3. Cellular Genetics
3.6. DNA Replication
The cell cycle
The DNA molecule has two functions:
- Carry recipes for proteins (genetic information).
- Carry the genetic information to the next generation.
By replicating, the genetic information may be carried to the next generation.
In an individual (or part of an individual) that is growing, the cells find themselves in the cell cycle.
- The cell is actively dividing, forming two new cells.
- The phase in between two periods of mitosis
The interphase is divided in three sub-phases:
- G1: Rapid growth, normal metabolic activity
- (Sometimes also G0, if the cell is no longer actively dividing.)
- S: Synthesis of new DNA
- G2: Some growth, preparation for mitosis
The replication fork
DNA may be copied because the two strands are complementary to each other. Flash animation by prof. Giannini can be found here.
- Opens up the DNA molecule (like a "zipper").
SSBPs (single-strand binding proteins)
- Stabilizing, prevent the single strands from joining again.
- Lays down a small strand of RNA (primer).
- The primer functions as a starting point for the DNA polymerase.
- Synthesizes new DNA.
- Nucleotides are base-paired with the nucleobases in the single DNA-strand (template).
- Nucleotides are joined to form a new DNA-strand.
Leading and lagging strand
- Leading strand: Synthesized in one fell swoop.
- Lagging strand: Because of the chemical structure of DNA, this strand must be synthesized "backward". This leads to the formation of Okazaki fragments.
- RNA primers replaced by DNA.
- Okazaki fragments ligated with help of a ligase.
- Ready for mitosis!
- 1. The Fundamentals of Life
- 2. Cellular Structure and Function
- 3. Cellular Genetics
- 4. Mendelian Genetics
- 5. Evolution and Systematics
- 5.1. Roadmap to a Theory of Evolution
- 5.2. The Pillars of Evolution
- 5.3. Evidence for Evolution
- 5.4. Convergent and Divergent Evolution
- 5.5. Coevolution
- 5.6. Stabilizing and Disruptive Selection
- 5.7. Speciation
- 5.8. How to Build a Family Tree
- 5.9. The History of Life
- 5.10. The Formation of Life
- 5.11. The Divisions of Life
- 5.12. Plant Systematics
- 5.13. Animal Systematics
- 5.14. Chordate Systematics
- 5.15. Human Evolution
- 6. Ethology and Behavioural Ecology
- 7. Ecology: Systems of Organisms
- 7.1. Ecosystems
- 7.2. Nutritional Chains and Food Webs
- 7.3. Flow of Energy in an Ecosystem
- 7.4. The Water Cycle
- 7.5. The Carbon Cycle
- 7.6. The Nitrogen Cycle
- 7.7. The Phosphorous Cycle
- 7.8. Populations: Size and Growth
- 7.9. Communities. Living Together
- 7.10. Ecological Succession
- 7.11. From Bedrock to Litter
- 7.12. The Lakes
- 7.13. The Oceans and Seas
- 7.14. Climate and Biomes
- 8. Environmental Science
- 9. Viruses and Biotechnology
- 10. Plant & Fungal Physiology
- 10.1. The Organs of the Plants
- 10.2. Plants With and Without Seeds
- 10.3. The Root. How the Plant Absorbs Water and Nutrients
- 10.4. The Trunk and Water Transport
- 10.5. Structure and Function of the Leaf
- 10.6. Photosynthesis
- 10.7. How Plants Grow
- 10.8. How Plants Reproduce
- 10.9. Classification of the Fungi
- 10.10. How Fungi Reproduce
- 10.11. Fungal Parasites and Pathogens
- 11. Human Physiology
- 11.1. Physiology Basics
- 11.2. The Nervous System
- 11.3. The Senses
- 11.4. The Endocrine System
- 11.5. Food and Digestion
- 11.6. The Locomotor System
- 11.7. Gas Exchange and Circulation
- 11.7.1. Respirational Systems
- 11.7.2. Human Respiration
- 11.7.3. Circulation in Different Animals
- 11.7.4. The Human Circulatory System. Heart, Blood Vessels and Blood Pressure
- 11.7.5. Activity in the Capillaries
- 11.7.6. Blood Constituents
- 11.7.7. Blood Groups
- 11.7.8. Coagulation
- 11.7.9. Some Blood Diseases
- 11.7.10. Water Balance. Kidneys
- 11.8. The Immune System
- 11.9. Sex, Love, and STDs