Human Anatomy & Physiology
Chapter 03
The Cell
PowerPoint^® Lectures created by Suzanne Pundt, University of Texas at Tyler
Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved
Second Edition

Module 3.1 Introduction to Cells
Basic Processes of Cells
The following basic processes are common to all cell types: 
•	Cell metabolism 
•	Transport of substances 
•	Communication 
•	Cell reproduction
Basic Processes of Cells
Cell metabolism – sum of all chemical reactions that a cell carries out to maintain life:
•	Anabolic reactions – building reactions; small molecules are bonded together to form macromolecules
•	Catabolic reactions break down macromolecules back into smaller molecules
•	 Oxidation-reduction reactions convert energy in chemical bonds of nutrients into form of energy cell can use to fuel its processes, namely ATP
Basic Processes of Cells
Transport of substances cell has produced or ingested to a variety of destinations is a vital process
Communication between cell and itself, its surrounding environment, and other cells is carried out by various methods including chemical and electrical signals
Cell reproduction by cell division – process that is necessary for growth and development and for replacement of old and damaged cells
Overview of Cell Structure
Most animal cells have 
3 basic components: 
•	Plasma membrane
•	Cytoplasm
•	Nucleus
Overview of Cell Structure
Plasma membrane surrounds each cell, isolating its internal structures and processes from external environment:
•	Provides cell with structural support, means of communication with its surroundings and other cells, and cell identification
•	Defines intracellular space (contains intracellular fluid (ICF)), or cytosol, and separates it from extracellular space (contains extracellular fluid (ECF)
Cytoplasm
•	The material outside the nucleus and inside the plasma membrane 
•	Site of most cellular activities

Overview of Cell Structure
Cytoplasm consists of:
•	Cytosol – intracellular fluid; mostly water with dissolved solutes, inclusions or storage molecules, and proteins; site of many important chemical reactions
•	Organelles – variety of cellular machines with very specific functions; suspended in cytosol; compartmentalization is essential for efficacy, it enables the cell to keep related enzymes and proteins together so they are not scattered throughout the cell also serves to separate potentially damaging chemical reactions from surrounding cell structures 
•	Cytoskeleton – network of protein filaments; creates and maintains shape; holds organelles in place; cell’s molecular “highways”, also involved in cellular movement and cell division.
Overview of Cell Structure
Most cells contain a single roughly spherical organelle called the nucleus:
•	Enclosed in phospholipid bilayer similar to plasma membrane; termed nuclear envelope
•	Contains most of cell’s DNA and is primary location for making most RNA
•	DNA and RNA control more specific organelle functions by coding for and synthesizing proteins
Overview of Cell Structure
Cell Size and Diversity: 
•	Cells vary widely in size and structure to enable them to better perform specialized functions
•	Note that this structural variation is an example of Structure-Function Core Principle

Module 3.2 Structure of the Plasma Membrane 
The Phospholipid Bilayer
In order for plasma membrane to form an effective barrier between ECF and cytosol, molecules that make up membrane (phospholipid bilayer) must have two key properties:
•	Molecules must have parts that interact with water in both fluid compartments without falling apart
•	Molecules must have parts that repel water, keeping ECF and cytosol separated
The Phospholipid Bilayer
In order for plasma membrane to form an effective barrier between ECF and cytosol, molecules that make up membrane (phospholipid bilayer) must have two key properties (continued):
•	Phospholipids are amphiphilic – have both a phosphate group (hydrophilic polar head) facing each fluid compartment and two fatty acids (hydrophobic tails) that face one another forming a water-resistant barrier
The Phospholipid Bilayer
Fluid Mosaic Model of the Plasma Membrane
•	To be able to perform all of the functions required by a living cell, the plasma membrane must contain many components in addition to its phospholipids. Scattered throughout the phospholipid bilayer of the plasma membrane are various proteins, other kinds of lipids, and carbohydrates. All of these components together are thought to resemble a mosaic.
•	This model defines the plasma membrane as a structure with multiple components whose arrangement is dynamic, meaning that it changes from moment to moment.

