UNIT 3

Chapter 9: Cellular RespirationChapter 10: Photosynthesis

Chapter 11: Cell Communication

The Basics

The sun is the ultimate source of energy for all living thingsLight energy trapped

in organic moleculesTrapped energy

available to autotrophs and heterotrophs

Cellular Respiration & Fermentation

Catabolic pathways can proceed with or without oxygen presentFermentation occurs when oxygen is NOT

presentCellular respiration occurs with oxygen and is

much more efficient than fermentation Most of cellular respiration occurs in the

mitochondria

Organic molecules + O2 CO2 + H20 + energy

ATP Hydrolysis & Redox Reactions

The removal of a phosphate group from ATP releases energy

Phosphorylation is a common tool used to power reactions

Redox (reduction-oxidation) reactions release energy when electrons are movedLoss of electrons = oxidationGain of electrons = reduction

Redox reactions are used to synthesize ATPCreating NaCl (table salt) is a redox reaction:

Na + Cl Na+ + Cl-

The electron donor is called the reducing agent and the electron recipient is called the oxidizing agent

Na + Cl Na+ + Cl-

The Function of Coenzymes

Glucose is not simply broken down in a single step to yield energySteps to break down components of glucose

using specific enzymesHydrogen atoms and electrons ripped off of

glucose and given to coenzymes like NAD+

Nicotinamide Adenine Dinucleotide

H-C-OH + NAD+ CO2 + NADH + H+

Steps of Cellular Respiration

Cellular respiration involves three steps:GlycolysisThe Krebs cycleThe Electron

transport chain and oxidative phosphorylation

Glycolysis – An Overview

Glycolysis occurs in the cytoplasm Glucose is split into two three-carbon

sugarsSugars are oxidized and rearranged to form

pyruvate 10 steps of glycolysis are catalyzed by

specific enzymesEnergy investment phase and energy payoff

phase

Energy investmentATP provides

energy to phosphorylate glucose

2 ATP per glucose

Energy payoff4 ATP and 2 NADH

are produced per glucose

Glycolysis produces a net of 2 ATP and 2 NADHHappens with or without oxygen and no CO2

is producedHowever, if oxygen is present, pyruvate

molecules can move in to the Krebs cycle NADH will play a role later in the process (the

electron transport chain)

The Krebs Cycle

Pyruvate still holds a lot of the original glucose molecule’s chemical energy

Pyruvate enters the mitochondria and is modifiedCO2 removed to produce acetyl CoA

Each pyruvate used to produce: 1 acetyl CoA,

which is used to produce:

1 ATP 3 NADH 1 FADH2 (an

electron transport carrier similar to NADH)

The Electron Transport Chain (E.T.C.)

Respiration ultimately produces 38 ATP (max), but so far, only 4 have been produced

8 NADH and 2 FADH2 molecules enter the electron transport chain

The electrons are used to power ATP synthesis

Each mitochondrion has thousands of sets of the E.T.C. in the cristae

The electron transport chain shuttles electrons from NADH towards increasingly more electronegative atoms, ultimately to oxygen

Process occurs in inner membrane of mitochondriaOxygen

“captures” e- and H+ to make water

Electrons from NADH and FADH2 are ultimately passed off to oxygenFor every two electron carriers (4 electrons),

one O2 molecule is reduced 2 H2O

The electrons moving down the E.T.C. are used to pump H+ ions into the inter membrane space of the mitochondrionAn H+ ion gradient is created and is referred

to as proton-motive force H+ ions diffuse back into the mitochondrial

matrix through ATP Synthase

As H+ ions move through ATP Synthase, that protein shifts its conformationShift joins a phosphate group to ADP

That entire process is called chemiosmosisChemiosmosis occurs in plants also, but it is

driven by light energy

Matrix

Intermembrane Space

NAD+

+

++ +

+

+

+

+

+

++

+

++

+

+

+O

+

H

HP P

Adenine PP PAdenine P

Summary of Cellular Respiration

Fermentation

Some cells can produce ATP whether oxygen is present (aerobic) or not (anaerobic)

