1. DNA, RNA structure. 2. DNA replication. 3. Transcription, translation

Transcription

1 1. DNA, RNA structure 2. DNA replication 3. Transcription, translation

2 DNA and RNA are polymers of nucleotides DNA is a nucleic acid, made of long chains of nucleotides Nucleotide Phosphate group Nitrogenous base Sugar Phosphate group Nitrogenous base (A, G, C, or T) Thymine (T) Sugar (deoxyribose) Polynucleotide Sugar-phosphate backbone DNA nucleotide Figure 10.2A

3 DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines Figure 10.2B

4 RNA is also a nucleic acid different sugar U instead of T Single strand, usually Nitrogenous base (A, G, C, or U) Phosphate group Uracil (U) Sugar (ribose) Figure 10.2C, D

5 DNA is a double-stranded helix James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B

6 Hydrogen bonds between bases hold the strands together: A and T, C and G Hydrogen bond Ribbon model Partial chemical structure Computer model Figure 10.3D

7 Untwisting and replication of DNA each strand is a template for a new strand helicase DNA polymerase Figure 10.4B

8 How can entire chromosomes be replicated during S phase? DNA replication begins at many specific sites Origin of replication Parental strand Daughter strand Bubble Two daughter DNA molecules Figure 10.5A

9 Each strand of the double helix is oriented in the opposite direction 5 end P P 3 end P P P P P P Figure 10.5B 3 end 5 end

10 DNA polymerase works in only one direction 5 3 Parental DNA 5 end P DNA polymerase molecule 3 5 Daughter strand synthesized continuously 3 5 Daughter strand synthesized in pieces Telomere sequences are lost with each replication. 5 3 P telomeres DNA ligase Overall direction of replication Figure 10.5C

11 The information constituting an organism s genotype is carried in its sequence of bases The DNA is transcribed into RNA, which is translated into the polypeptide DNA TRANSCRIPTION RNA TRANSLATION Protein Figure 10.6A

12 Transcription produces genetic messages in the form of mrna RNA polymerase RNA nucleotide Figure 10.9A Newly made RNA Direction of transcription Template strand of DNA

13 In transcription, DNA helix unzips RNA nucleotides line up along one strand of DNA, following the base-pairing rules Promoter DNA RNA polymerase DNA of gene Initiation Elongation Terminator DNA Area shown in Figure 10.9A single-stranded messenger RNA peels away and DNA strands rejoin Termination Growing RNA Completed RNA Figure 10.9B RNA polymerase

14 RNA transcripts of DNA

15 Eukaryotic RNA is processed before leaving the nucleus Noncoding segments, introns, are spliced out DNA Cap RNA transcript with cap and tail Exon Intron Exon Intron Exon Transcription Addition of cap and tail Introns removed Tail A cap and a tail are added to the ends mrna Coding sequence Exons spliced together NUCLEUS CYTOPLASM Figure 10.10

16 Translation of nucleic acids into amino acids The words of the DNA language are triplets of bases called codons The codons in a gene specify the amino acid sequence of a polypeptide

17 Gene 1 Gene 3 DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA TRANSLATION Codon Figure 10.7 Polypeptide Amino acid

18 First Base Virtually all organisms share the same genetic code unity of life Second Base U C A G UUU UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA AUG GUU GUC GUA GUG U C A G phe leu leu ile met (start) val UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG ser pro thr ala UAU UAC UAA UAG CAU CAC CAA CAG AAU AAC AAA AAG GAU GAC GAA GAG tyr stop stop his gln asn lys asp glu UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG cys stop trp arg ser arg gly U C A G U C A G U C A G U C A G Third Base

19 An exercise in translating the genetic code Transcribed strand DNA Transcription RNA Start codon Translation Stop codon Polypeptide Figure 10.8B

20 Transfer RNA molecules serve as interpreters during translation In the cytoplasm, a ribosome attaches to the mrna and translates its message into a polypeptide The process is aided by transfer RNAs Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon Figure 10.11A

21 Each trna molecule has a triplet anticodon on one end and an amino acid attachment site on the other Amino acid attachment site Anticodon Figure 10.11B, C

22 Ribosomes build polypeptides trna molecules Growing polypeptide Large subunit P site A site Growing polypeptide Next amino acid to be added to polypeptide trna mrna binding site P A mrna Codons mrna Small subunit Figure 10.12A-C

23 An initiation codon marks the start of an mrna message AUG = methionine Start of genetic message End Figure 10.13A

24 mrna, a specific trna, and the ribosome subunits assemble during initiation Initiator trna P site Large ribosomal subunit A site mrna Start codon Small ribosomal subunit 1 2 Figure 10.13B

25 Elongation The mrna moves a codon at a time relative to the ribosome A trna pairs with each codon, adding an amino acid to the growing polypeptide A STOP codon causes the mrna-ribosome complex to fall apart

26 Amino acid Polypeptide P site A site Anticodon mrna 1 Codon recognition mrna movement Stop codon New peptide bond 2 Peptide bond formation 3 Translocation Figure 10.14

27 Table 14.2 Types of RNA Type of RNA Functions in Function Messenger RNA (mrna) Nucleus, migrates to ribosomes in cytoplasm Carries DNA sequence information to ribosomes Transfer RNA (trna) Cytoplasm Provides linkage between mrna and amino acids; transfers amino acids to ribosomes Ribosomal RNA (rrna) Cytoplasm Structural component of ribosomes

28 Review: The flow of genetic information in the cell is DNA RNA protein The sequence of codons in DNA spells out the primary structure of a polypeptide Polypeptides form proteins that cells and organisms use

29 Mutations can change the meaning of genes Mutations are changes in the DNA base sequence caused by errors in DNA replication or by mutagens change of a single DNA nucleotide causes sickle-cell disease

30 Normal hemoglobin DNA Mutant hemoglobin DNA mrna mrna Normal hemoglobin Glu Sickle-cell hemoglobin Val Figure 10.16A

31 Types of mutations NORMAL GENE mrna Protein Met Lys Phe Gly Ala BASE SUBSTITUTION Met Lys Phe Ser Ala BASE DELETION Missing Met Lys Leu Ala His Figure 10.16B

32 Chromosomal changes can be large or small Deletion Homologous chromosomes Duplication Inversion Reciprocal translocation Nonhomologous chromosomes Figure 8.23A, B

33 Summary of transcription and translation DNA mrna Amino acid trna TRANSCRIPTION TRANSLATION Enzyme RNA polymerase Stage 1 mrna is transcribed from a DNA template. Stage 2 Each amino acid attaches to its proper trna with the help of a specific enzyme and ATP. mrna Initiator trna Start Codon Anticodon Large ribosomal subunit Small ribosomal subunit Stage 3 Initiation of polypeptide synthesis The mrna, the first trna, and the ribosomal subunits come together. Figure 10.15

34 Growing polypeptide Codons New peptide bond forming Stage 4 Elongation A succession of trnas add their amino acids to the polypeptide chain as the mrna is moved through the ribosome, one codon at a time. mrna Polypeptide Stop Codon Stage 5 Termination The ribosome recognizes a stop codon. The polypeptide is terminated and released. Figure (continued)