DNA Structure and Function Chapter 6

1.1 Impacts/Issues Here Kitty, Kitty, Kitty, Kitty, Kitty  Making clones (exact genetic copies) of adult animals is now a common practice in research and animal husbandry

Video: Goodbye, Dolly

6.2 Chromosomes  A eukaryotic chromosome is a molecule of DNA together with associated proteins  Chromosome Structure made of DNA and associated proteins Carries part or all of a cell’s genetic information

Chromosome Structure  Sister chromatid One of two attached members of a duplicated eukaryotic chromosome  Centromere Constricted region in a eukaryotic chromosome where sister chromatids are attached

Chromosome Structure  Proteins organize DNA structurally Allow chromosomes to pack tightly  Histone Type of protein that structurally organizes eukaryotic chromosomes  Nucleosome A length of DNA wound around a spool of histone proteins

Chromosome Structure

Animation: Chromosome structural organization

Chromosome Number  A eukaryotic cell’s DNA is divided into a characteristic number of chromosomes  Chromosome number Sum of all chromosomes in a cell of a given type A human body cell has 23 pairs of chromosomes  Diploid Cells having two of each type of chromosome characteristic of the species (2n)

Examples of Chromosome Number

Types of Chromosomes  There are two types of eukaryotic chromosomes: autosomes and sex chromosomes  Autosomes Paired chromosomes with the same length, shape, centromere location, and genes Any chromosome other than a sex chromosome  Sex chromosomes Members of a pair of chromosomes that differ between males and females

Sex Chromosomes: Sex Determination in Humans

Fig. 6-3a, p. 104 diploid reproductive cell in female diploid reproductive cell in male X X Y eggssperm X XXY XY XXXXY X XX XY union of sperm and egg at fertilization

Fig. 6-3a, p. 104 diploid reproductive cell in female diploid reproductive cell in male X X Y eggssperm X XXY XY X X XXXY XX XY union of sperm and egg at fertilization Stepped Art

Fig. 6-3b, p. 104

Animation: Human sex determination

Karyotype  Karyotyping reveals characteristics of an individual’s chromosomes  Karyotype Image of an individual’s complement of chromosomes arranged by size, length, shape, and centromere location

Constructing a Karyotype

Animation: Karyotype preparation

Video: ABC News: Picking your baby's gender; selecting sex causes controversy

Animation: Effects of the SRY gene

Animation: Human chromosomes

6.3 Fame and Glory  Erwin Chargaff Discovered the relationships between DNA bases  Rosalind Franklin Discovered the basic structure of DNA by x-ray crystallography  James Watson and Francis Crick Built the first accurate model of a DNA molecule

Key Players  Rosalind Franklin, Maurice Wilkins, James Watson, and Francis Crick

The Double Helix  A DNA molecule consists of two strands of nucleotide monomers running in opposite directions and coiled into a double helix  DNA nucleotide A five-carbon sugar (deoxyribose) Three phosphate groups One nitrogen-containing base (adenine, thymine, guanine, or cytosine)

The Double Helix  Two double-helix strands are held together by hydrogen bonds between nucleotide bases  Chargaff’s rules Bases of the two DNA strands in a double helix pair in a consistent way: A = T and C = G Proportions of A and G vary among species

The Four DNA Nucleotides

DNA Structure

Animation: DNA close up

Patterns of Base Pairing  The order of bases (DNA sequence) varies among species and among individuals Each species has characteristic DNA sequences  DNA sequence The order of nucleotide bases in a strand of DNA

Animation: Griffith’s experiment

Animation: Subunits of DNA

Animation: Structure of DNA

6.4 DNA Replication and Repair  A cell replicates its DNA before it divides  Each strand of the double helix serves as a template for synthesis of a new, complementary strand of DNA  DNA replication results in two double-stranded DNA molecules identical to the parent

DNA Replication and Repair  During DNA replication, the double-helix unwinds  DNA polymerase uses each strand as a template to assemble new, complementary strands of DNA from free nucleotides  DNA ligase seals any gaps to form a continuous strand

DNA Replication and Repair  DNA replication Duplication of a cell’s DNA before cell division  DNA polymerase DNA replication enzyme; assembles a new strand of DNA based on sequence of a DNA template  DNA ligase Enzyme that seals breaks in double-stranded DNA

DNA Replication

Fig. 6-8, p. 108 Stepped Art 4) DNA ligase seals any gaps that remain between bases of the “new” DNA, so a continuous strand forms. The base sequence of each half-old, half-new DNA molecule is identical to that of the parent. 3) Each parent strand serves as a template for assembly of a new DNA strand from nucleotides, according to base-pairing rules. 2) As replication starts, the two strands of DNA unwind at many sites along the length of the molecule. 1) The two strands of a DNA molecule are complementary: their nucleotides match up according to base-pairing rules (G to C, T to A).

Animation: DNA replication details

Animation: DNA replication

3D Animation: DNA Replication

DNA Replication: The Double Helix

Checking for Mistakes  DNA repair mechanisms fix damaged DNA Proofreading by DNA polymerase corrects most base-pairing errors  DNA repair mechanisms Any of several processes by which enzymes repair DNA damage

Mutations  Uncorrected errors in DNA replication may become mutations  Mutation A permanent change in DNA sequence

6.5 Cloning Adult Animals  Reproductive cloning technologies produce an exact genetic copy of an individual (clone)  Reproductive cloning Technology that produces genetically identical individuals

Somatic Cell Nuclear Transfer  Somatic cell nuclear transfer (SCNT) Method of reproductive cloning in which nuclear DNA from an adult somatic cell is transferred into an unfertilized, enucleated egg  Therapeutic cloning Using SCNT to produce human embryos for research

Somatic Cell Nuclear Transfer

Animation: How Dolly was created

Clones  Clone produced by somatic cell nuclear transfer

6.6 Impacts/Issues Revisited  Because of the difficulty of obtaining human eggs for SCNT, researchers have started to make hybrid embryos for research using adult human cells and pig eggs

Digging into Data: The Hershey Chase Experiments

Fig. 6-12a, p. 113

Fig. 6-12b-c, p. 113

35 S remains outside cells Virus proteins labeled with 35 S DNA being injected into bacterium 32 P remains inside cells Virus DNA labeled with 32 P Labeled DNA being injected into bacterium

Fig. 6-12d, p. 113

Animation: Hershey-Chase experiments