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Unit 4 Cellular Energetics
Photosynthesis (10) and Cellular Respiration (9)
Basic Key Terms
Heterotroph Autotroph Photoautotroph Consumer Producer
Structure of a Chloroplast
Parts of a Leaf
Mesophyll- interior tissue Stoma/stomata- pores that let gases in/out
Random FYI- about 30-40 choroplasts in a typical mesophyll cell
Calculate- if you crushed 100 mesophyll cells in spinach leaves, approximately how many chloroplasts did you open up?
light
6CO2 + 6H2O C6H12O6 + 6O2
**plants don’t actually make glucose, but a 3 carbon
sugar! Why do you think earlier biology classes tell you that glucose is made during photosynthesis?
Intro to Photosynthesis WS
Study off of the big ideas on that paper!
How does light work?
Pigments in photoautotrophs
Bottom picture, bacteria grow near largest
amounts of oxygen
If a plant only gets a single wavelength you can see which the plant
uses.
IMPORTANT BIG IDEA!!!
How do we know…
That the oxygen comes from the water and not the carbon dioxide???
1930’s researchers at Stanford Univ. found bacteria that use hydrogen sulfide instead of water for photosynthesis
They create a visible yellow waste product- and sulfur is yellow!
Purple sulfur bacteria
Further evidence
Set up photosynthesis experiments using water containing a 18O
Heavy oxygen formed only when water was split.
When carbon dioxide was split, normal O formed
THEREFORE Chloroplasts split water, then add Carbon
dioxide
Interesting and important, but unlikely to be asked to recall this exact experiment on the AP exam.
P.S. overview
Light reaction In thylakoids Water + light in Oxygen out
Calvin cycle In stroma Carbon dioxide in Sugar out
Batteries of P.S. e- from H in water given
to NADP+ making NADPH
Photophosphorylation- changing ADP ATP with light energy
Important summary! New AP exam will not ask you to recite each step of the Calvin cycle or eTC.
Calvin Cycle
Named for Melvin Calvin who worked to figure out the mechanism in the 1940’s
Uses process called carbon fixation
Aka dark reactions or light independent reactions
Chlorophyll gets excited by light!
SCIENCE- an e- moves to a higher energy orbital when a photon of light hits it
Each pigment gets excited by a different wavelength of light
Fluorescence- after glow of e- falling back to ground state, releasing heat
Photosystems
2 Photosystems in thylakoids
Photosystem II Reaction center called P680 because it absorbs
680nm light best (red spectrum) Chlorophyll a in reaction center Happens 1st!!!
Photosystem I Reaction center called P700 because it absorbs
700nm light best ( far red spectrum) Chlorophyll a in reaction center Happens 2nd!!!
Important! The PS labs are measuring the rate of the light reaction, so you do need to understand how it works.
Noncyclic electron flow mechanism for PS- main method
Translation from molecules to people
Cyclic electron flow- 2nd method
Purpose- to make ATP alone Why?- calvin cycle uses up ATP faster than
NADPH When?- when the calvin cycle is running low Trigger?- extra NADPH forms as calvin cycle
slows down
Cyclic electron flow mechanism for PS- no photosystem II
Chemiosmosis- making ATP
Calvin Cycle broken down
Phase 1- carbon fixation Carbon dioxide + ribulose biphosphate using RuBP carboxylase (aka rubisco) 1C + 5C 6C two 3C (3
phosphoglycerate) Phase 2- reduction
3C + ATP 1,3 biphosphoglycerate 2e- from NADPH reduce 1,3 biphospho. To G3P
(3C sugar for energy storage)
Reviewing this as an exercise because you DO need to know how to read these diagrams for the AP exam. Important concepts in red!
