Molecular Biology of DNA Structure

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What type of bond is responsible for linking the 3'-hydroxyl group of one sugar to the 5'-phosphate group of the next in a DNA strand?

Hydrogen bond

Phosphodiester bond (correct)

Ionic bond

Van der Waals interaction

Which of the following statements accurately describes the orientation of the two DNA strands in a double helix?

They are twisted around each other in a random orientation.

They are antiparallel and run in opposite directions. (correct)

They are parallel and run in the same direction.

They are perpendicular to each other.

What is the primary force that holds the two strands of a DNA double helix together?

Hydrogen bonds between complementary bases (correct)

Hydrophobic interactions between the sugar-phosphate backbones

Covalent bonds between the nucleotides

Electrostatic interactions between the phosphate groups

The polarity of a DNA strand is determined by the orientation of its __________.

sugar-phosphate backbone (B) Signup and view all the answers

Which of the following base pairs is NOT found in DNA?

G-U (B) Signup and view all the answers

Which of the following statements accurately describes the relationship between gene number, chromosome number, and total genome size?

There is no simple relationship between gene number, chromosome number, and total genome size. (A) Signup and view all the answers

What is the approximate percentage of the human genome that consists of protein-coding exons?

Less than 1% (C) Signup and view all the answers

Which of the following is NOT a type of repetitive nucleotide sequence found in the human genome?

Telomeres (D) Signup and view all the answers

What percentage of the human genome consists of unique sequences that are not part of introns or exons?

Around 50% (D) Signup and view all the answers

What is the primary function of regulatory DNA sequences?

Controlling gene expression (A) Signup and view all the answers

What is the best explanation for the observation that closely related species can have vastly different chromosome numbers?

Chromosomal rearrangements over evolutionary time (D) Signup and view all the answers

Which of the following is NOT a component of heterochromatin?

Protein-coding genes (D) Signup and view all the answers

The human genome was first completely sequenced In:

2021 (C) Signup and view all the answers

What is the primary reason why some individuals can digest milk into adulthood, while others cannot?

Mutations in the gene responsible for lactase production. (A) Signup and view all the answers

Domestication of cattle has had a significant impact on human evolution. What is the most direct connection between cattle domestication and the ability to digest lactose in adulthood?

Cattle domestication led to increased consumption of milk, creating a selective pressure for lactase persistence. (B) Signup and view all the answers

What is the relationship between the human genome and the ability to digest lactose into adulthood?

The human genome contains a gene that regulates the expression of lactase, and mutations in this regulatory gene can influence lactose tolerance. (A) Signup and view all the answers

What is the significance of the fact that the genetic variation for lactase persistence is found in populations that historically had access to domesticated cattle?

It suggests that the human genome is constantly evolving in response to changing environmental conditions. (D) Signup and view all the answers

The example of lactase persistence illustrates a concept that is central to human evolution. What is this concept?

Humans are constantly evolving to adapt to new environments and dietary changes. (B) Signup and view all the answers

How are human chromosomes distinguished from one another?

They come in different sizes and have unique molecular markers. (D) Signup and view all the answers

What is the primary function of a chromosome?

To carry genes. (D) Signup and view all the answers

What is a gene?

A segment of DNA that codes for a specific protein. (D) Signup and view all the answers

What is the difference between a genome and a gene?

A genome is the total genetic information in an organism, while a gene is a segment of DNA that codes for a protein. (C) Signup and view all the answers

What is the main reason for the difference in genome size between bacteria and humans?

Humans have more noncoding DNA than bacteria. (B) Signup and view all the answers

How is the human genome different from the genome of Saccharomyces cerevisiae?

All of the above. (D) Signup and view all the answers

What are the three techniques mentioned for distinguishing human chromosomes?

Karyotyping, SKY, and FISH. (C) Signup and view all the answers

Why is it important to study the organization and function of chromosomes?

All of the above. (D) Signup and view all the answers

What does the abbreviation 'ORF' stand for in the context of identifying protein-coding genes?

Open Reading Frame (A) Signup and view all the answers

What is the significance of a sequence exceeding 10,000 codons without encountering a stop codon for an ORF?

It suggests the sequence is highly likely to encode a protein. (C) Signup and view all the answers

What is the approximate percentage of the population that needs to have a single-nucleotide change for it to be considered a 'single-nucleotide polymorphism' (SNP)?

1% (C) Signup and view all the answers

How many possible reading frames exist for a given DNA sequence?

3 (B) Signup and view all the answers

What is the specific start signal for translation in cells?

AUG (A) Signup and view all the answers

What is the primary purpose of using oligo(dT) primers in mRNA purification?

To bind to the poly(A) tail of mRNA molecules (C) Signup and view all the answers

What is the role of reverse transcriptase (RT) in the process of converting mRNA to cDNA?

It synthesizes a complementary DNA strand from the mRNA template (A) Signup and view all the answers

What makes identifying protein-coding genes in genomic sequence challenging for complex eukaryotes compared to bacteria and simple eukaryotes like yeast?

