Tour of the Cell 1 2007-2008

Prokaryote bacteria cells Eukaryote animal cells Types of cells - no organelles - organelles Eukaryote animal cells Eukaryote plant cells

Why organelles? mitochondria chloroplast Golgi ER Specialized structures specialized functions cilia or flagella for locomotion Containers partition cell into compartments create different local environments separate pH, or concentration of materials distinct & incompatible functions lysosome & its digestive enzymes Membranes as sites for chemical reactions unique combinations of lipids & proteins embedded enzymes & reaction centers chloroplasts & mitochondria chloroplast Golgi Why organelles? There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions. Organelles as specialized structures An example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move. Organelles as Containers Nothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it. Organelle membranes as sites for chemical reactions An example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast. ER

Cells gotta work to live! What jobs do cells have to do? make proteins proteins control every cell function make energy for daily life for growth make more cells growth repair renewal

Building Proteins Organelles involved Nucleus Ribosomes Protects DNA Bound by double membrane that is covered in pores (openings) Darker center region that produces ribosomes Contains nucleolus Ribosomes Complex of 2 subunits Site of protein production 2 types Free – suspended in cytoplasm Synthesizes proteins that remain in cytoplasm Bound – attached to rough ER Synthesizes proteins to be exported or for membrane

Building Proteins continued… endoplasmic reticulum (ER) Processes proteins, manufactures membranes, used in synthesis and hydrolysis of compounds for rest of cell/body 2 kinds Rough er – studded with ribosomes Works with proteins that will be exported out of cell Large amounts found in pancreatic cells which secrete enzymes for digestion Smooth er – no attached ribosomes Synthesizes lipids Hydrolyzes macromolecules into smaller, usable molecules and detoxifies drugs and poisons Golgi apparatus Sorts and ships cell products Both around and out of cell

ATP Cells need power! Making energy take in food & digest it take in oxygen (O2) make ATP remove waste ATP

Making Energy Cells must convert incoming energy to forms that they can use for work mitochondria: from glucose to ATP chloroplasts: from sunlight to ATP & carbohydrates ATP = active energy carbohydrates = stored energy ATP ATP +

Mitochondria & Chloroplasts Important to see the similarities transform energy generate ATP double membranes = 2 membranes semi-autonomous organelles move, change shape, divide internal ribosomes, DNA & enzymes

Endosymbiosis theory 1981 | ?? Mitochondria & chloroplasts were once free living bacteria engulfed by ancestral eukaryote Endosymbiont cell that lives within another cell (host) as a partnership evolutionary advantage for both one supplies energy the other supplies raw materials & protection Lynn Margulis From hypothesis to theory! Paradigm shifting ideas in evolutionary biology. Lynn Margulis U of M, Amherst

Evolution of eukaryotes Endosymbiosis theory Evolution of eukaryotes

Vacuoles & vesicles Function little “transfer ships” Food vacuoles phagocytosis, fuse with lysosomes Contractile vacuoles in freshwater protists, pump excess H2O out of cell Central vacuoles in many mature plant cells

Where old organelles go to die! Lysosomes Function little “stomach” of the cell digests macromolecules “clean up crew” of the cell cleans up broken down organelles Structure vesicles of digestive enzymes synthesized by rER, transferred to Golgi only in animal cells

When things go bad… Diseases of lysosomes are often fatal digestive enzyme not working in lysosome picks up biomolecules, but can’t digest one lysosomes fill up with undigested material grow larger & larger until disrupts cell & organ function lysosomal storage diseases more than 40 known diseases example: Tay-Sachs disease build up undigested fat in brain cells

But sometimes cells need to die… Lysosomes can be used to kill cells when they are supposed to be destroyed some cells have to die for proper development in an organism apoptosis “auto-destruct” process lysosomes break open & kill cell ex: tadpole tail gets re-absorbed when it turns into a frog ex: loss of webbing between your fingers during fetal development Feedback mechanism There are sensors in the cell that monitor growth. They trigger self-destruct when they sense processes. Brown spots on leaves too. Virus infected plant cell auto-destructs and even cells around it to wall off virus.

Peroxisomes Other digestive enzyme sacs in both animals & plants breakdown fatty acids to sugars easier to transport & use as energy source detoxify cell detoxifies alcohol & other poisons produce peroxide (H2O2) must breakdown H2O2  H2O

Cells need to make more cells! Making more cells to replace, repair & grow, the cell must… copy their DNA make extra organelles divide the new DNA & new organelles between 2 new “daughter” cells organelles that do this work… nucleus centrioles

Centrioles Function Structure help coordinate cell division one pair in each cell “motor” proteins