BIO 101 EXAM 2

Cell Membranes

• How diffusion works

• Movement of molecules from a high concentration to a low concentration; “down the concentration gradient” 

• Molecules move because they all have inherent energy 

• Enables us to predict overall direction of molecule movement 

• Solutes are eventually evenly distributed

• How materials move across a cell membrane – diffusion, osmosis, facilitated diffusion, active transport 

• Diffusion: Movement of molecules from a high concentration to a low concentration; “down the concentration gradient” 

• Osmosis: facilitated diffusion of water (high water concentration to low concentration of water via aquaporin) 

• Facilitated Diffusion: diffusion of large and charged molecules across the cell membrane through a protein

• A lot of specificity; not just one type of transport protein; each molecule needs their own transport protein 

• Active Transport: pumping molecules against their concentration gradient (low to high concentration); energy required (ATP) 

• Passive Transport: diffusion of molecules down the concentration gradient (high to low concentration); no energy required 

• Simple Diffusion: diffusion of small and uncharged molecules across cell membrane without help of protein 

• Reverse Osmosis: filtering of water through a semipermeable membrane; proposed solution to dwindling water resources 

• The composition and properties of the cell membrane 

• All cell membranes contain a fluid phospholipid bilayer (embedded proteins and cholesterol models)  

• Phospholipid: polar head (hydrophilic) and 2 non polar hydrophobic fatty acid tails  

• Phospholipid chemical structure impacts their role in the cell  

• Independent and can move 

• Cholesterols and fatty acids influence movement 

• Heads form hydrogen bonds with water and tails cluster within     

• More saturated fatty acids have less fluidity and are more dense, while unsaturated fatty acids have greater fluidity and are less dense

• protein : extra help 

•   Connection protein - cell adhesion, communication, structural stability, barrier formation

•   Enzyme - signal processing, substance metabolism, ATP Production, maintain cell environment, cell communication

• Receptor protein: signal reception, signal transduction, cell communication, regulation of cell activity, homeostasis maintenance

•   Transport proteins help bring large and charged molecules into the cell

• Be able to predict how solutes will move based on concentrations on either side of a cell membrane. 

• Solution: solvent plus solute combination

• Solvent: fluid that dissolves a solute (ex: water- universal solvent) 

• Solute: dissolved in a solvent (ex: sugar, salt, pigments) 

• Concentration: amount of solute in the solvent 

• Gradient: concentration between 2 solutions 

• A solution will move from a more concentrated solution to a less concentrated solution in order to establish equal concentration. 

• Be able to predict how water will move based on solute potential on either side of a cell membrane. 

• Water diffuses from areas of high solute potential to areas of low solute potential

• Solute potential is analogous to water concentration 

• Pure water has a solute potential of 0 megapascals 

• As solutes are added to water, solute potential and water concentration decreases (becomes more negative) 

• The fluid mosaic model 

• Membrane with a mosaic of embedded proteins and cholesterol  

• Impacts how the protein functions 

Energy and Enzymes

• Potential and Kinetic energy – what are some examples in our daily life? In a cell? 

• Potential Energy: stored energy, includes chemical energy (examples: batteries, fuel, biological molecules) 

• Kinetic Energy: energy of movement, includes radiant (electromagnetic radiation - light/xrays), thermal, electrical, falling (rollercoaster), running water, etc

• How enzymes work – their function and inhibition 

• Enzyme: biological catalysts that speed up chemical reactions by lowering activation energy without being consumed in the chemical reaction

• Most are proteins and specified to the substrate they act on; forms enzyme-substrate complex at active site 

• Shape of active site crucial for enzyme function; any alterations lead to activity loss.  

• Protein catalysts; catalase (promotes) reactions; only perform one reaction; each has a specific show which determines which reactants can enter 

• Break down reactions via hydrolysis and combine reactants via dehydration synthesis 

• Regulate metabolism (sum of all chemical reactions inside cell) 

• Metabolic pathway: sequence of linked reactions  

• Photosynthesis and glucose breakdown are metabolic pathways  

• Main takeaway: lots of reactions in the cell and every single one is regulated by enzymes  

• Metabolism needs to be regulated for cells to properly function; some promote enzyme actions and others inhibit enzyme action 

• Enzyme inhibitors (outside metabolism) - poisons and venoms 

• With an inhibitor, the active site changes shape so substance/reactant no longer fits 

• Examples of inhibitors: penicillin and aspirin, ibuprofen, anticancer drugs

• Environmental conditions influence enzyme activity 

• Shape sensitive to PH, temp, salt concentration, etc

• Enzyme max activity happens at about ph 7-8

• Most human enzymes max activity occurs at about 98.6 degrees farenheit 

Photosynthesis

• What are pigments? 

