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Purdue University Globle
NU551 Advanced Physiology and Pathophysiology Across the Lifespan
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Cells are the basic structural and functional units of the human body, while DNA stores the genetic information that directs how cells grow, function, reproduce, and repair themselves. Understanding cell structure, DNA, genetics, cellular metabolism, membrane transport, and cell division is essential for nursing and healthcare students because abnormalities in these processes can contribute to disease and tissue damage. This guide reviews the major cellular and genetic concepts, including organelles, DNA organization, energy production, membrane transport, cellular injury, apoptosis, necrosis, and human genetics.
Cells are commonly divided into two major categories: prokaryotic cells and eukaryotic cells. The primary distinction is that eukaryotic cells contain a membrane-bound nucleus and specialized membrane-bound organelles, whereas prokaryotic cells do not.
Prokaryotic cells are relatively simple cells found primarily in bacteria and archaea. Their genetic material is not enclosed within a membrane-bound nucleus. Instead, the DNA is located in a region of the cytoplasm called the nucleoid.
Prokaryotic cells generally have circular DNA and lack organelles such as mitochondria, the Golgi apparatus, and the endoplasmic reticulum. They typically reproduce through binary fission, a process in which one cell divides into two daughter cells.
Eukaryotic cells are more structurally complex and include the cells of humans, other animals, plants, fungi, and protists. Their DNA is contained within a membrane-bound nucleus.
Eukaryotic cells also contain specialized organelles that perform specific functions. In humans, these structures allow cells to efficiently produce energy, synthesize proteins, communicate with other cells, transport substances, and maintain homeostasis.
| Feature | Prokaryotic Cells | Eukaryotic Cells |
|---|---|---|
| Nucleus | Absent | Present |
| DNA | Usually circular | Linear chromosomes |
| Membrane-bound organelles | Absent | Present |
| Typical size | Smaller | Larger |
| Cell division | Binary fission | Mitosis or meiosis |
The compartmentalization of eukaryotic cells allows different cellular processes to occur in specialized locations, supporting greater cellular organization and functional specialization.
DNA, or deoxyribonucleic acid, contains the genetic instructions used by cells to produce proteins and regulate cellular activities. Because DNA molecules are extremely long, they must be carefully organized and packaged within the nucleus.
Histones are proteins that help package DNA. DNA wraps around groups of histone proteins to form structures called nucleosomes. Nucleosomes are further organized into chromatin, allowing the large DNA molecule to fit inside the nucleus.
Histones have several important functions:
Organizing and compacting DNA
Protecting genetic material
Influencing gene expression
Supporting DNA replication
Contributing to DNA repair
Chemical modifications of histones can influence whether specific genes are more or less active. This is one component of epigenetic regulation, in which gene activity can change without altering the underlying DNA sequence.
Organelles are specialized structures within cells that perform specific functions. Understanding their roles helps explain how cells maintain normal physiology.
The nucleus contains most of a cell’s genetic material and acts as a major center for regulating gene expression. It plays an important role in cellular growth, metabolism, DNA replication, and cell division.
The nucleolus is a specialized region within the nucleus. It produces ribosomal RNA and helps assemble ribosomal subunits, which are necessary for protein synthesis.
The rough endoplasmic reticulum (rough ER) is covered with ribosomes. It synthesizes proteins that are destined for secretion, incorporation into cell membranes, or delivery to certain organelles.
The smooth endoplasmic reticulum (smooth ER) does not contain ribosomes. Its functions include lipid synthesis, steroid hormone production, detoxification of certain substances, and calcium storage.
The Golgi apparatus processes proteins and lipids received from the endoplasmic reticulum. It modifies, sorts, and packages these molecules for transport to different locations within or outside the cell.
Important functions include protein modification, glycosylation, sorting, packaging, and formation of certain vesicles and lysosomes.
Mitochondria are major sites of cellular energy production. They generate ATP through aerobic metabolism and oxidative phosphorylation.
Mitochondria also participate in calcium regulation, heat generation, and pathways involved in programmed cell death.
Lysosomes contain enzymes that break down cellular waste, damaged organelles, and certain foreign materials. This digestive function helps cells recycle components and maintain cellular quality control.
Cells need specialized connections to maintain the structural integrity of tissues. Desmosomes are strong cell-to-cell junctions that anchor neighboring cells together.
They are particularly important in tissues exposed to mechanical stress, including the skin, cardiac muscle, and certain epithelial tissues. By connecting cells to the cytoskeleton, desmosomes help tissues withstand stretching and physical forces.
