Biology Chapter: DNA and RNA Structures

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Questions and Answers

Which of the following is NOT a type of RNA?

transfer RNA (tRNA)

protein RNA (pRNA) (correct)

ribosomal RNA (rRNA)

messenger RNA (mRNA)

What is the role of messenger RNA (mRNA) in protein synthesis?

mRNA helps to assemble amino acids into proteins.

mRNA carries genetic information from DNA to the ribosomes. (correct)

mRNA provides structural support for ribosomes.

mRNA carries amino acids to the ribosomes.

According to Chargaff's rules, which of the following base pairings is always true in DNA?

Adenine pairs with Guanine.

Guanine pairs with Uracil.

Adenine pairs with Thymine. (correct)

Cytosine pairs with Thymine.

What does the term 'transforming molecule' refer to in the context of DNA and inheritance?

A molecule that can change the physical characteristics of an organism. (B) Signup and view all the answers

What was the significance of Photo 51 in the discovery of DNA's structure?

Photo 51 revealed the double helix structure of DNA. (B) Signup and view all the answers

What is the function of the 3’→5’ exonuclease activity of DNA polymerase I?

To proofread the newly synthesized DNA (B) Signup and view all the answers

Which DNA polymerase activity is responsible for removing RNA primers?

DNA polymerase I 5’→3’ exonuclease activity (A) Signup and view all the answers

What is the role of DNA polymerase III in DNA replication?

Synthesizing DNA in the 5’→3’ direction (A) Signup and view all the answers

When does DNA polymerase I become involved in DNA replication?

When DNA polymerase III encounters an RNA primer (D) Signup and view all the answers

Which of the following activities is NOT present in DNA polymerase III?

5’→3’ exonuclease activity (C) Signup and view all the answers

Which of the following statements regarding DNA polymerase I is TRUE?

It is essential for the removal of RNA primers. (A) Signup and view all the answers

How does the 3’→5’ exonuclease activity of DNA polymerase I contribute to the accuracy of DNA replication?

By removing incorrectly incorporated nucleotides (D) Signup and view all the answers

What is the primary function of DNA polymerase III's 3' to 5' exonuclease activity?

To proofread the newly synthesized DNA strand, removing any mismatched nucleotides. (A) Signup and view all the answers

Which of the following scenarios best illustrates the concept of "proofreading" during DNA replication?

The DNA polymerase III removing a mismatched nucleotide and replacing it with the correct one. (A) Signup and view all the answers

What is the purpose of the 5'→3' exonuclease activity of DNA polymerase I?

To remove RNA primers from the lagging strand (A) Signup and view all the answers

Which of the following enzymes is responsible for joining the two stretches of DNA synthesized by DNA polymerase III and DNA polymerase I?

DNA ligase (D) Signup and view all the answers

What is the primary function of nucleotide analogues in DNA replication?

To block DNA replication by interfering with the process of nucleotide addition. (C) Signup and view all the answers

How does the 5'→3' exonuclease activity differ from the 3'→5' exonuclease activity?

The 5'→3' exonuclease activity is used only by DNA polymerase I, while the 3'→5' exonuclease activity is used by both DNA polymerase I and DNA polymerase III. (C) Signup and view all the answers

What is the consequence of misreading the template sequence during DNA replication?

Deleterious mutations may be introduced in the DNA sequence. (D) Signup and view all the answers

What is the function of DNA polymerase α?

To lay down primers on the lagging strand (A) Signup and view all the answers

Which of the following best describes the function of DNA helicase in DNA replication?

To unwind the DNA double helix, separating the two strands. (C) Signup and view all the answers

What is the main reason why it is crucial for the survival of an organism that DNA replication is highly accurate?

To minimize the risk of introducing mutations that could lead to disease or dysfunction. (A) Signup and view all the answers

Which of the following statements about DNA polymerase III is TRUE?

It is responsible for the majority of DNA synthesis on the leading strand. (D) Signup and view all the answers

What is the source of energy used for joining the two DNA fragments synthesized by DNA polymerase III and DNA polymerase I?

ATP hydrolysis to AMP and PPi (A) Signup and view all the answers

Why is the leading strand synthesized continuously while the lagging strand is synthesized discontinuously?

DNA polymerase III can only add nucleotides to the 3’ end of the growing strand, and the strands run in opposite directions. (C) Signup and view all the answers

What is the role of DNA polymerase Β?

To proofread and repair DNA (B) Signup and view all the answers

What is the role of Okazaki fragments in DNA replication?

They are short segments of DNA synthesized on the lagging strand. (C) Signup and view all the answers

Which DNA polymerase is unique to mitochondria?

DNA polymerase Υ (D) Signup and view all the answers

What is the function of the type I DNA topoisomerase enzyme?

To unwind the DNA helix by breaking and resealing a single strand of DNA, without requiring ATP. (B) Signup and view all the answers

Which of the following describes the orientation of the two newly synthesized nucleotide chains during DNA replication?

One grows in the 5' → 3' direction towards the replication fork, and the other grows in the 5' → 3' direction away from the replication fork. (D) Signup and view all the answers

What is the role of the SSB (single-stranded binding) protein in DNA replication?

