Lecture 11 Pt. 1: Carbohydrate Biosynthesis in Plants and Bacteria

NADPH and ATP is used by carbon assimilation reactions to achieve what?

• reduce CO2 and generate trios phosphates and more complex compounds

What kind of compounds are synthesized from trios phosphates?

• glucose, sucrose, cellulose

Water is the source of what that get passed via what to the ultimate what?

• electrons

• chain of protein transporters

• electron acceptor, NADP+

Light energy is used to what in the context of photophosphorylation?

• separate charges on chlorophyll

• generate NADPH and phosphorylate ADP

What is the byproduct of water oxidation?

• oxygen

Catabolic

• generate chemical energy via oxidation of biomolecules

Anabolic

• synthesize cellular components from simple precursor molecules using chemical energy

• associated with reduction

Plants are autotrophs that rely on what to utilize what for what result?

• anabolic reactions

• inorganic carbon

• synthesize organic compounds

CO2 in an anabolic reaction is converted to what?

• trios phosphates and hexose phosphates

What are trios phosphates and hexose phosphates used for?

• synthesis of sucrose, starch, cell wall components, pentose phosphate pathway

  • make other metabolic intermediates

Starch

• high molecular weight polymer of D-glucose

• alpha 1,4 linkage

Where is starch made?

• chloroplasts → short term storage

• amyloplasts of non photosynthetic parts i.e., roots, seeds, tubers → long term storage

Starch provides the bulk of what for plants?

• stored energy

Where is sucrose made?

• cytosol for transport

Sucrose is considered what for plants?

• “blood glucose” of plants

Starch synthesis proceeds similarly to what process?

• glycogen synthesis

Gluconeogenesis of two glyceraldehyde-3-phosphates result in what?

• glucose-6-phosphate

Phosphoglucomutase converts glucose-6-phosphate to what?

• glucose-1-phosphate

Condensation of glucose-1-phosphate and NTP forms what?

• nucleotide sugar (NDP)

In the case of starch synthesis, the NDP-sugar is what?

• ADP-glucose

• via ADP-glucose pyrophosphorylase

Difference between glycogen and starch synthesis?

• glycogen → glucose monomers are UDP-glucose

• starch → glucose monomers are ADP-glucose

Starch synthase

• creates alpha 1,4 bonds i.e., amylose and catalyzes the addition of ADP-glucose to the growing starch molecule.

Amylopectin

• numerous alpha 1,6 branches

• added via branching enzyme

• similar to branching enzyme in glycogen synthesis

Amylose in starch is what?

• unbranched

Sucrose synthesis uses UDP-glucose to create…?

• alpha 1 → B2 bond

Most triose phosphates generated by CO2 fixation in plants is converted to…?

• starch

• sucrose

Sucrose is the transporter of what?

• carbon sources

Synthesis of sucrose occurs where?

• cytosol

What two compounds are transported out of the chloroplast into the cytosol during sucrose synthesis?

• DHAP i.e., dihydroxyacetone phosphate

• glyceradehyde-3-phosphate

Once DHAP and G3P are in the cytosol, what reaction do they undergo?

• condensation via aldolase

• forms fructose 1,6-bisphosphate

What happens to the fructose 1,6-bisphosphate?

• hydrolyzed to fructose 6-phosphate

• via fructose 1,6-bisphosphatase

Fructose 6 -phosphate + UDP-glucose → ?

• sucrose 6-phosphate

What catalyzes the formation of sucrose 6-phosphate?

• sucrose 6-phosphate synthetase

Sucrose 6-phosphate is converted to what? via what enzyme?

• sucrose

• sucrose 6-phosphate phosphatase

1) Aldolase combines ? to form ?

• DHAP + G3P

• fructose 1,6-bisphosphate

2) Fructose 1,6-bisphosphate is ? by ? to form ?

• dephosphorylated

• fructose 1,6-bisphosphatase

• fructose 6-phosphate

3) Sucrose 6-phosphate synthase adds ? to ? to make ?

• UDP-glucose

• fructose 6-phosphate

• sucrose 6-phosphate

4) Sucrose 6-phosphate cleaves ? to yield ?

• a phosphate group (PO₄^3-)

• sucrose

Cellulose provides what to prevent what of the cell and plasma membrane?

• strength and rigidity

• swelling and rupture

What is a major component of cell walls in plants?

• cellulose

Cell wall of plants is composed of cellulose…?

• microfibrils

Cellulose microfibrils are composed of…?

• linear polysaccharide > 1000 glucose units

• linked via 1,4 beta linkages i.e., cellulose chains

Cellulose is synthesized via ? but assembled where?

• intracellular precursors

• outside of plasma membrane

Of microfibrils, these polymers are bundled consisting of…? which aggregate…? and…? forming…? which then assemble into…?

• at least 18 chains

• side by side

• co-crystallize

• microfibrils

• macrofibrils

Cellulose biosynthesis: At the cytosolic end, there is…?

• a substrate binding site UDP-glucose

Cellulose biosynthesis: At the extracellular space…?

• cellulose molecules are elongated and crystallized

The enzyme complex involved in cellulose biosynthesis is composed of what?

• a catalytic sub unit with 8 transmembrane segments

• several other sub units involved in packaging the cellulose chains

UDP-glucose is used for?

• cellulose biosynthesis

• via cellulose synthase

• adds glucose monomers to non-reducing ends

Sucrose + UDP → ?

• UDP-glucose + fructose

UDP-glucose is produced from what during what?

• sucrose synthase

• photosynthesis

Catalytic sub units of cellulose synthase are found in?

• terminal complexes aka rosettes

Rosettes

• cellulose synthesis complex

• 6 large particles arranged in a hexagon

UDP-glucose is generated from?

• sucrose by-product during photosynthesis

• catalyzed via sucrose synthase on cytosolic end

What is required for cellulose synthesis?

• lipid primer

Initiation

• glucose from UDP-glucose associates with lipid primer

  • i.e., sitosterol

  • inner face of plasma membrane

• displacement of UDP

Carbohydrate chain is extended with continuous addition of what? received from what?

• glucose

• oncoming UDP-glucose

Intracellular cellulose synthase adds several more what? in what?

• glucose residues

• B1,4 linkages

What does the constant addition of glucose eventually yield in the initiation process with the lipid primer?

• short oligosaccharide chain

• attached to the sitosterol dextrin

Once an appropriate length of the oligosaccharide is reached, what happens?

• entire sitosterol dextrin flips from inner plasma membrane surface to outer plasma membrane surface

Endo-1,4-B-glucanase separates the…? from…?

• growing chain

• a short oligosaccharide attached to the sitosterol

The sitsterol-free polymer of what? is extended further by what enzyme? with what substrate?

• glycosyl

• cellulose synthase

• UDP-glucose

The sitosterol-linked short oligosaccharide returns back to where? to be reused as what?

• cytosolic face

• primer for another chain of cellulose synthesis

1) Glucose attaches to ? in the cell membrane

• lipid

2) Sucrose synthase generates ? with the help of ? to create?

• UDP-glucose

• cellulose synthase

• six chains

3) Cellulose synthase continues to ? outside of the ?

• extend the chain

• plasma membrane

4) Chains ? to form ? and eventually form ?

• crystallize

• microfibrils

• macrofibrils