Energy Flow:Photosynthesis

& Cellular Respiration

Functions of ATPFunctions of ATP• Chemical work – synthesizing compounds• Transport work – moving substances

across the plasma membrane• Mechanical work – moving cell structures

and cells•Energy couplingEnergy coupling: use : use of an exergonic process of an exergonic process to drive and endergonic to drive and endergonic process process •ATP mediates most ATP mediates most energy coupling in cellsenergy coupling in cells

ATPATP• Consist of

–a sugar called ribose

–N containing Adenine

–Three phosphate groups

UnstableUnstable w/3 PO w/3 PO4-4-

•All negative charge-repel each All negative charge-repel each otherother

ADP is more stableADP is more stable A changeA change from a from a less stableless stable

molecule to a molecule to a more stablemore stable molecule molecule releases energyreleases energy..

The structure and hydrolysis of ATPThe structure and hydrolysis of ATP

When bonds are broken from ATP to ADP (hydrolysis),

All are negatively charged – crowded and repel, creating instability

The ATP cycleThe ATP cycle

ATP is a renewable resource that can be regenerated…

FASTFAST – working muscle cell recycles its entire ATP pool once each minute; -Turnover represents 10 million molecules of ATP generated per second in a cell.

• The energy can then be used to drive other reactions–ATP “carries” Energy

• Photosynthesis is the process by which plants and other organisms use sunlight, CO2 & H20 to produce high energy carbohydrates such as sugars and starches.

• Prokaryotes- photosynthetic capability is present within five major groups of bacteria.

Where Photosynt

hesis Occurs

Section 23-4

Epidermis

Stomata

Guardcells

The Internal Structure of a LeafCO2 enters through the stomata

Chloroplasts

• Chloroplasts are only found in photosynthetic, eukaryotic cells. Chloroplasts are capable of harnessing energy from the sun's rays of light.

•Using this energy from the sunlight, chloroplasts are able to form ATP as well as synthesizing sugars from water and carbon dioxide.

Things to know about Chloroplasts

• have a double membrane • have their own DNA (carries the

info to make enzymes) • have their own ribosomes (more like

the ribosomes of prokaryotes) -used to synthesize proteins

• make their own enzymes required for photosynthesis

• require CO2 and H2Oproduce C6H12O6 • contain chlorophyll (green chemical

"traps" sunlight energy) Now let’s look at structure…

• The chloroplast is made up of 3 types of membrane:The chloroplast is made up of 3 types of membrane: 1.A smooth outer membrane which is freely permeable

to molecules.

2.A smooth inner membrane which contains many transporters

3.A system of thylakoid membranesthylakoid membranes

ChloroplastChloroplast• OrganelleOrganelle where photosynthesisphotosynthesis takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

ThylakoidThylakoid

Thylakoid Membrane

Thylakoid SpaceGranum

Light and PigmentsIn addition to water and carbon dioxide,

photosynthesis requires light. Light energy is absorbed by the pigment CHLOROPHYLL

and other accessory Pigments.

Sunlight is a mixture of many different wavelengths…

ROYGBIV (light energy is measured in units called photons)

Pigments• Substances in organisms that can absorb lightabsorb light.• The color that you see is the one being REFLECTED• CHLOROPHYLL is the major photosynthetic pigment in

plants• 2 types: chlorophyll a – directly involved in

transformation of photons to chemical energy

chlorophyll b – helps trap other wavelengths and transfers it to chlorophyll a

•Chlorophylls (green) and carotenoids (yellow, orange and red.)

Accessory Pigments

b

a

Chlorophyll A and B Absorption Spectrum• Absorb red,

blue, and violet range.

Chlorophyll Light Absorption

Location and structure of chlorophyll molecule

The pigment molecules have a large head section that is exposed to light in the surface of the membrane; the hydrocarbon tail anchors the pigment molecules into the lipid bilayer.

Double bonds are the source of the e- that flow

through the ETC

Photosystem

Accessory Pigments• Other pigments that trap other wavelengths --

found in chromoplasts– Capture light and pass the energy along to

chlorophyll A.• Ex. Carotenoids

* xanthophyll – yellows* beta carotene – oranges

– These are masked by presence of chlorophylls, except in autumn (when leaf cells stop synthesizing chlorophyll) – “fall colors”

– Also is very obvious in “ripe” fruits, veggies Ex. Apple, tomato

Photosystems• Chlorophyll molecules

are located in photosystems.

• PSs are light-harvesting complexes in the thylakoid membranes. (few 100 in each)

• Structure:– Reaction Center-

contains chlorophyll A and a region containing several 100 antenna pigments.

