DNA Replication Review

DNA Replication Review

• DNA replication begins with helicase unwinding the DNA double helix, breaking hydrogen bonds between base pairs.
• DNA polymerase III is essential for DNA replication, reading in the 3' to 5' direction.
• It can only attach to double-stranded DNA.
• Primase creates an RNA primer, enabling DNA polymerase III to begin DNA synthesis.
• DNA polymerase III builds a complementary strand in the 5' to 3' direction, opposite to the template strand.
• It continuously builds the leading strand.
• The lagging strand requires multiple RNA primer creation by primase and is synthesized in short segments called Okazaki fragments.
• DNA polymerase I removes RNA primers and adds DNA nucleotides.
• DNA ligase joins the Okazaki fragments by bonding phosphate and sugar backbones.
• The process results in two identical DNA molecules, each with one original (parental) and one new (daughter) strand—semiconservative replication.

Okazaki Fragments

• Short DNA segments synthesized on the lagging strand during replication.
• DNA polymerase I replaces RNA primers with DNA.
• DNA ligase seals the gaps between fragments, creating a continuous strand.

Telomeres

• Repetitive DNA sequences at chromosome ends.
• Protect crucial genetic information from loss during replication.
• DNA polymerase cannot replicate the very ends of chromosomes.
• Telomere shortening occurs with each cell division.
• This contributes to aging and limits cell lifespan.

Telomerase

• Enzyme adding telomeres to chromosome ends.
• Active during embryonic development and in some stem cells.
• Generally inactive in most adult cells.
• Reactivation in cancer cells allows for uncontrolled proliferation.

The Role of Telomeres and Telomerase in Aging

• Telomere shortening is a significant aspect of cellular aging.
• Gradual telomere shortening leads to chromosomal instability, eventual dysfunction, and cell death.
• Telomerase can potentially slow down aging by extending telomeres.
• However, telomerase reactivation is linked to cancer development.

Factors Affecting Telomere Length

• Lifestyle choices like exercise, diet, and stress influence telomere length.
• Healthy lifestyles may promote longer telomeres and slower aging.
• Factors like chronic stress, smoking, and poor diets are linked to shorter telomeres.

Applications of Telomere Research

• Telomere length measurements provide insight into biological age.
• Telomere length is studied as a potential marker for disease risk and aging.
• Research is exploring therapies targeting telomerase for age-related diseases.
• Potential for extending lifespan and improving health.

Telomeres and Aging

• Telomeres are terminal caps on chromosomes.
• Each cell division leads to telomere shortening.
• Telomere shortening contributes to cellular aging.
• Behaviors like smoking, alcohol consumption, and poor nutrition accelerate telomere shortening.
• Telomeres are reset to full length during the production of sperm or egg cells.

Fibrodysplasia Ossificans Progressiva (FOP)

• Rare genetic disorder causing bone growth in muscles, tendons, and ligaments.
• Progressive, meaning the condition consistently worsens over time.
• Caused by a mutation in the ACVR1 gene.
• Treatments can slow the progression but not reverse the condition.

Transcription and Gene Expression

• Transcription creates RNA from a DNA template.
• Starts at promoter sequences and ends at termination sequences.
• Regulatory sequences control gene activity:
  • Repressor proteins turn genes off.
  • RNA polymerase binds to promoters to initiate RNA production.
  • Gene activation occurs in response to signals (e.g., from damaged cells).
• FOP is due to a gene regulation problem leading to atypical bone formation.

Finding Genes in DNA

• Identifying genes involves finding sequences resembling known promoters and termination signals.
• Promoters are often rich in G and C bases.
• Gene annotation (bioinformatics algorithms) aids in locating these sequences in DNA.

Determining Gene Function

• Gene tagging (with fluorescent proteins) is a technique to understand gene function.
• The tagged protein's location indicates gene function. (e.g., location in the eyes suggests a role in vision).
• The Thousand Genome Project sequences various genomes aiding gene identification via comparison.
• Comparison with other organisms' genes can provide clues about gene functions.

This quiz covers the key concepts of DNA replication, including the roles of enzymes such as helicase and DNA polymerase 3. Understand how DNA strands separate and how new strands are synthesized in the 5' to 3' direction with the help of RNA primers. Test your knowledge on the leading and lagging strand processes involved in DNA replication.