1/18/2018. BIO 1101 Lecture 4 Chapters 4 & 5: Cells & The Working Cell. What is a Cell?

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1 BIO 1101 Lecture 4 Chapters 4 & 5: Cells & The Working Cell What is a Cell? The lowest level of structure that can perform all activities required for life. All organisms are made of cells Some organisms are single-celled: Bacteria Most Protists (i.e. amoeba, paramecium, etc.) Some organisms are multicellular: Plants, Animals, most Fungi and some Protists History of Microscopy Thanks to the invention of the light microscope, cells were first observed in 1665, by Robert Hooke mid-1800s -- Cell Theory Light Microscopes: Visible light passes through very thin slices of organisms, or very small organisms Glass lenses enlarge the subject Magnification = how much larger the object appears compared to its actual size (2X, 10X up to 1000X) Resolving Power = ability to show two objects as separate 1930s to 1950s Development of Electron Microscopes Uses beams of electrons instead of light Up to 10,000,000X magnification power Cells must be prepared and killed in order to view under electron microscopy Visualize organelles & cell surfaces Cell Types 2 Major Classes of Cells: Prokaryotic: Bacteria and Archaea No nucleus (nucleoid region instead) Smaller cells Eukaryotic Cells: 1

2 Possess membrane-bound organelles i.e., nucleus, mitochondria, endoplasmic reticulum, etc. Larger cells Found in protists, plants, fungi and animals Eukaryotic Cell Structure Both Plant and Animal Cells Have: Plasma membrane Surrounds cell and regulates movement of molecules into and out of cell Cytoplasm (cytosol + organelles) Nucleus Endoplasmic reticulum Golgi apparatus Mitochondria Ribosomes Etc. Animal Cell Plant Cells Have some structures not found in animal cells Cell Wall (rigid outer layer) Chloroplasts (for photosynthesis) Central vacuole (stores water) (see Figure 4.3) Plant Cell Nucleus Has a double membrane Contains DNA DNA is attached to proteins, forming long fibers called chromatin Each fiber = a chromosome Also contains a nucleolus (produces ribosome parts) 13 Ribosomes Small dots outside of nucleus Build proteins How? 2 Processes: Transcription (in nucleus: DNA mrna) Translation (in cytoplasm on ribosome: RNA Protein) Ribosomes use coded instructions from the DNA to build proteins, and those instructions are carried to the ribosomes out in the cytoplasm on a molecule called 2

3 mrna The Endomembrane System Includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles Some of these organelles have their membranes directly connected to each other For example, the nuclear membrane and the endoplasmic reticulum Others are connected indirectly, as pieces of membrane break off and are transferred among them For example, when a piece of endoplasmic reticulum buds off as a vesicle, and then fuses with the Golgi apparatus Endoplasmic Reticulum (ER) Two types: Smooth ER and Rough ER 17 Rough ER Looks bumpy due to presence of ribosomes Functions include Making more membrane Ribosomes produce proteins that get inserted into the membrane Cells in your mouth that secrete saliva have a lot of rough endoplasmic reticulum, which produces the enzyme saliva Gets carried to cell surface and secreted Other proteins produced by these ribosomes may be packaged and transported to other parts of the cell 18 Smooth ER Smooth appearance due to lack of ribosomes found in the rough ER Enzymes built into the smooth ER allow it to carry out many functions, including synthesis of steroid hormones So, cells in the testes and ovaries, which produce hormones testosterone and estrogen, are rich in smooth ER In liver cells, the smooth ER helps remove toxins/drugs A person s liver cells will increase in smooth ER as they are exposed to more of these drugs This can lead to tolerance to drugs, and potentially addiction Can also make certain drugs like antibiotics less effective 3

4 Golgi Apparatus Refines, stores, and distributes ER products LE LE LE Lysosomes (in animal cells; absent from most plant cells) A little sac of digestive enzymes (enzymes = proteins that catalyze (facilitate) a chemical reaction) A safe location for digestion Digest food, but also destroy harmful bacteria and recycle worn-out organelles Vacuoles Sacs that have budded from the ER, Golgi, or plasma membrane Different types of vacuoles: Food vacuoles Contractile vacuoles (regulate water) Central vacuole in plant cells very large, for storage of nutrients, water, pigments, or poisons LE 6-14a LE 6-14b Chloroplasts (in plants & protists) Site of photosynthesis Surrounded by a double membrane Inside, filled with thick fluid called stroma Suspended in that fluid are stacks of disks called grana LE 6-18 Mitochondria (found in essentially all eukaryotes plants, animals, protists and fungi) The site of Cellular Respiration The process where energy is obtained from food molecules This energy is stored in a molecule called ATP (adenosine triphosphate) 4

