Chapter 4
Cells and Organelles
Cells and Organelles

• Properties and Strategies of Cells
• The Eukaryotic Cell in Overview: Pictures
at an Exhibition
• Virus, viroids and Prions: Agents That
Invade Cells
Properties and Strategies of Cells
• To consider what cells • All cells are bacteria, archaea or
eukarya
are?
• Cells comes in many sizes and
• How they function?
shapes
• The classification of
• Eukaryotic cells use organelles to
cells based on
compartmentalize cellular
– Their organizational
function
complexity
– The sizes and shapes • Prokaryotes and eukaryotes differ
from each other in many way
– The specialization that
• Cell specialization demonstrates
cells undergo
the unity and diversity of biology
• Liver cells, kidney cells
Limitations on Cell Size
• Several factors limit cell size
– Surface area/ Volume ratio
• The exchanges between cell and its environment
– Diffusion rates of molecules
• In general, molecules move through the cytoplasm by
diffusion
– The need for adequate concentrations of reactants
and catalysts
• The size increase obviously taxes the synthetic
capabilities of the cell
All Organism Are Bacteria,
Archaea or Eukaryotes
Bacteria
Ancestral cell
Archaea
Eukarya
Prokaryote
vs
• Bacteria and
archaebacteria
• Appeared shortly after
earth cooled, 4 billion
years ago.
• No membrane bound
organelles
• Simple, looped DNA in
nucleoid region
Eukaryote
• Protists, plants, animals,
fungi
• First appeared ~ 1.8
billion years ago
• Cell functions
compartmentalized in
organelles
• DNA in chrosomes in
nucleus
Bacteria, Archaea and Eukaryotes
Differ from Each Other in Many Ways

• Presence or absence of a membraneenveloped nucleus
• Use of internal membrane to segregate
function
• Cytoskeleton
• Exocytosis and endocytosis
• Organization of DNA
• Segregation of genetic information
• Expression of DNA
Bacteria, archaea, and eukaryotes
differ from each other in many ways

• Presence or absence of a membraneenveloped nucleus
• Use of internal membrane to segregate
function
• Tubules and filaments
• Exocytosis and endocytosis
• Organization of DNA
• Segregation of genetic information
• Expression of DNA
Eukaryotic Cells Use Organelles to
Compartmentalize Cellular Function
• Chloroplast
– enzymes, compounds, pigments needed for
photosynthesis
Bacteria, Archaea and Eukaryotes Differ
from Each Other in Many Ways

• Presence or absence of a membraneenveloped nucleus
• Use of internal membrane to segregate
function
• Cytoskeleton
• Exocytosis and endocytosis
• Organization of DNA
• Segregation of genetic information
• Expression of DNA
Bacteria, Archaea and Eukaryotes Differ
from Each Other in Many Ways

• Presence or absence of a membraneenveloped nucleus
• Use of internal membrane to segregate
function
• Cytoskeleton
• Exocytosis and endocytosis
• Organization of DNA
• Segregation of genetic information
• Expression of DNA
Exocytosis（胞吐作用） and
Endocytosis（胞吞作用）
• Eukaryotic cells- to change materials
between the membrane-bounded
compartment within the cell and the exterior
of the cell
Bacteria, Archaea and Eukaryotes Differ
from Each Other in Many Ways

• Presence or absence of a membraneenveloped nucleus
• Use of internal membrane to segregate
function
• Cytoskeleton
• Exocytosis and endocytosis
• Organization of DNA
• Segregation of genetic information
• Expression of DNA
Bacteria, Archaea and Eukaryotes Differ
from Each Other in Many Ways

• Presence or absence of a membraneenveloped nucleus
• Use of internal membrane to segregate
function
• Cytoskeleton
• Exocytosis and endocytosis
• Organization of DNA
• Segregation of genetic information
• Expression of DNA
Bacteria, Archaea and Eukaryotes Differ
from Each Other in Many Ways

