Transcript Anatomy cell chpt 6

Cell Structure and Function
Chapter 4
Early Discoveries
• Mid 1600s - Robert Hooke observed
and described cells in cork
• Late 1600s - Anton van Leeuwenhoek
observed sperm, microorganisms
• 1820s - Robert Brown observed and
named nucleus in plant cells
Developing Cell Theory
• Matthias Schleiden
• Theodor Schwann
• Rudolf Virchow
Schleiden and Schwann proposed the idea that all living
things were composed of cells. Schleiden worked with
plants and Schwann worked with animals.
Virchow concluded that all cells come from cells.
Cell Theory
1) Every organism is composed of one or
more cells
2) The cell is smallest unit having properties
of life
3) Continuity of life arises from growth and
division of single cells (cells come from preexisting cells.)
Cell
• Smallest unit of life
• Can survive on its own or has potential
to do so
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce
Why Aren't All Cells Big?
1. Most cells are too small to be seen without a
microscope.
2. The small size of cells permits efficient
diffusion across the plasma membrane and within
the cell.
3. As the surface area of a cell increases by the
square of the diameter, the volume increases by
the cube of the diameter.
(Surface-to-volume ratio)
-The bigger a cell is, the less surface area there
is per unit volume.
-Above a certain size, material cannot be
moved in or out of cell fast enough
Microscopes
• Create detailed images of something
that is otherwise too small to see
• Light microscopes
– Simple or compound
• Electron microscopes
– Transmission EM or Scanning EM
Limitations of Light
Microscopy
• Wavelengths of light are 400-750 nm
• If a structure is less than one-half of a
wavelength long, it will not be visible
• Light microscopes can resolve objects
down to about 200 nm in size
Red blood cells
Plant cells
Onion cells
• Light Microscope Images
Electron Microscopy
• Uses streams of accelerated electrons
rather than light
• Electrons are focused by magnets
rather than glass lenses
• Can resolve structures down to 0.5 nm
Blood Cells
White Blood Cell infected with
HIv
Stem Cell from Human Bone Marrow
• Scanning Electron Microscope –
“scans” the surface of objects
Plant Root Cell
Liver Cell (color enhanced)
Animal Cell (type?)
• Transmission Electron Microscope –
“looks” inside an object
Structure of Cells
All start out life with:
Two types:
– Plasma membrane
– Prokaryotic
– Region where DNA
is stored (nucleus
or nucleoid)
– Eukaryotic
– Cytoplasm
Structural Organization of Cells
1. A plasma membrane separates each cell from the
environment, permits the flow of molecules across the
membrane, and contains receptors that can affect the
cell’s activities.
2. A nucleus or nucleoid region localizes the hereditary
material, which can be copied and read.
3. The cytoplasm contains membrane systems, particles
(including ribosomes), filaments (the cytoskeleton), and is
a semifluid substance.
4. There are basically two kinds of cells in nature:
A. Eukaryotic cells contain distinctive arrays of
organelles, including a membrane-bound nucleus.
B. Prokaryotic cells (bacteria) have no nucleus.
Lipid Bilayer
• Main component of cell membranes
• Gives the membrane its fluid properties
• Two layers of phospholipids
one layer
of lipids
one layer
of lipids
Figure 4.3
Page 56
Organization of Cell Membranes
1. The lipid bilayer of plasma membranes forms a
boundary between inside and outside of the cell,
subdivides the cytoplasm into compartments, and
regulates the entry/exit of substances.
2. Proteins positioned in the plasma membrane
serve as channels, pumps, or receptors.
(The proteins do most of the “work”).
Membrane Proteins
Recognition
protein
Receptor
protein
extracellular
environment
lipid bilayer
cytoplasm
Protein
pump across
bilayer
Protein
channel
across bilayer
Protein pump
Figure 4.4
Page 57
Prokaryotic Cells
• Archaebacteria and Eubacteria
• DNA is not enclosed in nucleus
• Generally the smallest, simplest cells
• No organelles
Prokaryotic Structure
pilus
cytoplasm
with ribosomes
DNA
flagellum
capsule
cell plasma
wall membrane
Prokaryotic Cells
A. The term prokaryotic (“before the nucleus”)
indicates existence of bacteria before evolution
of cells with a nucleus; bacterial DNA is
clustered in a distinct region of the cytoplasm
(nucleoid).
B. Bacteria are some of the smallest and
simplest cells (structurally).
1. Bacterial flagella project from the
membrane and permit rapid movement.
a. not the same structure as
eukaryotic flagella
2. A somewhat rigid cell wall supports the cell and surrounds the
plasma membrane, which regulates transport into and out of the
cell.
a. also different than eukaryotic cells
3. Ribosomes, protein assembly sites, are dispersed throughout
the cytoplasm.
