Cells and Tissues (Part I):
• Cytology: the study of cells
• Histology: the study of tissues
• Levels of Organization: cell---tissue---organ---system
• Cell as basic unit of life
 Bathed in interstitial fluid (salt H2O)
• Structure related to function
• Variety of cell types (sizes, shapes, functions)
• Unicellular Organism: consists of one cell (bacteria)
• Multicellular Organism: consists of more than one cell
• Prokaryotic Cell (Prokaryote): primitive
 Nuclear material spread out
 No nuclear membrane
 Examples: Bacteria and blue-green algae
• Eukaryotic Cell (Eukaryote): advanced
 Nuclear material confined within a nuclear membrane
 Examples: All cells except bacteria and blue-green algae
• Characteristics of Cells:





Nutrition: involves the cell’s need for taking in food
Digestion: the breakdown of food
Reproduction: to make a copy
Cellular Respiration: food being changed into energy
Excretion: getting rid of wastes
 Secretion: to release a product
 Synthesis: to make a product
 Irritability: response
• Cell Theory:
• Schleiden (1804-1881); Schwann (1810-1882)
 All living things are composed of cells.
 All cells are similar in structure and function.
 The structure and function of an organism involves the organization
and action of all its cells.
 All cells come from pre-existing cells (Virchow)
• Exceptions:
 Viruses
 Cell parts that reproduce (mitochondria, chloroplasts)
 Not all cells are separated by a cell membrane (muscle)
Cell Biology Discoveries:
• Robert Hooke (1665): coined the term “cell ” (cork)
• DuJardin: discovered cytoplasm
• Robert Brown: discovered the nucleus
Cell Organelles (Cell Parts):
• Protoplasm: a clear jelly-like material (colloid)
 Contains H2O, wastes, nutrients
 Cytoplasm: protoplasm within the cell membrane
 Keeps the cell hydrated
Nucleus
• “Control Center”
 Controls everything in the cell
 Contains DNA
• Has a double-layered
membrane with pores
• Shape of nucleus
conforms to the shape of
the cell
• Contains nucleoplasm
Chromosomes
• Control heredity
• Threads in the nucleus
• Contain DNA
• Human Body Cell (46)
• Human Sex Cell (23)
• Chromatin: inactive
(non-dividing genetic
material)
Nucleolus
• “Ribosome Factory”
• 1-4 in the nucleus
• Make ribosomes
Centrioles
• Involved in cellular
reproduction
• Only in animal cells
• Rods outside the nucleus
• Made up of fine
microtubules
• Hold up each end of the
mitotic spindle
Mitochondria
• “Powerhouse of the Cell”
• Involved with energy/
metabolism/cellular
respiration/form ATP
• Contains cristae
 hold enzymes
 increase surface area
Ribosomes
• Made by the nucleolus
• Involved in protein
synthesis
• Attached: on ER
(protein sent out of the
cell)
• Floating: in the cell
(protein within the cell)
• Made up of RNA
Endoplasmic Reticulum
• Channel inside the cell
• Rough ER: contains
ribosomes (protein sent
out of the cell)
• Smooth ER: does not
contain ribosomes (fats
sent out of the cell)
Golgi Bodies
• “Packaging Center”
• Stack of coins
• Secretion
Secretion
Vacuoles
• Clear bubbles
• Hold Water
• Prevent dehydration
• Animal (small, several)
• Plant (few, large)
Lysosomes
• “Suicide Sacks”
(membrane made fragile
by high amounts of
vitamin A)
• Contain digestive
enzymes
 Act as scavengers
 Eat old cell parts
• Related to aging,
arthritis?
