Molecular Biology: Chromosomes and DNA Structure

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Questions and Answers

What are the thread-like structures that package DNA in the nucleus of a cell called?

Genes

Nucleotides

Chromosomes (correct)

Histones

What is the role of histones in the structure of chromosomes?

To transport proteins

To replicate DNA

To help package DNA (correct)

To provide energy for cell division

How is DNA organized within chromosomes?

Coiled around proteins (correct)

As independent strands

Loosely arranged

In circular form

Which of the following statements is true regarding chromosomes?

Chromosomes provide structural support for DNA. Signup and view all the answers

What structural component is essential for maintaining the integrity of chromosomes?

Histones Signup and view all the answers

What is one aspect that can lead to changes in genetic material?

Chemical alterations to the DNA Signup and view all the answers

Which process involves proteins binding to DNA elements to regulate another biological process?

Transcription regulation Signup and view all the answers

What is a mechanism that can influence how mRNA is used in cells?

Modulation of mRNA translation Signup and view all the answers

Which of the following changes can affect transcription activity?

Binding of proteins to DNA elements Signup and view all the answers

What type of change to genetic material can involve both structural and chemical modifications?

Both structural and chemical changes Signup and view all the answers

What is the function of stop codons in protein synthesis?

They terminate protein synthesis. Signup and view all the answers

How many stop codons are there among the total codons?

Three Signup and view all the answers

What is true about most amino acids in terms of codon encoding?

Most amino acids can be encoded by multiple codons. Signup and view all the answers

What term is given to the triplets that terminate protein synthesis?

Stop codons Signup and view all the answers

Which of the following best describes the role of codons in translation?

They match with tRNA to incorporate amino acids into proteins. Signup and view all the answers

What is the primary role of the fifth subunit, σ, in transcription?

It is involved only in transcription initiation. Signup and view all the answers

How does σ confer transcriptional specificity?

By directing the polymerase to an appropriate initiation site. Signup and view all the answers

Which of the following statements is incorrect regarding the σ subunit?

The σ subunit only functions during mRNA elongation. Signup and view all the answers

What happens if the σ subunit is absent during the transcription process?

mRNA synthesis will begin at random sites. Signup and view all the answers

Which best describes the importance of the σ subunit in transcription?

It enables specificity in the binding of RNA polymerase to DNA. Signup and view all the answers

What is the primary objective of the polymerase chain reaction (PCR)?

To replicate a double-stranded DNA template Signup and view all the answers

Which component is NOT included in the PCR reaction mixture?

Ribonucleic acid (RNA) Signup and view all the answers

What is the role of primers in the polymerase chain reaction?

To bind to specific sequences on the DNA template Signup and view all the answers

In a PCR reaction, what is the function of Taq polymerase?

To synthesize new DNA strands from the template Signup and view all the answers

Why are deoxyribonucleoside triphosphates (dNTPs) included in excess during PCR?

To ensure adequate supplies for DNA strand synthesis Signup and view all the answers

What is the primary advantage of using Thermus aquaticus DNA polymerase in laboratory settings?

It can withstand high temperatures above 100°C. Signup and view all the answers

Which environment does Thermus aquaticus predominantly inhabit?

Hot springs Signup and view all the answers

What characteristic of Thermus aquaticus helps it maintain function at high temperatures?

The structure of its DNA polymerase Signup and view all the answers

What type of organism is Thermus aquaticus?

An extremophilic bacterium Signup and view all the answers

Which temperature does Thermus aquaticus DNA polymerase resist?

Higher than 100°C Signup and view all the answers

Study Notes

DNA Technology

DNA Technology is a broad field encompassing various techniques for manipulating and analyzing DNA.
The course content includes DNA structure, the Central Dogma, PCR, cloning, genomic and cDNA libraries, and DNA sequencing.
Lecture 1 content covers the reasons for studying DNA, DNA and RNA structure, RNA types, the Central Dogma, and DNA replication.
Key motivations for studying DNA involve disease treatments, better food crops, forensics, and genetic enhancement.

DNA: The Genetic Material

Griffith experiment (1928) was a pivotal experiment in discovering DNA as the genetic material. It used Streptococcus pneumoniae bacteria to demonstrate the transfer of genetic material.
Avery-MacLeod-McCarty experiment (1944) further solidified the idea that DNA is the genetic material. It showed that DNA, but not proteins or RNA, is responsible for transformation.
Hershey-Chase experiment (1952) confirmed that DNA is the genetic material by using bacteriophages.

