30 Questions
What is the key difference between the S (smooth) and R (rough) strains of Pneumococcus identified by Frederick Griffith?
The S strain is virulent and causes fatal pneumonia, while the R strain is avirulent and does not cause illness.
Which of the following was the key finding from Griffith's transformation experiment?
All of the above were key findings from Griffith's transformation experiment.
Why did geneticists in the 1940s favor proteins as the genetic material rather than DNA?
Proteins were known to be more abundant and diverse in cells compared to DNA.
What was the key finding from the Hershey-Chase experiment using bacteriophage T2?
Bacteriophage T2 injects its DNA into the bacterial host cell during infection.
What is the difference between a nucleoside and a nucleotide?
A nucleoside contains a nitrogenous base and a pentose sugar, while a nucleotide also contains a phosphate group.
What are Chargaff's rules of base composition in DNA?
Chargaff's rules state that the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine.
What is the role of phosphodiester bonds in the structure of DNA?
Phosphodiester bonds link the phosphate groups of adjacent nucleotides to form the DNA backbone.
What are the four characteristics that the genetic material must exhibit?
Replicate, store information, express information, allow variation by mutation
When were Mendel's hereditary principles rediscovered?
1900
Who independently described the parallels between chromosome partitioning into gametes and the inheritance of genes?
Walter Sutton and Theodor Boveri
In what year was DNA localized to chromosomes and made a candidate for the hereditary material?
1923
Why were both proteins and RNA also considered candidates for the hereditary material?
Due to their presence in chromosomes
Which criteria must a molecule meet to serve as genetic material?
Replication, storage of information, expression of information, allowance for mutation
Why were lipids and carbohydrates also considered candidates for the hereditary material?
Due to their abundance as energy sources
Which experimental result provided crucial data for Watson and Crick's DNA model?
Both A and B
Which of the following statements about DNA is correct according to the information provided?
All of the above
What did Rosalind Franklin's X-ray diffraction analysis reveal about the structure of DNA?
DNA has a 3.4-angstrom periodicity, characteristic of a helical structure
According to the Watson and Crick model, what is the structure of DNA?
A double helix with anti-parallel strands connected by base pairing
What did James Watson and Francis Crick receive for their DNA model?
The Nobel Prize in Chemistry in 1962
Which of the following statements about DNA is NOT supported by the information provided?
DNA is a circular molecule
Who was the British biophysicist and X-ray crystallographer whose experimental work contributed to the discovery of DNA's structure?
Rosalind Franklin
How many hydrogen bonds are formed between adenine (A) and thymine (T) in DNA base pairing?
Two
Which type of bond is present between guanine (G) and cytosine (C) in DNA base pairing?
Hydrogen bond
In the structure of DNA, what makes up the backbone of the molecule?
Sugar and phosphate
Which scientist(s) proposed the DNA double helix structure?
Watson and Crick
What experiment helped in establishing that DNA is the genetic material?
Hershey-Chase experiment
In Chargaff's rules of base composition, what is the ratio of adenine (A) to thymine (T)?
$1:1$
Which direction do DNA strands run in, as indicated by the notation 5’-3’?
-5' to -3'
What provides complementarity to the two strands of DNA?
$G-C$ base pairing
Which type of bond is responsible for providing chemical stability to the DNA helix?
$Hydrogen$ bond
Study Notes
Griffith's Transformation Experiment
- Frederick Griffith (1927) showed that avirulent strains of Streptococcus pneumoniae could be transformed to virulence
- He speculated that the transforming principle could be part of the polysaccharide capsule or a compound required for capsule synthesis
Avery, MacLeod, and McCarty's Experiment
- Demonstrated that DNA is the genetic material (1944)
- Used Streptococcus pneumoniae to show that DNA is the transforming principle
Hershey and Chase Experiment
- Used Escherichia coli and bacteriophage T2 to show that DNA enters the bacterial cell during infection and directs viral reproduction (1952)
- Demonstrated that DNA, not protein, is the genetic material
Composition and Structure of DNA
- Nucleotides are the building blocks of DNA
- Nucleotides consist of a nitrogenous base, pentose sugar, and phosphate group
- DNA contains deoxyribose, while RNA contains ribose sugar
Nucleosides and Nucleotides
- Nucleoside: a nitrogenous base and pentose sugar
- Nucleotide: a nucleoside with a phosphate group added
- Mono-, di-, and triphosphates: nucleotides with one, two, or three phosphate groups added
Phosphodiester Bonds
- Nucleotides are linked by phosphodiester bonds between the phosphate group at the C-5' position and the OH group at the C-3' position
Erwin Chargaff's Rules of Base Composition
- A = T, and G = C
- The amount of pyrimidine nucleotides (T+C) equals the amount of purine nucleotides (A+G)
Watson and Crick's Model
- Proposed structure of DNA as a double helix (1953)
- Two anti-parallel strands connected by base pairing, with stacked nitrogenous bases
Test your knowledge on topics like the structure and replication of DNA, evidence supporting DNA as the genetic material, and the chemistry essential to DNA structure. Explore the criteria for a molecule to serve as genetic material and the rediscovery of Mendel's work in genetics.
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