Peroxisomes
• “Detox Units”
 Filters all poisons
 Change free radicals to H2O2
 Enzyme catalase converts
H2O2 to H2O
• High number in kidneys
and liver
• Tiny bubbles
Microtubules/Microfilaments
• “Skeleton of the Cell”
• Microtubules (support or
shape); mini tubes
• Microfilaments (cell
movement);
threads
• Intermediate filaments:
Help to form
desmosomes
Plant Cell
• Cell Wall (to prevent
dehydration)
• Chloroplasts (contain
chlorophyll)
 Green organelles
 Involved in photosynthesis
• Large Vacuoles
Cell Membrane:
•
•


Surrounds both animal and plant cell to prevent dehydration
Semi-Permeable Membrane:
Contains pores
Some particles move inside the cell; Some particles move out of the
cell; Cell membrane is selective
 Movement depends on: size of particles, chemistry of particles,
temperature, pressure
• Sandwich Model (1935): Static model
 2 phospholipid layers (phosphate + fat) between 2 layers of protein
• Fluid Mosaic Model (1970): Dynamic model
 Proteins immersed in the 2 layers of phospholipids (fluid)
Specializations of the Cell membrane:
• Gap Junctions: allow communication between cells (heart, embryonic
cells)
• Microvilli: fingerlike projections that increase absorption
• Desmosomes: buttonlike thickenings which aid in protection from
mechanical stress
• Tight Junctions: zipperlike; leakproof
Movement of Molecules:
• Passive Transport:
 No energy required
 Movement from a high concentration to a low concentration
• Diffusion:
 A type of passive transport
 Movement of molecules from a high concentration to a low
concentration
• Osmosis:
 A type of passive transport
 Movement of H2O molecules from a high concentration to a low
concentration (down a concentration gradient) through a membrane
• Facilitated Transport:
 Use of carrier proteins which carry molecules through the membrane
• Filtration:
 Process by which H2O and solutes are forced through a membrane
(or capillary wall) by fluid, or hydrostatic pressure (usually exerted by
the blood)
 Uses a pressure gradient to push solute-containing fluid from a
higher-pressure area to a lower-pressure area
 Not a very selective process
 Necessary for the kidneys to operate
Types of Solutions:
• Isotonic Solution:
• Concentration of solute (dissolved materials) in the
solution = the concentration of dissolved materials
inside the cell
 The concentration of H2O in the solution = the concentration of
H2O inside the cell
 Cells retain their normal shape
• Hypertonic Solution:
• Concentration of solute (dissolved materials) outside the
cell is higher than the concentration of dissolved materials
inside the cell
 There is more H2O inside the cell than outside the cell
 H2O will move out of the cell
 Pressure decreases and the cell shrivels
• Animal cell: Cell shrivels up (Plasmolysis)
• Plant cell: Cell membrane and cytoplasm pull away from
the cell wall; Plant wilts
• Hypotonic Solution:
• Concentration of solute (dissolved materials) is lower in
the solution outside the cell than the concentration of
dissolved materials inside the cell
 There is more H2O outside the cell than inside the cell
 H2O will move into the cell
 Pressure increases and the cell swells
• Animal Cell: Cell could burst (Cytolysis)
• Plant Cells: Cell wall prevents cytolysis; high turgor
pressure and plant cell becomes firm (stiff)
• Active Transport:
 Energy (AP) required
 Movement of molecules from a low
concentration to a high concentration
 Called solute pumping
 Nerve cells with Sodium (out) –
Potassium (in) Pump
• Bulk transport: movement of
large molecules across the
membrane
• Endocytosis: movement of large molecules into the cell
 Pinocytosis: “cell drinking”; taking in liquid and forming a
vacuole
 Phagocytosis: “cell eating”: taking in a solid particle;
dissolved by digestive enzymes of a lysosome
 Exocytosis: movement of large molecules out of the cell
Preparation of a Wet Mount:
• Place a drop of H2O on a
clean slide
• Place the specimen in the
drop of H2O
• Add stain (emphasizes
cell parts)
• Place cover slip over
specimen at a 450 angle
• Press out bubbles on the
cover slip
Lab Techniques:
• Growing cells on glass (cell culture)
 Cell food (medium)
• Cell Fractionation: separation of cell parts by high
velocity (20,000X/min.) using a centrifuge
 Most dense cell parts settle to the bottom of the test tube
• Autoradiography: injecting radioactive isotopes into
cells/organisms as tracers
Cell Division
• Mitosis: occurs in
somatic cells; 1 2
• Cell Cycle continuous;
Varies in different tissues
at different times
• Interphase:
 G1, G2 (gap): Cell duplicates
specific protein molecules
 S (synthesis): replicates
genetic material
Mitosis
• Why do cells divide?
