Biology Chapter on Nucleotides and DNA Structure

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Questions and Answers

What are the components of a nucleotide?

A nitrogenous base, ribose sugar, and a lipid

A nitrogenous base, a phosphate group, and deoxyribose sugar (correct)

Phosphate group, ribose sugar, and amino acids

Amino acids, a nitrogenous base, and deoxyribose sugar

Chargaff's rule indicates that the amount of which nitrogenous bases are equal?

Adenine and guanine

Adenine and thymine, cytosine and guanine (correct)

Cytosine and thymine

Guanine and thymine

Which scientist is associated with the discovery of the helical structure of DNA using X-ray diffraction?

Erwin Chargaff

Rosalind Franklin (correct)

James Watson

Linus Pauling

What is the structural organization of eukaryotic DNA?

Linear DNA organized into nucleosomes Signup and view all the answers

In prokaryotic cells, what is the function of topoisomerases?

To unwind and supercoil DNA Signup and view all the answers

What is the primary characteristic of plasmids in prokaryotic cells?

They often carry non-essential genes. Signup and view all the answers

Which of the following describes the genome of most prokaryotes?

They are haploid with one set of chromosomes. Signup and view all the answers

What role do regulatory sequences play in prokaryotic genomes?

They determine when certain genes are activated. Signup and view all the answers

What is the primary function of telomeres in eukaryotic chromosomes?

To protect chromosome ends from nucleases Signup and view all the answers

Which model of DNA replication was confirmed by the experiments conducted by Meselson and Stahl?

Semi-conservative model Signup and view all the answers

During DNA replication, which type of enzyme is primarily responsible for unwinding the DNA double helix?

Helicase Signup and view all the answers

What is a nucleosome in the context of eukaryotic DNA organization?

A structure formed when DNA wraps around histones Signup and view all the answers

What initiates the unwinding process during DNA replication?

Initiator proteins Signup and view all the answers

What type of DNA replication occurs in prokaryotic cells?

Single, circular and bidirectional Signup and view all the answers

Which component is NOT essential for DNA replication in prokaryotic cells?

Histones Signup and view all the answers

What is formed at each end of the replication bubble during DNA replication?

Replication fork Signup and view all the answers

What initiates the process of transcription in protein synthesis?

The promoter region (TATA box) Signup and view all the answers

During RNA processing, what happens to introns?

They are spliced out by spliceosomes Signup and view all the answers

Which of the following uses DNA fingerprinting techniques?

Forensics Signup and view all the answers

What is the role of elongation factors in translation?

To facilitate H-bonding between mRNA codons and tRNA anticodons Signup and view all the answers

What is a major benefit of using PCR in molecular biology?

It can amplify specific DNA segments rapidly Signup and view all the answers

Which of the following diseases can be diagnosed using PCR technology?

Cystic fibrosis Signup and view all the answers

What signifies the termination of translation?

The binding of a release factor to a stop codon Signup and view all the answers

Which component is essential for the initiation of translation?

Small and large ribosomal subunits along with mRNA Signup and view all the answers

In which application are transgenic organisms known for their ability to resist pests and diseases commonly used?

Agricultural biotechnology Signup and view all the answers

What is the primary function of RNA polymerase during transcription?

To separate DNA strands and link RNA nucleotides Signup and view all the answers

Which genetic engineering approach is used for extracting heavy metals from the environment?

Bioremediation Signup and view all the answers

What cellular location do mature RNA molecules enter after processing?

Cytoplasm Signup and view all the answers

Which of the following is NOT a function of DNA technology in medicine?

Direct coding of RNA into protein Signup and view all the answers

What distinguishes the leading strand during DNA replication?

It is synthesized continuously in the 5′ to 3′ direction. Signup and view all the answers

What role does primase play in DNA replication?

It provides an RNA primer for DNA polymerase. Signup and view all the answers

During DNA replication, which event occurs at the termination stage?

The newly synthesized DNA strands separate. Signup and view all the answers

What is the approximate error rate during human DNA replication?

1 in 1 billion Signup and view all the answers

What are Okazaki fragments?

Short segments synthesized away from the replication fork. Signup and view all the answers

Which proteins are involved in mismatch repair during DNA replication?

A group of proteins that identify and fix deformities. Signup and view all the answers

What defines the genetic code in DNA?

A triplet of bases controls the production of a specific amino acid. Signup and view all the answers

What does the central dogma of genetics describe?

The flow of genetic information from DNA to RNA to protein. Signup and view all the answers

Study Notes

Nucleotide Structure

Nucleotides consist of a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).

