Case 2a

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Questions and Answers

What is the primary function of DNA?

To produce energy for the cell

To provide structural support to organelles

To protect the cell from external damage

To contain biological instructions for species (correct)

Which bases are considered purines in DNA?

Adenine and Cytosine

Adenine and Guanine (correct)

Cytosine and Thymine

Thymine and Uracil

How is the structure of DNA characterized?

Double-stranded helix with complementary bases (correct)

Single-stranded with a simple backbone

Single helix allowing easy access to bases

Linear molecule without hydrogen bonds

What type of bond connects the bases in DNA?

Hydrogen bonds Signup and view all the answers

What is supercoiling in DNA?

A form of twisting that organizes DNA Signup and view all the answers

Which pairing of bases in DNA is held together by two hydrogen bonds?

Adenine and Thymine Signup and view all the answers

How many base pairs are approximately present in each turn of the DNA helix?

10.4 base pairs Signup and view all the answers

What role do histones play in DNA structure?

They provide structural support by forming fibers Signup and view all the answers

What type of proteins are H2A and H2B classified as?

Core histone proteins Signup and view all the answers

How many base pairs typically occur per turn of the DNA helix?

10.4 Signup and view all the answers

What is the role of H1 in nucleosomes?

Stabilizes wrapped DNA around core histones Signup and view all the answers

What term describes the twisting of DNA that occurs when it is overwound?

Positive supertwist Signup and view all the answers

Which type of topoisomerase cleaves one strand of the DNA double helix?

Type I topoisomerase Signup and view all the answers

What primary structural feature distinguishes eukaryotic DNA from prokaryotic DNA?

Presence of histones Signup and view all the answers

Which of the following describes the conditions that lead to negative supertwisting?

Underwound condition Signup and view all the answers

In the context of DNA supercoiling, what is predominantly observed in prokaryotes?

Plectonemic supercoils Signup and view all the answers

What characteristic is unique to prokaryotic cells compared to eukaryotic cells?

Circular DNA Signup and view all the answers

What is the function of silencers in genetic regulation?

Reduce transcription from target promoters Signup and view all the answers

Which of the following statements is true regarding mitochondrial DNA?

Each mitochondrion has multiple genomes Signup and view all the answers

Which enzyme is primarily responsible for the assembly of new DNA segments during replication?

DNA polymerase Signup and view all the answers

What is the primary role of a TATA box in a gene sequence?

Indicate the site of transcription initiation Signup and view all the answers

What type of ploidy is commonly found in prokaryotic organisms?

Haploid Signup and view all the answers

During DNA replication, what is the first major step involved?

Separation of DNA strands Signup and view all the answers

Which of the following accurately describes ribosomes found in prokaryotes?

70S ribosomes Signup and view all the answers

What role do initiator proteins play in DNA replication?

They unwind the double helix and bind to origins of replication. Signup and view all the answers

How does helicase contribute to DNA replication?

It unwinds the DNA by breaking hydrogen bonds. Signup and view all the answers

What is the directionality of DNA polymerase during replication?

5' to 3' for assembling new strands and reading the template in the opposite direction. Signup and view all the answers

What is the primary function of DNA polymerase I in prokaryotes?

It removes RNA primers and fills in the gaps with DNA. Signup and view all the answers

Which statement about DNA polymerase III is true?

It is the major enzyme for DNA replication in E. coli. Signup and view all the answers

What advantage does the 3'-exonuclease activity of DNA polymerase III provide?

It improves the accuracy of DNA replication by proofreading. Signup and view all the answers

What type of bonds do nucleases cleave in nucleic acids?

Phosphodiester bonds in nucleic acids. Signup and view all the answers

What initial structure forms as DNA unwinds during replication?

The replication fork. Signup and view all the answers

What is the primary role of exonucleases?

Removing nucleotides from the ends of DNA strands Signup and view all the answers

How does DNA polymerase III proofread its newly synthesized DNA?

By removing incorrectly paired nucleotides with its 3′-exonuclease activity Signup and view all the answers

Why is the synthesis of the lagging strand discontinuous?

Because it requires repeated synthesis of Okazaki fragments Signup and view all the answers

What is the function of RNA primers in DNA replication?

To initiate the synthesis of new DNA strands Signup and view all the answers

How is energy derived for the action of DNA ligase in bacteria?

From the cleavage of phosphoanhydride bonds in NAD Signup and view all the answers

What structure is responsible for linking the phosphorylated 5′ terminus of one Okazaki fragment to the free 3′ terminus of another?

DNA ligase Signup and view all the answers

What type of supercoiling occurs in front of the helicase during DNA replication?

Positive supercoiling Signup and view all the answers

Which site on DNA polymerase III is responsible for polymerase activity?

P site Signup and view all the answers

Study Notes

DNA Function

DNA contains the genetic instructions for an organism, determining traits and functions.
DNA is passed down from parent to offspring.
The sequence of DNA bases forms genes, responsible for protein synthesis.

DNA Structure

DNA structure consists of a double helix with two antiparallel strands.
The backbone of each strand is composed of alternating phosphate and deoxyribose sugar molecules linked by phosphodiester bonds.
The four bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T).
A pairs with T, while G pairs with C through hydrogen bonds.
The double helix has two grooves, a major groove and a minor groove.

DNA Supercoiling

Supercoiling is a process that compacts DNA.
Negative supercoiling is predominant in most cellular DNA, making it easier to unwind.
Topoisomerases regulate supercoiling, Type I relaxes negative supercoiling, and Type II relaxes positive supercoiling.

DNA Replication

DNA replication is a semi-conservative process.
DNA replication involves three major steps: unwinding of the double helix, priming, and assembly of a new DNA segment.
The process is initiated by initiator proteins binding to origin of replication, followed by helicase unwinding the DNA.
DNA primase adds RNA primers to initiate new DNA synthesis.
DNA polymerase III synthesizes new DNA strands in the 5' to 3' direction.
DNA polymerase III has exonuclease activity for proofreading.
Leading strand is synthesized continuously, while the lagging strand is synthesized in fragments called Okazaki fragments.
DNA ligase joins Okazaki fragments together.

Eukaryotic DNA

Eukaryotic DNA is packaged around histone proteins to form nucleosomes.
Nucleosomes are further compacted into 30nm fibers and then higher-order structures.
Non-histone proteins assist in further compaction.

Prokaryotic DNA

Prokaryotes have a single circular chromosome.
Prokaryotic DNA is less complex than eukaryotic DNA.

Mitochondrial DNA

Mitochondria contain their own DNA, separate from the nuclear DNA.
Mitochondrial DNA is circular and relatively small, encoding for specific proteins.
Each mitochondrion contains 5-10 copies of its own genome.

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Description

Explore the intricate details of DNA's function, structure, supercoiling, and replication. Learn about how genetic information is stored and transmitted across generations. This quiz covers key concepts like the double helix formation and base pairing, along with the regulatory mechanisms involved in DNA supercoiling.