Two types of fermentation exist:Alcoholic fermentationLactic acid fermentation

In alcoholic fermentation, pyruvate is ultimately converted to ethanol

In lactic acid fermentation, pyruvate is converted into lactic acid

Some organisms, like bacteria and yeast can produce enough ATP to surviveThese organisms are called facultative

anaerobesHuman muscle cells can behave as

facultative anaerobes, for a very short time Cori Cycle

The presence of oxygen allows for the production of up to 38 ATP molecules, but without oxygen, only 2 ATP are created

END

Chloroplasts Make Chloroplasts Make Photosynthesis PossiblePhotosynthesis Possible

Any green part of a plant possesses Any green part of a plant possesses chloroplastschloroplasts which contain a green which contain a green photopigmentphotopigment: : chlorophyllchlorophyllChloroplasts are found Chloroplasts are found mainly in the mainly in the mesophyllmesophyll cells in the interior of cells in the interior of the plant’s leavesthe plant’s leaves

OO22 exits and CO exits and CO22 enters through pores enters through pores called called stomatastomata on the on the leaf’s surfaceleaf’s surface

Chloroplasts are Chloroplasts are double-membrane double-membrane organelles around a organelles around a central space: central space: stromastroma

In the stroma are In the stroma are membranous sacs membranous sacs called called thylakoidsthylakoids Internal space called Internal space called

thylakoid spacethylakoid space Stacked into Stacked into granagrana

The Basics of PhotosynthesisThe Basics of Photosynthesis

The general reaction of The general reaction of photosynthesis:photosynthesis:

Basically, carbon is extracted from Basically, carbon is extracted from carbon dioxide to make sugar, while carbon dioxide to make sugar, while oxygen is released into the oxygen is released into the atmosphereatmosphere

6CO6CO22 + 12H + 12H22O O C C66HH1212OO66 + 6H + 6H22O + 6OO + 6O22

SUN

The Light Reactions & The The Light Reactions & The Calvin CycleCalvin Cycle

Photosynthesis is a two step processPhotosynthesis is a two step process Light reactionsLight reactions

Converts solar energy into chemical energyConverts solar energy into chemical energy Calvin cycleCalvin cycle

Incorporates COIncorporates CO22 into organic molecules into organic molecules and uses chemical energy from light and uses chemical energy from light reactions to create sugarreactions to create sugar

The light reactions – an overviewThe light reactions – an overview Water is split, hydrogen and electrons Water is split, hydrogen and electrons

used to reduce used to reduce NADP+NADP+ to to NADPHNADPH (an (an electron carrier)electron carrier)

ATP is generated by ATP is generated by photophosphorylationphotophosphorylation

The Calvin cycle – an overviewThe Calvin cycle – an overview COCO22 is incorporated into what will is incorporated into what will

become sugar during become sugar during carbon fixationcarbon fixation NADPH and ATP are used to create the NADPH and ATP are used to create the

new organic moleculenew organic molecule

The light reactions & Calvin cycle:The light reactions & Calvin cycle:

The Photopigments of The Photopigments of PhotosynthesisPhotosynthesis

A number of pigments exist in A number of pigments exist in plants, but only one, plants, but only one, chlorophyll chlorophyll aa, is , is directly involved in the directly involved in the photosynthetic reactionsphotosynthetic reactions Accessory Accessory pigmentspigments can can funnel light funnel light energy to energy to chlorophyll chlorophyll aa Chlorophyll Chlorophyll bb CarotenoidsCarotenoids XanthophyllsXanthophylls

Photons of light are absorbed by Photons of light are absorbed by pigments in thylakoid membranespigments in thylakoid membranes

In the thylakoid membrane, a “light antenna” In the thylakoid membrane, a “light antenna” called a called a photosystemphotosystem channels light energy channels light energy

Energy Energy transferred from transferred from molecule to molecule to molecule until it molecule until it reaches the reaches the reaction centerreaction center chlorophyll chlorophyll aa

