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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
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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