Fluid Mosaic Model of the Plasma Membrane
Fluid Mosaic Model– describes plasma membrane as dynamic fluid structure with multiple components, some with ability to move within bilayer as phospholipids move themselves
Fluid Mosaic Model of the Plasma Membrane
Membrane proteins, a main component of plasma membranes, exist in two basic types:
•	Integral proteins – typically span entire plasma membrane; when they do called transmembrane 
proteins
•	Peripheral proteins are 
found only on one 
side of plasma 
membrane or other
Fluid Mosaic Model of the Plasma Membrane
Functions of membrane proteins include:
•	Transport substances across plasma membrane as protein channels; others are carrier proteins that bind and directly transport substances into and out of cell
Fluid Mosaic Model of the Plasma Membrane
Functions of membrane proteins include (continued):
•	Receptors that bind to chemical messengers called ligands; trigger sequence of events within cell when bound; note that this is an 
example of Cell-Cell 
Communication Core 
Principle
Fluid Mosaic Model of the Plasma Membrane
Functions of membrane proteins include (continued):
•	Enzymes – speed up chemical reactions; vital to maintaining homeostasis
Fluid Mosaic Model of the Plasma Membrane
Functions of membrane proteins include (continued):
•	Structural support – when 
bound to cytoskeleton; give 
cells shape and help maintain 
structural integrity 
Fluid Mosaic Model of the Plasma Membrane
Functions of membrane proteins include (continued):
•	Link adjacent cells to one 
another, anchoring cells 
within a tissue and/or 
allowing cell to cell 
communication
Fluid Mosaic Model of the Plasma Membrane
Other membrane components include lipids, carbohydrates, glycolipids, and glycoproteins:
•	Cholesterol – lipid molecule, stabilizes plasma membrane’s structure during temperature changes
•	Glycolipids and glycoproteins, 
carbohydrate bound to either 
lipid or protein respectively, 
function in cell 
recognition
Drugs and Membrane Receptors
Many drugs are designed to resemble ligands that bind to membrane receptors:
•	Agonists – mimic ligand’s actions by stimulating receptor (example: narcotic pain killers such as morphine mimic actions of endorphins)
•	Antagonists – inhibit ligand’s actions by blocking receptor (example: antihistamines block receptors for histamine)

Module 3.3 Transport Across the Plasma Membrane 
Selective Permeability
The phospholipid bilayer is selectively permeable, allowing certain molecules to cross it while prohibiting passage of other molecules; critical to survival of cell
•	Substance may cross plasma membrane in several ways; some do not require expenditure of energy (passive transport mechanisms); other processes do require energy (active transport processes)
Selective Permeability
•	Three variables determine how a substance is able to move across the plasma membrane by passive or active transport: 
•	Type of substance
•	Plasma membrane permeability to substance
•	Concentration of substance in cytosol and ECF
Passive Transport Processes
Passive transport include the following processes:
•	Diffusion 
•	Simple diffusion 
•	Facilitated diffusion 
•	Osmosis 
Passive Transport Processes
•	Concentration gradient – basic force that drives many types of passive transport
•	Notice that more dye molecules are found in fluid on bottom of beaker than on top; difference is a concentration gradient, a form of potential energy; Core Principle
Passive Transport Processes
Diffusion – movement of solute molecules from an area of higher solute concentration to area of lower solute concentration; moving down or with its concentration gradient until equilibrium is reached
Passive Transport Processes
•	Simple diffusion – mostly nonpolar solutes like oxygen, carbon dioxide, lipids, and hydrocarbons; pass straight through 
phospholipid bilayer 
without need for 
membrane protein
Passive Transport Processes
•	Facilitated diffusion involves charged or polar solutes such as ions and glucose; cross phospholipid bilayer with help of a membrane protein (carrier or channel)
Passive Transport Processes
•	Osmosis is a passive process in which a solvent (in the body is water) moves across a membrane
•	Water moves from area with 
lower concentration of solute 
(more water molecules) across 
membrane to area with higher 
concentration of solute (less 
water molecules)
•	Osmotic pressure – “pulling” force exerted by solute on water molecules

A solution with a HIGHER solute concentration has GREATER osmotic pressure than one with a lower solute concentration.

