PART 5: PHOTOSYNTHESISChapter 10

Date: 10/6/16

AP Bio Vocabulary of the Day

(Stems, Prefixes, and Suffixes…Oh my!)

chrom- color

Example: chromatography (a lab

technique that separates color mixtures)

Fabulous Fact

Astronauts cannot belch – there is

no gravity to separate liquid from

gas in their stomachs.

What you need to know:

The summary equation of photosynthesis including the source and fate of the reactants and products.

How leaf and chloroplast anatomy relates to photosynthesis.

How photosystems convert solar energy to chemical energy.

How linear electron flow in the light reactions results in the formation of ATP, NADPH, and O2.

How chemiosmosis generates ATP in the light reactions.

How the Calvin Cycle uses the energy molecules of the light reactions to produce G3P.

The metabolic adaptations of C4 and CAM plants to arid, dry regions.

Examples of endergonic and exergonic reactions.

The key role of ATP in energy coupling.

AP Biology Standards addressed: Big Idea 2, Science Practices 3,4,5

People to Ponder

Melvin Calvin

Born in 1911 in St. Paul Minnesota

Calvin was the son of immigrant parents from two different parts of the Russian Empire

His father’s name was changed to Calvin at Ellis Island because he was from Kalvaria, Lithuania

Calvin showed an interest and talent in science early on and in 1927 got a full scholarship to Michigan

Technological University

He was the school’s first chemistry major and not many courses were offered so he took courses in

mineralogy, geology, paleontology, and engineering- all served him well later

After his sophomore year Calvin took a year off and worked as an analyst at a brass factory to earn

money

He got his degree in 1931 and then his PhD in 1935

Calvin then worked at the University of Manchester in England where he was introduced to an

interdisciplinary approach to science

In 1937 he joined the faculty of UC Berkeley- the first chemist hired who had trained elsewhere since

1912

Melvin Calvin

He started working on molecular genetics (H-bonding in nucleic acids) and electronic structures in

molecules

During World War II, Calvin worked on an oxygen-generating apparatus for subs and was part of the

Manhattan Project

In 1942 he married Genevieve Jemtegaard who was a juvenile probation officer

The two collaborated on interdisciplinary projects- they investigated chemical factors on Rh blood

groups and figured out the structure of one Rh antigen- they named it elinin for their daughter Elin

Calvin rose through the ranks at Berkeley and became the director of bioorganics at the Lawrence

Radiation Lab (now Lawrence Livermore Lab) in 1946

He started working on photosynthesis with Andrew Benson and James Bassham

They added C14 to single celled green algae and stopped growth at different stages

They then used paper chromatography to isolate and identify radioactive compounds

From this the team identified most of the intermediate steps of photosynthesis and discovered the

Calvin Cycle

They also became the first to use C14 as a tracer to explain a chemical pathway

Melvin Calvin

The Calvin cycle is really the Calvin-Benson-Bassham Cycle

Calvin fired Benson and did not mention his role in his autobiography Following the Trail of Light: A

Scientific Odyssey

In 1961 Calvin was the sole recipient from the team of the Nobel Prize

His other work included photoelectric behavior, work on lunar rocks for NASA, heavy hydrogen in

biochemical cycles, biochemistry of learning, philosophy of science, and processes leading to the

origins of life

Eventually Calvin’s bioorganics group needed more space so he designed the Laboratory of Chemical

Biodynamics- a round building with few walls to encourage interdisciplinary interaction

Calvin directed the lab until the mandatory retirement age in 1980 when it was renamed the Melvin

Calvin Laboratory

He continued to work with a small research group until 1996

Calvin died in 1997

In addition to winning the Nobel Prize he wrote 7 books, 600 articles, and received numerous other

awards including the National Medal of Science, the highest US civilian science award

Metabolism is the totality of an organism’s chemical reactions

Manage the materials and energy resources of a cell

Catabolic pathways release energy by

breaking down complex molecules into

simpler compounds

Eg. digestive enzymes break down food

release energy

Anabolic pathways consume energy to build

complex molecules from simpler ones

Eg. amino acids link to form muscle protein

Energy = capacity to do work

Kinetic energy (KE): energy associated with

motion

Heat (thermal energy) is KE associated with

random movement of atoms or molecules

Potential energy (PE): stored energy as a result of

its position or structure

Chemical energy is PE available for release in a

chemical reaction

Energy can be converted from one form to

another

Eg. chemical mechanical electrical

A closed system, such as liquid in a thermos, is isolated from its surroundings

In an open system, energy and matter can be transferred between the system and its surroundings