• Two Types:– PS I and PS II– PS II acts BEFORE PS

I……..go figure...

PS II680nm rangeAlso referred to as P680.

PSI700nm rangeAlso referred to as P700

Where is the chlorophyll located?

Now that you know all of that……let’s actuallyactually look at the process of

photosynthesis Mr. Anderson’s Photosynthesis

Photosynthesis: Quick Overview

STAGE 1

Photosynthesis: Quick Overview

STAGE 1

Photosynthesis: Quick Overview

STAGE 1STAGE 2

Light Dependent Reaction

Light Independent

Reaction

The Process of Photosynthesis does NOT Happen all at The Process of Photosynthesis does NOT Happen all at Once; rather it occurs in  Once; rather it occurs in  TWO STAGESTWO STAGES: :

STAGE 1: LIGHT DEPENDENT REACTIONS. – PS I (P700) and PS II (P680) capture energy from

sunlight.  – Water is Split (photolysis) into Hydrogen Ions,

Electrons, and Oxygen (O2).  – The O2Diffuses out of the Chloroplasts (Byproduct). – The Light Energy is Converted to Chemical Energy,

which is Temporarily Stored in ATP and NADPH.

•Two possible routs for the e- flow:

•Cyclic photophosphorylation

•noncyclic

Overview:–e- enter two electron transport chains

–ATP is formed– Carries energy to Calvin Cycle

–NADPH (Nicotinamide dinucleotide phosphate) is formed

– Carries H+ and e- to Calvin Cycle

Steps of Light Dependent Reaction(Noncyclic Photophosphorylation)

Overview clip

Steps of Light Dependent Reaction(Noncyclic Photophosphorylation)

1. PSII absorbs energy.1. e- from double bonds in the head of ChloroA become energized and

move to a higher energy level. They are captured by a primary electron acceptor.

2. Photolysis: H2O gets split apart into 2 e- , 2 H+, and one oxygen atom.. The e- replace those lost by ChloroA.

3. 2 oxygen molecules combine and is released into the air.4. H+ are released into the inner thylakoid space, which creates a higher

[ H+ ] inside the thylokoid.5. e- from ChloroA are passes along a ETC consisting of plastoquinone

(PQ)---complex of 2 cytochromes and several other proteins.• This flow is exergonic and provided energy to produce ATP by chemiosmosis.

(photophosphorylation)• The ATP is used to power the Light Independent Reaction (Calvin Cycle)….this is a coupled

reaction!

2. The e- end up at PS I.1. PS I absorbs energy.2. e- from double bonds in the head of ChloroA become energized and

move to a higher energy level. They are captured by a primary electron acceptor.

3. E- that are lost are replaced by the e- from PSII (step7).4. e- from ChloroA are passes along a ETC – consisting of ferrodoxin.5. NADPH is produced.6. NADP in the stroma pick up 2 H+ and form NADPH and enter the calvin

cycle.

The light reactionslight reactions and chemiosmosis: organization of the thylakoid membrane

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

The production of ATP using the energy of sunlight is called photophosphorylation.

P700P680

photolysis

Animation

ChemiosmosisChemiosmosis“Chemiosmotic

Theory”-Peter Mitchell -1961

• Energy coupling mechanism.– Uses potential

energy stored in the form of a proton gradient to phosphorylate ADP to produce ATP.

ATP synthase-The Movie

ChemiosmosisChemiosmosisProtons can not diffuse through the membrane.

SO they must flow through the ATP synthase protein channel.

90% of all ATP is produced this way.

“Proton Motive Force” generates ATP

Photosynthesis: Light Dependent Reaction

Clip

Cyclic Photophosphorylation

a primary e- acceptor, then back to the cytochrome complex in the P680 ETC.

• No NADPH is produced.

• No O2 is released.

•Periodically the chloroplasts runs low on ATP.•Does this to replenish ATP levels.•e- travel from the P680 ETC to P700 then to

Animation

STAGE 2: Dark Reaction /Light Independent reaction/Calvin-Benson Cycle).

•The ATP and NADPH created in the light reaction are used to power the formation of Organic Compounds (Sugars), using CO2. •This is a light Independent reaction. It can happen during the daylight, it just does NOT need light be completed.•Occurs in the stroma.•Cyclical pathway where carbon enters as CO2

and exits as PGAL (phosphoglyceraldehyde.)•Carbon is fixed into PGAL. (2 PGAL=1 Glucose)

•Called carbon fixation.•This is a reduction reaction (carbon is GAINING hydrogen)•Must repeat 6 times.

