Molecular Structure of DNA and RNA
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183 Terms
What is molecular genetics?
The study of DNA structure and function at the molecular level.
What are the four criteria that the genetic material must fulfill?
- Information: must contain information to make an organism. 2. Transmission: must be passed from parent to offspring. 3. Replication: must be copied for transmission. 4. Variation: must allow for changes to account for phenotypic variation.
Who conducted experiments that identified DNA as the genetic material?
Frederick Griffith.
What bacterium did Frederick Griffith study?
Streptococcus pneumoniae.
What are the two strains of Streptococcus pneumoniae?
Type S (Smooth) and Type R (Rough).
What is a characteristic of Type S Streptococcus pneumoniae?
It secretes a polysaccharide capsule that protects it from the immune system.
What is a characteristic of Type R Streptococcus pneumoniae?
It is unable to secrete a capsule and produces rough colonies.
What happened when Griffith injected a mouse with live type S bacteria?
The mouse died and type S bacteria were recovered from its blood.
What happened when Griffith injected a mouse with live type R bacteria?
The mouse survived and no living bacteria were isolated from its blood.
What was the result of injecting a mouse with heat-killed type S bacteria?
The mouse survived and no living bacteria were isolated from its blood.
What occurred when Griffith injected a mouse with live type R and heat-killed type S cells?
The mouse died and type S bacteria were recovered from its blood.
What is the significance of Griffith's experiments?
They demonstrated genetic transformation, showing that genetic material could be transferred between bacteria.
What is the role of the polysaccharide capsule in Type S bacteria?
It protects the bacterium from the immune system of animals.
What does the term 'genetic transformation' refer to in Griffith's experiments?
The process by which type R bacteria were transformed into type S bacteria by acquiring genetic material from heat-killed type S bacteria.
Why is it important to identify the chemical nature of genetic material?
To understand how genetic information is transmitted and expressed.
What advancements have contributed to our understanding of molecular genetics?
Dramatic advances in techniques and approaches in molecular biology.
What term did Griffith use to describe the process of transforming type R bacteria into type S?
He called this process transformation.
What is the transforming principle?
The substance that allowed the transformation of type R bacteria into type S.
What did Griffith not know about the transforming principle?
He did not know what type of substance it was.
Who conducted experiments to identify the genetic material based on Griffith's observations?
Avery, MacLeod, and McCarty.
What major constituents of living cells were known during the 1940s?
DNA, RNA, proteins, and carbohydrates.
What did Avery, MacLeod, and McCarty find when they purified macromolecules from type S cells?
Only the extract containing purified DNA could convert type R bacteria into type S.
What happened when the DNA extract was treated with DNase?
Treatment with DNase eliminated transformation.
What did Hershey and Chase provide evidence for regarding genetic material?
They provided evidence that DNA is the genetic material of T2 phage.
What radioisotopes did Hershey and Chase use to distinguish DNA from proteins?
32P labels DNA specifically and 35S labels proteins specifically.
What was the outcome when radiolabeled phages infected non-radioactive E. coli cells?
Most of the 32P entered the bacterial cells, indicating DNA, while most of the 35S remained outside, indicating protein.
What are DNA and RNA collectively known as and why?
Nucleic acids, because they release H+ in water, making them acid
Who first identified DNA and what did he name it?
Friedrich Miescher identified DNA in 1869 and named it 'nuclein'.
What are the repeating units of nucleic acids?
Nucleotides.
What structure do nucleotides form in DNA and RNA?
They are linked to form a linear strand.
What is the structure formed by two strands of DNA?
A double helix.
What are the three components of a nucleotide?
A phosphate group, a pentose sugar (ribose in RNA, deoxyribose in DNA), and a nitrogenous base.
What is the significance of the 3-D structure of DNA?
It results from the folding and bending of the double helix and allows interaction with proteins to produce chromosomes.
What is the repeating unit of ribonucleic acid (RNA)?
A ribonucleotide.
What is the repeating unit of deoxyribonucleic acid (DNA)?
A deoxyribonucleotide.
What is a nucleoside composed of?
A base plus a sugar.
What are examples of nucleosides?
Adenosine (adenine + ribose) and Deoxyadenosine (adenine + deoxyribose).
What is a nucleotide composed of?
A base, a sugar, and one or more phosphate groups.
What are examples of nucleotides?
Adenosine monophosphate (AMP), Adenosine diphosphate (ADP), and Adenosine triphosphate (ATP).
How are nucleotides linked together in a DNA strand?
By covalent bonds known as ester bonds.
What type of linkage connects the 5' carbon of one nucleotide to the 3' carbon of another nucleotide?
Phosphodiester linkage.
What directionality does a DNA strand have?
5' to 3' directionality.
What forms the backbone of a nucleic acid strand?
Phosphates and sugar molecules.
Who elucidated the double helical structure of DNA in 1953?
James Watson and Francis Crick.
Which scientists provided the scientific framework for the discovery of the DNA double helix?
Linus Pauling, Rosalind Franklin, Maurice Wilkins, and Erwin Chargaff.
