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Cytoplasm

•The contents of a cell, consisting of the cellular organelles, (except the nucleus and cell membrane), suspended in a liquid called the cytosol. The cytoplasm surrounds the nucleus and is contained within the cell membrane.

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Organelles

Endoplasmic Reticulum (ER): composed of interconnected membrane-bound sacs, canals, and vesicles. Provides for a transport systemthroughout the cell.

• Rough ER – has ribosomes• Protein synthesis

• Smooth ER• Lipid synthesis – lipids

added to proteinsarriving from rough ER

• Break down of drugsRibosomes – tiny spheres composed of rRNA and protein:

• Free floating or connected to ER• Provide the structure and the enzymes needed to link

amino acids to form protein

Membranes

Ribosomes

Membranes

(b) (c)

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Organelles

Golgi apparatus – “Post office”:• Stack of flattened, membranous sacs• Modifies, packagesand delivers proteins

Vesicles:• Membranous sacs• Storage of materials

Inner membrane

Outer membrane

Cristae

(a) (b)

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Mitochondrion:Membranous sacs with inner partitions – highly folded membrane forms cristae• Generate energy in the form of ATP

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Organelles

Lysosomes “Garbage disposal”• digestive enzymes for digesting worn

out cell parts and other cellular debris

Peroxisomes• over 40 different enzymes for

catalyzing reactions• Enzyme catalase – breaks down

hydrogen peroxide (toxic to cell)

Centrosome• Two rod-like centrioles• Used to produce cilia and flagella• Forms mitotic spindle to distributes

chromosomes during mitosis

(a) (b)

Centriole(cross-section)

Centriole(longitudinal section)

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Organelles

Cilia• Short hair-like projections• Propel substances on cell surface

Flagellum• Long tail-like projection• Provides motility to sperm

(a)

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Microfilaments and microtubules(Cytoskeleton)

• Thin rods and tubules• Support cytoplasm• Allows for movement of

organelles

Organelles

Inclusions

• Temporary nutrients and pigments

Microtubules

Microfilaments

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Cell Nucleus

•Control center of the cell• Nuclear envelope

• Porous double membrane• Separates nucleoplasm from

cytoplasm

• Nucleolus• Dense collection of RNA and proteins• Site of ribosome production

• Chromatin (loosely coiled chromo-somes)

• strands of DNA and proteins called histones.

• Stores information in the form of genesfor synthesis of proteins

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Nucleus

Nucleolus

Chromatin

Nuclearpores

Nuclearenvelope

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Active Transport•Carrier proteins, (often called “pumps”) move particles across the cell membrane from a region of lower concentration to higher concentration (ie. movement against the concentration gradient)•Requires energy in the form of ATP•Sugars, amino acids, sodium ions, potassium ions, etc.•Almost half of a cell’s energy supply may be used for active transport

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ACTIVE TRANSPORT Endocytosis• Cell engulfs a substance by forming a vesicle around the substance• Three types:

• Pinocytosis – substance is liquid - mostly water• Phagocytosis – substance is a solid• Receptor-mediated endocytosis – requires the substance to bind to a

membrane-bound receptor

Nucleus Nucleolus

VesicleCellmembrane

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ACTIVE TRANSPORT Endocytosis

Cytoplasm

Vesicle

(a) (b) (c) (d)

Receptorprotein

Cellmembrane

Moleculesoutside cell

Cellmembraneindenting

Receptor-ligandcombination

Nucleus Nucleolus

Particle VesiclePhagocytizedparticle

Cellmembrane

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ACTIVE TRANSPORT Exocytosis• Reverse of endocytosis• Substances in a vesicle fuse with cell membrane• Contents released outside the cell• Release of neurotransmitters from nerve cells

Nucleus

Endoplasmicreticulum

Golgiapparatus

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ACTIVE TRANSPORT Transcytosis

• Endocytosis followed by exocytosis•Substance is moved quickly from one side of the cell to the other•Example: HIV crossing a cell layer

Viruses budHIV

Exocytosis

Receptor-mediated endocytosis

HIV-infectedwhite blood cells Anal or

vaginal canal

Lining of anusor vagina(epithelial cells)

Virus infectswhite blood cells onother side of lining

Receptor-mediatedendocytosis

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Cellmembrane