PHOTOSYNTHESIS

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PHOTOSYNTHESIS
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Overview A. Step One Transferring radiant
energy to chemical energy
e-
Energy of photon
Transferred to an electron
e-
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Overview A. Step Two storing that chemical
energy in the bonds of molecules
e-
C6 (glucose)
ATP
ADPP
6 CO2
e-
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Overview A. Step Two storing that chemical
energy in the bonds of molecules
e-
C6 (glucose)
ATP
ADPP
6 CO2
e-
Light Independent Reaction
Light Dependent Reaction
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation
e-
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.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation
e- acceptor
e-
PS I
photosystems are complexes of chlorophyll
molecules containing Mg, nested in the inner
membrane of bacteria and chloroplasts.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation
e- acceptor
e-
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.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation
e- acceptor
e-
ATP
e-
ADPP
The electron is passed down the chain, H are
pumped out, they flood back in and ATP is made.
PS I
The electron transport chain is nested in the
inner membrane, as well like in mitochondria
and chemiosmosis occurs.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation
e- acceptor
e-
ATP
e-
ADPP
An electron is excited by sunlight, and the
energy is used to make ATP. The electron is
returned to the photosystem.CYCLIC
PHOSPHORYLATION.
PS I
The electron transport chain is nested in the
inner membrane, as well like in mitochondria
and chemiosmosis occurs.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation b
. Sulpher bacteria
e- acceptor
e-
Purple and green sulphur bacteria
ATP
e-
ADPP
PS I
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
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation b
. Sulpher bacteria
e- acceptor
e-
NADP
NADPH
ATP
e-
ADPP
PS I
The electron can be passed to NADP, reducing NADP
to NADP- (H)
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation b
. Sulpher bacteria
e- acceptor
e-
NADP
NADPH
ATP
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-
ADPP
PS I
The electron can be passed to NADP, reducing NADP
to NADP- (H)
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation b
. Sulpher bacteria
e- acceptor
e-
NADP
NADPH
ATP
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
e-
ADPP
PS I
The Photosystem is more electronegative than H2S,
and can strip electrons from this molecule
releasing sulphur gas.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation b
. Sulpher bacteria
e- acceptor
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).
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems a. Cyclic phosphorylation b
. Sulpher bacteria
e- acceptor
e-
NADP
NADPH
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).
ATP
e-
ADPP
PS I
If photosynthesis could evolve to strip electrons
from a more abundant electron donor, life could
expand from these limited habitats hmmm. H2S.
H2S.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems 2. Advanced System
e- acceptor
Cyanobacteria, algae, plants
PS I
PS II
RIGHT! H2O!!! But water holds electrons more
strongly than H2S this process didnt evolve
until a PS evolved that could strip electrons
from water PSII.
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems 2. Advanced System
e- acceptor
e-
e-
PS I
PS II
Photons excite electrons in both photosystems
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems 2. Advanced System
e- acceptor
e-
e-
ATP
ADPP
PS I
PS II
The electron from PSII is passed down the ETC,
making ATP, to PSI
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems 2. Advanced System
e- acceptor
e-
ATP
ADPP
PS I
e-
PS II
The electron from PSI is passed to NADP to make
NADPH
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems 2. Advanced System
e- acceptor
e-
ATP
ADPP
PS I
e-
The e- from PSII has filled the hole vacated by
the electron lost from PSI.
PS II
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A. Step 1 The Light Dependent Reaction 1.
Primitive Systems 2. Advanced System
e- acceptor
e-
ATP
ADPP
PS I
e-
Water is split to harvest electrons oxygen gas
is released as a waste product.
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Those were the light dependent reactions
reactions in which photosynthetic organisms
transform radiant energy into chemical bond
energy in ATP (and NADPH).
e-
C6 (glucose)
ATP
ADPP
6 CO2
e-
Light Independent Reaction
Light Dependent Reaction
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A. Step 1 The Light Dependent Reaction B Step
2 The Light-Independent Reaction
e-
C6 (glucose)
ATP
ADPP
6 CO2
e-
Light Independent Reaction
Light Dependent Reaction
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CO2
B. The Light Independent Reaction
C6
C5
RuBP
2 C3 (PGA)
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)
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6CO2
B. The Light Independent Reaction
6C6
6C5
RuBP
12 C3 (PGA)
Now, it is easier to understand these reactions
if we watch the simultaneous reactions involving
6 CO2 molecules
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6CO2
B. The Light Independent Reaction
6C6
6C5
RuBP
12 C3
ATP ADPP
10 C3
2 C3 C6 (Glucose)
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.
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B. The Light Independent Reaction
More energy is used to rearrange the 10 C3
molecules (30 carbons) into 6 C5 molecules (30
carbons) regenerating the 6 RuBP.
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Review
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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)
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A History of Photosynthesis
What kind of photosynthesis was this???
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A History of Photosynthesis
What kind of photosynthesis was this??? Cyclic
phosphorylation and Sulphur photosynthesis,
because it was non-oxygenic.
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A History of Photosynthesis
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.
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Carboniferous 354-290 mya
This 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 CO2lots of photosynthesis
and less decomposition means a decrease in CO2
and an increase in O2 in the atmosphere
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Cell Biology I. Overview II. Membranes How
Matter Get in and Out of Cells III. Harvesting
Energy Respiration and Photosynthesis IV.
Protein Synthesis
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IV. Protein Synthesis Why is this
important? Wellwhat do proteins DO?
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IV. Protein Synthesis Why is this
important? Wellwhat do proteins DO?

