Cell Structure and Organelles

Overview of Cell Components

Cells are the basic units of life, containing specialized structures called organelles that perform distinct functions necessary for survival and growth.

• rRNA: Ribosomal RNA is a type of RNA that forms the core of ribosomes and catalyzes protein synthesis.

• Ribosomes: Organelles that synthesize proteins. They can be found free in the cytoplasm or attached to the endoplasmic reticulum. Ribosomes are assembled in the nucleolus inside the nucleus.

• Endoplasmic Reticulum (ER): Network of membranes involved in protein and lipid synthesis.

  • Smooth ER: Lacks ribosomes. Synthesizes lipids and phospholipids, detoxifies drugs and poisons.

  • Rough ER: Studded with ribosomes. Synthesizes proteins, especially those destined for secretion or membrane insertion.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Membrane-bound sacs containing hydrolytic enzymes for digesting macromolecules. Important for recycling cell material and defense (e.g., in neutrophils and monocytes).

• Peroxisomes: Produce hydrogen peroxide and contain catalase to break it down. Involved in lipid metabolism and detoxification.

• Mitochondria: "Powerhouse" of the cell. Site of ATP (energy) production via cellular respiration. Contains its own DNA.

• Chloroplasts: Found in plant cells. Site of photosynthesis, converting light energy into chemical energy (glucose).

• Cytoskeleton: Network of protein fibers (microfilaments, microtubules, intermediate filaments) that provide structural support, shape, and movement for the cell.

• Cell Wall: Rigid outer layer found in plant cells, fungi, and some bacteria. Provides protection and structural support.

Example: Mitochondria generate ATP through cellular respiration, which powers cellular activities.

Cell Membrane and Transport

Structure and Function

The cell membrane is a selectively permeable barrier composed of a phospholipid bilayer with embedded proteins, controlling the movement of substances in and out of the cell.

• Diffusion: Movement of molecules from an area of high concentration to an area of low concentration. Does not require energy.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Solvent: Substance that dissolves a solute to form a solution (e.g., water).

• Solute: Substance that is dissolved in a solvent.

• Hypertonic Solution: Higher solute concentration compared to another solution; water moves out of the cell.

• Hypotonic Solution: Lower solute concentration compared to another solution; water moves into the cell.

• Active Transport: Movement of substances against their concentration gradient using energy (ATP).

Equation:

Example: In a hypertonic environment, plant cells lose water and may undergo plasmolysis.

Cellular Energy and Metabolism

ATP and Cellular Respiration

Cells require energy to perform work, which is supplied by ATP produced during cellular respiration and fermentation.

• ATP (Adenosine Triphosphate): Main energy currency of the cell.

• Fermentation: Anaerobic process that generates ATP without oxygen, producing lactic acid or ethanol.

• Glycolysis: First step of cellular respiration; breaks down glucose into pyruvate, generating ATP and NADH.

• Krebs Cycle (Citric Acid Cycle): Occurs in mitochondria; oxidizes acetyl-CoA to CO2, producing NADH, FADH2, and ATP.

• Electron Transport Chain: Uses NADH and FADH2 to generate ATP via oxidative phosphorylation.

Equation:

Example: Muscle cells use fermentation to produce ATP during intense exercise when oxygen is limited.

Photosynthesis

Process and Significance

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.

• Light Reaction: Occurs in the thylakoid membrane; converts light energy into chemical energy (ATP and NADPH).

• Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to fix carbon dioxide and produce glucose.

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

• Heterotrophs: Organisms that consume other organisms for energy (e.g., animals).

• Stomata: Pores on leaf surfaces that regulate gas exchange.

Equation:

Example: Chlorophyll in chloroplasts absorbs sunlight, driving the synthesis of glucose from CO2 and water.

Cell Cycle and Division

Phases and Regulation

The cell cycle is a series of events that cells go through as they grow and divide. It consists of interphase (growth and DNA replication) and mitotic phase (division).

• Interphase: Non-dividing phase; includes G1 (growth), S (DNA synthesis), and G2 (growth and preparation for division).

• Mitosis: Division of the nucleus, resulting in two genetically identical daughter cells.

• Cytokinesis: Division of the cytoplasm, completing cell division.

• Chromatin: DNA-protein complex that packages DNA in the nucleus.

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

Example: Skin cells undergo mitosis to replace damaged tissue.

Genetics and Heredity

Basic Principles

Genetics is the study of heredity and variation in organisms. Traits are inherited according to specific patterns.

• Punnett Squares: Diagram used to predict the outcome of a genetic cross. Capital letters represent dominant alleles; lowercase letters represent recessive alleles.

• Binary Fission: Asexual reproduction in prokaryotes, resulting in two identical cells.

Example: If one parent is Bb and the other is Bb, there is a 75% chance of the dominant trait appearing in the offspring.

Summary Table: Cell Organelles and Functions

Additional info: Some explanations and examples have been expanded for clarity and completeness.