Cellular Processes: Energy, Transport, Respiration, Photosynthesis, Cell Division, and Cancer

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The Working Cell

Basic Requirements for Life

All living organisms require certain fundamental resources to sustain life and maintain internal balance.

Energy: Needed to perform cellular work.
Water: Essential for biochemical reactions.
Nutrients: Provide building blocks and energy.
Homeostasis: Maintenance of stable internal conditions.

Energy and Its Forms

Energy is the capacity to perform work. It exists in different forms:

Kinetic Energy: Energy of motion.
Potential Energy: Stored energy.

First Law of Thermodynamics: Energy can be transformed from one form to another, but cannot be created or destroyed.

Entropy: A measure of disorder or randomness in a system.

Calories and Cellular Energy

Calorie (cal): The energy needed to raise 1g of water by 1°C.
Calorie (Cal): A kilocalorie (1,000 calories), used in food energy.

ATP and Metabolism

ATP (Adenosine Triphosphate): The main energy currency of cells.
ADP (Adenosine Diphosphate): ATP after losing one phosphate group; contains less energy.
Metabolism: The sum of all chemical reactions in an organism.

Enzymes and Enzyme Inhibitors

Enzymes are biological catalysts that speed up reactions by lowering activation energy.

Substrate Specific: Each enzyme acts on a specific substrate.
Affected by Temperature and pH: Optimal conditions are required for activity.
Cofactors: Inorganic (e.g., zinc, iron, copper) or organic (coenzymes, e.g., vitamins) molecules required for enzyme function.
Activation Energy: The energy needed to start a reaction; enzymes lower this barrier.
Active Site: The region of the enzyme where the substrate binds.

Enzyme Inhibitors: Molecules that reduce enzyme activity by binding to the active site or elsewhere, altering enzyme shape.

Enzymes	Enzyme Inhibitors
Speed up reactions	Slow or stop reactions
Bind substrates	Block substrate binding
Lower activation energy	Prevent enzyme activity

Transport Across Membranes

Passive Transport: Movement without energy, along concentration gradient.
Examples: Diffusion, Facilitated Diffusion, Osmosis.
Active Transport: Requires energy (ATP), moves substances against gradient.
Examples: Exocytosis, Endocytosis, Receptor-Mediated Endocytosis, Signal-Transduction Pathways.

Diffusion: Movement of any molecule from high to low concentration.

Osmosis: Diffusion of water across a membrane.

Solution Type	Solute Concentration	Effect on Animal Cells	Effect on Plant Cells
Hypertonic	Higher	Cell shrinks (crenation)	Plasmolysis
Hypotonic	Lower	Cell swells/bursts (lysis)	Turgid (healthy)
Isotonic	Equal	Cell stays normal	Flaccid (limp)

Direction of Osmosis: Water moves from hypotonic to hypertonic solution (toward higher solute concentration).

Cellular Respiration: Obtaining Energy from Food

Producers, Consumers, Autotrophs, and Heterotrophs

Producer: Makes its own food (e.g., plants, algae).
Consumer: Eats other organisms.
Autotroph: Produces food using light or chemicals.
Heterotroph: Obtains energy by consuming others.

Cellular Respiration and Photosynthesis Equations

Photosynthesis:
Cellular Respiration:

Cellular Respiration vs. Breathing

Cellular Respiration: Chemical process in cells producing ATP.
Breathing: Physical process of gas exchange (O2 in, CO2 out).

Aerobic and Anaerobic Metabolism

Aerobic Metabolism: Occurs when oxygen is available; normal activities.
Anaerobic Metabolism: Occurs when oxygen is limited; short bursts of activity.

Stages of Cellular Respiration

Stage 1: Glycolysis (cytoplasm): Glucose → pyruvate, produces 2 ATP.
Stage 2: Citric Acid Cycle (mitochondria matrix): Breaks down carbon, releases CO2, produces 2 ATP.
Stage 3: Electron Transport Chain (inner mitochondrial membrane): Produces most ATP (~32-34), requires oxygen.

Total ATP produced: ~36-38 per glucose molecule.

Electron Transport Chain and ATP Synthase

Electrons pass through proteins, energy pumps H+ ions, creating a gradient.
ATP Synthase: Enzyme that uses H+ gradient to produce ATP.

Fermentation

Fermentation: Anaerobic process sustaining microorganisms.
End Products: Lactic acid (in bacteria), ethanol + CO2 (in yeast).
Examples: Bread, beer, wine.

Photosynthesis, CO2, O2, and Global Warming

Plants remove CO2 via photosynthesis, produce O2.
Increased CO2 contributes to global warming; photosynthesis helps reduce atmospheric CO2.

Photosynthesis: Using Light to Make Food

Chloroplasts and Stomata

Photosynthesis occurs in: Chloroplasts.
Stomata: Leaf openings for CO2 entry, O2 exit, and water regulation.

Light and the Electromagnetic Spectrum

Light behaves as both waves (wavelengths) and particles (photons).
Visible light: 400-700 nm; main wavelengths for photosynthesis are blue (450 nm) and red (680 nm).
Electromagnetic spectrum: Gamma rays → X-rays → UV → visible → infrared → radio waves.

Light Reactions and Calvin Cycle

Light Reactions: Occur in thylakoid membrane; convert light energy to ATP and NADPH, split water, release O2.
Calvin Cycle: Occurs in stroma; uses ATP and NADPH to make glucose from CO2.

Photosystems and Pigments

Photosystem II: Splits water, releases O2, starts electron transport, produces ATP.
Photosystem I: Re-energizes electrons, produces NADPH.
Pigments: Chlorophyll a & b (reflect green), carotenoids (reflect yellow/orange).