• Presence or absence of a membraneenveloped nucleus
• Use of internal membrane to segregate
function
• Cytoskeleton
• Exocytosis and endocytosis
• Organization of DNA
• Segregation of genetic information
• Expression of DNA
Cell Specialization Demonstrates the
Unity and Diversity of Biology
• Plant cells and animal cells
• Different tissue, different
cell type, different function
Cells and Organelles
• Properties and Strategies of Cells
 • The Eukaryotic Cell in Overview: Pictures
at an Exhibition
• Virus, viroids and Prions: Agents That
Invade Cells
• 細胞核(nucleus)
• 細胞質(cytoplasm)
• 細胞表面(surface)
Four Major Structural Features
(at least)
•
•
•
•
Plasma membrane
Nucleus
Membrane-bounded organelles
Cytosol
– cytoskeleton
• Cell wall
• Extracellular matrix
The Eukaryotic Cell in Overview

• The plasma membrane defines cell
boundaries and retains contents
• The nucleus is the cell’s information center
• Intracellular membranes and organelles
define compartment
• The cytoplasm of eukaryotic cells contains
the cytosol and cytoskeleton
• The extracellular matrix and the cell wall
are outside of the cell
The Plasma Membrane Defines Cell
Boundaries and Retains Contents
• Lipid bilayer
– Phospholipids：amphipathic- two hydrophobic
“tail” and a hydrophilic “head”
• Proteins：amphipathic (amphiphilic)
– Enzymes
– Transport proteins
• Carbohydrates
– Glycoproteins
• These membranes also participate in metabolism as
many enzymes are built into membranes.
• The barriers created by membranes provide different
local environments that facilitate specific metabolic
functions.
• The general structure of a biological membrane is a
double layer of phospholipids with other lipids and
diverse proteins.
• Each type of membrane has a unique combination of
lipids and proteins for its specific functions.
– For example, those in the membranes of
mitochondria function in cellular respiration.
The Eukaryotic Cell in Overview

• The plasma membrane defines cell
boundaries and retains contents
• The nucleus is the cell’s information center
• Intracellular membranes and organelles
define compartment
• The cytoplasm of eukaryotic cells contains
the cytosol and cytoskeleton
• The extracellular matrix and the cell wall
are outside of the cell
The nucleus contains a eukaryotic
cell’s genetic library
• The nucleus contains most of the genes in a eukaryotic
cell.
– Some genes are located in mitochondria and chloroplasts.
• The nucleus averages about 5 m in diameter.
• The nucleus is separated from the cytoplasm by a double
membrane- called nuclear envelope.
– Inner and outer nuclear membrnes
• Where the double membranes are fused, a pore allows
large macromolecules and particles to pass through
– Such as ribosomal subunit, mRNA, chromosomal protein and
enzymes
• Within the nucleus, the DNA and associated
proteins are organized into fibrous material,
chromatin（核染質）.
• In a normal cell they appear as diffuse mass.
• However when the cell prepares to divide, the
chromatin fibers coil up to be seen as separate
structures, chromosomes.
• Each eukaryotic species has a characteristic
number of chromosomes.
– A typical human cell has 46 chromosomes, but sex
cells (eggs and sperm) have only 23 chromosomes.
The Eukaryotic Cell in Overview

• The plasma membrane defines cell
boundaries and retains contents
• The nucleus is the cell’s information center
• Intracellular membranes and organelles
define compartment
• The cytoplasm of eukaryotic cells contains
the cytosol and cytoskeleton
• The extracellular matrix and the cell wall
are outside of the cell
Intracellular Membranes and
Organelles Define Compartment

