Molecular Biology of the Gene DNA Lesson Part 1 Dr. Wilson Muse Schoolcraft College

10.1 Experiments showed that DNA is the genetic material –Frederick Griffith discovered that a “ transforming factor ” could be transferred into a bacterial cell –Disease-causing bacteria were killed by heat –Harmless bacteria were incubated with heat-killed bacteria –Some harmless cells were converted to disease- causing bacteria, a process called transformation –The disease-causing characteristic was inherited by descendants of the transformed cells Copyright © 2009 Pearson Education, Inc.

10.1 Experiments showed that DNA is the genetic material –Alfred Hershey and Martha Chase used bacteriophages to show that DNA is the genetic material –Bacteriophages are viruses that infect bacterial cells –Phages were labeled with radioactive sulfur to detect proteins or radioactive phosphorus to detect DNA –Bacteria were infected with either type of labeled phage to determine which substance was injected into cells and which remained outside Copyright © 2009 Pearson Education, Inc.

10.1 Experiments showed that DNA is the genetic material –The sulfur-labeled protein stayed with the phages outside the bacterial cell, while the phosphorus- labeled DNA was detected inside cells –Cells with phosphorus-labeled DNA produced new bacteriophages with radioactivity in DNA but not in protein Copyright © 2009 Pearson Education, Inc. Animation: Hershey-Chase Experiment Animation: Phage T2 Reproductive Cycle

Head Tail fiber DNA Tail

Head Tail fiber DNA Tail

Batch 1 Radioactive protein Bacterium Radioactive protein DNA Phage Pellet Radioactive DNA Batch 2 Radioactive DNA Empty protein shell Phage DNA Centrifuge Radioactivity in liquid Measure the radioactivity in the pellet and the liquid. 4 Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. 3 Agitate in a blender to separate phages outside the bacteria from the cells and their contents. 2 Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. 1 Pellet Centrifuge Radioactivity in pellet

Batch 1 Radioactive protein Bacterium Radioactive protein DNA Phage Radioactive DNA Batch 2 Radioactive DNA Agitate in a blender to separate phages outside the bacteria from the cells and their contents. 2 Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. 1 Empty protein shell Phage DNA

Pellet Empty protein shell Phage DNA Centrifuge Radioactivity in liquid Measure the radioactivity in the pellet and the liquid. Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. Pellet Centrifuge Radioactivity in pellet 4 3

Phage attaches to bacterial cell. Phage injects DNA.Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble. Cell lyses and releases new phages.

DNA DNA.DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell.

Nucleotides CC C O Phosphate O C C O -P O O O O O O O One deoxyribose together with its phosphate and base make a nucleotide. Nitrogenous base Deoxyribose

10.2 DNA and RNA are polymers of nucleotides –The monomer unit of DNA and RNA is the nucleotide, containing –Nitrogenous base –5-carbon sugar –Phosphate group Copyright © 2009 Pearson Education, Inc.

–DNA and RNA are polymers called polynucleotides –A sugar-phosphate backbone is formed by covalent bonding between the phosphate of one nucleotide and the sugar of the next nucleotide –Nitrogenous bases extend from the sugar- phosphate backbone Copyright © 2009 Pearson Education, Inc. Animation: DNA and RNA Structure

Sugar-phosphate backbone DNA nucleotide Phosphate group Nitrogenous base Sugar DNA polynucleotide DNA nucleotide Sugar (deoxyribose) Thymine (T) Nitrogenous base (A, G, C, or T) Phosphate group

Sugar (deoxyribose) Thymine (T) Nitrogenous base (A, G, C, or T) Phosphate group

Pyrimidines Guanine (G) Adenine (A) Cytosine (C)Thymine (T) Purines

Sugar (ribose) Uracil (U) Nitrogenous base (A, G, C, or U) Phosphate group

Hydrogen Bonds, Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine, And adenine always pairs up with thymine. (Adenine and thymine are shown here.) C C C C N N N N N C C C C C N N O O C

C C C C N N O N C C C C N N O N N N C Hydrogen Bonds The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. (The bonds between cytosine and guanine are shown here.)

Twist

Hydrogen bond Base pair Partial chemical structureComputer model Ribbon model

Base pair Ribbon model

Hydrogen bond Partial chemical structure

10.4 DNA replication depends on specific base pairing –DNA replication follows a semiconservative model –The two DNA strands separate –Each strand is used as a pattern to produce a complementary strand, using specific base pairing –Each new DNA helix has one old strand with one new strand Copyright © 2009 Pearson Education, Inc. Animation: DNA Replication Overview

Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases but why do they stick together?

DNA by the numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only m. The earth is 150 billion m or 93 million miles from the sun.

Copyright © 2009 Pearson Education, Inc. DNA REPLICATION Makin’ copies

10.4 DNA replication depends on specific base pairing –DNA replication follows a semiconservative model –The two DNA strands separate –Each strand is used as a pattern to produce a complementary strand, using specific base pairing –Each new DNA helix has one old strand with one new strand Copyright © 2009 Pearson Education, Inc. Animation: DNA Replication Overview

Parental molecule of DNA

Parental molecule of DNA Nucleotides Both parental strands serve as templates

Parental molecule of DNA Nucleotides Both parental strands serve as templates Two identical daughter molecules of DNA

–DNA replication begins at the origins of replication –DNA unwinds at the origin to produce a “ bubble ” –Replication proceeds in both directions from the origin –Replication ends when products from the bubbles merge with each other –DNA replication occurs in the 5 ’ 3 ’ direction –Replication is continuous on the 3 ’ 5 ’ template –Replication is discontinuous on the 5 ’ 3 ’ template, forming short segments 10.5 DNA replication proceeds in two directions at many sites simultaneously Copyright © 2009 Pearson Education, Inc.

Animation: Leading Strand 10.5 DNA replication proceeds in two directions at many sites simultaneously –Proteins involved in DNA replication –DNA polymerase adds nucleotides to a growing chain –DNA ligase joins small fragments into a continuous chain Copyright © 2009 Pearson Education, Inc. Animation: Lagging Strand Animation: DNA Replication Review Animation: Origins of Replication

Origin of replication Parental strand Daughter strand Bubble Two daughter DNA molecules

3 end 5 end 3 end 5 end  P P P P P P P P

Parental DNA 3 5 DNA polymerase molecule DNA ligase 3 5 Overall direction of replication Daughter strand synthesized continuously Daughter strand synthesized in pieces

Copyright © 2009 Pearson Education, Inc. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN

10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits –A gene is a sequence of DNA that directs the synthesis of a specific protein –DNA is transcribed into RNA –RNA is translated into protein –The presence and action of proteins determine the phenotype of an organism Copyright © 2009 Pearson Education, Inc.

10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits –Demonstrating the connections between genes and proteins –The one gene – one enzyme hypothesis was based on studies of inherited metabolic diseases –The one gene – one protein hypothesis expands the relationship to proteins other than enzymes –The one gene – one polypeptide hypothesis recognizes that some proteins are composed of multiple polypeptides Copyright © 2009 Pearson Education, Inc.

Cytoplasm Nucleus DNA

Cytoplasm Nucleus DNA Transcription RNA

Cytoplasm Nucleus DNA Transcription RNA Translation Protein