Today’s Agenda: Variations on photosynthesis (end of yesterday) Variations on electron transport

Today’s Agenda:

• Variations on photosynthesis (end of yesterday)• Variations on electron transport

• Heat generation• Poisons

• CSI – ATP• Open review and question time

Lecture 9: Cellular Energy Extensions

LightReactions:Thylakoid

Membranes

CO2

NADP+ADPPi+

RuBP

3-PhosphoglycerateCalv

inCycl

e:StromaG3P

ATP

NADPH

Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2Fig. 10.21

Yesterday’s Exit Ticket

When H2O varies:

Light, CO2, H2O, (nutrients)Travelsfy.com; minnestota.publicradio.org; mccullagh.org

In wet environments • Stomata can stay wide open• CO2 is relatively unlimited in

plant cells

In semi-arid environments

• Stomata are kept ajar to reduce water loss

• CO2 is acquired more slowly

In dry environments

• Stomata are kept closed in the heat of the day

• Stomata are opened at night to acquire CO2

“C3”Most plants

More “C4” plantsMany grasses

More “CAM” plantsCacti, many other desert succulents

Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate).

LightReactions:

Light collection & electron transport

CO2

NADP+

ADP

Pi+

RuBP

3-Phosphoglycerat

eCalv

inCycl

e

G3P

ATP

NADPH

Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2Fig. 10.21

Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate).

Fig. 10.19

The C4 pathway

CO2PEP carboxylase

Oxaloacetate (4C)

Malate (4C)

PEP (3C) AD

PATP

Pyruvate (3C)CO2

CalvinCycle

Sugar

Vasculartissue

Some plants (C4 plants) use an additional CO2 fixation cycle before the Calvin cycle:

• The enzyme PEP carboxylase “fixes”

CO2 into a sugar with 4 carbons

• Once enough new CO2 has been

stored in the 4-C sugar, it moves into the Calvin

Cycle

C4 plants:• This process allows the Calvin Cycle to run smoothly

despite low CO2 conditions

Fig. 10.19

The C4 pathway

CO2PEP carboxylase

Oxaloacetate (4C)

Malate (4C)

PEP (3C) AD

PATP

Pyruvate (3C)CO2

CalvinCycle

Sugar

Vasculartissue

CAM plants:• Take the C4 process one step further

• CO2 is collected and converted to 4-carbon sugar at night

• Sugar is stored in vacuoles

• In the morning, stomata close and malic acid is broken down to enter the Calvin Cycle

LightReactions:

Light harvestingand photosynthetic electron transport

CO2

NADP+

ADP

Pi+

RuBP

3-Phosphoglycerate

CalvinCycleG3PATP

NADPH Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

Fig. 10.21

Why isn’t every plant a C4 plant?

Advantage of C3 plants

C3 plants need less energy since they don’t run two cycles

C3 plants do better than C4 plants in less sunny, moist, cool, CO2-rich climates. Typically more cold-tolerant.

Mountainphotographer.com

Today’s Agenda:

• Variations on electron transport• Heat generation• Cyanide and carbon monoxide

• CSI – ATP• Open review and question time

Fig. 34.27(e)

Basal metabolic rate, in kcal per day (p. 870)

Human, adult male Adult Alligator 1,600-1,800 60 (at 20°C)

Fig. 15.6(a)

2nd law of thermodynamics: Every energy transformation leads to a loss of usable energy as heat (=unusable energy)

Thermogenesis“warm-blooded” versus “cold-blooded” Endothermic versus ectothermic

http://www.vivo.colostate.edu/hbooks/pathphys/misc_topics/brownfat.html; see Fig. 4.6(a)

Brown fat cells have many mitochondria

Brown fat cells produce heat in newborns, small mammals in cold climates, & hibernating animals.

and use uncoupling proteins to separate electron transport from ATP formation to generate only heat and no ATP

Fig. 10.16

How does the mitochondrial uncoupling protein do this?

Fig.8.7

http://www.nature.com/nrm/journal/v6/n3/fig_tab/nrm1592_F1.html

The mitochondrial uncoupling protein provides a channel across the membrane through which protons (H+) flow back downhill without

making ATP, releasing all energy as heat

UCP = uncoupling protein

H+s have a choice:• Work to get back

in (via ATP synthase)

• Flow back in for free (via UCP)

2009 report on brown fat cells in adult humans too!!

http://www.sciencedaily.com/releases/2009/06/090611142529.htm

Skunk cabbage in Japan.

http://www.asknature.org/strategy/7e985ec13e9adf0cbca843df1225fa98

Figure 1 Thermal image of flower of Philodendron selloum during thermogenesis (Ito and Seymour 2005). http://4e.plantphys.net/article.php?ch=e&id=126

Skunk cabbage in the northeastern US

http://www.damninteresting.com/?author=865

Electron Thieves: Cyanide

2 H+ + 1/2O2

H2OADP +

H+

ATP synthase

ATP

H+

H+H+

Fig.8.7 Protein complexof electroncarriers

H+

H+H+

Cyt c

Q

V

FADH2 FADNAD+NADH

(carrying electronsfrom food)

Electron transport chain & pumping of protons

2 H+ + 1/2O2 H2O

ADP + Pi

H+

H+

ATP synthase

ATP

21

Intermembranespace

Mitochondrial matrix

Innermembrane

Fig. 9.16

ATP synthesis via H+ flow

Cyanide blocks O2's ability to mop up electrons so NADH and FADH2 never go back to NAD+ and FAD. It also inhibits proton pumping in IV and can “uncouple” proton diffusion from ATP production

Dinitrophenol

DNP used in 1930s in diet pills after first report on drug's ability to increase metabolic rate. DNP is an uncoupler that moves protons across the inner mitochondrial membrane and releases energy as heat. DNP overdose causes fatal fever. By end of 1938, DNP use no longer legal in US.