Cell Structures
A Tour of the Cell
Overview: The Fundamental Units of Life
• All organisms are made of cells
• Cell: collection of living matter enclosed by a
barrier
– Basic unit of all forms of life
Prokaryotic vs. Eukaryotic
• The basic structural and functional unit of every
organism is one of two types of cells:
prokaryotic or eukaryotic
• Prokaryotic: bacteria
• Eukaryotic: protists, fungi, animals, and plants
Comparing Prokaryotic and
Eukaryotic Cells
• Basic features of all cells:
– Plasma (cell) membrane
– Semifluid substance called cytoplasm
(cytosol)
– Chromosomes (carry genes)
– Ribosomes (make proteins)
• Prokaryotic cells are characterized by:
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A cell wall and cell membrane
No nucleus
Cytoplasm bound by the cell membrane
DNA in the cytoplasm
No membrane-enclosed organelles
• Eukaryotic cells are characterized by:
– DNA in a nucleus bound by a membrane
• The membrane is the nuclear membrane (envelope)
– Membrane-bound organelles
– Cytoplasm between the cell membrane and
nucleus
• Eukaryotic cells are generally much larger
than prokaryotic cells
• The cell membrane
is a phospholipid
bilayer
– It is a selective
barrier
• Only allows certain
things into and out of
the cell
– Oxygen, nutrients,
and waste
• A eukaryotic cell has internal membranes that
separate the cell into organelles
– Only plant cell organelles will be discussed
– Organelle: specialized structure that performs important
cellular functions
Cytoplasm (Cytosol)
• Jelly-like fluid and materials containing
everything between the cell membrane and
nucleus
• Including organelles
• Where most of the cell’s work is done
The Nucleus
• The nucleus is the control center of the cell
– Usually the easiest organelle to see under the microscope
– Contains most of the cell’s DNA
• Instructions (blueprints) for making proteins and other
molecules
• The nuclear envelope encloses the nucleus,
separating it from the cytoplasm
– The nuclear membrane is a double membrane
• Thousands of pores within the membrane allows for passage of
materials in and out to receive messages and send instructions
• The nucleolus is the small dense (dark) area
within the nucleus
– Where ribosome production occurs
• Ribosomes then move into the cytoplasm
Ribosomes
• Ribosomes are made of RNA and protein
• Ribosomes produce proteins in two areas:
– In the cytoplasm (free ribosomes)
– Attached to the outside of the endoplasmic reticulum
(bound ribosomes)
• Produce proteins by following instructions
(orders) sent from the
nucleus
The Endoplasmic Reticulum
• The endoplasmic reticulum
(ER) is an internal membrane
system (made of membranes)
• The ER membrane connects to
the nuclear envelope
• Used to produce and transport
materials such as proteins
• There are two distinct regions of
the ER:
– Smooth ER, which lacks
ribosomes
– Rough ER, with ribosomes on
its surface
Functions of Rough ER
• The rough ER
– Has bound ribosomes
• Proteins made (synthesized) in ribosomes are moved
to the ER to be modified (changed or added to)
– Then these proteins are released into the cell or exported
out of the cell
– Is a membrane factory for the cell
• Makes many proteins found on the cell membrane
Functions of Smooth ER
• The smooth ER
– Synthesizes (produces) lipid components of the
cell membrane
• Sometimes stores lipids after making them
– Detoxifies drugs
• Makes poisons no longer poisonous (neutralizes)
The Golgi Apparatus
• The Golgi apparatus is made of membranes
– Look like flattened stacks of membranes
• Functions of the Golgi apparatus:
– Modifies, sorts, and packages products of the ER
• Customizes proteins and other materials
• Stores for later use
• Packages and ships products outside the cell
Vacuoles
• A plant cell may have
one or more vacuoles
• Vacuoles hold organic
compounds (salts,
proteins, and
carbohydrates) as well
as water for later use
– Makes it possible for
plants to support leaves
and flowers (heavy
structures)
Chloroplasts and Mitochondria
• Chloroplasts and mitochondria
– Have a double membrane
• Two membranes make up the organelles
– Have proteins made by free ribosomes
– Contain their own DNA
Chloroplasts
• Chloroplasts, found in plants and are the sites of
photosynthesis
– Captures energy from sunlight and converts it into
chemical energy (food)
– Solar power plant
• Contain large stacks of membranes containing
chlorophyll
– Chlorophyll is the green pigment that function in
photosynthesis by capturing light energy
• Chloroplasts are found in leaves and other green organs of
plants and in algae
Mitochondria
• Mitochondria convert the chemical energy in
food into compounds the cells can use
– The site of cellular respiration, a metabolic process
that produces ATP
• ATP is the molecule cell’s use for energy (to do their work)
• Mitochondria are in nearly all eukaryotic cells
– Inherited from your mother through the egg
(ovum)
Cell Walls of Plants
• The cell wall is an extracellular structure that
distinguishes plant cells from animal cells
– Extracellular: outside the cell membrane
• Also found in algae, fungi, and many
prokaryotes
• Porous (contains mini holes) to allow for
water, oxygen, carbond dioxide, and small
molecules to pass through
• The cell wall in made within the cell itself
• The cell wall helps protect the plant cell by
providing extra shape and support for the cell
– Make up of cellulose
• Cellulose is a carbohydrate polymer that strengthens the
plant cell wall and only found in plants
– Not the same thing as cellulite (found in animals)
– Cellulose is the primary component of wood and paper
– Prevents excessive uptake of water
• What happens in animal cells when too much water is taken
into the cell?
Lab
• Wednesday
– We will meet as normal to discuss the
experiment
• The experiment will explore how the plant’s cell
wall helps maintain shape when under harsh
conditions.
• This experiment uses the microscope so review
how to use the microscope from your notes of the
first 9 weeks.