4. also; capsule, membrane and pili
5. 2 main types: archaebacteria and eubacteria
Eukaryotic Cells
• Have a nucleus and other organelles compartmentalized portions within the cytoplasm that
allow reactions to be separated with respect to time
(allowing proper sequencing) and space (allowing
incompatible reactions to occur in close proximity).
• Eukaryotic organisms
– Plants
– Animals
– Protistans
– Fungi
Animal Cell Features
•
•
•
•
•
•
•
•
Plasma membrane
Nucleus
Ribosomes
Endoplasmic
reticulum
Golgi body
Vesicles
Mitochondria
Cytoskeleton
Figure 4.10b
Page 61
Plant Cell Features
•
•
•
•
•
•
•
•
Plasma membrane
Nucleus
Ribosomes
Endoplasmic
reticulum
Golgi body
Vesicles
Mitochondria
Cytoskeleton
• Cell wall
• Central vacuole
• Chloroplast
Figure 4.10a
Page 61
Defining Features of Eukaryotic Cells
A. Major Cellular Components
1. The nucleus controls access to DNA and
permits easier packing of DNA during cell division.
2. The endoplasmic reticulum (ER) modifies/delivers
proteins and is also involved with lipid synthesis.
3 Golgi bodies also modify proteins, sort and ship
proteins, and play a role in the biology of lipids for
secretion or internal use.
Major Cellular Components, continued
4. Various vesicles transport, store, and digest various
materials within the cell.
5. Mitochondria have enzymes responsible for ATP
formation.
6. Ribosomes , either “free” or attached to membranes
are the assembly sites of polypeptide chains.
7. The cytoskeleton determines cell shape and internal
organization; it also provides for motility.
Functions of Nucleus
• Keeps the DNA molecules of eukaryotic
cells separated from metabolic
machinery of cytoplasm
• Makes it easier to organize DNA and to
copy it before parent cells divide into
daughter cells
Components of Nucleus
nuclear envelope
nucleoplasm
nucleolus
chromatin
Figure 4.11b
Page 62
The Nucleus
A. The nucleus isolates DNA—which contains the
code for protein assembly, from the sites—ribosomes
in cytoplasm, where proteins will be assembled.
1. the fluid within the nucleus is called
nucleoplasm
B. Nuclear Envelope
1. The nuclear envelope consists of two lipid
bilayers with pores.
2. The inner surface has attachment sites for
protein filaments, which anchor the DNA
molecules and keep them organized.
3. The outer surface is studded with ribosomes.
Nuclear Envelope
• Two outer membranes (lipid bilayers) – 4
layers
• Innermost surface has DNA attachment sites
Nuclear pore
bilayer facing cytoplasm
Nuclear envelope
bilayer facing
nucleoplasm
Figure 4.12b
Page 63
The Nucleus, continued
C. Nucleolus
1. The nucleolus appears as a dense, globular
mass of material within the nucleus.
2. It is a region where RNA subunits of
ribosomes are pre-fabricated before shipment
out of the nucleus.
D. Chromosomes
1. Chromatin refers to the total collection of
DNA and proteins. (uncoiled form)
2. Each chromosome is a single molecule of
DNA and its associated proteins; it may take on
different appearances depending on the events
currently happening within the cell.
Cytomembrane/Endomembrane
System
• Group of related organelles in which
lipids are assembled and new
polypeptide chains are modified
• Products are sorted and shipped to
various destinations
Components of
Cytomembrane/endomembrane
System
Endoplasmic reticulum
Golgi bodies
Vesicles
Endoplasmic Reticulum
• In animal cells, continuous with nuclear
membrane
• Extends throughout cytoplasm
• Two regions - rough and smooth
A. Endoplasmic Reticulum
1. The endoplasmic reticulum is a collection of
interconnected tubes and flattened sacs that begins
at the nucleus and winds its way through the
cytoplasm.
2. Two kinds of ER may be found in a cell:
a. Rough ER consists of stacked, flattened
sacs with many ribosomes attached;
oligosaccharide groups are attached to
polypeptides as they pass through on their
way to other organelles or to secretory
vesicles.
b. Smooth ER has no ribosomes; Lipid
synthesis (including phospholipids and
hormones). It is the area from which vesicles
carrying proteins and lipids are budded; it
also helps inactivate harmful chemicals.
Golgi Body
• Puts finishing touches on proteins and
lipids that arrive from ER
• Packages finished material for shipment to
final destinations
• Material arrives and leaves in vesicles
budding
vesicle
Figure 4.15
Page 65
C. Golgi Bodies
1. A Golgi body consists of flattened sacs—resembling a
stack of pancakes—whose edges break away as secretory
vesicles.