It prevents the single-stranded DNA from re-forming a double helix, keeping the strands separated. (B) Signup and view all the answers

Which enzyme is responsible for adding nucleotides to the growing DNA strand during replication?

DNA polymerase III (D) Signup and view all the answers

How does type II DNA topoisomerase (DNA gyrase) contribute to DNA replication?

It removes supercoils in the DNA, making it easier to unwind. (D) Signup and view all the answers

Which of the following enzymes is involved in the removal of RNA primers from the newly synthesized DNA strand?

DNA polymerase I (A) Signup and view all the answers

During DNA replication, how do the two new DNA strands differ in their synthesis?

One strand is synthesized continuously, while the other is synthesized discontinuously in short fragments. (A) Signup and view all the answers

What is the primary role of the enzyme primase in DNA replication?

To synthesize short RNA primers that provide a starting point for DNA polymerase. (A) Signup and view all the answers

What is the primary function of helix destabilizing proteins (HD proteins) during DNA replication?

To unwind the DNA helix ahead of the replication fork. (C) Signup and view all the answers

Which of the following is NOT a characteristic of helix destabilizing proteins (HD proteins)?

They are enzymes that catalyze DNA unwinding. (D) Signup and view all the answers

Why is the separation of parental strands necessary for DNA replication?

To provide a template for DNA polymerases. (C) Signup and view all the answers

What is the role of single-stranded DNA binding proteins (SSB) in DNA replication?

They help to keep the separated strands of DNA from re-annealing. (A) Signup and view all the answers

How do HD proteins (SSB) shift the equilibrium of DNA towards single-stranded DNA?

They bind cooperatively to the DNA helix, destabilizing it. (D) Signup and view all the answers

Which of the following would most likely be the consequence of a deficiency in HD proteins?

Increased susceptibility to DNA damage. (B) Signup and view all the answers

What is the significance of the 'V'-shaped region formed during DNA replication?

It is the site where the two strands of DNA separate. (A) Signup and view all the answers

What is the role of DNA topoisomerases in DNA replication?

To prevent the formation of supercoils in the DNA helix. (B) Signup and view all the answers

Study Notes

DNA Structure and Function

DNA is a double helix, formed by two strands running antiparallel.
The strands are held together by hydrogen bonds between base pairs (A-T, C-G).
The diameter of the helix is consistent at 20 angstroms.
The bases are stacked 3.4 angstroms apart along the axis.
The helix completes one turn every 34 angstroms.

RNA Structure and Function

RNA is a single-stranded molecule.
It differs structurally from DNA by having a ribose sugar instead of deoxyribose.
Uracil replaces thymine as a base in RNA.
Involved in protein synthesis (mRNA), ribosomal structure (rRNA), and transportation of amino acids (tRNA)

Erwin Chargaff's Rules

The percentage of adenine equals the percentage of thymine in DNA.
The percentage of guanine equals the percentage of cytosine in DNA.
The percentages of A/T and G/C bases vary among species.

Oswald Avery

Discovered that DNA is the genetic material

DNA Replication

DNA replication is semiconservative, meaning each new DNA molecule contains one original strand and one newly synthesized strand.
Enzymes like Helicase unwind the DNA double helix, creating replication forks.
DNA polymerase III synthesizes new DNA strands using the existing strands as templates.
Leading strand is synthesized continuously while lagging strand is synthesized in short fragments (Okazaki fragments).
DNA polymerase I removes RNA primers and replaces them with DNA.
DNA ligase joins the Okazaki fragments together.

DNA Replication Proteins

Helicase unwinds the DNA double helix
Single-stranded binding proteins (SSBs) stabilize the unwound strands.
Topoisomerases relieve the tension ahead of the replication fork.
DNA polymerase III synthesizes new DNA strands.
DNA polymerase I removes RNA primers and replaces them with DNA.
DNA ligase joins Okazaki fragments.

DNA Replication Steps

Strand separation
Primer formation
Chain elongation
Excision
Joining

DNA Polymerases

DNA polymerase III is the main enzyme responsible for DNA synthesis during replication
DNA polymerase I replaces the RNA primers with DNA.
DNA polymerase has a proofreading mechanism to reduce replication errors.
Different types of DNA polymerases exist in eukaryotes.

RNA Primer

RNA primer is a short RNA sequence that DNA polymerase uses as a starting point for DNA synthesis.

Chain elongation

DNA chain elongation involves the addition of nucleotides to the growing DNA chain by DNA polymerase.

Excision

Excision involves the removal and replacement of RNA primers with DNA.

Ligase

Ligase joins the Okazaki fragments together.

DNA Topoisomerases

DNA topoisomerases resolve the knots and tangles in the DNA molecule during DNA replication.

Types of DNA Topoisomerases

Type I topoisomerases: break and rejoin one of the two DNA strands.
Type II topoisomerases (DNA gyrase): breaks and rejoins both DNA strands.

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Description

Explore the fundamental concepts of DNA and RNA structures, including their unique properties and functions. This quiz covers essential topics such as Chargaff's rules and the discovery of DNA as genetic material by Oswald Avery. Test your understanding of these crucial biomolecules and their roles in genetics.