Cell Structure Review

http://en.wikipedia.org/wiki/Cell_(biology)

Cells

“fundamentalunits of life...”

Figure 1-1d Essential Cell Biology (© Garland Science 2010)

Figure 1-1b Essential Cell Biology (© Garland Science 2010)

Figure 1-1a Essential Cell Biology (© Garland Science 2010)

Figure 1-1c Essential Cell Biology (© Garland Science 2010)

Figure 1-1e Essential Cell Biology (© Garland Science 2010)

Structure-FunctionRelationship

Number of cells in a human body

10 - 100 trillion cells

Bright field, 400xHematoxylin stained

Microscopes

Bright field, 1000xHematoxylin stained

EukaryoticCells

Membranes

The PlasmaMembrane

Phospholipid bilayer+ membrane proteins+ cholesterol

Surfaces are important!They are the parts of an object that are readily accessibleby things outside the object.

Heat exchangehappens via surfaces.

Gas exchangehappens via surfaces.

MembraneProteins

TransmembraneProteins

PeripheralMembraneProteins

Text

http://en.wikipedia.org/wiki/

Peripheral_membrane_protein

Fluid Mosaic Model

Organelles

“...a specialized subunit within a cellthat has a specific function, and is usually separately enclosed within its own lipid bilayer.”

http://en.wikipedia.org/wiki/Organelle

Table 4.2aCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

TABLE 4.2 EUKARYOTIC CELL STRUCTURES AND THEIR FUNCTIONS

The hallmark of the eukaryotic cell is compartmentalization, achieved by anextensive endomembrane system that weaves through the cell interior. Themembrane network is called the endoplasmic reticulum, or ER. The ER begins atthe nuclear envelope and extends out into the cytoplasm, its sheets of membraneweaving through the cell interior. Rough ER contains numerous ribosomes that giveit a bumpy appearance. These ribosomes manufacture protein destined for the ERor for other parts of the cell. ER without these attached ribosomes is called smoothER, which often functions to detoxify harmful substances or to aid in the synthesisof lipids. Sugar side chains are added to molecules as they pass through the ER.Delivery of molecules to other parts of the cell is via vesicles that pinch off from theborders of the rough ER.

Every cell contains DNA, the hereditary material. The DNA of eukaryotes is isolatedwithin the nucleus, a spherical organelle surrounded by a double membranestructure called the nuclear envelope. This envelope is studded with pores thatcontrol traffic into and out of the nucleus. The DNA contains the genes that codefor the proteins synthesized by the cell. Stabilized by proteins, it forms chromatin,the major component of the nucleus. When the cell prepares to divide, thechromatin of the nucleus condenses into threadlike chromosomes.

The plasma membrane is a phospholipid bilayer embedded with proteins thatencloses a cell and separates its contents from its surroundings. The bilayer resultsfrom the tail-to-tail packing of the phospholipid molecules that make up themembrane. The proteins embedded in the lipid bilayer are in large part responsiblefor a cell’s ability to interact with its environment. Transport proteins providechannels through which molecules and ions enter and leave the cell across theplasma membrane. Receptor proteins induce changes within the cells when theycome in contact with specific molecules in the environment, such as hormones, orwith molecules on the surface of neighboring cells.

DescriptionStructure

Secretoryvesicles

Lysosome

Golgi Complex

Plasma Membrane

ProteinPhospholipid

Cholesterol

Nucleus

Nuclear envelope

Nucleolus

Nuclear pore

Ribosome

Smooth ER

Transport vesicles

Rough ER

Endoplasmic Reticulum

At various locations within the cytoplasm flattened stacks of membranes occur.Animal cells may contain 20, plant cells several hundred. Collectively, they arereferred to as the Golgi complex. Molecules manufactured in the ER pass to the Golgi complex within vesicles. The Golgi sorts and packages these molecules andalso synthesizes carbohydrates. The Golgi adds sugar side chains to molecules asthey pass through the stacks of membranes. The Golgi then directs the moleculesto lysosomes, secretory vesicles, or the plasma memrane.

Table 4.2b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The green color of plants and algae results from cell organelles called chloroplastsrich in the photosynthetic green pigment chlorophyll. Photosynthesis is thesunlight-powered process at converts CO2 in the air to the organic moleculesof which all living things are composed. Chloroplasts, like mitochondria, arecomposed of two membranes separated by an intermembrane space. In achloroplast, the inner membrane pinches into a series of sacs called thylakoids,which pile up in columns called grana. The chlorophyll-facilitated light reactionsof photosynthesis take place within the thylakoids. These are suspended in asemiliquid substance called the stroma.