 The larger the cell, the more demands are placed on its
DNA
 Trouble with a larger cell moving nutrients and wastes
across the cell membrane
• Cell Cycle: the sequence of growth (preparation)
and division of a cell
• Accurate cell division and regulation of the cell
cycle is critical to the health of the cell
 Mistake in cell cycle can lead to cancer (uncontrolled cell
division)
• Guarantees genetic continuity, growth, repair
Stages of Mitosis:
Interphase
• DNA doubles
• Centrioles double
• Chromosomes difficult to
see (dots)
• Nucleolus and nuclear
membrane visible
• “Resting Stage”
Prophase
• Longest Stage
• Chromosomes long
and thin
• Nucleolus and nuclear
membrane disappear
• Spindle forms
• Centromere hooks
doubled chromosomes
to the spindle
• Centrioles at both ends
of the spindle
Metaphase
• Middle Stage
• Shortest Stage
• Doubled chromosomes
line up at equator
Anaphase
• Chromosomes pull apart
to opposite poles
Telophase
• Last Stage of Mitosis
• Animal Cell breaks apart
• Plant Cell breaks apart
• Result: 2 identical
daughter cells
Deoxyribonucleic Acid (DNA)
• The ‘blueprint of life”
• Unique and unrepeatable
• Located in genes
 Genes make up chromosomes
 Chromosomes in the nucleus of the cell
• DNA composed of units called
nucleotides
 Each nucleotide is made up of a sugar,
phosphate, and hydrogen base.
• Double Helix model of Watson and
Crick
• X ray photos by Rosalind Franklin
• Sides of ladder (S-P) with covalent
bonds
• Sugar: deoxyribose
• Steps of ladder (bases)
• Complementary Base Pairs




Purines (Adenine/Guanine)
Pyrimidines (Cytosine/Thymine)
A-T (2 hydrogen bonds)
C-G (3 hydrogen bonds)
The Race for the DNA Model
King’s College
London
Cavendish Lab
London
Rosalind Franklin
James Watson
Francis Crick
(X ray Diffraction Studies)
Photo
#51
Maurice Wilkins
Nobel Prize
1962
(Double Helix Model)
• Mutation: a mistake in nitrogen base pairs
• Pattern of bases codes for a specific amino acid
• Codon: 3 letter (bases) code for 1 amino acid
• Replication of DNA (Making an identical
copy)
 DNA unzips and hydrogen bases separate (action of
DNA polymerase)
 Free-floating nucleotides match up on each side
 Hydrogen bonds reform
 Result: 2 identical DNA molecules (Each contain 1 of
the original DNA strands)
 Semi-Conservative Model of Replication
• Each DNA molecule with
a new strand and an old
strand
• DNA never leaves the
nucleus
Ribonucleic Acid (RNA)
•
•
•
•
•
•
Made up of nucleotides
Sugar called ribose
Nitrogen Bases: A, C,G,U
Single-stranded
Located in the nucleus and in the ribosomes
3 Types:
 Messenger RNA (mRNA); carries message of DNA to ribosomes (3
letter code – codon); single strand of letters
 Transfer RNA (tRNA): reads the mRNA code at the ribosomes (3
letter code – anticodon); carries an amino acid; shamrock shape
 Ribosomal RNA (rRNA): joins mRNA to tRNA
Transcription
• Making of mRNA from one
side of DNA in nucleus
 DNA polymerase unzips DNA
 Hydrogen bonds break and
energy is released
 One side of DNA acts as a
“template” (model) for making
mRNA
 Free-floating nucleotides line up
and form mRNA
 DNA reforms
 mRNA carries the message of
DNA to ribosomes
Translation
• Occurs at the ribosomes
• Anticodon of tRNA joins
with codon of mRNA
(rRNA helps)
• Amino acid pops off end of
tRNA
• Amino acids string together
to form a protein (Protein
Synthesis)