Review step 1 / Intro to step 2 Clip

The Calvin cycle

CO2 attaches to a 5-C sugar-RuBP.Ribulose biphosphate.

This forms a 6-C molecule (PGA)

Catalyzes by the enzyme Rubisco.

6C3 plants

The Calvin cycle

6-C molecule breaks (PGA) down into 2 3-C molecules (3-PGAL-3-phosphoglycerate)

Catalyzes by the enzyme Rubisco.

PGAL

PGA

PGAL

6

12

12

12

21

The Calvin cycle

PGAL converted to RuBP

PGAL

PGA

PGAL

Summary:

6CO2 + 18 ATP + 12 NADPH + H+ 18ADP + 18 Pi + 12NADP+ + 1 Glucose

6

12

12

12

21

Photorespiration• Occurs when the CO2 levels inside a leaf become low.

– Happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss.

– If the plant continues to attempt to fix CO2 when its stomata are closed, the CO2 will get used up and the O2 ratio in the leaf will increase relative to CO2 concentrations.

• When the CO2 levels inside the leaf drop to around 50 ppm, Rubisco starts to combine O2 with RuBP instead of CO2.

• The net result of this is that instead of producing 2 3C PGA molecules, only one molecule of PGA is produced and a toxic 2C molecule called phosphoglycolate is produced.

– The plant must get rid of the phosphoglycolate – Converts it to glycolic acid, which is then transported to the peroxisome and converted to

glycine. – The glycine is then transported into a mitochondria where it is converted into serine. – The serine is then used to make other organic molecules. All these conversions cost the

plant energy and results in the net lost of CO2 from the plant.

• To prevent this process, C-4 plants have changed their anatomy to prevent this process….let’s look at them

Problem: RUBISCO catalyzes two different reactions.

C3, C4 & CAM Plants• C-3

– Calvin cycle occurs in all photosynthetic cells.

• C-4– C4 plants separate the

site of oxygen production (PSII) from rubisco (Calvin cycle).

– Called C-4 because the CO2 is first incorporated into a 4-carbon compound.

– Keeps O2 Away from RuBP (NO Photorespiration)

– Light reaction occurs ONLY in the mesophyll cells & Calvin cycle occurs in bundle-sheath cells.

– SPATIAL SEPARTATION

C4 leaf anatomy and the C4 pathway

Different anatomy

from a C-3 plant

Photosynthesis:

A dry climate adaptation:

• CAM Plants (Crassulacean Acid Metabolism) plants live in very dry condition and, unlike other plants, open their stomata to fix CO2 only at night.-Fix CO2 at night and store it. C4 plants that also have a TEMPORAL SEPARTAION

.

Factors affecting Photosynthesis

•Amount of water available – too little, stop photosynthesis

•Temperature – best between O°C & 35°C (too high, damage enzymes; too low, stop photosynthesis)

•Intensity of light – up to a point, increasing light intensity increases rate of photosynthesis

Cellular Cellular RespirationRespiration

-The process that occurs in cells in which cells break down sugar for ENERGY!

Cellular Respiration Overview:

• We get our energy from the food we eat.• The unit for energy is the calorie.• Plants are producers and make glucose

by the process of photosynthesis.• Heterotrophs (consumers) breakdown

glucose for energy.• There are two important ways a cell can

harvest energy from food: fermentation and cellular respiration.

Basic overview

•Step 1: gylcolysis– Splitting of

glucose

9 steps

fermentation

cellular respiration

GlycolysisOverall Important Points:

• Occurs in Cytoplasm

• Does not require oxygen– Glycolysis occurs in both aerobic (With oxygen) and

anaerobic (without oxygen) respiration.– Evolved early in Earth’s history (evolutionary

relationships)

• First 3 steps are endothermic– Energy of activation = 2 ATP

• Last 6 steps are exothermic– producing 4 ATPs.

• 4-2= 2 ATP (net yield)• Releases less then 25% of energy from glucose.

Clip; McGraw

Hill

TYPES of Phosphorlation• Substrate Level:

– When an enzyme transfers a PO4- from a substrate DIRECTLY to ADP.

