Unit 3 Topic 2: cell types and structures
By the end of this topic, you should be able to…
1. Discuss similarities and differences between prokaryotic and eukaryotic cells
2. Identify a cell as being prokaryotic or eukaryotic based on cellular components
3. Explain the function of cellular organelles
4. Compare and contrast plant and animal cells
5. Explain how cells work together in multicellular organisms
Types of cells■ There are MANY types of cells (skin, brain, liver…), but cells are generally classified
as either prokaryotic or eukaryotic.
■ Some things that all cells, regardless of type, have in common are:
1. Water- nearly 70% of the mass of each cell is water
2. Macromolecules-
1. Every cell contains a genetic code (nucleic acids)
2. Every cell has hundreds of proteins with unique functions, like cellular
communication or transport or structure (keratin)
3. Every cell contains lipids that are used for energy storage, cell communication,
and protective barriers (cell membrane contains lipids, as does nuclear
membrane)
4. Every cell contains carbohydrates, also used in cellular communication, energy
storage, and used for structural support
3. Cell membrane, cytoplasm, and ribosomes
Revisiting unit 2 ☺
Before continuing…■ What is the monomer for:
– Carbohydrates:
– Lipids:
– Proteins:
– Nucleic acids:
■ Explain what the phrase “water is polar” means
– How does this allow water to dissolve so many solutes?
■ Describe how invention of the microscope helped scientists understand cells
Answers■ What is the monomer for:
– Carbohydrates: monosaccharides/simple sugars
– Lipids: fatty acids/ triglycerides
– Proteins: amino acids (build a polypeptide)
– Nucleic acids: nucleotides
Answers■ What is the monomer for:
– Carbohydrates: monosaccharides/simple sugars
– Lipids: fatty acids/ triglycerides
– Proteins: amino acids (build a polypeptide)
– Nucleic acids: nucleotides
■ Explain what the phrase “water is polar” means
There is an uneven distribution of electrons, giving one side (the oxygen) a partially negative charge and the other side (the hydrogen) a slightly positive charge
– How does this allow water to dissolve so many solutes?
The negative end attracts positive molecules and the positive end attracts negative molecules
■ Describe how invention of the microscope helped scientists understand cells
Answers■ What is the monomer for:
– Carbohydrates: monosaccharides/simple sugars
– Lipids: fatty acids/ triglycerides
– Proteins: amino acids (build a polypeptide)
– Nucleic acids: nucleotides
■ Explain what the phrase “water is polar” means
– How does this allow water to dissolve so many solutes?
■ Describe how invention of the microscope helped scientists understand cells
Before the microscope was invented, cells could not been seen. Once the
microscope was invented, scientists could see individual cells as well as what is
inside of them.
Examples of Cells
Amoeba Proteus
Plant Stem
Red Blood Cell
Nerve Cell
Bacteria
Types of cellsAgain, there are two general types:
1. Prokaryotic: pro means before, kary refers to karyon (kernel)
1. Before kernel (before nucleus)
2. Older, simpler, smaller… bacteria
2. Eukaryotic: eu means true
1. True kernel (true nucleus)
2. Younger, more complex, larger… animal, plant, protist, fungi
Prokaryotic cells
■ Smaller than eukaryotic cells (smaller surface area to volume ratio)
– Size is important because the smaller the cell, the easier it is to have
nutrients reach inner parts of the cell (they also get through the cell
quicker)
■ Eukaryotic cells have organelles that assist in moving nutrients/waste
■ DNA is circular and located in the cytoplasm (“nucleoid region”)
■ Less complex than eukaryotic cells (no membrane bound organelles)
– Do contain ribosomes (site of protein synthesis)
■ Surrounded by a cell wall outside of the cell membrane
Evolution of cells■ Prokaryotic cells likely appeared on earth
approximately 3.8 billion years ago
– We will look at how these cells could have
developed later in the year (evolution unit)
■ It involves conditions of earth’s early
atmosphere (lacked oxygen) and the
synthesis of organic molecules
– Photosynthetic bacteria evolved ~3 billion
years ago (oxygen released into atmosphere)
■ Eukaryotic cells evolved around 2.7 billion years
ago
– Endosymbiotic theory
■ Multicellular organisms evolved roughly 1.7
billion years ago (plants & animals)
cells
Note that
archaebacteria and
eubacteria are both
closer to eukaryotic
cells than they are to
one another. Scientists
have found that
archaebacterial genes
are more similar to
eukaryotic genes than
they are to eubacterial
genes, suggesting that
archaebacteria share a
common line of
evolutionary descent
with eukaryotes.
Endosymbiotic theoryDefine theory (again): A well-substantiated explanation of some aspect of the
natural world, based on a body of facts that have been repeatedly confirmed
through observation and experiment.
The endosymbiotic theory explains how scientists believe that eukaryotic cells
evolved from prokaryotic cells
endosymbiosis
What is happening?
Essentially, a larger prokaryotic cell engulfs (but does not digest) a
smaller prokaryotic cell. The smaller cell is then living within the larger
cell and operating as a specialized organelle.