Passive Transport Processes
Water moves across plasma membranes by two methods:
•	Water passes through channel proteins known as aquaporins; primary route for osmosis of water
•	A small amount of water is able to pass through phospho-lipid bilayer directly
Passive Transport Processes
•	Membrane permeable to water (not glucose) 
•	B-more concentrated glucose solution (right); A – less concentrated (left)
•	During osmosis, water moves from solution with lower solute concentration to one with higher concentration (A to B)
Passive Transport Processes 
•	At equilibrium, concentration of water molecules on either side of membrane is equal; gradient is gone
•	Results in change in volume of fluid on each side; water molecules leave A (volume decreases); water molecules move into B (volume increases)
•	Volume changes have important consequences for cells; discussed next
Passive transport: osmosis.
Concept Boost: Understanding Water Movement in Osmosis
Passive Transport Processes
Tonicity – way to compare osmotic pressure gradients between two solutions – cytosol and ECF
•	Normally ECF is isotonic to cytosol; both fluids have approximately same concentration of solute; no net movement of water 
across plasma 
membrane and no 
volume changes in 
either fluid 
compartment
Passive Transport Processes
Tonicity (continued):
•	Hypertonic ECF – solute concentration of ECF is higher than inside cell; more water molecules inside cell than outside; osmotic pressure gradient pulls water out of cell and cell shrinks or crenates
Passive Transport Processes
Tonicity (continued):
•	Hypotonic ECF – solute concentration of ECF is lower than inside cell; more water molecules in ECF than inside cell; osmotic pressure gradient pulls water into cell causing the cell to swell 
and possibly rupture 
or lyse
Passive Transport Processes
Dehydration, Sports 
Drinks, and Water
•	Strenuous exercise results in water and electrolyte loss through sweating; ECF becomes hypertonic; hypertonic ECF draws water out of cells by osmosis
•	Sports drinks (many contain mixtures of water, electrolytes, and carbohydrates) are hypotonic; drinking them helps replenish water and electrolytes in your ECF and make it mildly hypotonic to cells; causes water to move back into cells until normal cytosol concentration is restored
•	Plain water generally rehydrates just as well but care must be taken in severe dehydration; water can rehydrate cells too quickly and result in cellular swelling and possibly water poisoning
Comparing Diffusion and Osmosis
•	Diffusion – movement of solute across plasma membrane from higher solute concentration to lower solute concentration (with concentration gradient)
•	Osmosis – movement of solvent across plasma membrane from area of lower solute concentration to area of higher solute concentration
Active Transport via Membrane Proteins
•	Active transport processes require energy in form of ATP to proceed as solutes move against their concentration gradients from low concentration to high concentration
•	Both primary and secondary active transport processes use plasma membrane carrier proteins called pumps
Active Transport via Membrane Proteins
There are 3 types of pumps found in the plasma membrane:
•	Uniport pumps transport a single substance through plasma membrane in one direction, either into or out of cell
•	Symport pumps transport two or more substances through plasma membrane in same direction, either into or out of cell
•	Antiport pumps transport two or more substances in opposite directions through plasma membrane
Active Transport via Membrane Proteins
Primary active transport involves pump in plasma membrane that binds and transports solute against its concentration gradient using energy from hydrolysis of ATP
•	The major primary active transport pump in the body is the antiport pump known as the sodium-potassium pump (Na^+/K^+ pump or Na^+/K^+ ATPase) (Figure 3.10)
•	Normally, Na^+ concentration is 10 times greater in ECF than cytosol and K^+ concentration is 10 times greater in cytosol than in ECF, it is critical to our homeostasis to maintain concentration gradients of Na^+ and K^+
•	Pump maintains these steep concentration gradients by transporting 3 Na^+ out and 2 K^+ into the cell against their concentration gradients
Active Transport via Membrane Proteins
Active Transport via Membrane Proteins
Secondary active transport uses ATP indirectly to fuel a transport pump
•	ATP is used to create a concentration gradient of one substance
Active Transport via Membrane Proteins
Secondary active transport (continued): 
Remember that potential energy exists in every concentration gradient, so once the concentration gradient of the first substance is established, the cell then harnesses that potential energy to power the active transport of another substance against its concentration gradient. 
Consequences of Ion Transport across the Plasma Membrane
Introduction to Electrophysiology 
•	You have learned about the different ways that ions cross the plasma membrane of a cell (through passive processes such a facilitated diffusion and active processes such as primary and secondary active transport). These mechanisms cause ions to have unequal concentrations between the cytosol and ECF. This results in a separation of charges across the plasma membrane.
•	A thin layer of positive charges is present in the ECF and a thin layer of negative charges is found in  the cytosol

