Cellular Level of Organization
Cells
 There are approximately 200 different types
of cells that make up the basic structures of
the human body.
 Cell division creates new cells. A “parent”
cell divides into two new “daughter” cells.
 Different types of cells carry out different
functions in the body.
Parts of a Cell
 Plasma membrane
 Cytoplasm
 Cytosol
 Organelles
 Nucleus
 Chromosomes
 Genes
3 main parts of a cell
 Plasma membrane – the cells flexible outer
surface.
 Cytoplasm – all the cellular contents between
the plasma membrane and the nucleus.
 Nucleus – a large organelle that houses most
of the cell’s DNA. Chromosomes and genes
are contained here.
Typical Structures
Plasma Membrane
 A flexible, yet sturdy barrier that surrounds
and contains the cytoplasm of a cell.
 Fluid mosaic model.
 Lipid Bilayer
 Membrane proteins
 Membrane Permeability – Selective
Plasma Membrane continued…
 Gradients


Concentration
Electrochemical
 Osmosis
 Diffusion
 Active Transport
Lipid Bilayer
 Phospholipids – 2 layers
 Amphipathic – polar and nonpolar
 Hydrophilic
 Hydrophobic
Membrane Proteins
 Integral Proteins – extend into or through the
lipid bilayer.

Transmembrane proteins
 Peripheral Proteins – attached to either the
inside or outside of the membrane.
Functions of Membrane
Proteins
 Ion channel
 Transporter
 Receptor
 Enzyme
 Cell Identity Marker
 Linker
Membrane Permeability
 Selectively Permeable
 Permeable to nonpolar, uncharged molecules,
such as oxygen, carbon dioxide, & steroids.
 Impermeable to ions and charged or polar
molecules, such as glucose.
 Slightly permeable to water and urea.
Gradients
 Concentration Gradient – A difference in the
concentration of a chemical from one place
to another.
 Electrochemical Gradient – The combination
of the effects of the concentration gradient
and the membrane potential.
Transport Across the
Membrane
 Passive Transport – does not require cellular
energy.

Substances move down their concentration or
electrochemical gradients using only their own
kinetic energy.
 Active Transport – requires cellular energy in
the form of ATP.
3 Types of Passive Transport
 Diffusion through the lipid bilayer.
 Diffusion through membrane channels.
 Facilitated diffusion.
Endocytosis
 Material enters the cell in vesicles.
Exocytosis
 Material leaves the cell in vesicles.
Diffusion
 Materials diffuse from areas of high
concentration to areas of low concentration.
They move down their concentration
gradient.
 Equilibrium – molecules are mixed
uniformly throughout the solution.
Factors Influencing Diffusion
 Steepness of the concentration gradient.
 Temperature.
 Mass of the diffusing substance.
 Surface Area.
 Diffusion distance.
Osmosis
 The net movement of a solvent (water)
across a selectively permeable membrane.
 Water moves from an area of higher water
concentration to an area of lower water
concentration.
Osmotic Pressure
 A solution containing solute particles that
cannot cross the membrane exerts a force
called osmotic pressure.
 The greater the number of solute particles the
greater the pressure.
Tonicity
 A solution’s tonicity measures the solution’s
ability to change the volume of cells by
altering their water content.
 Isotonic – cell maintains shape
 Hypotonic – cell swells and bursts
 Hypertonic – cell shrinks - crenation
Cytoplasm
 2 components

Cytosol – fluid portion that surrounds organelles.
55% of total cell volume
 Water with dissolved and suspended components

 Ions, glucose, amino acids, fatty acids, proteins, lipids, ATP,
and waste products.

Organelles – specialized structures
Specific shapes
 Specific functions

Cytoskeleton
 Network of protein filaments.
 Structural framework for the cell.
 3 Types of filaments



Microvilli – small – increase surface area
Intermediate filaments
Microtubules – largest – in cilia and flagella –
participate in cell division.
Centrosome
 Located near the nucleus
 Plays a critical role in cell division
Cilia and Flagella
 Comprised of microtubules.
 Cilia – short, hairlike projections that extend from
the surface of the cell.


Line respiratory tract
Movement is paralyzed by nicotine
 Flagella – longer than cilia


Usually move an entire cell
Sperm’s tail
Ribosomes
 Sites of protein synthesis
 Free Ribosomes – located in cytosol
 Attached to nuclear membrane and ER
 In mitochondria
Endoplasmic Reticulum ER
 Plasmic = cytoplasm; reticulum = network
 Network of folded membranes
 Transports substances throughout cell
 Rough ER – ribosomes attached –
synthesizes proteins
 Smooth ER – synthesizes fatty acids and
steroids
Rough ER
Smooth ER
Golgi Complex
 Consists of 3 – 20 golgi cisternae
(membranous sacs)
 Modifies, sorts, and packages proteins for
distribution
 Proteins leave through secretory vesicles,
membrane vesicles, or transport vesicles.
Lysosomes
 Lyso = dissolving; somes = bodies
 Contain powerful digestive enzymes and
hydrolytic enzymes
 Lysosomal enzymes can destroy their own
cell – autolysis (due to pathology)
Lysosome
Mitochondria
 Generate ATP – “powerhouses” of the cell
Mitochondrian with Matrix
Mitochondria
Nucleus
 Spherical or oval shaped
 Most prominent feature in the cell
 Most structures have a single nucleus,
although mature RBCs have none
 Contain genes arranged in chromosomes
 Genome – total genetic information for an
organism
Nucleus
Nucleus
Cell Division
 Somatic Cell Division – replaces dead or
injured cells and adds new ones for growth.


Mitosis
Produces 2 identical daughter cells
 Reproductive Cell Division – produces
gametes – sperm and oocytes.

meiosis
Cell Cycle
 2 major phases


Interphase – the cell is not dividing
Mitotic phase – the cell is dividing
Interphase
 The cell replicates its DNA during this phase.
 Produces additional organelles and cytosolic
components.
Mitotic Phase
 Nuclear Division – Mitosis
 Cytoplasmic Division - Cytokinesis
Mitosis
 Prophase

Chromatin fibers condense and shorten.
 Metaphase

The microtubules align the centromeres of the chromatid
pairs.
 Anaphase

The centromeres split separating the two members of
each chromatid pair.
 Telophase

Identical chromosomes uncoil and a nuclear envelope
forms around each mass.
Cytokinesis
 Division of the parent cell’s cytoplasm and
organelles into two daughter cells.
Cellular Diversity
 The body of an average human adult is
composed of nearly 100 trillion cells.
 Approximately 200 different types.
 The largest cell is the oocyte