Molecular Biology of the Human Genome

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Questions and Answers

What percentage of the human genome is made up of exons?

1-2% (correct)

90%

45%

10%

Which type of DNA makes up the largest portion of the human genome?

Alpha-satellite DNA

Introns

Dispersed repetitive DNA (correct)

Exons

How long can LINEs (Long Interspersed Elements) be?

Up to 7,000 bp (correct)

Up to 500 bp

Less than 100 bp

Between 90 and 500 bp

What is the role of introns in the DNA sequence?

Non-coding regions within genes Signup and view all the answers

What proportion of the human genome is estimated to be made up of repetitive sequences?

90% Signup and view all the answers

What are tandem repeats and alpha-satellite DNA primarily found at?

Centromeres of chromosomes Signup and view all the answers

What role do histone tail modifications play in gene regulation?

They control how tightly or loosely DNA is packed, affecting gene activity. Signup and view all the answers

What structure is formed when nucleosomes coil together?

Solenoid structure Signup and view all the answers

Which enzyme is responsible for adding acetyl groups to histone tails?

Histone Acetyltransferases (HATs) Signup and view all the answers

What is the primary reason for DNA compaction in cells?

To fit DNA inside the cell nucleus. Signup and view all the answers

What happens to the DNA when methyl groups are added to histone tails?

DNA becomes tightly packed, silencing genes. Signup and view all the answers

Which type of chromatin is associated with active genes that can be transcribed?

Euchromatin Signup and view all the answers

How many base pairs of DNA are typically wrapped around a single nucleosome?

150 base pairs Signup and view all the answers

What is the function of scaffold proteins in DNA organization?

They support chromatin loops and maintain structure. Signup and view all the answers

What is the primary role of DNA polymerase during DNA replication?

To proofread and correct errors in DNA synthesis Signup and view all the answers

How does Type I DNA Topoisomerase relieve strain in a DNA molecule?

By cleaving one strand of DNA at the phosphodiester bond Signup and view all the answers

What process occurs after DNA ligase activates the phosphate group at the nick?

A new bond is formed between the 3′-OH and 5′-phosphate Signup and view all the answers

What is the significance of SSBs (single-stranded DNA-binding proteins) during DNA replication?

They prevent single-stranded DNA from folding back on itself Signup and view all the answers

What does exonuclease activity refer to in DNA enzymes?

The action of cutting nucleotides from the end of the DNA strand Signup and view all the answers

How does the proofreading function of DNA polymerase enhance replication accuracy?

By allowing corrections that improve accuracy by 100 to 1,000 times Signup and view all the answers

What is the primary function of DNA helicase during DNA replication?

To separate the double helix into two single strands Signup and view all the answers

What role do single-stranded binding proteins (SSBs) serve during DNA replication?

They prevent the strands from re-annealing Signup and view all the answers

Which enzyme is primarily responsible for joining Okazaki fragments on the lagging strand?

DNA ligase Signup and view all the answers

How does DNA polymerase maintain a low error rate during DNA replication?

It employs a proofreading mechanism. Signup and view all the answers

Which type of topoisomerase makes single-strand nicks to relieve tension during replication?

Type I Signup and view all the answers

What occurs to the phosphates when a new nucleotide is added during DNA replication?

Two phosphates are removed as pyrophosphate. Signup and view all the answers

What specific function does the exonuclease activity of DNA polymerase serve?

It corrects incorrectly paired nucleotides. Signup and view all the answers

Which statement best describes the synthesis of the leading and lagging strands during DNA replication?

The leading strand is synthesized continuously while the lagging strand is in fragments. Signup and view all the answers

Which of the following is not a challenge addressed during DNA replication?

Poor fidelity of DNA synthesis Signup and view all the answers

What effect do histone tail modifications have on gene activity?

They regulate gene activity by altering DNA packaging. Signup and view all the answers

Study Notes

Genetics, Immunology and Molecular Biology

The course is divided into two sections
The first part covers essential molecular biology and cytogenetics
The second part delves into the immune system
Both topics build upon knowledge gained in the Human Biology course

Revision of relevant human biology, including DNA structure and function
Mendelian inheritance, including variations in dominant and recessive inheritance and mitochondrial disorders
Organisation of the human genome and DNA replication
Cell cycle and mitosis/meiosis
RNA structure & function, RNA synthesis, processing and modifications
Regulation of gene expression and epigenetics
Protein biosynthesis, modification and inhibitors
Chromosomes and karyotyping
Chromosome abnormalities (numerical and structural)
Population genetics
Complex diseases (Polygenic/Multifactorial inheritance and Congenital/adult onset complex diseases)
Prenatal diagnosis
Genetic services
Genetic basis of cancer
Genetics and precision medicine

Cell biology revision

The diagram shows the parts of a typical cell
Some key cells parts include: Microfilaments, Cilia, Cytoplasm, Vault, Cell junction (desmosome), Free ribosome, Ribosome, Chromosomes, Nucleolus, Nucleus, Nuclear Membrane, Centrioles, Plasma membrane, Smooth endoplasmic reticulum, Rough endoplasmic reticulum, Peroxisome, Microtubule, Microvilli, Vesicle, Lysosome, and Mitochondrion

Introduction to Cellular Biology

Cells are the fundamental units of life with specialized functions for organism survival
Understanding cell diversity helps comprehend biological complexity
Studying diverse cell types provides insights into physiological processes and disease mechanisms for targeted medical interventions.

