ch 10: molecular biology of the gene dna rna protein

CH 10: Molecular CH 10: Molecular Biology of the GeneBiology of the Gene

DNA DNA RNA RNA Protein Protein

Sections Covered Sections Covered with my titles for each sectionwith my titles for each section

10.1: DNA as the genetic material10.1: DNA as the genetic material

10.2/3: Structure of DNA and RNA10.2/3: Structure of DNA and RNA

10.4/5: DNA replication10.4/5: DNA replication

10.6-10.14: Transcription and translation10.6-10.14: Transcription and translation

10.15: review10.15: review

10.16: Mutations 10.16: Mutations

History of DNAHistory of DNA

DNA as the genetic materialDNA as the genetic material Griffith (1928)Griffith (1928)

• Found that the genetic component of pathogenic Found that the genetic component of pathogenic bacterial cells was not destroyed when the cells bacterial cells was not destroyed when the cells were heatedwere heated

• He did not follow-up on what that component was He did not follow-up on what that component was and how/why it survived.and how/why it survived.

• Griffith Experiment Experiment

DNA as the Genetic MaterialDNA as the Genetic Material

Avery (1944)Avery (1944) Most believed Most believed proteinprotein to be genetic material at to be genetic material at

this time.this time. Avery found that pathogenic bacterial cells Avery found that pathogenic bacterial cells

treated with protein digesting enzymes could treated with protein digesting enzymes could still transform harmless bacterial cells.still transform harmless bacterial cells.

Cells treated with a DNA digesting enzyme Cells treated with a DNA digesting enzyme could not.could not.


Avery (1944)Avery (1944) Avery concluded that DNA and not protein Avery concluded that DNA and not protein

must be the genetic material.must be the genetic material. Many refused to accept this conclusion.Many refused to accept this conclusion.

• Thought his findings only applied to bacteria and Thought his findings only applied to bacteria and not eukaryotic cells.not eukaryotic cells.


Hershey-Chase Experiment (~1950)Hershey-Chase Experiment (~1950) Their work confirmed to the scientific Their work confirmed to the scientific

community that DNA was the genetic material.community that DNA was the genetic material. Considered an “elegant” experiment.Considered an “elegant” experiment.

• Very simple and demonstrates a great deal.Very simple and demonstrates a great deal.

See page 183See page 183

Hershey-Chase ExperimentHershey-Chase Experiment

They took advantage in a chemical They took advantage in a chemical difference between DNA and proteindifference between DNA and protein

DNA contains the elements: C, H, O, N, DNA contains the elements: C, H, O, N, PP Protein contains the elements: C, H, O, N, Protein contains the elements: C, H, O, N, SS


Experiment utilized bacteriophagesExperiment utilized bacteriophages Bacteriophages are viruses that infect Bacteriophages are viruses that infect

bacteria.bacteria. Knew that a virus’ genetic material enters Knew that a virus’ genetic material enters

the host cellthe host cell• as a result the bacterial cell makes more virus as as a result the bacterial cell makes more virus as

directed by the virus’ genetic materialdirected by the virus’ genetic material


More on viruses…..More on viruses….. Viruses have two components:Viruses have two components:

• An outer protein coat with nucleic acid insideAn outer protein coat with nucleic acid inside


The ExperimentThe Experiment

1.1. Allowed one sample of viruses to infect Allowed one sample of viruses to infect bacteria grown on a bacteria grown on a radioactive (RA) radioactive (RA) sulfur-35 sulfur-35 mediummedium

• Viruses made had Viruses made had RA Sulfur-35 RA Sulfur-35 in their in their proteinprotein coats. coats.


The ExperimentThe Experiment

2.2. Allowed another sample of viruses to Allowed another sample of viruses to infect bacteria grown on a infect bacteria grown on a radioactive radioactive (RA) phosphorus-32(RA) phosphorus-32 medium medium

• Viruses made had Viruses made had RA phosphorus-32 RA phosphorus-32 in in their their DNADNA..


3.3. The two RA viral cultures were isolated The two RA viral cultures were isolated and each was allowed to infect a new and each was allowed to infect a new (non RA) bacterial culture.(non RA) bacterial culture.

Exp’t was done in a liquid medium called the Exp’t was done in a liquid medium called the supernatant.supernatant.

4.4. Cultures were gently shaken in a blender Cultures were gently shaken in a blender to shake the virus off of the outside of the to shake the virus off of the outside of the bacteria.bacteria.

Virus infecting bacterial cellVirus infecting bacterial cell


5.5. Each culture was centrifuged to separate Each culture was centrifuged to separate the liquid medium (supernatant) from the the liquid medium (supernatant) from the infected bacteria.infected bacteria.

6.6. The bacteria and the supernatant were The bacteria and the supernatant were checked for radioactivity.checked for radioactivity.

