DNA replication. Begins at specific sites on a double helix. Proceeds in both directions. Is initiated at many points in eukaryotic chromosomes.

Transcription

1 DNA replication Begins at specific sites on a double helix. Proceeds in both directions. Is initiated at many points in eukaryotic chromosomes.

2 Figure 10.8

3 DNAi_replication_schematic-lg.mov DNAi_replication_vo1-lg.mov

4 DNA replication is semiconservative. Each new DNA molecule consists of one strand of parental DNA and one newly synthesized strand.

5

6 Meselson-Stahl Experiment

7 Meselson-Stahl Experiment

8 Meselson-Stahl Experiment

9 Meselson-Stahl Experiment

10 Process of Replication 1. Unwinding of double helix. 2. Enzyme helicase separates the strands. 3. On the leading strand DNA polymerase III builds a complementary strand in the 5 to 3 direction by adding free floating nucleotides.

11 -Free floating nucleotides are Deoxynucleoside triphosphates (dntps)

12 As dntps are added, the phosphates provide the energy needed to form covalent bonds of the sugar-phosphate backbone. dntp animation

13 Process of replication 4. The lagging strand is formed in fragments called Okazaki fragments that are later joined together.

14

15 Lagging Strand 1. Primase synthesizes a short RNA primer which is later removed.

16 2. DNA polymerase III extends RNA primer with short lengths of complimentary DNA.

17 3. DNA Polymerase I digests RNA primer and replaces it with DNA.

18 4. DNA ligase joins neighboring fragments together into longer strands.

19 molgenetics/dna-rna2.swf TromboneFinald.swf micro04.swf

20 -Mistakes in replication are very rare. -DNA polymerase proofreads the DNA. -Mismatched pairs are excised and repaired.

21 Result of replication DNA molecules rewind after replication. Occurs during S phase of interphase. Replication results inidentical sister chromatids joined at the centromere.

22 The Flow of Genetic Information from DNA to RNA to Protein DNA functions as the inherited directions for a cell or organism. How are these directions carried out? Copyright 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

23 How an Organism s Genotype Produces Its Phenotype An organism s genotype, its genetic makeup, is the sequence of nucleotide bases in DNA. The phenotype is the organism s specific traits, which arise from the actions of a wide variety of proteins. Copyright 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

24 DNA specifies the synthesis of proteins in two stages: Transcription Translation

25 Figure 10.9

26 The one gene one polypeptide hypothesis states that the function of an individual gene is to dictate the production of a specific polypeptide. Originally thought one gene coded for one protein many proteins consist of several polypeptide chains

27 From Nucleotides to Amino Acids: An Overview Genetic information in DNA is transcribed into RNA and then translated into polypeptides.

28 What is the language of nucleic acids? In DNA, it is the linear sequence of nucleotide bases.

29 Figure 10.10

30 When DNA is transcribed, the result is an RNA molecule. RNA is then translated into a sequence of amino acids in a polypeptide.

31 RNA How is RNA different from DNA? Has uracil instead of thymine Is single stranded Has ribose instead of deoxyribose

32 What are the rules for translating the RNA message into a polypeptide?

33 Triplets of bases Specify all the amino acids. Are called codons.

34 The Genetic Code The genetic code is the set of rules relating nucleotide sequence to amino acid sequence.

35 Figure 10.11

36 The genetic code is shared by all organisms.

37 Figure 10.12