Energy in Biological Systems

Potential and Kinetic Energy

Energy is fundamental to all biological processes. It exists in different forms, including potential and kinetic energy.

• Potential Energy: Stored energy due to position or structure. In biology, chemical bonds in molecules store potential energy.

• Kinetic Energy: The energy of motion. For example, molecules moving in a cell possess kinetic energy.

• Example: A ball at the top of a hill has potential energy; as it rolls down, this is converted to kinetic energy.

Chemical Energy

• Chemical Energy: A form of potential energy stored in chemical bonds of molecules, such as glucose or ATP.

• Application: Cells extract chemical energy from food molecules to perform work.

Endergonic and Exergonic Reactions

Chemical reactions in cells can either require energy input or release energy.

• Endergonic Reaction: Absorbs energy from surroundings; products have more energy than reactants.

• Exergonic Reaction: Releases energy; products have less energy than reactants.

• ATP Usage: Endergonic reactions often require ATP, while exergonic reactions can produce ATP.

• Examples: Photosynthesis is endergonic; cellular respiration is exergonic.

ATP and Cellular Energy

• ATP (Adenosine Triphosphate): The primary energy carrier in cells.

• ATP Hydrolysis: ATP is broken down into ADP and inorganic phosphate, releasing energy for cellular processes.

Enzymes and Metabolism

Enzyme Structure and Function

• Enzymes: Biological catalysts that speed up chemical reactions without being consumed.

• Lock and Key Model: Enzymes have specific active sites that fit substrates precisely, like a lock and key.

• Reusability: Enzymes are not used up during reactions and can be reused.

Factors Affecting Enzyme Activity

• Temperature: High heat can denature enzymes, reducing activity.

• pH and Salt: Extreme pH or salt concentrations can alter enzyme shape and function.

• Allosteric Control: Regulation of enzyme activity by molecules binding at sites other than the active site.

• Feedback Inhibition: End product of a pathway inhibits an earlier step, preventing overproduction.

• Cofactors: Non-protein helpers (e.g., metal ions) required for enzyme activity.

Cellular Respiration

Aerobic Respiration

Aerobic respiration is the process by which cells extract energy from glucose using oxygen.

• Purpose: To produce ATP for cellular activities.

• Oxygen Requirement: Yes, oxygen is required.

• Equation:

• Stages:

  1. Glycolysis (cytoplasm)

  2. Krebs Cycle (mitochondrial matrix)

  3. Electron Transport Chain (mitochondrial inner membrane)

• ATP Yield: Glycolysis (2 ATP), Krebs Cycle (2 ATP), Electron Transport Chain (about 32-34 ATP)

• Relationship to Photosynthesis: Products of photosynthesis (glucose, O2) are reactants in respiration.

• Redox Reactions: Involve transfer of electrons; respiration is a redox process.

• Exergonic: Respiration releases energy.

Anaerobic Respiration and Fermentation

• Anaerobic Respiration: Occurs without oxygen; less efficient ATP production.

• Evolution: Anaerobic respiration evolved before aerobic respiration.

• First Step: Glycolysis.

• ATP Yield: 2 ATP per glucose.

• Fermentation Types:

  • Lactic Acid Fermentation: Produces lactic acid (e.g., in muscles).

  • Alcoholic Fermentation: Produces ethanol and CO2 (e.g., in yeast).

• Application: Yeast fermentation causes bread dough to rise by producing CO2.

Photosynthesis

Importance and Process

• Importance: Provides energy and organic molecules for nearly all life on Earth.

• Photoautotrophs: Organisms that use light to synthesize food (e.g., plants, algae).

• Main Pigment: Chlorophyll.

• Organelle: Chloroplast.

• Reactants and Products: Uses CO2 and H2O; produces glucose and O2.

• Equation:

Stages of Photosynthesis

• Light Reactions: Occur in thylakoid membranes; use light to produce ATP and NADPH, release O2.

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

• Endergonic: Photosynthesis requires energy input.

Cell Cycle and Mitosis

Binary Fission

• Definition: Asexual reproduction in prokaryotes.

• Cell Types: Prokaryotic cells (bacteria, archaea).

• Chromosome Number: Prokaryotes have a single circular chromosome.

• Offspring: Genetically identical to parent.

Somatic Cells and Chromosomes

• Somatic Cells: All body cells except gametes (e.g., skin cells).

• Diploid: Somatic cells have two sets of chromosomes.

• Chromosomes: Structures containing DNA; humans have 46 chromosomes.

• Sister Chromatids: Identical copies of a chromosome joined at the centromere.

• Centromere: Region where sister chromatids are attached.

Cell Cycle and Mitosis

• Stages of Cell Cycle: Interphase (G1, S, G2), Mitosis, Cytokinesis.

• Interphase:

  • G1: Cell growth

  • S: DNA replication

  • G2: Preparation for division

• Purpose of Mitosis: Produce identical diploid cells for growth and repair.

• Plant vs. Animal Cell Division: Plant cells form a cell plate; animal cells form a cleavage furrow.

Cancer

Overview and Types

• Prevalence: Cancer is a common disease in the US.

• Common Types: Breast, lung, prostate, colorectal cancers.

• Leading Cause of Death: Lung cancer causes the most cancer deaths.

Benign vs. Malignant Tumors

Cancer Biology Terms

• Metastasis: Spread of cancer cells to new areas.

• Angiogenesis: Formation of new blood vessels to supply tumors.

• Telomeres: Protective chromosome ends.

• Telomerase: Enzyme that extends telomeres, often active in cancer cells.

• Immortalized Cells: Cells that can divide indefinitely.

Causes and Treatment

• Causes: Mutations in DNA, often multiple mutations required.

• Repair Mechanisms: Cells have systems to repair DNA damage.

• Treatments: Surgery, chemotherapy, radiation therapy.

Meiosis and Sexual Reproduction

Sexual vs. Asexual Reproduction

• Sexual Reproduction: Increases genetic variation; involves fusion of gametes.

• Asexual Reproduction: Produces identical offspring.

Gametes and Cell Division

• Male Gametes: Sperm

• Female Gametes: Eggs (ova)

• Cell Division: Meiosis produces gametes.

• Stages of Meiosis: Meiosis I and II, each with prophase, metaphase, anaphase, telophase.

• Spermatogenesis: Produces four haploid sperm cells.

• Oogenesis: Produces one haploid egg and polar bodies.

• Fertilization: Fusion of sperm and egg to form a diploid zygote.

• Variation: Crossing over, independent assortment, and random fertilization introduce genetic diversity.