Chapter 6
A Tour of the Cell
AP Biology
Smiley
Basic Structure of every Organism
• Based on 1 of 2 types of cells
– Prokaryotic
– Eukaryotic
Basic Structure of every Organism
• Based on 1 of 2 types of cells
– Prokaryotic
• ‘pro’ =before
• ‘karyon’ = kernel
– Eukaryotic
• ‘eu’ = true
• ‘karyon’ = kernel
Basic Structure of every Organism
• Based on 1 of 2 types of cells
– Prokaryotic
• Only exist in domains of Bacteria or Archaea
Basic Structure of every Organism
• Based on 1 of 2 types of cells
– Prokaryotic
• Only exist in domains of Bacteria or Archaea
– Eukaryotic
• Protists, fungi, animals, and plants
Eukaryotic Cell (plant)
Eukaryotic Cell (animal)
Prokaryotic Cell (Bacteria)
Basic Common Feature of Both
• Bound by selective barrier (plasma
membrane)
• Have cytosol (jellylike substance)
– Where organelles and other components are
found
• Contain chromosomes
– Carry genes in the form of DNA
• Have ribosomes
Different Features of Both
• Location of DNA
– Eukaryotes
• Most DNA is in nucleus
• Nucleus is bound by double membrane
– “true kernel”
– Prokaryotes
• DNA is concentrated in region not membrane-enclosed
– Nucleoid
• Cytoplasm
Different Features of Both
• Cytoplasm
– Eukaryotes
• Region between the nucleus and plasma membrane
• Contains a variety of organelles of specialized form and
function
– Prokaryotes
• Interior of prokaryotic cell
Different Features of Both
• Organelles
– Eukaryotes
• Membrane- bound organelles are Present
• Specialized form and function
– Prokaryotes
• Absence of organelles
Different Features of Both
• Size
– Eukaryotes
• Generally Larger than prokaryotes
• Size relates to function
• Logistics of carrying out cellular metabolism limits cell
size
• 10 – 100um in diameter
• Metabolic requirements limit size practicality of cells
– Prokaryotes
• Smallest cells known
• 1 – 5 um in diameter
Plasma Membrane
• Acts as a selective barrier
• Allows sufficient passage of oxygen, nutrients,
and wastes to service entire cell
• Example:
– For 1 um2 of membrane, only a limited amount of
particular substance can cross per second
• SA to V ratio is critical
Plasma Membrane
• As a cell increases in size, its volume grows
proportionately more than surface area
– Area is proportional to linear dimension square
– Volume is proportional to linear dimension cubed
– THEREFORE, smaller object has greater ratio of SA
to V
How does this relate to the size of
cells?
How does this relate to the size of
cells?
• Specialized cells
– Some longer, shorter, thinner depending on
function
– Sometimes there are more of one type instead of
an increase in size
Surface Area vs. Volume
When would you need a higher SA:V?
When would you need a higher SA:V?
• Cells that exchange a lot of material with
surroundings
• May have projections from surface (microvilli)
– This increases SA without increasing volume
Surface Area of the lungs (alveoli)
Digestive Tract
Small Intestine averages 23 feet.
Villi and Microvilli on
the interior of the small
intestine
Key
Vein carrying blood
to hepatic portal
vessel
Nutrient
absorption
Microvilli
(brush border)
Blood
capillaries
Epithelial
cells
Muscle layers
Epithelial cells
Large
circular
folds
Villi
Lacteal
Villi
Intestinal wall
Lymph
vessel
Excretory Structures
Nitrogenous Waste filtering
Eukaryotic Cells
• Focus of this chapter
Parts of the Cell
Nucleus
• Contains: Nuclear envelope, nucleolus, and
chromatin.
• Nuclear envelope: double membrane enclosing
the nucleus; perforated by pores; continuous
with ER
• Nucleolus: structure involved in production of
ribosomes; a nucleus has one or more nucleoli.
• Chromatin: material consisting of DNA and
proteins; visible as individual chromosomes in a
dividing cell.
.