Organisms are open systems

Thermodynamics is the study of

energy transformations that occur in

nature

The First Law of Thermodynamics

The energy of the universe is constant

Energy can be transferred and transformed

Energy cannot be created or destroyed

Also called the principle of Conservation of

Energy

The Second Law of Thermodynamics

Every energy transfer or transformation increases the entropy (disorder) of the universe

During every energy transfer or transformation, some energy is unusable, often lost as heat

Free energy: part of a system’s energy

available to perform work

G = change in free energy

Exergonic reaction: energy is released

Spontaneous reaction

G < 0

Endergonic reaction: energy is required

Absorb free energy

G > 0

A cell does three main kinds of work:

Mechanical

Transport

Chemical

Cells manage energy resources to do work by

energy coupling: using an exergonic process to

drive an endergonic one

ATP (adenosine triphosphate) is the cell’s main

energy source in energy coupling

ATP = adenine + ribose + 3 phosphates

When the bonds between the phosphate groups

are broken by hydrolysis energy is released

This release of energy comes from the chemical

change to a state of lower free energy, not in the

phosphate bonds themselves

How ATP Performs Work

Exergonic release of Pi is used to do the

endergonic work of cell

When ATP is hydrolyzed, it becomes ADP

(adenosine diphosphate)

NH2

Glu

P i

Pi

P i

P i

GluNH3

P

P

P

ATP

ADP

Motor protein

Mechanical work: ATP phosphorylates motor proteins

Protein moved

Membrane

protein

Solute

Transport work: ATP phosphorylates transport proteins

Solute transported

Chemical work: ATP phosphorylates key reactants

Reactants: Glutamic acidand ammonia

Product (glutamine)made

+ +

+

Photosynthesis Overview

Heterotroph: “other” feeders (consumers)

Autotroph: self-feeders (producers)

Some autotrophs use photosynthesis- conversion

of light energy to chemical energy. They are

called photoautotrophs

Photoautotrophs

Photosynthesis: Converts light energy to

chemical energy of food

Chloroplasts: sites of photosynthesis in plants

Thylakoid space

Sites of Photosynthesis

mesophyll: chloroplasts

mainly found in these

cells of leaf

stomata: pores in leaf

(CO2 enter/O2 exits)

chlorophyll: green

pigment in thylakoid

membranes of

chloroplasts

Photosynthesis Equation

6CO2 + 6H2O + light energy C6H12O6 +6O2

Oxygen is derived from H2O

Redox Reaction:

water is split e- transferred with H+ to CO2 sugar

2 stages

1. Light reactions (photo)

Convert solar to chemical energy

2. Calvin Cycle (synthesis)

Carbon fixation to produce carbohydrates

Photosynthesis = Light Reactions + Calvin Cycle

“photo” “synthesis”

Photosynthesis Details

Light Reactions: Convert solar E to chemical

E of ATP and NADPH

Nature of sunlight

Light = Energy = electromagnetic radiation

Shorter wavelength (λ): higher E

Visible light - detected by human eye

Light: reflected, transmitted or absorbed

Electromagnetic Spectrum

Interaction of light with chloroplasts

Pigments absorb different λ of light

chlorophyll – absorb violet-blue/red light,

reflect green

chlorophyll a (blue-green): light reaction, converts

solar to chemical E

chlorophyll b (yellow-green): conveys E to

chlorophyll a

carotenoids (yellow, orange): photo protection,

broaden color spectrum for photosynthesis

Types: xanthophyll (yellow) & carotenes (orange)

anthocyanin (red, purple, blue): photoprotection,

antioxidants

Photosynthetic pigments

Absorption Spectrum: determines effectiveness of

different wavelengths for photosynthesis

Light Reactions

Photosystem: made up of a reaction center complex

surrounded by light harvesting complexes

Contains chlorophyll a- light capturing pigment

When light is absorbed energy is transferred between

pigment molecules in the light harvesting complex

The reaction center complex has primary electron

acceptors

The thylakoid has two photosystems: Photosystem I (PSI)

and Photosystem II (PSII)

Light Reactions

Summary:

1. Light energy splits H2O to O2 releasing

high energy electrons (e-)

2. Movement of e- used to generate ATP

3. Electrons end up on NADP+, reducing it to

NADPH

Electrons in chlorophyll molecules are

excited by absorption of light

Photosystem: reaction center & light-harvesting

complexes (pigment + protein)

Electron Flow – It’s All About

Electron Flow!

