 DNA must be copied (before a cell divides)  The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing: A-T, G-C Each strand of the original DNA serves as a template for the new strandEach strand of the original DNA serves as a template for the new strand

 The hydrogen bonds between base pairs are broken  DNA replication begins at many specific sites  The main enzyme responsible is DNA Polymerase How can entire chromosomes be replicated during Mitosis (S-phase)? Figure 10.5A

 1. DNA unwinds (helicase)  2. DNA “unzips”  (DNA Polymerase)  3. Free-floating nucleotides base pair with the original strand of DNA Parental DNA DNA Template New DNA  4. 2 identical DNA molecules are formed

1. Why is replication necessary? 2. When does replication occur? 3. Describe how replication works. 4. Use the complementary rule to create the complementary strand: A--- ? G--- ? C--- ? T--- ? A--- ? G--- ? A--- ? G--- ? C--- ? A--- ? G--- ? T--- ? Replication Quiz

1. Why is replication necessary? So both new cells will have the correct DNA 2. When does replication occur? During Mitosis. 3. Describe how replication works. Enzymes unzip DNA and complementary nucleotides join each original strand. 4. Use the complementary rule to create the complementary strand: A--- T G--- C C--- G T--- A A--- T G--- C A--- T G--- C C--- G A--- T G--- C T--- A Replication Quiz

 DNA can “unzip” itself and RNA nucleotides match up to the DNA strand.  Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC acids.

RNA polymerase RNA nucleotide Direction of transcription Template strand of DNA

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

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

 …DNA controlled cell function by serving as a template for PROTEIN structure.  3 Nucleotides = a triplet or CODON (which code for a specific AMINO ACID)  AMINO ACIDS are the building blocks of proteins.

 DNA from a single human cell extends in a single thread for almost 2 meters long!!!  It contains information equal to some 600,000 printed pages of 500 words each!!! (a library of about 1,000 books)