NU551 Completed Study Guide

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Purdue University Globle 

NU551 Advanced Physiology and Pathophysiology Across the Lifespan

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Cells and DNA: Structure, Function, Genetics, and Cellular Processes

Cells are the fundamental units of life responsible for carrying out every biological process in the human body. They generate energy, synthesize proteins, regulate metabolism, store genetic information, and maintain tissue function. Understanding cell biology and DNA is essential for nursing, medicine, and other healthcare disciplines because cellular dysfunction often leads to disease. This guide explains the structure and function of cells, DNA organization, energy production, membrane transport, genetics, and cell division in a simplified, evidence-based format that supports both academic learning and clinical practice.

Understanding Prokaryotic and Eukaryotic Cells

Cells are broadly classified into prokaryotic and eukaryotic cells based on the presence or absence of a nucleus and membrane-bound organelles.

Prokaryotic Cells

Prokaryotic cells are relatively simple and are primarily found in bacteria and archaea. They lack a true nucleus, meaning their DNA is located freely within the cytoplasm. They also do not contain membrane-bound organelles such as mitochondria or the Golgi apparatus.

Key characteristics include:

• No nucleus

• Circular DNA

• No membrane-bound organelles

• Small cell size

• Divide through binary fission

Eukaryotic Cells

Eukaryotic cells are more complex and make up plants, animals, fungi, and protists. Their DNA is enclosed within a membrane-bound nucleus, and they contain specialized organelles that perform distinct cellular functions.

Characteristics include:

• Membrane-bound nucleus

• Linear chromosomes

• Specialized organelles

• Larger cell size

• Divide through mitosis or meiosis

Research consistently demonstrates that compartmentalization in eukaryotic cells allows greater specialization and more efficient regulation of cellular activities.

DNA Organization and Histones

DNA contains the genetic instructions necessary for cell growth, repair, and reproduction. Because DNA molecules are extremely long, they must be tightly packaged inside the nucleus.

What Are Histones?

Histones are positively charged proteins around which DNA wraps to form structures known as nucleosomes. This packaging creates chromatin, allowing DNA to fit within the nucleus while remaining accessible for gene expression and replication.

Histones help:

• Organize DNA

• Protect genetic material

• Regulate gene expression

• Control DNA replication and repair

Proper histone modification plays a significant role in epigenetics by determining which genes are activated or silenced.

Major Cell Organelles and Their Functions

Every organelle contributes to maintaining normal cellular activity.

Nucleus

The nucleus serves as the cell’s control center. It stores DNA and regulates gene expression, metabolism, protein synthesis, growth, and cell division.

Nucleolus

Located inside the nucleus, the nucleolus synthesizes ribosomal RNA (rRNA) and assembles ribosomal subunits required for protein production.

Rough Endoplasmic Reticulum

The rough endoplasmic reticulum contains ribosomes attached to its surface. It produces proteins that will become membrane proteins, enzymes, or secreted proteins.

Smooth Endoplasmic Reticulum

Unlike the rough ER, the smooth ER lacks ribosomes. It is responsible for:

• Lipid synthesis

• Steroid hormone production

• Drug detoxification

• Calcium storage

Golgi Apparatus

The Golgi complex receives proteins from the endoplasmic reticulum, modifies them, packages them, and directs them to their final destinations.

Its major roles include:

• Protein modification

• Glycosylation

• Protein sorting

• Formation of secretory vesicles

• Lysosome production

Mitochondria

Often called the “powerhouse of the cell,” mitochondria generate ATP through aerobic respiration and oxidative phosphorylation.

Additional functions include:

• Calcium regulation

• Heat production

• Apoptosis regulation

Lysosomes

Lysosomes contain digestive enzymes that degrade damaged organelles, bacteria, and cellular waste through intracellular digestion.

Cell Junctions: Desmosomes

Desmosomes are specialized intercellular junctions that anchor adjacent cells together.

They are especially abundant in tissues exposed to mechanical stress, including:

• Skin

• Cardiac muscle

• Epithelial tissue

Their primary function is to maintain structural integrity during stretching and mechanical force.

Cellular Communication: First and Second Messengers

Cells communicate through signaling molecules.

