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.