PHOTOSYNTHESIS

PHOTOSYNTHESIS

Overview:

A. Step One: Transferring radiant energy to chemical energy

Energy of photon

e-

e-

Transferred to an electron

Overview:

A. Step Two: storing that chemical energy in the bonds of molecules

e-

e-

6 CO2

C6 (glucose)ATP

ADP+P

Overview:

A. Step Two: storing that chemical energy in the bonds of molecules

e-

e-

6 CO2

C6 (glucose)ATP

ADP+P

Light Independent Reaction

Light Dependent Reaction

A. Step 1: The Light Dependent Reaction:

1. Primitive Systems

a. Cyclic phosphorylatione-

PS I

“photosystems” are complexes of chlorophyll molecules containing Mg, nested in the inner membrane of bacteria and chloroplasts.

Used by photoheterotrophs:Purple non-sulphur bacteria, green non-sulphur bacteria, and heliobacteria




PS I

“photosystems” are complexes of chlorophyll molecules containing Mg, nested in the inner membrane of bacteria and chloroplasts.

e- acceptor




PS I

The electron transport chain is nested in the inner membrane, as well; like in mitochondria….

e- acceptor

e-

The electron is transferred to an electron transport chain




PS I

The electron transport chain is nested in the inner membrane, as well; like in mitochondria… and chemiosmosis occurs.

e- acceptor

e-

The electron is passed down the chain, H+ are pumped out, they flood back in and ATP is made.

ADP+P

ATP




PS I

The electron transport chain is nested in the inner membrane, as well; like in mitochondria… and chemiosmosis occurs.

e- acceptor

e- ADP+P

ATP

An electron is excited by sunlight, and the energy is used to make ATP. The electron is returned to the photosystem….CYCLIC PHOSPHORYLATION.


1. Primitive Systemsa. Cyclic phosphorylationb. Sulpher bacteria

e-

PS I

e- acceptor

e- ADP+P

ATP

An electron is excited by sunlight, and the energy is used to make ATP. The electron is returned to the photosystem….CYCLIC PHOSPHORYLATION…..BUT something else can happen…

Purple and green sulphur bacteria



e-

PS I

e- acceptor

e- ADP+P

ATP

NADP NADPH

The electron can be passed to NADP, reducing NADP to NADP- (+H+)



e-

PS I

e- acceptor

e- ADP+P

ATP

NADP NADPH

The electron can be passed to NADP, reducing NADP to NADP- (+H+)

IF this happens, the electron is NOT recycled back to PSI.

For the process to continue, an electron must be stripped from another molecule and transferred to the PS to be excited by sunlight…



e-

PS I

e- acceptor

e- ADP+P

ATP

NADP NADPH

IF this happens, the electron is NOT recycled back to PSI.

For the process to continue, an electron must be stripped from another molecule and transferred to the PS to be exited by sunlight… H2S 2e + 2H+ + S

The Photosystem is more electronegative than H2S, and can strip electrons from this molecule – releasing sulphur gas….



e- acceptor

e-

PS I

e- ADP+P

ATP

NADP NADPH

H2S 2e + 2H+ + S

So, through these reactions, both ATP and NADPH are produced; sulphur gas is released as a waste product. These organisms are limited to living in an environment with H2S!!! (Sulphur springs).



e-

PS I

e- acceptor

e- ADP+P

ATP

NADP NADPH

H2S 2e + 2H+ + S

So, through these reactions, both ATP and NADPH are produced; sulphur gas is released as a waste product. These organisms are limited to living in an environment with H2S!!! (Sulphur springs).

If photosynthesis could evolve to strip electrons from a more abundant electron donor, life could expand from these limited habitats… hmmm…. H2S…. H2S….


1. Primitive Systems2. Advanced System

PS I

e- acceptor

RIGHT! H2O!!! But water holds electrons more strongly than H2S; this process didn’t evolve until a PS evolved that could strip electrons from water… PSII.

PS II

Cyanobacteria, algae, plants



PS I

e- acceptor

PS II

Photons excite electrons in both photosystems…

e-

e-



PS I

e- acceptor

PS II

The electron from PSII is passed down the ETC, making ATP, to PSI

e-

e-

ADP+P

ATP



PS I

e- acceptor

PS II

The electron from PSI is passed to NADP to make NADPH

e-

e-

ADP+P

ATP

NADP NADPH



PS I

e- acceptor

PS IIThe e- from PSII has “filled the hole” vacated by the electron lost from PSI.

e-

e-

ADP+P

ATP

NADP NADPH



PS I

e- acceptor

Water is split to harvest electrons; oxygen gas is released as a waste product.

e-

e-

ADP+P

ATP

NADP NADPH

PS II

2H2O 4e + 4H+ + 2O (O2)

