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DNA: The Carrier of Genetic Information. AP Biology. How was DNA discovered to be the chemical unit of heredity?. Frederick Griffith's Experiment - the discovery of transformation Using two varieties of streptococcus, he originally searched for a vaccine.

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How was dna discovered to be the chemical unit of heredity
How was DNA discovered to be the chemical unit of heredity?

  • Frederick Griffith's Experiment - the discovery of transformation

    • Using two varieties of streptococcus, he originally searched for a vaccine.

    • One variety of bacteria had a capsule (like a cell wall) the other did not have a capsule.

1. Injection with live encapsulated bacteria -- mice contracted pneumonia and died

2. Injection with live naked bacteria -- mice lived, immune system destroyed the bacteria

3. Injection with heat killed encapsulated bacteria -- mice remained healthy

4. Injection with dead encapsulated bacteria and live naked bacteria -- mice contracted pneumonia and died

*note that neither of this forms caused disease before, but when placed together something occurred to make the living naked bacteria virulent.

What conclusions can be drawn from the experiment
What conclusions can be drawn from the experiment? contracted pneumonia and died

  • Living bacteria acquired genetic information from dead bacteria - particularly the instructions for making capsules, thus transforming the naked bacteria into incapsulated bacteria.

  • The Transforming agent was discovered to be DNA.

  • DNA was isolated and added to live naked bacteria, and they were transformed into the incapsulated kind.

  • 1. Hershey and Chase forced one population of phages to synthesize DNA using radioactive phosphorous.

  • 2. The radioactive phosphorous "labeled" the DNA.

  • 3. They forced another group of phages to synthesize protein using radioactive sulfur.

  • 4. The radioactive sulfur "labeled" the protein.

History of dna
History of DNA protein did not show any radioactivity.

  • Chargaff analyzed the amounts of the four nucleotides found in DNA and noticed a pattern.

  • He discovered that the amounts of adenine always was the same as the amounts of thymine.

  • Guanine and Cytosine was also the same. From this, the base-pair rule was formed.

History of dna1
History of DNA protein did not show any radioactivity.

  • Rosalind Franklin – used x-ray diffraction to study DNA structure

History of dna2
History of DNA protein did not show any radioactivity.

  • 1953 – James Watson and Francis Crick proposed a model for the structure of DNA

    • Used the work of many other scientists to develop their model

Dna structure
DNA Structure protein did not show any radioactivity.

  • DNA molecules are very long!

    • Millions of bases

  • Double Helix – like a twisted ladder

  • Two sides of the ladder are held together by hydrogen bonds

  • WEB

Nucleotide protein did not show any radioactivity.

  • Building block of DNA = nucleotide

    • Sugar – deoxyribose

    • Phosphate

    • 4 nitrogenous bases

      • Purines: Adenine and Guanine

      • Pyrimidines: Thymine and Cytosine

      • A always bonds with T, G always bonds with C

  • Nucleotides linked by covalent bonds to form alternating sugar-phosphate backbone

Nitrogen bases
Nitrogen Bases protein did not show any radioactivity.

Dna structure1
DNA Structure protein did not show any radioactivity.

  • The phosphate is attached to the 5' carbon (the 5 is a number given to sugar molecules).

  • The DNA strand has a free phosphate on the 5' end, and a free sugar on the 3' end

    • these numbers will become important later.

The dna double helix
The DNA Double Helix the ladder has an opposite orientation.

Dna chromosomes
DNA & Chromosomes the ladder has an opposite orientation.

  • DNA must be twisted and folded (with the help of proteins) to fit inside the cell.

    • Proteins – Histones

  • Together with DNA form structures called Nucleosomes

Dna chromosomes1
DNA & Chromosomes the ladder has an opposite orientation.

  • Nucleosomes are part of the chromatin (which makes up the chromosomes)

  • Nucleosomes are like spools – they prevent DNA strands from becoming tangled

  • Diagram p.258

Nucleosomes the ladder has an opposite orientation.

  • Consist of 146 base pairs of DNA wrapped around 8 histone molecules

  • DNA looks like a string of beads.

    • Bead = 8 histones

    • String = DNA wrapped around the histones and in between the histone beads

  • Nucleosomes are organized into large coiled loops held together by nonhistone scaffolding proteins.

Dna replication
DNA Replication the ladder has an opposite orientation.

  • the process by which DNA makes a copy of itself

  • occurs during interphase, prior to cell division

  • each new cell receives a copy of the DNA

Steps of dna replication
Steps of DNA Replication the ladder has an opposite orientation.

  • 1. DNA helicase (enzyme) unwinds the DNA.

    • The junction between the unwound part and the open part is called a replication fork.

  • 2. DNA polymerase adds the complementary nucleotides and binds the sugars and phosphates.

    • DNA polymerase travels from the 3' to the 5' end.

Steps continued
Steps (continued) the ladder has an opposite orientation.

  • 3. DNA polymerase adds complementary nucleotides on the other side of the ladder.

    • Traveling in the opposite direction.

  • 4. One side is the the ladder has an opposite orientation. leading strand - it follows the helicase as it unwinds.

