A & P: Chapter 3 - Cells
Cytology - the study of cells
• The cell is the basic unit of life.
• Robert Hooke discovered the cell in 1665.
• All cells are made of the elements carbon, hydrogen, oxygen, and nitrogen; plus iron, sodium, and
potassium. Iron is needed to make hemoglobin which carries oxygen. Cells also contain trace
elements such as calcium that is needed for blood clotting.
• Most of the cell structure is protein.
• The cell is 60% water. Cells are bathed in a dilute saltwater solution called interstitial fluid.
• Cells vary in length and shape.
3 Main Regions of a Generalized Cell:
• Nucleus
• Cytoplasm (cytosol)
• Cell Membrane (also called PLASMA MEMBRANE)
Extremely thin
Outpouchings and infoldings
Selectively Permeable = controls what
enters and leaves the cell, it allows
some things to pass but not others, this
is the MAIN FUNCTION of the cell
membrane
Lipid bilayer
Fatty acids
Proteins
Structures Common to All Cells:
•
Outer Limiting membrane
•
Cytoplasm
•
Organelles
• Specific cell parts – each perform a specific function.
• Almost all cells have a nucleus.
• Eukaryote – does contain a true nucleus
• Prokaryote – does not contain a nucleus; bacteria, red blood cell
• Any cell that DOES NOT contain a nucleus is considered to be prokaryotic
Protoplasm – stuff of life
• 2 Regions of Protoplasm
– Cytoplasm – watery substance; the area between the plasma membrane and nucleus.
Where most metabolic reactions/activities take place
• Contains 3 Major Elements
– 1. cytosol – semitransparent fluid that suspends the other elements
– 2. organelles – specific cell parts
– 3. inclusions – nonfunctioning units (most are stored nutrients or cell
products)
– Nucleoplasm – dense, protein-rich, jelly-like substance
• Contains chromatin – combination of DNA and proteins
•
When a cell divides, the chromatin coil up into rod-like structures called
chromosomes – contain the genetic information of the cell
Specialized Structures:
1. Microvilli – increase the absorption surface of the cell
2. Cilia – hair-like projections that are needed for movement
3. Flagella – similar to cilia but they are longer and fewer in number
4. Membrane junctions – vary in structure
1. Tight junctions – bind cells
together; prevent leakage (prevent
digestive enzymes from leaking
into bloodstream in small
intestines)
2. Desmosomes – anchor; prevent
cells from being pulled apart due
to stress (skin/muscle cells)
3. Gap junctions – allow
communication; direct passage of
molecules from cell to cell
(heart/embryonic cells)
The mass transportation of substances across a cell membrane can be classified as:
1. Physical processes (passive)
2. Physiological processes (active)
A transport system which requires energy from chemical reactions within a cell physiological (active –
can move only through living cell membranes)
• Examples of physiological processes
- Phagocytosis – move large solid particles into/out of the cell
- Pinocytosis – moves extremely small particles or fluids into/out of the cell
If the energy is from a source other than the cell’s chemical reactions, then the transport system is
physical (passive – can move materials through a living or dead membranes)
• Examples of physical processes:
- Diffusion – scattering or spreading out of particles across a membrane
- Osmosis – diffusion of a solvent through a selectively permeable membrane
- Filtration – forcing of water and solutes through a membrane by fluid or
hydrostatic pressure
- Dialysis – the separation of substances in solution by means of their unequal
diffusion through semi- permeable membranes; the process where
uric acid and urea are removed from circulating blood (kidney
machine)
•
•
Endocytosis – when the cell surrounds and takes in large particles
Exocytosis – when particles leave the cell
•
Metabolism – includes all the chemical reactions that occur in the body
•
•
Catabolic reactions – releases energy
Anabolic reactions – consumes energy
•
•
Catabolism – furnishes the energy necessary for all cellular activity
Catalyst – agent that affects the speed of a chemical reaction without itself being permanently
changed by the reaction
Enzymes – require assistance of other substances known as co-enzymes (enzyme activators)
•
ORGANELLES
NUCLEUS - directs the activities of a cell a.k.a. “the brain of the cell”; contains genetic materials (DNA)
in the form of chromatin; surrounded by a selectively permeable membrane called the NUCLEAR
MEMBRANE or ENVELOPE; filled with fluid called NUCLEOPLASM
1. NUCLEOLUS – small, dense structures within nucleus, made of proteins and RNA. No
membrane
Function = PRODUCES RIBOSOMES
2. CHROMATIN – loosely coiled “fibers” in nucleoplasm. Forms CHROMOSOMES during
cell reproduction. Composed mainly of DNA (deoxyribonucleic acid) and PROTEIN.
Contains coded information that directs protein synthesis in the cell
RIBOSOMES - The most numerous in a cell
– Where proteins are made
– The site of protein synthesis
– Free-floating or Attached
• Free-floating – produces proteins that will be used in the cell
• Attached – to the Endoplasmic Reticulum – produces proteins that will be excreted
for use outside the cell
ENDOPLASMIC RETICULUM (E.R.) – complex system or network of interconnected
membranes, canals, or channels. Connected to cell membrane, nuclear membrane, and
organelles
Function = TRANSPORT SYSTEM
- Rough ER - where ribosomes are located. RIBOSOMES manufacture (synthesize)
proteins
- Smooth ER – no ribosomes, where lipid synthesis takes place; serves as a storage
area for proteins that will be exported later
GOLGI APPARATUS (BODIES) – series of flattened, membranous sacs near the nucleus
• Flattened membranes; function to package and deliver proteins produced by the ribosomes
• The processing, packaging, and secreting organelle of the cell
• Consists of a stack of membranes or sacs filled with fluid and dissolved/suspended
substances
•
•
Operates like a production line – product assembled at one end, then packaged, and
finally put into a mail bag at the other end
Proteins are exported in vesicles
Function = REFINING, PACKAGING, AND
DELIVERY OF PROTEINS
Vesicles = the “packages” that are exported
MITOCHONDRIA (-ion = sing.) – Usually numerous, double layer
membrane - inner layer folded to form CRISTAE.
