Transcript Chapter 7 Body Systems

Chapter 3
Anatomy of Cells
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Slide 1
Functional Anatomy of Cells

The typical cell (Figure 3-1)

Also called composite cell

Varies in size; all are microscopic (Table 3-1)

Varies in structure and function (Table 3-2)
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Slide 2
Functional Anatomy of Cells

Cell structures

Plasma membrane—separates the cell from its
surrounding environment

Cytoplasm—thick gel-like substance inside of the
cell composed of numerous organelles suspended
in watery cytosol; each type of organelle is suited
to perform particular functions (Figure 3-2)

Nucleus—large membranous structure near the
center of the cell
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Slide 3
Cell Membranes

Each cell contains a variety of membranes:

Plasma membrane (Figure 3-3)

Membranous organelles—sacs and canals made
of the same material as the plasma membrane
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Slide 4
Cell Membranes

Fluid mosaic model—theory explaining how
cell membranes are constructed

Molecules of the cell membrane are arranged in a
sheet

The mosaic of molecules is fluid; that is, the
molecules are able to float around slowly

This model illustrates that the molecules of the cell
membrane form a continuous sheet
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Slide 5
Cell Membranes

Chemical attractions are the forces that hold
membranes together

Groupings of membrane molecules form rafts,
each of which float as a unit in the membrane
(Figure 3-4)

Rafts may pinch inward, bringing material into the
cell or organelle
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Slide 6
Cell Membranes

Primary structure of a cell membrane is a double
layer of phospholipid molecules

Heads are hydrophilic (water-loving)

Tails are hydrophobic (water-fearing)

Molecules arrange themselves in bilayers in water

Cholesterol molecules are scattered among the
phospholipids to allow the membrane to function
properly at body temperature

Most of the bilayer is hydrophobic; therefore water or
water-soluble molecules do not pass through easily
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Slide 7
Cell Membranes

Membrane proteins (Table 3-4)

A cell controls what moves through the membrane
by means of membrane proteins embedded in the
phospholipid bilayer

Some membrane proteins have carbohydrates
attached to them, forming glycoproteins that act as
identification markers

Some membrane proteins are receptors that react
to specific chemicals, sometimes permitting a
process called signal transduction
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Slide 8
Cytoplasm and Organelles

Cytoplasm—gel-like internal substance of
cells that includes many organelles
suspended in watery intracellular fluid called
cytosol
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Slide 9
Cytoplasm and Organelles

Two major groups of organelles (Table 3-3):

Membranous organelles are specialized sacs or
canals made of cell membranes

Nonmembranous organelles are made of
microscopic filaments or other nonmembranous
materials
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Slide 10
Cytoplasm and Organelles

Endoplasmic reticulum (Figure 3-5)

Made of canals with membranous walls and flat,
curving sacs arranged in parallel rows throughout
the cytoplasm; extend from the plasma membrane
to the nucleus

Proteins move through the canals
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Slide 11
Cytoplasm and Organelles

Endoplasmic reticulum (cont.)

Two types of endoplasmic reticulum:
• Rough endoplasmic reticulum

Ribosomes dot the outer surface of the membranous walls

Ribosomes synthesize proteins, which move toward the
Golgi apparatus and then eventually leave the cell

Function in protein synthesis and intracellular
transportation
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Slide 12
Cytoplasm and Organelles

Two types of endoplasmic reticulum (cont.)
• Smooth endoplasmic reticulum

No ribosomes border membranous wall

Functions are less well established and probably more
varied than for rough endoplasmic reticulum

Synthesizes certain lipids and carbohydrates and creates
membranes for use throughout cell

Removes and stores Ca++ from cell’s interior.
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Slide 13
Cytoplasm and Organelles

Ribosomes (Figure 3-6)

Many are attached to the rough endoplasmic
reticulum and many lie free, scattered through the
cytoplasm

Each ribosome is a nonmembranous structure
made of two pieces, a large subunit and a small
subunit; each subunit is composed of rRNA

Ribosomes in the endoplasmic reticulum make
proteins for “export” or to be embedded in the
plasma membrane; free ribosomes make proteins
for the cell’s domestic use
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Slide 14
Cytoplasm and Organelles

Golgi apparatus

Membranous organelle consisting of cisternae
stacked on one another and located near the
nucleus (Figure 3-7)

Processes protein molecules from the
endoplasmic reticulum (Figure 3-8)

Processed proteins leave the final cisterna in a
vesicle; contents may then be secreted to outside
the cell
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Slide 15
Cytoplasm and Organelles

Lysosomes (Figure 3-9)

Made of microscopic membranous sacs that have
“pinched off” from Golgi apparatus

The cell’s own digestive system; enzymes in
lysosomes digest the protein structures of
defective cell parts, including plasma membrane
proteins, and particles that have become trapped
in the cell
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Slide 16
Cytoplasm and Organelles