Eukaryotic cells■ Larger than prokaryotic
■ More complex
– Contain specialized organelles
■ Exist either as single-celled organisms or as part of multicellular organelles
– Human body is made of more than 200 kindsof cells! These cells work together to make up five main types of tissue: epithelial, connective, blood, nervous, and muscle tissue.
– Recall: cells of the same organism contain the same DNA, but not all of the genes are activated in every type of specialized cell
■ Each type of cell is modified to work in the way the organism needs it to (may differ in size, shape, or function)
Specialized cellsA stem cell is a non-
specialized cell that can
either replicate itself
(produce more stem cells)
or differentiate into a
specialized cell. A stem cell
can differentiate into a liver
cell, but a liver cell cannot
change into a nerve cell. A
cell specializes (often)
during interphase before
cell division. Stem cells are
either embryonic (derived
from an embryo) or can be
adult stem cells
(undifferentiated cells from
a mature organism).
General eukaryotic cell
■ Cell membrane
■ Cilia/flagella
■ Cytoplasm
■ Cytoskeleton
■ Nucleus
■ Ribosomes
■ Endoplasmic Reticulum
■ Golgi Body
■ Mitochondria
■ Lysosome
■ Vacuole
■ Chloroplast
■ Cell wall
Plant v animal cellplant animal
Chloroplasts/ Cell wall/ Large Vacuole Lysosome
Cell membrane■ Also referred to as the plasma
membrane
■ Surrounds the cytoplasm
■ Is the outermost part of animal cells, but not for plant cells
■ Plays a large roll in cell transport (topic 3 this unit)
– Controls movement of materials into and out of the cell
– Selectively permeable(does not allow all things into the cell)
Cilia/flagella■ Used for cell movement
■ Cilia:
– Shorter/greater in number
– Move fluids using sweeping
motion
■ Flagella:
– Longer and typically one
per cell
– Propels cell using whip-like
motions
cytoplasm
■ Suspends the organelles
■ Jelly-like fluid within the cell
membrane
■ Also known as the cytosol
cytoskeleton■ A structure that maintains the shape and size of cells
■ A network of microtubules (thicker) and microfilaments (thinner)
– Long protein strands
nucleus■ The control center of the cell,
housing the DNA (master copy
of a cell’s genetic material)
■ The nucleus is surrounded by
the nuclear membrane, which
has lots of little pores (RNA exits
through these)
■ Within the nucleus is the
nucleolus, and this is where
ribosomes are produced
ribosome
■ Small particles of RNA and protein scattered
throughout the cytoplasm
■ This is the site of protein synthesis (proteins are
made here)
Endoplasmic reticulum■ An interconnected network of flattened
sacs
■ Joins with the outer membrane of the
nucleus
■ Two types:
– Rough ER: coated in ribosomes
(makes proteins)
– Smooth ER: lacks the ribosomes on
its exterior
■ Known as the “highway” or the
transportation system because it folds
and moves proteins
– Sends them to the golgi
apparatus/body
Golgi apparatus (golgi body)
■ Made of membrane-bound sacs
■ Processes, sorts, and packages
cellular components (proteins and
lipids) “Post Office”
■ Can produce lysosomes
■ Works directly with the ER
mitochondria■ Acts as the powerhouse of the cell
– Produces ATP, the energy currency
of the cell
■ Contains DNA (not unique to an
individual though, runs through the
family- get it from your mom because it is
carried in the female egg)
■ Double membrane
■ Varies from 1 to 10,000 mitochondria in
a single (specialized) cell
– Muscle cells contain lots of
mitochondria. Why? Need lots of
energy!
lysosome■ Membrane-enclosed organelles with
lots of enzymes used to break down
polymers
– Lysis = to break or to burst
■ Functions as the digestive system of
the cell
■ Maintain an acidic pH within the
lysosome
■ Debate as to whether this is only found
in animal cells… leaning towards this
organelle being found in both animal
and plant cells
vacuole■ Fluid filled organelle that stores enzymes,
waste, and water
■ Often the largest organelle in plant cells-
can take up to 80% size of the cell (much
smaller in animal cells)
chloroplast■ Found only in plant cells,
this is the location of
photosynthesis
– Converts light energy
to chemical energy
■ Double membrane
■ Contains DNA
■ Green in color because it
contains the pigment
chlorophyll
Cell wall
■ Found in plant cells (and bacteria and fungi), not in animal cells
■ Located outside the cell membrane
■ Leads to plant cells having a square/rectangular shape
■ Supports and protects the cell
■ Made of cellulose (in plant cells)
– Remember, this is a polysaccharide!
centrioles
■ Only found in animal cells-
located near nucleus
■ Assists in cell division
– Develops spindle fibers
Animal cell
Mitochondria
Nucleus
Golgi
Cytoplasm
ER
Ribosomes
Cell Membrane
Plant cell
Cytoplasm
Vacuole
Cell wall
Cell membrane
Chloroplast
Nucleus
Mitochondria
ER
Ribosome
Golgi body