Complex eukaryotes have more introns within their genes. (D) Signup and view all the answers

In the Sanger method of DNA sequencing, what is the purpose of adding dideoxyribonucleotides (ddNTPs) to the reaction mix?

ddNTPs terminate DNA synthesis by lacking a 3' hydroxyl group. (C) Signup and view all the answers

What is the role of DNA polymerase in the Sanger method of DNA sequencing?

DNA polymerase is responsible for synthesizing new DNA strands using a template and a primer. (A) Signup and view all the answers

Which of the following is NOT a key difference between the Maxam-Gilbert and Sanger methods of DNA sequencing?

The Maxam-Gilbert method is less accurate, while the Sanger method is more accurate. (A) Signup and view all the answers

In modern automated DNA sequencing, what is the purpose of using fluorescently labeled ddNTPs?

Fluorescent labels provide a visual marker for DNA fragments during electrophoresis. (D) Signup and view all the answers

What is the significance of the "central dogma" of molecular biology?

It outlines the flow of genetic information from DNA to mRNA to protein. (D) Signup and view all the answers

Which of the following accurately describes the process of transcription?

Transcription is the process of copying a DNA sequence into a complementary RNA sequence. (D) Signup and view all the answers

What is the primary function of mRNA in the process of protein synthesis?

mRNA acts as a template for the synthesis of a protein during translation. (A) Signup and view all the answers

Which of the following describes the relationship between DNA, RNA, and protein in the central dogma of molecular biology?

DNA is copied into RNA, which is then used to synthesize protein. (A) Signup and view all the answers

Study Notes

Lecture Overview

Lecture 2 covers DNA, chromosomes, genes, genomes, DNA sequencing, and SNPs.

DNA Structure

DNA is a long polymer comprised of four nucleotide subunits.
Nucleotides consist of a phosphate, sugar, and a nitrogenous base.
Pyrimidines include Cytosine and Thymine.
Purines include Adenine and Guanine.
Nucleotides are linked together by phosphodiester bonds.
A DNA strand has a 5' end and a 3' end.
DNA strands are antiparallel.
DNA is a double helix.
Bases lie perpendicular to the axis of the helix.
Complementary base pairing: A=T and C=G.

Eukaryotic DNA Packaging

Nucleosomes are basic units of eukaryotic chromosome structure.
Nucleosomes are formed by DNA wrapped around histone proteins.
DNA+specialized proteins = histones.
Eukaryotic DNA is packed into chromatin, which further packs into chromosomes.
Interphase chromosomes are not uniformly packed with some regions more condensed (heterochromatin) than others (euchromatin).
The human cell contains about 2 meters of DNA, yet its nucleus is only (5-8 µm) in diameter.
Chromosomes can be distinguished by size and are identifiable by various techniques.
Including: karyotype, FISH, SKY.

Genes and Genomes

Genes are functional units of heredity.
A gene is a segment of DNA that codes for a particular protein or RNA molecule.
The total genetic information of a cell or organism is its genome.
Complete genome sequences exist for thousands of organisms, ranging from E. coli to humans.
Organisms vary significantly in their genome size, from the smallest to the largest.
In eukaryotes, genome size refers to the haploid genome (number of nucleotide pairs in a single set of chromosomes)
The human genome size is approximately 3.1 billion nucleotide pairs.

DNA Sequencing

Maxam-Gilbert method: chemical cleavage of DNA at specific nucleotides.
Sanger method: enzymatic extension of DNA strands to a defined terminating base.
Modern sequencing methods involve automated DNA sequencing, where labelled chain-terminating nucleotides are incorporated and subsequently identified by electrophoresis in capillary tubes.

Central Dogma of Molecular Biology

The flow of genetic information is from DNA to mRNA to protein.
Transcription is the process where cells synthesize mRNA using DNA as a template.
Translation is the process where cells use the information in mRNA to build proteins.

Human Genome

The first draft of the human genome was published in 1999, and the complete sequence was achieved in 2021.
Human genes are not uniformly distributed.
Most of the human genome consists of non-protein-coding DNA, including repetitive nucleotide sequences and introns.
Only a small portion of the genome (~1.5%) encodes for proteins.
Regions of the genome may be very conserved in closely related species or variable.

Single Nucleotide Polymorphisms (SNPs)

SNPs are single-base changes that are present in at least 1% of a population.
Two human genomes from anywhere in the world will differ by about 2.5 million SNPs scattered throughout the genome.
Examples of gene regulation differences.

Identifying Protein-coding Genes

Genes contain ORFs (open reading frames) sequences greater or equal to 100 codons that lack stop codons, which can suggest if a region encodes protein or not.
In bacteria and simple eukaryotes, the protein-coding region is usually a contiguous stretch of coding sequence.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz tests your understanding of the molecular structure of DNA, including the types of bonds involved, the orientation of DNA strands, and various aspects of the human genome. Dive deep into the specifics of DNA functions, base pairings, and genomic composition to enhance your knowledge in molecular biology.