In-depth Exploration of Cell Types

Somatic cells form the majority of the body, carrying functions from structural support to metabolism.
- Neurons are specialized for rapid signal transmission
- Muscle cells are responsible for contraction and force generation for movements.
Germ cells are specialized for sexual reproduction, crucial for genetic diversity.
- Oocytes are larger and nutrient-rich for supporting early embryonic development
- Spermatozoa are highly motile for delivering genetic material

Comprehensive Overview of Organelles

Nucleus: controls gene expression and DNA replication; aberrations can cause uncontrolled cell division (cancer)
Mitochondria: site of the Krebs cycle and oxidative phosphorylation (energy production); disorders affect energy-dependent organs, causing neuromuscular diseases

Endoplasmic Reticulum (ER)

Rough ER is involved in protein synthesis and quality control; Smooth ER plays a role in lipid metabolism and detoxification.
ER dysfunction is implicated in metabolic syndrome and protein folding diseases, illustrated by cystic fibrosis.

Golgi Aparatus

Modifies proteins from the ER and directs them to their destinations.
Errors in processing result in disorders like congenital glycosylation disorders.

Lysosomes

Contains acid hydrolases to break down various biomolecules for cellular recycling
Defects in lysosomes cause lysosomal storage disorders, such as Gaucher's disease, impacting multiple organs.

Molecular biology revision

DNA has five prime and three prime ends.
DNA has a sugar-phosphate backbone, with bases (Adenine, Thymine, Cytosine, Guanine) with hydrogen bonding.
Chargaffs rules state the ratio of Purines and Pyrimidines

DNA double helix structure

DNA has a double helix-based structure
DNA has a double-helix structure with specific dimensions: 34Å is the distance between base pairs in the helix.
Major and Minor grooves are present

Types of DNA

Repetitive DNA makes up 45% of the genome
Short interspersed elements (SINES): 90-500bp
- Alu repeat element is a prominent example, comprising approximately 10% Alu is a restriction site used to classify this DNA.
Long interspersed elements (LINES): up to 7kb
Exons (coding sequence): makes up only 1-2% of the genome

DNA replication

Human DNA polymerase: slow (40-50 nucleotides/second)
Human chromosomes contain millions of nucleotides
Multiple replication origins to speed up the replication process

DNA Replication steps

DNA polymerase: required for replication
DNA unwinds to form a replication fork
Replication proceeds in the 5' to 3' direction.
Multiple origins of replication (to speed up) are required

DNA replication is very accurate

Enzyme mechanisms correct errors; about 1 in 10,000-100,000 nucleotides
Proofreading (rechecks) and error correction (deletions) processes are significant

Histone tail modification

N-terminal histone tails key to transcriptional regulation.
Histone Acetyltransferases (HATs) and Histones Deacetylases (HDACs) and Histone Methyltransferases (HMTs)
Acetylation of tails causes a relaxation and permits transcription factors to bind to DNA
Methylation causes a tightening, silencing genes which inhibit transcription.

DNA polymerase

The enzyme is important in DNA replication because it has two functional domains
- Polymerizing domain which adds nucleotide to the three prime end of a strand.
- Editing domain which can remove a nucleotide from the three prime end if it is not the correct pair.

Tautomers

Hydrogen atoms can change position, which results in different bonding
These can lead to non-standard base pairs and contribute to errors in replication

Replication errors

Mismatches may occur during replication, which need correction.
DNA repair mechanisms correct the mistake once the mistake is found

Supercoiling is relieved by Topoisomerases

Type I topoisomerases breaks the DNA to allow some conformational changes in the single strand DNA
Type II topoisomerases break the DNA in both strands, allowing conformational changes in the double-stranded DNA, and restoring

DNA Replication Fork

Both the leading strand, and the lagging strand undergo replication.
The leading strand replicates continuously; the lagging strand in short fragments (Okazaki fragments)
DNA primase produces small RNA primers in the lagging strand

DNA ligase

Seals the gaps between Okazaki fragments to make DNA continuous

ssDNA-binding proteins

Maintain stability of unwound DNA, preventing hairpin formation and providing straight DNA for DNA Polymerase

The "winding problem"

Ahead of the replication fork (unwrapping of the DNA), DNA becomes supercoiled
Topoisomerases relieve DNA supersoiling

Conclusion

DNA has much more than its classical function of encoding proteins.
DNA's precise packaging within chromosomes is essential for cell function.
Replication is a complex process involving many steps and safeguards ensuring accuracy
Various mechanisms of correction and maintenance of DNA integrity.
DNA replication is critical to many fundamental cellular processes.

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Description

Test your knowledge of the human genome with this quiz that covers key topics such as exons, introns, repetitive sequences, and the role of histone modifications. Explore essential concepts in molecular biology and DNA organization, including structural elements like nucleosomes and chromatin. Perfect for students studying genetics and molecular genetics.