DNA Structure and Function Chapter 8
So ? ? • What is DNA?
DNA is • Information • It is how your parents “made” you. • It is how every cell in your body - was made by other cells
Structure of the Hereditary Material • Experiments in the 1950s showed that DNA is the hereditary material • Scientists raced to determine the structure of DNA • 1953 - Watson and Crick proposed that DNA is a double helix
What does this molecule do • Contains information that codes for proteins • Transfers that information to the next generation of cells via mitosis • And the next generation via meiosis • In other words DNA makes the biological machinery that copies itself • Now that is truly a which came first question??
Animal Cell Fig. 4-14, p.58
Board Drawing • Relate cell cycle • And dna • And Protein synthesis
Structure of Nucleotides in DNA • Each nucleotide consists of • Deoxyribose (5-carbon sugar) • Phosphate group • A nitrogen-containing base • Four bases • Adenine, Guanine, Thymine, Cytosine
Nucleotide Bases 8.2 ADENINE (A) GUANINE (G) phosphate group deoxyribose THYMINE (T) CYTOSINE (C)
A T G C A T A T
T A C G G C C G A T C G A T T A
THE BINDING PATTERN A binds to T and G binds to C
Watson-Crick Model • DNA consists of two nucleotide strands • Strands run in opposite directions • Strands are held together by hydrogen bonds between bases • A binds with T and C with G • Molecule is a double helix
Watson-Crick Model 2-nanometer diameter overall 0.34-nanometer distance between each pair of bases 3.4-nanometer length of each full twist of the double helix In all respects shown here, the Watson–Crick model for DNA structure is consistent with the known biochemical and x-ray diffraction data. The pattern of base pairing (A only with T, and G only with C) is consistent with the known composition of DNA (A = T, and G = C). Fig. 13-6, p.211
DNA Structure Helps Explain How It Duplicates • DNA is two nucleotide strands held together by hydrogen bonds • Hydrogen bonds between two strands are easily broken • Each single strand then serves as template for new strand
Wait a minute • What are we talking about - Making babies and growing up Making genes !!!
DNA Replication Each parent strand remains intact Every DNA molecule is half “old” and half “new” Fig. 13-7, p.212
aA parent DNA molecule with two complementary strands of base-paired nucleotides. bReplication starts; the strands unwind and move apart from each other at specific sites along the molecule’s length. cEach “old” strand is a structural pattern (template) for attaching new bases, according to the base-pairing rule. dBases positioned on each old strand are joined together as a “new” strand. Each half-old, half-new DNA molecule is like the parent molecule. Fig. 13-8a, p.213
Enzymes in Replication • Helicase Enzymes unwind the two strands • DNA polymerase attaches complementary nucleotides • DNA ligase fills in gaps • Enzymes wind two strands together
And where does DNA replication occur • In the nucleus
DNA Repair • Mistakes can occur during replication • DNA polymerase can read correct sequence from complementary strand and, together with DNA ligase, can repair mistakes in incorrect strand
When does replication occur? • When does DNA replication occur???
Board Drawing • Figure 8.4 • Work off of notes
Cloning • Making a genetically identical copy of an individual • Researchers have been creating clones for decades • These clones were created by embryo splitting
Cloning 1 A microneedle 2 The microneedle has emptied the sheep egg of its own nucleus. 3 DNA from a donor cell is about to be deposited in the enucleated egg. 4 An electric spark will stimulate the egg to enter mitotic cell division. the first cloned sheep Fig. 13-9, p.214
Cloning Quotations Conservative position: . . . . . the moral issues rather than protect mankind. As such, cloning embryonic human life under any circumstance crosses an ethical line, takes an irrevocable step, from which science can never turn back."
Cloning Quotations Liberal position: "Therapeutic cloning will in time allow scientists to create organs that are a perfect match for those in need of a transplant. Therapeutic cloning represents the ideal in organ transplantation, as it would provide an unlimited source of organs to anyone who needs them. The need for these organs is dire."
Stems cells • What is the debate?? • http://en.wikipedia.org/wiki/Stem_cells • http://en.wikipedia.org/wiki/Stem_cell_controversy