Inquiry into Life Twelfth Edition Chapter 24 Lecture PowerPoint to accompany Sylvia S. Mader Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24.1 DNA Structure and Replication Hershey-Chase Experiments (1952) –Demonstrated that DNA is the genetic material –DNA stands for Deoxyribonucleic Acid

Hershey-Chase Experiments

24.1 DNA Structure and Replication Structure of DNA –James Watson and Francis Crick determined the structure of DNA in 1953 –DNA is a chain of nucleotides –Each nucleotide is a complex of three subunits Phosphoric acid (phosphate) A pentose sugar (deoxyribose) A nitrogen-containing base

24.1 DNA Structure and Replication Structure of DNA –Four Possible Bases Adenine (A) - a purine Guanine (G) - a purine Thymine (T) - a pyrimidine Cytosine (C) - a pyrimidine –Complimentary Base Pairing Adenine (A) always pairs with Thymine (T) Guanine (G) always pairs with Cytosine (C)

Overview of DNA Structure

24.1 DNA Structure and Replication Replication of DNA –Semi-conservative replication Each daughter DNA molecule consists of one new chain of nucleotides and one from the parent DNA molecule –The two daughter DNA molecules will be identical to the parent molecule

24.1 DNA Structure and Replication Replication of DNA –Before replication begins, the two strands of the parent molecule are hydrogen-bonded together –Enzyme DNA helicase unwinds and “unzips” the double- stranded DNA –New complementary DNA nucleotides fit into place along divided strands by complementary base pairing. These are positioned and joined by DNA polymerase –DNA ligase repairs any breaks in the sugar-phosphate backbone –The Two double helix molecules identical to each other and to the original DNA molecule

Overview of DNA Replication

Ladder Configuration and DNA Replication

24.2 Gene Expression Gene:A segment of DNA that specifies the amino acid sequence of a polypeptide DNA does not directly control protein synthesis, instead its information is transcribed into RNA

24.2 Gene Expression RNA (ribonucleic acid)

24.2 Gene Expression Three Classes of RNA –Messenger RNA (mRNA) Takes a message from DNA to the ribosomes –Ribosomal RNA (rRNA) Makes up ribosomes (along with proteins) –Transfer RNA (tRNA) Transfers amino acids to ribosomes

24.2 Gene Expression Gene Expression Requires Two Steps: –Transcription –Translation

24.2 Gene Expression Transcription –During transcription, a segment of the DNA serves as a template for the production of an RNA molecule –Messenger RNA (mRNA) RNA polymerase binds to a promoter DNA helix is opened so complementary base pairing can occur RNA polymerase joins new RNA nucleotides in a sequence complementary to that on the DNA

24.2 Gene Expression Transcription –Processing of mRNA Primary mRNA becomes mature mRNA Contains bases complementary to both intron and exon segments of DNA –Introns are intragene segments –Exons are the portion of a gene that is expressed Intron sequences are removed, and a poly-A tail is added –Ribozyme splices exon segments together

Transcription of DNA to form mRNA

mRNA Processing

24.2 Gene Expression Translation –The Genetic Code Triplet code- each 3-nucleotide unit of a mRNA molecule is called a codon There are 64 different mRNA codons –61 code for particular amino acids »Redundant code-some amino acids have numerous code words »Provides some protection against mutations –3 are stop codons signal polypeptide termination

Messenger RNA Codons

24.2 Gene Expression Transfer RNA –tRNA transports amino acids to the ribosomes –Single stranded nucleic acid that correlates a specific nucleotide sequence with a specific amino acid –Amino acid binds to one end, the opposite end has an anticodon –the order of mRNA codons determines the order in which tRNA brings in amino acids

Transfer RNA: Amino Acid Carrier

24.2 Gene Expression Ribosome and Ribosomal RNA –Ribosome has a binding site for mRNA and for 2 tRNAs –Facilitate complementary base pairing –Ribosome moves along mRNA and new tRNAs come in and line up in order –This brings amino acids in line in a specific order to form a polypeptide –Several ribosomes may move along the same mRNA Multiple copies of a polypeptide may be made The entire complex is called a polyribosome

Polyribosome Structure and Function

Overview of Gene Expression

24.2 Gene Expression Translation Requires Three Steps –Initiation (requires energy) –Elongation (requires energy) –Termination

Initiation

Elongation

Termination

Summary of Gene Expression

24.2 Gene Expression Genes and Gene Mutations –A gene mutation is a change in the sequence of bases within a gene. –Gene mutations can lead to malfunctioning proteins in cells.

24.2 Gene Expression Genes and Gene Mutations –Causes of Mutations Errors in replication –Rare –DNA polymerase “proofreads” new strands and errors are cleaved out Mutagens –Environmental influences –Radiation, UV light, chemicals –Rate is low because DNA repair enzymes monitor and repair DNA Transposons –“jumping genes” –Can move to new locations and disrupt sequences

Transposon

24.2 Gene Expression Types of Mutations –Frameshift Mutations One or more nucleotides are inserted or deleted Results in a polypeptide that codes for the wrong sequence of amino acids –Point Mutations The substitution of one nucleotide for another –Silent mutations –Nonsense mutations –Missense mutations

24.3 DNA Technology The Cloning of a Gene –Cloning: Production of many identical copies of an organism through some asexual means. –Gene Cloning:The production of many identical copies of a single gene –Two Ways to Clone a Gene: –Recombinant DNA –Polymerase Chain Reaction

Cloning of a Human Gene / Recombinant DNA

24.3 DNA Technology Using Recombinant DNA Technology –Restriction enzymes breaks open a plasmid vector at specific sequence of bases “sticky ends” –Foreign DNA that is to be inserted is also cleaved with same restriction enzyme so ends match –Foreign DNA is inserted into plasmid DNA and “sticky ends” pair up –DNA ligase seals them together

Restriction Enzymes and Stick Ends

24.3 DNA Technology Polymerase Chain Reaction –Amplifies a targeted DNA sequence –Requires DNA polymerase, a set of primers, and a supply of nucleotides Primers are single stranded DNA sequences that start replication process –Amount of DNA doubles with each replication cycle –Process is now automated

Polymerase Chain Reaction (PCR) (insert figure 24.18)

24.3 DNA Technology DNA Fingerprinting –Permits identification of individuals and their relatives –Based on differences between sequences in nucleotides between individuals –Detection of the number of repeating segments (called repeats) are present at specific locations in DNA Different numbers in different people PCR amplifies only particular portions of the DNA Procedure is performed at several locations to identify repeats

DNA Fingerprints

24.3 DNA Technology Biotechnology –Biotechnology uses natural biological systems to create a product or to achieve a goal desired by humans. –Transgenic organisms have a foreign gene inserted into their DNA

24.3 DNA Technology Transgenic Bacteria –Medical Uses: Production of Insulin, Human Growth Hormone, Tissue Plasminogen Activator, Hepatitis B Vaccine –Agricultural Uses: Bacteria that protects plants from freezing, bacteria that protect plant roots from insects –Environmental: Bacteria that degrade oil (clean up after oil spills), bacteria that remove sulfur from coal

24.3 DNA Technology Transgenic Plants –Plants have been engineered to secrete a toxin that kills insects –Plants have been engineered to be resistant to herbicides

24.3 DNA Technology Transgenic Animals –Fish, cows, pigs, rabbits and sheep have been engineered to produce human growth hormone in order to increase size of the animals

Transgenic Animals