Those were the light dependent reactions; reactions in which photosynthetic organisms transform radiant energy into chemical bond energy in ATP (and NADPH).

e-

e-

6 CO2

C6 (glucose)ATP

ADP+P



e-

e-

6 CO2

C6 (glucose)ATP

ADP+P



A. Step 1: The Light Dependent Reaction:B: Step 2: The Light-Independent Reaction:

B. The Light Independent Reaction

C5

RuBP

CO2

C6

A molecule of CO2 binds to Ribulose biphosphate, making a 6-carbon molecule. This molecule is unstable, and splits into 2 3-carbon molecules of phosphoglycerate (PGA)

2 C3 (PGA)


6C5

RuBP

6CO2

6C6

Now, it is easier to understand these reactions if we watch the simultaneous reactions involving 6 CO2 molecules

12 C3 (PGA)


6C5

RuBP

6CO2

6C6

12 C3

2 C3

C6

(Glucose)

10 C3

ATP

ADP+P

NADPH

NADP

2 of the 12 PGA are used to make glucose, using energy from ATP and the reduction potential of NADPH… essentially, the H is transferred to the PGA, making carbohydrate from carbon dioxide.


More energy is used to rearrange the 10 C3 molecules (30 carbons) into 6 C5 molecules (30 carbons); regenerating the 6 RuBP.

6C5

RuBP

6CO2

6C6

12 C3

2 C3

C6

(Glucose)

10 C3

ATP

ADP+P

NADPH

NADP

ATP

ADP+P

Review

A History of Photosynthesis

Photosynthesis evolved early; at least 3.8 bya – bacterial mats like these stromatolites date to that age, and earlier microfossils exist that look like cyanobacteria. Also, CO2 levels drop (Calvin cycle + dissolved in rain)


What kind of photosynthesis was this???


What kind of photosynthesis was this???

Cyclic phosphorylation and Sulphur photosynthesis, because it was non-oxygenic.


And 2.3 bya is when we see the oldest banded iron formations, demonstrating for the first time that iron crystals were exposed to atmospheric oxygen during sedimentation.

Carboniferous: 354-290 myaThis is the period when our major deposits of fossil fuel were laid down as biomass that did NOT decompose. So, that carbon was NOT returned to the atmosphere as CO2…lots of photosynthesis and less decomposition means a decrease in CO2 and an increase in O2 in the atmosphere…

Cell Biology

I. OverviewII. Membranes: How Matter Get in and Out of CellsIII. Harvesting Energy: Respiration and PhotosynthesisIV. Protein Synthesis

IV. Protein Synthesis

Why is this important?

Well…what do proteins DO?


Why is this important?

Well…what do proteins DO?

Think about it this way:

1)sugars, fats, lipids, nucleic acids and proteins, themselves, are broken down and built up through chemical reactions catalyzed by enzymes. 2)So everything a cell IS, and everything it DOES, is either done by proteins or is done by molecules put together by proteins.


A. Overview

A T G C T G A C T A C T G

T A C G A CT G A T G A C

Genes are read by enzymes and RNA molecules are produced… this is TRANSCRIPTION

U G C U G A C U A C U (m-RNA)

(r-RNA)(t-RNA)


A. Overview



Genes are read by enzymes and RNA molecules are produced… this is TRANSCRIPTION

U G C U G A C U A C U (m-RNA)

Eukaryotic RNA and some prokaryotic RNA have regions cut out… this is RNA SPLICING

(r-RNA)(t-RNA)


A. Overview



U G C U G A C U A C U

(m-RNA)

(r-RNA)(t-RNA)

R-RNA is complexed with proteins to form ribosomes. Specific t-RNA’s bind to specific amino acids.

ribosome

Amino acid


A. Overview




(m-RNA)

(r-RNA)(t-RNA)

The ribosome reads the m-RNA. Based on the sequence of nitrogenous bases in the m-RNA, a specific sequence of amino acids (carried to the ribosome by t-RNA’s) is linked together to form a protein. This is TRANSLATION.

ribosome

Amino acid


A. Overview




(m-RNA)

(r-RNA)(t-RNA)

The protein product may be modified (have a sugar, lipid, nucleic acid, or another protein added) and/or spliced to become a functional protein. This is POST-TRANSLATIONAL MODIFICATION.

ribosome

Amino acid

glycoprotein

IV. Protein SynthesisA. OverviewB. The Process of Protein Synthesis

1. Transcription a. The message is on one strand of the double helix - the sense strand:

3’

3’

5’

5’

“TAG A CAT” message makes ‘sense’“ATC T GTA” ‘nonsense’ limited by complementation

A C T A T A C G T A C A A A C G G T T A T A C T A C T T T

T G A T A T G C A T G T T T G C C A A T A T G A T G A A A

sense

nonsense


1. Transcription a. The message is on one strand of the double helix - the sense strand:

3’

3’

5’

5’

In all eukaryotic genes and in some prokaryotic sequences, there are introns and exons. There may be multiple introns of varying length in a gene. Genes may be several thousand base-pairs long. This is a simplified example!



sense

nonsense

intronexon exon


1. Transcription b. The cell 'reads' the correct strand based on the location of the promoter, the

anti-parallel nature of the double helix, and the chemical limitations of the 'reading' enzyme, RNA Polymerase.