Proteasomes (Figure 3-10)

Hollow, protein cylinders found throughout the
cytoplasm

Break down abnormal/misfolded proteins and
normal proteins no longer needed by the cell

Break down protein molecules one at a time by
tagging each one with a chain of ubiquitin
molecules and unfolding it as it enters the
proteasome, then breaking apart peptide bonds
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Slide 17
Cytoplasm and Organelles

Peroxisomes

Small membranous sacs containing enzymes that
detoxify harmful substances that enter the cells

Often seen in kidney and liver cells
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Slide 18
Cytoplasm and Organelles

Mitochondria (Figure 3-11)

Made up of microscopic sacs; wall composed of
inner and outer membranes separated by fluid;
thousands of particles make up enzyme molecules
attached to both membranes

The “power plants” of cells; mitochondrial
enzymes catalyze series of oxidation reactions
that provide about 95% of cell’s energy supply

Each mitochondrion has a DNA molecule, allowing
it to produce its own enzymes and replicate copies
of itself
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Slide 19
Nucleus

Definition—spherical body in center of cell;
enclosed by an envelope with many pores
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Slide 20
Nucleus

Structure

Consists of nuclear envelope (composed of two
membranes each with essentially the same
molecular structure as plasma membrane)
surrounding nucleoplasm; nuclear envelope has
holes called nuclear pores (Figure 3-12)
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Slide 21
Nucleus

Structure (cont.)

Contains DNA (heredity molecules), which appear
as the following:
• Chromatin threads or granules in nondividing cells
• Chromosomes in early stages of cell division
• Functions of nucleus are functions of DNA molecules;
DNA determines both structure and function of cells and
heredity
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Slide 22
Cytoskeleton

The cell’s internal supporting framework
made up of rigid, rodlike pieces that provide
support and allow movement and
mechanisms that can move the cell or its
parts (Figure 3-13)
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Slide 23
Cytoskeleton

Cell fibers

Intricately arranged fibers of varying lengths that
form a three-dimensional, irregularly shaped
lattice

Fibers appear to support the endoplasmic
reticulum, mitochondria, and “free” ribosomes
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Slide 24
Cytoskeleton

Cell fibers (cont.)

Smallest cell fibers are microfilaments
(Figure 3-14)
• “Cellular muscles”
• Made of thin, twisted strands of protein molecules that lie
parallel to the long axis of the cell
• Microfilaments can slide past each other, causing
shortening of the cell
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Slide 25
Cytoskeleton

Cell fibers (cont.)

Intermediate filaments are twisted protein strands
slightly thicker than microfilaments; they form
much of the supporting framework in many types
of cells

Microtubules are tiny, hollow tubes that are the
thickest of the cell fibers; they are made of protein
subunits arranged in a spiral fashion; their function
is to move things around in the cell
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Slide 26
Cytoskeleton

Centrosome

An area of the cytoplasm near the nucleus that
coordinates the building and breaking of
microtubules in the cell

Nonmembranous structure also called the
microtubule-organizing center (MTOC)

Plays an important role during cell division

The general location of the centrosome is
identified by the centrioles
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Slide 27
Cytoskeleton

Cell extensions

Cytoskeleton forms projections that extend the
plasma membrane outward to form tiny, fingerlike
processes
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Slide 28
Cytoskeleton

There are three types of these processes; each
has specific functions (Figure 3-15):
• Microvilli—found in epithelial cells that line the intestines
and other areas where absorption is important; they help
to increase the surface area manyfold
• Cilia and flagella—cell processes that have cylinders
made of microtubules at their core; cilia are shorter and
more numerous than flagella; flagella are found only on
human sperm cells
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Slide 29
Cell Connections

Cells are held together by fibrous nets that
surround groups of cells (e.g., muscle cells),
or cells have direct connections to each other

There are three types of direct cell
connections (Figure 3-16)
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Slide 30
Cell Connections

Desmosome

Fibers on the outer surface of each desmosome
interlock with each other; anchored internally by
intermediate filaments of the cytoskeleton

Spot desmosomes, connecting adjacent
membranes, are like “spot welds” at various points

Belt desmosomes encircle the entire cell like
a collar
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Slide 31
Cell Connections

Gap junctions—membrane channels of
adjacent plasma membranes adhere to each
other; have two effects:

Form gaps or “tunnels” that join the
cytoplasm of two cells

Fuse two plasma membranes into a single
structure
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Slide 32
Cell Connections

Tight junctions

Occur in cells that are joined by “collars” of tightly
fused material

Molecules cannot permeate the cracks of tight
junctions

Occur in the lining of the intestines and other parts
of the body, where it is important to control what
gets through a sheet of cells
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Slide 33