Carbohydrates and Glycolysis Flashcards
Polysaccharides
Repeating units (either mono- or di-saccharides) joined together by glyosidic bonds.
Monosaccharides
The most basic units of biologically important carbohydrates
Glycosidic bond and the 2 types of glycosidic linkages
Chaining relies on ‘bridging’ of oxygen atoms to form glycosidic bonds
Alpha 1.4 glycosidic linkage, alpha because the OH is below the plane of the 1st carbon
Beta 1,4 glycosidic linkage, beta because the OH is above the plane of the 1st carbon
1 water molecule is removed, condensation reaction
4 types of monosaccharides
Monosaccharide - 1 sugar unit
Disaccharide - 2 sugar units
Oligosaccharide - 2-10 sugar units
Polysaccharides - more than 10 sugar units
List 4 biological functions of carbohydrate, give 1 example for each function
- Energy metabolism (glycogen for glucose storage)
- Structural (peptidoglycan for bacterial cell wall, cell membrane linked to glycoprotein, cartilage and exoskeletons in animals )
- Precursors of DNA and RNA (ribose, deoxyribose, 1 OH in deoxyribose has a O removed)
- Cell surface markers( blood group markers, antigens made up of carbohydrates)
What are the pathways for gluconeogensis, glycolysis, glycogenolysis, glycolysis and pentose phosphate pathway?
Gluconeogenesis is pyruvate -> glucose 6 phosphate -> glucose
Glycolysis is glucose -> glucose 6p -> pyruvate
Glycogenolysis is Glycogen -> glucose 1p -> Glucose 6p
Glycogenesis is Glucose -> UDP-glucose -> glycogen
Pentose phosphate pathway is glucose 6p -> ribulose 5p
UDP is a activated form of glucose
List characteristics of glycolysis
- 1st stage in glucose breakdown
- Used by plants and animals
- Anaerobic, do not require oxygen
- Occurs in cytoplasm
- Small amounts of energy is made in form of ATP and NADH while glucose is stepwise converted to pyruvate
3 stages of glycolysis according to Mr Tai
Investment - ATP is used, glucose is trapped and destabilized (steps 1-3)
Conversion - Formation of 2 inter-convertible 3 carbon molecules (steps 4-5)
Harvesting - ATP is generated (step 6-10)
Step 1 glycolysis
Step 1 (glucose swap out a H for a new phosphate group at carbon 6)
Phosphorylation of glucose, irreversible reaction,
Ch2-OH carbon 6 of glucose is converted to CH2-OPO32- to carbon 6 of glucose
Hexokinase help ATP gives 1 phosphate group to ADP, cofactor magnesium
Glucose becomes glucose-6-phosphate
Glucose-6-phosphate is trapped and cannot leave cell via transporters, phosphoryl group (−PO32−), destabilizing glucose
Step2 glycolysis
(Glucose-6 phosphate transforms into fructose-6-phosphate, the 1st carbon seem to form a CH2OH group on top of carbon 2)
Changing the isomer of glucose to fructose, reversible reaction
Phosphoglucoisomerase, Mg 2+ as cofactor
Glucose-6-phosphate become fructose-6-phosphate
1 CH2PO32- groups on carbon 4 and a CH2OH on carbon 1, on top of the 5 ring there is oxygen
Step 3 glycolysis
(H on carbon 1 is swapped out for a phosphate group, making 2 phosphate groups)
Fructose-6-phosphate become Fructose-1,6-bisphosphate
Phosphorylation, ATP lose phosphate group to become ADP, not reversible
Requires Mg2+ cofactor, kinase(catalyze transfer of phosphate group to a molecule)
Phosphofructo-kinase-1,
An allosteric enzyme that control rate of glycolysis
Step 4 glycolysis
(aldol cleave fructose 1,6 bisphosphate at carbon 3-4 bond)
Cleavage of fructose 1,6 bisphosphate into 2 molecules
We get ketone and aldehyde
Phosphate group is located on carbon 3 of aldehyde, thus Glyceraldehyde-3-phosphate
Dihydroxyacetone Phosphate, 3 carbon ketone is an acetone
Aldolase make aldol reversible reaction
Steps 1,3,10 are irreversible
Step 5 glycolysis
Dihydroxyacetone phosphate isomerized into glyceraldehyde-3-phosphate)
DAP is isomerized into Glyceraldehyde-3-phosphate by Triosephosphate isomerase
3 carbon keto sugar, with a phosphate group attached
Reversible reaction
Triosephosphate isomerase, 2 molecules of G-3=P happens now onwards, double everything now onwards
Step 6 glycolysis
(carbon 1 gains phosphate group swapping out H)
Glyceraldehyde-3-phosphate combines with phosphate group, phosphate on carbon 1 and 3 on new product
1.3-bisphosphoglycerate is formed
