General Biology Study Notes: Genetics, Cellular Respiration, Photosynthesis, and DNA

Genetics and Inheritance

Basic Genetic Terminology

Genetics is the study of heredity and variation in living organisms. Understanding key terms is essential for grasping how traits are passed from one generation to the next.

• Gene: A segment of DNA that codes for a specific protein or trait.

• Allele: Different forms of a gene found at the same locus on homologous chromosomes.

• Genotype: The genetic makeup of an organism; the combination of alleles present.

• Phenotype: The observable characteristics or traits of an organism, resulting from the genotype and environment.

• Homozygous: Having two identical alleles for a particular gene (e.g., AA or aa).

• Heterozygous: Having two different alleles for a particular gene (e.g., Aa).

Example: In pea plants, the allele for purple flowers (P) is dominant over the allele for white flowers (p). A plant with genotype PP or Pp will have purple flowers, while pp will have white flowers.

Mendelian Inheritance and Punnett Squares

Mendelian genetics describes how traits are inherited through dominant and recessive alleles. Punnett squares are used to predict the probability of offspring genotypes.

• Monohybrid Cross: A cross between two organisms involving one trait.

• Punnett Square: A diagram used to predict the outcome of a genetic cross.

Example: Crossing two heterozygous pea plants (Bb x Bb):

	B	b
B	BB	Bb
b	Bb	bb

Genotypic ratio: 1 BB : 2 Bb : 1 bb Phenotypic ratio (if B is dominant): 3 dominant : 1 recessive

Additional info: Probability of homozygous recessive offspring (bb) is 25%.

Cellular Respiration

Overview and Purpose

Cellular respiration is the process by which cells convert glucose and other nutrients into ATP, the energy currency of the cell.

• ATP (Adenosine Triphosphate): The molecule that stores and transfers energy within cells.

• Purpose: To break down glucose and release energy for cellular activities.

Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Stages of Cellular Respiration

• Glycolysis: Occurs in the cytoplasm; breaks glucose into pyruvate, producing 2 ATP.

• Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondria; processes pyruvate, producing CO2, NADH, FADH2, and 2 ATP.

• Electron Transport Chain (ETC): Occurs in the inner mitochondrial membrane; uses NADH and FADH2 to produce up to 34 ATP.

Additional info: Most ATP is produced during the ETC.

Fermentation

When oxygen is not available, cells undergo fermentation to produce ATP.

• Lactic Acid Fermentation: Occurs in muscle cells; produces lactic acid.

• Alcoholic Fermentation: Occurs in yeast; produces ethanol and CO2.

Photosynthesis

Overview and Purpose

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.

• Equation:

$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

• Purpose: To produce glucose and oxygen from carbon dioxide and water using sunlight.

Stages of Photosynthesis

• Light Reactions: Occur in the thylakoid membranes; convert solar energy to chemical energy (ATP and NADPH).

• Calvin Cycle (Dark Reactions): Occur in the stroma; use ATP and NADPH to fix CO2 into glucose.

DNA, RNA, and Protein Synthesis

Structure and Function of DNA and RNA

DNA and RNA are nucleic acids that store and transmit genetic information.

• DNA (Deoxyribonucleic Acid): Double-stranded molecule; contains genetic instructions for development and function.

• RNA (Ribonucleic Acid): Single-stranded molecule; involved in protein synthesis.

• Types of RNA: mRNA (messenger RNA), tRNA (transfer RNA), rRNA (ribosomal RNA).

Central Dogma and Protein Synthesis

The central dogma describes the flow of genetic information from DNA to RNA to protein.

• Transcription: DNA is used as a template to make mRNA.

• Translation: mRNA is decoded by ribosomes to assemble amino acids into a protein.

Example: The genetic code table is used to translate mRNA codons into amino acids.

Codon	Amino Acid
AUG	Met (Start)
UUU	Phe
UAA	Stop
GCU	Ala
Additional info: ...	Other codons code for specific amino acids

Mutations

Mutations are changes in the DNA sequence that can affect protein function.

• Types: Substitution, insertion, deletion.

• Effects: Can be beneficial, neutral, or harmful.

Cell Division and Growth

Mitosis and Meiosis

Cell division is essential for growth, repair, and reproduction.

• Mitosis: Produces two identical daughter cells; used for growth and repair.

• Meiosis: Produces four genetically unique gametes; used for sexual reproduction.

Additional info: Meiosis reduces chromosome number by half, ensuring genetic diversity.

Growth and Development

• Cell Cycle: Series of events that cells go through as they grow and divide.

• Interphase: Cell grows and replicates DNA.

• Prophase, Metaphase, Anaphase, Telophase: Stages of mitosis.

Summary Table: Key Processes in General Biology

Process	Main Purpose	Location	Key Products
Cellular Respiration	Produce ATP from glucose	Cytoplasm & Mitochondria	ATP, CO2, H2O
Photosynthesis	Produce glucose from CO2 and H2O	Chloroplasts	Glucose, O2
Mitosis	Cell growth and repair	Nucleus	2 identical cells
Meiosis	Gamete production	Nucleus	4 unique gametes
Transcription	Make mRNA from DNA	Nucleus	mRNA
Translation	Make protein from mRNA	Cytoplasm (ribosome)	Protein