• The Golgi apparatus

– Receives (on the cis-side) many of the transport vesicles produced in the rough ER

– Consists of flattened membranous sacs called cisternae

– Exports many substances (from the trans-side) in transport vesicles

The Golgi Apparatus: Shipping and Receiving Center

Golgiapparatus

TEM of Golgi apparatus

cis face(“receiving” side ofGolgi apparatus)

Vesicles movefrom ER to Golgi Vesicles also

transport certainproteins back to ER

Vesicles coalesce toform new cis Golgi cisternae

Cisternalmaturation:Golgi cisternaemove in a cis-to-transdirection

Vesicles form andleave Golgi, carryingspecific proteins toother locations or tothe plasma mem-brane for secretion

Vesicles transport specificproteins backward to newerGolgi cisternae

Cisternae

trans face(“shipping” side ofGolgi apparatus)

0.1 0 µm16

5

2

3

4

Functions of the Golgi apparatus

Figure 6.13

- Modification of the products of the rough ER

- Manufacture of certain macromolecules

-Probably evolved from ER

Lysosomes: Digestive Compartments• Lysosomes are

membranous sacs of hydrolytic enzymes, and they carry out intracellular digestion.

• They digest food from food vacuoles that form by phagocytosis and they recycle old cell parts in autophagy.

Figure 6.14 A(a) Phagocytosis: lysosome digesting food

1 µm

Lysosome containsactive hydrolyticenzymes

Food vacuole fuses with lysosome

Hydrolyticenzymes digestfood particles

Digestion

Food vacuole

Plasma membraneLysosome

Digestiveenzymes

Lysosome

Nucleus

Lysosomes

• different lysosomes have different enzymes for breaking down different macromolecules

• They have a low pH (around 5); pump H+ ions in from the cell

• Example of a lysosomal disease: Tay-Sachs disease, caused by a missing lysosomal enzyme for lipid breakdown, leads to buildup of lipids in the brain, killing the individual in infancy.

Figure 6.14 B(b) Autophagy: lysosome breaking down damaged organelle

Lysosome containingtwo damaged organelles 1 µ m

Mitochondrionfragment

Peroxisomefragment

Lysosome fuses withvesicle containingdamaged organelle

Hydrolytic enzymesdigest organellecomponents

Vesicle containingdamaged mitochondrion

Digestion

Lysosome

Vacuoles: Diverse Maintenance Compartments

• Vacuoles are fluid filled and membrane enclosed.

• A cell may have one or several vacuoles.

– Food vacuoles

• Are formed by phagocytosis

– Contractile vacuoles

• Pump excess water out of protist cells

Vacuoles: Diverse Maintenance Compartments

• Central vacuoles– Found in plant cells

– Function in cell size and turgidity

– Store reserves of important organic compounds and water

Central vacuole

Cytosol

Tonoplast

Centralvacuole

Nucleus

Cell wall

Chloroplast

5 µmFigure 6.15

Plasma membrane expandsby fusion of vesicles; proteinsare secreted from cell

Transport vesicle carriesproteins to plasma membrane for secretion

Lysosome availablefor fusion with anothervesicle for digestion

4 5 6

Nuclear envelope isconnected to rough ER, which is also continuous

with smooth ER

Nucleus

Rough ER

Smooth ERcis Golgi

trans Golgi

Membranes and proteinsproduced by the ER flow in

the form of transport vesiclesto the Golgi Nuclear envelop

Golgi pinches off transport Vesicles and other vesicles

that give rise to lysosomes and Vacuoles

1

3

2

Plasmamembrane

The Endomembrane System: A Review• Relationships among membranes/organelles of the

endomembrane system

Figure 6.16

Organelles of Endosymbiotic Origin

• Mitochondria and chloroplasts change energy from one form to another

• Mitochondria

– Are sites of cellular respiration

• Plastids

– Found only in plants, are sites of photosynthesis

Mitochondria: Chemical Energy Conversion• Mitochondria (powerhouse of the cell)

– Are found in nearly all eukaryotic cells

– Have their own DNA- derived from the mother. This DNA changes very slowly over time because there is no recombination, only change is due to drift (chance).

Mitochondrion

Intermembrane spaceOuter

membrane

Freeribosomesin the mitochondrialmatrix

MitochondrialDNA

Innermembrane

Cristae

Matrix

100 µmFigure 6.17

Mitochondria: Chemical Energy Conversion– Are the site of oxidative metabolism (conversion of glucose to ATP, carbon

dioxide, and water), also known as cellular respiration.

