Biology
Cell Structure
& Function
What is a cell?
• The smallest unit that is capable of
performing life functions.
• After observing many cells, scientists came
up with the cell theory:
• All living things are made of 1 or more cells.
• Cells are the basic units of structure and
function in organisms.
• All cells come from existing cells.
Cell Size
•To function efficiently, cells must be small. Why?
• If a cell is the shape of a cube and has 1 mm sides,
calculate the surface area of the cube using the formula 6S2.
Also, calculate the volume using the formula S3. What is the
surface area to volume ratio?
•Do the same calculations for a cell having 2 mm sides.
•What happens to the SA/volume ratio as the cell gets
bigger? Why is this bad?
2 Main Cell Types
Prokaryotic
• Originated approximately
3.5 billion years ago
• 0.5- 2µm (µ is the symbol
for “micro” which means
1/1,000,000
• Simple- no nucleus nor
other special
compartments
• Single, circular DNA
molecule
• Example- bacterium
Eukaryotic
• Originated approximately
1.5 billion years ago
• 2-100µm; typical
plant/animal cell is 10-50µm
• Organized- Have a nucleus
and other organelles
(structures that carry out
specific functions for the
cell)
• DNA is in the form of
chromosomes
• Example- animal and plant
cells
Prokaryotic Bacterial Cell
Eukaryotic Plant Cell
Eukaryotic Animal Cell
Characteristics of ALL Cells
All pro and eukaryotic cells have the following:
• Cell membrane- An outer boundary which is also
called the plasma membrane
• Cytoplasm- The interior of a cell; just the liquid is
called cytosol.
• Cytoskeleton (microtubules/microfilaments)Protein filaments (thread-like structures) that are
important in cell movement, shape and division
• Ribosomes- Structures that do not have a
membrane and make proteins
• DNA- hereditary information
Eukaryotic
Organelles
Organelles that Surround the Cell
• Cell membrane- “Selects” what can enter and
leave the cell. More about this later!
• Cell wall
– Most commonly found in plant cells and
bacteria- NOT IN ANIMAL CELLS!
– Surrounds the cell membrane and provides
structure and support
– Made of cellulose- long carbohydrate chain
• Cilia- Short, numerous hairs that move the cell
and/or substances outside the cell
– What human cells have cilia?
• Flagella- Long tail(s) that moves the cell
and/or substances outside the cell
– Both cilia and flagella are made of protein
filaments like the cytoskeleton.
– What human cell has a flagellum?
Organelles inside the cell
• Nucleus
– Directs the cell’s activities
– Houses DNA
– Houses the nucleolus
• where ribosomes are made
– Surrounded by a double membrane
called the nuclear envelope
• controls what exits the nucleus like
ribosomes and RNA
• has openings called nuclear pores
• Endoplasmic reticulum
– System of membranes that move proteins
around inside the cell- “intracellular highway”
– Can be smooth or rough
• rough has ribosomes attached to it and smooth
does not
• ribosomes can also be found in the cytosol
• Golgi apparatus
• Flattened sacs
• Processes proteins into vesicles (membrane
bound sacs)
• Mitochondria
– Produces ATP- form of energy that can be
used by the cell. What cells of the body have
lots of mitochondria?
– Has a double membrane
• Outer membrane is smooth and the inner
membrane (cristae) is folded.
– Has its own DNA
• Chloroplast
– In plants, some protists and some bacteriaNOT IN ANIMAL CELLS!
– Where photosynthesis occurs
– Has its own DNA and a double membrane
Mitochondria
Chloroplast
• Lysosome
– Spherical organelle where digestion occurs
• Remove the web between fingers of a fetus
• Usually in animal cells
• Central Vacuole
– Large
– Stores water, nutrients and waste
– Only in plant cells
• Animal cells have vacuoles- but not central
vacuoles
“Typical” Animal Cell
http://web.jjay.cuny.edu/~acarpi/NSC/images/cell.gif
“Typical” Plant Cell
How do animal and plant cells differ?
Animal
Plant
• Spherical
• Might have flagella or
cilia
•
•
•
•
Rectangular
Have a cell wall
Have chloroplasts
Have a central
vacuole
Evolution of the Eukaryotic Cell
• A possible explanation for how eukaryotic cells
came into existence is the endosymbiotic theory.
• Symbiosis is a relationship between organisms
where every member benefits.
• The endosymbiotic theory states that
chloroplasts and mitochondria were once
prokaryotic bacteria. They entered a larger
prokaryotic cell and all parties benefited.
• The chloroplast and mitochondria got extra
protection and the larger cell developed the
ability to make its own food and energy.
3-24
Evidence of the endosymbiotic theory
• Both chloroplasts and mitochondria have
their own circular DNA (like prokaryotic
cells).
• Both chloroplasts and mitochondria have a
double membrane.
• Mitochondria are approximately the size of
bacteria.
3-25
Game to Review Organelles