Post on 20-Feb-2023
Cell:
A basic unit of living matter separated from
its environment by a plasma membrane.
The smallest structural unit of life.
Microscopy
First observations of cells were made with
light microscopes:
Robert Hooke (1665): Used primitive microscope to
observe cork (dead plant cells). Coined the word
cell.
Anton van Leeuenhoeck (1670s): Made single lens
microscopes. First person to observe live cells
under microscope: “animalcules” (protists) in
water, red blood cells, sperm, bacteria, and insect
eggs.
Theodor Schwann (1830s): Observed harder to view
animal cells. Called cells “elementary particles” of
both plants and animals.
Cell Theory: Developed in late 1800s.
1. All living organisms are made up of one or
more cells.
2. The smallest living organisms are single
cells, and cells are the functional units of
multicellular organisms.
3. All cells arise from preexisting cells.
Microscope FeaturesMagnification:
Increase in apparent size of an object.
Ratio of image size to specimen size.
Resolving power: Measures clarity of image.
Ability to see fine detail.
Ability to distinguish two objects as separate.
Minimum distance between 2 points at which
they can be distinguished as separate and
distinct.
Microscopes
Light Microscopes: Earliest microscopes
used.
Lenses pass visible light through a specimen.
Magnification: Highest possible from 1000 X to
2000 X.
Resolving power: Up to 0.2 mm (1 mm = 1/1000
mm).
Types of Microscope
Electron Microscopes: Developed in 1950s.
Electron beam passes through specimen.
Magnification: Up to 200,000 X.
Resolving power: Up to 0.2 nm (1nm =
1/1’000,000 mm).
Two types of electron microscopes:
1. Scanning Electron Microscope: Used to study
cell or virus surfaces.
2. Transmission Electron Microscope: Used to
study internal cell structures.
Components of All Cells:
1. Plasma membrane: Separates cell contents
from outside environment. Made up of
phospholipid bilayers and proteins.
2. Cytoplasm: Liquid, jelly-like material inside
cell.
3. Ribosomes: Necessary for protein synthesis.
Procaryotic versus Eucaryotic Cells
Feature Procaryotic Eucaryotic
Organisms Bacteria All others (animals, plants,
fungi, and protozoa)
Nucleus Absent Present
DNA One chromosome Multiple chromosomes
Size Small (1-10 um) Large (10 or more um)
Membrane Absent Present (mitochondria,Bound golgi, chloroplasts, etc.)Organelles
Division Rapid process Complex process
(Binary fission) (Mitosis)
Relative Sizes of Structures
1 nanometer (10-9 m) water molecule
10 nanomters (10-8 m) small protein
100 nanometers (10-7 m) HIV virus
1 micron (10-6 m) cell vacuole
10 microns (10-5 m) bacterium
100 microns (10-4 m) large plant cell
1 millimeter (10-3 m) single cell embryo
Prokaryotic Cells
Bacteria and blue-green algae.
Small size: Range from 1- 10 micrometers in length.
About one tenth of eukaryotic cell.
No nucleus: DNA in cytoplasm or nucleoid region.
Ribosomes are used to make proteins
Cell wall: Hard shell around membrane
Other structures that may be present:
• Capsule: Protective, outer sticky layer. May be used for
attachment or to evade immune system.
• Pili: Hair-like projections (attachment)
• Flagellum: Longer whip-like projection (movement)
Eucaryotic Cells
Include protist, fungi, plant, and animal cells.
Nucleus: Protects and houses DNA
Membrane-bound Organelles: Internal
structures with specific functions.
