Tour of the Cell 2012-2013

I. Why do cells have organelles (little organs)? mitochondria I. Why do cells have organelles (little organs)? 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

II. Isolation of organelles A. Occurs by process of cell fractionation II. Isolation of organelles A. Occurs by process of cell fractionation. B. Based on various densities of organelles. C. Begins with breaking open cell membranes without damaging organelles; Called homogenization.

Homogenate is spun in a centrifuge to separate the pellet of organelles from the liquid (supernatant). Pellet is removed, and the supernatant is spun again at higher speed to cause heaviest of remaining organelles to settle out.

Heaviest to lightest cell fractions are nuclei, mitochondria/chloroplasts, parts of membranes, then ribosomes. G. Specific metabolic processes are identified with certain cell fractions, and then tied to specific organelles.

(Show “Cell Fractionation Animation” from microbiology web site.)

Prokaryote bacteria cells Eukaryote animal cells Types of cells Prokaryote bacteria cells Eukaryote animal cells Eukaryote plant cells

II. General Types of cells Basic cell structures 1. Plasma membrane 2. Cytosol (jelly-like substance) 3. Ribosomes 4. DNA B. Prokaryotic cells have DNA in nucleiod region; No membrane around DNA.

C. Eukaryotic cells have DNA in membrane-bound nucleus. D. Eukaryotes also have membrane-bound organelles floating in cytoplasm (region between nucleus and cell membrane). E. Eukaryotes are bigger than prokaryotes.

F. Eukaryotes have many internal membranes that divide internal space into compartments. G. Compartmentalization allows for multiple metabolic processes to occur at the same time.

Limits to cell size Lower limit Upper limit smallest bacteria mycoplasmas 0.1 to 1.0 micron (µm = micrometer) most bacteria 1-10 microns Upper limit eukaryotic cells 10-100 microns micron = micrometer = 1/1,000,000 meter diameter of human hair = ~20 microns

Why is a huge single-celled creature not possible? What limits cell size? Surface to volume ratio as cell gets bigger its volume increases faster than its surface area smaller objects have greater ratio of surface area to volume Why is a huge single-celled creature not possible? square - cube law As cell gets larger, volume increases cubically, but surface area only increases by the square. The volume of the cell is demanding… it needs exchange. The surface area is the exchange system… as cell gets larger, the surface area cannot keep up with demand. Instead of getting bigger, cell divides -- mitosis. s:v 6:1 ~1:1 6:1

Limits to cell size Metabolic requirements set upper limit in large cell, cannot move material in & out of cell fast enough to support life O2 aa CHO CH CO2 NH3 aa O2 CH CHO CO2 What process is this? diffusion What’s the solution? cell divides make a multi-celled creature = lots of little cell, rather than one BIG cell aa NH3 CHO CH O2 aa What’s the solution?

How to get bigger? Become multicellular (cell divides) aa O2 aa aa aa But what challenges do you have to solve now? aa CO2 NH3 O2 CH CHO aa O2 CH CHO CO2 Larger organisms do not generally have larger cells than smaller organisms — simply more cells What’s challenges do you have to solve now? how to bathe all cells in fluid that brings nutrients to each & removes wastes from each aa NH3 CHO CH O2 aa

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

Why study protein production? proteins DNA cells organism Repeat after me… DNA gets the glory, but Proteins do all the work!

