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Plant Biochemistry -

Plant Biochemistry

A leaf cell consists of several metabolic compartments


-:- A leaf cell consists of several metabolic compartments
-:- The cell wall gives the plant cell mechanical stability
-:- Vacuoles have multiple functions
-:- Plastids have evolved from cyanobacteria
-:- Mitochondria also result from endosymbionts
-:- Peroxisomes are the site of reactions in which toxic intermediates are formed
-:- The endoplasmic reticulum and golgi apparatus form a network for the distribution of biosynthesis products
-:- Functionally intact cell organelles can be isolated from plant cells
-:- Various transport processes facilitate the exchange of metabolites between different compartments
-:- Translocators catalyze the specific transport of metabolic substrates and products
-:- Ion channels have a very high transport capacity
-:- Porins consist of β-sheet structures

The use of energy from sunlight by photosynthesis is the basis of life on earth


-:- The use of energy from sunlight by photosynthesis is the basis of life on earth
-:- How did photosynthesis start?
-:- Pigments capture energy from sunlight
-:- The energy content of light depends on its wavelength
-:- Chlorophyll is the main photosynthetic pigment
-:- Light absorption excites the chlorophyll molecule
-:- An antenna is required to capture light
-:- How is the excitation energy of the photons captured in the antennae and transferred to the reaction centers?
-:- The function of an antenna is illustrated by the antenna of photosystem II
-:- Phycobilisomes enable cyanobacteria and red algae to carry out photosynthesis even in dim light

Photosynthesis is an electron transport process


-:- The photosynthetic machinery is constructed from modules
-:- A reductant and an oxidant are formed during photosynthesis
-:- The basic structure of a photosynthetic reaction center has been resolved by X-ray structure analysis
-:- How does a reaction center function?
-:- Two photosynthetic reaction centers are arranged in tandem in photosynthesis of algae and plants
-:- Water is split by photosystem II
-:- The cytochrome-b6/f complex mediates electron transport between photosystem II and photosystem I
-:- Photosystem I reduces NADP
-:- In the absence of other acceptors electrons can be transferred from photosystem I to oxygen
-:- Regulatory processes control the distribution of the captured photons between the two photosystems

ATP is generated by photosynthesis


-:- A proton gradient serves as an energy-rich intermediate state during ATP synthesis
-:- The electron chemical proton gradient can be dissipated by uncouplers to heat
-:- H -ATP synthases from bacteria, chloroplasts, and mitochondria have a common basic structure
-:- The synthesis of ATP is effected by a conformation change of the protein

Mitochondria are the power station of the cell


-:- Biological oxidation is preceded by a degradation of substrates to form bound hydrogen and CO2
-:- Mitochondria are the sites of cell respiration
-:- Degradation of substrates applicable for biological oxidation takes place in the matrix compartment
-:- How much energy can be gained by the oxidation of NADH?
-:- The mitochondrial respiratory chain shares common features with the photosynthetic electron transport chain
-:- Electron transport of the respiratory chain is coupled to the synthesis of ATP via proton transport
-:- Plant mitochondria have special metabolic functions
-:- Compartmentation of mitochondrial metabolism requires specific membrane translocators

The Calvin cycle catalyzes photosynthetic CO2 assimilation


-:- CO2 assimilation proceeds via the dark reaction of photosynthesis
-:- Ribulose bisphosphate carboxylase catalyzes the fixation of CO2
-:- The reduction of 3-phosphoglycerate yields triose phosphate
-:- Ribulose bisphosphate is regenerated from triose phosphate
-:- Besides the reductive pentose phosphate pathway there is also an oxidative pentose phosphate pathway
-:- Reductive and oxidative pentose phosphate pathways are regulated

Phosphoglycolate formed by the oxygenase activity of RubisCO is recycled in the photorespiratory pathway

Polysaccharides are storage and transport forms of carbohydrates produced by photosynthesis


-:- Starch is synthesized via ADP-glucose
-:- Degradation of starch proceeds in two different ways
-:- Surplus of photosynthesis products can be stored temporarily in chloroplasts as starch
-:- Sucrose synthesis takes place in the cytosol
-:- The utilization of the photosynthesis product triose phosphate is strictly regulated
-:- In some plants assimilates from the leaves are exported as sugar alcohols or oligosaccharides of the raffinose family
-:- Fructans are deposited as storage compounds in the vacuole
-:- Cellulose is synthesized by enzymes located in the plasma membrane

Nitrate assimilation is essential for the synthesis of organic matter


-:- Nitrate assimilation is essential for the synthesis of organic matter
-:- The reduction of nitrate to NH3 proceeds in two reactions
-:- Nitrate assimilation also takes place in the roots
-:- Nitrate assimilation is strictly controlled
-:- The end product of nitrate assimilation is a whole spectrum of amino acids
-:- Glutamate is the precursor for chlorophylls and cytochromes

Nitrogen fixation enables plants to use the nitrogen of the air for growth


-:- Nitrogen fixation enables plants to use the nitrogen of the air for growth
-:- Legumes form a symbiosis with nodule-inducing bacteria
-:- N2 fixation can proceed only at very low oxygen concentrations
-:- The energy costs for utilizing N2 as a nitrogen source are much higher than for the utilization of NO3-
-:- Plants improve their nutrition by symbiosis with fungi
-:- Root nodule symbioses may have evolved from a pre-existing pathway for the formation of arbuscular mycorrhiza

