Download Chapter 6 *The Cell*

 Cell
1.
2.
3.
Theory:
All living things are made up of
cells
Cells are the basic units of
structure & function in living things
New cells are produced from
existing cells
1.
A barrier called a cell membrane
that surrounds the cell, and
2. At some point in their lives they
contain DNA. DNA is the molecule that
carries biological information.
1. Prokaryotes: do not have nuclei. They have
genetic material that is not contained in a
nucleus. Bacteria are prokaryotes.
2. Eukaryotes are cells
that have nuclei.
Eukaryotes have a
nucleus in which their
genetic material is
separated from the
rest of the cell.
• Plants, animals,
fungi, and protists
are eukaryotes.
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The eukaryotic cell
is divided into 2
main parts: the
nucleus and the
cytoplasm.
The cytoplasm is
the part of the cell
outside the
nucleus.
The nucleus contains most of a cell’s DNA. The
DNA contains the coded instructions for making
proteins and other important molecules.
• The nucleus is surrounded by a double
membrane called a nuclear envelope
• Inside the nucleus is chromatin. Chromatin is
made up of DNA bound to proteins. When the
cell divides, this chromatin condenses into
chromosomes.
• Most nuclei also have a small, dense
region known as the nucleolus where
ribosomes are made.
•
 Ribosomes
are small particles of RNA and
protein spread throughout the cytoplasm.
Proteins are made on ribosomes.
 The endoplasmic reticulum (ER) is an internal
membrane system. The ER is where lipids are
assembled, along with proteins and other
materials that are exported from the cell.
 2 types of ER: (1) Rough ER has
ribosomes on its surface and is
the site of protein synthesis;
and, (2) Smooth ER which
has no ribosomes and helps make lipids.
 Golgi
Apparatus: job is to change, sort,
and package proteins and other materials
from the ER for storage in the cell or
secretion outside of the cell.
 Lysosomes
are small organelles filled with
enzymes.
 They help break down lipids,
carbohydrates, and proteins into smaller
molecules that can be used by the rest of
the cell.
 Lysosomes can also play an important role
in destroying harmful substances or
bacteria that enter the cell.
 Vacuoles
are saclike structures that
are used to store materials.
 Almost
all
eukaryotic cells
contain
mitochondria.
 Mitochondria
convert the
chemical energy
stored in food into
compounds that are
more convenient for
the cell to use.
 Plants
and some
other organisms
contain
chloroplasts.
 Chloroplasts
capture the energy
in sunlight and
convert it into
chemical energy.
 The
structure that
helps support the
cell is called the
cytoskeleton.
 The cytoskeleton is
a network of protein
filaments that helps
the cell maintain its
shape.
 It is also involved in
movement.
 The
ER is
continuous with the
nuclear envelope
 It encloses a
network of
interconnected
tubules called
cisternae.
Smooth ER serves diverse functions
in different cells
 Its enzymes are involved in
phospholipid and steroid synthesis,
carbohydrate metabolism, and
detoxification of drugs & poisons.
 Alcohol and drugs increase a liver
cell’s production of smooth ER,
leading to an increased tolerance
 Smooth ER also functions in storage
and release of calcium ions during
muscle contraction

 Rough
ER manufactures
membranes for the cell.
 Enzymes built into the
membrane assemble
phospholipids, and membrane
proteins formed by bound
ribosomes are inserted into the
ER membrane
 Transport vesicles transfer ER
membrane to other parts of
the endomembrane system.
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The Golgi apparatus consists of a stack
of flattened sacs.
Vesicles that bud from the er join to
the cis face of a Golgi stack, adding to
their contents and membrane
Golgi products are processed and
tagged from the cis to the trans face
Glycoproteins often have their attached
carbohydrates modified
Golgi products are sorted into vesicles,
which pinch off from the trans face
These vesicles may have surface
molecules that help direct them to the
plasma membrane or to other
organelles.
Lysosomes are membrane-enclosed sacs
of hydrolytic enzymes used by animal
cells to digest macromolecules
 Lysosomes provide an acidic pH for these
enzymes
 In some protists, lysosomes fuse with
food vacuoles to digest material ingested
by phagocytosis.
 Macrophages, a type of wbc, use
lysosomes to destroy ingested bacteria
 Lysosomes also recycle a cell’s own
macromolecules by engulfing damaged
organelles or small bits of cytosol, a
process known as autophagy