Cells communicate by releasing or responding to signaling molecules. This communication allows cells to coordinate processes such as growth, metabolism, immune responses, and tissue repair.
First messengers are extracellular signaling molecules that bind to receptors on or within target cells. Examples include hormones, neurotransmitters, and growth factors.
When a first messenger activates its receptor, it can trigger a chain of intracellular events.
Second messengers are intracellular molecules that transmit and amplify signals after a receptor has been activated.
Important examples include:
Cyclic adenosine monophosphate (cAMP)
Calcium ions (Ca²⁺)
Inositol trisphosphate (IP₃)
Diacylglycerol (DAG)
Second-messenger systems allow cells to produce rapid and coordinated responses to external signals.
Cells require energy to maintain membranes, transport substances, synthesize proteins, divide, and perform other physiological functions. Adenosine triphosphate (ATP) is the primary energy currency used by cells.
Glycolysis is the first major stage of glucose metabolism. It occurs in the cytoplasm and breaks one glucose molecule into two molecules of pyruvate.
Glycolysis does not directly require oxygen and produces a net gain of 2 ATP molecules per glucose molecule, along with NADH.
When oxygen availability is insufficient for normal aerobic metabolism, cells can rely more heavily on anaerobic glycolysis. Pyruvate is converted to lactate, allowing glycolysis to continue producing ATP.
This pathway generates ATP quickly but is much less efficient than complete aerobic oxidation of glucose.
Aerobic metabolism uses oxygen and occurs largely within mitochondria after glycolysis. It includes the citric acid cycle, electron transport chain, and oxidative phosphorylation.
These processes extract energy from nutrients and use it to generate substantially more ATP than glycolysis alone.
Oxidative phosphorylation occurs at the inner mitochondrial membrane. Electrons move through the electron transport chain, creating a proton gradient that powers ATP synthase.
Oxygen serves as the final electron acceptor and is reduced to water. Depending on the conditions and accounting convention, complete oxidation of one glucose molecule is commonly estimated to produce approximately 30–32 ATP in eukaryotic cells.
The cell membrane regulates what enters and leaves the cell. Transport mechanisms allow cells to obtain nutrients, eliminate waste, maintain ion concentrations, and regulate water balance.
Diffusion is the passive movement of particles from an area of higher concentration toward an area of lower concentration. Because it is passive, diffusion does not directly require cellular ATP.
Osmosis is the movement of water across a selectively permeable membrane. Water moves toward the side with the greater concentration of osmotically active solutes until equilibrium is approached.
Osmosis is particularly important for maintaining cell volume and fluid balance.
Filtration occurs when hydrostatic pressure pushes water and small dissolved substances through a membrane.
A major physiological example is glomerular filtration in the kidneys, where blood pressure contributes to the movement of water and small solutes from the glomerular capillaries into the nephron.
Hydrostatic pressure is the force exerted by a fluid against a surface. In physiology, blood pressure and pressure within the renal glomeruli are important examples.
Hydrostatic pressure works alongside osmotic forces to influence fluid movement between blood vessels, tissues, and body compartments.
Metabolism includes all of the chemical reactions that occur within cells. These reactions can generally be divided into anabolic and catabolic pathways.
Anabolism involves building larger and more complex molecules from smaller components. These reactions generally require energy.
Examples include the synthesis of proteins, nucleic acids, and other cellular structures. Anabolism supports growth, tissue maintenance, and repair.
Catabolism breaks larger molecules into smaller molecules and generally releases usable energy.
Catabolic pathways contribute to ATP production and provide building blocks that can later be used in anabolic processes.
| Anabolism | Catabolism |
|---|---|
| Builds larger molecules | Breaks down larger molecules |
| Generally requires energy | Generally releases energy |
| Supports growth and repair | Supports energy production |
| Uses cellular energy | Helps generate cellular energy |
The interaction between molecules and water is central to understanding cell membranes.
Hydrophobic molecules do not readily interact with water. Many are nonpolar and include lipids and cholesterol.
Their water-repelling properties contribute to the formation of biological membranes.
Hydrophilic molecules interact readily with water. They may be polar or electrically charged.
Examples include many carbohydrates, ions, and other polar substances.
Amphipathic molecules contain both hydrophilic and hydrophobic regions. Phospholipids are a key example.
Because phospholipids have a water-attracting head and water-repelling tails, they naturally organize into the phospholipid bilayer that forms the basic structure of cell membranes.
