Studied by 0 people
Explain the process of Griffith’s transformation experiment
Griffith' Transformation experiment used 3 different variety of streptococcus pneumoniae. He used the living S (smooth-coated) cells and injected them into mice, which was deadly due to the inability for the body’s immune system to kill the S strand. He then went on to test the non-deadly R strand, which didn’t kill the mice. Third, he went on to test heat killed S cells, which were also not deadly. However the critical part of his experiment included the Living R cells and the Dead S cells which by themselves were not deadly but together were. This proved his theory that “some transforming principle” had caused the R-strand to become dangerous. This result was the live R-strand had acquired some type of deadly component from the S-strand, that deadly component was the transforming principle that was later identified as DNA by A very, Mcloud, and Mccraty.
What did P.A. Levene discover?
P.A. Levene discovered the structure of nucleotides, the building blocks of DNA and RNA. He proposed that DNA consists of a sugar (deoxyribose), a phosphate group, and four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). Additionally, he determined that DNA has a consistent backbone structure composed of alternating sugar and phosphate units, forming a repeating pattern. This foundational work laid the groundwork for later discoveries regarding the double helix structure of DNA and its role in genetic inheritance.
Does DNA synthesis occur from 5’ to 3’ or 3’ to 5’
5’ to 3’
If the % of adenine in a sample of DNA is 30%, what is the % of guanine?
20% because the A = T and G=C and together they add up to 100.
What is the backbone of DNA made of?
Multiple sugar and phosphate group, (rotating pattern)
What does the term double helix mean?
There are two strands formed into a helix rather than one.
Why cant 2 strands of DNA be synthesized continuously
The two strands are anti-parallel. Meaning while the two stands are parallel they are oriented in opposite directions. SInce they are anti-parallel and DNA polymerase can only extend from the 5’ to the 3’ ends, the “lagging” strand must be discontinuous and broken into okazaki fragments.
Where does the energy come from that DNA polymerase uses to build the new strands?
The energy comes from the high-energy bonds in the nucleotide triphosphates (e.g., dATP, dGTP). When a nucleotide is added to the growing DNA strand, two phosphate groups are cleaved off, releasing energy which DNA polymerase uses to facilitate the bonding.
What is the origin of replication?
The origin of replication is a specific sequence in the DNA where replication begins. It is recognized by initiator proteins that bind to the DNA and start the unwinding process.
What role does helicase play in DNA synthesis?
Helicase is an enzyme that unwinds the double-stranded DNA by breaking the hydrogen bonds between the nucleotide bases, creating a replication fork.
What are single-stranded binding proteins?
Single-stranded binding proteins bind to the separated DNA strands during replication to prevent them from re-annealing and keep them stable.
What is formed at the replication fork?
The replication fork is the area where the double helix is unwound, allowing for the synthesis of complementary strands of DNA.
What occurs in a replication bubble?
A replication bubble forms when DNA unwinds and separates, creating two replication forks that move away from each other, allowing for simultaneous replication from both sides of the origin.
What is the role of RNA primase in DNA synthesis?
RNA primase synthesizes a short RNA primer that provides the starting point for DNA polymerase to begin DNA synthesis.
What are leading and lagging strands?
The leading strand is synthesized continuously in the same direction as the replication fork, while the lagging strand is synthesized discontinuously in the opposite direction, forming Okazaki fragments.
What are Okazaki fragments?
Okazaki fragments are short segments of DNA synthesized on the lagging strand during DNA replication, which are later joined together by DNA ligase.
What does DNA ligase do?
DNA ligase is an enzyme that joins Okazaki fragments together by sealing the nicks in the sugar-phosphate backbone.
What is the function of DNA polymerase in DNA synthesis?
DNA polymerase adds nucleotides complementary to the template strand during DNA synthesis, extending the growing DNA strand in the 5’ to
How did Meselson and Stahl prove which was the correct model of DNA synthesis?
Meselson and Stahl performed the famous 'semi-conservative' experiment using isotopes of nitrogen. They cultured bacteria in a medium containing heavy nitrogen (N-15) and then transferred them to a medium with lighter nitrogen (N-14). After each generation, they used density gradient centrifugation to separate the DNA based on density. The results showed that after one generation, the DNA had an intermediate density, and after two generations, there were light and intermediate density bands, confirming that DNA replication is semi-conservative.
What is the conservative model of DNA replication?
In the conservative model, the original double-stranded DNA molecule remains intact, and a completely new double-stranded DNA molecule is synthesized.
What is the semi-conservative model of DNA replication?
In the semi-conservative model, each of the two original strands serves as a template for new strands, resulting in two DNA molecules, each with one old strand and one new strand.
What is the dispersive model of DNA replication?
In the dispersive model, the original DNA strands are broken into segments, with each strand undergoing replication, resulting in strands that contain both parental and newly synthesized DNA interspersed.
