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The Cell
The smallest unit
of life that can
perform all life processes.
“Life is macromolecules that can perform unique
functions because they are enclosed in a structural
compartment that is separate from the external
environment. This separation allows living things to
maintain a constant internal environment
(homeostasis)”.
Inner life of the cell animation
All living organisms are composed of cells that can:
• Respond to their environment
• Grow, develop and reproduce
• Metabolize
• Maintain homeostasis
A little bit of history
“cells”
Robert Hooke
Looked at cork and saw square compartments. They reminded him of prison cells so he coined the term “cell”.
“little wretched beasties”
Antone van Leeuwenhoek - lenses
Made lenses for glasses. He applied the magnification of a lens to a device to view pond water up closely.
He observed small single-celled organisms moving around and wrote in his journal of these “little wretched beasties”.
Anton van Leeuwenhoek (1673)
Made microscopes with better magnification
First person to observe living cells
Spirogyra
The Cell Theory (3 parts)
1. All organisms are made of one or more cells.
2. The cell is the basic unit of all living things.
3. All cells come from pre-existing cells.
Theodor Schwann (zoologist)
Matthias Schleiden (botonist)
• the belief at the time was that life could spontaneously
“spring up” out of nothing (spontaneous generation)
3. All cells come from pre-existing cells
Redi – disproved spontaneous generation through experimentation
Pasteur – disproved spontaneous generation
Cell Theory - confirmed
1. The cell is the basic unit of life.
2. All life forms are made of one or more cells.
3. Cells only arise from pre-existing cells.
Why are cells so special?
Able to differentiate
◼ Stem cell = general, unspecialized cell
◼ Becomes specialized with time
◼ Examples: skin cells, macrophage cells, neurons
Differentiation
How cells become specialized
examples
You can use different terms to describe the type of cell(s) you’re looking at.
3 different sets of words:
Cells in general
Amoeba sisters – Grand cell tour
1) Unicellular vs. Multicellular
Unicellular
Uni = one
One cell
Multicellular
Multi = many
Many cells
prokaryote eukaryote
Cells that DO NOT have a cell membrane around their nucleus.
example –Bacteria
Cells that have a membrane around their nucleus.
Plant and Animal Cells
Eukaryote cells usually 10X larger than Prokaryote cells.
2) Prokaryote vs Eukaryote
2) Prokaryote vs EukaryoteProkaryotic Cells
No nucleus- DNA unbound
No membrane-bound organelles
All unicellular organisms
All microscopic
Eukaryotic Cells
Have nucleus with DNA
Organelles membrane-bound
Unicellular OR multicellular organisms
microscopic OR macroscopic
3. Plant or Animal
Plant
Have cell walls
Have chloroplasts
Have large vacuoles
Tend to have a square shape
Animal
No cell walls
Have small vacuoles, if any
Not so square
(Eukaryote cells)
CELL ANALOGYA look at organelle function of the eukaryotic cell
typical animal cell typical plant cell
Crash course: Eukaryopolis
Eukaryotic Cell structures:
structure and function
Hank – crash course video
Organelles
Structures within cells that have specific jobs
“Little organs”
cell membranes
a dynamic structure – fluid mosaic model
functions:
Separates cell from its environment
Allows cell to maintain homeostasis
Acts as selectively permeable membrane (regulates molecules entering and
leaving the cell)
Cell-cell communication
Surface markers - recognition
Amoeba sisters – homeostasis video
Made of phospholipid bilayer with embedded proteins
Harvard animation
In a “typical” membrane, there is the passive phospholipid bilayer part (75-95%) and the active protein part (5-25%).
Those cells that do more exchanging of materials, such as gland cells, have more of the protein membrane.
Those cells that have minimal exchange of materials, such as fat cells, have less protein membrane.
Special designs for specific function:
The protein part of the cell membrane provides:communication, "I.D." tags, anchors to microtubules, gates of exchange for large molecules and pumps for maintaining ionic balance.
the cell membrane Selectivelypermeable
semi-fluid
the nucleus
contains the genetic material
Nucleus
Function: store and
protect
genetic info (DNA)
◼ NOT THE BRAIN- just stores the info
◼ Chromosomes: DNA wound up
◼ Nuclear envelope: double membrane with pores
ribosomes
site of protein synthesis
Genetic information carried from nucleus (DNA) to the ribosome via mRNA
https://www.youtube.com/watch?v=TfYf_rPWUdY
Mitochondria
Function: supply energy by converting food to ATP
Other:
◼ Highly folded membranes
◼ Has own DNA and ribosomes
microfilaments & microtubules
structure
movement
Cytoskeleton
Function: Framework for the cell-shape, organize, and support cell
Other: made of proteins
Cilia and Flagella
Function: assist in movement
Other:
◼ Cilia- short, hair-like
◼ Flagella- long, tail-like
centrioles
Molecular "tags" on microtubules direct traffic inside cells
Cytoplasm
Function: fill the spaces between organelles and the plasma membrane
endomembrane system
endoplasmic reticulum
rough ER
• alters proteins
• folds into tertiary structures
• transports newly synthesized proteins
smooth ER
• site for hydrolysis of glycogen
• modifies (detox.) small molecules
• site for synthesis of lipids and steroids
golgi apparatus
• recieves proteins from ER – further modifications
• Concentrates, packages, sorts proteins
• Polysacc. for plant cell walls synthesized
One way materials can pass out of cells
inside the celloutside the cell
Vesicles and vacuoles
The function and importance of vacuoles varies greatly according to the type of cell in which they are present.
Isolating materials that might be harmful or a threat to the cell.
Breaking down products taken into the cell to be used in metabolism.
Exporting unwanted substances from the cell.
Allows plants to support structures such as leaves and flowers.
Exporting manufactured products from the cell.
functions of the vacuole include:
special vesicles and vacuoles
peroxisomes
• the most common vesicle in cells
• found in all eukaryotes
• contain enzymes to rid the cell of hydrogen peroxide (convert
the hydrogen peroxide to water)
• some detoxify alcohol and other harmful compounds by
transferring hydrogen from the poisons to molecules of oxygen
(oxidation).
• others initiate production of phospholipids
special vesicles and vacuoles
lysosomes
contain hydrolytic enzymes - break
down cellular waste products, fats,
carbohydrates, proteins, and other
macromolecules into simple compounds,
which are then transferred back into the
cytoplasm as new cell-building materials
• autophagy - recycles the cell's organic material
special vesicles and vacuoles
central vacuole
contractile vacuole
Helps maintain homeostasis for water balance (osmotic equilibrium)
contractile vacuole (animals ONLY)
found in certain unicellular organisms
pumps fluid from in the cell to the outside by alternately filling and then contracting
plant cells ONLY
cell wall
cellulose
cell wall
• Rigid structure• Allows plant stem
to “stand up”• Made of cellulose
which humans can’t digest.
Chloroplasts – plant cells ONLY
Chloroplast
Function: carry out photosynthesis, which turns light energy to chemical energy
Other: has own DNA and ribosomes
central vacuole (plants ONLY)
Maintaining internal hydrostatic pressure or turgor within the cell