Nucleus
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
Surface of nuclear envelope
Ribosome
1 µm
0.25 µm
Close-up of nuclear
envelope
Pore complexes (TEM)
Nuclear lamina (TEM)
Nucleus
• contains most of the genes in the eukaryotic
cell
• Chromatin: material consisting of DNA and
proteins; visible as individual chromosomes in
a dividing cell.
• DNA is organized into discrete units called
chromosomes
• Each chromosome is made up of chromatin
• typical human cell has 46 chromosomes in its
nucleus
Chromatin vs. Chromosomes
appearance within the cell.
Nucleolus
• rRNA is synthesized from instructions in the
DNA is here
• proteins imported from cytoplasm are
assembled with rRNA into ribosomal subunits
here
Ribosomes and RNA
• Ribosomes translate messenger RNA (mRNA) into
a protein.
– A ribosome binds to the 5’ end of the mRNA.
– Transfer RNA attached to an amino acid carries a
codon (3 nucleotide sequences) to bind to the mRNA.
– This process continues with more tRNA and amino
acids forming peptide bonds.
– The process stops when a codon reaches a stop
codon.
– By then a protein is formed, releases itself from the
ribosome and curls up into a secondary or tertiary
structure.
Free and Bound Ribosomes
• Both free and bound ribosomes are
structurally the same (both make proteins)
• Bound Ribosomes (attached to the ER)
– Make proteins that are to be inserted into
membranes, secreted or packaged
• Free Ribosomes (free in the cytosol)
– Make proteins and release them into the cytosol
Ribosomes
Endomembrane System
Endomembrane System
• Encompasses the variety of different
membranes
What is it responsible for?
• Synthesis of proteins
• Transport of proteins into membranes and
organelles or out of cell
• Metabolism and movement of lipids
• Detoxification of poisons
Endomembrane System
• Related through direct contact or through
transfer of vesicles
What is a vesicle?
• Sac made up of membrane
Endomembrane System
• Pieces are not identical
– Vary in structure and function
• Vary in chemical reactions carried out in the
given membrane
Endomembrane System
• Includes:
– the Nuclear envelope
– Golgi Apparatus
– Lysosomes
– Vacuoles
– Plasma Membrane
Endoplasmic Reticulum
Function
• The endoplasmic reticulum (ER) is a network of
flattened sacs and branching tubules that extends
throughout the cytoplasm in plant and animal
cells.
• The endoplasmic reticulum manufactures,
processes, and transports a wide variety of
biochemical compounds for use inside and
outside of the cell.
• Accounts for more than half the total membranes
in many eukaryotic cells
Smooth ER
• The smooth ER functions in diverse metabolic
processes, which vary with cell type
• Lacks ribosomes
• (Barbiturates, alcohol, and many other drugs
induce the proliferation of smooth ER and its
associated detoxification enzymes thus
increasing the rate of detoxification)-increase
tolerance to other helpful drugs
Function of Smooth ER
• Process includes synthesis of Lipids, metabolism
or carbohydrates, and detoxification of drugs and
poisons (in Liver cells)
• In animal cells the steroids produced are the sex
hormones of vertebrates and the various steroid
hormones secreted by the adrenal glands
• Detoxification usually involves adding Hydroxyl
groups to drug molecules making them more
soluble and easier to flush from the body
Function of Smooth ER
• Stores Calcium
– Important to muscle cells
– When stimulated, calcium ions rush back across
the ER membrane into the cytosol and trigger
contraction of the muscle cell
Rough ER
• • A complex membrane bound organelle that is
composed of a greatly convoluted but flattish
sealed sac that is continuous with the nuclear
membrane.
• • Called a ROUGH Endoplasmic Reticulum
because it is studded on the outside with
ribosomes.
• • Found in eukaryotic cells - the cells of plants,
animals, and humans.
Function of Rough ER
• • The RER is involved in transport of proteins made by
ribosomes on its surface.
• • The Rough ER changes with the needs of the cells.
When the cell is actively making proteins, the rough ER
can enlarge and become more complex.
• • Ribosomes on the rough endoplasmic reticulum are
called 'membrane bound' and are responsible for the
assembly of many proteins. This process is called
translation.
