Ch 16 Molecular Basis of Inheritance Chromosomes are

Ch 16 Molecular Basis of Inheritance

Chromosomes are made of ? Proteins ? specificity of function Lots of heterogenity Role of DNA as the hereditary factor was determined by studying bacteria infected by viruses Nucleic Acids? too uniform

Transformation of Bacteria Griffith 1928

1944 Avery, Mc. Carty, and Mac. Leod announced that the transforming substance was… 3 main candidates: 1. DNA 2. RNA 3. protein

Avery, Mac. Leod, Mc. Carty (1944) • Purified various molecules from heat killed pathogenic bacteria A C G U protein A C G T RNA Now tried to transform nonpathogenic bacteria… DNA

Avery, Mac. Cloud and Mc. Carty chemically show that DNA is the genetic material R R R • used the S (virulent) and R (avirulent) strains of D. pneumococci • chemically isolated and purified proteins, DNA, RNA of the S strain • They treated the living avirulent R strain with each of these chemicals. • only purified DNA changed the avirulent R strain into a virulent S strain

Avery, Mac. Cloud and Mc. Carty chemically show that DNA is the genetic material Still R strain S Strain Conclusion: DNA is the genetic material because it could change the genetic composition of a cell

The Hershey-Chase experiment: phages verified DNA was transforming agent Mc. Graw hill hershey chase experiment

Fig. 16 -4 -1 EXPERIMENT Phage Radioactive protein Bacterial cell Batch 1: radioactive sulfur (35 S) DNA Radioactive DNA Batch 2: radioactive phosphorus ( 32 P)

Fig. 16 -4 -2 EXPERIMENT Phage Empty Radioactive protein shell protein Bacterial cell Batch 1: radioactive sulfur (35 S) DNA Phage DNA Radioactive DNA Batch 2: radioactive phosphorus ( 32 P)

Fig. 16 -4 -3 activity campbell EXPERIMENT Phage Empty Radioactive protein shell protein Radioactivity (phage protein) in liquid Bacterial cell Batch 1: radioactive sulfur (35 S) DNA Phage DNA Centrifuge Pellet (bacterial cells and contents) Radioactive DNA Batch 2: radioactive phosphorus ( 32 P) Centrifuge Pellet Radioactivity (phage DNA) in pellet

Phages

Chargaff’s Rule Remember…. Cut my py

Building block of DNA?

The double helix Activity: DNA RNA structure

Watson and Crick

Rosalind Franklin and her X-ray diffraction photo of DNA

Purine and pyridimine

Base pairing in DNA

A model for DNA replication: the basic concept (Layer 1)

A model for DNA replication: the basic concept (Layer 2)

A model for DNA replication: the basic concept (Layer 3)

A model for DNA replication: the basic concept (Layer 4)

Three alternative models of DNA replication

Meselson-Stahl experiment tested three models of DNA replication (Layer 1) Mc. Graw Hill Messelson and Stahl

Meselson-Stahl experiment tested three models of DNA replication (Layer 2)

Meselson-Stahl experiment tested three models of DNA replication (Layer 3)

Meselson-Stahl experiment tested three models of DNA replication (Layer 4)

Origin of Replication in Bacteria Specific DNA sequence

Origins of replication in eukaryotes DNA replication video

Proteins used in DNA replication

The main proteins of DNA replication and their functions helicase Single stranded binding proteins topoisomerase Primase DNA polymerase III DNA polymerase I how nucleotides are added DNA ligase

Table 16 -1

The two strands of DNA are antiparallel Can only add to 3’ end

Incorporation of a nucleotide into a DNA strand • Each nucleotide that is added to a growing DNA strand is a nucleoside triphosphate • d. ATP supplies adenine to DNA and is similar to the ATP of energy metabolism • The difference is in their sugars: d. ATP has deoxyribose while ATP has ribose • As each monomer of d. ATP joins the DNA strand, it loses two phosphate groups as a molecule of pyrophosphate

Fig. 16 -14 New strand 5 end Sugar 5 end 3 end T A T C G G C T A A Base Phosphate Template strand 3 end DNA polymerase 3 end A T Pyrophosphate 3 end C Nucleoside triphosphate 5 end C 5 end

Direction of replication bioflix Activity DNA replication

Synthesis of leading strand activity : DNA replication a closer look Activity DNA replication

recap The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells

Synthesis of lagging strand Overview Origin of replication Leading strand Lagging strand 2 1 Leading strand Overall directions of replication

Fig. 16 -16 b 1 3 Template strand 5 5 3

Fig. 16 -16 b 2 3 Template strand 3 5 5 RNA primer 5 3 1 3 5

Fig. 16 -16 b 3 3 Template strand 3 5 5 RNA primer 5 3 3 1 Okazaki fragment 3 1 5 5 3 5

Fig. 16 -16 b 4 3 5 5 Template strand 3 RNA primer 5 3 1 5 3 5 Okazaki fragment 3 3 3 1 5 5 2 1 3 5

Fig. 16 -16 b 5 3 5 5 Template strand 3 RNA primer 5 3 1 3 5 1 5 5 2 3 5 Okazaki fragment 3 3 3 1 3 5 5 2 1 3 5

Fig. 16 -16 b 6 3 5 5 Template strand 3 RNA primer 5 bio flix Lagging strand video 3 1 5 2 3 5 1 5 2 3 3 5 1 5 3 5 Okazaki fragment 3 3 3 3 5 1 5 2 1 Overall direction of replication 3 5

Synthesis of lagging strand

Priming DNA synthesis with RNA

A summary of DNA replication

The main proteins of DNA replication and their functions Activity: DNA replication review

Nucleotide excision repair of DNA damage

Fig. 16 -18 Nuclease DNA polymerase DNA ligase

The endreplication problem

Telomere = Aglet

Fountain of Youth! Only in germ line cells

Fig. 16 -19 5 Ends of parental DNA strands Leading strand Lagging strand 3 Last fragment Previous fragment RNA primer Lagging strand 5 3 Parental strand Removal of primers and replacement with DNA where a 3 end is available 5 3 Second round of replication 5 New leading strand 3 New lagging strand 5 3 Further rounds of replication Shorter and shorter daughter molecules

Telomeres and telomerase: Telomeres of mouse chromosomes

Telomeres and telomerase

Levels of DNA coiling and folding Nucleosome (10 nm in diameter) DNA double helix (2 nm in diameter) H 1 Histones DNA, the double helix Histones activity DNA packing Histone tail Nucleosomes, or “beads on a string” (10 -nm fiber)

Fig. 16 -21 b Chromatid (700 nm) 30 -nm fiber Loops Scaffold 300 -nm fiber Replicated chromosome (1, 400 nm) 30 -nm fiber Looped domains (300 -nm fiber) Metaphase chromosome