2. Here proteins and lipids undergo final processing,
sorting, and packaging.
D. A Variety of Vesicles – tiny membranous sacs that are used for
exocytosis, endocytosis, storage, membrane building and digestion
1. Lysosomes are vesicles that bud from Golgi bodies;
they carry powerful enzymes that can digest the contents of
other vesicles, worn-out cell parts, or bacteria and foreign
particles.
2. Peroxisomes are small vesicles that contain enzymes
using oxygen to degrade fatty acids and amino acids,
forming a harmful byproduct, hydrogen peroxide, which is
then converted to water.
Vesicles
• Membranous sacs that
move through cytoplasm
• Lysosomes
• Peroxisomes
What Happens to the Proteins Specified by DNA?
1. Within the cytoplasm, newly formed polypeptide chains
may be stockpiled in solution or may enter the
endomembrane system (ER, Golgi bodies, and vesicles).
2. Some of the proteins will be used within the cell in
which they were made, other will be exported for use
elsewhere.
Mitochondria
• ATP-producing powerhouses
• Membranes form two distinct
compartments
• ATP-making machinery embedded
in inner mitochondrial membrane
Mitochondria
A. Mitochondria are the primary organelles for transferring the
energy in carbohydrates to ATP under oxygen-plentiful
conditions. (powerhouse)
B. Each mitochondrion has an outer membrane and an inner
folded membrane (cristae).
1. Two compartments are formed by the membranes.
2. Hydrogen ions and electrons move between the
compartments during ATP formation.
C. Mitochondria have their own DNA and ribosomes, a fact which
points to their origination from ancient bacteria engulfed by
predatory cells.
Mitochondrial Origins
• Mitochondria resemble bacteria
– Have own DNA, ribosomes
– Divide on their own
• May have evolved from ancient bacteria
that were engulfed but not digested
Specialized Plant Organelles
• Plastids
• Central Vacuole
Chloroplasts
Convert sunlight energy to ATP and
carbohydrates through photosynthesis
Chloroplasts and Other Plastids (organelles specialize in
photosynthesis and storage)
1. Chloroplasts are oval or disk shaped, bounded by a
double membrane, and are critical to the process of
photosynthesis.
a. In the stacked disks (grana), pigments and
enzymes trap sunlight energy to form ATP.
-the inner membrane, that makes-up the
grana, is called the thylakoid membrane
b. Sugars are formed in the fluid substance
(stroma) surrounding the stacks.
c. Pigments such as chlorophyll (green) confer
distinctive colors to the chloroplasts.
-also carotenoids – yellow, red, orange
2. Chromoplasts store red and brown pigments that give
color to petals, fruits, and roots. No chlorophyll
3. Colorless amyloplasts store starch granules.
Other Plastids
• Chromoplasts
– No chlorophyll
– Abundance of carotenoids
– Color fruits and flowers red to yellow
• Amyloplasts
– No pigments
– Store starch
Central Vacuole
1. In a mature plant, the central vacuole may occupy
50 to 90 percent of the cell interior.
A. Central vacuoles store amino acids, sugars,
ions, and wastes.
B. The vacuole enlarges during growth and
greatly increases the cell’s outer surface area.
2. The enlarged cell, with more surface area, has an
enhanced ability to absorb nutrients.
Cytoskeleton
• Present in all eukaryotic cells
• Basis for cell shape and internal
organization
• Allows organelle movement within cells
and, in some cases, cell motility
The cytoskeleton gives cells their internal organization,
shape, and capacity to move.
1. It forms an interconnected system of bundled
fibers, slender threads, and lattices that extends
from the nucleus to the plasma membrane.
2. The main components are microtubules,
microfilaments, and intermediate filaments—all
assembled from protein subunits.
3. Some portions are transient, such as the
“spindle”
microtubules used in chromosome
movement during cell division; others are
permanent, such as filaments operational in
muscle contraction.
Cytoskeletal Elements
intermediate
filament
microtubule
microfilament
tubulin
subunit
Microtubules
• Largest elements
• Composed of tubulin
• Arise from microtubule
organizing centers (MTOCs)
• Involved in shape, motility,
cell division
Figure 4.21
Page 71
Microtubules—The Big Ones
1. Microtubules, the largest structural elements in the
cytoskeleton, are composed of tubulin subunits which
compose a cylinder.
2. Microtubule organizing centers (MTOCs) are small
masses of proteins in the cytoplasm that give rise to
microtubules.
3. Microtubules govern the division of cells and some
aspects of their shape as well as many cell movements.
