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Comprehensive Study Notes: Cellular Respiration, Photosynthesis, Cell Communication, Cell Cycle, Genetics, and Molecular Biology

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Cellular Respiration

Overview of Pathways

Cellular respiration is the process by which cells extract energy from glucose and other organic molecules. It occurs in several stages, each with specific locations and outputs.

  • Glycolysis (cytoplasm): Glucose is split into two pyruvate molecules, producing a net gain of 2 ATP and NADH.

  • Pyruvate Oxidation (mitochondrial matrix): Each pyruvate is converted to acetyl-CoA, releasing CO2.

  • Citric Acid Cycle (Krebs Cycle): Acetyl-CoA is oxidized, generating CO2, NADH, FADH2, and ATP.

  • Electron Transport Chain (inner mitochondrial membrane): NADH and FADH2 donate electrons, creating a proton gradient used to produce ATP. Oxygen is the final electron acceptor, forming water.

Final Products: ATP (main energy currency), CO2, and H2O.

  • Equation:

Photosynthesis

Overview and Organisms

Photosynthesis is the process by which autotrophs convert light energy into chemical energy, producing glucose and oxygen. It occurs in plants, algae, and some bacteria (e.g., cyanobacteria).

  • Chloroplast Structure: Outer and inner membranes, thylakoids (site of light reactions), grana (stacks of thylakoids), and stroma (site of Calvin cycle).

Stages of Photosynthesis

  • Light Reactions (thylakoid membrane): Use light and water to produce O2, ATP, and NADPH.

  • Calvin Cycle (stroma): Uses CO2, ATP, and NADPH to produce G3P (a sugar precursor).

Equation:

Photosystem I vs II

Feature

PSII

PSI

Order

First

Second

Function

Splits water

Produces NADPH

Electron role

Replaces lost electrons

Final electron boost

Product

ATP + O2

NADPH

Autotroph vs Heterotroph

  • Autotroph: Organism that makes its own food (e.g., plants).

  • Heterotroph: Organism that consumes other organisms for food (e.g., animals).

Cell Communication

Overview

Cell communication is the process by which cells detect and respond to signals in their environment, essential for growth, immune response, and homeostasis.

  • Local signaling: Paracrine and synaptic signaling.

  • Long-distance signaling: Hormones (endocrine system).

Types of Cell Signals

  • Hormones

  • Neurotransmitters

  • Growth factors

  • Pheromones

Signaling Process (3 Stages)

  1. Reception: Ligand binds to receptor.

  2. Transduction: Signal is relayed via a cascade, often involving second messengers.

  3. Response: Activation of genes or cellular changes.

Cell Surface Receptors

  • G-protein coupled receptors

  • Tyrosine kinase receptors

  • Ligand-gated ion channels

Second Messengers

  • Examples: cAMP, Ca2+

  • Advantages: Amplify signals, enable fast and branched responses

Chromosomes & Cell Cycle

Chromosome Structure

  • Composed of DNA and proteins (histones)

Cell Cycle Phases

  • G1: Cell growth and normal function

  • S: DNA replication

  • G2: Preparation for mitosis

Mitosis Stages

  1. Prophase: Chromosomes condense

  2. Metaphase: Chromosomes align at the cell's equator

  3. Anaphase: Sister chromatids separate

  4. Telophase: Nuclear envelopes reform

  • Mitotic spindle: Microtubules attach to kinetochores

  • Cytokinesis: Division of cytoplasm (cleavage furrow in animals, cell plate in plants)

  • Result: Two genetically identical diploid cells

Checkpoints and Cancer

  • Checkpoints: G1 (growth), G2 (DNA integrity), M (spindle attachment)

  • Cancer: Uncontrolled cell division due to checkpoint failure

  • Benign: Non-spreading tumors

  • Malignant: Tumors that spread (metastasis)

Meiosis & Genetics

Asexual vs Sexual Reproduction

  • Asexual: Offspring are genetically identical to parent

  • Sexual: Offspring have genetic variation

Ploidy and Chromosomes

  • Diploid (2n): Two sets of chromosomes

  • Haploid (n): One set (gametes)

  • Homologous chromosomes: Same genes, possibly different alleles

Meiosis

  • Meiosis I: Homologous chromosomes separate (ploidy reduced 2n → n)

  • Meiosis II: Sister chromatids separate

  • Result: Four genetically unique haploid cells

Mitosis vs Meiosis

Feature

Mitosis

Meiosis

Cells produced

2

4

Genetic variation

No

Yes

Function

Growth

Gamete production

Sources of Genetic Variation

  1. Crossing over

  2. Independent assortment

  3. Random fertilization

Mendelian Genetics

Key Concepts

  • Gene: Unit of inheritance

  • Allele: Variant of a gene

  • Genotype: Genetic makeup

  • Phenotype: Physical expression

Dominance Types

  • Complete dominance: One allele masks another

  • Incomplete dominance: Heterozygote shows intermediate phenotype

  • Codominance: Both alleles expressed equally

Punnett Squares and Pedigrees

  • Punnett square: Predicts offspring genotype probabilities

  • Pedigree: Diagram tracking inheritance patterns

  • Autosomal: Traits on non-sex chromosomes

  • Sex-linked: Traits on X chromosome

  • Linked genes: Genes close together on a chromosome, inherited together

DNA & Molecular Genetics

DNA Structure and Replication

  • Double helix: Two antiparallel strands

  • Base pairing: A-T, C-G

  • Semiconservative replication: Each new DNA has one old and one new strand

Key Scientists

  • Griffith: Transformation principle

  • Watson & Crick: DNA double helix model

  • Franklin: X-ray diffraction images

  • Chargaff: Base pairing rules

  • Meselson & Stahl: Semiconservative replication

DNA Replication Proteins

  • Helicase: Unwinds DNA

  • DNA polymerase: Synthesizes new DNA

  • Ligase: Joins Okazaki fragments

  • Leading strand: Synthesized continuously

  • Lagging strand: Synthesized in Okazaki fragments

Central Dogma

  • Information flows from DNA → RNA → Protein

Transcription

  • DNA is transcribed to mRNA

  • Stages: Initiation (TATA box), elongation, termination

Translation

  • mRNA is translated into protein

  • Stages: Initiation (ribosome binds start codon), elongation, termination (stop codon)

  • Codon: mRNA triplet coding for amino acid

  • Anticodon: tRNA sequence complementary to codon

Mutations

  • Not all mutations are harmful

  • Types: Point, silent, missense, nonsense, frameshift

Gene Regulation

  • Bacteria (Operon system): e.g., lac operon (lactose present → transcription ON)

  • Eukaryotes: Chromatin structure and epigenetic modifications regulate expression

Epigenetics

  • DNA methylation silences genes

  • Histone modification affects gene expression

  • Alternative splicing increases protein diversity

Cancer Genetics

  • Oncogenes: Promote cancer

  • Tumor suppressor genes: Prevent cancer

High-Yield Summary

  • Energy pathways: Photosynthesis and cellular respiration

  • Cell signaling steps

  • Mitosis vs meiosis differences

  • DNA replication and central dogma

  • Mendelian genetics and Punnett squares

  • Mutations and gene regulation

Additional info: Where brief points were expanded, standard Campbell Biology content and terminology were used for clarity and completeness.

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