The cytoplasm of all eukaryotic cells is crisscrossed by a network of protein fiberscalled the cytoskeleton that supports the shape of the cell and anchors organellesto fixed locations. The cytoskeleton is a dynamic structure, composed of threekinds of fibers. Long actin filaments are responsible for cellular movements suchas contraction, crawling, and the “pinching” that occurs as cells divide. Hollowmicrotubule tubes, constantly forming and disassembling, facilitate cellularmovements an are responsible for moving materials within the cell. Specialmotor proteins move organelles around the cell on microtubular “tracks.” Durableintermediate filaments provide the cell with structural stability.

Mitochondria are bacteria-like organelles that are responsible for extracting mostOf the energy a cell derives from the food molecules it consumes. Two membranesEncase each mitochondrion, separated by an intermembrane space. The keyenergy-harvesting chemical reactions occur within the interior matrix. The energy isUsed to pump protons from the matrix into the intermembrane space; their returnAcross this membrane drives the synthesis of ATP, the energy currency of the cell.

Centrioles are barrel-shaped organelles found in the cells of animals and mostprotists. They occur in pairs, usually located at right angles to each other nearthe nucleus. Centrioles help assemble the animal cell’s microtubules, playinga key role in producing the microtubules that move chromosomes during celldivision. Centrioles are also involved in the formation of cilia and flagella, whichare composed of sets of microtubules. Cells of plants and fungi lack centrioles, andcell biologists are still in the process of characterizing their microtubule-organizingcenters.

Cytoskeleton

Microtubule

Actin filament

Stroma

Chloroplast

Structure

Mitochondrion

Intermembrane space

Intermediate filament

Centrioles

Microtubule triplet

Outermembrane

Innermembrane

Matrix

Outer membrane

Inner membrane

Granum

Thylakoid

Description

Why is having organelles advantageous?

The Nucleus“information center”

The Endomembrane System

Nuclear EnvelopeEndoplasmic ReticulumGolgi ApparatusLysosomesVacuolesVesiclesCell Membrane

http://en.wikipedia.org/wiki/Endomembrane_system

“...the set of membranes that form a single functional and developmental unit, either being connected together directly, or exchanging material through vesicle transport.”

http://en.wikipedia.org/wiki/Endomembrane_system

EndoplasmicReticulumwhere proteins are madeand processed

http://en.wikipedia.org/wiki/Endoplasmic_reticulum

Lots of surface area!

Vesiclescontainers for storage, transport and digestion

The Golgi Complexwhere proteins are processed,sorted and packaged

Mitochondria

http://en.wikipedia.org/wiki/Mitochondrion

Cytoskeleton

IntracellularTransport

Putting itall together

ExtracellularMatrix

Movementinto and out ofthe cell

Diffusion

The wanderingaround of molecules

Thewandering

around moleculesof

The wanderingaround

molecules

of

Fig. 4.21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hum

an R

ed B

lood

Cel

lsPl

ant C

ells

0.55 µm0.55 µm0.55 µm

HypotonicSolution

HypertonicSolution

IsotonicSolution

Cells swell andeventually burst

Shriveled cells Normal cells

Normal turgid cellFlaccid cellCell body shrinksfrom cell wall

(all): © David M. Phillips/Visuals Unlimited

Endocytosis

Exocytosis

SelectivePermeability

http://en.wikipedia.org/wiki/Cell_(biology)

http://www.npr.org/2011/03/18/134622044/tracing-the-immortal-cells-of-henrietta-lacks

In 1951, an African-American woman named Henrietta Lacks was diagnosed with terminal cervical cancer. She was treated at Johns Hopkins University, where a doctor named George Gey snipped cells from her cervix without telling her. Gey discovered that Lacks' cells could not only be kept alive, but would also grow indefinitely.

For the past 60 years Lacks' cells have been cultured and used in experiments ranging from determining the long-term effects of radiation to testing the live polio vaccine. Her cells were commercialized and have generated millions of dollars in profit for the medical researchers who patented her tissue.

http://www.npr.org/2011/03/18/134622044/tracing-the-immortal-cells-of-henrietta-lacks

Lacks' family, however, didn't know the cell cultures existed until more than 20 years after her death. Medical writer Rebecca Skloot examines the legacy of Lacks' contribution to science — and effect that has had on her family — in her new book, The Immortal Life of Henrietta Lacks.

Skloot is a freelance science writer and a contributing editor at Popular Science. She has written feature stories for The New York Times, Discover Magazine, and RadioLab.