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PHOTOSYNTHESIS
Overview:
A. Step One: Transferring radiant energy to chemical energy
eEnergy of photon
Transferred to
an electron
e-
Overview:
A. Step Two: storing that chemical energy in the bonds of molecules
eATP
e-
ADP
+P
C6 (glucose)
6 CO2
Overview:
A. Step Two: storing that chemical energy in the bonds of molecules
eATP
e-
ADP
+P
C6 (glucose)
6 CO2
Light Dependent Light Independent
Reaction
Reaction
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.
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.
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
e- acceptor
a. Cyclic phosphorylation
e-
eThe 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….
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
e- acceptor
a. Cyclic phosphorylation
eATP
eThe electron is passed down
the chain, H+ are pumped out,
they flood back in and ATP is
made.
ADP+P
PS I
The electron transport chain is nested in the inner membrane, as
well; like in mitochondria… and chemiosmosis occurs.
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
e- acceptor
a. Cyclic phosphorylation
eATP
eAn electron is excited by
sunlight, and the energy is
used to make ATP. The
electron is returned to the
photosystem….CYCLIC
PHOSPHORYLATION.
ADP+P
PS I
The electron transport chain is nested in the inner membrane, as
well; like in mitochondria… and chemiosmosis occurs.
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
a. Cyclic phosphorylation
b. Sulpher bacteria
Purple and green
sulphur bacteria
e- acceptor
eATP
e-
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…
ADP+P
PS I
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
a. Cyclic phosphorylation
b. Sulpher bacteria
e- acceptor
eNADP
NADPH
ATP
e-
ADP+P
PS I
The electron can be passed to NADP,
reducing NADP to NADP- (+H+)
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
a. Cyclic phosphorylation
b. Sulpher bacteria
e- acceptor
eNADP
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…
NADPH
ATP
e-
ADP+P
PS I
The electron can be passed to NADP,
reducing NADP to NADP- (+H+)
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
a. Cyclic phosphorylation
b. Sulpher bacteria
e- acceptor
eNADP
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…
ATP
e-
ADP+P
PS I
H2S
2e + 2H+ + S
The Photosystem is more electronegative than H2S, and can strip
electrons from this molecule – releasing sulphur gas….
NADPH
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
a. Cyclic phosphorylation
b. Sulpher bacteria
So, through these reactions,
both ATP and NADPH are
produced; sulphur gas is
released as a waste
eproduct. These organisms
are limited to living in an
environment with H2S!!!
(Sulphur springs).
e- acceptor
eNADP
ATP
ADP+P
PS I
H2S
2e + 2H+ + S
NADPH
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
a. Cyclic phosphorylation
b. Sulpher bacteria
So, through these reactions,
both ATP and NADPH are
produced; sulphur gas is
released as a waste
eproduct. 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….
e- acceptor
eNADP
ATP
ADP+P
PS I
H2S
2e + 2H+ + S
NADPH
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 didn’t evolve until a PS evolved that
could strip electrons from water… PSII.
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
2. Advanced System
e- acceptor
ee-
PS I
PS II
Photons excite electrons in both photosystems…
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
2. Advanced System
e- acceptor
ee-
ATP
ADP+P
PS I
PS II
The electron from PSII is passed down the ETC, making ATP, to PSI
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
2. Advanced System
e- acceptor
eNADP
ATP
ADP+P
e- PS I
PS II
The electron from PSI is passed to NADP to make NADPH
NADPH
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
2. Advanced System
e- acceptor
eNADP
NADPH
ATP
ADP+P
e- PS I
PS II
The e- from PSII has “filled
the hole” vacated by the
electron lost from PSI.
A. Step 1: The Light Dependent Reaction:
1. Primitive Systems
2. Advanced System
e- acceptor
eNADP
NADPH
ATP
ADP+P
e- PS I
PS II
2H2O
4e + 4H+ + 2O
Water is split to harvest
electrons; oxygen gas is
released as a waste product.
(O2)
Those were the light dependent reactions; reactions in which
photosynthetic organisms transform radiant energy into chemical bond
energy in ATP (and NADPH).
eATP
e-
ADP
+P
Light Dependent
Reaction
C6 (glucose)
6 CO2
Light Independent
Reaction
A. Step 1: The Light Dependent Reaction:
B: Step 2: The Light-Independent Reaction:
eATP
eLight Dependent
Reaction
ADP
+P
C6 (glucose)
6 CO2
Light Independent
Reaction
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)
B. The Light Independent Reaction
6CO2
6C6
6C5
RuBP
12 C3 (PGA)
Now, it is easier to understand these
reactions if we watch the simultaneous
reactions involving 6 CO2 molecules
B. The Light Independent Reaction
6CO2
6C6
6C5
RuBP
12 C3
ATP
10 C3
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.