•
•
•
•
Mitochondrion
Chloroplast
The endoplasmic reticulum
The Golgi complex
– Secretory vesicles
• The Lysosome
• Vacuoles
• Ribosomes
Mitochondrion（粒線體）
• Surrounded by two membrane- inner and outer
mitochondrial membrane
• Circular DNA (RNA and protein)
• Most of the chemical reactions involved in the
oxidation of sugars and other cellular ‘fuel’
molecules occur within the mitochondria
– Transporting electrons located in or on
cristae (皺摺)
– TCA cycle and fat oxidation occur in matrix
Mitochondrial Disorders
• Muscle or nerve tissue
• Myopahties：disease or disorders of muscle
cells
• Leigh syndrome(利氏病)： a devastating
neurodegenerative (神經退化) disorder
• Fetal infantile respiration defect
The Endosymbiont Theory
(內共生學說)
Did mitochondria and chloroplasts
evolve from ancient bacteria?
• Having their own DNA and ribosome
• Enable to carry out the synthesis of both RNA and
proteins
– rRNA sequences, ribosome size
– Sensitivity to inhibitor of RNA and protein synthesis
• DNA organization- circular form without associated with
histone
• Resemble bacterial cells in size and shape
• Protoeukaryotes- ancestor of eukaryotic cells
– Mitochondria：Ancient purple bacteria
– Chloroplast：Ancient Cyanobacteria (藍綠菌)
The Endoplasmic Reticulum（內質網）
• Extending throughout the cytoplasm
• A network of membrane
• Cisternae(扁囊)- consists of tubular
membrane and flatted sacs that are
interconnected
• 參與細胞內各種膜的包裝工作（佔細胞
質總數的一半）
The endoplasmic reticulum manufacturers
membranes and performs many other
biosynthetic functions
• The endoplasmic reticulum (ER) accounts for
half the membranes in a eukaryotic cell.
• The ER includes membranous tubules and
internal, fluid-filled spaces, the cisternae (扁囊).
• The ER membrane is continuous with the nuclear
envelope and the cisternal space of the ER is
continuous with the space between the two
membranes of the nuclear envelope.
Smooth ER
• The smooth ER is rich in enzymes and plays a role
in a variety of metabolic processes.
• Enzymes of smooth ER synthesize lipids and
steroids
– oils, phospholipids, cholesterol and steroid hormones
• The smooth ER also catalyzes a key step in the
mobilization of glucose from stored glycogen in
the liver.
• Other enzymes in the smooth ER of the liver help
detoxify drugs and poisons.
• Muscle cells are rich in enzymes that pump
calcium ions from the cytosol to the cisternae.
Rough ER
• Rough ER is especially abundant in those cells
that secrete proteins.
– As a polypeptide is synthesized by the ribosome, it
is threaded into the cisternal space through a pore
formed by a protein in the ER membrane.
– Many of these polypeptides are glycoproteins, a
polypeptide to which an oligosaccharide is attached.
• These secretory proteins are packaged in
transport vesicles that carry them to their next
stage.
Rough ER
• Rough ER is also a membrane factory.
– Membrane bound proteins are synthesized
directly into the membrane.
– Enzymes in the rough ER also synthesize
phospholipids from precursors in the cytosol.
– As the ER membrane expands, parts can be
transferred as transport vesicles to other
components of the endomembrane system.
The Golgi Complex（高基氏體）
• Closely related to the smooth ER
– Vesicle（囊泡） arise by budding off the ER
and accepted by Golgi complex
• Play an important role in the processing and
packaging of secretory proteins and in