  • 5. The other side is the lagging strand - its moving away from the helicase

Steps of dna replication cont d
Steps of DNA Replication (cont’d) the ladder has an opposite orientation.

  • Problem: it reaches the replication fork, but the helicase is moving in the opposite direction. It stops, and another polymerase binds farther down the chain.

  • This process creates several fragments, called Okazaki Fragments, that are bound together by DNA ligase.

  • Replication is called that are synthesized at the same time (multiple replication forks). semi-conservative, because one half of the original strand is always saved, or "conserved"



Dna expression

DNA Expressionhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf

Transcription and Translation

3 important points to remember
3 Important Points to Remember:http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf

  • Chromosomes are made of DNA

  • Segments of DNA code for a protein

  • Protein in turn, relates to a trait (eye color, enzymes, hormones..)

How proteins are synthesized from dna
How Proteins are Synthesized from DNAhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf

  • 1. DNA is trancribed into mRNA (messenger RNA) in the nucleus2. mRNA leaves the nucleus and travels to the cytoplasm3. Ribosomes in the cytoplasm use the code on mRNA to translate it into amino acids4. Amino acids form a chain - a protein

The central dogma of genetics
The Central Dogma of Geneticshttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf


  • RNA is very similar to DNA with the following exceptions:

    • it is single stranded

    • it has uracil instead of thymine

    • it has the sugar ribose, instead of deoxyribose


  • The base-pair rule is followed during transcription, except, instead of pairing thymine with adenine, when creating an RNA strand, uracil is used

  • DNA Strand: T G C A T C A G A

  • RNA Strand: A C G U A G U C U

  • Transcription

  • Transcription2

Transcription begins on the area of dna that contains the gene
Transcription begins on the area of DNA that contains the gene.

  • Each gene has three regions:

    1. Promotor - turns the gene on or off2. Coding region - has the information on how to construct the protein3. Termination sequence - signals the end of the gene

  • RNA Polymerase is responsible for reading the gene, and building the mRNA strand.

    • It reads only the 3' to 5' strand.

Translation gene.

1. The mRNA travels to the cytoplasm

2. Amino acids exist freely in the cytoplasm, many of them you acquire from your dietPKU

3. Each 3 bases (codon) translates to a single amino acid. (See codon chart)

Translation gene.

4. The ribosome looks for the "start" codon - AUG, this is where the chain begins

5. Transfer (tRNA), has an anticodon at one end and an amino acid at the other, it binds to a complementary codon.

6. Another tRNA reads the next codon, the amino acid attached to it binds with the amino acid on the previous tRNA using a peptide bond. The first tRNA falls off.

Translation gene.

7. This process continues until the "stop" codon is reached.8. The amino acid chain folds into a 3 dimensional structure, now a protein.9. That protein can be an enzyme, a hormone, or any other structure in the body that gives it traits and functionality.


Test for understanding
Test for Understanding gene.

  • A DNA sequence has the following bases:

    T A C - A G A - T T A - G G G - A T T

    What amino acids does it code for?

    (You'll need to use the codon chart)

Answer: gene.

  • First transcribe to its RNA sequence:

    A U G - U C U - A A U - C C C - U A A

  • Now translate to the amino acids:

    start - ser - asn - gly - stop

  • The amino acid chain is:



Mutations gene.

What causes mutations
What causes mutations? gene.

  • Most occur infrequently/spontaneously because of defects in the separation of chromosomes during

    • mitosis/meiosis

    • DNA replication

  • Some regions of DNA = hot spots

    • More likely to undergo mutation

  • Not all mutations occur spontaneously, many mutations are caused by mutagens

    • Ex. UV rays, X-rays (high dose)

    • Many mutagens are also carcinogens (cancer causing)

Mutations gene.

Point Mutation - substitute one base for another

Original: A T A C A C Mutant : T T A C A C

Frameshift Mutation - a base is either added or removed which causes a shift in the reading frame. Many genes affected – can be disastrous

Original: A T A C A C A A G C C AMutant: A T T A C A C A A G C C A

Mutations gene.

*Silent Mutation - a base is changed but the resulting amino acid is the same as in the non mutant DNA. No outward changes.

Original: A A A C A GMutant: A A G C A G

*Occur relatively frequently

Nonsense Mutation - a codon is changed to a STOP codon

Original: A T A C C C A A AMutant: A T T C C C A A A

Mutations gene.

  • Transposon - Jumping Gene, a stretch of DNA that inserts itself into a different spot on a chromsome or another chromosome

    • Can activate/inactivate genes

  • Mutations in DNA can cause a change in species --> Evolution

  • HOX mutations can cause major changes in morphology

Karyotype gene.

  • Picture of a person's chromosomes, arranged by size and grouped into homologous pairs.

  • Pairs are grouped together

    • Ex. Human Karyotype: chromosome pairs 1-23

Pedigrees in the offspring receiving too many or too few chromosomes.

  • = male

  • = female

  • = male affected

  • = female affected

  • Roman Numerals represent generations

  • married, siblings