Sulfate assimilation enables the synthesis of sulfur containing compounds


-:- Sulfate assimilation enables the synthesis of sulfur containing compounds
-:- Sulfate assimilation proceeds primarily by photosynthesis
-:- Glutathione serves the cell as an antioxidant and is an agent for the detoxification of pollutants
-:- Methionine is synthesized from cysteine
-:- Excessive concentrations of sulfur dioxide in the air are toxic for plants

Phloem transport distributes photoassimilates to the various sites of consumption and storage


-:- Phloem transport distributes photoassimilates to the various sites of consumption and storage
-:- There are two modes of phloem loading
-:- Phloem transport proceeds by mass flow
-:- Sink tissues are supplied by phloem unloading

Products of nitrate assimilation are deposited in plants as storage proteins

Phloem transport distributes photoassimilates to the various sites of consumption and storage


-:- Globulins are the most abundant storage proteins
-:- Prolamins are formed as storage proteins in grasses
-:- 2S-Proteins are present in seeds of dicot plants
-:- Special proteins protect seeds from being eaten by animals
-:- Synthesis of the storage proteins occurs at the rough endoplasmic reticulum
-:- Proteinases mobilize the amino acids deposited in storage proteins

Lipids are membrane constituents and function as carbon stores


-:- Lipids are membrane constituents and function as carbon stores
-:- Polar lipids are important membrane constituents
-:- Triacylglycerols are storage compounds
-:- The de novo synthesis of fatty acids takes place in the plastids
-:- Glycerol 3-phosphate is a precursor for the synthesis of glycerolipids
-:- Triacylglycerols are synthesized in the membranes of the endoplasmatic reticulum
-:- Storage lipids are mobilized for the production of carbohydrates in the glyoxysomes during seed germination
-:- Lipoxygenase is involved in the synthesis of oxylipins, which are defense and signal compounds

Secondary metabolites fulfill specific ecological functions in plants


-:- Secondary metabolites often protect plants from pathogenic microorganisms and herbivores
-:- Alkaloids comprise a variety of heterocyclic secondary metabolites
-:- Some plants emit prussic acid when wounded by animals
-:- Some wounded plants emit volatile mustard oils
-:- Plants protect themselves by tricking herbivores with false amino acids

A large diversity of isoprenoids has multiple functions in plant metabolism


-:- A large diversity of isoprenoids has multiple functions in plant metabolism
-:- Higher plants have two different synthesis pathways for isoprenoids
-:- Prenyl transferases catalyze the association of isoprene units
-:- Some plants emit isoprenes into the air
-:- Many aromatic compounds derive from geranyl pyrophosphate
-:- Farnesyl pyrophosphate is the precursor for the synthesis of sesquiterpenes
-:- Geranylgeranyl pyrophosphate is the precursor for defense compounds, phytohormones, and carotenoids
-:- A Prenyl chain renders compounds lipid-soluble
-:- The regulation of isoprenoid synthesis
-:- Isoprenoids are very stable and persistent substances

Phenylpropanoids comprise a multitude of plant secondary metabolites and cell wall components


-:- Phenylpropanoids comprise a multitude of plant secondary metabolites and cell wall components
-:- Phenylalanine ammonia lyase catalyzes the initial reaction of phenylpropanoid metabolism
-:- Monooxygenases are involved in the synthesis of phenols
-:- Phenylpropanoid compounds polymerize to macromolecules
-:- The synthesis of flavonoids and stilbenes requires a second aromatic ring derived from acetate residues
-:- Flavonoids have multiple functions in plants
-:- Anthocyanins are flower pigments and protect plants against excessive light
-:- Tannins bind tightly to proteins and therefore have defense functions

Multiple signals regulate the growth and development of plant organs


-:- Multiple signals regulate the growth and development of plant organs and enable their adaptation to environmental conditions
-:- Signal transduction chains known from animal metabolism also function in plants
-:- Phytohormones contain a variety of very different compounds
-:- Auxin stimulates shoot elongation growth
-:- Gibberellins regulate stem elongation
-:- Cytokinins stimulate cell division
-:- Abscisic acid controls the water balance of the plant
-:- Ethylene makes fruit ripen
-:- Plants also contain steroid and peptide hormones
-:- Defense reactions are triggered by the interplay of several signals
-:- Light sensors regulate growth and development of plants

A plant cell has three different genomes


-:- A plant cell has three different genomes
-:- In the nucleus the genetic information is divided among several chromosomes
-:- The DNA of the nuclear genome is transcribed by three specialized RNA polymerases
-:- DNA polymorphism yields genetic markers for plant breeding
-:- Transposable DNA elements roam through the genome
-:- Viruses are present in most plant cells
-:- Plastids possess a circular genome
-:- The mitochondrial genome of plants varies largely in its size

Protein biosynthesis occurs in three different locations of a cell


-:- Protein biosynthesis occurs in three different locations of a cell
-:- Protein synthesis is catalyzed by ribosomes
-:- Proteins attain their three-dimensional structure by controlled folding
-:- Nuclear encoded proteins are distributed throughout various cell compartments
-:- Proteins are degraded by proteasomes in a strictly controlled manner

Biotechnology alters plants to meet requirements of agriculture nutrition and industry


-:- Biotechnology alters plants to meet requirements of agriculture, nutrition and industry
-:- A gene is isolated
-:- Agrobacteria can transform plant cells
-:- Ti-Plasmids are used as transformation vectors
-:- Selected promoters enable the defined expression of a foreign gene
-:- Genes can be turned off via plant transformation
-:- Plant genetic engineering can be used for many different purposes