synthesizing complex polysaccharides.
• Most membrane proteins and secretory
proteins are glycoprotein.
– Initial steps in glycosylation take place with
the lumen of the rough ER, but completed
with the Golgi.
• 細胞內消化的場所 （pH約在5）能消許多的化大分子（如蛋
白質、多糖類、脂肪以及核酸）
– 吞噬作用（phagocytosis）
– 自食作用（autophagy）：水解細胞本
身的物質（胞器或其他大分子）-更新
作用
• 生物發育
• 細胞凋亡（apoptosis）
Autophagy
• Macrophagy
– Autophagic vacuole (autophagosome)
– Derived from ER
• Microphagy
– Small bits of cytoplasm rather than whole
organelles
• chaperone-mediated autophagy
– p354
• The lysosomes play a critical role in the
programmed destruction of cells in
multicellular organisms.
– This process allows reconstruction during the
developmental process.
• Several inherited diseases affect lysosomal
metabolism. (more than 40 heritable lysosomal
storage disease -harmful accumulation of a specific substance：
polysaccharides or lipids)
– These individuals lack a functioning version of a
normal hydrolytic enzyme.
– Lysosomes are engorged with indigestable
substrates.
– These diseases include Pompe’s disease（龐培氏
症） in the liver and Tay-Sachs disease in the brain.
龐培氏症
•龐培氏症是一種溶小體（lysosome）肝醣
（Glycogen）儲積症，又常被稱為肝醣儲
積症第二型。其發生的原因是溶小體一種
酸性麥芽糖酵素的缺乏，使得進入溶小體
的肝醣無法被分解而持續堆積，進而影響
到細胞的功能。
•龐培氏症影響的範圍是全身性的，但最為
嚴重的是在肌肉組織。肝醣的堆積造成肌
肉肥大（如舌頭及心臟），並影響其功能，
造成肌肉無力。病情持續發展，肌肉則逐
漸退化，而以纖維組織取代。
Tay-Sachs disease
•
病因：
–
•
罹患此症的嬰兒因缺乏一種己醣胺酵素A
(Hexosaminidase A)，而此酵素的重要功能
在於與神經節甘脂(Gangliosides：一種
glycolipid)代謝有關，特別是GM2,；這些
GM2物質會聚集並逐漸毀壞腦部與神經細
胞，直到中樞神經系統功能完全停止。
臨床特徵：
–
嬰兒通常症狀表現於3~6個月大時；罹患此
症的患孩可能會有聽力與視力方面障礙，
合併四肢麻痺，大約死於5歲 。
The Peroxisome (過氧化小體)
• Surrounded by a single membrane
• Found in plant and animal cells, fungi, protozoa and
algae
– In animal, most found in liver and kidney
• Generating and degrading H2O2
• 將脂肪酸氧化分解成較小的分子運送至粒線體，
當作細胞呼吸的燃料。
– Peroxisomal enzymes: defective or absent- cause serious
disease (ALD: 腎上腺腦白質營養不良neurological
debilitation)
• 肝細胞的過氧化小體有解毒的作用（如解酒精）
• May play a role in aging.
Vacuoles (液泡)
• In animals- temporary storage or transport
• Some protozoa– take up food particles-phagocytosis
– 伸縮泡（contractile vacuole）
• In plants- central vacuoles中央液泡
–
–
–
–
一般植物細胞：無機離子如鉀、氯離子
種子：堆積有機物（蛋白質）
花瓣：色素
其他：對動物的毒物或是味道極差之物質
Vacuoles have diverse functions in
cell maintenance
• Vesicles and vacuoles (larger versions) are
membrane-bound sacs with varied functions.
– Food vacuoles, from phagocytosis, fuse with
lysosomes.
– Contractile vacuoles, found in freshwater protists,
pump excess water out of the cell.
– Central vacuoles are found in many mature plant
cells.
• The membrane surrounding the central vacuole,
the tonoplast, is selective in its transport of
solutes into the central vacuole.
• The functions of the central vacuole include
stockpiling（儲存） proteins or inorganic ions,
depositing metabolic byproducts, storing
pigments, and storing defensive compounds
against herbivores.
• It also increases surface to volume ratio for the
whole cell.
• Cell types that synthesize large quantities of
proteins (e.g., pancreas,胰腺) have large
numbers of ribosomes.
• Some ribosomes, free ribosomes, are suspended
in the cytosol and synthesize proteins that
function within the cytosol.
• Other ribosomes, bound ribosomes, are attached
to the outside of the endoplasmic reticulum.
– These synthesize proteins that are either included
into membranes or for export from the cell.
The Eukaryotic Cell in Overview