5 LE 6-17 Cilia and Flagella Extend from some cells to allow them to move, or to move the solution around the cell Cilia are shorter and usually more numerous than flagella Examples of ciliated cells found on many protists (a whole group of protists are actually called Ciliates) they are also found in certain cells of larger organisms (such as the lining of your windpipe) Examples of flagellated cells Sperm cells move using a single flagellum Many protists and bacteria move using one or more flagella Cilia Break Cells are Surrounded by Membranes Fluid Mosaic Model of membranes Cell membranes are composed of a double-layer of phospholipids Within the phospholipids are embedded proteins Membrane Transport: How do substances move across a semipermeable membrane? Materials can be exchanged across a membrane in two ways Active transport (e.g. using ATP and transport proteins) Passive transport (no energy input required) Passive Transport Mechanisms Osmosis = movement of water from an area of low solute concentration to area of high solute concentration Diffusion = movement of solute from area of high solute concentration to low solute concentration Comparing solute concentrations of two solutions: 5

6 Hypertonic = the solution with the greater concentration of solultes Hypotonic = the solution with the lower concentration of solutes Isotonic = two solutions with equal solute concentrations Diffusion Passive transport is important in cells Example: it is the mechanism by which oxygen enters, and carbon dioxide exits, red blood cells diffusion Water also passes across membranes passively, via process of osmosis Moves from hypotonic solution to hypertonic solution Now, let s define diffusion using the terms hypertonic, hypotonic, and isotonic In Active Transport, a cell spends energy to pump molecules across the membrane against their concentration gradient From low to high concentration Uses ATP Passive transport and protein pumps work to move small molecules or ions across membranes For large molecules (such as proteins or carbohydrates), a different mechanism is needed Endocytosis and Exocytosis The Working Cell The earth is solar-powered The energy in our food can be traced back to the sun Plants and some protists capture that energy from the sun and store it in organic molecules such as sugars and carbohydrates via photosynthesis Plants are called Producers or Autotrophs Some Basic Energy Concepts What is energy? The capacity to do work Energy can neither be created nor destroyed; it can only be converted into another form = law of conservation of energy (1 st Law of Thermodynamics) Kinetic energy is the energy of motion Dropping an object 6

7 Potential energy is energy that is stored Lifting an object and putting it on a shelf Entropy A measure of disorder, or randomness There is a tendency toward disorder in the universe (= the 2nd Law of Thermodynamics) Chemical Energy A form of potential energy Due to the arrangement of atoms in a molecule Molecules such as carbohydrates, fats, and gasoline store much energy in their chemical bonds A larger molecule, with many bonds, is broken down into smaller waste products; as the bonds break, energy is released Cellular Respiration NOT the same as breathing (although they are related) Releases energy when food molecules are broken down Process occurs in the mitochondria of both plant and animal cells C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O +ATP Calories How many calories in a large order of fries at McDonalds? what does this mean? A Calorie is the amount of energy that raises the temperature of 1 gram of water by 1 degree Celsius. Calories are tiny units of energy, so it is more practical to use kilocalories to describe energy content of food ( calories listed on packages are actually kilocalories remember, kilo = 1,000) A 150-lb person would have to run for over 50 minutes to use up the energy in one large order of fries! (see: calorielab.com website) How do organisms obtain energy from food? The energy stored in the bonds of food molecules is released when broken down in cellular respiration That energy is transferred to molecules called ATPs (adenosine triphosphate) Adenosine is an organic molecule; three negatively charged phosphate groups are 7

8 attached The phosphate groups repel each other and readily transfer from ATP to other molecules This transfer of a phosphate group to another molecule is what causes cells to do work ATP can do 3 kinds of work: It may cause a protein to contract ( mechanical work ) It may facilitate pumping of molecules across a membrane ( transport work ) It may facilitate a chemical reaction ( chemical work ) LE 8-9 When a phosphate group is lost from an ATP, the molecule become Adenosine Diphosphate (ADP) ATP is renewable, though another phosphate group can be added back to the ADP, making it ATP again The energy for restoring ATP from ADP is obtained through cellular respiration (See Figure 5.6) LE 8-12 Enzymes Enzymes are proteins that speed up chemical reactions Chemical reactions involve breaking bonds in the reactant molecules This activation energy can come from heat Alternatively, enzymes can lower the amount of activation energy necessary for reaction Binds to reactant molecules, putting them in physical or chemical stress Enzyme specificity Unique shape of each enzyme fits only specific substrates Active site = location of binding to substrate Induced fit = a change in shape of the enzyme once bound to the substrate, to catalyze a reaction After catalyzing a reaction, the product(s) are released, and the enzyme is capable of catalyzing another reaction Enzyme inhibitors 8

9 Some molecules block enzyme function by Acting as a substrate imposter and blocking the active site Binding to another portion of the enzyme and changing its shape Beneficial uses of enzyme inhibitors Feedback regulation (e.g. blocking production of some substance in your body once you ve produced enough of it) Often reversible Many antibiotics also work by inhibiting enzymes in bacterial cells Poisons that are enzyme inhibitors The insecticide Malathion inhibits an enzyme needed in the nervous system of insects All for today, except Random Animal of the Day! The Northern Hairy Nosed Wombat! A critically endangered marsupial in Australia Scientists working on artificial insemination to save the species Large heads, short legs, and strong claws to dig their burrows Detect food (grasses and roots) by smell 9