PhotosystemsPhotosystems

Two types of Two types of photosystemsphotosystems work in work in the light reactions of photosynthesisthe light reactions of photosynthesis Photosystem IPhotosystem I & & Photosystem IIPhotosystem II

Photosystem I (Photosystem I (P700P700) absorbs light best at ) absorbs light best at 700nm (far red)700nm (far red)

Photosystem II (Photosystem II (P680P680) absorbs light best at ) absorbs light best at 680nm680nm

1.1. P680 is hit by light and excites 2 electrons, P680 is hit by light and excites 2 electrons, sending it to the primary electron acceptorsending it to the primary electron acceptor

2.2. Water is split creating ½ O Water is split creating ½ O22, which , which is joined with another ½ Ois joined with another ½ O22 to form to form OO22

3.3. Excited electrons are passed down Excited electrons are passed down an E.T.C. (which creates ATP) to an E.T.C. (which creates ATP) to P700P700

4.4. An electron acceptor in P700 An electron acceptor in P700 captures the electrons and uses captures the electrons and uses them to reduce NADPthem to reduce NADP++

Electron flow takes electrons from Electron flow takes electrons from water, and uses them to reduce water, and uses them to reduce NADPNADP++

ATP created on the way through E.T.C.ATP created on the way through E.T.C. OO22 is a byproduct of splitting water is a byproduct of splitting water

ATP SynthesisATP Synthesis

Chloroplasts and mitochondria both Chloroplasts and mitochondria both create ATP using create ATP using chemiosmosischemiosmosis

ChloroplastChloroplasts transform s transform light energy light energy into into chemical chemical energyenergy

The Calvin CycleThe Calvin Cycle

The Calvin cycle uses ATP and NADPH The Calvin cycle uses ATP and NADPH to create sugarto create sugar Not actually “glucose,” but Not actually “glucose,” but glyceraldehyde-glyceraldehyde-

3-phosphate3-phosphate ( (G3PG3P), a 3-Carbon sugar), a 3-Carbon sugar Each turn through the Calvin cycle fixes Each turn through the Calvin cycle fixes

one carbonone carbon There are three phases to the Calvin There are three phases to the Calvin

cyclecycle Carbon fixationCarbon fixation, , ReductionReduction, , Regeneration of Regeneration of

the COthe CO22 acceptor acceptor

3CO3CO22 are attached to 3 5-Carbon are attached to 3 5-Carbon sugars (RuBP) by sugars (RuBP) by rubiscorubisco

The new 6-Carbon sugars split into 6, The new 6-Carbon sugars split into 6, 3-carbon sugars3-carbon sugars

ATP is used to add another phosphate ATP is used to add another phosphate group to EACH of the 3-Carbon group to EACH of the 3-Carbon sugarssugars

NADPH is used to remove one of the NADPH is used to remove one of the phosphates from each sugar, phosphates from each sugar, creating a G3P sugarcreating a G3P sugar

Some G3P sugars are modified by 3 Some G3P sugars are modified by 3 more ATP molecules to regenerate more ATP molecules to regenerate RuBPRuBP

Net cost per G3P = 9 ATP + 6 NADPH Net cost per G3P = 9 ATP + 6 NADPH + 3 CO+ 3 CO22

rub

isco

rub

isco

rub

isco

The Calvin Cycle: CARBON FIXATION

C C C CCP P C C C CCP P C C C CCP P

RuBP RuBP RuBP

O OC O OC O OC

CCCP

C C C P

CCCP

C C C P

CCCP

C C C P

ADP

P

ADP

ADP

ADP

ADP

ADPP P

PP

P

ATP

ATP ATP

ATP

ATP

ATP

The Calvin Cycle: REDUCTION

CCCP P

NADPH

NADP+

G3P

CCCP P

NADPH

NADP+

G3PCCCP P

NADPH

NADP+

G3P

CCCP P

NADPH

NADP+

G3PCCCP P

NADPH

NADP+

G3P

CCCP P

NADPH

NADP+

G3P

EX

ITS

CY

CL

E

The Calvin Cycle: REGENERATION OF THE CO2 ACCEPTOR (RuBP)

CCCP

CCCP

CCCP

CCCP

CCCP

CCCP

G3P

CCCP CC P

CCCP CC P

CCCP CC P

15 Carbons 5 Phosphates

ADP

P

P

ADP

ADP

15 Carbons 6 Phosphates 3 RuBP molecules

Two G3P molecules will be combined to form one glucose

molecule.