Golgi Apparatus
• After leaving the ER, transport vesicles go to
the golgi apparatus
• FedEx
– Manufacturing
– Warehousing
– Sorting
– Shipping
• Here, products of the ER (such as proteins) are
modified and stored and then sent to other
destinations
• In a lot of cells used for secretion
Structure
• Flattened membranous sacs called cisternae
• Looks like a stack of pita bread
• Distinct structural polarity
– Membranes of cisternae on opposite sides of the
stack differ in thickness and molecular
composition
• Cis face and trans face
– Cis: receiving; trans: shipping
• Cis face—located near the ER
Movement
• Transport vesicles move material from the ER to
the Golgi apparatus
• A vesicle that buds from the ER can add its
membrane and the contents of its lumen to the
cis face by fusing with a Golgi membrane
• The trans face gives rise to vesicles, which pinch
off of the golgi body and travel to other sites.
• Products of the ER are usually modified during
their transit from the cis region to the trans
region of the Golgi
Non-protein Golgi Products
• In addition, the Golgi apparatus manufactures
certain macromolecules by itself.
• Many polysaccharides secreted by cells are
Golgi products
– Including pectins and certain other noncellulose
polysaccharides
• Non-protein Golgi products that will be
secreted depart from the trans face inside
transport vesicles
Cis to Trans
• The Golgi manufactures and refines its
products in stages, with different cisternae
containing unique teams of enzymes
• The cisternae of the Golgi actually progress
forward from the cis to the trans face of the
Golgi, carrying and modifying their cargo as
they move
– Good example in book on page 106, Figure 6.13
Before exiting…
• Before a Golgi stack dispatches its products by budding
vesicles from the trans face, it sorts these products and
targets them for various parts of the cell
• Molecular identification tags, such as phosphate
groups added to the Golgi products, aid in sorting
– act like ZIP codes on mailing labels
• Transport vesicles budded from the Golgi may have
external molecules on their membranes that recognize
“docking sites” on the surface of specific organelles or
on the plasma membrane, thus targeting the vesicles
appropriately
Lysosomes: the cell’s garbage disposal
• Break down old
organelles
• Destroy invaders
– Viruses
– bacteria
• Break down
macromolecules
–
–
–
–
Proteins
Carbohydrates
Nucleic acids
lipids
Lysosomal Acid Hydrolysis
• Contain about 50 degradative enzymes
– Hydrolyze proteins, DNA, RNA, lipids
• Lysosomes maintain an acidic pH (5)
– Controlled by a hydrogen ion pump
– Uses ATP hydrolysis
• Double protection
– Enzymes only active in acidic pH
• Enzymatic genetic diseases
– “lysosomal storage diseases”
– Gaucher’s affects breakdown of glycolipids
Lysosome formation
• Cell membrane buds
• Becomes an early endosome
• Introduction of hydrolases
and enzymes
– Created by the ER then
transferred to the Golgi bodies
• Becomes a late endosome
– Lowering of pH
• New lysosomes are formed
with acquisition of adequate
hydrolases
Phagocytosis and Autophagy
• Phagocytes fuse with
lysosomes
– Becomes phagolysosome
– Digests extracellular
substances
– Ex: bacteria, viruses, food
substances
• Autophagosomes fuse
with lysosomes
– Endoplasmic reticulum
encloses old organelles
– Vesicle fuses with
lysosome
.
1 µm
Nucleus
Lysosome
Lysosome contains Food vacuole Hydrolytic
active hydrolytic
enzymes digest
fuses with
enzymes
food particles
lysosome
Digestive
enzymes
Plasma
membrane
Lysosome
Digestion
Food vacuole
Phagocytosis: lysosome digesting food
Vacuoles
• Two types:
– Food
• Formed by phagocytosis
– Contractile
• Pumps excess water out of the cell
• Helps maintain a suitable concentration of ions
Vacuoles
• Different in Plants and Animals
• Animal
– General description
• Plant
– Versatile
– Take the job of lysosomes
• Carry out hydrolysis
–
–
–
–
Disposal site for metabolic by-products
Contain pigments
Contain unpalatable compounds
Aid in growth
Central Vacuole of a plant
Phagocytosis & Pinocytosis
Contractile Vacuole
Removes excess water in aquatic single
celled organisms
Mitochondria
.
