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

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Cell Structure and Organelles

Membranous and Nonmembranous Organelles

Cells contain various organelles, each with specific structures and functions essential for cellular activity and homeostasis. Organelles are classified as either membranous (surrounded by a membrane) or nonmembranous (not surrounded by a membrane).

Structure	Description
Plasma membrane	Phospholipid bilayer that surrounds the cell, controlling entry and exit of substances and facilitating communication.
Cytosol	Fluid portion of the cytoplasm where metabolic reactions occur; contains ions, nutrients, and proteins.
Mitochondria	Double-membraned organelle responsible for ATP production via aerobic respiration; contains its own DNA.
Nucleus	Membrane-bound organelle housing genetic material (DNA); controls cellular activities and gene expression.
Golgi apparatus	Stack of flattened membranes that modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes	Membrane-bound vesicles containing digestive enzymes; break down waste materials and cellular debris.
Peroxisomes	Small vesicles containing enzymes for oxidation reactions; detoxify harmful substances and metabolize fatty acids.
Endoplasmic Reticulum (ER)	Network of membranes; Rough ER has ribosomes and synthesizes proteins, Smooth ER lacks ribosomes and synthesizes lipids and detoxifies chemicals.
Cytoskeleton	Network of protein filaments (microtubules, microfilaments, intermediate filaments) providing structural support, shape, and movement.
Centrioles	Nonmembranous structures involved in organizing microtubules during cell division.
Cilia	Hair-like projections that move substances across cell surfaces.
Flagella	Long, whip-like structures enabling cell movement (e.g., sperm cells).
Ribosomes	Nonmembranous organelles composed of RNA and protein; site of protein synthesis.

Plasma Membrane Properties

Hydrophobic vs. Hydrophilic

The plasma membrane is a selectively permeable barrier composed of a phospholipid bilayer. The hydrophobic (water-fearing) tails face inward, while the hydrophilic (water-loving) heads face outward.

Hydrophobic: Nonpolar, repels water, forms the interior of the membrane.
Hydrophilic: Polar, attracts water, forms the exterior surfaces of the membrane.
This arrangement allows the membrane to control the movement of substances and maintain cellular integrity.

Endoplasmic Reticulum

Smooth vs. Rough ER

Rough ER: Studded with ribosomes; synthesizes and processes proteins for secretion or membrane insertion.
Smooth ER: Lacks ribosomes; synthesizes lipids, metabolizes carbohydrates, and detoxifies drugs and poisons.
Comparison: Rough ER is primarily involved in protein synthesis, while smooth ER is involved in lipid metabolism and detoxification.

Golgi Apparatus

Protein Processing Steps

The Golgi apparatus modifies, sorts, and packages proteins. The five steps proteins undergo in the Golgi are:

Transport vesicles deliver proteins from the ER to the Golgi.
Proteins enter the cis face (receiving side) of the Golgi.
Proteins are modified (e.g., glycosylation, phosphorylation) as they move through the Golgi stacks.
Proteins are sorted and packaged into vesicles at the trans face (shipping side).
Vesicles transport proteins to their final destinations (e.g., plasma membrane, lysosomes, secretion).

Cellular Respiration and ATP Production

Stages of Aerobic Metabolism

Glycolysis: Occurs in the cytosol; breaks down glucose into pyruvate, producing 2 ATP and 2 NADH.
Citric Acid Cycle (Krebs Cycle): Occurs in mitochondria; oxidizes acetyl-CoA to CO2, generating NADH, FADH2, and 2 ATP per glucose.
ATP Synthase Action: Occurs in the mitochondrial inner membrane; uses the proton gradient to synthesize ATP from ADP and inorganic phosphate.

DNA Structure and Bases

DNA Bases and Bonding

Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Bases are held together by hydrogen bonds: A pairs with T (2 bonds), G pairs with C (3 bonds).

Central Dogma of Biology

Flow of Genetic Information

DNA is transcribed into RNA.
RNA is translated into protein.
This process governs how genetic information directs cellular function.

Translation

Product of Translation

The product of translation is a polypeptide chain (protein).
Translation occurs at ribosomes, where mRNA is decoded into amino acids.

Membrane Transport

Passive vs. Active Transport

Feature	Passive Transport	Active Transport
Energy Requirement	No ATP required	Requires ATP
Direction	Down concentration gradient	Against concentration gradient
Examples	Diffusion, osmosis, facilitated diffusion	Pumps (Na+/K+), endocytosis, exocytosis

Types of Vesicular Transport

Endocytosis: Uptake of materials into the cell via vesicles.
Exocytosis: Release of materials from the cell via vesicles.
Phagocytosis: Engulfment of large particles or cells.
Pinocytosis: Uptake of fluids and small molecules.
Receptor-mediated endocytosis: Specific uptake of molecules via receptor binding.

Osmosis and Tonicity

Red Blood Cells in Solutions

Isotonic solution: No net movement of water; cell maintains shape.
Hypertonic solution: Water leaves the cell; cell shrinks (crenation).
Hypotonic solution: Water enters the cell; cell swells and may burst (lysis).

Cell Cycle and Mitosis

Phases of the Cell Cycle

G1 phase: Cell growth and normal functions.
S phase: DNA replication.
G2 phase: Preparation for mitosis.
M phase (Mitosis): Division of the nucleus and cytoplasm.

Phases of Mitosis

Prophase: Chromatin condenses, spindle forms.
Metaphase: Chromosomes align at the cell equator.
Anaphase: Sister chromatids separate to opposite poles.
Telophase: Nuclear envelopes reform, chromosomes decondense.
Cytokinesis: Division of cytoplasm, forming two daughter cells.

Cancer and Cell Cycle Regulation

Cell Division and Cancer

Cancers often originate in cells that divide frequently due to increased risk of mutations during replication.
Cell cycle checkpoints monitor and regulate progression, preventing damaged cells from dividing.
Loss of checkpoint control leads to uncontrolled cell division (cancer).

Metastasis

Metastasis is the spread of cancer cells from the original site to other parts of the body.
Cancer cells invade blood or lymph vessels, travel to distant tissues, and establish new tumors, worsening the patient's condition.

Additional Info

Cellular organelles enclosed by membranes are protected from the cytosol, allowing specialized environments for specific reactions.
Muscle cells are large and multinucleated to support their function; alternative mechanisms for large cells include increased surface area via membrane folding.