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Cell Structure and Function
Cell Structure and Function
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The discovery and the basic theory of cells.
Cell size and number.
The two major kinds of cells.
Plant cells and animal cells.
Cell membrane (plasma membrane).
Cytoplasm.
Nucleus.
Ribosomes.
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Endoplasmic reticulum (rough and smooth).
Golgi complex (body).
Lysosomes.
Peroxisomes.
Mitochondria.
Chloroplasts.
Cytoskeleton.
Vacuoles.
The Two Major Kinds of Cells
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Each cell must have three features:
1. Plasma (cell) membrane: forms the
boundary of the cell.
2. DNA-containing region: inheritable
instructions.
3.Cytoplasm: fills interior of the cell
between the plasma membrane and DNA
region.
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There are two major types of cells
• prokaryotic
• lacks a nucleus and does not have an extensive
system of internal membranes
• all bacteria and archae have this cell type
• eukaryotic
• has a nucleus and has internal membrane-bound
compartments
• all organisms other than bacteria or archae have this
cell type
The Two Major Kinds of Cells
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Prokaryotic
Eukaryotic
Animal Cell- Eukaryotic
Plant Cell- Eukaryotic
Prokaryotic cell
Animal Cell
Plant Cell
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not all eukaryotic cells are alike
• the cells of plants, fungi, and many protists
have a cell wall beyond the plasma membrane
• all plants and many protists contain organelles
called chloroplasts
• plants contain a central vacuole
• only animal cells contain centrioles
Cell membrane (Plasma Membrane)
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The backbone of cell membranes is a
molecule called phospholipid
Each phospholipid molecule has one
hydrophilic head (phosphate), and two
hydrophobic tails (two fatty acids).
hydrophilic (water-loving)
hydrophobic (water-fearing)
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When surrounded by water, heads point
outward, tails point inward. Water is
excluded from the middle, thus forming two
layers called lipid bilayer.
heads
water
tails
Water
excluded
tails
heads
water
Phospholipid molecule
The Lipidbilayer
Another major component of the
membrane is a collection of membrane
proteins
• some proteins form channels that span the
membrane
• these are called transmembrane proteins
• other proteins are integrated into the structure
of the membrane
• for example, cell surface proteins are
attached to the outer surface of the
membrane and act as markers
Endocytosis and Exocytosis
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Refer to Endocytosis and Exocytosis
(animation in my website)
Phagocytosis: a form of endocytosis
in which cells engulf organisms
Pinocytosis: a form of endocytosis
through which a cell takes in fluid
Exocytosis: a process by which substances are
moved out of a cell by vesicles
The Nucleus: The Cell’s Control Center
(nuclear envelope, chromosomes, nucleolus)
Nuclear envelope
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The nuclear surface is bounded by a doublemembrane called the nuclear envelope
• groups of proteins form openings called
nuclear pores that permit proteins and RNA to
pass in and out of the nucleus
Chromosomes
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The nucleus stores hereditary information
The DNA of eukaryotes is packaged into
segments and associated with a protein
• this complex is called a chromosome
Nucleolus
The nucleus is the site for the subunits of
the ribosome to be synthesized
The nucleolus is a dark-staining region of
the nucleus
It contains the genes that code for the rRNA
(ribosomal RNA) that makes up the
ribosomal subunits
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The subunits leave the nucleus via the
nuclear pores and the final ribosome is
assembled in the cytoplasm
Ribosomes, Endoplasmic Reticulum (Rough
and Smooth), Golgi Complex
Ribosomes
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Beadlike clusters in the cytoplasm
Are made up of a number of proteins and
ribosomal RNA (rRNA), which are
produced in the nucleolus
They participate in protein synthesis.
Endoplasmic Reticulum (rough and smooth):
system of internal membranes and channels
* The segment of the ER dedicated to protein
synthesis is called the rough ER
• the rough spots are due to embedded ribosomes
* The segment of the ER that aids in the
manufacture of carbohydrates and lipids is
called the smooth ER
• the surface of this region looks smooth because
it contains no embedded ribosomes
Golgi Complex
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After synthesis in the ER, the newly-made
molecules are passed to the Golgi bodies
• Golgi bodies are flattened membranes that form
collective stacks called the Golgi complex
• their numbers vary depending on the cell
• their function is to collect, package, and
distribute molecules manufactured in the cell
Lysosomes
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Spherical vesicles that contain digestive
enzymes.
1. Digest worn-out organelles and cell
debris.
2. Act as a “minute cellular stomach”. They
digest bacteria
3. Act as “suicide bags” breaking open and
spilling their contents and digesting the cell.
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Refer to lysosomes- animation in my
website
Peroxisomes
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Vesicles containing oxidative and other
enzymes, such as catalase.
Catalase detoxifies hydrogen peroxide,
converting it into water and oxygen.
Mitochondrion
Mitochondria are
cellular powerhouses
Sites for chemical
reactions called cellular
respiration
The organelle is
surrounded by two
membranes
Chloroplast
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Chloroplasts are
the location for
photosynthesis
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The organelle is
also surrounded
by two
membranes
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Both mitochondria and chloroplasts possess
circular DNA that is not found elsewhere in
the cell
Cytoskeleton
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Three-dimensional latticework of minute
protein fibers.
Acts as internal skeleton, supporting the
cell’s shape and activities.
Three types of protein fibers:
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Microfilaments
Microtubules
Intermediate filaments
3-6 nm in diameter
20-25 nm in diameter
10 nm in diameter
Actin
Tubulin
Keratin and others
Lengthen and shorten
Lengthen and shorten
Cause with other proteins move colored pigment maintain cell shape
the contraction of muscles granules around
make cell tough
can move organelles
help maintain cell shape make up most of
Make up the spindle
the matter in skin
Central and Contractile Vacuoles
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Found only in plant cells
Occupies 5-95% of the total cell volume
It contains water and stores sugar, proteins,
ions, and other materials (orange juice)
It makes surface-to-volume ratio favorable
Review contractile vacuoles in the
following slide (video clip)
Name the following organelles:
Label the organelles in this cell
Question
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All of the following are likely components
of plant cells except:
A. chloroplasts.
B. mitochondria.
C. central vacuole.
D. flagella.
E. cell walls.