2 C3
NADPH
NADP
ADP+P
C6
(Glucose)
B. The Light Independent Reaction
6CO2
6C6
6C5
RuBP
12 C3
ATP
ATP
ADP+P
More energy is used to rearrange
the 10 C3 molecules (30 carbons)
into 6 C5 molecules (30 carbons);
regenerating the 6 RuBP.
10 C3
2 C3
NADPH
NADP
ADP+P
C6
(Glucose)
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)
A History of Photosynthesis
What kind of
photosynthesis was this???
A History of Photosynthesis
What kind of
photosynthesis was this???
Cyclic phosphorylation and
Sulphur photosynthesis,
because it was nonoxygenic.
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.
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
CO2…lots of
photosynthesis and
less decomposition
means a decrease in
CO2 and an increase
in O2 in the
atmosphere…
Cell Biology
I. Overview
II. Membranes: How Matter Get in and Out of Cells
III. Harvesting Energy: Respiration and Photosynthesis
IV. Protein Synthesis
IV. Protein Synthesis
Why is this important?
Well…what do proteins DO?
IV. Protein Synthesis
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.
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
Genes are read by enzymes and
RNA molecules are produced… (r-RNA)
this is TRANSCRIPTION
UGCUGACUACU
(m-RNA)
(t-RNA)
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
Genes are read by enzymes and
RNA molecules are produced… (r-RNA)
this is TRANSCRIPTION
UGCUGACUACU
(m-RNA)
Eukaryotic RNA and some
prokaryotic RNA have regions
cut out… this is RNA SPLICING
(t-RNA)
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
UGCUGACUACU
R-RNA is complexed with
proteins to form ribosomes.
Specific t-RNA’s bind to specific
amino acids.
(r-RNA)
(t-RNA)
Amino acid
(m-RNA)
ribosome
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
UGCUGACUACU
The ribosome reads the m-RNA.
Based on the sequence of
(r-RNA)
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.
(m-RNA)
ribosome
(t-RNA)
Amino acid
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
UGCUGACUACU
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.
(r-RNA)
Amino acid
(m-RNA)
ribosome
glycoprotein
(t-RNA)
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 TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
“TAG A CAT” message makes ‘sense’
“ATC T GTA” ‘nonsense’ limited by complementation
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 TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
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!
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 antiparallel nature of the double helix, and the chemical limitations of the 'reading'
enzyme, RNA Polymerase.
3’
Promoter
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
exon
Promoters have sequences recognized by the RNA
Polymerase. They bind in particular orientation.
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 antiparallel nature of the double helix, and the chemical limitations of the 'reading'
enzyme, RNA Polymerase.
3’
Promoter
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
G C A U GUUU G C C A A U AUG A U G A
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
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).
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
c. Transcription ends at a sequence called the 'terminator'.
3’
Promoter
Terminator
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
G C A U GUUU G C C A A U AUG A U G A
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
exon
Terminator sequences destabilize the RNA Polymerase and the
enzyme decouples from the DNA, ending transcription
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
c. Transcription ends at a sequence called the 'terminator'.
3’
Promoter
Terminator
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
G C A U GUUU G C C A A U AUG A U G A
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
3’
exon
Initial RNA
PRODUCT:
nonsense
intron
exon
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
c. Transcription ends at a sequence called the 'terminator'.
3’
Promoter
Terminator
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
3’
exon
Initial RNA
PRODUCT:
nonsense
intron
exon
G C A U GUUU G C C A A U AUG A U G A
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
exon
Initial RNA
PRODUCT:
intron
exon
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”.
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
intron
exon
exon
AUG A
Final RNA
PRODUCT:
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 mRNA and a recipe for a protein.
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 CAU G U U U G C CAAU U GA
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 CAU G U U U G C CAAU U GA
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.
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.
Meth
M-RNA:
G CAU G U U U G C CAAU U GA
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
Phe
Meth
M-RNA:
G CAU G U U U G C CAAU U GA
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:
Phe
G CAU G U U U G C CAAU U GA
The amino acids are bound and the ribosome moves 3-bases “downstream”
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
3. Translation
e. polymerization proceeds
Meth
M-RNA:
Ala
Asn
Phe
G CAU G U U U G C CAAU U GA
The amino acids are bound and the ribosome moves 3-bases “downstream”
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
3. Translation
e. polymerization proceeds
Meth
M-RNA:
Asn
Phe
Ala
G CAU G U U U G C CAAU U GA
The amino acids are bound and the ribosome moves 3-bases “downstream”
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
Meth
M-RNA:
Phe
Ala
Asn
G CAU G U U U G C CAAU U GA
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.
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.
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
C. 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”.