Separate and store compounds
Store energy
Work surfaces
Maintain concentration gradients
Membrane-Bound Organelles of Eucaryotic
Cells
Nucleus
Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)
Golgi Apparatus
Lysosomes
Vacuoles
Chloroplasts
Mitochondria
Nucleus
Structure
Double nuclear membrane (envelope)
Large nuclear pores
DNA (genetic material) is combined with histones
and exists in two forms:
• Chromatin (Loose, threadlike DNA, most of cell life)
• Chromosomes (Tightly packaged DNA. Found only
during cell division)
Nucleolus: Dense region where ribosomes are made
Functions
House and protect cell’s genetic information (DNA)
Ribosome synthesis
Endoplasmic Reticulum (ER)
“Network within the cell”
Extensive maze of membranes that branches
throughout cytoplasm.
ER is continuous with plasma membrane and
outer nucleus membrane.
Two types of ER:
Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)
Rough Endoplasmic Reticulum (RER)
Flat, interconnected, rough membrane sacs
“Rough”: Outer walls are covered with
ribosomes.
Ribosomes: Protein making “machines”.
May exist free in cytoplasm or attached to ER.
RER Functions:
Synthesis of cell and organelle membranes.
Synthesis and modification of proteins.
Packaging, and transport of proteins that are
secreted from the cell.
• Example: Antibodies
Smooth Endoplasmic Reticulum (SER)
Network of interconnected tubular smooth
membranes.
“Smooth”: No ribosomes
SER Functions:
Synthesis of phospholipids, fatty acids, and
steroids (sex hormones).
Breakdown of toxic compounds (drugs, alcohol,
amphetamines, sedatives, antibiotics, etc.).
Helps develop tolerance to drugs and alcohol.
Regulates levels of sugar released from liver into
the blood
Calcium storage for cell and muscle contraction.
Golgi Apparatus
Stacks of flattened membrane sacs that may be
distended in certain regions. Sacs are not
interconnected.
First described in 1898 by Camillo Golgi (Italy).
Works closely with the ER to secrete proteins.
Golgi Functions:
Receiving side receives proteins in transport vesicles from ER.
Modifies proteins into final shape, sorts, and labels proteins for proper transport.
Shipping side packages and sends proteins to cell membrane for export or to other parts of the cell.
Packages digestive enzymes in lysosomes.
Lysosomes
Small vesicles released from Golgi containing at least 40 different digestive enzymes, which can break down carbohydrates, proteins, lipids, and nucleic acids.
Optimal pH for enzymes is about 5
Found mainly in animal cells.
Lysosome Functions:
Molecular garbage dump and recycler of
macromolecules (e.g.: proteins).
Destruction of foreign material, bacteria, viruses,
and old or damaged cell components.
Digestion of food particles taken in by cell.
After cell dies, lysosomal membrane breaks down,
causing rapid self-destruction.
Lysosomes, Aging, and Disease
As we get older, our lysosomes become leaky,
releasing enzymes which cause tissue damage and
inflammation.
Example: Cartilage damage in arthritis.
Steroids or cortisone-like anti-inflammatory agents
stabilize lysosomal membranes, but have other
undesirable effects (affect immune function).
Diseases from “mutant” lysosome enzymes are
usually fatal:
Pompe’s disease: Defective glycogen breakdown in liver.
Tay-Sachs disease: Defective lipid breakdown in brain.
Common genetic disorder among Jewish people.
Vacuoles
Membrane bound sac.
Different sizes, shapes, and functions:
Central vacuole: In plant cells. Store starch, water,
pigments, poisons, and wastes. May occupy up to
90% of cell volume.
Contractile vacuole: Regulate water balance, by
removing excess water from cell. Found in many
aquatic protists.
Food or Digestion Vacuole: Engulf nutrients in
many protozoa (protists). Fuse with lysosomes to
digest food particles.
Chloroplasts
Site of photosynthesis in plants and algae.
CO2 + H2O + Sun Light -----> Sugar + O2
Number may range from 1 to over 100 per
cell.
Disc shaped structure with three different
membrane systems:
1. Outer membrane: Covers chloroplast surface.
2. Inner membrane: Contains enzymes needed to
make glucose during photosynthesis. Encloses
stroma (liquid) and thylakoid membranes.
3. Thylakoid membranes: Contain chlorophyll,
green pigment that traps solar energy. Organized
in stacks called grana.