Avery-MacLeod-McCarty experiment 1944

This experiment determined that DNA is the hereditary material.
Lipids and carbohydrates were removed from a solution of heat-killed S cells.
Treatments involved enzymes to destroy proteins, RNA or DNA.
A small portion of the sample was added to a culture containing R cells.
Transformation occurred based on whether virulent S cells appeared.
The conclusion was that transformation cannot occur unless DNA is present and consequently DNA must be the hereditary material

Hershey-Chase experiment 1952

Used radioactive labeling to trace DNA and protein.
Concluded that viral DNA was injected into the cell, providing the genetic information needed for new viruses.

Watson and Crick model 1953

Built a model of the double helix, a twisted ladder.
Two outside strands consist of alternating deoxyribose and phosphate.
Cytosine and guanine pair by three hydrogen bonds, while thymine and adenine pair by two hydrogen bonds.

Nucleic acid structure

Nucleotides are the fundamental building blocks of nucleic acids.
They consist of a nucleoside (pentose and nitrogenous base) and a phosphate group.
DNA contains deoxyribose, while RNA contains ribose.
Nitrogenous bases include purines (adenine, guanine) and pyrimidines (cytosine, thymine, and uracil).
Phosphates link nucleotides in nucleic acids, conferring a negative charge.
N-glycosidic linkage connects the sugar and base in a nucleotide.

Phosphodiester bond

A phosphodiester bond links nucleotides in a nucleic acid.
A reaction with water (hydrolysis) removes a phosphate group to break the bond.

DNA Replication

DNA replication is a process by which DNA makes a copy of itself.
The process involves identifying replication origins, unwinding the dsDNA, forming replication forks, initiating DNA synthesis and elongation, forming replication bubbles, and reconstituting chromatin structure.
Enzymes like DNA polymerase, helicase, and ligase are crucial.

Classes of proteins involved in replication

Different proteins are involved, each having specific roles.

Types of RNA

mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA) are major types of RNA.
Other types include non-coding RNAs (ncRNAs) like lncRNAs (long non-coding RNAs), miRNAs (microRNAs), and piRNAs (piRNAs).
Various ncRNAs have regulatory roles.

Central Dogma: DNA to RNA to Protein

The central dogma describes the flow of genetic information from DNA to RNA to protein.
This process includes replication, transcription, and translation.

DNA Cloning

Cloning involves producing exact copies of a gene or DNA sequence.
Cloning vectors are used to carry DNA fragments into host organisms for replication.
Recombinant DNA is created by combining DNA fragments from different sources (often including a bacterial plasmid and gene of interest). Vectors carry the desired genetic material to be copied.

Cloning Vectors

Cloning vectors are DNA molecules that transport cloned sequences between bacterial hosts and a test tube.
They provide an origin of replication, a selectable marker, and multiple cloning sites.
Types of vectors include bacterial plasmids, bacteriophages, cosmids, BACs, and YACs.

Significance of DNA Cloning

DNA cloning is crucial in isolating genes, determining their sequences, analyzing mutations, investigating protein/RNA/DNA function, and modifying organisms for specific applications.

Recombinant Bacteria Screening

This stage selects bacteria containing the recombinant DNA.
There are techniques like blue-white screening or PCR screening to identify successful cloning.

PCR

Polymerase Chain Reaction (PCR) is a technique that amplifies a specific DNA fragment.
It involves cycles of denaturation, annealing, and elongation.

Real-Time qPCR and COVID-19

Applications include gene expression analysis.
Real-time PCR assesses the amplification progress in real-time.
Real-time PCR is important in detecting diseases like COVID-19.
Different types of PCR, such as reverse transcriptase, multiple PCR, and real-time PCR, are applicable to various scenarios.

Probes

Probes detect specific DNA or RNA sequences.
Techniques include gel electrophoresis for separating target sequences from a DNA sample and subsequent visualization by staining.

Sanger Sequencing

One method of determining DNA molecule nucleotide sequence.
Uses dideoxyribonucleotides to terminate DNA polymerization at specific bases providing differing fragments for analysis.
Electrophoresis, then visualization/analysis to ascertain the order of nucleotides.

Maxam-Gilbert Sequencing

Another method of determining DNA molecule nucleotide sequence.
Uses chemical treatments that react selectively with specific nucleotides, ultimately creating fragments that can be analyzed for the order of nucleotides.

General

The use of various techniques allows for amplification (duplication) of desired DNA sequences and the identification of specific sequences.
DNA technology is widely applicable to diverse areas.

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Description

Test your knowledge on the structure and function of chromosomes and DNA in the nucleus. This quiz covers important concepts like histones, transcription activity, and the role of stop codons in protein synthesis. Perfect for students studying molecular biology or genetics.