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

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IV. Protein Synthesis 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
(t-RNA)
(r-RNA)
U G C U G A C U A C U
(m-RNA)
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IV. Protein Synthesis 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
(t-RNA)
(r-RNA)
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
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IV. Protein Synthesis 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
R-RNA is complexed with proteins to form
ribosomes. Specific t-RNAs bind to specific
amino acids.
(t-RNA)
(r-RNA)
U G C U G A C U A C U
Amino acid
(m-RNA)
ribosome
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IV. Protein Synthesis 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
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-RNAs) is linked together to form a
protein. This is TRANSLATION.
(t-RNA)
(r-RNA)
U G C U G A C U A C U
Amino acid
(m-RNA)
ribosome
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IV. Protein Synthesis 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
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.
(t-RNA)
(r-RNA)
U G C U G A C U A C U
Amino acid
(m-RNA)
ribosome
glycoprotein
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription a. The
message is on one strand of the double helix -
the sense strand
3
5
sense
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
nonsense
3
5
TAG A CAT message makes sense ATC T
GTA nonsense limited by complementation
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription a. The
message is on one strand of the double helix -
the sense strand
3
5
sense
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
nonsense
3
5
intron
exon
exon
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!
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 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.
Promoter
3
5
sense
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
nonsense
3
5
intron
exon
exon
Promoters have sequences recognized by the RNA
Polymerase. They bind in particular orientation.
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 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.
Promoter
3
5
sense
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
G C A U GUUU G C C A A U AUG A U G A
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
nonsense
3
5
intron
exon
exon

1. Strand separate
2. RNA Polymerase can only synthesize RNA in a 5?3
   direction, so they only read the anti-parallel,
   3?5 strand (sense strand).

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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription c.
Transcription ends at a sequence called the
'terminator'.
Promoter
Terminator
3
5
sense
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
G C A U GUUU G C C A A U AUG A U G A
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
nonsense
3
5
intron
exon
exon
Terminator sequences destabilize the RNA
Polymerase and the enzyme decouples from the DNA,
ending transcription
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription c.
Transcription ends at a sequence called the
'terminator'.
Promoter
Terminator
3
5
sense
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
G C A U GUUU G C C A A U AUG A U G A
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
nonsense
3
5
intron
exon
exon
Initial RNA PRODUCT
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription c.
Transcription ends at a sequence called the
'terminator'.
Promoter
Terminator
3
5
sense
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
nonsense
3
5
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing
G C A U GUUU G C C A A U
AUG A
U G A
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.
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing
AUG A
G C A U GUUU G C C A A U
U G A
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.
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. 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 U
U G A
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. 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 U
U G A
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.
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. 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.
M-RNA
G C A U G U U U G C C A A U
U G A
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. 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. c. A second
t-RNA-AA binds to the second site
M-RNA
G C A U G U U U G C C A A U
U G A
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. 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. c. A second
t-RNA-AA binds to the second site d.
Translocation reactions occur
Meth
M-RNA
G C A U G U U U G C C A A U
U G A
The amino acids are bound and the ribosome moves
3-bases downstream
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation e.
polymerization proceeds
Meth
Phe
M-RNA
G C A U G U U U G C C A A U
U G A
The amino acids are bound and the ribosome moves
3-bases downstream
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation e.
polymerization proceeds
Meth
Phe
Ala
M-RNA
G C A U G U U U G C C A A U
U G A
The amino acids are bound and the ribosome moves
3-bases downstream
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation e.
polymerization proceeds f. termination of
translation
M-RNA
G C A U G U U U G C C A A U
U G A
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.
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation 4.
Post-Translational Modifications
Meth
Phe
Ala
Asn
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.
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IV. Protein Synthesis A. Overview B. The Process
of Protein Synthesis C. Regulation of Protein
Synthesis 1. Regulation of Transcription -
DNA bound to histones cant 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.