Chloroplasts
Contain their own DNA, ribosomes, and
make some proteins.
Can divide to form daughter chloroplasts.
Type of plastid: Organelle that produces and
stores food in plant and algae cells.
Other plastids include:
Leukoplasts: Store starch.
Chromoplasts: Store other pigments that give
plants and flowers color.
Mitochondria (Sing. Mitochondrion)
Site of cellular respiration:
Food (sugar) + O2 -----> CO2 + H2O + ATP
Change chemical energy of molecules into the
useable energy of the ATP molecule.
Oval or sausage shaped.
Contain their own DNA, ribosomes, and
make some proteins.
Can divide to form daughter mitochondria.
Structure: Inner and outer membranes.
Intermembrane space
Cristae (inner membrane extensions)
Matrix (inner liquid)
Origin of Eucaryotic Cells
Endosymbiont Theory: Belief that
chloroplasts and mitochondria were at one
point independent cells that entered and
remained inside a larger cell.
Both organelles contain their own DNA
Have their own ribosomes and make their own
proteins.
Replicate independently from cell, by binary
fission.
Symbiotic relationship
Larger cell obtains energy or nutrients
Smaller cell is protected by larger cell.
The Cytoskeleton
Complex network of thread-like and tube-
like structures.
Functions: Movement, structure, and structural
support.
Three Cytoskeleton Components:
1. Microfilaments: Smallest cytoskeleton fibers.
Important for:
Muscle contraction: Actin & myosin fibers in
muscle cells
“Amoeboid motion” of white blood cells
Three Cytoskeleton Components:
2. Intermediate filaments: Medium sized fibers
Anchor organelles (nucleus) and hold cytoskeleton
in place.
Abundant in cells with high mechanical stress.
3. Microtubules: Largest cytoskeleton fibers.
Found in:
Centrioles: A pair of structures that help move
chromosomes during cell division (mitosis and
meiosis).
Found in animal cells, but not plant cells.
Movement of flagella and cilia.
Cilia and Flagella
Projections used for locomotion or to move
substances along cell surface.
Enclosed by plasma membrane and contain
cytoplasm.
Consist of 9 pairs of microtubules surrounding
two single microtubules (9 + 2 arrangement).
Flagella: Large whip-like projections.
Move in wavelike manner, used for locomotion.
Example: Sperm cell
Cilia: Short hair-like projections.
Example: Human respiratory system uses cilia to
remove harmful objects from bronchial tubes and
trachea.
Cell Surfaces
A. Cell wall: Much thicker than cell membrane,
(10 to 100 X thicker).
Provides support and protects cell from lysis.
Plant and algae cell wall: Cellulose
Fungi and bacteria have other polysaccharides.
Not present in animal cells or protozoa.
Plasmodesmata: Channels between adjacent plant
cells form a circulatory and communication system
between cells.
Sharing of nutrients, water, and chemical messages.
Cell SurfacesB. Extracellular matrix: Sticky layer of glycoproteins
found in animal cells.
Important for attachment, support, protection, and
response to environmental stimuli.
Junctions Between Animal Cells:
Tight Junctions: Bind cells tightly, forming a leakproof
sheet. Example: Between epithelial cells in stomach lining.
Anchoring Junctions: Rivet cells together, but still allow
material to pass through spaces between cells.
Communicating Junctions: Similar to plasmodesmata in
plants. Allow water and other small molecules to flow
between neighboring cells.
Important Differences Between
Plant and Animal Cells
Plant cells Animal cells
Cell wall None (Extracellular matrix)
Chloroplasts No chloroplasts
Large central vacuole No central vacuole
Flagella rare Flagella more usual
No Lysosomes Lysosomes present
No Centrioles Centrioles present
Summary of Eucaryotic Organelles
Function: Manufacture
Nucleus
Ribosomes
Rough ER
Smooth ER
Golgi Apparatus
Function: Breakdown
Lysosomes
Vacuoles