* Which type of cell would you expect to have a lot of mitochondria?

– Are enclosed in a double membrane. Inner membrane is folded for increased surface area. This is where the metabolism occurs; enzymes are embedded in the membrane.

Mitochondrion

Intermembrane spaceOuter

membrane

Freeribosomesin the mitochondrialmatrix

MitochondrialDNA

Innermembrane

Cristae

Matrix

100 µmFigure 6.17

Plastids: Capture of Light Energy

• Plastids

– have a double membrane

– have their own DNA

– function in photosynthesis (the chloroplast is an example)

– contain pigments such as chlorophyll, carotenoids

– can also be for storage (leukoplasts)

Chloroplasts– Are found in leaves and other green organs of plants and in algae

– Their structure includes

• Thylakoids, membranous sacs

• Stroma, the internal fluid

Chloroplast

ChloroplastDNA

RibosomesStromaInner and outermembranes

Thylakoid

1 µm

Granum

Figure 6.18

Peroxisomes: Oxidation

• Peroxisomes

– Produce hydrogen peroxide and convert it to water

ChloroplastPeroxisome

Mitochondrion

1 µm

Figure 6.19

The CytoskeletonCytoplasm – includes all the space inside the plasma membrane but outside the nucleus (includes organelles, cytosol, and cytoskeleton)

Cytoskeleton: microlattice of fibers supports the cell and gives it 3-dimensional shape. Organelles attach to the fibers.

The cytoskeleton gives the cell spatial information, which is very important in development

The cytoskeleton is not stationary, it is dynamic.

The Cytoskeleton– Is a network of fibers extending throughout the

cytoplasm, and it organizes cell structures and activities.

Figure 6.20

Microtubule

0.25 µm MicrofilamentsFigure 6.20

Roles of the Cytoskeleton: Support, Motility, and Regulation

– Gives mechanical support to the cell

– Is involved in cell motility, which utilizes motor proteins

VesicleATPReceptor formotor protein

Motor protein(ATP powered)

Microtubuleof cytoskeleton

(a) Motor proteins that attach to receptors on organelles can “walk”the organelles along microtubules or, in some cases, microfilaments.

Microtubule Vesicles 0.25 µm

(b) Vesicles containing neurotransmitters migrate to the tips of nerve cell axons via the mechanism in (a). In this SEM of a squid giant axon, two  vesicles can be seen moving along a microtubule. (A separate part of the experiment provided the evidence that they were in fact moving.)Figure 6.21 A, B

Components of the Cytoskeleton

• There are three main types of fibers that make up the cytoskeleton

Table 6.1

Microtubules

• Microtubules

– Shape the cell

– Cilia and flagella for motility

– Guide the movement of organelles

– Help separate the chromosome copies in dividing cells

Centrosomes and Centrioles

• The centrosome

– Is considered to be a “microtubule-organizing center” and it organizes the spindle fibers used to guide the movement of chromosomes during cell division.

In animal cells, the centrosome:– Contains a pair of centrioles which are made

of microtubules in a nine-triplets pattern.

Centrosome

Microtubule

Centrioles0.25 µm

Longitudinal sectionof one centriole

Microtubules Cross sectionof the other centrioleFigure 6.22

Cilia and flagella – locomotory organelles• Cilia and flagella share a common ultrastructure of microtubules

in a 9 + 2 arrangement. The base structure is similar to that of centrioles (nine triplets).

(a)

(c)

(b)

Outer microtubuledoubletDynein arms

CentralmicrotubuleOuter doublets cross-linkingproteins inside

Radialspoke

Plasmamembrane

Microtubules

Plasmamembrane

Basal body

0.5 µm

0.1 µm

0.1 µm

Cross section of basal body

Triplet

Figure 6.24 A-C

Cilia and Flagella move through the action of motor proteins

• The protein dynein

– Is responsible for the bending movement of cilia and flagella

Microtubuledoublets ATP

Dynein arm

Powered by ATP, the dynein arms of one microtubule doublet grip the adjacent doublet, push it up, release, and then grip again. If the two microtubule doublets were not attached, they would slide relative to each other.

