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Lysosomes

• important in breakingdown bacteria and old cellcomponents

• contains many digestiveenzymes

• The ‘garbage disposal’ or‘recycling unit’ of a cell

• Malfunctioning lysosomesresult in some diseases(Tay-Sachs disease)

• Or may self-destruct cellsuch as in asbestosis

Lysosomes• Structure:• contents are contained within vesicles.• Contains about 40 different enzymes that are capable of

breaking down virtually every large biological molecule,including DNA, RNA, proteins, and certain lipids.

• contain digestive enzymes to digest macromolecules.• found in both animal and plant cells but rare in plant cells.• are built in the Golgi apparatus.• name comes from the Greek words "lysis" which means

dissolution or destruction and "soma" which means body.• nicknamed "suicide-bags" by cell biologists due to their role in

autolysis.

Lysosomes• Function:

– digest and dispose of foreign particles, malfunctioning structures, and worn outorganelles.

– pH 4.8 ; interior of the lysosome is more acidic than the cytosol (pH 7).– lysosome single membrane stabilizes the low pH by pumping in protons (H+) from

the cytosol, and also protects the cytosol, and therefore the rest of the cell,from the degradative enzymes within the lysosome.

– digestion of macromolecules from:• Phagocytosis• cell's own recycling process (where old components such as worn out

mitochondria are continuously destroyed and replaced by new ones, andreceptor proteins are recycled)

• autophagic cell death, a form of programmed self-destruction, or autolysis, ofthe cell, which means that the cell is digesting itself.

– digesting foreign bacteria that invade a cell– helping repair damage to the plasma membrane by serving as a membrane patch,

sealing the wound.– do much of the cellular digestion required to

• digest tails of tadpoles• remove the web from the fingers of a 3-6 month old fetus.

Peroxisomes• Small membrane-bound spaces in most plant and animal cells (all

eukaryotic cells)• Structure

– are ubiquitous organelles in eukaryotes that function to rid the cell of toxicsubstances. They have a single membrane that separates their contents fromthe cytosol (the internal fluid of the cell) and that contains membrane proteinscritical for various functions, such as importing proteins into the organelles andaiding in proliferation. Unlike lysosomes, which are formed in the secretorypathway, peroxisomes usually self-replicate by enlarging and then dividing,although there is some indication that new ones may be formed directly.

• Function– transport macromolecules into and out of the cell– carry materials between organelles in the cell.– Prokaryotes lack peroxisomes, so are more vulnerable to toxic

substances like hydrogen peroxide.– breakdown of fatty acid molecules, in a process called beta-

oxidation.• fatty acids are broken down two carbons at a time, converted to Acetyl-

CoA, which is then transported back to the cytosol for further use.• In animal cells, beta-oxidation can also occur in the mitochondria. In yeast

and plant cells this process is exclusive for the peroxisome.

Cytoskeleton

• Composed of 3 filamentousproteins:

MicrotubulesMicrofilaments

Intermediate filaments• All produce a complex

network of structuralfibers within cell

The specimen is human lung cell double-stained toexpose microtubules and actin microfilaments using amixture of FITC and rhodamine-phalloidin. Photo takenwith an Olympus microscope.

Microtubules

• Universal in eukaryotes• Involved in cell shape,

mitosis, flagellarmovement, organellemovement

• Long, rigid, hollow tubes~25nm wide

• Composed of a and ßtubulin (small globularproteins)

http://www.cytochemistry.net/Cell-biology/

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Microfilaments

• Thin filaments (7nm diam.)made of the globular proteinactin.

• Actin filaments form a helicalstructure

• Involved in cell movement(contraction, crawling, cellextensions)

Intermediate filaments

• Fibers ~10nm diam.• Very stable,

heterogeneous group• Examples:Lamins: hold nucleus shapeKeratin: in epithelial cellsVimentin: gives structure to

connective tissueNeurofilaments: in nerve

cellsImage of Lamins which reside in the nucleus just under the nuclear envelope

Cell Motility:Flagella & Cilia

• Cilia and flagella have the sameinternal structure.

• The major difference is in theirlength.

• In cross section: 9+2 arrangement ofmicrotubules (MT)

• MTs slide against each other toproduce movement

Human Sperm: TOTO-3 iodide for DNA (blue) and Nile red for membrane lipid (red)

How Flagella Move a Cell

Cilia• STRUCTURE:

– projections from the cell– made up of microtubules They are– motile and designed either to move

the cell itself or to movesubstances over or around the cell.

• FUNCTION– primary purpose of cilia in

mammalian cells is to move fluid,mucous, or cells over their surface.

• Cilia found in all animals, rare inplants, except cycads

•• Protozoans (ciliates) have only

motile cilia used for locomotionor to move liquid over theirsurface.

Motile cilia

• Some have groups of cilia fused together into largemobile projections called cirri (singular, cirrus).

• Larger eukaryotes, ex. mammals, have motile cilia• Motile cilia are present on a cell's surface in large

numbers and beating in coordinated waves.• In humans, for example, motile cilia are found in the

lining of the trachea (windpipe), where they sweepmucus and dirt out of the lungs.

• In the oviducts, the beating of cilia moves the ovumfrom the ovary to the uterus

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Non-motile cilia• usually occur one per cell• almost all mammalian cells have a single non-motile "primary

cilium."• primary cilium has historically been ignored by scientists• recent findings regarding its physiological roles in chemical

sensation, signal transduction, and control of cell growth, haveled scientists to re-evaluate its importance

• outer segment of the rod photoreceptor cell in the human eyeis connected to its cell body with a specialized non-motilecilium.

• dendritic knob of the olfactory neuron, where the odorantreceptors are located, is also carrying non-motile cilia (about10 cilia / dendritic knobs).,

• nematodes and arthropods only have non-motile cilia on somesensory nerve cells.

Only in Animal Cells:Centrioles

Centrioles

• Structure:– 9 triplets

• Functions• forms spindle fibres to separate chromosomes

during cell division of animal cells• Plant cells do not have centrioles

– In plant cell division, a centrosome does thisjob

Chloroplasts

• Found in plants, algaeand some bacteria.Responsible forcapturing sunlight andconverting it to food =photosynthesis.

• Surrounded by 2membranes

• And…contain DNA

Cell Wall

• Made of cellulose for rigidity• Function - to support plant cell

Vacuole• Structure

– Fluid pressure builds up in the vacuolecausing the cell to become elongated andextended increasing surface area and cellsize. It is bounded by a cell membrane.

• Function– In plants it can act as a

storage area for ions,metabolic products suchas sugars and aminoacids, and toxiccompounds.

– Its main functionhowever is to increasecell size and surfacearea so that theabsorption of ions isenhanced.

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Central Vacuole• Take up most of the cell’s internal space• Stores enzymes, wastes, anything that

needs to be kept separate from the rest ofthe cell

• contains water, and a place to store wastesthat may be harmful to the cell.

• can also store sugars and amino acids.• another essential function of the central

vacuole is that it provides turgor pressure.– the pressure of the water within the vacuole.– By pushing the fluid of the cytoplasm onto the

cell wall, the turgor pressure determines thecell's shape and is also able to provide support.