1. 1
CHLOROPLAST
• members of plastid
family
• present in all living plant
cells
• all plastids contain
genome
• plastids compose of 2
membrane layers
• Chloroplast has 3
membrane layers
4. 4
STROMA
• colourless fluid inside
inner membrane
• analogous to the
mitochondrial matrix
• contains many metabolic
enzymes, CO2 fixation
• contains a special set of
ribosomes, RNAs, and
DNA
• H+ for electron transport
and ADP, Pi source
5. 5
THYLAKOIDS
• Membrane that form a set
of flattened disc like sacs
• Different protein functions:
– electron-transport chains
– photosynthetic light-
capturing systems
– ATP synthase
• thylakoid space – lumen
connects to other thylakoid
form a space
6. 6
Chloroplast functions
• Photosynthesis
• Biosyntheses:
–fatty acids and a number of amino acids
–reduction of nitrite (NO2
-) to ammonia
(NH3) for
•amino acids
•nucleotides.
7. 7
Photosynthesis
Electrons play a primary role in photosynthesis
In eukaryotes, photosynthesis takes place in
chloroplasts
Autotrophs use energy to make their own organic
molecules from CO2 and inorganic sources such as
water
Photoautotrophs use light as an energy source
Heterotrophs consume or decompose organic
molecules
8. 8
Two stages of photosynthesis:
Light-dependent reactions – energy from sunlight is
converted into chemical energy to replenish ATP and
NADPH
Light-independent reactions (Calvin cycle) – excess
energy is stored by building high-energy sugar molecules
to be used when sunlight is not available
9. 9
The two stages of photosynthesis are
linked together and occur at the same
time.
10. 10
Light-Dependent Reactions
Two main processes:
Light absorption
LIGHT behaves as if it were composed of "units" or
"packets" of energy that travel in waves. These packets are
photons.
Synthesis of ATP and NADPH
11. 11
Synthesis of ATP and NADPH Summary
Energy from sunlight is captured in excited electrons and used to
synthesize more useful ATP and NADPH
Electron transfer systems are used to extract energy from excited
electrons
Some of the energy is used to create a gradient of H+ across the
thylakoid membranes that provides energy for ATP synthesis
Electrons are ultimately passed along to reduce NADP+ to NADPH
12. 12
Water Splitting
Water splitting complex provides a source of
electrons to be excited during light-dependent
reactions
2 H2O → 4 H+ + 4 e– + O2
Located close to photosystem II
13. 13
Light-Independent Reactions
Light-independent reactions (Calvin cycle) store
some of the energy captured from sunlight in the
form of high-energy molecules such as sugar
When sunlight is not available, stored carbohydrates
are broken down by aerobic respiration in the
mitochondria to replenish ATP and NADH
14. 14
Calvin Cycle
During the Calvin cycle, CO2 is reduced and
converted into organic substances
NADPH provides electrons and hydrogen
ATP provides additional energy
Carbon fixation involves capturing CO2 molecules
with the key enzyme rubisco (RuBP
carboxylase/oxygenase)
15. 15
Rubisco
As rubisco provides the source of organic molecules
for most of the world’s organisms
100 billion tons of CO2 are converted into
carbohydrates each year
Represents 50% or more of the total protein in
leaves
16. 16
Calvin Cycle
Each turn of the Calvin cycle captures one CO2 molecule
Three turns of the Calvin cycle are needed to capture
the three carbons in one G3P molecule
Six turns are needed to make a six-carbon sugar such as
glucose
6 CO2 + 12 NADPH + 18 ATP
↓
C6H12O6 + 12 NADP+ + 18 ADP + 18 Pi
17. 17
Calvin Cycle Summary
Carbon fixation – CO2 added
to RuBP to produce two 3PGA
molecules
Reduction – NADPH and ATP
used to convert 3PGA into
G3P, a higher energy molecule
used to build sugars
Regeneration – remaining
G3P molecules are used to
recreate the starting material
RuBP
Fig. 9-13a, p. 192
18. 18
Photosynthetic Products
Surplus G3P formed in the Calvin cycle can be the
starting material for many organic molecules
Carbohydrates, lipids, proteins, nucleic acids
Sucrose (disaccharide) is used to circulate
photosynthetic products from cell to cell in plants
Starch is used for longer storage of energy
19. 19
What is ribosome?
• Ribosome - protein synthesizer
consisting of two subunits
• Basically the protein factory.
Subunits each have role in
making of proteins.
• Larger one, “50S”, is upper
picture. Smaller is “30S”
(They look the same size here
because of space restrictions.)
20. 20
• 50S (left) and 30S. This time you can see them from different
angles, through different style of picture
• Related to their respective sizes. Numbers actually measures of
how quickly each subunit sinks to the bottom of a container of
liquid when spun in a centrifuge
• One subunit smaller than other, but both are larger than average
protein
21. 21
Protein synthesis
• Process starts from DNA
through “transcription”
• “Translation” is where
ribosome comes in.
Translation occurs when
protein formed from code
on mRNA
• Ribosome carries out the
translation of the
nucleotide triplets
22. 22
Initiation: The first phase of translation
• Translation begins when
mRNA attaches to the
30S
• tRNA comes and binds to
mRNA where nucleotide
code matches
• This triggers 50S binding
to 30S. 50S is where all
tRNAs will bind. Now we
move on to elongation
23. 23
Elongation: The second phase
• Two binding sites on 50S:
A site and P site, which
aid in continuing
translation
• First tRNA connected at A
site. Now moves to P site
as another tRNA
approaches
• Second tRNA binds to A
site
24. 24
Elongation (continued)
• Peptide bond forms
between amino acids of
tRNAs (methionine and
proline)
• First tRNA now detached
from its amino acid, and
it leaves ribosome.
Second tRNA still has
proline and methionine
attached
25. 25
Elongation (continued)
• The tRNA left now
moves to P site.
Ribosome ready to
accept another tRNA
and continue process
• Each tRNA adds another
amino acid to growing
peptide chain (thus
“elongation”)
• Eventually process has
26. 26
End of translation
• Ribosome was moving
along nucleotide triplets
one by one
• Ribosome reaches “stop
codon,” peptide chain
finished. Last tRNA
leaves ribosome,
leaving behind
completed peptide
chain
27. 27
End of translation (continued)
• Ribosome separates
from mRNA
• Ribosome subunits
also separate, and
will remain this way
until another mRNA
comes along to
restart the process