(a)

Figure 6.25 A

Outer doubletscross-linkingproteins

Anchoragein cell

ATP

In a cilium or flagellum, two adjacent doublets cannot slide far because they are physically restrained by proteins, so they bend. (Only two ofthe nine outer doublets in Figure 6.24b are shown here.)

(b)

Ciliary/flagellar motion

Figure 6.25 B

Microfilaments (Actin Filaments)– Are built from molecules of the protein actin

– Are found in microvilli

0.25 µm

Microvillus

Plasma membrane

Microfilaments (actinfilaments)

Intermediate filaments

Figure 6.26

Microfilaments of muscle

• Microfilaments that function in cellular motility

– Contain the protein myosin in addition to actin

Actin filament

Myosin filament

Myosin motors in muscle cell contraction. (a)

Muscle cell

Myosin arm

Figure 6.27 A

Amoeboid motion– Involves the contraction of actin and myosin

filaments

Cortex (outer cytoplasm):gel with actin network

Inner cytoplasm: sol with actin subunits

Extendingpseudopodium

(b) Amoeboid movementFigure 6.27 B

Cytoplasmic streaming– Is another form of locomotion created by

microfilaments

Nonmovingcytoplasm (gel)

ChloroplastStreamingcytoplasm(sol)

Parallel actinfilaments Cell wall

(b) Cytoplasmic streaming in plant cellsFigure 6.27 C

Intermediate Filaments– Support cell shape

– Fix organelles in place

– Are fixed and do not disassemble.

Extracellular components and connections between cells

help coordinate cellular activities

Cell Walls of Plants– Extracellular structures of plant cells that distinguish

them from animal cells

– Are made of cellulose fibers embedded in other polysaccharides and protein

– May have multiple layersCentral vacuoleof cell

PlasmamembraneSecondarycell wallPrimarycell wall

Middlelamella

1 µm

Centralvacuoleof cell

Central vacuole CytosolPlasma membrane

Plant cell walls

PlasmodesmataFigure 6.28

The Extracellular Matrix (ECM) of Animal Cells

• Animal cells

– Lack cell walls

– Are covered by an elaborate matrix, the ECM

The ECM– Is made up of glycoproteins and other

macromolecules. Some of these molecules can be part of self-recognition or membrane-membrane interactions (e.g. tissue glue that holds cells together).

Collagen

Fibronectin

Plasmamembrane

EXTRACELLULAR FLUID

Micro-filaments

CYTOPLASM

Integrins

Polysaccharidemolecule

Carbo-hydrates

Proteoglycanmolecule

Coreprotein

Integrin

Figure 6.29

A proteoglycan complex

Functions of the ECM include

– Support

– Adhesion

– Movement

– Regulation

Intercellular Junctions in Plants• Plasmodesmata are channels that perforate plant cell

walls. The cell membranes of neighboring cells are continuous through these pores in the cell walls. This allows cells to share molecules and communicate.

Interiorof cell

Interiorof cell

0.5 µm Plasmodesmata Plasma membranes

Cell walls

Figure 6.30

Animal Cell Junctions• In animals, there are three types of intercellular

junctions

– Tight junctions

– Desmosomes

– Gap junctions

Animal Cell Junctions

• Types of intercellular junctions in animals

Tight junctions prevent fluid from moving across a layer of cells

Tight junction

0.5 µm

1 µm

Spacebetweencells

Plasma membranesof adjacent cells

Extracellularmatrix

Gap junction

Tight junctions

0.1 µm

Intermediatefilaments

Desmosome

Gapjunctions

At tight junctions, the membranes ofneighboring cells are very tightly pressedagainst each other, bound together byspecific proteins (purple). Forming continu-ous seals around the cells, tight junctionsprevent leakage of extracellular fluid acrossA layer of epithelial cells.

Desmosomes (also called anchoringjunctions) function like rivets, fastening cellsTogether into strong sheets. IntermediateFilaments made of sturdy keratin proteinsAnchor desmosomes in the cytoplasm.

Gap junctions (also called communicatingjunctions) provide cytoplasmic channels fromone cell to an adjacent cell. Gap junctions consist of special membrane proteins that surround a pore through which ions, sugars,amino acids, and other small molecules maypass rapidly. Gap junctions are necessary for commu-nication between cells in many types of tissues,including heart muscle and animal embryos.

TIGHT JUNCTIONS

DESMOSOMES

GAP JUNCTIONS

Figure 6.31