Proteins are essential to virtually every aspect of cellular function. They can serve structural, enzymatic, transport, signaling, and regulatory roles.
Cellular proteins are found in structures such as:
Cell membranes
Cytoskeletons
Ribosomes
Receptors
Ion channels
Transport proteins
Enzymes
The shape and chemical properties of a protein determine how it interacts with other molecules and what function it performs.
Enzymes are biological catalysts that increase the rate of chemical reactions without being permanently consumed during the reaction.
Enzyme activity can be affected by several factors, including temperature, pH, substrate concentration, and enzyme concentration. Changes outside an enzyme’s optimal conditions may reduce its activity or alter its structure.
Membrane proteins allow cells to interact with their surroundings and selectively transport substances across the lipid bilayer.
Peripheral membrane proteins are associated with the surface of the membrane rather than being embedded through the entire lipid bilayer.
They may contribute to cell signaling, structural organization, and attachment of the membrane to the cytoskeleton.
Integral membrane proteins are embedded within the lipid bilayer. Many span the membrane completely and function as channels, carriers, receptors, enzymes, or adhesion molecules.
They are important for both passive and active transport and for communication between the cell and its environment.
Glycoproteins are proteins with carbohydrate groups attached to them. Many are located on the cell surface and contribute to cell recognition, immune responses, adhesion, and cellular communication.
Transport proteins can move substances across membranes in different ways.
A uniporter transports one type of substance across the membrane in one direction.
A symporter moves two different substances in the same direction across a membrane. The movement of one substance may provide the driving force for transporting the other.
An antiporter moves two substances in opposite directions across the membrane.
These transport systems are important for maintaining ion gradients and cellular homeostasis.
Cells can become injured when they are exposed to stress that exceeds their ability to adapt. The severity and duration of the stress influence whether the injury is reversible or progresses to cell death.
Common causes of cellular injury include:
Oxygen deprivation or hypoxia
Infections
Chemical toxins
Physical trauma
Radiation
Nutritional imbalances
Genetic abnormalities
Extreme temperature changes
Hypoxia occurs when tissues do not receive enough oxygen to meet their metabolic needs. Oxygen deficiency can impair mitochondrial ATP production, disrupt membrane function, increase cellular stress, and eventually lead to irreversible injury if prolonged.
Because many cellular processes depend on ATP, prolonged oxygen deprivation can have serious consequences for tissues with high metabolic demands.
Cell death occurs through different mechanisms. Two major forms are apoptosis and necrosis.
Apoptosis is a regulated form of programmed cell death. It removes cells that are no longer needed or have become damaged while generally producing little surrounding inflammation.
Apoptosis is important for:
Normal embryonic development
Tissue homeostasis
Removal of damaged cells
Regulation of cell populations
Dysregulation of apoptosis can contribute to diseases such as cancer and certain degenerative disorders.
Necrosis is a form of cell death associated with severe cellular injury. The affected cells lose membrane integrity, release intracellular contents, and can trigger an inflammatory response in surrounding tissues.
Unlike apoptosis, necrosis is generally associated with significant inflammation and tissue damage.
DNA is a double-stranded molecule that stores hereditary information. Each DNA strand consists of repeating units called nucleotides.
Every nucleotide contains three components:
A phosphate group
A deoxyribose sugar
A nitrogenous base
The four nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).
Adenine pairs with thymine, while cytosine pairs with guanine. These complementary base-pairing rules allow DNA to be accurately copied during replication.
DNA replication occurs before cell division so that genetic information can be passed to daughter cells.
Several enzymes coordinate this process.
| Enzyme | Primary Function |
|---|---|
| Helicase | Separates the DNA strands by unwinding the double helix |
| DNA polymerase | Builds new DNA strands and helps proofread the sequence |
| DNA ligase | Joins DNA fragments together |
DNA replication is described as semiconservative because each newly formed DNA molecule contains one original strand and one newly synthesized strand.
Understanding basic genetic terminology is important for nursing and healthcare students.
A promoter is a DNA sequence that helps initiate gene transcription. It provides a binding region for RNA polymerase and other transcription-related proteins.
A codon is a sequence of three nucleotides in messenger RNA (mRNA) that specifies an amino acid or signals termination of translation.
An anticodon is a three-nucleotide sequence on transfer RNA (tRNA) that pairs with a complementary codon on mRNA during protein synthesis.
Most human somatic cells contain 46 chromosomes arranged into 23 pairs.