Function = WHERE CHEMICAL ENERGY (FOOD
SUBSTANCES) IS TRANSFORMED INTO A
USEABLE FORM – molecules of ATP
(adenosine triphosphate) that are like “packets”
of energy. The process of releasing/transforming
the energy from food involves oxygen and is
called cellular respiration
LYSOSOMES – quite variable in size and shape; contain 40 kinds of enzymes which work in oxygenpoor areas and lower pH levels (Digest food particles, bacteria, worn-out parts of
the cell – also play a role in early development) – breakdown and destroy foreign
particles, microorganisms, damaged or worn out cells and cell parts (think garbage
disposals)
PEROXISOMES – contain digestive oxidative enzymes (enzymes that require oxygen) that break down
toxic materials (digest fatty acids, amino acids, alcohol); byproduct of digestion is
Hydrogen Peroxide
CENTROSOME (central body) - Usually near the G.A. and nucleus. Composed of 2 “cylinders” called
CENTRIOLES (each composed of numerous microtubules), which
always lie perpendicular to each other. Active involved in cell
reproduction – SPINDLE forms from the centrioles
VESICLES – tiny sacs in which substances are transported, packaged by Golgi Apparatus
MICROTUBULES AND MICROFILAMENTS
 Threadlike structures
 Help support and shape cells
 Form the cytoskeleton – the framework of the cell
 Maintains shape

Functions in movement – can assemble when needed, break down, and reassemble to form
new structures
• MICROTUBULES – long, slender protein tubes
– Spindle fibers – aid in movement of chromosomes during cell division
– larger than filaments, maintain shape (“skeleton” of the cell =
CYTOSKELETON)
• MICROFILAMENTS – fine protein threads
– Lie just under the cell membrane
– Help move cellular materials and play a role in cytoplasmic streaming
– involved in cellular movement, as in muscle cells
CILIA AND FLAGELLA
 Structures that extend out from the surface of the cell and function in movement
 Anchored to the cell by a cylindrical structure called a basal body
 CILIA – short, hairlike extensions that occur in large number on the surface of some cells
- Oar-like movement
- Example: upper respiratory system – move fluids and mucus
 FLAGELLA – whiplike; longer than cilia
- Occur singularly or in pairs
- Fast moving – whipping back and forth
- Example: sperm cell
Movement of Substances Through the Cell Membrane
DIFFUSION – molecules move spontaneously (no cellular energy used) from an area of higher
concentration to an area of lower concentration
FACILITATED DIFFUSION – molecules diffuse through a membrane by means of a carrier molecule
transports (requires no energy = PASSIVE TRANSPORT)
OSMOSIS – the diffusion of water through a selectively permeable membrane.
- OSMOTIC PRESSURE = pressure to stop osmosis
SOLUTION – a mixture of solvent and solute
 Solute = Substance dissolved
 Solvent = Substance in which a solute is dissolved (usually water)
3 Types of Solutions:
 Isotonic Solution = concentration of solute particles is the same inside and outside the cell
 Hypertonic Solution = concentration of solute particles is greater outside the cell
 Hypotonic Solution = concentration of solute particles is lower outside the cell
Isotonic Solution
Hypertonic Solution
Hypotonic Solution
The result is Plasmolysis
(cytoplasm shrinks)
The result is Cytolysis
(cell swells)
FILTRATION – molecules are forced through a membrane by hydrostatic pressure, Kidneys
ACTIVE TRANSPORT – molecules are moved against the concentration gradient. This requires the
use of cellular energy, also usually involves a carrier molecule: ATP
• Exocytosis = transport of particles out of the cell
• Endocytosis = transport of particles into the cell
- Pinocytosis – liquids taken in, cell engulfs a droplet of water
- Phagocytosis –solids taken in. a vesicle forms.
The Life Cycle of a Cell
A. Mitosis (nuclear division)
B. Cytoplasmic Division (cytokinesis)
C. Interphase (growth) – chromosomes are duplicated and
other structures and organelles are produced
D. Differentiation – cells become specialized, developing
characteristics in structure and function; occurs as cells
multiply and organism develops and grows
MITOSIS
A. PROPHASE
- chromosomes visible (chromatids)
- centrioles migrate to the poles
- nuclear membrane disappears
- nucleolus disappears
- spindle forms
B. METAPHASE
- chromosomes line up on the equator, spindle attaches
C. ANAPHASE
- chromatids separate and move to opposite poles
D. TELOPHASE
- chromosomes disappear  chromatin
- nuclear membrane reforms
- nucleoli reappears
- spindle disappears
- centrioles duplicate
E. CYTOKINESIS
- division of the cytoplasm to form 2 new daughter cells
- organelles are divided
- daughter cells are genetically identical