3’

3’

5’

5’

Promoters have sequences recognized by the RNA Polymerase. They bind in particular orientation.



sense

nonsense

intronexon exon

Promoter


1. Transcription b. The cell 'reads' the correct strand based on the location of the promoter, the

anti-parallel nature of the double helix, and the chemical limitations of the 'reading' enzyme, RNA Polymerase.

3’

3’

5’

5’

1) Strand separate2) RNA Polymerase can only synthesize RNA in a 5’3’ direction,

so they only read the anti-parallel, 3’5’ strand (‘sense’ strand).



sense

nonsense

intronexon exon

Promoter

G C A U GUUU G C C A A U AUG A U G A


1. Transcription c. Transcription ends at a sequence called the 'terminator'.

Terminator sequences destabilize the RNA Polymerase and the enzyme decouples from the DNA, ending transcription

3’

3’

5’

5’



sense

nonsense

intronexon exon

Promoter


Terminator



3’

3’

5’

5’



sense

nonsense

intronexon exon

Promoter


Terminator

Initial RNA PRODUCT:



3’

3’

5’

5’



sense

nonsense

Promoter Terminator

intronexon exon

G C A U GUUU G C C A A U AUG A U G AInitial RNA PRODUCT:


1. Transcription2. Transcript Processing

intronexon exon

Initial RNA PRODUCT:

Introns are spliced out, and exons are spliced together. Sometimes these reactions are catalyzed by the intron, itself, or other catalytic RNA molecules called “ribozymes”.

G C A U GUUU G C C A A UAUG A U G A


1. Transcription2. Transcript Processing

intron

exon exon

Final RNA PRODUCT:

This final RNA may be complexed with proteins to form a ribosome (if it is r-RNA), or it may bind amino acids (if it is t-RNA), or it may be read by a ribosome, if it is m-RNA and a recipe for a protein.

G C A U GUUU G C C A A U

AUG A

U G A


1. Transcription2. Transcript Processing3. Translation a. m-RNA attaches to the ribosome at the 5' end.

M-RNA: G C A U G U U U G C C A A UU G A


1. Transcription2. Transcript Processing3. Translation a. m-RNA attaches to the ribosome at the 5' end.


It then reads down the m-RNA, one base at a time, until an ‘AUG’ sequence (start codon) is positioned in the first reactive site.


1. Transcription2. Transcript Processing3. Translation a. m-RNA attaches to the ribosome at the 5' end. b. a specific t-RNA molecule, with a complementary UAC anti-codon sequence,

binds to the m-RNA/ribosome complex.


Meth



binds to the m-RNA/ribosome complex. c. A second t-RNA-AA binds to the second site


MethPhe



binds to the m-RNA/ribosome complex. c. A second t-RNA-AA binds to the second site d. Translocation reactions occur


Meth Phe

The amino acids are bound and the ribosome moves 3-bases “downstream”


1. Transcription2. Transcript Processing3. Translation e. polymerization proceeds


Meth Phe


Ala

Asn


1. Transcription2. Transcript Processing3. Translation e. polymerization proceeds


Meth Phe


Ala

Asn


1. Transcription2. Transcript Processing3. Translation e. polymerization proceeds f. termination of translation


Some 3-base codon have no corresponding t-RNA. These are stop codons, because translocation does not add an amino acid; rather, it ends the chain.

Meth Phe Ala Asn


1. Transcription2. Transcript Processing3. Translation4. Post-Translational Modifications

Most initial proteins need to be modified to be functional. Most need to have the methionine cleaved off; others have sugar, lipids, nucleic acids, or other proteins are added.

Meth Phe Ala Asn

IV. Protein SynthesisA. OverviewB. The Process of Protein SynthesisC. Regulation of Protein Synthesis

1. Regulation of Transcription

- DNA bound to histones can’t be accessed by RNA Polymerase - but the location of histones changes, making genes accessible (or inaccessible)

Initially, the orange gene is “off”, and the green gene is “on”

Now the orange gene is “on” and the green gene is “off”.

PHOTOSYNTHESIS

Documents

primitive systemsa

acceptoreadp patpan

cyclic phosphorylationb

e acceptore

electron transport chaina

sulpher bacteriaeps

inner membrane of bacteria

nadp h