Two routes for electron flow:

A. Linear (noncyclic) electron flow

(photosystem II)

B. Cyclic electron flow

(photosystem I)

Light Reaction (Linear electron flow)

1. Chlorophyll excited by light absorption

2. E passed to reaction center of

Photosystem II (protein + chlorophyll a)

3. e- captured by primary electron acceptor

Redox reaction e- transfer

e- prevented from losing E (drop to

ground state)

4. H2O is split to replace e- O2 formed

5. e- passed to Photosystem I via ETC

6. E transfer pumps H+ to thylakoid space

7. ATP produced by photophosphorylation

8. e- moves from PS I’s primary electron acceptor to 2nd ETC

9. NADP+ reduced to NADPH

Mechanical analogy for the light reactions

Cyclic Electron Flow: uses PS I only; produces ATP

for Calvin Cycle (no O2 or NADPH produced)

Chemiosmosis is used to generate ATP

Summary: the light reactions use H2O and produce O2,

NADPH, and ATP

Calvin Cycle

Also called the Dark Reaction or Light-Independent

Reaction

These reactions can happen in the light OR dark (they’re

light independent)

The ATP and NADPH made in the light reaction are used

to fuel the light-independent reaction by donating

electrons

Calvin Cycle: Uses ATP and NADPH to convert

CO2 to sugar

Occurs in the stroma

Uses ATP, NADPH, CO2

Produces 3-C sugar G3P (glyceraldehyde-3-phosphate)

Three phases:

1. Carbon fixation

2. Reduction

3. Regeneration of RuBP (CO2 acceptor)

Phase 1: 3 CO2 + RuBP (5-C sugar ribulose

bisphosphate)

• Catalyzed by enzyme rubisco (RuBP

carboxylase)

Phase 2: Use 6

ATP and 6 NADPH

to produce 1 net

G3P

Phase 3: Use 3 ATP

to regenerate RuBP

CO2 is taken in through the stomata of the leaf

CO2 is incorporated one molecule at a time to produce

intermediate carbon compounds like RuBP and PGAL (aka

G3P)

It’s a continual cycle that releases one PGAL at a time

and recycles the other carbon fragments- for every 6

molecules one is released and five are recycled

The PGAL exits the chloroplast stroma and goes into the

cell to be made into glucose

Summary: the Calvin Cycle uses CO2, ATP and NADPH

and produces carbohydrates, NADP+, and ADP

Evolutionary Adaptations

1. Problem with C3 Plants:

CO2 fixed to 3-C compound in Calvin cycle

Ex. Rice, wheat, soybeans

Hot, dry days:

partially close stomata, ↓CO2

Photorespiration

↓ photosynthetic output (no sugars made)

2. C4 Plants:

CO2 fixed to 4-C compound

Ex. corn, sugarcane, grass

Hot, dry days stomata close

2 cell types = mesophyll & bundle sheath cells

mesophyll : PEP carboxylase fixes CO2 (4-C), pump CO2 to bundle sheath

bundle sheath: CO2 used in Calvin cycle

↓photorespiration, ↑sugar production

WHY? Advantage in hot, sunny areas

C4 Leaf Anatomy

3. CAM Plants:

Crassulacean acid metabolism (CAM)

NIGHT: stomata open CO2 enters converts to organic acid, stored in mesophyll cells

DAY: stomata closed light reactions supply ATP, NADPH; CO2 released from organic acids for Calvin cycle

Ex. cacti, pineapples, succulent (H2O-storing) plants

WHY? Advantage in arid conditions

Comparison

C3 C4 CAM

C fixation &

Calvin together

C fixation &

Calvin in different

cells

C fixation &

Calvin at different

TIMES

Rubisco PEP carboxylase Organic acid

Photosynthesis

Light

Reaction

Light

ENERGY

H2O

split

organic

molecules

O2

evolved

ETC

regenerate

RuBP

photophosphorylation

ATPchemiosmosis

energized

electrons

Calvin

Cycle

NADPH

CO2 fixed

to RuBP

C3

phosphorylated

and reduced

G3P

glucose &

other

carbs

stored in in which

involves both

Reduce

NADP+ to

using

in process

called

to form

Credit: Modified from

Anna VanDordrecht

(SCOE) & Mrs. Chou

(Longmont High School)