• Absorb visible light; different pigments absorb different light wavelengths, whereas others are reflected or transmitted

• The chemical reaction that describes photosynthesis – reactants and products 

• CO2+H2O+Light Energy = C6H12O6 (GLUCOSE) + H2O 

• The light reactions – what happens here? What is its purpose? Reactants, products. 

• Light energy is converted to chemical energy 

• Occurs in the thylakoids of the chloroplasts of plant cells  

• Chloroplasts: solar powered battery recharging stations 

• Thylakoids; transform light energy into chemical energy (ATP/NADPH)   

• Used to generate glucose  

• Split h2o, generates ATP and Nadph (energy carriers “batteries”) 

• Within the thylakoid membrane are PHOTOSYSTEMS - help recharge batteries  by capturing energy and transferring it to electrons 

• This movement drives photosynthesis  

• Main idea with thylakoid membrane: solar energy stored in the chemical bonds of ATP and NADPH   

• MAIN TAKEAWAY FROM LIGHT REACTIONS: energy (photons) from sun pass to electrons in photosystems (proteins) in the thylakoids 

• Electron movement through ETC (proteins) recharges energy of ATP/NADPH 

• The Calvin cycle – what happens here? What is its purpose? Reactants, products. 

• ATP/NADPH released to stroma where cycle takes place; CO2 and H2O fixed into glucose using ATP and NADPH as main energy source  

• TAKES PLACE IN STROMA OF CHLOROPLASTS!!   

• CO2 and H20 linked into sugar molecules during calvin cycle; process powered by chemical energy of ATP/NADPH generated from light reactions 

• Chemical energy stored in sugar molecules      

• Atp is consumed, not produced

• What is ATP, NAD (electron carriers) 

• ATP - vital molecule for energy transfer in cells  

• “Currency” for biological energy needed for various cellular processes, including conversion to ATP to be utilized for growth, movement and other cell functions  

• Made up of adenine, ribose and 3 phosphate groups (unstable while together) 

• Release of one phosphate group generates energy and transforms ATP into ADP (hydrolysis) 

• NAD - enzyme consisting of an adenine base and a nicotinamide group with 2 main forms: 

• NAD+ (oxidized form) that can accept electrons    

• NADH (reduced form) that carries the electrons after NAD+ has accepted them  

• Function: electron transport  and energy production 

• Role in metabolism: 

• Glycolysis and Calvin Cycle: NAD+ reduced to NADH when it picks up electrons in pathways  

• ETC: NADH donates its electrons to the ETC, where they pass thru a series of protein complexes driving ATP synthesis  

• Where is the electron transport chain found and what does it do?  

• THE BIG ATP PRODUCER!!

1. Electron carriers donate electrons 

2. Electrons are transported through membrane 

3. ETC stores energy from electron carriers to produce 32ATP

Cell Respiration and Fermentation

• The chemical reaction that describes cell respiration – reactants and products 

• Glucose plus oxygen produces energy (atp), Carbon dioxide and water 

• Formula for cellular respiration is the reverse of photosynthesis  

• Transforms glucose from food into usable energy (ATP) with oxygen as a neccesary component 

• Chemical reaction of cell respiration converts glucose and o2 into co2, water and energy

• Glycolysis in cytosol diffuses into the mitochondria, undergoes Krebs cycle and electrons are carried via NADH/FADH2 to ETC which yields 32 ATP 

• Glycolysis – what is this process and where does it occur?  

