BackCell Structure, Function, and Energy: Study Guide for General Biology
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CHAPTER 4: A TOUR OF THE CELL
The Microscopic World of Cells
Cells are the fundamental units of life, and understanding their structure and function is essential in biology. This section covers the major categories of cells, cell theory, and key differences among cell types.
Major Categories of Cells: There are two main types of cells: prokaryotic and eukaryotic cells. Prokaryotic cells (such as bacteria and archaea) lack a nucleus and membrane-bound organelles, while eukaryotic cells (such as plant, animal, fungi, and protist cells) have a nucleus and various organelles.
Cell Theory: The cell theory states that all living things are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.
Prokaryotic vs. Eukaryotic Cells: Prokaryotes are generally smaller, lack a nucleus, and have simpler structures. Eukaryotes are larger, have a nucleus, and possess complex organelles.
Plant vs. Animal Cells: Plant cells have a cell wall, chloroplasts, and a large central vacuole, while animal cells do not. Both have mitochondria, a nucleus, and other organelles.
Membrane Structure
The cell membrane, also known as the plasma membrane, is a selectively permeable barrier that surrounds the cell.
Plasma Membrane: Composed mainly of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates. It regulates the movement of substances in and out of the cell.
The Nucleus and Ribosomes: Genetic Control of the Cell
The nucleus and ribosomes are essential for storing genetic information and synthesizing proteins.
Nucleus: Contains the cell's DNA, which is organized into chromosomes. The nucleus controls gene expression and mediates the replication of DNA during the cell cycle.
Ribosomes: Small structures either free in the cytoplasm or attached to the endoplasmic reticulum. They are the sites of protein synthesis, translating genetic information from mRNA into polypeptides.
The Endomembrane System: Manufacturing and Distributing Cellular Products
The endomembrane system is a group of organelles involved in the synthesis, modification, and transport of cellular materials.
Endoplasmic Reticulum (ER): Rough ER has ribosomes and synthesizes proteins; smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for storage or transport out of the cell.
Other Organelles: Lysosomes contain digestive enzymes for breaking down waste; vacuoles store materials; peroxisomes break down fatty acids and detoxify harmful substances.
Chloroplasts and Mitochondria
These organelles are responsible for energy conversion in cells.
Chloroplasts: Found in plant cells, they carry out photosynthesis, converting solar energy into chemical energy (glucose).
Mitochondria: Present in both plant and animal cells, they are the site of cellular respiration, converting glucose into ATP (usable energy).
The Cytoskeleton: Cell Shape and Movement
The cytoskeleton is a network of protein fibers that provides structural support, shape, and movement to the cell.
Cytoskeleton: Composed of microfilaments, intermediate filaments, and microtubules. It maintains cell shape, anchors organelles, and is involved in cell movement.
Flagella and Cilia: Flagella are long, whip-like structures for movement (e.g., sperm cells). Cilia are shorter and more numerous, moving fluid or materials past the cell surface (e.g., respiratory tract cells).
Some Basic Energy Concepts
Energy is essential for all cellular processes. This section introduces key energy concepts relevant to biology.
Kinetic Energy: The energy of motion.
Potential Energy: Stored energy due to position or structure.
Heat: Energy transferred due to temperature difference.
Chemical Energy: Potential energy stored in chemical bonds.
Calories: A unit of energy; specifically, the amount of heat needed to raise the temperature of 1 gram of water by 1°C.
ATP and Cellular Work
ATP (adenosine triphosphate) is the primary energy carrier in cells, driving many biological processes.
ATP Structure: Composed of adenine, ribose, and three phosphate groups.
ATP Function: Provides energy for cellular work by transferring a phosphate group to other molecules (phosphorylation).
ATP Cycle: ATP is regenerated from ADP and inorganic phosphate through cellular respiration.
Equation:
Enzymes
Enzymes are biological catalysts that speed up chemical reactions in cells without being consumed.
Definition: Enzymes are proteins that lower the activation energy of reactions.
How Enzymes Work: They bind to substrates at their active site, facilitating the conversion to products.
Catalysis: Enzymes are highly specific for their substrates and can be regulated by inhibitors or activators.
Membrane Function
Cell membranes control the movement of substances into and out of cells, maintaining homeostasis.
Passive Transport: Movement of molecules down their concentration gradient without energy input (e.g., diffusion, osmosis).
Facilitated Transport: Passive movement via transport proteins.
Active Transport: Movement against the concentration gradient, requiring energy (usually from ATP).
Osmosis: Diffusion of water across a selectively permeable membrane.
Water Balance: Maintaining proper water levels is crucial for cell survival.
Exocytosis and Endocytosis: Processes for moving large molecules or particles into (endocytosis) or out of (exocytosis) the cell via vesicles.
CHAPTER 6: CELLULAR RESPIRATION: OBTAINING ENERGY FROM FOOD
Energy Flow and Chemical Cycling in the Biosphere
Energy flows through ecosystems, while chemical elements are recycled. Producers (autotrophs) convert solar energy to chemical energy, and consumers (heterotrophs) obtain energy by eating other organisms.
Photosynthesis: Converts light energy to chemical energy in glucose.
Respiration: Breaks down glucose to release energy for cellular work.
Cellular Respiration
Cellular respiration is the process by which cells extract energy from food molecules.
Overall Chemical Formula:
Stages of Cellular Respiration:
Glycolysis: Occurs in the cytoplasm; breaks glucose into pyruvate.
Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix; completes the breakdown of glucose.
Electron Transport Chain: Occurs in the inner mitochondrial membrane; produces most of the ATP.
Inputs and Outputs: Inputs are glucose and oxygen; outputs are carbon dioxide, water, and ATP.
Results of Cellular Respiration: Production of ATP, release of CO2 and H2O.
Fermentation: Anaerobic Harvest of Food Energy
Fermentation allows cells to produce energy without oxygen.
Definition: Fermentation is an anaerobic process that enables ATP production in the absence of oxygen.
Types: Lactic acid fermentation (in muscle cells) and alcoholic fermentation (in yeast and some bacteria).
Microbial Fermentation: Used in food production (e.g., yogurt, bread, alcohol).
Importance of Oxygen: Oxygen is the final electron acceptor in aerobic respiration, allowing for efficient ATP production.