These chromosomes consist of:
22 pairs of autosomes
1 pair of sex chromosomes
Human gametes, including sperm and eggs, normally contain 23 chromosomes rather than 46.
Mitosis and meiosis are different forms of cell division with distinct biological purposes.
| Mitosis | Meiosis |
|---|---|
| Produces two daughter cells | Produces four daughter cells |
| Maintains chromosome number | Reduces chromosome number by half |
| Daughter cells are generally genetically similar to the parent cell | Produces genetically diverse cells |
| Important for growth, repair, and cell replacement | Produces gametes |
| Occurs in somatic cell lineages | Occurs in cells that give rise to gametes |
Genetic variation during meiosis results from processes such as crossing over and independent assortment.
Healthcare professionals encounter genetic concepts in areas ranging from prenatal care to oncology.
Trisomy refers to the presence of three copies of a chromosome rather than the usual two. Trisomy 21 is associated with Down syndrome.
Monosomy occurs when one chromosome from a normally paired set is missing.
Aneuploidy refers to an abnormal chromosome number caused by the gain or loss of individual chromosomes.
Homozygous describes having two identical alleles for a particular gene, while heterozygous describes having two different alleles.
A dominant allele can contribute to a phenotype when only one copy is present, whereas a recessive allele generally contributes to a phenotype when two copies are present. However, inheritance patterns can be more complex than a simple dominant-recessive model.
Congenital anomalies are structural or functional abnormalities that develop before or at birth. Their causes may include genetic factors, environmental exposures, nutritional deficiencies, infections, and interactions among multiple factors.
Examples include:
Cleft lip and palate
Neural tube defects
Congenital heart defects
Limb abnormalities
Adequate folic acid intake before conception and during early pregnancy can substantially reduce the risk of neural tube defects. Prenatal care also provides opportunities to identify and manage maternal and fetal risk factors.
Cell biology provides the foundation for understanding many clinical conditions. When cellular metabolism, DNA replication, membrane transport, signaling, or programmed cell death becomes abnormal, tissues and organs can lose their normal function.
For nursing students, connecting cellular concepts to clinical findings can make complex topics easier to understand. For example, oxygen deprivation can impair ATP production, abnormal DNA can contribute to cancer, and disruptions in membrane transport can affect fluid and electrolyte balance.
Understanding these mechanisms also helps healthcare professionals connect molecular processes with symptoms, laboratory findings, disease progression, and treatment responses.
Prokaryotic cells do not have a membrane-bound nucleus or membrane-bound organelles, while eukaryotic cells have a nucleus and specialized membrane-bound organelles.
DNA stores genetic information that provides instructions for producing proteins and regulating cellular processes such as growth, development, repair, and reproduction.
Mitochondria are major sites of ATP production through aerobic metabolism and oxidative phosphorylation. They also participate in calcium regulation and pathways involved in programmed cell death.
Histones are proteins that help package DNA into chromatin. They also contribute to the regulation of gene accessibility and expression.
Glycolysis occurs in the cytoplasm. It breaks glucose into pyruvate and produces a net gain of 2 ATP per glucose molecule.
Apoptosis is a regulated form of cell death that generally limits inflammation, whereas necrosis is associated with severe cell injury, loss of membrane integrity, and inflammation.
A typical human somatic cell contains 46 chromosomes organized into 23 pairs.
DNA polymerase builds new DNA strands during replication and contributes to replication accuracy through proofreading and repair-related functions.
Diffusion is the movement of particles from higher to lower concentration, while osmosis specifically describes the movement of water across a selectively permeable membrane.
The four nitrogenous bases in DNA are adenine, thymine, cytosine, and guanine. Adenine pairs with thymine, while cytosine pairs with guanine.
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Hall, J. E. (2021). Guyton and Hall textbook of medical physiology (14th ed.). Elsevier. https://www.elsevier.com/books/guyton-and-hall-textbook-of-medical-physiology/hall/978-0-323-59712-8
Kumar, V., Abbas, A. K., & Aster, J. C. (2020). Robbins & Cotran pathologic basis of disease (10th ed.). Elsevier. https://www.elsevier.com/books/robbins-and-cotran-pathologic-basis-of-disease/kumar/978-0-323-53113-9
National Human Genome Research Institute. (2024). DNA basics. Genome.gov. https://www.genome.gov/about-genomics/fact-sheets/DNA-Basics
OpenStax. (2023). Biology 2e. Rice University. https://openstax.org/details/books/biology-2e