Building Proteins Organelles involved nucleus ribosomes endoplasmic reticulum (ER) Golgi apparatus vesicles The Protein Assembly Line Golgi apparatus nucleus ribosome ER vesicles

Making proteins Putting it together… cytoplasm nucleus cell membrane transport vesicle Golgi apparatus smooth ER rough ER nuclear pore nucleus ribosome cell membrane protein secreted cytoplasm

endoplasmic reticulum TO: nucleus protein on its way! TO: DNA RNA vesicle TO: TO: vesicle ribosomes TO: protein finished protein Golgi apparatus Making Proteins

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

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

Where old organelles go to die! 1960 | 1974 Lysosomes Christian de Duve Function little “stomach” of the cell digests macromolecules “clean up crew” of the cell cleans up broken down organelles Structure vesicles of digestive enzymes Where old organelles go to die! only in animal cells

Lysosomal enzymes Lysosomal enzymes work best at pH 5 organelle creates custom pH how? proteins in lysosomal membrane pump H+ ions from the cytosol into lysosome why? enzymes are very sensitive to pH enzymes are proteins — pH affects structure why is this an adaptation: digestive enzymes which function at pH different from cytosol? digestive enzymes won’t function well if some leak into cytosol = don’t want to digest yourself! lysosomes create a space where cell can digest macromolecules safely rupturing a few lysosomes has little impact on a cell (pH of cytosol affects functionality of the lysosomal enzymes), but massive leakage from lysosomes can destroy cell why evolve digestive enzymes which function at pH so different from cytosol? digestive enzymes won’t function well if leak into cytosol = most times don’t want to digest yourself! low pH = acid environment cause oxidation (removing electrons) & promotes hydrolysis

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 ex: self-destruct of cancerous cell 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.

syndactyly Fetal development 6 weeks 15 weeks

When things go wrong… 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

From food to 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 = immediate energy carbohydrates = stored energy ATP ATP +

Mitochondria & Chloroplasts Lynn Margulis U of M, Amherst 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

Membrane-bound Enzymes glucose + oxygen  carbon + water + energy dioxide C6H12O6 6O2 6CO2 6H2O ATP  +

Membrane-bound Enzymes + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  +

Mitochondria are everywhere!! animal cells plant cells

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

Cytoskeleton Function structural support motility regulation maintains shape of cell provides anchorage for organelles protein fibers microfilaments, intermediate filaments, microtubules motility cell locomotion cilia, flagella, etc. regulation organizes structures & activities of cell

Cytoskeleton actin microtubule nuclei

Centrioles Cell division in animal cells, pair of centrioles organize microtubules guide chromosomes in mitosis

Cell Size 2012-2013

Limits to cell size Lower limit Upper limit smallest bacteria mycoplasmas 0.1 to 1.0 micron (µm = micrometer) most bacteria 1-10 microns Upper limit eukaryotic cells 10-100 microns micron = micrometer = 1/1,000,000 meter diameter of human hair = ~20 microns

Why is a huge single-celled creature not possible? What limits cell size? Surface to volume ratio as cell gets bigger its volume increases faster than its surface area smaller objects have greater ratio of surface area to volume Why is a huge single-celled creature not possible? square - cube law As cell gets larger, volume increases cubically, but surface area only increases by the square. The volume of the cell is demanding… it needs exchange. The surface area is the exchange system… as cell gets larger, the surface area cannot keep up with demand. Instead of getting bigger, cell divides -- mitosis. s:v 6:1 ~1:1 6:1

Limits to cell size Metabolic requirements set upper limit in large cell, cannot move material in & out of cell fast enough to support life O2 aa CHO CH What process is this? CO2 NH3 aa O2 CH CHO CO2 What process is this? diffusion What’s the solution? cell divides make a multi-celled creature = lots of little cell, rather than one BIG cell aa NH3 CHO CH O2 aa What’s the solution?

How to get bigger? Become multicellular (cell divides) aa O2 aa aa aa But what challenges do you have to solve now? aa CO2 NH3 O2 CH CHO aa O2 CH CHO CO2 Larger organisms do not generally have larger cells than smaller organisms — simply more cells What’s challenges do you have to solve now? how to bathe all cells in fluid that brings nutrients to each & removes wastes from each aa NH3 CHO CH O2 aa

Cell membrane Exchange structure plasma membrane functions as selective barrier allows passage of O2 & nutrients IN allows passage of products & wastes OUT Phospholipid Cholesterol Membrane proteins

Any Questions?? 2012-2013