4. involved in sustained directional movements of
organelles
5. straight hollow cylinders - figure 4.21, p71
Microfilaments
• Thinnest elements
• consist of two helically twisted
polypeptide chains assembled
from actin monomers.
• Take part in movement, formation,
and maintenance of cell shape
– Microfilaments are particularly
important in movements that
take place at the cell surface;
they also contribute to the
shapes of animal cells and
actin
subunit
cytoplasmic streaming.
Figure 4.21
Page 71
Myosin and Other Accessory Proteins
1. Extending from the microfilaments of muscle cells,
myosin plays a vital role in contraction.
2. Other proteins attach microfilaments to the inner
surface of the plasma membrane (spectrin) or span the
plasma membrane to connect microfilaments to
outside proteins (integrins).
Intermediate Filaments
• Only in animal cells of certain
tissues
• Most stable cytoskeletal
elements
• Six known groups
• Examples include desmins and
vimentins (support machinery by
which muscle cells contract) and
lamins (form a scaffold that
reinforces the nucleus).
•
one
polypeptide
chain
help strengthen and maintain
cell shape
Figure 4.21
Page 71
How Do Cells Move?
A. Chugging Along With Motor Proteins
1. Through controlled assembly and disassembly of their
subunits, microtubules; and microfilaments grow or
diminish in length, thereby the structures attached to
them are thereby pushed or dragged through the
cytoplasm.
2. Parallel arrays of microfilaments or microtubules actively
slide past one another to bring about contraction,
as in
muscle.
3. Microtubules or microfilaments shunt organelles from
one location to another as in cytoplasmic streaming.
4. kinesins and dyneins with microtubules, myosin with
microfilaments
a. kinesin “walking” along a microtubule with its
other end attached to an organelle
Motor Proteins
• Kinesins and dyneins move along
microtubules
• Myosins move along microfilaments
kinesin
microtubule
Figure 4.24b, Page 72
B.
Cilia, Flagella, and False Feet
1. Microtubular extensions of the plasma membrane have a
9 + 2 cross-sectional array that arises from a centriole (a
type of MTOC) and are useful in propulsion.
2. Flagella are quite long, not usually numerous, and found on
one-celled protistans and animal sperm cells.
3. Cilia are shorter and more numerous and can provide
locomotion for free-living cells or may move surrounding
water and particles if the ciliated cell is anchored.
4. Cilia and Flagella move by sliding mechanism
5. Pseudopods are temporary lobes that project from the
cell, used in locomotion and food capture.
a. microfilaments rapidly elongate
Flagella and Cilia
microtubule
• Structures for
cell motility
• 9 + 2 internal
structure
Figure 4.25
Page 73
dynein
Eukaryotic Cell Walls
1. Cell walls are carbohydrate frameworks for mechanical
support in bacteria, protistans, fungi, and plants; cell walls
are not found in animals.
2. In growing plant parts, bundles of cellulose strands
form a primary cell wall that is pliable enough to allow
enlargement under pressure.
3. Later, more layers are deposited on the inside of the
primary wall to form the secondary wall.
4. Lignin composes up to 25 percent of the secondary wall
in woody plants; it makes plant parts stronger, more
waterproof, and less inviting to insects.
5. the cells themselves secrete the wall forming materials
Plant Cell Walls
Secondary cell wall
(3 layers)
Primary cell wall
Plant Cuticle
• Cell secretions and waxes accumulate
at plant cell surface
• Semitransparent
• Restricts water loss
Cell Junctions
1. In plants tiny channels called plasmodesmata cross
the adjacent primary walls and connect the cytoplasm
2. Animal cells display three types of junctions:
a. Tight junctions occur between cells of
epithelial tissues in which cytoskeletal strands
of one cell fuse with strands of neighboring cells
causing an effective seal.
b. Adhering junctions are like spot welds at the
plasma membranes of two adjacent cells that
need to be held together during stretching as in
the skin and heart.
c. Gap junctions are small, open channels that
directly link the cytoplasm of adjacent cells.
Cell-to-Cell Junctions
• Plants
– Plasmodesmata
• Animals
– Tight junctions
– Adhering junctions
– Gap junctions
plasmodesma
Animal Cell Junctions
tight
junctions
adhering
junction
gap
junction
Matrixes between Animal Cells
• Animal cells have no cell walls
• Some are surrounded by a matrix of cell secretions and
other material
• The matrix between animal cells includes cell secretions
and materials drawn from the surroundings between
cells.
• For example, cartilage consists of scattered cells and
collagen embedded in a "ground substance" of modified
polysaccharides; bone is similarly constructed
Cell Communication
1. Signals and receptors allow cells to change their
activities.
2. Hormones are well known stimulators of cell
activity.
We will look at cell communication more in depth on
another powerpoint!