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DNA RNA & Proteins
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James Watson & Francis Crick and Their DNA Model
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Winning the Nobel Prize
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Watson & Crick on the 50 th anniversary of their discovery
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Rosalind Franklin’s Famous Photo 51 of DNA
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Rosalind Franklin’s Lab
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Erwin Chargaff, Jerry Donahue, Lawrence Bragg
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DNA Polymer of nucleotides (phosphate group bonded to deoxyribose bonded to a nitrogen base)
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DNA Nucleotide
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A Nucleotide
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4 Nitrogen Bases of DNA Adenine (A) Thymine (T) Guanine (G) Cytosine (C)
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Adenine and guanine are purines Cytosine and thymine are pyrimidines
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Purines
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Pyrimidines
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Nucleotides Bond Together in Long Chains The two chains of nucleotides are bonded in the middle by the paired bases
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Base Pairing Rule Adenine bonds to Thymine Guanine bonds to Cytosine BASES THAT BOND ARE CALLED COMPLEMENTARY BASES
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Bases Bond by Hydrogen Bonds
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The 2 DNA Chains are Anti- Parallel
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DNA Replication Before cell division, cells copy (replicate) their DNA
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An enzyme breaks the hydrogen bonds holding the paired bases together (unzips the DNA)
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Complementary nucleotides bond to the separated DNA chains (A to T and G to C) DNA polymerase enzymes bond new DNA nucleotides to the original DNA strands The original strand serves as a template for the new strand
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DNA Replication
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At the end of DNA replication, there are two identical DNA molecules Each DNA molecule contains an original strand and a new strand (semi- conservative)
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Proofreading enzymes check for mistakes during replication (bonding 50 base pairs per second means mistakes will be made!) http://www.youtube.com/watch?v=Bju4C5GxeQs&feature=r elated
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RNA Ribonucleic acid A polymer of nucleotides The sugar in RNA is ribose (instead of deoxyribose, as in DNA)
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Comparison of Ribose and Deoxyribose
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RNA nucleotides do not have thymine, but contain uracil instead
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RNA is one strand of nucleotides (DNA is two chains of nucleotides) So RNA is a single helix, but DNA is a double helix
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3 Types of RNA tRNA (transfer RNA) mRNA (messenger RNA) rRNA (ribosomal RNA) http://www.dnatube.com/video/1017/Co mpare-DNA-and-RNA-in-structural- basis
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tRNA
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TRANSCRIPTION (RNA Synthesis) A gene for a specific protein is turned on DNA “unzips” and unwinds (as in replication) Complementary RNA nucleotides bond to one strand of DNA (function of RNA polymerase)
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Bases must be complementary C on DNA bonds to G on RNA G on DNA bonds to C on RNA T on DNA bonds to A on RNA A on DNA bonds to U on RNA
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RNA breaks away from the DNA template DNA strands reform the hydrogen bonds RNA can then exit the nucleus via pores in the nuclear membrane
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Transcription
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http://www.youtube.com/watch?v=vJSmZ3D sntU&feature=related
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Translation – the making of a protein Begins when mRNA attaches to a ribosome The genetic code of mRNA is read three bases at a time (codons)
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Each codon specifies a particular amino acid that will be placed in the chain to build the protein molecule
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The tRNA with its specific amino acid pairs to the codon of the mRNA When a second tRNA with its specific acid pairs to the next codon, the attached amino acid breaks from the first tRNA and attaches to the amino acid of the 2 nd tRNA The ribosome forms a peptide bond between the amino acids
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The empty tRNA moves off and picks up another matching amino acid from the cytoplasm in the cell This sequence is repeated until the ribosome reaches a stop codon on the mRNA, which signs the end of protein synthesis
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Beginning of Translation
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Translation
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Termination of Translation
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http://www.youtube.com/watch?v=NJxobgkP EAo
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The Central Dogma of Biochemistry
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http://www.dnatube.com/video/1027/Central- Dogmahttp://www.dnatube.com/video/1027/Central- Dogma
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