UNIT 3:

Part 2

Cellular Respiration and

photosynthesis

Hillis Textbook Chapter 6

Cellular respiration is a major catabolic pathway.

Glucose is oxidized:

Photosynthesis is a major anabolic pathway. Light

energy is converted to chemical energy:

tecarbohydraOenergylightOHCO 222 666

energychemicalOHCOOtecarbohydra 222 666

Cellular Respiration is AEROBIC (uses oxygen)

A lot of energy is released when reduced

molecules with many C—C and C—H bonds are

fully oxidized to CO2.

Oxidation occurs in a series of small steps in three

pathways, followed by generation of ATP:

1. Glycolysis

2. Pyruvate Oxidation

3. Citric Acid Cycle

4. Electron Transport Chain

CELLULAR RESPIRATION:

LEARN THE

NAMES OF THE

STEPS AND

WHERE IT

TAKES PLACE!

REACTANTS: Glucose and oxygen

PRODUCTS: Carbon Dioxide,

water and ATP

Oxygen ATP

Glycolysis: ten total reactions.

Takes place in the cytosol.

Starts with glucose

Final products:

2 molecules of NADH

2 molecules of ATP

2 molecules of pyruvate

(pyruvic acid)

These ATP molecules were

produced, however they don’t

count because we USED two

molecules at the beginning

STEP ONE: GLYCOLYSIS

Pyruvate Oxidation:

Happens in the mitochondria

Starts with TWO separate pyruvates from glycolysis

Products: CO2 and acetate; acetate is then bound

to coenzyme A (CoA)

STEP TWO: PYRUVATE OXIDATION

2 pyruvate

in

Results in:

2 CO2 and 2

Acetyl CoA

total

Citric Acid Cycle:

Takes place in the mitochondrial matrix

8 reactions

Starts with the two Acetyl CoA produced by

pyruvate oxidation

So, the cycle operates twice for every ONE

glucose molecule that enters glycolysis

Each acetyl group is oxidized to two CO2.

Oxaloacetate is regenerated in the last step to be

re-used again when another acetyl CoA comes

along.

Energy carriers are produced: 6 NADH, 2 FADH2, 2 GTP

STEP THREE: CITRIC ACID CYCLE

Every glucose forms

TWO acetyl CoA from

pyruvate…

End result = 4

CO2, 6 NADH, 2

FADH2 and 2 GTP

STEP THREE: CITRIC ACID CYCLE

ALERT!!!

The Citric Acid

Cycle is also known

as The Kreb’s Cycle

and the TCA cycle

Electron transport/ATP Synthesis:

NADH is reoxidized to NAD+ and O2 is reduced to H2O in a

series of steps.

Respiratory chain—series of redox carrier proteins embedded

in the inner mitochondrial membrane.

Electron transport—electrons from the oxidation of NADH and

FADH2 pass from one carrier to the next in the chain.

STEP FOUR: ELECTRON TRANSPORT CHAIN

The oxidation reactions are exergonic; the

energy is used to actively transport H+ ions out of

the mitochondrial matrix, setting up a proton

gradient.

ATP synthase in the membrane uses the H+

gradient to synthesize ATP by chemiosmosis.

About 32 molecules of ATP are produced for

each fully oxidized glucose.

The role of O2: most of the ATP produced is

formed by oxidative phosphorylation, which is

due to the reoxidation of NADH.

STEP FOUR: ELECTRON TRANSPORT CHAIN

Alcoholic fermentation:

End product is ethyl alcohol (ethanol).

Lactic acid fermentation:

End product is lactic acid (lactate).

Under anaerobic conditions (NO OXYGEN IS AVAILABLE), NADH is reoxidized by

fermentation. The overall yield of ATP is only two—the ATP made in glycolysis.

Metabolic

pathways are

linked.

Carbon skeletons

(molecules with

covalently linked

carbon atoms) can

enter catabolic or

anabolic

pathways.

How do you

think prokaryotes

perform

respiration?

Photosynthesis involves two pathways:

1. Light reactions convert light energy into chemical

energy (in ATP and the reduced electron carrier

NADPH).

2. Carbon-fixation reactions use the ATP and NADPH,

along with CO2, to produce carbohydrates.

Light is a form of electromagnetic radiation,

which travels as a wave but also behaves as

particles (photons).

Photons can be absorbed by a molecule, adding

energy to the molecule—it moves to an excited

state.

In plants, two chlorophylls absorb light energy

chlorophyll a and chlorophyll b.

LIGHT REACTIONS:

Chlorophyll molecule

LIGHT REACTIONS:

The light

reactions use

CHLOROPHYLL

to trap energy

from the sun!

That is why they

are considered

“light” reactions.

When chlorophyll (Chl) absorbs light, it enters an excited state

(Chl*), then rapidly returns to ground state, releasing an

excited electron.

Chl* gives the excited electron to an acceptor and becomes

oxidized to Chl+.

The acceptor molecule is reduced.

The electron acceptor is first in an electron transport system in the thylakoid membrane.

Final electron acceptor is NADP+, which gets reduced:

ATP is produced chemiosmotically during electron transport

(photophosphorylation).

acceptorChlacceptorChl *

LIGHT REACTIONS:

NADPHeHNADP 2

Two photosystems:

•Photosystem I absorbs light energy at 700 nm, passes an

excited electron to NADP+, reducing it to NADPH.

• Photosystem II absorbs light energy at

680 nm, produces ATP, and oxidizes water molecules.

LIGHT REACTIONS:

The Calvin

cycle: CO2

fixation. It

occurs in the

stroma of the

chloroplast.

Each reaction

is catalyzed by

a specific

enzyme.

CALVIN CYCLE:

1. Fixation of CO2:

CO2 is added to ribulose 1,5-bisphosphate (RuBP).

Ribulose bisphosphate carboxylase/oxygenase

(rubisco) catalyzes the reaction.

A 6-carbon molecule results, which quickly breaks

into two 3-carbon molecules: 3-phosphoglycerate

(3PG).

2. 3PG is reduced to form glyceraldehyde 3-

phosphate (G3P).

3. The CO2 acceptor, RuBP, is regenerated from

G3P.

When glucose accumulates, it is linked to form

starch, a storage carbohydrate.

The C—H bonds generated by the Calvin cycle

provide almost all the energy for life on Earth!

Photosynthetic organisms (autotrophs) use most

of this energy to support their own growth and

reproduction.

Heterotrophs cannot photosynthesize and

depend on autotrophs for chemical energy.

Do we rely on plants?

Do plants rely on us?

ALCOHOL PRODUCTION USING RESPIRATION:

Catabolism of the beet sugar is a cellular process,

so living yeast cells must be present.

With air (O2) yeasts used aerobic metabolism to

fully oxidize glucose to CO2.

Without air, yeasts used alcoholic fermentation,

producing ethanol, less CO2, and less energy

(slower growth).

PATHWAYS THAT HARVEST ENERGY

RESPIRATION OVERVIEW:

RESPIRATION OVERVIEW:

GLYCOLYSIS

PYRUVATE OXIDATION FOR EACH PYRUVATE

KREB’S CYCLE FOR EACH

ACETYL CoA

ELECTRON TRANSPORT CHAIN

USES ALL THE ENERGY

CARRIERS AND OXYGEN TO MAKE ATP

RESPIRATION OVERVIEW:

Photosynthesis Overview:

Photosynthesis Overview: Light Reactions in the

thylakoid membranes

Calvin Cycle in the stroma