Whatever entered the bacteria is the genetic Whatever entered the bacteria is the genetic material.material.


What they found:What they found: Bacteria infected with the virus with a Bacteria infected with the virus with a RA S-RA S-

35 (protein)35 (protein) coat coat• The infected bacteria were NOT RAThe infected bacteria were NOT RA• The The supernatant was RAsupernatant was RA

This is evidence that the protein did not This is evidence that the protein did not enter the bacteria and thus, could not be the enter the bacteria and thus, could not be the genetic material.genetic material.


For the bacteria infected by virus with For the bacteria infected by virus with RA P-RA P-32 32 in theirin their DNADNA• The infected bacteria were RAThe infected bacteria were RA• The supernatant was not RAThe supernatant was not RA• This is evidence that the This is evidence that the DNADNA entered the bacteria entered the bacteria

and thus, MUST be the genetic material.and thus, MUST be the genetic material.

• http://www.accessexcellence.org/RC/VL/GG/http://www.accessexcellence.org/RC/VL/GG/hershey.phphershey.php

Structure of DNAStructure of DNA

What was known about DNAWhat was known about DNA Chemical components are:Chemical components are:

• Deoxyribose – 5 carbon sugarDeoxyribose – 5 carbon sugar• Phosphate groupsPhosphate groups• Nitrogenous basesNitrogenous bases

AdenineAdenine GuanineGuanine CytosineCytosine ThymineThymine


Nitrogenous bases were of 2 types:Nitrogenous bases were of 2 types: Purines: have a double-ring structurePurines: have a double-ring structure

• Adenine (A)Adenine (A)• Guanine (G)Guanine (G)

Pyrimidines: have a single-ring structurePyrimidines: have a single-ring structure• Cytosine (C)Cytosine (C)• Thymine (T) Thymine (T)

• Page 185Page 185


Chargaff’s findings (1949)Chargaff’s findings (1949) Studied DNA from many organismsStudied DNA from many organisms Found that the amount of guanine is always Found that the amount of guanine is always

equal to the amount cytosine and the amount equal to the amount cytosine and the amount of adenine is equal to the amount of thymine.of adenine is equal to the amount of thymine.• G=CG=C• A=TA=T


X-Ray Crystallography Data on DNAX-Ray Crystallography Data on DNA Maurice Wilkins and Rosalind FranklinMaurice Wilkins and Rosalind Franklin

• Franklin’s data suggested that DNA was a long Franklin’s data suggested that DNA was a long thin molecule of 2 nm diameterthin molecule of 2 nm diameter

• Data also indicated a repeating pattern consistent Data also indicated a repeating pattern consistent with a helix.with a helix.

• Wilkins shared Franklin’s data and lab notes with Wilkins shared Franklin’s data and lab notes with Watson and Crick without her permission.Watson and Crick without her permission.

Rosalind FranklinRosalind Franklin As a scientist Miss As a scientist Miss

Franklin was distinguished Franklin was distinguished by extreme clarity and by extreme clarity and perfection in everything perfection in everything she undertook. Her she undertook. Her photographs are among photographs are among the most beautiful X-ray the most beautiful X-ray photographs of any photographs of any substance ever taken. substance ever taken. Their excellence was the Their excellence was the fruit of extreme care in fruit of extreme care in preparation and mounting preparation and mounting of the specimens as well of the specimens as well as in the taking of the as in the taking of the photographs.photographs. -- J. D. Bernal -- J. D. Bernal [1958 N]

Franklin’s X-Ray DataFranklin’s X-Ray Data


"The instant I saw the picture my mouth "The instant I saw the picture my mouth fell open and my pulse began to race.... fell open and my pulse began to race....

the black cross of reflections which the black cross of reflections which dominated the picture could arise only dominated the picture could arise only

from a helical structure... mere from a helical structure... mere inspection of the X-ray picture gave inspection of the X-ray picture gave

several of the vital helical parameters." several of the vital helical parameters." WatsonWatson


In 1953 Watson, Crick, and Wilkins put the In 1953 Watson, Crick, and Wilkins put the pieces together and proposed their pieces together and proposed their famous double helix structure for DNA.famous double helix structure for DNA. Watson, Crick, and Watson, Crick, and Wilkins were awarded a were awarded a

Nobel Prize for deciphering the structure of Nobel Prize for deciphering the structure of DNA DNA