Chargaff’s Rule

Erwin Chargaff discovered that adenine equals thymine and cytosine equals guanine, demonstrating equal proportions of purines (A and G) and pyrimidines (C and T).

DNA Structure Contributions

Linus Pauling identified helical structures in proteins in 1951.
Rosalind Franklin and Maurice Wilkins used X-ray diffraction to reveal DNA’s helical structure with nitrogen bases inside and a sugar-phosphate backbone outside.
James Watson and Francis Crick proposed the double helix structure of DNA in 1953, featuring antiparallel complementary strands.

Genetic Material Organization

Genes are specific DNA sequences coding for proteins and RNA molecules.
Most of an organism's genome consists of non-coding regions.
Prokaryotic cells, such as Escherichia coli, have a circular, double-stranded DNA chromosome that is tightly packed.
Eukaryotic cells have linear, double-stranded DNA organized with histones into nucleosomes.

Prokaryotic DNA

E. coli contains a circular DNA molecule that has to be tightly packed within the nucleoid through coiling and supercoiling.
DNA supercoiling is controlled by topoisomerase I and II enzymes.
Prokaryotes may contain plasmids, small DNA molecules with non-essential genes.
Prokaryotic genomes primarily consist of gene regions and regulatory sequences that activate certain genes.

Eukaryotic DNA

Eukaryotic cells bear double-stranded linear DNA compacted in the nucleus, involving various levels of organization with histones forming nucleosomes.
Telomeres at chromosome ends protect against degradation.

DNA Replication

Involves producing two identical DNA molecules during the cell cycle.
Proposed models include semi-conservative, conservative, and dispersive.
Meselson and Stahl used density gradient centrifugation to support the semi-conservative model, demonstrating DNA strands containing one old and one new strand.

Prokaryotic Replication

Occurs with a single circular DNA and begins at one origin, proceeding bidirectionally.
Replication involves initiator proteins and helicase to unwind DNA, forming replication forks.

Steps of DNA Replication

Initiation: Unwinding starts at the origin, with helicase breaking hydrogen bonds.
Elongation (Leading Strand): DNA polymerase III builds a complementary strand in the 5′ to 3′ direction.
Elongation (Lagging Strand): Synthesized in short Okazaki fragments; requires RNA primers and involves DNA polymerase III.
Termination: Completion of new DNA strands leads to separation and dismantling of replication machinery.

Errors in DNA Replication

Human cells replicate DNA quickly (error rate ~1 in 1 billion).
Errors can lead to mutations from base mispairing or strand slippage.

Error Correction during Replication

DNA polymerase I and II possess proofreading abilities to correct errors.
Mismatch repair proteins address deformities in newly synthesized DNA.

Genetic Code

DNA base sequences dictate the genetic code, with triplet sequences coding for specific amino acids.
The sequence of amino acids determines protein structure.

Central Dogma of Genetics

Genetic information flows from DNA to RNA to protein; this flow is one-directional and irreversible.

Protein Synthesis

Entails transcription, RNA processing, and translation.

Transcription Process

RNA strands are synthesized from DNA templates at the promoter and terminator regions.
RNA polymerase links nucleotides into RNA after unwinding DNA.

RNA Processing

Pre-RNA molecules undergo splicing to remove introns, allowing mature RNA to exit the nucleus.

Translation

Initiation: Links mRNA, tRNA, and ribosomal subunits; initiator tRNA attaches at the start codon.
Elongation: Involves sequential addition of amino acids.
Termination: Triggered by stop codons, releasing polypeptide and ribosomal complex.

Applications of DNA Technology

Medicine: Diagnosis of diseases, gene therapy for conditions like heart disease and cancer, production of pharmaceuticals.
Forensics: DNA fingerprinting with simple tandem repeats; analysis of variable genome regions.
Environmental: Genetically engineered organisms for waste treatment and pollution cleanup.
Agricultural: Transgenic organisms for enhanced productivity and disease resistance.

Polymerase Chain Reaction (PCR)

Amplifies specific DNA segments, producing billions of copies quickly.
Essential in genetic testing for conditions such as Huntington's, cystic fibrosis, and HIV.

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Description

Explore the foundational concepts of nucleotides, including their structure and the critical contributions of scientists like Erwin Chargaff and Linus Pauling to our understanding of DNA. This quiz will help reinforce your knowledge of the nitrogenous bases, sugar components, and the rules governing base pairing. Test your comprehension of these essential elements of molecular biology.