First Messengers

First messengers are extracellular signaling molecules such as:

• Hormones

• Neurotransmitters

• Growth factors

They bind to receptors on the cell membrane.

Second Messengers

Second messengers transmit signals inside the cell after receptor activation.

Common second messengers include:

• cAMP

• Calcium ions

• IP₃

• DAG

These molecules amplify cellular responses rapidly.

Cellular Energy Production

Cells require continuous ATP production to perform physiological functions.

Glycolysis

Glycolysis occurs in the cytoplasm where one glucose molecule is converted into two pyruvate molecules.

Characteristics include:

• Does not require oxygen

• Produces 2 ATP

• First stage of cellular respiration

Anaerobic Glycolysis

When oxygen is unavailable, pyruvate converts into lactate.

This process:

• Occurs in the cytoplasm

• Produces ATP rapidly

• Is less efficient than aerobic metabolism

Aerobic Respiration

Aerobic respiration occurs inside mitochondria and uses oxygen to generate significantly more ATP than anaerobic metabolism.

Major stages include:

• Krebs cycle

• Electron transport chain

• Oxidative phosphorylation

Oxidative Phosphorylation

Oxidative phosphorylation is the final stage of aerobic respiration.

During this process:

• Electrons pass through the electron transport chain.

• Oxygen serves as the final electron acceptor.

• ATP synthase generates approximately 26–28 ATP molecules.

Transport Across Cell Membranes

Cells constantly exchange nutrients, gases, and waste products with their environment.

Diffusion

Diffusion is the passive movement of molecules from an area of higher concentration to lower concentration.

No energy is required.

Osmosis

Osmosis refers specifically to the diffusion of water across a selectively permeable membrane.

Water moves toward the area with the higher solute concentration.

Filtration

Filtration occurs when hydrostatic pressure forces water and dissolved substances across a membrane.

It plays a vital role in kidney filtration and capillary exchange.

Hydrostatic Pressure

Hydrostatic pressure is the force exerted by fluids against vessel walls.

Examples include:

• Blood pressure

• Glomerular filtration pressure

Anabolism and Catabolism

Metabolism consists of two complementary pathways.

Anabolism

Anabolism builds larger molecules from smaller ones.

Characteristics:

• Requires energy

• Supports growth

• Promotes tissue repair

Catabolism

Catabolism breaks down complex molecules into simpler substances.

Characteristics:

• Releases energy

• Produces ATP

• Supports cellular activities

Hydrophobic, Hydrophilic, and Amphipathic Molecules

Understanding molecular interactions with water helps explain membrane structure.

Hydrophobic Molecules

Hydrophobic molecules repel water and are typically nonpolar.

Examples include lipids and cholesterol.

Hydrophilic Molecules

Hydrophilic molecules readily interact with water because they are polar or charged.

Examples include glucose and electrolytes.

Amphipathic Molecules

Amphipathic molecules contain both hydrophobic and hydrophilic regions.

Phospholipids are classic examples and form the phospholipid bilayer of cell membranes.

Proteins Within the Cell

Proteins perform nearly every cellular function.

They are found in:

• Cell membrane

• Cytoskeleton

• Ribosomes

• Receptors

• Transport channels

• Enzymes

Enzymes

Enzymes are biological catalysts that accelerate chemical reactions without being consumed.

Their activity depends on:

• Temperature

• pH

• Substrate concentration

• Enzyme concentration

Membrane Pores and Transport Proteins

Membrane pores allow selective movement of ions and molecules.

Peripheral Membrane Proteins

Peripheral proteins primarily function in:

• Cell signaling

• Structural support

• Cytoskeletal attachment

Integral Membrane Proteins

Integral proteins span the lipid bilayer and facilitate:

• Active transport

• Passive transport

• Signal transduction

• Cell adhesion

Glycoproteins

Glycoproteins participate in:

• Cell recognition

• Immune identification

• Cell communication

Membrane Transport Systems

Transport proteins move substances across membranes using different mechanisms.

Uniport

Moves one molecule in one direction.

Symport

Moves two molecules simultaneously in the same direction.

Antiport

Moves two molecules in opposite directions.

Cellular Injury

Cells can be damaged by numerous internal and external factors.