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Mitochondrial
DNA
100 nm
Mitochondria
Mitochondria: An Organelle
● Mitochondria are important to the cell
because they are the “powerhouse” of the
cell.
● Mitochondria are the sites of cellular
respiration; cellular respiration is the
metabolic process by which ATP is produced.
● Mitochondria are enclosed by membranes,
however, they are not considered part of the
endomembrane system.
Mitochondria: An Organelle
● Mitochondria are unique in the sense that
they have two membranes in order to
function correctly.
● Found only in Eukaryotic cells.
● Mitochondria are typically 0.5 to 1.0
micrometer in length.
● Amount of mitochondria in the cell varies
depending on the type of tissue the cell is
found in and on the organism that the cell is
found in.
Diagram
CRISTAE
MITOCHONDRIAL DNA
GRANULE
INNER MEMBRANE
RIBOSOME
MATRIX
ATP SYNTHASE
INTERMEMBRANE SPACE
OUTER
PORINS
MEMBRANE
Energy Processing
❖ “Powerhouse of the cell”
❖ site of cellular respiration
❖ converts energy from sugar to forms that cell can use
❖ involved in other cell processes
❖ semiautonomous
❖ Cellular Respiration
❖ Glycolysis
❖ Citric acid cycle
Prokaryotic Cell (Bacteria)
Chloroplast
What are Chloroplasts?
• Specialized member of a family of closely related
plant organelles called plastids
• Lens shaped organelles, 2-5 micrometers
• Found in leaves, green organs of plants, and algae
• Contain:
– The green pigment chlorophyll
– Enzymes
– Molecules that function in the photosynthetic
production of sugar
The Structure
• Enclosed by two membranes separated by a
intermembrane space
– Outer compartment
• Second, inner compartment holding the fluid or
stroma
– surrounds the thylakoid space
• Membranous system in the form of connected,
flattened disks called thylakoids
– Stacked like poker chips which is called granum
Origin
• Chloroplasts are one of the many different types of organelles
in the plant cell.
• Considered to have originated from
cyanobacteria through endosymbiosis—when a eukaryotic
cell engulfed a photosynthesizing cyanobacterium which
remained and became a permanent resident in the cell.
• Mitochondria are thought to have come from a similar event,
where a aerobic prokaryote was engulfed.
• This origin of chloroplasts was first suggested by Konstantin
Mereschkowski in 1905 after Andreas Schimper observed that
chloroplasts closely resemble cyanobacteria in 1883.
• Chloroplasts are similar to mitochondria in that they both
originate from an endosymbiotic event, but chloroplasts are
found only in plants and some protists.
Chloroplasts
Prokaryotic Cell (Bacteria)
Lynn Margulis
Endosymbiotic Hypothesis
Modern Day Eukaryotic Cells
Animal
Plants
Cytoskeleton
Cytoskeleton
•
•
•
•
•
A network of fibers
Gives mechanical support
Stabilized by a system of opposing forces
Aids in cell motility
Interact with motor proteins
Cytoskeleton
• Three main types of fibers
– Microtubules
– Microfilaments
– Intermediate filaments
Cytoskeleton
• Three main types of fibers
– Microtubules
• Hollow rods
• Globular protein called tubulin
• Grow out from centrosome
– Within there are a pair of centrioles
• Examples:
– Cilia
– flagella
Centrioles
Cellular Movement
Cytoskeleton
• Three main types of fibers
– Microtubules
– Microfilaments
• Built from Molecules of actin
• Double chain of actin subunits
Microfilaments in muscle tissue
Muscle Tissue under the
Microscope
Cytoskeleton
• Three main types of fibers
– Microtubules
– Microfilaments
– Intermediate Filaments
• Larger than microfilaments
• Smaller than microtubules
A cell is the sum of it’s parts.
Protective Cell Wall in Plants
Cell walls composed of Chitin sugar.
Extra Cellular Matrix
(ECM)
Collagen
fiber
EXTRACELLULAR FLUID
Fibronectin
Plasma
membrane
Integrin
CYTOPLASM
Microfilaments
Proteoglycan
complex