Cellular Organelles: A Spotlight on Research
Student Guided Notes
Organelles are membrane-bound structures with specific functions in the cell.
Today we will learn the functions of the organelles by studying real scientific research.
Scientists perform experiments to test hypotheses. Scientific theories explain observed
phenomena or events in nature and are based on evidence.
Nucleus:
 The nucleus was the first organelle discovered. It was first described by Anton van
Leeuwenhoek in 1719.
 The nucleus is the control center of the cell, where genetic information is stored as
DNA.
Ribosome:
 Ribosomes are organelles made from proteins and RNA. They are made in a part of the
nucleus called the nucleolus.
 Ribosomes are important for making proteins based on instructions stored in DNA.
 3 scientists won the 2009 Nobel Prize in Chemistry for discovering the structure of
ribosomes. Scientists had been trying to do this since the 1960’s.
 List the two locations where ribosomes can be found:
1) Endoplasmic Reticulum
2) Cytoplasm (“free ribosomes”)
Endoplasmic Reticulum:
 Scientists believe that the ER developed from infoldings of the plasma membrane.
 There are two types of ER
1) Rough ER contains ribosomes and makes proteins.
2) Smooth ER has no ribosomes and makes lipids.
Golgi Body:
 The Golgi body is responsible for processing and packaging proteins.
 Proteins from the Golgi go to either the cell membrane or other organelles.
 Scientists use a protein called green fluorescent protein (GFP) to “track” the movement
of proteins through the cell. This protein comes from jellyfish.
Cell Membrane:
 The cell membrane is composed of a lipid bilayer with some proteins on its surfaces.
 Gorter & Grendel did an experiment that proved the existence of a bilayer. He found
the area of red blood cell membranes was two times the area of the cells themselves.
 How did this experiment prove the existence of a bilayer?
The hydrophilic heads of lipids all were attracted to the water, so they spread
out in a single flat layer. If lipids had a different structure, this experiment
would not have worked.

List the functions of the cell membrane:
1) Separate cell from outside surroundings
2) Selectively permeable – controls movement of substances in and out of cell
3) Protects the cell
Mitochondrion:
 Mitochondria are the energy producing organelles in all eukaryotic cells.
 The energy made in mitochondria is in the form of adenosine triphosphate (ATP).
 Research provides evidence for the endosymbiotic theory, the idea that mitochondria and
other organelles originated as prokaryotes engulfed by a eukaryotic cell.
 List three pieces of evidence for this theory:
1) Similar size of mitochondria and bacteria
2) Circular shape of DNA
3) Double membrane, one from prokaryote and one from eukaryote
4) Evolutionary history links mitochondria to purple bacteria
Chloroplast:
 Found only in plant cells.
 The chlorophyll in chloroplasts provide plants’ green color.
 Chloroplasts absorb energy from the sun to make glucose (sugar).
 This process is called photosynthesis.
Vacuole:
 While they exist in both plant and animal cells, plants have a large, central vacuole.
 Plant vacuoles can occupy as much as 90 percent of the cell.
 List three functions of vacuoles in plants:
1) Stores water
2) Contains toxic chemicals to protect the plant
3) Water pressure provides support for the cell wall
Cell Wall:
 Cell walls, found in plant cells, are located outside the plasma membrane.
 The cell wall was the first structure to be viewed with a microscope.
o Robert Hooke’s observation of cork in the year 1665.
 Freeze-fracture techniques and scanning electron microscopy were used to determine
how the cell wall is built.
Other Important Organelles:
 Lysosomes – Digest wastes and cellular debris.
 Cytoskeleton – Provide structure and a transport network for proteins within the cell.
o Molecular motors
 Centriole – Specialized organelle used in cell division.
 Cilia & Flagella – Extensions of the cytoskeleton used for cell movement.