The Golgi Apparatus: Shipping and Receiving Center
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Transcript of The Golgi Apparatus: Shipping and Receiving Center
• 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
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2
3
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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
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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
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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.
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
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