Consequences of Ion Transport across the Plasma Membrane
Introduction to Electrophysiology (continued):
•	A separation of charges is known as an electrical potential (a source of potential energy), an electrical potential is really  just an electrical gradient, similar to concentration gradients
•	Electrical potential found across plasma membrane is known as a membrane potential; study of these potentials is called electrophysiology
•	Resting membrane potential – membrane potential when cell is at rest; measured in millivolts (mV); value is negative meaning inside of cell is more negative than surrounding ECF

Active Transport via Vesicles
Carrier proteins and channels are effective but have size limitations; polar macromolecules are too big to bind to a carrier or fit through a channel, so must be transported by other means – vesicles:
•	Vesicles are small sacs filled with large molecules too big to transport by other means
•	Enclosed in a phospholipid bilayer; formed from cell membranes and can fuse with plasma membrane or other membrane-bound organelles
•	Active process called vesicular transport; requires energy from ATP to proceed
Active Transport via Vesicles
Endocytosis: 
•	Phagocytosis (“cell eating”) – process where cells ingest large particles
Active Transport via Vesicles
Endocytosis (continued): 
•	Pinocytosis (fluid-phase endocytosis or “cell drinking”) – process where cells engulf fluid droplets from ECF 
Active Transport via Vesicles
Endocytosis (continued): 
•	Receptor-mediated endocytosis – similar to pinocytosis; uses receptors, fill vesicles with a specific molecule
Active Transport via Vesicles
•	Exocytosis – large molecules exit cell
•	 Transcytosis – molecules are brought into cell by endocytosis, transported across cell to opposite side, and then secreted by exocytosis
Active Transport via Vesicles
Plasma Membrane Transport
Plasma Membrane Transport
Plasma Membrane Transport
A&P Flix: Membrane Transport

Module 3.4 Cytoplasmic Organelles 
Cytoplasmic Organelles
•	Organelles are cellular machinery with specific functions vital to maintaining homeostasis; some are separated from cytosol by membrane while others are not enclosed in a membrane 
•	Membrane-bound include: mitochondria, peroxisomes, endoplasmic reticulum, Golgi apparatus, and lysosomes
•	Organelles that are not enclosed in membrane include: ribosomes and centrosomes
Cytoplasmic Organelles
Mitochondria
Mitochondria- “power plant” of cell; membrane-bound organelles involved in energy production; provide majority of ATP used in cell:
•	Each mitochondrion has its own DNA, enzymes, and ribosomes (organelle involved in protein synthesis)
•	Membrane is double bilayer 
structure with smooth outer 
membrane and inner 
membrane that is highly 
folded into cristae
Mitochondria
•	Each membrane has its own unique enzymes and proteins required to perform specific functions:
•	Outer membrane – large channels that allow molecules from cytosol to enter intermembrane space (space between two membranes)
•	Inner membrane – more selective; essentially impermeable to most solutes except those for which it has specific transport proteins; as a result matrix (innermost space) contains DNA, mitochondrial proteins, and enzymes
•	Matrix contains enzymes and proteins that break down organic fuels via a series of reactions called oxidative catabolism (produces ATP)
Mitochondria
Peroxisomes
Peroxisomes – membrane-
bound organelles
•	Use oxygen to carry out variety 
of reactions,  one of their main reactions uses oxygen to produce hydrogen peroxide (H_2O_2); hydrogen peroxide along with oxidative enzymes perform various functions:
•	1. Oxidizing toxic substances-Converts toxic chemicals into less toxic compounds which are then eliminated from the body
•	2. Break down fatty acids
•	3. Synthesizing certain phospholipids-critical components of plasma membrane