Calvin cycle broken down
Phase 3 regeneration of rubisco 5 molec. G3P rearranged to 3 molec rubisco
ATP net usage =9 NADPH net usage=6 Light reactions regenerate ATP and NADPH G3P NOT used to make rubisco is starting
material for other chem reactions
Calvin cycle visual
Video clips of PS mechanisms
Put the following terms in the correct order:
Electron transport chain, Calvin cycle, photosystem I, RuBP forms, photosystem II, split water, electron transport chain , carbon fixation, G3P forms, ATP synthase
Alternative forms of PS: C3 and C4
WHY? Dehydration HOW? When stomata open to release
oxygen, and gain carbon dioxide they also lose water (transpiration)
Photorespiration- use oxygen in place of carbon dioxide in calvin cycle, 2C compounds are made, sent to mitochondria and broken into carbon dioxide
Side effects of C3 plants
Produce less sugar from PS Produce less ATP Theory- this started when atmosphere had
more carbon dioxide and less oxygen
Rice, wheat, soy beans
C4 alternate to carbon fixation
C4 PS in words (sugarcane)
2 types of PS cells Mesophyll, bundle sheath cells
Carbon dioxide + PEP (phosphophenol pyruvate) oxaloacetate, using enzyme PEP carboxylase
Oxaloacetate (4C) malate (4C) 4C compound to bundle sheath cells via
plasmodesmata 4C releases carbon dioxide for calvin cycle
CAM PS
CAM PS in words
Succulents, cacti, pinapples Open stomata at night close during day Carbon dioxide only enters cells at night CAM- crassulacean acid metabolism- carbon
fixation at night into organic acids Organic acids stored in vacuoles until day
when light can power PS
CHAPTER 9
CELLULAR RESPIRATION: HARVESTING CHEMICAL ENERGY
MAIN IDEA How do cells use Stored energy in food?
2 methods
Catabolic pathway- metabolic pathways that release stored energy from complex molecules
Cellular respiration Requires oxygen More efficient than fermentation
Fermentation Anaerobic Alcohol or lactic acid are biproducts
THE BIG PICTURE
Like PS, you will not be tested on the recitation of each chemical step of Cellular respiration, but in order to answer the Q you do need to understand what is going on!
Reverse PS
C6H12O6 + 6O2 6CO2 + 6H2O + ATP/heat
Exergonic ΔG = -686kcal/mol glucose
-ΔG = products have less potential energy than reactants
ATP is a rechargable battery
Recharge ~10million molecules per second!
REDOX REACTIONS- reaction in which e- are passed from one reactant to another Oxidation- loss of e- from a substance Reduction- addtion of e- to a substance
Cellular respiration is a redox reaction
Electrons “fall” toward oxygen
Carbs and lipids are storage of e- associated with the H
CR is a controlled reaction! 1. H atoms taken from glucose 2. H passed to coenzyme NAD+ using
enzymes called dehydrogenases NADH is like a charged battery, waiting to be
used to make ATP
Electron transport chain
A chain of proteins built into the inner membrane of mitochondria
ΔG = -53 kcal/mol glucose
HOW??
Electronegativity Each step “down” the chain is more and
more electronegative. Last acceptor is oxygen- very greedy for e-
Cellular Respiration 3 steps
Vocab in the figure
Oxidative phosphorylation- energy released at each step stored in the form that the mitochondria can use for ATP synthesis
Substrate level phosphorylation- enzyme transfers a phosphate group from substrate to ADP
Glycolysis 1. Split sugar
2. Form 2 3-C sugars
3. Sugars modified into pyruvate molecules
Glycolysis movie 9.9
What to know of Glycolysis mechanism for the exam Location of process Net energy production Oxygen independent process How many ATP are used? How many ATP are created? What is the net production of ATP? What method was used to create these ATP’s?
Classwork Task: Teaching
I will randomly split the class into two groups Group 1 will have 1 class period to create an
analogy/story that will help everyone understand and remember the mechanism of glycolysis.
Group 2 will have 1 class period to create an analogy/story that will help everyone understand and remember the mechanism of the Krebs cycle
We may or may not do this exercise depending on time.
Criteria for Teaching
1. You may NOT use ONLY chemical terms OR ONLY comparison terms
2. The teaching method is up to you- drawing/powerpoints/acting/handouts
3. You must present the lesson as an alter-ego (real or fictional) in about 20 min.
4. Ms. Bjelko will only assist with the lesson IF you are saying something totally incorrect.
***powerpoint must be accessible on 2003 version of the program…2007 will not open on Ms. Bjelko’s computer
Goal for Teaching
All students and Ms. Bjelko must be able to explain the mechanisms in both chemical terms and as some analogy
HINT: the stranger/sillier analogies are most likely to be remembered and the most fun to teach!!!