What secondary structure did Linus Pauling propose for proteins?
The α-helix.
What technique did Rosalind Franklin use to study DNA fibers?
X-ray diffraction of wet DNA fibers.
What structural features of DNA did Rosalind Franklin's diffraction pattern suggest?
Helical structure, more than one strand, and 10 base pairs per complete turn.
What was Erwin Chargaff known for in relation to DNA?
- Pioneering biochemical techniques for the isolation, purification, and measurement of nucleic acids.
- Analyzed the base composition of DNA isolated from various species to reveal important structural features. (discovery-based science)
What were the steps of Chargaff's experimental protocol?
Extract the chromosomal material from cells. (use of high salt, detergent, or mild alkali treatment)
Remove the protein. (protease)
Hydrolyze the DNA to release the bases from the DNA strands. (treat with strong acid)
Separate the bases by chromatography. Paper chromatography provides an easy way to separate the four type of bases.
Extract bands from paper into solutions and determine the amounts of each base by spectroscopy. Each base will absorb light at a particular wavelength. By examining the absorption profile of a sample of base, it is then possible to calculate the amount of base.
Compare the base content in the DNA from different organisms.
- Remove the protein. (protease)
- Hydrolyze the DNA to release the bases from the DNA
strands. (treat with strong acid)
- Separate the bases by chromatography. Paper chromatography
provides an easy way to separate the four type of bases.
- Extract bands from paper into solutions and determine the
amounts of each base by spectroscopy. Each base will absorb
light at a particular wavelength. By examining the absorption
profile of a sample of base, it is then possible to calculate the
amount of base.
- Compare the base content in the DNA from different
organisms.
What technique is used to separate DNA bases in Chargaff's protocol?
Paper chromatography.
How are the amounts of each base determined after chromatography?
By spectroscopy, as each base absorbs light at a specific wavelength.
What is the significance of examining the absorption profile of a sample of base?
It allows for the calculation of the amount of base present.
What observation is known as Chargaff's rule?
The percent of adenine equals the percent of thymine, and the percent of cytosine equals the percent of guanine.
What was a crucial piece of evidence used by Watson and Crick to elucidate the structure of DNA?
Chargaff's rule.
What did Watson and Crick use to model the structure of DNA?
Ball-and-stick models incorporating all known experimental observations.
What is the orientation of the sugar-phosphate backbone in the DNA structure?
The sugar-phosphate backbone is on the outside of the double helix.
How do the bases in DNA strands interact according to Watson and Crick's findings?
The bases project toward each other and form hydrogen bonds according to the AT/GC rule.
What is the structure of the DNA double helix?
Two strands twisted together around a common axis, forming a right-handed helix. 10 base pairs (bp) per complete turn.
What is the distance between each base pair in the DNA helix?
3.4 nm per complete turn.
What is the directionality of the two strands in the DNA double helix?
The strands are antiparallel, with one running 5' to 3' and the other 3' to 5'.
Who were awarded the Nobel Prize in 1962 for their work on DNA structure?
Watson, Crick, and Maurice Wilkins.
Why was Rosalind Franklin not awarded the Nobel Prize for her contributions to DNA research?
She died in 1958, and Nobel prizes are not awarded posthumously.
What was the initial incorrect assumption made by Watson and Crick regarding base pairing?
They initially thought bases formed hydrogen bonds with identical bases in the opposite strand.
What prompted Watson and Crick to further model DNA interactions?
They realized that the hydrogen bonding of A to T was structurally similar to that of C to G.
What stabilizes the double-helical structure of DNA?
Hydrogen bonding between complementary bases and base stacking.
How many hydrogen bonds connect adenine (A) to thymine (T)?
Two hydrogen bonds.
How many hydrogen bonds connect cytosine (C) to guanine (G)?
Three hydrogen bonds.
What are the two types of grooves found on the DNA double helix?
Major groove and minor groove.
What is the predominant form of DNA found in living cells?
B DNA.
What type of DNA is characterized as a left-handed helix with 12 base pairs per turn?
Z DNA.
What conditions favor the formation of Z DNA?
-Alternating purine/pyrimidine sequences at high salt concentrations
-cytosine methylation at low salt concentrations
-negative supercoiling.
What are the functions of Z DNA?
- May play a role in transcription and chromosome structure
- Recognized by cellular proteins
- May alter chromosome compaction
What is the primary structure of an RNA strand compared to that of DNA?
RNA uses uracil instead of thymine and ribose with a 2' OH instead of deoxyribose.
How long are RNA strands typically?
Several hundred to several thousand nucleotides in length.
What is the typical handedness of RNA double helices?
Right-handed.
What base pairs with adenine (A) in RNA?
Uracil (U).
What base pairs with cytosine (C) in RNA?
Guanine (G).
What types of secondary structures can RNA form?
-Stem loops
-internal loops
-multibranched loops
-bulge loops.
What is the significance of base-pairing and base stacking in RNA?
They contribute to the tertiary structure of RNA.