Common causes include:

• Hypoxia

• Infection

• Chemical toxins

• Physical trauma

• Radiation

• Nutritional deficiencies

• Genetic mutations

Hypoxia

Hypoxia refers to inadequate oxygen availability at the tissue level.

Persistent hypoxia reduces ATP production and eventually causes cell injury or death.

Apoptosis and Necrosis

Apoptosis

Apoptosis is programmed cell death that eliminates damaged or unnecessary cells while minimizing inflammation.

It is essential for:

• Embryonic development

• Tissue homeostasis

• Cancer prevention

Necrosis

Necrosis is uncontrolled cell death caused by severe injury.

Unlike apoptosis, necrosis triggers inflammation and damages surrounding tissues.

DNA Structure

DNA consists of repeating units called nucleotides.

Each nucleotide contains:

• Phosphate group

• Deoxyribose sugar

• Nitrogenous base

The four nitrogenous bases are:

• Adenine (A)

• Thymine (T)

• Cytosine (C)

• Guanine (G)

DNA Replication Enzymes

DNA replication ensures that genetic information is accurately copied before cell division.

Key enzymes include:

Important Genetic Terms

Promoter

A promoter is the DNA sequence where RNA polymerase binds to initiate transcription.

Codon

A codon is a three-nucleotide sequence on messenger RNA that specifies an amino acid.

Anticodon

An anticodon is a complementary three-base sequence found on transfer RNA.

Human Chromosomes

Most human somatic cells contain 46 chromosomes organized into 23 pairs.

These include:

• 22 pairs of autosomes

• 1 pair of sex chromosomes

Mitosis vs. Meiosis

Essential Genetics Terminology

Healthcare professionals frequently encounter these genetic concepts.

• Trisomy: Presence of an extra chromosome (e.g., Down syndrome)

• Monosomy: Loss of one chromosome from a pair

• Aneuploidy: Abnormal chromosome number

• Homozygous: Two identical alleles

• Heterozygous: Two different alleles

• Dominant allele: Expressed with one copy

• Recessive allele: Expressed only when two copies are inherited

Common Congenital Birth Defects

Birth defects develop during fetal development and vary in severity.

Common examples include:

• Cleft lip and palate

• Neural tube defects

• Congenital heart disease

• Limb abnormalities

Early prenatal care and folic acid supplementation significantly reduce the risk of several congenital abnormalities.

Cells function as the body’s basic structural and functional units, while DNA stores the genetic instructions that guide growth, development, and repair. Efficient energy production, accurate DNA replication, healthy membrane transport, and regulated cell division are all essential for maintaining human health. Disruptions in these processes contribute to numerous diseases, making cellular biology a foundational topic in nursing and medical education.

Frequently Asked Questions

What is the primary difference between prokaryotic and eukaryotic cells?

Prokaryotic cells lack a membrane-bound nucleus and organelles, whereas eukaryotic cells possess both, allowing for greater cellular specialization.

Why are mitochondria called the powerhouse of the cell?

Mitochondria produce most of the cell’s ATP through aerobic respiration and oxidative phosphorylation, providing energy for cellular activities.

What is the function of histones?

Histones package DNA into chromatin, protect genetic material, and regulate gene expression.

What is the difference between apoptosis and necrosis?

Apoptosis is a controlled, programmed process of cell death that usually does not cause inflammation. Necrosis is uncontrolled cell death caused by injury and often results in inflammation.

Where does glycolysis occur?

Glycolysis occurs in the cytoplasm of both prokaryotic and eukaryotic cells and is the first step in glucose metabolism.

How many chromosomes are found in human somatic cells?

Human somatic cells contain 46 chromosomes arranged into 23 pairs.

What is the role of DNA polymerase?

DNA polymerase synthesizes new DNA strands during DNA replication and helps maintain genetic accuracy through proofreading mechanisms.

References

Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K., & Walter, P. (2022). Molecular Biology of the Cell (7th ed.). Garland Science. https://wwnorton.com/books/molecular-biology-of-the-cell

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

NU551 Completed Study Guide

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. https://www.genome.gov/about-genomics/fact-sheets/DNA-Basics

OpenStax. (2023). Biology 2e. https://openstax.org/details/books/biology-2e