1. Pharmacognosy Photosynthesis Prof. Suleiman OLimat

2. THE BASICS OF PHOTOSYNTHESIS

3. Plant Metabolism

4. Light Energy Harvested by Plants & Other Photosynthetic Autotrophs
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

5. AN OVERVIEW OF PHOTOSYNTHESIS
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
Carbon dioxide
Water
Glucose
Oxygen gas
PHOTOSYNTHESIS

6. The Most Important Equation in Biology

7. AN OVERVIEW OF PHOTOSYNTHESIS
The light reactions convert solar energy to chemical energy
Produce ATP & NADPH
Light
Chloroplast
NADP
ADP
+ P
The Calvin cycle makes sugar from carbon dioxide
ATP generated by the light reactions provides the energy for sugar synthesis
The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose
Calvin
cycle
Light
reactions

9. Steps of Photosynthesis
Light hits reaction centers of chlorophyll, found in chloroplasts
Chlorophyll vibrates and causes water to break apart.
Oxygen is released into air
Hydrogen remains in chloroplast attached to NADPH
“THE LIGHT REACTION”

10. Steps of Photosynthesis
The DARK Reactions= Calvin Cycle
CO2 from atmosphere is joined to H from water molecules (NADPH) to form glucose

11. Photosynthesis occurs in chloroplasts
In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts
A chloroplast contains:
stroma, a fluid
grana, stacks of thylakoids
The thylakoids contain chlorophyll
Chlorophyll is the green pigment that captures light for photosynthesis

12. Chloroplast Pigments Chloroplasts contain several pigments
Chlorophyll a
Chlorophyll b
Carotenoids
Xanthophyll
Figure 7.7

13. Chlorophyll a & b Chl a has a methyl group Chl b has a carbonyl group
Porphyrin ring
delocalized e-
Phytol tail

14. In the light reactions, electron transport chains generate ATP, NADPH, & O2
Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons
The excited electrons are passed from the primary electron acceptor to electron transport chains
Their energy ends up in ATP and NADPH

15. Chemiosmosis powers ATP synthesis in the light reactions
The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane
The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP
In the stroma, the H+ ions combine with NADP+ to form NADPH

16. Introduction
Metabolism: (Gr. metabole = change) the totality of the chemical changes in living cells which involves the buildup and breakdown of chemical compounds.
Primary metabolism: biosynthesis, utilization and breakdown of the essential compounds and structural elements of the living organism, such as: sugars and polysaccharides; amino acids, peptides and proteins (including enzymes); fatty acids; and nucleotides. The starting materials are CO2, H2O and NH3. All organisms possess similar primary metabolic pathways and use similar primary metabolites.

17. Primary Metabolites
Primary metabolites are compounds that are commonly produced by all plants and that are directly used in plant growth and development.
The main primary metabolites are carbohydrates, proteins, nucleic acids, and lipids.

18. Carbohydrates
Carbohydrates are the sugars made up of glucose and its isomers
Carbohydrates come in many different sizes:
Monosaccharides made up of one sugar unit (glucose or fructose)
Disaccharides made up of two sugar units (sucrose is a glucose and a fructose)
Polysaccharides are polymers made up of more than two sugar units

19. Structural Polysaccharides
The most common structural polysaccharide in plants is cellulose. It makes up 40 to 60% of the cell wall. It is also the most common polymer on earth
Cellulose is extremely strong due to its chemical organization. It is made of a long chain of beta-glucose molecules – 100 to 15,000 glucose molecules

20. Proteins
Proteins make up most of the remaining biomass of living plant cells.
A protein consists of one or more polypeptides made up of amino acids. Plants make amino acids from the products of photosynthesis through a very complex process involving the acquisition of N, usually in the form of NH4, and involving the use of large amounts of energy, in the form of ATP and NADPH.

21. Enzymes
Enzymes catalyze biochemical reactions. Most proteins in living cells are enzymes.
Pure enzymes that maintain their activity when removed from plants are commercially important to us.

22. Introduction
Secondary metabolism: refers to the biosynthesis, utilization and breakdown of smaller organic compounds found in the cell. These compounds, called secondary metabolites, arise from a set of intermediate building blocks : acetyl coenzyme A (acetyl-CoA), mevalonic acid (MVA) and methyl erythritol phosphate (MEP), shikimic acid, and the amino acids phenylalanine/tyrosine, tryptophan, ornithine and lysine.

23. Introduction Relationship between primary and secondary metabolism:
The processes and products of primary metabolism are similar in most organisms, while those of secondary metabolism are more specific.
In plants, primary metabolism is made up of photosynthesis, respiration, etc., using CO2, H2O, and NH3 as starting materials, and forming products such as glucose, amino acids, nucleic acids. These are similar among different species.
In secondary metabolism, the biosynthetic steps, substrates and products are characteristic of families and species. Species which are taxonomically close display greater similarities (and metabolites); those which are distant have greater differences.

25. * Metabolites found in higher organisms only
Overview of Secondary Metabolism
* Metabolites found in higher organisms only *
3. Secondary metabolites and Biosynthesis (Dayrit)

26. Plant Secondary Metabolites
Plants make a variety of less widely distributed compounds such as morphine, caffeine, nicotine, menthol, and rubber. These compounds are the products of secondary metabolism, which is the metabolism of chemicals that occurs irregularly or rarely among plants, and that have no known general metabolic role in plants.
Secondary metabolites or secondary compounds are compounds that are not required for normal growth and development, and are not made through metabolic pathways common to all plants.
Most plants have not been examined for secondary compounds and new compounds are discovered almost daily.

27. Plant Secondary Metabolites
Secondary compounds are grouped into classes based on similar structures, biosynthetic pathways, or the kinds of plants that make them. The largest such classes are the alkaloids, terpenoids, and phenolics.
Secondary compounds often occur in combination with one or more sugars. These combination molecules are known as glycosides. Usually the sugar is a glucose, galactose or rhamnose. But some plants have unique sugars. Apiose sugar is unique to parsley and its close relatives.

28. Functions of Secondary Compounds
The most common roles for secondary compounds in plants are ecological roles that govern interactions between plants and other organisms.
Many secondary compounds are brightly colored pigments like anthocyanin that color flowers red and blue. These attract pollinators and fruit and seed dispersers.
Nicotine and other toxic compounds may protect the plant from herbivores and microbes.
Other secondary compounds like rubber and tetrahydrocannabinil (THC) from cannabis plants have no known function in plants.