DNA History, structure and replication quiz

Conservative replication

Make brand new molecule but parent one remains intact

Dispersive replication

• parent molecule is scattered/dispersed into two daughter molecules

Semiconservative replication

new daughter molecule is made of one of the parent DNA molecules and one new molecule

What did Meselson-Stahl’s experiment confirm?

DNA replicates using the semi-conservative model

Explain the steps and results of the Meselson-Stahl’s experiment

1. Parent DNA molecule is tagged with ¹⁵N (radioactive). DNA settles to the bottom because of heavy ¹⁵N

2. ¹⁵N was placed in a solution with lighter free floating nucleotide (¹⁴N). Results showed that the DNA Replicated and had a medium weight → conservative replication was eliminated

3. First generation DNA was placed in another solution of lighter free floating nucleotide (¹⁴N). Results showed that the DNA replicated and had both a lighter weighing and medium weight → must be semi-conservative

Why couldn’t the results of Meselson-Stahl’s experiment be dispersive replication?

• If it was dispersive there would only be a results with a middle weight

What are the steps of DNA replication?

1. Unwinding and unzipping of DNA

2. Synthesis of strands (both leading and lagging are made simultaneously

What happens during the unwinding and unzipping of DNA

1. gyrase and helicase help unwind and unzip DNA

   • Helicase: breaks the hydrogen bonds between the complementary base pairs

   • Gyrase relieves the tension from the coiling

2. SSB(single stranded binding) proteins stabilize the arms

How does the leading strand synthesis DNA?

1. RNA primase makes RNA Primer

2. DNA nucleotides will pair up with complementary strand

3. New strand is formed by DNA polymerase III( can only add to existing strand of DNA)

4. DNA Polymerase I comes in and replaces the primer with DNA

How does DNA Synthesis work for the lagging strand?

1. Okazaki fragments are created

   1. RNA Primer is made by primase

   2. DNA polymerase III builds the complementary strand from 5’ to 3’

   3. DNA Polymerase I replaces primer

2. RNA Primer is replaced with DNA

3. Ligase joins Okazaki fragments together through phosphodiester bonds

4. other enzymes will repair mistakes if any

Telomeres:

• serve as caps on DNA

• consist of repetitive non coding sequences

• can be linked to ageing by shortening over time.

Who is the Father of Modern Genetics?

Gregory Mendel

What did Gregory Mendel discover?

• both parents contribute

  • combination of both parents DNA determines the characteristics of a child

• Law of Segregation

• Law of Independent Assortment

What is Fred Griffith’s Transforming Principal? (1928)

Tests:

1. Smooth S-strain with capsule (deadly)

2. Rough R-strain no capsule (healthy)

3. Heat - dead S-Strain (Healthy)

4. Live R-Strain and Heat Killed S-Strain(Deadly)

Learned that something must have transformed from the heat killed S-Strain into R-strain’s phenotype

Who discovered the conveyer of inheritance and when?

Thomas Morgan in 1911

What did Thomas Morgan discover about DNA in 1911

• Found that chromosomes were linked with inheritance

• Chromosomes are made up of DNA and protein (still unsure which is responsible for inheritance

Chromosomes are made up of _____ wound around ______

1. DNA

2. Protein

DNA is made up of _________ some segments form _____ which code fore _______ that determine _____

1. Nucleotides (ATGC)

2. Gene

3. Protein

4. Traits

What did Avery et al. experiment test in 1944?

Is DNA or Protein the hereditary molecule?

Oswald Avery’s Experiment

1. Took heated S-strain and broke it down into a mixture of organic molecules (Proteins, RNA, DNA, lipids and carbohydrates)

2. used process of elimination by using specific enzymes that only destroyed one type of molecule

3. Tested to see if heated/dead S-strain mixed with R-strain would still transform

Results: Only experiment with DNA being destroyed prevented the transformation

Conclusion: DNA is the hereditary molecule

What did the Hershey and Chase experiment in 1952 study

Is DNA or Protein the hereditary molecule?

Explain Hershey and Chase’s experiment

1. Experimented with two types of bacteriophages

2. Radioactively labeled

   1. 32P - attached to phosphorus (DNA)

   2. 35S - attached to protein or Virus

Results: Only when testing DNA did Phosphorus show that it was present within the cell

Conclusion: DNA is the hereditary molecule

What did Fredrich discover in 1868?

• collected pus from bandages + isolated an acidic substance with large amounts of phosphorus and nitrogen which he called nuclein

What did P. Levene discover in 1928?

• anatomy of the nucleotide

  • Nucleotide consists of sugar, phosphate and nitrogen base

  • 4 types: ACGT

• Proposed that 4 nucleotides were connected

What did Erwin Chargaff discover in 1949

• He isolated DNA from different organism and measured levels of each 4 nitrogen bases

• Conclusion: not tetranucleotide - dinucleotide

Who stole Rosalind Franklin’s Research?

Maurice Wilkins

What did Rosalind discover?

• Used x-ray diffraction to analyze the structure of DNA - found that is was a helix-like structure

• X-ray diffraction:

  • sample molecules are subjected to X ray which are diffracted by other molecules that they encounter

  • diffraction patter is captured on photographic film

  • pattern was interpreted to determine molecular structure

What did James Watson and Francis Crick propose in 1952?

• Model of DNA with double helix of two anti-parallel strands

• Won Nobel Peace Prize in 1962

The monomer of the DNA Polymer is _____

the nucleotide

Each nucleotide contains:

1. phosphate group

2. deoxyribose sugar

3. nitrogen containing base

What is a purine?

Nitrogen bases that have two fused rings (A and G)

What are pyrimidine?

nitrogen bases that have a single ring (C and T)

Differences between structure of RNA and DNA

• RNA has same basic structure, except ribose sugar is used (OH on Carbon 2)

• Thymine is not present uses Uracil instead

• RNA is single stranded

Modern DNA Model

• two polypeptide strands that twist around each other to form a double helix

• Complementary base pairing (Purine is always paired with a pyrimidine

  • A + T

  • G + C

• two strands are anti parallel

• sugars are connected 5’ to 3’

• nucleotides of same strand are joined through phosphodiester bond