• The plasma membrane defines cell
boundaries and retains contents
• The nucleus is the cell’s information center
• Intracellular membranes and organelles
define compartment
• The cytoplasm of eukaryotic cells contains
the cytosol and cytoskeleton
• The extracellular matrix and the cell wall
are outside of the cell
Providing structural support to the cell, the
cytoskeleton also functions in cell motility
and regulation
• The cytoskeleton provides mechanical support
and maintains shape of the cell.
• The fibers act like a geodesic dome to stabilize a
balance between opposing forces.
• The cytoskeleton provides anchorage for many
organelles and cytosolic enzymes.
Intermediate filaments
• The most stable and the least soluble
constituents of the cytoskeleton.
• As a scaffold that supports the entire
cytoskeleton framework.
• In contrast to microtubules and
microfilaments, intermediate filaments
differ in their protein composition from
tissue to tissue
The Eukaryotic Cell in Overview

• The plasma membrane defines cell
boundaries and retains contents
• The nucleus is the cell’s information center
• Intracellular membranes and organelles
define compartment
• The cytoplasm of eukaryotic cells contains
the cytosol and cytoskeleton
• Beyond the cell：Cell Adhesions, Cell
Junctions, and Extracellular Structures (Ch 17)
Beyond the Cell：Cell Adhesion, Cell
Junctions, and Extracellular Structures
• Cell-Cell Recognition and Adhesion
• Cell-Cell Junctions
• The Extracellular Matrix of Animal Cells
Cell-Cell Recognition and Adhesion
• Transmembrane proteins mediate cell-cell
adhsion
• Carbohydrate Groups are Important in CellCell Recognition and Adhesion
– Lectins
– Selectins and Leukocyte Adhesion
Transmembrane proteins mediate
cell-cell adhsion
• CAMs- cell adhesion molecules (IgSF:
immunoglobulin superfamily)
• Cadherins- glycoproteins
Carbohydrate Groups are Important in
Cell-Cell Recognition and Adhesion
• Lectins：carbohydrate-binding proteins
– Promote cell-cell adhesion by binding to a
specific sugar.
• Selectins and Leukocyte Adhesion
Cell-Cell Junctions
Animal have 3 main types of
intercellular links
• Adhesive junctions link adjoining cells to
each other
• Tight junctions prevent the movement of
molecules across cell layers
• Gap junctions allow direct electrical and
chemical communication between cells
Adhesive Junctions Link Adjoining Cells
to Each Other
• Adhesive Junctions- common in epithelia
– Connect the external environment to the actin
microfilaments or inetrmediate filaments
– Provide a potential pathway for signals to be transmitted from
the cell exterior to the cytoplasm.
– Fasten cells together into strong sheets,
• such as desmosome- much like rivets (鉚釘).
• Adhesive Junctions
– Focal adhesion
– Hemidesmosome
– Adherens Junctions：cadherin-medeated adhesive junctions
(Fig 17-3a)
– Desmosome
Tight Junctions
• Prevent the movement of molecules across
cell layers
• Membranes of adjacent cells are fused,
forming continuous belts around cells.
– Sealing spaces between cells
• Transmembrane junctional proteins
– Prevents leakage of extracellular fluid.
Gap junctions
• allow direct electrical and chemical
communication between cells
• communicating junctions provide cytoplasmic
channels between adjacent cells.
– Special membrane proteins surround these
pores.
– Salt ions, sugar, amino acids, and other
small molecules can pass.
– In embryos, gap junctions facilitate chemical
communication during development.
Extracellular Structure
• Animal cells- Extracellular matrix (ECM)
– Collagen fibers and proteoglycans
• Plant cells and fungal cells- Cell wall
– Cellulose microfibrils embedded in a matrix
other polysaccharides and small amounts of
proteins.
• Bacteria- Cell wall
– peptidoglycans
ECM
• Primary function- Support
• Other functions：
–
–
–
–
–
–
Cell motility
Cell migration
Cell division
Cell recognition
Cell adhesion
Cell differentiation during embryonic
development
The extracellular matrix (ECM) of animal
cells functions in support, adhesion,
movement, and regulation
• Lacking cell walls, animals cells do have an
elaborate extracellular matrix (ECM).
• The primary constituents of the extracellular
matrix are glycoproteins, especially collagen
fibers, embedded in a network of proteoglycans.
• In many cells, fibronectins(纖維結合素) in the
ECM connect to integrins(整合速), intrinsic
membrane proteins.
• The integrins connect the ECM to the
cytoskeleton.
• The ECM can regulate cell behavior.
– Embryonic cells migrate along specific pathways by
matching the orientation of their microfilaments to
the fibers in the extracellular matrix.
– The extracellular matrix can influence the activity
of genes in the nucleus via a combination of
chemical and mechanical signaling pathways.
• This may coordinate all the cells within a tissue.
The Plant cell SurfaceCell Wall
• The cell wall, found in prokaryotes, fungi, and
some protists, has multiple functions.
• In plants, the cell wall protects the cell, maintains
its shape, and prevents excessive uptake of water.
• It also supports the plant against the force of
gravity.
• The thickness and chemical composition of cell
walls differs from species to species and among
cell types.
Cell Walls
• Provide a structural framework and serve as
a permeability barrier
• A network of culluose microfibrils,
polysaccharides, and glycoproteins