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Chapter 4
Organization of the Cell
Recall:

Cell Theory:
All living things are made up of one or
more cells
 Cells are the basic unit of organization
and function in all organisms
 All cells come from other cells

Cells Maintain Homeostasis
Homeostasis - process of maintaining
constant internal environment
 Due to organization and size

Organization

Similar in all cells

Due to plasma
membrane
• Surrounds cells
• Selective barrier

Cells have internal
structures called
organelles
• Important activities
Cell Size

Most are microscopic


Micrometer (1/1000) of a millimeter
Ratio of surface area to volume
Upper limit on cell size
 As the cell increases in size, its surface
area becomes too small to support its
internal structures.

• Oxygen and other important substances cannot
diffuse fast enough.
Cell Shape

Variation in cell shape

To increase the ratio of surface area
to volume
• Plant cells often long and thin
• Microvilli - finger-like projections of the
plasma membrane
Microvilli
Cell Size and Shape are
Related to Function

Examples:
Amoeba - can change shape to move
 Sperm - have flagella
 Nerve cells - long, thin extensions to
transmit messages

Nerve Cells
Prokaryotes vs. Eukaryotes

Prokaryotic cells – without nucleus
Lacks other membrane-bound
organelles
 Bacteria and Archaea
 Small


Eukaryotic cells – nucleus
Organelles
 All other cells (animals, plants,
protists, fungi)

Prokaryotes
DNA is located in nuclear area/
nucleoid
 Plasma membrane
 Cell walls
 Flagella
 Ribosomes


RNA and protein
Eukaryotes
Cytoplasm – contains fluid (cytosol)
and organelles
 Nucleoplasm – inside nucleus
 Membrane-bound organelles

Membranes

Membranes divide cell into compartments
Sites of chemical reactions
 Enzymes embedded in membranes
 Part of endomembrane system

• Organelles connect directly or indirectly
• ER, nucleus, Golgi complex, lysosomes,
vacuoles, plasma membrane

Vesicles – membrane-bound transport sacs
• Carry materials from one organelle to another
Plasma Membrane
Surrounds cell
 Regulates what enters/exits the cell
 Maintains structure of cell
 Separates internal structures of cell
from outside cell

Cell Wall
Prokaryotic cells & Plant cells
 Support
 Protection
 Surrounds plasma membrane

Cell Nucleus
Control center of cell
 Most cells have only one
 Nuclear Envelope – controls what
enters/exits nucleus
 Nuclear pores – allow materials to
pass in/out of nucleus

Cell Nucleus
Contains majority of cell’s DNA
 Genes – segments of DNA that code
for proteins
 Takes form of chromosomes during
cell division
 Not dividing – chromatin (DNA
loosely arranged)

Ribosomes
Manufacture proteins
 Composed of RNA and protein



Free or attached to ER
Assembled in the nucleolus
Endoplasmic Reticulum
Network of internal membranes
 Synthesizes lipids and modifies many
proteins
 Origin of intracellular transport
vesicles that carry proteins
 Smooth – lack ribosomes
 Rough – ribosomes on outer surface

Rough ER

Studded with ribosomes

Connect directly
ER modifies the proteins with enzymes
 Proteins transferred to other sites
within cell or outside the cell

• Via transport vesicles
Smooth ER
No ribosomes
 Site of phospholipid, steroid, and fatty
acid metabolism
 Some types of cells have extensive
amounts

Liver cells – synthesizes/processes
cholesterol and other lipids
 Enzymes that break down toxins such as
carcinogens

Golgi Complex

Stacks of flattened membranous sacs
Cisternae
 Not all connected


Processes, sorts and packages
proteins


Products are then passed to other
organelles or to plasma membrane
Manufactures lysosomes (animal cells)
Lysosomes

Small sacs of digestive enzymes

Break down:
• Lipids, proteins, carbohydrates, and
nucleic acids
Cytoplasm
 Rarely, tissue can be damaged from
“leaky” lysosomes

Peroxisomes

Contain enzymes, catalase, that split
hydrogen peroxide


H2O2 is toxic to the cell
Most common in cells that synthesize,
store, or break down lipids
Vacuoles
Large, fluid-filled sacs
 Mostly in plants, fungi, algae
 May be up to 90% of the volume of a
plant cell

Vacuoles - Functions
Store wastes, water, and materials
such as sugars and ions
 Maintain hydrostatic pressure


Applies pressure to the cell
membrane, causing it to expand and
stick close to the cell wall
Vacuoles

Unique functions:
Contain compounds poisonous to
herbivores
 Food vacuoles – found in protists

• Fuse with lysosomes so their food can be
digested

Contractile Vacuoles – also in protists
• Remove excess water from the cell
Mitochondria

Sacs consisting of 2 membranes

Membranes form 2 compartments:
• Intermembrane space – between 2
membranes
• Matrix – enclosed by inner membrane

Inner membrane is folded to form
cristae
• Increase surface area of the inner
membrane
Mitochondria
Site of most reactions of cellular
respiration
 Transformation of energy originating
from glucose or lipids



Convert ->ATP
Numerous in cells with high energy
requirements

Ex. Liver cells – more than 1000 in a
single cell!
Mitochondria
Contains circular molecules of DNA
 1% of total DNA
 Mutations more frequent
 Mutations linked to certain diseases


Ex. Young adult blindness, muscle
degeneration
Mitochondria

Involved in apoptosis
Programmed cell death
 Inappropriate apoptosis may be involved in
cancer, AIDS, and Alzheimer’s Disease

Involved in the metamorphosis of
amphibians
 Responsible for human diseases:


Tay-Sachs disease – lipid can not be
broken down, accumulates in brain cells
Chloroplasts
Convert light energy to chemical
energy -> Photosynthesis
 Contain chlorophyll – green pigment
that traps light energy for
photosynthesis


Also contain carotenoids
• Yellow and orange light-absorbing
pigments
Chloroplasts
Larger than mitochondria
 Leaf cell may contain 20-100
 Disc-shaped

Cytoskeleton
Eukaryotic cells
 Dense network of protein fibers
 Functions:

Mechanical support
 Cell movement
 Transport of materials within the cell
 Cell division

Cytoskeleton

Made of 3 types of protein filaments:

Microtubules
• Hollow cylinders
• Cilia and flagella
• Cell division
Microfilaments
 Intermediate filaments


Centrioles – cell division
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