Packet 6 Cellular Energy

ATP: cellular energy

Why do cells need energy? Cells carry out three kinds of energy-requiring work: Chemical Mechanical Transport Examples of work: Chemical work: dehydration synthesis reactions Mechanical: muscle contraction Transport: shuttling molecules across the membrane with transport proteins (active transport)

Making ATP: Aerobic cellular respiration

glucose      pyruvate Glycolysis (Stage 1) Breaking down glucose “glyco – lysis” (splitting sugar) Occurs in the cytoplasm A little ATP energy is harvested, but it’s inefficient generate only 2 ATP for every 1 glucose glucose      pyruvate 2x 6C 3C

Substrate-level phosphorylation Substrate-level phosphorylation Overview 10 reactions convert glucose (6C) to 2 pyruvate (3C) produces: 4 ATP & 2 NADH consumes: 2 ATP net yield: 2 ATP & 2 NADH Substrate-level phosphorylation 1st ATP used is like a match to light a fire… initiation energy / activation energy. Destabilizes glucose enough to split it in two Substrate-level phosphorylation

Products of glycolysis move on to stage 2 or 3

Mitochondria — Structure Double membrane smooth outer membrane highly folded inner membrane intermembrane space Matrix DNA, ribosomes enzymes intermembrane space inner membrane outer matrix cristae intermembrane space fluid-filled space between membranes matrix inner fluid-filled space enzymes free in matrix & membrane-bound mitochondrial DNA

Stage 2: Pyruvate grooming and the Kreb’s Cycle This happens twice for each glucose molecule that started glycolysis…why? A 2 carbon sugar went into the Krebs cycle and was taken apart completely. Two CO2 molecules were produced from that 2 carbon sugar. Glucose has now been fully oxidized! But where’s all the ATP???

Cellular respiration

Electron Transport Chain and Chemiosmosis: ATP payoff! series of proteins built into inner mitochondrial membrane

Remember the Electron Carriers? Krebs cycle Glycolysis 2 NADH 8 NADH 2 FADH2 Time to break open the piggybank!

Electron Transport Chain What powers the proton (H+) pumps?… NADH  NAD+ + H H  e- + H+ Electronegativity!

Chemiosmosis and oxidative phosphorylation Ideally, each NADH yields 3 ATP; each FADH2 yields 2 ATP oxidative phosphorylation

~38 ATP Cellular respiration + + 2 ATP 2 ATP 34 ATP

Summary of cellular respiration C6H12O6 6O2 6CO2 6H2O ~34-38 ATP  + Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What is recycled for use again? Why do we breathe? Where did the glucose come from? from food eaten Where did the O2 come from? breathed in Where did the CO2 come from? oxidized carbons cleaved off of the sugars (grooming & Krebs Cycle) Where did the CO2 go? exhaled Where did the H2O come from? from O2 after it accepts electrons in ETC Where did the ATP come from? mostly from ETC What else is produced that is not listed in this equation? NAD, FAD, heat!

Taking it beyond… What is the final electron acceptor in Electron Transport Chain? O2 So what happens if O2 unavailable? ETC backs up nothing to pull electrons down chain NADH & FADH2 can’t unload H ATP production ceases cells run out of energy What if you have a chemical that punches holes in the inner mitochondrial membrane?

Anaerobic respiration Making ATP without oxygen

All cells carry out glycolysis: prokaryotes and eukaryotes. Eukaryotes and many prokaryotes also carry out oxidative phosphorylation (remember this requires oxygen). How can some bacteria carry out aerobic respiration if they don't have mitochondria? FUN FACT: many bacteria have ETC’s in their cell membranes.

Reminders! New considerations A net of 2 ATP is generated in glycolysis. NAD+ must be present available for this process. New considerations For aerobic organisms this is not a problem, NAD+ is regenerated by the ETC. Not all organisms can use oxygen, they are anaerobic Anaerobic organisms use glycolysis only to make ATP They regenerate , NAD+ through fermentation processes Fermentation is the pathway that some prokaryotes always have to take (obligate anaerobes). This pathway is also used by prokaryotes and yeasts that are facultative anaerobes. Fermentation is also used by your own muscles when you are working out strenuously and gas exchange is not happening fast enough to replenish ATP through oxidative phosphorylation.

Alcohol fermentation Bacteria and yeast NADH is recycled back to NAD+ when pyruvate is converted to ethanol. Alcohol is released into the organism's environment as waste. Fun fact: Bubbles in beer and champagne are CO2 released in the conversion of pyruvate to alcohol.

Lactic acid fermentation Animals, fungi NADH is recycled back to NAD+ when pyruvate is converted to lactate (enzyme-catalyzed) Once O2 is available, lactate is converted back to pyruvate by the liver Cells can then resume aerobic respiration using pyruvate (starts Stage 2).

Review: Answer all of the following questions in your notebook. What are the products of pyruvate grooming for 1 molecule of glucose? What are the products of the citric acid cycle for 1 molecule of glucose? After glycolysis, pyruvate grooming, and the citric acid cycle, what are your net products? What is phosphorylation? What is substrate-level phosphorylation? What is the main goal for stages 1-3?

Review: Answer all of the following questions in your notebook What is the summary equation for cellular respiration? If oxidation is a loss of electrons (in the form of hydrogen atoms) and reduction is the gain of electrons (in the form of hydrogen atoms), what is oxidized during cellular respiration? what is reduced during cellular respiration? How does glucose get to your cells for cellular respiration? What is the point of cellular respiration? What are the net molecular products of glycolysis?

Where does glucose come from for cellular respiration? Photosynthesis!

Photosynthesis

Leaf structure Mesophyll cells Vascular tissue Stomate Guard cells

Chloroplast structure Double membrane Grana Thylakoid Stroma

Light-dependent reactions Stage 1: Light-dependent reactions Photosynthesis is a net endergonic reaction because there is more energy in the bonds of glucose than there are in the bonds of the reactants. Light energy is converted to chemical energy (as NADPH and ATP). Glucose is made from CO2 and hydrogens carried by NADPH using ATP energy. Stage 2: Calvin cycle

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Calvin cycle 1. A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2 dissolved in the stroma. This process, called CO2 fixation, is catalyzed by the enzyme RuBP carboxylase, forming an unstable six-carbon molecule. This molecule quickly breaks down to give two molecules of the three-carbon 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA). 2. The two 3PG molecules are converted into glyceraldehyde 3-phosphate (G3P, a.k.a. phosphoglyceraldehyde, PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADH + H+. 3. Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose.

What factors might affect the rate of photosynthetic reactions? SUMMARY What factors might affect the rate of photosynthetic reactions? 37