How do the models differ in terms of DNA strand composition post-replication?
In the conservative model, one molecule is entirely new and the other is entirely old; in the semi-conservative model, each molecule consists of one old and one new strand; in the dispersive model, each strand has segments from both old and new DNA.
Which model was confirmed by the Meselson and Stahl experiment?
The semi-conservative model of DNA replication was confirmed by the Meselson and Stahl experiment.
What key experiment was conducted to disprove the conservative and dispersive models?
Meselson and Stahl's experiment using nitrogen isotopes demonstrated that after replication, DNA consisted of both old and new strands, supporting the semi-conservative model.
Explain what anti-parallel means in the context of DNA.
In the context of DNA, anti-parallel refers to the arrangement of the two strands that make up the double helix structure, where one strand runs in the 5' to 3' direction while the other runs in the opposite direction, from 3' to 5'. This orientation is crucial for the proper alignment of the nucleotide bases and allows DNA polymerase to synthesize new strands
What is meant by a complementary strand in DNA?
A complementary strand in DNA refers to the opposite strand that pairs with a specific strand during replication or synthesis, ensuring that the bases align correctly according to base pairing rules (adenine pairs with thymine, and guanine pairs with cytosine).
What does the term double helix signify?
The term double helix signifies the structural formation of DNA, which consists of two spiraled strands that are intertwined, resembling a twisted ladder.
Describe the structure of DNA.
DNA is a double helix composed of two long strands of nucleotides. Each nucleotide contains a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine). The strands are held together by hydrogen bonds between complementary bases (A-T and G-C) and connected by a sugar-phosphate backbone formed through phosphodiester bonds.
What are phosphodiester bonds?
Phosphodiester bonds are covalent bonds that link the phosphate group of one nucleotide to the sugar of the next nucleotide, forming the backbone of each DNA strand.
What are nucleotides composed of?
Nucleotides are the building blocks of DNA and RNA, composed of a phosphate group, a five-carbon sugar (deoxyribose in DNA), and one of four nitrogenous bases (adenine, thymine, cytosine, or guanine).
What is the role of hydrogen bonds in DNA structure?
Hydrogen bonds form between the nitrogenous bases of the two DNA strands, holding them together and stabilizing the double helix structure. There are two hydrogen bonds between adenine and thymine, and three between guanine and cytosine.
How are the 5’ and 3’ ends significant in DNA structure?
The 5’ end of a DNA strand has a phosphate group attached to the 5th carbon of the sugar, while the 3’ end has a hydroxyl (-OH) group attached to the
What did Frederick Griffith contribute to the discovery of DNA as genetic material?
Frederick Griffith demonstrated the phenomenon of bacterial transformation through his experiments with streptococcus pneumoniae, showing that a non-virulent strain could gain virulence by acquiring a 'transforming principle' from a heat-killed virulent strain, which was later identified as DNA.
How did P.A. Levene contribute to the understanding of DNA structure?
P.A. Levene discovered the structure of nucleotides, identifying the sugar, phosphate, and nitrogenous bases components, thereby laying the foundation for understanding DNA's composition and structure.
What is Chargaff's contribution to molecular biology?
Erwin Chargaff formulated Chargaff's rules, indicating that in DNA, the amount of adenine equals thymine (A=T) and the amount of guanine equals cytosine (G=C), providing key insights into base pairing and the structure of DNA.
What was the significance of the Hershey-Chase experiment?
The Hershey-Chase experiment used radioactively labeled phages to show that DNA, not protein, is the genetic material that is injected into bacterial cells, further confirming DNA's role in heredity.
How did Watson and Crick contribute to the DNA structure model?
James Watson and Francis Crick proposed the double helix structure of DNA based on X-ray diffraction data and Chargaff’s rules, illustrating how the two strands are complementary and anti-parallel.
What was Rosalind Franklin's role in the discovery of DNA?
Rosalind Franklin's X-ray diffraction images of DNA were crucial in revealing the helical structure and dimensions of DNA, which provided the evidence that helped Watson and Crick formulate
Describe the function and structure of bacteriophages.
Bacteriophages, or phages, are viruses that specifically infect bacteria. They consist of a protein coat called a capsid, which encloses their genetic material (either DNA or RNA). Phages attach to bacterial cells and inject their genetic material into the host, hijacking the bacterial machinery to replicate and produce new phages, often leading to the lysis (destruction) of the bacterial cell.
Explain how the Hershey and Chase experiment proved that DNA was the genetic material, rather than protein.
The Hershey and Chase experiment used radioactively labeled DNA and protein in bacteriophages. They found that only the radioactive DNA entered the bacterial cells and not the protein, demonstrating that DNA is the genetic material responsible for inheritance.
Note 
Flashcard (27)