Ribosomes
•	Ribosomes-tiny granular nonmembrane-bound organelles where protein synthesis takes place
•	Composed of large and small subunits; each made of ribosomal proteins and ribosomal RNA (rRNA)
•	Can be free or bound, structurally identical (only differ in location)
•	Free-suspended in cytosol; make proteins mainly used in cytosol itself
•	Bound-Are associated with the membranes of other cellular structures, all start out free, but some attach themselves to the endoplasmic reticulum or nuclear envelope, typically make proteins that will be exported from the cell, transported to certain organelles such as lysosomes, or inserted into membrane
The Endomembrane System
The Endomembrane System :
Form vesicles that exchange proteins and other molecules; Organelles that transfer molecules in this manner are part of a system called the endomembrane system, whose components together synthesize, modify, and package molecules produced within cell
The Endomembrane System
The Endomembrane System (continued): 
•	Plasma membrane, nuclear envelope, and following organelles are components of the system:
•	Endoplasmic reticulum (ER) 
•	Rough endoplasmic reticulum (RER)
•	Smooth endoplasmic reticulum (SER) 
•	Golgi apparatus
•	Lysosomes
The Endomembrane System
Endoplasmic reticulum (ER) – large, folded membrane surrounding nucleus, highly-folded phospholipid bilayer continuous with the nuclear envelope; 2 distinct regions of ER membrane-rough ER (RER) has ribosomes bound to it and smooth ER (SER) does not

•	Recall that proteins must be folded into their proper shape before they become functional. Yet ribosomes, the sites of protein synthesis only assemble amino acids into a polymer called a polypeptide (the protein’s primary structure) without a three-dimensional shape. So, ribosomes by themselves do not synthesize fully functional proteins.
The Endomembrane System
Rough endoplasmic reticulum – ribosomes bound to membrane, the polypeptides synthesized pass through the RER membrane into its lumen, where enzymes catalyze reactions that FOLD polymers into their correct 3-dimensional shapes.
•	RER recognizes proteins that have folded into incorrect shape and sends them to be degraded. 
•	Many proteins that enter RER to be folded are destined for export from the cell
•	When a secretory protein is fully assembled, it leaves RER packaged in a small, membrane-bounded structure called a transport vesicle. 
The Endomembrane System
Smooth endoplasmic reticulum (SER) – not associated with ribosomes; essentially no role in protein synthesis; performs following vital functions:
•	Stores calcium ions 
•	Detoxification reactions; limits damage caused by certain substances
•	Lipid synthesis- Synthesizes the bulk of cells lipid membrane components
The Endomembrane System
The Endomembrane System
Golgi apparatus – located between RER and plasma membrane – group of flattened membranous sacs filled with enzymes and other molecules 
Proteins and lipids made by ER are further modified, sorted, and packaged for export in the Golgi
•	Products packaged in Golgi can be secreted 
from cell by exocytosis, become part of the 
plasma membrane, or sent to the lysosome
The Endomembrane System
Cystic Fibrosis
•	The RER recognizes and helps dispose of misfolded proteins, but sometimes the RER’s selectivity can actually be detrimental as in the case with some forms of cystic fibrosis.
•	Certain cells are missing a protein that forms a chloride ion channel in plasma membrane
•	Causes deficient chloride ion transport that impacts ion and water secretions in lungs, digestive and integumentary systems; results in abnormally thick mucus; blocks airways, digestive enzyme deficiencies, and very salty sweat
•	DNA mutation causes chloride channel protein to misfold slightly in RER; protein therefore destroyed even though it would generally be functional if inserted into membrane
•	In short, disease is caused by “overprotective” RER
The Endomembrane System
Lysosomes – organelles responsible for digestion of worn out cell components, or whole cells in some cases:
•	Contain enzymes called acid hydrolases
•	Macromolecules are broken down into smaller subunits that can be released to cytosol for disposal or for use in protein synthesis and various metabolic reactions
Summary of Events Involving Endomembrane System Functions
The Endomembrane System
Summary of endomembrane system events: 
(1a) SER makes lipids and (1b) Ribosomes on rough ER makes proteins, the proteins then enter RER where proteins are folded and modified(2) these products and products from SER are packaged  into vesicles for transport to Golgi
(3)	Golgi sorts, further modifies and packages the products into vesicles; may take three pathways once exiting Golgi:
	(4a) Sent to lysosomes to undergo catabolic reactions
	(4b) Incorporated into plasma membrane or membrane of another organelle in cell
	(4c) Sent to plasma membrane where secreted (exocytosis)
Lysosomal Storage
Diseases
•	Group of diseases resulting from deficiency of one or more acid hydrolases of lysosomes; examples include:
•	Gaucher’s disease – deficiency causes accumulation of glycolipids in cells of blood, spleen, liver, lungs, bone, and sometimes brain; most severe form is fatal in infancy or early childhood
•	Tay-Sachs disease – glycolipids accumulate in brain lysosomes, leading to progressive neural dysfunction and death by age 4–5
Lysosomal Storage
Diseases
•	Group of diseases resulting from deficiency of one or more acid hydrolases of lysosomes; examples include (continued):
•	Hurler syndrome – large polysaccharides accumulate in many cells (heart, liver, brain); death can result in childhood from organ damage
•	Niemann-Pick disease – lipids accumulate in lysosomes, affects spleen, liver, brain, lungs, and bone marrow; severe form causes organ damage and neural dysfunction
Cytoplasmic Organelles
Cytoplasmic Organelles

