DNA Structure and Function

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Questions and Answers

What role do introns play in protein-coding genes?

They influence the stability of mRNA.

They are involved in translation.

They contain regulatory information. (correct)

They encode protein sequences directly.

What is the function of enhancers in gene regulation?

They increase the basal level of transcription.

They entirely inhibit transcription.

They act as a binding site for RNA polymerase.

They bind transcription factors to enhance transcription levels. (correct)

Which of the following accurately describes a promoter?

It directly translates mRNA into polypeptides.

It enhances the overall gene stability.

It solely determines the protein-coding sequence.

It is the site for assembly of transcriptional machinery. (correct)

Which statement about alternate splicing is true?

It allows the generation of different protein variants. Signup and view all the answers

What percentage of the human genome is comprised of repetitive DNA sequences?

50% Signup and view all the answers

Which type of RNA is involved in the regulation of mRNA?

miRNA Signup and view all the answers

What is the primary function of UTRs in mRNA?

They ensure mRNA stability. Signup and view all the answers

Which of the following correctly describes the role of cis-regulatory sequences?

They are involved in transcriptional activation. Signup and view all the answers

What are tandem repeats in the context of DNA sequences?

Repetitive motifs like (AT)n and (GC)n. Signup and view all the answers

What is the primary role of transcription factors in gene regulation?

They regulate the transcriptional activation of genes. Signup and view all the answers

What is the primary function of heterochromatin in the cell?

To suppress transcription of alternate lineage genes Signup and view all the answers

Which statement accurately describes euchromatin?

It is loosely packed and transcriptionally active Signup and view all the answers

What describes an epigenetic change?

A heritable change influencing cell function without altering the DNA sequence Signup and view all the answers

Which of the following statements is true regarding gene activation in different cell types?

Each cell type expresses a unique set of genes. Signup and view all the answers

What role does histone H1 play in chromatin structure?

It represses transcription by compacting chromatin. Signup and view all the answers

Which cellular process is NOT influenced by epigenetic changes?

DNA replication Signup and view all the answers

How are heterochromatin and euchromatin structured in terms of accessibility?

Euchromatin is accessible, heterochromatin is inaccessible. Signup and view all the answers

What is a key consequence of having genes in a heterochromatic state?

Suppressed gene expression Signup and view all the answers

What function do telomeres serve in chromosomes during mitosis?

They protect against degradation during mitosis. Signup and view all the answers

Which technique is progressively replacing karyotyping for detecting large chromosomal anomalies?

Real-time quantitative PCR Signup and view all the answers

What critical information is contained within sequences of nucleotides?

Information necessary for cell division and replication Signup and view all the answers

What does karyotyping detect?

Chromosomal anomalies such as duplications or deletions Signup and view all the answers

What is the significance of the Human Genome Project that was completed in 2003?

It determined the nucleotide sequence of the entire human genome. Signup and view all the answers

Which components of chromosomes are located at the central region?

Centromeres Signup and view all the answers

What does the acronym ALT stand for in the context of the GPT2 gene?

Alanine Transaminase Signup and view all the answers

Which alternative method would NOT be typically used for genomic analysis?

Chromatography Signup and view all the answers

What role do origins of replication play in chromosome organization?

They allow for the duplication of the genome. Signup and view all the answers

How are sequences of nucleotides represented in terms of their chemical components?

By the four bases: A, T, G, and C. Signup and view all the answers

What is the primary function of histone acetylation?

To recruit proteins that open chromatin Signup and view all the answers

Which histone modification indicates tri-methylation on Lysine 27 of Histone H3?

H3K27me3 Signup and view all the answers

Which statement best describes the effect of DNA methylation on gene expression?

It typically results in gene repression Signup and view all the answers

What role does MeCP2 play in relation to DNA methylation?

It binds to methylated cytosines Signup and view all the answers

Which histone mark is associated with heterochromatin?

H3K9me3 Signup and view all the answers

What is the typical percentage of CpG sites that are methylated in the genome?

70-80% Signup and view all the answers

Which enzymes are responsible for adding and removing methyl groups from histones?

Histone Methyl Transferases and Histone Demethylases Signup and view all the answers

What is the key characteristic of CpG islands in relation to gene promoters?

They are generally rich in unmethylated CpGs Signup and view all the answers

In Rett Syndrome, what is often the underlying genetic cause?

De novo mutation of MeCP2 Signup and view all the answers

Which histone modification is associated with the opening of chromatin?

H4K16ac Signup and view all the answers

What is the main structural feature of DNA that contributes to its stability?

Hydrogen bonds between complementary bases Signup and view all the answers

Which of the following describes the directionality of DNA strands?

DNA is read from 5' to 3' Signup and view all the answers

What type of bond connects the deoxyribose sugar and phosphate group in a DNA strand?

Phosphodiester bond Signup and view all the answers

Which base pairs in DNA are connected by two hydrogen bonds?

A-T Signup and view all the answers

What is the primary charge of the DNA molecule?

Negatively charged due to phosphate groups Signup and view all the answers

How do hydrophobic interactions play a role in the structure of DNA?

They promote base stacking and stabilize the helical structure. Signup and view all the answers

Which of the following statements about nucleosomes is correct?

Nucleosomes help package DNA into a compact structure. Signup and view all the answers

What is the length range of autosomal chromosomes in terms of base pairs?

50-250 million base pairs Signup and view all the answers

What is the effect of histones on DNA?

Histones help to condense DNA into nucleosomes. Signup and view all the answers

Which of the following correctly states a property of the DNA double helix?