NAD+ -> NADH, produce a H+ ion, oxidation, reversible
H part of phosphate group ends up on NADH, hydrogen on G-3-P ends up removed
Glyceraldehyde 3-phosphate dehydrogenase (removing hydrogen, reduce NAD+ to NADH,
Phosphate comes from a external inorganic phosphate
Produces 3 molecules, H+, NADH and 1,3-bisphosphoglycerate
Step 7 glycolysis
1,3 bisphosphoglycerate is converted to 3-phosphoglycerate, +2 ATP, substrate level phosphorylation
2ADP->2ATP , substrate level phosphorylation, phosphate group is removed from carbon 1, leaving a O- together with a double bond
Phosphoglycerate Kinase
Magnesium ion (2+) as cofactor, produce ATP here , reversible
1,3 bisphosphoglycerate have high phosphoryl transfer potential
Step 8 glycolysis
3-phosphoglycerate to 2 phosphoglycerate, phosphate group is positioned from position 3 to position 2 where OH is, CH2 now binds to OH instead of OPO32-
Mutase, move a functional group to another, a type of isomerase
Swap OH on position 2 with OPO3 on position 3
Phosphoglycerate mutase, reversible, use Mg 2+ as cofactor
Step 9 glycolysis
Losing H (connected to centre carbon) and OH group, water is lost, dehydration reaction
2-phosphoglycerate become phosphoenol pyruvate
Pyruvate have carboxylic group, attached to carbon you have ketone
Enol is a alcohol attached to alkene OH and C=C
Enolase
Total lose 2H molecules and O, leaving a CH2 double bonded to central carbon, with 3 groups left connected to central carbon
Phosphoenolpyruvate look like 2 oxygen atoms connected to carbon 1, in resonance, sharing a -charge, connected to carbon 2 with a OPO32- and second group, double bonded with CH2
Phosphoenolpyruvate have high phosphoryl transfer potential
Step 10 glycolysis
Phosphoenolpyruvate become pyruvate, substrate level phosphorylation
PO32- is removed
Cofactors are magnesium and potassium ions
Losing phosphate group using pyruvate kinase
Where is ATP generated
ATP is converted from step 7 and 10, 2 molecules each, 2 ATP each
2 ATP is used for investment is used in steps 1 and 3
Overall formula for glycolysis
Glucose (6C) + 2 NAD+ 2 ADP +2 inorganic phosphates (Pi) yields 2 pyruvate (3C) + 2 NADH + 2 H+ + 2 net ATP
Which enzyme produce NADH
Step 6 Glyceraldehyde 3-phosphate dehydrogenase
Which step is doubling step
Step 5
Which 2 enzymes produce ATP
Step 7 and 10
Phosphoglycerate kinase produce 2 ATP
Pyruvate kinase produce 2 ATP
Which 3 steps are irreversible
Step 1,3 and 10 is irreversible
Hexokinase, phosphofructokinase, pyruvate kinase
The most regulatory enzyme in glycolysis
Phosphofructokinase is the most prominent regulatory enzyme in glycolysis, but it is not the only one.
Phosphofructokinase is regulated by energy change in the cell. ATP inhibits the phosphofructokinase reaction and AMP activate the reaction.
It is inhibited by citrate.
It is activated by fructose 2,6 bisphosphate.
Fructose‐2,6‐bisphosphate allosterically activates PFK I by decreasing the K m for fructose‐6‐phosphate.
The 2nd most regulatory enzyme in glycolysis
Hexokinase, the enzyme catalyzing the first step of glycolysis, is inhibited by its product, glucose 6-phosphate. step 1
Which step uses ATP
1 and 3, hexokinase and phosphofructokinase
The 3rd most regulatory enzymes in glycolysis
Pyruvate kinase step 10
What do all regulatory enzymes have in common. Step 1,3 ,10
- They are irreversible
- They are kinases
- They control glycolysis
What are the 2 steps involved in substrate level phosphorylation?
Step 7 and 10
They are the 2 ATP producing steps
A transfer of phosphate group from a high-energy substrate molecule to ADP, to form ATP.
High phosphoryl transfer potential molecules such as 1,3 biphosphoglcyerate and phosphoenolpyruvate have a high tendency to transfer phosphate group vice versa.
Significance of products of glycolysis
Produce ATP and NADH, which are energy rich molecules
Produce pyruvate for amino acid synthesis or fatty acid synthesis or generate energy in the Krebs cycle
Note that all NADH must be oxidized back to NAD+ for glycolysis to continue.
The primary role of respiration and fermentation is to allow NADH to be oxidized back to NAD+, allowing glycolysis to occur.