 As
membranes move from the ER to the Golgi
and then to other organelles, their
compositions, functions, and contents are
modified.
 Cellular
respiration, the metabolic processing
of fuels to produce ATP, occurs within the
mitochondria
 Photosynthesis occurs in the chloroplasts of
plants and algae, which produce organic
compounds from CO2 & H2O by absorbing
solar energy
 Each contain a small amount of DNA that
direct the synthesis of some of their proteins
The folds of the inner
membrane, called
cristae, create a large
surface area and
enclose the
mitochondiral matrix.
 Many respiratory
enzymes,
mitochondrial DNA,
and ribosomes are
housed in the matrix

 Plastids
are plant organelles that include
amyloplasts, which store starch
 Chromoplasts, which contain green pigments,
and
 Chloroplasts which contain the green
pigment chlorophyll and function in
photosynthesis
Chloroplasts are bounded by 2
membranes separated by a
thin intermembrane space
 Inside the inner membrane is
a fluid called the stroma
surrounding a membranous
system of flattened sacs
called thylakoids
 Photosynthetic enzymes are
embedded in the thylakoids,
which may be stacked
together to form structures
called grana.
 Chloroplast DNA, ribosomes,
and many enzymes are
contained in the stroma.

 Peroxisomes
are oxidative organelles filled
with enzymes that function in a variety of
metabolic pathways
 They break down fatty acids for energy or
detoxifying alcohol and other toxins
 An enzyme that converts hydrogen peroxide
(H2O2), a toxic by-product of these
pathways, to water is also packaged within
 The
cytoskeleton is a network of protein
fibers that give mechanical support, function
in cell motility, & transmit mechanical
signals from the cell’s surface to its interior.
 The cytoskeleton interacts with special
proteins called motor proteins to produce
cellular movements
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Three main types of fibers:
microtubules, microfilaments,
and intermediate filaments
ALL eukaryotic cells have
microtubules, which are
hollow rods constructed of
columns of globular proteins
called tubulins
Microtubules change length
through the addition or
subtraction of tubulin dimers
In addition to providing a
supportive framework, they
also serve as tracks along
which organelles move with
the aid of motor molecules
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In many animal cells,
microtubules grow out
from a region near the
nucleus called a
centrosome
A pair of centrioles,
each composed of nine
sets of triplet
microtubules arranged
in a ring, is associated
with the centrosome
and replicates before
cell division
Yeast and plant cells
lack centrosomes
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Cilia and flagella are
locomotor extensions of
some eukaryotic cells
Cilia are numerous and
short
Flagella occur one or
two to a cell and are
longer
Many protists use cilia
or flagella to move
through aqueous media
Cilia or flagella
attached to stationary
cells of a tissue move
fluid past the cell
 Plant
cell walls are composed of microfibrils
of cellulose embedded in a matrix of
polysaccharides and protein
 The primary cell wall secreted by a young
plant cell is relatively thin and flexible
 Adjacent cells are glued together by the
middle lamella, a thin layer of
polysaccharides (pectin).
 When they stop growing, some cells secrete
a thicker and stronger secondary cell wall
between the plasma membrane & primary
cell wall.
 the
secondary wall, often deposited in
several laminated layers, has a strong and
durable matrix that affords the cell
protection and support
 Wood, for ex., consists mainly of secondary
walls.
 Plant cell walls are commonly perforated by
channels between adjacent cells called
plasmodesmata
Animal cells lack cell walls but do have an
elaborate ECM.
 The ecm is made of glycoproteins. The most
abundant glycoprotein is collagen, which forms
strong fibers outside the cells
 In fact, collagen accounts for about 40% of the
total protein in the human body.
 Cell surface receptor proteins called integrins
that are built into the plasma membrane
 Integrins are in a position to transmit signals
between the ecm and cytoskeleton and thus to
integrate changes occurring outside and inside
the cell

 Plasmodesmata
are channels in plant cell
walls through which the plasma membranes
of bordering cells connect
 Water, small solutes, and even some proteins
and RNA molecules can move through these
channels
1. Tight junctions:
proteins hold
adjacent cell
membranes tightly
together, creating
an impermeable seal
across a layer of
epithelial cells.
2. Desmosomes (aka
anchoring
junctions): are
reinforced by
intermediate
filaments and rivet
cells into strong
sheets
3. Gap junctions aka
communicating
junctions: are
cytoplasmic
connections that
allow for the
exchange of ions
and small molecules
between cells
through proteinlined pores