It has uniform width due to base pairing. Signup and view all the answers

What distinguishes RNA from DNA at a molecular level?

The sugar component in the backbone. Signup and view all the answers

Which of the following correctly describes an interaction that stabilizes the DNA structure?

Hydrophobic interactions among adjacent bases Signup and view all the answers

What component of DNA allows for the formation of the double helix structure?

Base pairing through hydrogen bonds Signup and view all the answers

Which of the following is a key feature of chromatin?

It allows for the accessibility of DNA for transcription. Signup and view all the answers

Study Notes

Deoxyribonucleic Acid (DNA)

DNA is a polymer of nucleotides.
DNA is a double helix structure.
Double helix structure consists of:
- Deoxyribose-phosphate backbone: Forms the outside of the helix.
- Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C) are located inside the helix.
The DNA double helix structure:
- Stable due to:
  - Hydrogen bonds between bases: A-T (2 bonds) and G-C (3 bonds).
  - Phosphodiester bonds between deoxyribose and phosphate (form the backbone)
  - Hydrophobic interactions between stacked bases.
- Directional: Read from 5' to 3' (by convention).
- Negatively charged due to the phosphate groups in the backbone.
James Watson and Francis Crick described and published the DNA double helix model in 1953.

Histones, Nucleosomes, Chromatin

Histones are proteins which DNA wraps around to form nucleosomes.
Nucleosomes are the basic unit of chromatin.
Chromatin is the complex of DNA and proteins within the nucleus of a eukaryotic cell.
Chromosomes are composed of chromatin.
Humans have 22 autosomal chromosomes and 2 sex chromosomes (either XX or XY).
The total length of the human diploid genome is approximately 6.5 feet.

Chromosome Organization

The ends of chromosomes are called telomeres, they are rich in TTAGGG repeats and protect from degradation and joining.
Centromeres are located in the central region of chromosomes, act as handles during mitosis and allow DNA replication.
Karyotypes are used to detect chromosomal anomalies but are progressively being replaced by PCR and genome sequencing.

Organization and Regulation of Genomic Information

Sequences of nucleotides (ATGC) carry genetic information.
Human genome consists of ~30,000 protein-coding genes and many more non-coding genes.
Genes contain regulatory regions that control gene expression, which influence the production of proteins and functional RNA.
Central dogma of molecular biology states that information flows from DNA to RNA to protein.
Protein-coding genes contain exons, which encode protein sequences, and introns, which contain regulatory information.
mRNA can be alternatively spliced, creating different protein isoforms from a single gene.
Genes coding for functional RNA include rRNA, tRNA, and miRNA, all involved in mRNA translation and regulation.
Cis-regulatory sequences, like promoters, are located near the gene they regulate, while trans-regulatory sequences, such as enhancers, are located further away.
Promoters are sites where the transcription machinery assembles, including general transcription factors and RNA polymerase 2.
Enhancers bind to transcription factors and increase transcriptional levels, influencing the promoter activity.
Some transcription factors can repress transcriptional activation.

Intergenic Regions: Repetitive DNA Sequences

About 50% of the human genome is composed of repeats of DNA motifs.
Tandem repeat sequences, like satellites, are characterized by repetitive motifs (e.g., (AT)n, (GC)n, (TTAGGG)n) and are involved in epigenetic regulation.

Epigenetics

Epigenetics is the study of heritable changes in cell function that are not caused by alterations in the DNA sequence.
Different cell types express different sets of genes, resulting in diverse cell functions and phenotypes.
Epigenetic mechanisms involve changes in chromatin structure to regulate gene expression.

Heterochromatin and Euchromatin

Heterochromatin is densely packed, inaccessible, and transcriptionally repressed.
Heterochromatin typically comprises alternative lineage genes, repeated DNA sequences (transposons), centromeres, and telomeres.
euchromatin is loosely packed, accessible, and transcriptionally active.

Histone Post-Translational Modifications

Histone tails harbor various chemical modifications that influence chromatin structure and regulate gene expression.
Acetylation, methylation, phosphorylation, ubiquitinylation, and other modifications affect histone amino acids.
Histone acetylation typically leads to chromatin decondensation and increases transcription, while histone deacetylation promotes chromatin compaction and gene silencing.
Histone methylation can have varying effects on gene expression, depending on the specific lysine residue.
H3K9me3 is associated with chromatin compaction and heterochromatin formation, whereas H3K4me3 is linked to chromatin opening and euchromatin formation.

DNA Methylation

CpG methylation occurs mainly on cytosine nucleotides that are followed by guanine.
DNA methylation primarily contributes to gene repression and chromatin compaction.
CpG islands are genomic regions rich in unmethylated CpGs and play a crucial role in gene regulation.
Aberrant methylation of CpG islands is linked to pathological conditions and cancer.
DNA methylation and histone marks interact to fine-tune gene expression.
Methyl-CpG-binding protein 2 (MeCP2) binds to methylated CpGs, recruiting histone deacetylases (HDACs), resulting in chromatin compaction and gene silencing.

Rett Syndrome

Over 95% of Rett syndrome cases involve de novo mutations in the MeCP2 gene, leading to developmental disabilities affecting primarily females.

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Description

Explore the fascinating world of deoxyribonucleic acid (DNA) and its critical components such as the double helix structure, nucleotides, and the role of histones. This quiz covers the molecular architecture of DNA and its essential functions in genetics. Test your knowledge of the foundational concepts introduced by Watson and Crick.