromosomes. histonesnucleic acids Chemical analysis of nuclei showed chromosomes are made up largely of proteins called histones and nucleic acids.
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  • 25-10 The Molecules of Heredity deoxyribonucleic acids (DNA) By the 1940s, it became clear that deoxyribonucleic acids (DNA) carry the hereditary information. Other work in the 1940s demonstrated that each gene controls the manufacture of one protein. Thus the expression of a gene in terms of an enzyme protein led to the study of protein synthesis and its control.
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  • 25-11 Nucleic Acids There are two kinds of nucleic acids in cells: Ribonucleic acids (RNA). Deoxyribonucleic acids (DNA). Both RNA and DNA are polymers built from monomers called nucleotides. A nucleotide is composed of: A base, a monosaccharide, and a phosphate.
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  • 25-12 Purine/Pyrimidine Bases
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  • 25-13 Nucleosides Nucleoside: Nucleoside: A compound that consists of D-ribose or 2- deoxy-D-ribose bonded to a purine or pyrimidine base by a -N-glycosidic bond.
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  • 25-14 Nucleotides Nucleotide: Nucleotide: A nucleoside in which a molecule of phosphoric acid is esterified with an -OH of the monosaccharide, most commonly either at the 3 or the 5-OH.
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  • 25-15 Nucleotides Adenosine 5-triphosphateATP Adenosine 5-triphosphate (ATP) serves as a common currency into which energy gained from food is converted and stored.
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  • 25-16 DNAPrimary (1) Structure For nucleic acids, primary structure is the sequence of nucleotides, beginning with the nucleotide that has the free 5 terminus. The strand is read from the 5end to the 3end. Thus, the sequence AGT means that adenine (A) is the base at the 5 terminus and thymine (T) is the base at the 3 terminus.
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  • 25-17 Structure of DNA and RNA Figure 25.2 Schematic diagram of a nucleic acid molecule. The four bases of each nucleic acid are arranged in various specific sequences. Schematic diagram of a nucleic acid molecule. The four bases of each nucleic acid are arranged in various specific sequences. The base sequence is read from the 5 end to the 3 end.
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  • 25-18 DNA2 Structure Secondary structure: Secondary structure: The ordered arrangement of nucleic acid strands. The double helix model of DNA 2 structure was proposed by James Watson and Francis Crick in 1953. Double helix: Double helix: A type of 2 structure of DNA in which two polynucleotide strands are coiled around each other in a screw-like fashion.
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  • 25-19 THE DNA Double Helix Figure 25.4 Three- dimensional structure of the DNA double helix.
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  • 25-20 Base Pairing Figure 25.5 A and T pair by forming two hydrogen bonds. G and C pair by forming three hydrogen bonds.
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  • 25-21 Superstructure of Chromosomes histones. DNA is coiled around proteins called histones. Histones are rich in the basic amino acids Lys and Arg, whose side chains have a positive charge. The negatively-charged DNA molecules and positively- charged histones attract one another and form units called nucleosomes. Nucleosome: Nucleosome: A core of eight histone molecules around which the DNA helix is wrapped. chromatin. Nucleosomes are further condensed into chromatin. chromosomes. Chromatin fibers are organized into loops, and the loops into the bands that provide the superstructure of chromosomes.
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  • 25-22 Superstructure of Chromosomes Figure 25.8
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  • 25-23 Superstructure of Chromosomes Figure 25.8 contd
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  • 25-24 Superstructure of Chromosomes Figure 25.8 contd
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  • 25-25 DNA and RNA The three differences in structure between DNA and RNA are: T U. DNA bases are A, G, C, and T; the RNA bases are A, G, C, and U. 2-deoxy-D-riboseD- ribose. the sugar in DNA is 2-deoxy-D-ribose; in RNA it is D- ribose. double stranded single-stranded. DNA is always double stranded; there are several kinds of RNA, all of which are single-stranded.
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  • 25-26 Information Transfer
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  • 25-27 RNA Table 25.3 The roles of Different kinds of RNA
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  • 25-28 Structure of tRNA Figure 2.10 Structure of tRNA.
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  • 25-29 Structure of rRNA Figure 25.11 The structure of a typical prokaryotic ribosome.
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  • 25-30 Ribosome Figure 25.11 contd
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  • 25-31 Genes, Exons, and Introns Gene: Gene: A segment of DNA that carries a base sequence that directs the synthesis of a particular protein, tRNA, or mRNA. There are many genes in one DNA molecule. In bacteria, the gene is continuous. In higher organisms, the gene is discontinuous. Exon: Exon: A section of DNA that, when transcribed, codes for a protein or RNA. Intron: Intron: A section of DNA that does not code for anything functional.
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  • 25-32 Genes, Exons, and Introns Figure 25.12 The properties of mRNA molecules in prokaryotes versus eukaryotic cells during transcription and translation.
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  • 25-33 Genes, Exons, and Introns Figure 2.12 contd
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  • 25-34 Replication of DNA The DNA in the chromosomes carries out two functions: replication (1) It reproduces itself. This process is called replication. (2) It supplies the information necessary to make all the RNA and proteins in the body, including enzymes. replication fork Replication begins at a point in the DNA called the origin of replication or a replication fork.
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  • 25-35 Replication of DNA Figure 25.13 General features of the replication of DNA. The two strands of the DNA double helix are shown separating at the replication fork.
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  • 25-36 Replication of DNA The replication of DNA occurs in number of distinct steps. 1. Opening up of the superstructure of the chromosomes. One key step is this process is acetylation- deacetylation of lysine residues on histones. This reaction eliminates some of the positive charges on histones and weakens the strength of the DNA-histone interaction.
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  • 25-37 Replication of DNA 3.Unwinding the DNA Double Helix. helicases Replication of DNA molecules starts with the unwinding of the double helix which can occur at either end or in the middle. Special unwinding proteins called helicases, attach themselves to one DNA strand and cause the separation of the double helix. 2. Relaxation of Higher-Order Structures of DNA. Tropoisomerasesgyrases Tropoisomerases (also called gyrases) temporarily introduce either single-or double strand breaks in DNA. Once the supercoiling is relaxed, the broken strands are joined together and the tropoisomerase diffuses from the location of the replication fork.
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  • 25-38 Replication of DNA 4. Primers/Primases Primers are short4 to 15 nucleotides longRNA oligonucloetides synthesized from ribonucleoside triphosphates. They are needed to initiate the primase- catalyzed synthesis of both daughter strands. 5. DNA Polymerase Once the two strands are separated at the replication fork, the DNA nucleotides must be lined up. In the absence of DNA polyme