Module 2
1. Introduction to Cell Theory and Enzymes
1.1 Cell Theory
Fundamental principles of biology:
All living things are made of cells.
Cells are the smallest unit of life.
All cells come from other cells.
The nucleus stores DNA.
1.2 Chemical Reactions in Cells
Enzymes:
Proteins that catalyze (speed up) chemical reactions.
Highly specific in their function.
Named based on the reaction they catalyze, with a suffix '-ase' (e.g., sucrase breaks down sucrose).
A catalyst lowers the activation energy required to start a reaction.
1.3 Key Features of Enzymes
Different cells have various types of enzymes.
Not all cells utilize enzymes continuously.
Enzymes are not consumed or broken down in the reactions they catalyze.
1.4 Enzyme Specificity
Enzymes are selective, typically catalyzing only one reaction.
As proteins, their functionality can be compromised by environmental changes, such as:
Excess heat.
pH levels.
Salt concentration.
2. Enzymatic Reactions and Conditions
2.1 Environmental Factors Affecting Enzymes
Changes in environmental conditions can disrupt hydrogen bonds and disulfide bridges that stabilize enzyme structure, affecting their function.
Presence or absence of cofactors (like vitamins) can influence enzyme activity.
2.2 Glucose Transport and Cellular Respiration
Digestive enzymes break down macromolecules into smaller pieces, increasing surface area for cell absorption.
3. Cell Biology of Lactase
3.1 Function of Lactase
Lactase is an enzyme that breaks down lactose (a disaccharide in milk) into glucose and galactose, which serve as energy sources.
3.2 Lactase Persistence
High levels of lactase in enterocytes (cells lining the digestive tract) are crucial for lactase function during infancy when milk is a primary nutrient source.
3.3 Regulation of Lactase Production
Many mammals, including 65% of humans, experience decreased lactase production post-weaning.
This reduction is an energy conservation mechanism by cells, reducing unnecessary energy use for enzyme production when milk consumption ceases.
3.4 Consequences of Lactase Deficiency
Undigested lactose in the large intestine leads to symptoms of lactose intolerance:
Increased osmotic gradient drawing water, causing cramps and diarrhea.
Bacterial fermentation of lactose produces gases, resulting in flatulence.
4. Genetics and Biochemistry
4.1 Central Dogma of Molecular Biology
DNA serves as an instruction manual for protein synthesis, with proteins playing essential roles in cellular functions.
Proteins are made from amino acids, and their arrangement is dictated by the genetic code stored in nucleic acids (DNA and RNA).
4.2 Structure of Nucleic Acids
DNA:
Stores genetic information as chromatin in the nucleus.
Double-stranded with deoxyribose sugar.
RNA:
Single-stranded and involved in protein synthesis with ribose sugar.
4.3 Basis of Nucleic Acids
DNA bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).
RNA bases: Adenine (A), Uracil (U), Guanine (G), Cytosine (C).
5. The Central Dogma
5.1 Transition from DNA to Protein
Central dogma: DNA -> RNA -> Protein.
Transcription produces mRNA from DNA; translation converts mRNA into proteins.
5.2 Steps in Protein Synthesis
Transcription:
Occurs in the nucleus, where a segment of DNA is copied into mRNA.
Initiated by RNA polymerase binding to the promoter region.
Edited mRNA then exits the nucleus.
Translation:
Takes place on ribosomes, where mRNA codons interact with tRNA to synthesize proteins.
6. Genetics of Lactase
6.1 Lactase Gene Structure
The lactase gene consists of 55,000 base pairs, encoding a protein of 1,925 amino acids.
6.2 Regulation by Transcription Factors
Transcription factors are critical for regulating the lactase gene's expression, allowing for variability in lactase production.
A mutation affecting these factors contributes to lactase persistence.
6.3 Variability of Lactase Production
In normal mammals, lactase production decreases after weaning due to reduced transcription factor activity, resulting in lactose intolerance.
In lactase persistent individuals, a mutation enhances lactase gene transcription, allowing continued dairy consumption in adulthood.
7. Evolution and Natural Selection
7.1 Principles of Evolution
Evolution involves changes in the genetic composition of populations over time.
Groups of the same species, while somewhat independent, may adapt differently to environmental pressures.
Convergent evolution and shared traits indicate a common ancestral lineage.
7.2 Natural Selection Processes
Natural selection results in favorable traits becoming more common in populations.
Variability within populations is crucial, with some traits being heritable and thus passed to offspring.
7.3 Darwin's Observations
Variability exists in all populations, with some traits enhancing survival and reproduction.
Successful traits lead to higher fitness, which progresses through generations via natural selection.
8. Lactase Persistence and Human Populations
8.1 Lactase Persistence in Evolution
Lactase persistence varies among populations, influenced by the historical use of dairy.
Positive and negative selection processes determine the spread of lactase persistence in populations using dairy.
Mutations leading to lactase persistence emerged independently in different populations, showcasing convergent evolution principles.
8.2 Historical Context
The Neolithic Revolution catalyzed dietary shifts, incorporating dairy into human diets and driving the need for lactose digestion.
Cultural practices like pastoralism influenced the evolution of lactase persistence, demonstrating biocultural coevolution between humans and their environments.
9. Conclusion
Understanding the genetic basis of lactase persistence reveals insights into human evolution and dietary adaptations, highlighting the interplay of genetics, nutrition, and environmental factors.