Genetics: DNA Structure, Genetic Code, and Inheritance Patterns

DNA Structure:
- Double helix model with sugar-phosphate backbone and nitrogenous bases (A, C, G, and T)
- Base pairing: A-T and G-C
Genetic Code:
- 64 codons (triplets of nucleotides) that code for 20 amino acids and 3 stop codons
- Codons are read in sequence to form a polypeptide chain
Inheritance Patterns:
- Mendel's Laws: segregation, independent assortment, and dominance
- Types of inheritance: autosomal dominant, autosomal recessive, X-linked, and polygenic

Cell Structure:
- Plasma membrane: semi-permeable membrane that surrounds the cell
- Cytoplasm: jelly-like substance inside the cell where metabolic reactions occur
- Nucleus: contains DNA
- Mitochondria: energy-producing organelles
- Ribosomes: site of protein synthesis
Cellular Processes:
- Photosynthesis: light-dependent reaction and Calvin cycle
- Cellular respiration: aerobic and anaerobic respiration
- Cell division: mitosis and meiosis
Cell Signaling:
- Signal transduction pathways: reception, transmission, and response
- Types of signaling: autocrine, paracrine, and endocrine

Ecosystems:
- Biotic factors: living organisms (producers, consumers, decomposers)
- Abiotic factors: non-living components (light, temperature, water, nutrients)
- Energy flow: producers -> primary consumers -> secondary consumers -> decomposers
Population Dynamics:
- Population growth: exponential and logistic growth
- Population regulation: density-dependent and density-independent factors
Community Ecology:
- Species interactions: competition, predation, mutualism, commensalism
- Community structure: species richness, diversity, and composition

DNA is structured as a double helix with a sugar-phosphate backbone, consisting of nitrogenous bases: adenine (A), cytosine (C), guanine (G), and thymine (T).
Base pairing rules dictate that A pairs with T, and G pairs with C, ensuring genetic stability.
The genetic code comprises 64 codons formed by triplets of nucleotides, responsible for coding 20 amino acids and includes 3 stop codons to terminate translation.
Codons are read sequentially during translation to create a polypeptide chain, which folds into functional proteins.
Gregor Mendel established foundational inheritance patterns through his laws: segregation, independent assortment, and dominance.
Types of inheritance include autosomal dominant (one allele sufficient for phenotype), autosomal recessive (two alleles required), X-linked (associated with sex chromosomes), and polygenic traits (influenced by multiple genes).

The plasma membrane is semi-permeable, regulating the movement of substances in and out of the cell.
Cytoplasm is the viscous liquid within the cell where metabolic processes occur, hosting various organelles.
The nucleus houses the cell's DNA, acting as the control center for genetic information.
Mitochondria are known as the powerhouses of the cell, generating adenosine triphosphate (ATP) through cellular respiration.
Ribosomes, found in the cytoplasm and on the endoplasmic reticulum, are crucial for protein synthesis through translation.
Photosynthesis involves light-dependent reactions occurring in the thylakoid membranes and the Calvin cycle in the stroma of chloroplasts to convert light energy into glucose.
Cellular respiration can occur aerobically (with oxygen) to produce ATP efficiently or anaerobically (without oxygen) through fermentation processes.
Cell division occurs through mitosis for somatic cells (growth and repair) and meiosis for gamete formation (sexual reproduction).
Signal transduction pathways facilitate cell communication through steps of reception, transmission, and response to external signals.
Types of signaling include:
- Autocrine: cells respond to signals they produce.
- Paracrine: signals affect nearby cells.
- Endocrine: long-distance signaling through hormones in the blood.

Ecosystems consist of biotic factors (living organisms) such as producers (autotrophs), consumers (heterotrophs), and decomposers that recycle nutrients.
Abiotic factors include non-living elements like light, temperature, water availability, and nutrient levels, which influence ecosystem health.
Energy flows through ecosystems starting with producers (photosynthetic organisms), followed by primary consumers (herbivores), secondary consumers (carnivores), and ending with decomposers that break down organic matter.
Population growth can be exponential (uncontrolled growth in favorable conditions) or logistic (growth that slows as resources become limiting).
Population regulation is influenced by density-dependent factors (e.g., competition, disease) and density-independent factors (e.g., natural disasters, climate).
Community ecology examines species interactions, including:
- Competition: struggle for limited resources.
- Predation: predator-prey dynamics.
- Mutualism: both species benefit.
- Commensalism: one species benefits, the other is unaffected.
Community structure is characterized by species richness (number of different species), diversity (variety of species), and species composition (the identity and abundance of species).