BIO 103 Final Exam Study Guide: Cellular Respiration, Photosynthesis, Cell Cycle, Meiosis, Mendelian Genetics, DNA, and Gene Expression

Cellular Respiration and Fermentation

Overview of Cellular Respiration

Cellular respiration is a series of metabolic processes by which cells extract energy from organic molecules, primarily glucose, to produce ATP, the cell's main energy currency.

• Purpose: To convert biochemical energy from nutrients into ATP, releasing waste products.

• Equation:

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

• Main Stages:

  1. Glycolysis (cytoplasm): Glucose is split into two pyruvate molecules; produces 2 ATP and 2 NADH.

  2. Citric Acid Cycle (Krebs Cycle) (mitochondrial matrix): Pyruvate is oxidized, generating CO2, 2 ATP, 6 NADH, and 2 FADH2 per glucose.

  3. Electron Transport Chain (ETC) & Oxidative Phosphorylation (inner mitochondrial membrane): NADH and FADH2 donate electrons, driving ATP synthesis (about 26-28 ATP).

• Total ATP Yield: Approximately 30-32 ATP per glucose molecule.

Fermentation

• Types:

  • Lactic Acid Fermentation: Pyruvate is reduced to lactic acid; occurs in muscle cells and some bacteria.

  • Alcohol Fermentation: Pyruvate is converted to ethanol and CO2; occurs in yeast and some bacteria.

• ATP Production: Both processes regenerate NAD+ to allow glycolysis to continue, producing 2 ATP per glucose.

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which autotrophs convert light energy into chemical energy stored in glucose.

• Purpose: To synthesize organic molecules from CO2 and H2O using light energy.

• Equation:

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

• Main Stages:

  1. Light-Dependent Reactions (thylakoid membranes): Convert light energy to chemical energy (ATP, NADPH); O2 is released.

  2. Light-Independent Reactions (Calvin Cycle) (stroma): Use ATP and NADPH to fix CO2 into glucose.

• Importance: Provides energy and organic molecules for nearly all life; produces O2 for aerobic respiration.

Roles of Autotrophs and Heterotrophs

• Autotrophs: Organisms (e.g., plants, algae) that produce their own food via photosynthesis.

• Heterotrophs: Organisms that consume other organisms for energy.

• Biosphere Connection: Autotrophs form the base of food chains; heterotrophs depend on autotrophs for energy and oxygen.

The Cell Cycle

Phases of the Cell Cycle

• Interphase: Cell grows (G1), replicates DNA (S), and prepares for division (G2).

• Mitosis: Division of the nucleus into two genetically identical nuclei (prophase, metaphase, anaphase, telophase).

• Cytokinesis: Division of the cytoplasm, forming two daughter cells.

Cell Cycle Checkpoints

• G1 Checkpoint: Checks for cell size, nutrients, growth factors, and DNA damage.

• G2 Checkpoint: Ensures DNA replication is complete and checks for DNA damage.

• M Checkpoint (Spindle Checkpoint): Ensures all chromosomes are attached to the spindle before anaphase.

Consequences of Errors in Cell Cycle Control

• Cancer: Uncontrolled cell division due to checkpoint failures.

• Benign Tumors: Non-invasive, non-cancerous growths.

• Malignant Tumors: Invasive, cancerous growths that can metastasize.

• Cancer Treatments: Surgery, radiation, chemotherapy, targeted therapy.

Binary Fission in Prokaryotes

• Simple cell division process in bacteria and archaea.

• DNA replicates, cell elongates, and divides into two identical cells.

Meiosis & Sexual Reproduction

Chromosome Behavior During Meiosis

• Meiosis I: Homologous chromosomes separate, reducing chromosome number by half.

• Meiosis II: Sister chromatids separate, similar to mitosis.

Meiosis vs. Mitosis

• Meiosis: Two divisions, produces four non-identical haploid cells (gametes).

• Mitosis: One division, produces two identical diploid cells.

Genetic Variation in Meiosis

• Crossing Over: Exchange of genetic material between homologous chromosomes during prophase I.

• Independent Assortment: Random orientation of homologous pairs during metaphase I.

• Random Fertilization: Any sperm can fertilize any egg, increasing variation.

Mendel & The Gene Idea

Mendel’s Laws of Inheritance

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Probability in Genetics

• Probability laws (product and sum rules) are used to predict genetic outcomes.

• Example: Probability of two independent events both occurring is the product of their individual probabilities.

Patterns of Inheritance

• Complete Dominance: One allele completely masks another.

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed (e.g., AB blood type).

• Multiple Alleles: More than two alleles exist for a gene (e.g., ABO blood group).

• Pleiotropy: One gene affects multiple traits.

• Epistasis: One gene affects the expression of another gene.

• Polygenic Inheritance: Multiple genes influence a single trait (e.g., skin color).

Pedigrees

• Diagram showing inheritance patterns of traits in families.

• Used to track dominant, recessive, and sex-linked traits.

The Molecular Basis of Inheritance

Structure of DNA

• Double helix composed of nucleotides (A, T, C, G).

• Sugar-phosphate backbone with complementary base pairing (A-T, C-G).

• Experiments (e.g., Hershey-Chase) demonstrated DNA is genetic material.

Chromatin Packing

• Nucleosome: DNA wrapped around histone proteins.

• 30-nm Fiber: Nucleosomes coiled into a thicker fiber.

• Looped Domains: 30-nm fiber forms loops attached to scaffold proteins.

• Chromosome: Highly condensed structure during cell division.

DNA Replication and the Meselson-Stahl Experiment

• Meselson-Stahl experiment showed DNA replication is semiconservative: each new DNA molecule has one old and one new strand.

• Replication involves unwinding DNA, synthesizing new strands using DNA polymerase.

From Gene to Protein

Gene Structure and Function

• A gene is a DNA sequence that codes for a functional product (usually a protein).

• Genes are expressed via transcription and translation.

Gene Expression

• Evidence from experiments (e.g., Beadle and Tatum) established the one gene–one polypeptide hypothesis.

• Gene expression involves transcription (DNA to RNA) and translation (RNA to protein).

Transcription

• RNA polymerase synthesizes RNA from a DNA template.

• Key molecules: promoter, RNA polymerase, transcription factors.

Eukaryotic RNA Processing

• Pre-mRNA is modified by adding a 5' cap, poly-A tail, and splicing out introns.

Mutations

• Point Mutations: Change a single nucleotide (silent, missense, nonsense).

• Frameshift Mutations: Insertions or deletions that alter the reading frame.

• Mutations can alter protein structure and function, sometimes causing disease.

Polypeptide Synthesis in Bacteria and Eukaryotes

• Bacteria: Transcription and translation are coupled; multiple polypeptides can be made from polycistronic mRNA.

• Eukaryotes: Transcription occurs in the nucleus, translation in the cytoplasm; each mRNA usually codes for one polypeptide.