• Glucose breakdown: transfer chemical energy in glucose to chemical energy in ATP (plants and animals)  

• Occurs outside mitochondria of the cell (cytosol) 

• Pyruvate 2 (3 carbon sugars) 

• Generates 2 ATP molecules and 2 electron carrier molecules (NADH and FADH2) (NADH makes more ATP)

• Aerobic Respiration 

• Contains both the krebs cycle and electron transport chain 

• Breaks down pyruvate into carbon dioxide and water and ATP 

• 2 pyruvate molecules produces 34 ATP  

• Both plants and animals perform cell respiration

• The 3 different steps in cell respiration and what/how many is produced in each 

1. Glycolysis - outside of mitochondria generates 2 ATP and 2 pyruvate  

2. Aerobic respiration (inside of mitochondria)

• Krebs Cycle (citric acid cycle): breaks pyruvate down; occurs inside the mitochondria 

• Pyruvate comes in and chemical reactions occur to produce electron carriers  

• Input: 2 pyruvate molecules , NAD+, ADP, and water

• Output:  3 NADH, 1 ATP, 2 CO2

3. Electron Transport Chain (ETC)   

• Occurs within inner membrane of the mitochondria 

• INPUT: oxygen and multiple electron carriers 

• OUTPUT: 32 atp and water 

• How are mitochondria and chloroplasts similar in terms of their form and function? 

• Double membrane structure: both have an outer membrane and an inner membrane 

• Inner membrane is both highway folded which form structures that increase the surface area for chemical reactions to take place. 

• Energy Conversion: 

• Mitochondria convert chemical energy from nutrients (ex: glucose) into ATP via cell respiration 

• Chloroplasts convert light energy stored in glucose through photosynthesis

• Presence of DNA and Ribosomes: both have their own circular DNA and Ribosomes

• Endosymbiotic Origin: both believed to have originated from endosymbiosis (theory proposing they were once free living prokaryotes engulfed in a host cell) 

• Proton Gradient for ATP Production: generate proton gradient across inner membranes as part of energy conversion

• Role in Energy Metabolism: essential for energy metabolism in cells 

• Where is the electron transport chain found and what does it do? 

• Found in the inner mitochondrial membrane 

• Electrons are transferred through the chain from NADH and FADH2 to oxygen (final electron receptor) forming water molecules. 

• What is fermentation and when does it occur? 

• Energy extraction without oxygen; in anaerobic conditions; occurred before photosynthesis produced oxygen 

• What are the different types of fermentation and what are the waste products? 

•  Lactic acid - produces lactic acid and atp 

• Animal cells with low oxygen 

• Converts pyruvate to lactic acid as a waste product 

• Muscles use up all oxygen; lactic acid thought to cause soreness in muscles 

• Bacteria use this, and can convert milk into yogurt and cheese 

• Alcohol - produces alcohol and atp  

• Pyruvate is converted into alcohol (ethanol) and carbon dioxide as a byproduct 

• Yeast cells do the work 

• Example is brewing beer 

• Both produce pitiful amounts of atp  

• Glycolysis still happens (only 2 atp per glucose); inefficient and only way to do it without oxygen  

• How efficient is fermentation? 

• Much less efficient than cellular respiration in terms of ATP production: 

• Produces only 2 ATP 

• Glucose is partially oxidized  

• Only captures about 2% of glucose’s energy as ATP 

• How do humans take advantage of fermentation?  

• Food Production: 

• Breadmaking 

• Alcoholic Beverages 

• Dairy Products 

• Fermented Vegetables

• Food Preservation: byproducts of fermentation (lactic acid and ethanol) inhibit harmful bacteria growth and therefore extending shelf life of foods

• Health: 

• Probiotics: beneficial bacteria that support gut health and digestion 

• Nutrient Bioavailability: breaks down complex molecules in food which makes nutrients more accessible

• Biofuel Production: microbes ferment plant sugars into ethanol which can be used as a renewable energy source

• Strenuous Exercise: cells switch to lactic acid fermentation to meet energy demands when there is a limited oxygen supply 

Be able to apply your knowledge of respiration and photosynthesis to monarchs and milkweed 

• Monarchs and milkweed are in a mutualistic relationship; both benefit from each other

• Migration powered by muscle contractions (atp); ingest nectar as chemical energy and convert it to chemical energy (atp)  and/or store it as starch and fats for later   

• Nectar made up of glucose, sucrose and fructose  

• Milkweed uses to 2 different enzymes to make nectar via enzymbolic reactions that are reversible (can form and break bonds

1. Phosphate Isomerase - converts glucose into fructose

2. Sucrose Synthase - converts fructose into sucrose