Cell Structure, Function, and Processes: Study Notes for Anatomy & Physiology

Cell Structure and Function

Overview of Cells

Cells are the fundamental units of life, forming the basis of all living organisms. Each cell is composed of various organelles and structures that perform specialized functions necessary for survival and homeostasis.

• Cells: Basic units of structure and function in living things.

• Organelles: Specialized structures within cells, each with distinct roles.

Major Cell Organelles and Their Functions

• Cell Membrane (Plasma Membrane): A selectively permeable barrier that regulates the movement of substances in and out of the cell. Composed of a phospholipid bilayer with embedded proteins (Fluid Mosaic Model).

• Nucleus: Contains genetic material (DNA) and controls cellular activities. Surrounded by a nuclear envelope with pores for molecular transport.

• Ribosomes: Sites of protein synthesis. Can be free in the cytoplasm or attached to the endoplasmic reticulum.

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes and transports proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

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

• Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.

• Peroxisomes: Contain enzymes for fatty acid metabolism and detoxification of harmful substances.

• Cytoskeleton: Network of protein filaments (microtubules, microfilaments) that provide structural support, shape, and facilitate movement.

• Centrioles: Involved in organizing microtubules during cell division.

• Cell Inclusions: Non-living materials such as glycogen, lipid droplets, and pigments stored in the cytoplasm.

DNA, RNA, and Protein Synthesis

Structure of DNA and RNA

• DNA (Deoxyribonucleic Acid): Double-stranded helix composed of nucleotides (adenine, thymine, cytosine, guanine). Stores genetic information.

• RNA (Ribonucleic Acid): Single-stranded; contains uracil instead of thymine. Functions in protein synthesis.

Gene Expression: Transcription and Translation

• Transcription: The process by which a segment of DNA is copied into mRNA in the nucleus.

  • Enzyme RNA polymerase binds to the promoter region and synthesizes mRNA from the DNA template.

  • mRNA carries the genetic code from the nucleus to the cytoplasm.

• Translation: The process by which ribosomes synthesize proteins using the mRNA template.

  • tRNA molecules bring amino acids to the ribosome, matching codons on the mRNA with anticodons on the tRNA.

  • The sequence of amino acids determines the structure and function of the protein.

Key Equations:

• Central Dogma: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Plasma Membrane Structure and Transport Mechanisms

Fluid Mosaic Model

The plasma membrane is composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates. This structure allows for selective permeability and fluidity.

Membrane Transport

• Passive Transport: Movement of molecules without energy input.

  • Diffusion: Movement from high to low concentration.

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

  • Facilitated Diffusion: Movement via membrane proteins.

• Active Transport: Movement against the concentration gradient, requiring energy (ATP).

  • Example: Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ ATPase)

• Vesicular Transport: Movement of large particles via vesicles (endocytosis, exocytosis, phagocytosis).

Osmosis and Tonicity

• Isotonic Solution: Equal solute concentration inside and outside the cell; no net water movement.

• Hypertonic Solution: Higher solute concentration outside the cell; water moves out, causing cell shrinkage (crenation).

• Hypotonic Solution: Lower solute concentration outside the cell; water moves in, causing cell swelling or lysis.

Cell Cycle and Mitosis

Phases of the Cell Cycle

• Interphase: Period of cell growth and DNA replication.

  • G1: Cell growth

  • S: DNA synthesis (replication)

  • G2: Preparation for mitosis

• Mitosis: Division of the nucleus into two genetically identical daughter cells.

  • Prophase

  • Metaphase

  • Anaphase

  • Telophase

• Cytokinesis: Division of the cytoplasm, resulting in two separate cells.

Purpose of Mitosis

• Growth

• Tissue repair

• Replacement of old or damaged cells

Summary Table: Major Cell Organelles and Functions

Organelle	Main Function
Nucleus	Stores DNA, controls cell activities
Ribosome	Protein synthesis
Endoplasmic Reticulum (Rough)	Protein modification and transport
Endoplasmic Reticulum (Smooth)	Lipid synthesis, detoxification
Golgi Apparatus	Processing and packaging of proteins and lipids
Lysosome	Digestion of macromolecules
Peroxisome	Breakdown of fatty acids, detoxification
Mitochondrion	ATP production (cellular respiration)
Cytoskeleton	Structural support, movement

Additional info: These notes expand on the provided outline by including definitions, examples, and a summary table for clarity and completeness. The content is structured to align with standard Anatomy & Physiology curriculum topics on cells and their functions.