Module 3.5 
The Cytoskeleton
The Cytoskeleton
Cytoskeleton –  made of several types of protein filaments; dynamic structure able to change function based on needs of cell; plays a variety of critical roles: 
•	Gives the cell its characteristic shape and size by creating an internal framework
•	Supporting the plasma and nuclear membranes as well as the organelles
•	Functioning in movement
•	Performing specialized functions in different cell types; for example, phagocytosis, contraction by muscle cells, and nerve cell long “arms”
Types of Filaments
Cytoskeleton contains three types of long protein filaments; composed of smaller protein subunits that allow for rapid disassembly and reassembly
•	Actin filaments 
•	Intermediate filaments 
•	Microtubules
Types of Filaments
Actin filaments (microfilaments) are the thinnest filament in cytoskeleton; composed of two intertwining strands of actin subunits
•	Provide structural support, bear tension, and maintain cell’s shape
•	Involved in cellular motion when combined with the motor protein myosin
Types of Filaments
Intermediate filaments – ropelike; made of diverse fibrous proteins including keratin, form more permanent structures in the cell
•	Form much of framework of cell and anchor organelles within it 
•	Help organelles and nucleus maintain their shape and size
•	Help cells and tissues 
withstand mechanical stresses
Types of Filaments
Microtubules – largest protein filaments in cytoskeleton; hollow rods or tubes composed of the protein subunits tubulins; can be rapidly added or removed allowing for size and shape changes within cell
•	Gives cell characteristic shape/size
•	Maintain internal architecture of cell
•	Associated with motor proteins called dynein 
and kinesin, move along microtubules like a train on a track, they carry their “cargo” to appropriate destinations
Types of Filaments
Types of Filaments
Microtubules extend out from centrosome (consists of a gel matrix containing tubulin proteins necessary for microtubule formation) 
•	When cell is not dividing, centrosome is a microtubule-organization center located close to nucleus
•	The centrosome also contains a pair of centrioles, composed of a ring of nine groups of three modified microtubules and other proteins, is critical for cellular division
•	Basal bodies – modified centrioles found on internal surface of plasma membrane where flagella and cilia sprout from
Types of Filaments
Cellular Extensions
Cytoskeleton forms the inner framework of cell surface extensions in many cells, these extensions include:
•	Microvilli 
•	Cilia 
•	Flagella
Cellular Extensions
•	Microvilli 
•	Plasma membrane folded into tiny finger-like extensions Structure-Function Core Principle
•	Increase surface area 
of cells in organs 
specialized for 
absorption
Cellular Extensions
•	Cilia 
•	Larger than microvilli
•	Hairlike projections composed of microtubules and motor proteins, enable cilia to be motile
•	Coordinated beating motion sweeps substances past the cell 
•	Ex, cells that line our respiratory passages have cilia  

Cellular Extensions
•	Flagella  
•	Solitary; long extension from cell, move in whiplike motion to propel whole cell
•	Found only on sperm cells
Cellular Extensions
Cellular Extensions
Primary 
Ciliary Dyskinesia
•	Rare genetic disorder characterized by defect in one or more protein components of cilia and flagella
•	Affects many types of cells: respiratory passage linings, middle ear, uterine tubes (females), sperm (males)
•	Leads to buildup of mucus in lungs; increases risk of infection; commonly progressive damage to lungs
•	May experience repeated ear infections can lead to hearing loss
•	Males may be infertile due to lack of sperm motility