Calvin Cycle Steps

Carbon Fixation: CO2 attaches to RuBP (enzyme: RuBisCO).
Reduction: ATP & NADPH convert molecules into G3P.
Regeneration: Some G3P used to regenerate RuBP.

G3P: Used to make glucose and regenerate RuBP.

RuBP: Ribulose-1,5-bisphosphate.

Types of Plants

Type	CO2 Usage	Example
C3	Uses CO2 directly from air	Most plants
C4	Closes stomata in hot/dry weather, still photosynthesizes	Corn, sugar cane
CAM	Opens stomata at night to conserve water	Pineapple

Cellular Reproduction: Cells from Cells

Asexual vs. Sexual Reproduction

Type	Divisions	Cells Produced	Chromosome Number	Purpose
Mitosis	1	2 identical	46	Growth/repair
Meiosis	2	4 different	23	Gamete production

Cell Division and Chromosomes

Cell Division: Replaces damaged/lost cells, permits growth, allows reproduction.
Somatic Cells: Body cells, 46 chromosomes, made by mitosis.
Reproductive Cells: Egg & sperm, 23 chromosomes, made by meiosis.
Histones: Proteins DNA wraps around for packaging.
Nucleosomes: DNA wrapped around histones; "beads on a string" structure.
Sister Chromatids: Duplicates of chromosomes joined at centromere.

Phases of Mitosis and Cell Cycle

Prophase: Chromosomes condense, nuclear membrane breaks down, spindle forms.
Metaphase: Chromosomes line up in middle.
Anaphase: Sister chromatids separate.
Telophase: Nuclear membrane reforms, chromosomes unwind.
Cytokinesis: Division of cytoplasm.

How Genes are Controlled: Cancer and Cell Cycle Regulation

Genes and Cancer

p53 gene: Codes for protein suppressing tumor formation.
BRCA1/BRCA2: Tumor-suppressor genes; mutations increase cancer risk.
Oncogenes: Cancer-causing genes (often from viruses).
Proto-oncogenes: Normal genes regulating growth; can become oncogenes via mutation, amplification, or rearrangement.
Tumor-suppressor genes: Inhibit cell division, prevent uncontrolled growth.
Apoptosis: Programmed cell death.

Cancer Cell Cycle vs. Normal Cell Cycle

Normal Cells: Respond to checkpoints, stop dividing when needed.
Cancer Cells: Ignore checkpoints, divide uncontrollably, avoid apoptosis.

Types of Tumors and Cancer

Tumor Type	Description	Example
Benign	Cells remain at original site	Non-spreading
Malignant	Cells can spread (metastasis)	Spreading cancer

Cancer Type	Location	Example
Carcinoma	External/internal covering	Intestine
Sarcoma	Support tissues	Muscle, bone
Leukemia	Bone marrow	Blood
Lymphoma	Lymph glands	Lymphatic system

Cancer Causes and Prevention

Random DNA mutation, mutagens (chemicals, radiation), viruses, inherited defective genes.
Prevention: Not smoking, avoiding sun, high-fiber/low-fat diet, regular doctor visits, self-examinations.

Cancer Treatments

Surgery: Physical removal of tumor.
Radiation Therapy: Disrupts cell division.
Chemotherapy: Drugs that disrupt cell division.

Cellular Reproduction: Meiosis and Genetic Variation

Meiosis and Chromosome Number

Meiosis: Cell division producing gametes, reduces chromosome number by half, results in 4 genetically different haploid cells.
Haploid Cells: One set of chromosomes (n); human gametes have 23.
Diploid Cells: Two sets of chromosomes; human somatic cells have 46.
Fertilization: Fusion of sperm and egg, creates zygote.
Homologous Chromosomes: Matching pairs.
Gene: Segment of DNA coding for a trait.
Allele: Different versions of a gene.
Locus: Specific location of a gene on a chromosome.

Karyotypes and Sex Determination

Karyotype: Chromosome organization by number, size, type.
Female: XX; Male: XY.
Sex Determination: Father determines sex (X or Y sperm).
Autosomes: Chromosomes 1-22; non-sex chromosomes.

Stages of Meiosis

Meiosis I	Meiosis II
Prophase I	Prophase II
Metaphase I	Metaphase II
Anaphase I	Anaphase II
Telophase I	Telophase II

Genetic Variation

Crossing Over: Exchange of DNA between homologous chromosomes (Prophase I).
Independent Assortment: Random alignment of homologous chromosomes (Metaphase I).
Random Fertilization: Increases genetic diversity.

Comparison: Mitosis vs. Meiosis

Feature	Mitosis	Meiosis
Divisions	1	2
Cells Produced	2 identical	4 different
Chromosome Number	46	23
Crossing Over	No	Yes

Chromosome Alignment and Separation

Metaphase I: Homologous pairs line up.
Metaphase II: Chromosomes line up single file.
Anaphase I: Homologous chromosomes separate.
Anaphase II: Sister chromatids separate.

DNA Replication and Cell Count

DNA replicates once before Meiosis I; no replication before Meiosis II.
Start: 1 cell; End Meiosis I: 2 cells; End Meiosis II: 4 haploid cells.

Chromosomal Disorders

Down Syndrome: Extra chromosome 21 (trisomy 21).
Non-disjunction: Failure of chromosome pair separation during anaphase; produces gametes with incorrect chromosome number.
Klinefelter’s Syndrome: XXY; male, sterile, small testes, enlarged breasts.
Turner’s Syndrome: XO; female, sterile, sex organs don’t mature, extra skin at neck base; only known viable 45-chromosome condition.