COMPLEX

REACTIONS!

The Need for Alternative The Need for Alternative Methods of Carbon FixationMethods of Carbon Fixation

The Calvin cycle is not the only way The Calvin cycle is not the only way plants fix carbonplants fix carbon

Dehydration is a huge problem for Dehydration is a huge problem for plants since water can evaporate plants since water can evaporate through the stomatathrough the stomata Hot dry days Hot dry days plants close stomata plants close stomata

Most plants, called Most plants, called CC33 plants, fix CO plants, fix CO22 to RuBP using rubiscoto RuBP using rubisco

On hot, dry days, COn hot, dry days, C33 plants close their plants close their stomatastomata COCO22 levels drop as it’s used in the Calvin levels drop as it’s used in the Calvin

cyclecycle OO22 levels rise as it cannot escape the leaf levels rise as it cannot escape the leaf

Rubisco will then fix ORubisco will then fix O22 to RuBP, which to RuBP, which then degrades and produces no G3Pthen degrades and produces no G3P

This process is called This process is called photorespirationphotorespiration and can severely and can severely affect the productivity of affect the productivity of photosynthesis in a plantphotosynthesis in a plant

Avoiding PhotorespirationAvoiding Photorespiration

A number of plants, called A number of plants, called CC44 plants, will plants, will first fix COfirst fix CO22 to a 4-carbon compound to a 4-carbon compound (organic acid)(organic acid)

PEP carboxylasePEP carboxylase has a high affinity for CO has a high affinity for CO22 and is much more efficient than rubiscoand is much more efficient than rubisco 4-carbon compound moved to 4-carbon compound moved to bundle sheath bundle sheath

cellscells where the Calvin cycle can take place where the Calvin cycle can take place

CC44 plants are usually found in very hot plants are usually found in very hot regions with intense sunlightregions with intense sunlight

A second strategy for avoiding A second strategy for avoiding photorespiration can be found in photorespiration can be found in CAMCAM plantsplants Cacti, pineapples, succulentsCacti, pineapples, succulents

CAM plants close their stomata during CAM plants close their stomata during the day, and open them at nightthe day, and open them at night Night: plants fix CONight: plants fix CO22 into organic acids in into organic acids in

the mesophyll cellsthe mesophyll cells Day: CODay: CO22 released from organic acids and released from organic acids and

light reactions create ATP and NADPHlight reactions create ATP and NADPH

In CIn C44 plants, plants, carbon fixation carbon fixation and the Calvin and the Calvin cycle are cycle are spatiallyspatially separatedseparated

In CAM plants, In CAM plants, carbon fixation carbon fixation and the Calvin and the Calvin cycle are cycle are temporallytemporally separatedseparated

END

Stages of Signal Transduction

• The three stages of signal transduction are:• Reception, transduction, response

• Cells can communicate with other cells they are physically connected to • Across great distances using hormones• Target cell is intended recipient for signal

Reception

• A Chemical signal called a ligand binds to protein in the target cell’s membrane• Protein changes conformation

• Change in conformation sets in motion a series of other changes inside the cell

Transduction

• Transduction relays signals from reception to cellular responses

• At each step, the signal is transduced in a different form• Usually a protein changing its comformation

• Kinases are a common group of intracellular proteins

Cellular Response

• Response can include activities within the cell or stimulate transcription in the nucleus• Can increase or decrease metabolism within a

cell

• Protein synthesis may be induced to create proteins needed

• Certain pathways help to amplify responses

• Various cells may receive the same signal, but have different responses• Ex. adrenalin in heart muscle cells triggers

rapid heartbeat; adrenalin in liver cells triggers release of glucose into the blood

END