Watson and CrickWatson and Crick


DNA is a double-stranded helixDNA is a double-stranded helix Each strand is a long chain of covalently Each strand is a long chain of covalently

bonded nucleotidesbonded nucleotides• Phosphates can bond to carbon 5 or carbon 3 of Phosphates can bond to carbon 5 or carbon 3 of

deoxyribosedeoxyribose Phoshpates link the sugars to form the backbone of the Phoshpates link the sugars to form the backbone of the

chainchain

• Bases bond to carbon 1 of deoxyriboseBases bond to carbon 1 of deoxyribose

• Page 187Page 187


Each strand has a 5’ and a 3’ endEach strand has a 5’ and a 3’ end Two DNA strands run in opposite directionsTwo DNA strands run in opposite directions

• One runs 5’ One runs 5’ 3’ and the other 3’ 3’ and the other 3’ 5’ 5’


The two strands are joined by hydrogen The two strands are joined by hydrogen bonds between the basesbonds between the bases

• Two H bonds form between A and T.Two H bonds form between A and T.• Three H bonds form between G and C. Three H bonds form between G and C.

GC

A T

Structure DNAStructure DNA

DNA ReplicationDNA Replication

DNA replication – DNA synthesisDNA replication – DNA synthesis Occurs in the nucleus during ___ of the cell Occurs in the nucleus during ___ of the cell

cyclecycle Goal is to make an exact copy of the cell’s Goal is to make an exact copy of the cell’s

DNADNA• Put another way -- goal is to duplicate the Put another way -- goal is to duplicate the

chromosomes.chromosomes.

Replication

Semi-Conservative ModelSemi-Conservative Model Each newly made piece of DNA is ½ old Each newly made piece of DNA is ½ old

DNA and ½ new DNA DNA and ½ new DNA (page 188)(page 188)

Simple animation of replication

DNA Replication-enzymes neededDNA Replication-enzymes needed

HelicasesHelicases• Open the H bonds between the strandsOpen the H bonds between the strands

Stabilizing proteinsStabilizing proteins

• Hold the two strands apartHold the two strands apart

DNA Replication: enzymes neededDNA Replication: enzymes needed

DNA polymerase IIIDNA polymerase III• Adds nucleotides to the 3’ end of DNAAdds nucleotides to the 3’ end of DNA• Say…synthesizes DNA in the 5’ Say…synthesizes DNA in the 5’ 3’ direction 3’ direction• It cannot initiate (start) a new DNA strandIt cannot initiate (start) a new DNA strand

DNA polymerase IDNA polymerase I• Removes primer sequences and fills in the Removes primer sequences and fills in the

gaps with DNAgaps with DNA Other DNA polymerasesOther DNA polymerases

• Proofread the DNA and correct mutationsProofread the DNA and correct mutations

DNA Replication-enzymes neededDNA Replication-enzymes needed

““Primer” enzyme – Primer” enzyme – not shown in textnot shown in text

• Starts synthesis in the 5’ Starts synthesis in the 5’ 3’ direction 3’ direction • Makes a primer sequence to which DNA Makes a primer sequence to which DNA

polymerase III can add DNApolymerase III can add DNA

DNA ligaseDNA ligase• Joins newly made DNA segments after the primer Joins newly made DNA segments after the primer

sequences have been removed sequences have been removed and replaced by and replaced by DNA polymerase I.DNA polymerase I.


1.1. Helicases and stabilizing proteins open Helicases and stabilizing proteins open and unwind small sections of DNA and and unwind small sections of DNA and hold the strands apart.hold the strands apart.

• Occurs at specific locations on the DNA – Occurs at specific locations on the DNA – called origins of replicationcalled origins of replication

2.2. Primer enzymes synthesize primer Primer enzymes synthesize primer strands in the 5’ strands in the 5’ 3’ direction on each 3’ direction on each DNA strand.DNA strand.


3.3. DNA polymerase III adds DNA to each DNA polymerase III adds DNA to each primer sequence in the 5’ primer sequence in the 5’ 3’ direction. 3’ direction.


4.4. Proteins open more of the DNA Proteins open more of the DNA (replication fork opens more).(replication fork opens more).

5.5. DNA synthesis continues in the 5’DNA synthesis continues in the 5’ 3’ 3’ direction on one strand. direction on one strand. (leading strand)(leading strand)

• Another primer is laid down on the other Another primer is laid down on the other strand and then DNA synthesis continues. strand and then DNA synthesis continues. (lagging strand)(lagging strand)

Primer sequences


6.6. Process continues until all of the DNA Process continues until all of the DNA has been replicated.has been replicated.

7.7. Primer sequences are cut out, the gaps Primer sequences are cut out, the gaps filled in with DNAfilled in with DNA

8.8. DNA ligase joins the new DNA DNA ligase joins the new DNA sequences.sequences.

http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swfAnimationhttp://highered.mcgraw-hill.com/olc/dl/120076/bio23.swfAnimation

ch 10: molecular biology of the gene dna rna protein

Documents

protein dna

history of dna dna

genetic material avery

virus genetic material

genetic material griffith

dna replication

structure of dna

gene dna rna protein