Where are we now???
Link to Krebs Cycle
From carboxyl group on pyruvate
e- from acetate used to make NADH
Needed for Krebs cycle
Krebs Cycle Summary
Krebs cycle movie 9.12
What to know of Krebs cycle mechanism for the exam Where does acetyl CoA come from? Each step uses a different enzyme- names not vital How many total chemical reactions must occur for the
oxaloacetate (needed for the cycle to restart) to be re-formed ?
How many ATP molecules are made during this process? What other energy/electron carrying molecules are formed
in this process? Where do the energy/electron carrying molecules go next?
Where are we now???
Electron transport chain- most of energy formation
Only 4 ATP formed so far, 2 from each step Each step of the chain molecules are reduced and
oxidized as electrons passed to and from them. e- carried from the Krebs cycle to e- transport chain
by NADH and FADH2 . Cytochrome molecules (cyt) have a heme group-
Fe surrounded by 4-C rings. Similar as in hemoglobin of RBC’s (Why would this be useful!- back to chemistry!)
Electron transport chain
Water produced
NO ATP produced DIRECTLY-
Chemiosmosis and ATP synthase make ATP
Chemiosmosis- energy coupling reaction using H+ gradient across mitochondrial membrane
Electron transport chain movie 9.15
Discovery of chemiosmosis
1961 Peter Mitchell proposed the idea 1981 it was confirmed in bacteria,
mitochondria, and chloroplasts 1981 Peter Mitchell received Nobel Prize
And the point is…research scientists must be very patient!
Energy totals from cellular respiration
Krebs cycle and Electron transport chain are aerobic processes
What happens when there is no O?
FERMENTATION Use e- from NADH made in glycolysis to
transform pyruvate Biproducts are either lactic acid or ethanol Only 2 ATP formed compared to 38 with CR
Movies 9.17a (alcoholic) and 9.17b (lactic acid)
Faculative Anaerobes
Organisms/cells that can create energy using either CR or fermentation
Yeast, many bacteria, mammalian muscle cells
CR is much more efficient!!!
Evolution and Glycolysis
Early earth lacked oxygen prokaryotes just used glycolysis
Oxygen would be the biproduct at that time Evidence: Glycolysis widespread through
living organisms Evidence: glycolysis happens in cytosol-
even prokaryotes can perform it
HOW could this have led to the evolution of CR?
Catabolism
Many carbohydrates can be hydrolized to be used for glycolysis
Beta oxidation- breaks fatty acids into 2-C fragments sent to Krebs cycle
Anabolic pathways (biosynthesis)
Using molecules to create needed materials for cells/the body
Amino acids obtained from protein used to make proteins for cell
About 10 of the 20 AA’s can be synthesized by modifying molecules taken from Krebs
Glucose made from pyruvate Fatty acids from acetyl CoA Extra proteins and carbs transformed into fats using
intermediate steps of glycolysis and Krebs cycle
Controlling CR: the ON/OFF switchesDO NOT MAKE MORE THAN YOU NEED!
FEEDBACK INHIBITION- end product of a reaction acts as an inhibitor of the enzyme that starts chain reaction
TARGET KEY ENZYMES IN THE PROCESS
SUMMARY
Cellular respiration and fermentation RELEASE energy from the chemical compounds ingested
Remember: Energy is neither created nor destroyed, it is simply transferred and transformed.
The New Test
This is the first unit that clearly shows the edits made from the previous exam.
You will NOT be asked to recite a list of chemical reactions in order, but instead you will be presented with stories/diagrams showing you chemical reactions in order.
The questions will ask you to interpret the story/diagram, or make a prediction based on the story/diagram.
Teacher note: as much as the college board says you don’t have to know the mechanisms…if you don’t have a clue about them, you will STRUGGLE to answer their questions. The new predict/interpret questions are challenging to both teachers and students.