• Oxidatative: – During Chemiosmosis.– 90% of all ATP is produced

this way in the ETC– NAD & FAD lose protons

(become oxidized) to the ETC…pumps protons to innermembrane space creating a gradient. This powers the phosphorlation of ADP

A closer look at glycolysis: The 9 Steps

Step 1

Step 2

Step 3

Step 4

Important regulatory step;

PFK is inhibited by ATP

Step 5

Step 6

Step 7

A closer look at glycolysis: The 9 Steps"high energy" e- carrying molecule

Nicotinamide adenine dinucleotide

Substrate-level phosphorylation

Step 8

Step 9

Step 5

Step 6

Step 7

A closer look at glycolysis: The 9 Steps

3- Carbon Cpd

• 2 NADH

• 2 ATP

In the presence of In the presence of OXYGEN:OXYGEN:

Step 2:Step 2: Krebs CycleStep 3:Step 3: Electron

Transport• Happens in the Mitochondria

• Starts with Pyruvate.

• Pyruvate moves into the mitochondria and is broken completely down into CO2 , O2 & ATP.

What happens next???

Krebs and ETC take place in a mitochondrion

Double membrane

Mitochondria AnatomyMitochondria Anatomy

Step 2:Step 2: Krebs Cycle (aka: Citric Acid Cycle)-Mitochondrial Matrix

Step 3:Step 3: Electron Transport-Cristae

Krebs Cycle Overview (Citric Acid Cycle)

• Occurs in the mitochondrial matrix

• Pyruvate (product of glycolysis) enters the mito. and combines with coenzyme A (vitamin A) to form acetyl coenzyme A.

Yields 1 NADH

• Krebs starts with acetyl coA.

• Cyclical series of enzyme-catalyzed reactions.

• Each turn (cycle) uses 1 pyruvate and yields • 3 NADH, 1 ATP, 1 FADH

• Byproduct= CO2

NAD & FADCoenzymes that carry protons (H+)

and electrons from glycolysis & Krebs to the ETC

Clip; McGraw

Hill

A summary of the Krebs cycle

NAD+ & FAD

-Coenzymes that carry protons (H+) and electrons from glycolysis & Krebs

to the ETC

• Occurs in the mitochondrial matrix

• Pyruvate (product of

glycolysis) enters the mito. and combines with coenzyme A (vitamin A) to form acetyl coenzyme A.

Yields 1 NADH

• Krebs starts with acetyl coA.

• Cyclical series of enzyme-catalyzed reactions.

•Each turn (cycle) uses 1 pyruvate

•yields 3 NADH, 1 ATP, 1 FADH•Byproduct= CO2

Substrate-level phosphorylation

The Story So Far…

ETC Clip;

McGraw Hill

• 2 NADH

• 2 ATP

• 3 NADH, 1 ATP, 1 FADH2

• Byproduct= CO2

Electron Transport• The ETC is a proton

pump in the inner mito membrane.

• Its uses the energy released from the exergonic flow of electrons to pump protons from the matrix to the inner membrance space.

• This sets up a proton gradient across the membrane =chemiosmosis.

Step 3:Step 3: Electron TransportWhat happens next???

The production of ATP using the energy of electrons is called oxidatative phosphorylation. (where have we seen this before)

Overview Clip

Oxidative Phosphorylation and Chemiosmosis

Energy from falling e- (exergonic) is used to pump H+ across the membrane (endergonic).

H+ can’t get through the membrane, so they MUST pass through the channel.Ex: Hydroelectric plant…

Oxygen is the final e-

acceptor!!

What happens next???

Clip 2; Formation

of ATP

oxidatative phosphorylation

Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis

36-38 Total ATP

Oxidative Phosphorylation; The Phosphorlation of ADP into ATP by the oxidation of carrier molecules (NADH & FADH2)

Glucose

Glycolysis Krebs cycle

Electrontransport

Fermentation (without oxygen)

Alcohol or lactic acid

With & With out Oxygen

Go to Section:

With oxygen

With out oxygen

Fermentation• Without oxygen:Without oxygen: Pyruvate is

converted into Lactic AcidLactic Acid or AlcoholAlcohol during Fermentation.

• Lactic Acid- Muscle cells• Alcohol- Yeast

40

Anaerobic Respiration

Glucose Pyruvic acidLactic acid

Lactic Acid FermentationSection 9-1

Go to Section:

Without a means to convert NADH to NAD+, Glycolysis would shut down

Mr. Anderson’s Cellular Respiration

Alternative Energy Sources

• From Fats:– Enzymes cleave the bonds

between the glycerol and the fatty acids, which enter the blood stream. Enzymes in the liver convert the glycerol into PGAL.

– Enzymes in cells break apart the fatty acids acetyl-CoA.

– More C-H bonds, so yields more ATP.

• From Proteins:– Cells don’t store protein.

– Enzymes breakdown proteins—into AA units, then strip of the NH3+ group.

– Carbon backbone either gets converted into fats or carbohydrates.

– Or, enter krebs cycle.

Alternative Energy Sources