ORGANELLES OF THE CYTOPLASM

Cytoplasm• Located between plasma membrane and nucleus• Cytosol• Water with solutes (protein, salts, sugars, etc.)

• Cytoplasmic organelles• Metabolic machinery of cell

Cytoplasmic Organelles

• Membranous• Mitochondria• Peroxisomes• Lysosomes• Endoplasmic reticulum• Golgi apparatus

• Nonmembranous• Cytoskeleton • Centrioles • Ribosomes

Mitochondria

• Double-membrane structure with shelflike cristae• Provide most of cell’s ATP via aerobic cellular respiration• Contain their own DNA and RNA

Figure 3.17

Enzymes

Matrix

Cristae

Mitochondrial DNA

Ribosome

Outer mitochondrial membrane

Inner mitochondrial membrane

(b)

(a)

(c)

Ribosomes

• Site of protein synthesis• Free ribosomes synthesize soluble proteins • Membrane-bound ribosomes synthesize proteins destined for

membranes or secretion

Endoplasmic Reticulum (ER)

• System of Interconnected tubes and parallel membranes enclosing cisternae• Continuous with nuclear membrane• Two varieties:• Rough ER• Smooth ER

Figure 3.18a

Nuclearenvelope

Ribosomes

Rough ER

Smooth ER

(a) Diagrammatic view of smooth and rough ER

Rough ER

• External surface studded with ribosomes• Manufactures all secreted proteins• Synthesizes membrane integral proteins and phospholipids

Smooth ER

• Its enzymes catalyze reactions involved with:• In the liver-Lipid metabolism, cholesterol synthesis, synthesis of lipid

components of lipoproteins• In testes: Synthesis of steroid-based hormones (testes)• In skeletal & cardiac muscle—storage & release of calcium

Golgi Apparatus

• Stacked and flattened membranous sacs• Modifies, concentrates, and packages proteins and lipids• Proteins exit via secretory vesicles

Figure 3.20

Protein-containing vesicles pinch off rough ERand migrate to fuse with membranes ofGolgi apparatus.

Proteins aremodified withinthe Golgi compartments.

Proteins arethen packagedwithin differentvesicle types, depending ontheir ultimatedestination.

Plasmamem-brane

Secretion byexocytosis

Vesicle becomeslysosome

Golgiapparatus

Rough ER ERmembrane

Phagosome

Proteins incisterna

Pathway B:Vesicle membraneto be incorporatedinto plasmamembranePathway A:

Vesicle contentsdestined for exocytosis Extracellular fluid

Secretoryvesicle

Pathway C:Lysosome containing acid hydrolaseenzymes

1

3

2

Lysosomes

• Spherical membranous organelles containing digestive enzymes (acid hydrolases)• Can degrade/breakdown:• Ingested bacteria, viruses, and toxins• Nonfunctional organelles• Break down and release glycogen• Break down bone to release Ca2+

Figure 3.22

Golgiapparatus

Transportvesicle

Plasmamembrane

Vesicle

Smooth ER

Rough ER

Nuclear envelope

Lysosome

Nucleus

Peroxisomes

• Membranous sacs containing powerful oxidases and catalases• Detoxify harmful or toxic substances• Neutralize dangerous free radicals

Cytoskeleton• Elaborate series of rods throughout cytosol• Microtubules -hollow tubes, mostly radiating from a

centrosome; determine overall shape of cell and distribution of organelles• Microfilaments -actin strands attached to cytoplasmic

side of plasma membrane; Involved in cell motility, change in shape, endocytosis and exocytosis• Intermediate filaments-Tough, insoluble ropelike protein

fibers ;Resist pulling forces on the cell and attach to desmosomes

Figure 3.23a

Strands made of sphericalprotein subunits called actins

(a) Microfilaments

Actin subunit

Microfilaments form the blue networksurrounding the pink nucleus in thisphoto.

Figure 3.23b

(b) Intermediate filaments

Tough, insoluble protein fibersconstructed like woven ropes

Fibrous subunits

Intermediate filaments form the purplebatlike network in this photo.

Figure 3.23c

(c) MicrotubulesHollow tubes of spherical protein

subunits called tubulins

Tubulin subunits

Microtubules appear as gold networkssurrounding the cells’ pink nuclei inthis photo.

Centrioles

• Involved in: cell division• Found within the centrosome

Figure 3.25a

Centrosome matrix

(a)

Centrioles

Microtubules

Cellular Extensions

• Flagella• Whiplike, motile extensions on surfaces of certain cells• propel whole cells (tail of sperm)

• Cilia move substances across cell surfaces

Figure 3.26

Plasmamembrane

Outer microtubuledoublet

Dynein arms

Centralmicrotubule

Radial spoke

Radial spoke

TEM

TEM

Triplet

Basal body(centriole)

Cilium

Microtubules

Plasmamembrane

Basal body

Cross-linkingproteins insideouter doublets

Cross-linkingproteins insideouter doublets

A longitudinal section of acilium shows microtubules running the length of thestructure.

The doubletsalso have attached motor proteins, the dynein arms.

The outermicrotubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes.

A cross section through thebasal body. The nine outer doublets of a cilium extend into a basal body where each doublet joins another microtubule to form a ring of nine triplets.

A cross section through thecilium shows the “9 + 2”arrangement of microtubules.

TEM

Figure 3.27

(a) Phases of ciliary motion.

(b) Traveling wave created by the activity ofmany cilia acting together propels mucusacross cell surfaces.

Power, orpropulsive,stroke

Layer of mucus

Cell surface

Recovery stroke, whencilium is returning to itsinitial position

1 2 3 4 5 6 7

Cellular Extensions

• Microvilli• Fingerlike extensions of plasma membrane• Increase surface area for absorption

Figure 3.28

Microvillus

Actinfilaments

Terminalweb

Nucleus

• Genetic library with blueprints for nearly all cellular proteins• Responds to signals and dictates kinds and amounts of proteins to be

synthesized• Surrounded by nuclear envelope (perforated for exit of material)• Contains threadlike strands of DNA (30%), histone proteins (60%),

and RNA (10%) called chromatin• Also contains nucleoli : dark-staining spherical bodies involved in

ribosome assembly

Figure 3.29a

Chromatin (condensed)

Nuclear envelope Nucleus

Nuclear pores

Nucleolus

Cisternae of rough ER

(a)

Figure 3.29b

Nucleus

Nuclearpores

Fractureline of outermembrane

Nuclear pore complexes.Each pore is ringed byprotein particles.

Surface of nuclear envelope.

Nuclear lamina. The netlikelamina composed of inter-mediate filaments formed bylamins lines the inner surfaceof the nuclear envelope.

(b)

Figure 3.30

Metaphasechromosome(at midpointof cell division)

Nucleosome (10-nm diameter; eight histone proteins wrapped by two winds of the DNA double helix)

Linker DNA

Histones

(a)

(b)

1 DNA doublehelix (2-nm diameter)

2 Chromatin(“beads on a string”) structurewith nucleosomes

3 Tight helical fiber(30-nm diameter)

5 Chromatid(700-nm diameter)

4 Looped domain structure (300-nm diameter)