D1 absorptive state Flashcards
what is glycolysis
seq of reactions that metabolises 1 mol of glucose to 2 mols of pyruvate
net production of 2 mols of ATP
glycolysis eqn
D-glucose+2NAD+2ADP+2Pi—2 pyruvate+2 ATP+2NADH+2H+2H20
what do the 2 phosphorylation rxns form
fructose 1,6-biphosphate
what 2 mols are cleaved from each fructose 1,6-biphosphate
triose phosphate
what 2 molecular rearrangements occur in glycolysis
- 2 phosphorylations of ADP = 2 ATP per triose phosphate
- 1 oxidation forming NADH per triose phosphate
whats the product per glucose
2 mols of pyruvate
what is phosphoryl transfer
transfer of a phosphoryl group from ATP to an alcohol
what occurs after phosphoryl transfer
alcohol gives up the hydrogen while ADP and an organic phosphate are yielded
what is aldose ketose isomerisation
conversion of an aldose (glucose) to a ketose (fructose) or a ketose to an aldose
what is alcohol hydrogen transferred to and what does this result in
to the oxygen in the aldehyde group transforming the original alcohol group to a carbonyl and the original aldehyde to an alcohol
what is aldol cleavage
splitting of a carbon-carbon bond
what does aldol cleavage yield
an aldehyde and a ketose
what is a phosphoryl shift
movement of a phosphoryl group from oxygen to an alcohol oxygen in the same mol
result of a phosphoryl shift
alcohol hydrogen is removed and binds to the formerly phosphorous bound oxygen
what is dehydration
removal of a water mol from an alcohol
what does dehydration yield
a carbon-carbon double bond in the original mol
how many rxns take place during glycolysis
10 rxns
what balance in the cell has to be maintained during glycolysis
redox balance
how is NAD* regenerated
through metabolism of pyruvate
what happens without regeneration of NAD*
glycolysis will stop
what is the dual role of the glycolytic pathway
- degradation of glucose to generate ATP
- provision of building blocks for synthetic reactions eg fatty acids
what can be sites of control in glycolytic pathway
enzymes catalysing irreversible reactions are potential sites of control
what are the control sites in glycolysis
-hexokinase
-phosphofructokinase
-pyruvate kinase
hexokinase control site
inhibited by its product glucose 6-phosphate
phosphofructokinase control site
committed step
inhibition by; ATP, low pH, citrate;activation by; AMP and fructose 2,6-bisphosphate
pyruvate kinase control site
ATP and alanine inhibit; fructose 1,6-bisphosphate activates
origin of fructose 2,6-bisphosphate
generated by phosphofructokinase 2
what is phosphofructokinase 2
bifunctional enzyme responsible for synthesis and hydrolysis of fructose 2,6-biphosphate into
phosphofructokinase-phosphofructobisphosphatase
how is phosphofructokinase 2 regulated
reciprocal control by phosphorylation of serine 460 by protein kinase a
what is active in phosphorylated form
phosphatase
what is active in dephosphorylated form
kinase
what happens to pyruvate in anaerobic setting
converts to ethanol
lactic acid fermentation occurs how
pyruvate into lactate by a reduction rxn using lactate dehydrogenase
what is lactate produced by
muscles when the body cannot supply enoughoxygen
what lacks mitochondria and so cannot oxidise glucose completely
erythrocytes
body can create more ATP at a cost of what
creating an oxygen debt
what must lactate be converted back into
pyruvate
what does glycogen function as
reserve of glucose when metabolic demand for glucose outpaces the cells ability to obtain it from extracellular sources
what does controlled release of glucose from glycogen maintain
blood glucose levels
main storage of glycogen
liver and skeletal muscle
main storage of glycogen
liver and skeletal muscle
what is glycogen very similar to
amylopectin
but more branches from every 10th glucose
what are the two names of the stages of glycogen anabolism
initiation and elongation
what is the initiation stage of glycogen synthesis catalysed by
catalysed in an autocatalytic manner by glycogenin
what is the elongation stage of glycogen synthesis catalysed by
by glycogen synthase in concert with the branching enzyme
what is glycogenin
enzyme involved in glycogen biosynthesis
what is glycogenin classified as
glycosyl-transferase
what does glycogenin act as
the primer to which further glucose monomers can be added
how does glycogenin bind glucose
from UDP-glucose to a hydroxyl group of tyrosine 194
what is glycogen synthase (GS)
main enzyme involved in glycogen polymerisation
GS can only be added to what
an existing chain of at least 8 glucose residues (elongation stage)
GS regulated by
covalent modifications and an allosteric mechanism
what 2 things is GS phosphorylated by
protein kinase A
glycogen synthase kinase 3 (GSK3)
what does phosphorylation convert GS into
active a form into inactive b form
when is b form still active
when a high level of the allosteric activator glucose 6-phosphate is present
what is the activated form of glucose that is the immediate precursor for glycogen synthesis
uridine diphosphate glucose (UDP-glucose)
what are nucleotide diphosphate sugars precursors for
synthesis of complex carbohydrates
including oligosaccharide chains of glycoproteins
what is UDP-glucose formed from
glucoses-1-phosphate
overall eqn for UDP-glucose synthesis
glucose-1-phosphate+UTP=UDP-glucose+2Pi
is the rxn for UDP-glucose reversible or irreversible
irreversible
what makes the UDP-glucose rxn irreversible
spontaneous hydrolysis of the ~P bond in pyrophosphate PPi (P~P) drives the overall rxn
what is the only energy cost for glycogen synthesis
cleavage of PPi
(one~P bond per glucose residue)
where are glucose residues added to
non-reducing terminal residues of glycogen
what is the rxn product released from UDP-glucose
UDP
what is the linkage formed from glycogen synthesis
a-1,4-glycosidic linkage
what is amylo (1,4-1,6) transglycosylase
branching enzyme
how many residues and from where is transferred to a more interior site
7 residues from the non reducing end of the chain
what must the block include
non reducing terminus
what linkage and where are the 7 residues attached by
a-(1,6) linkage at least 4 residues from the nearest branch point
why is branching so important
increases solubility of glycogen
what does branching allow
generation of a large osmotically inactive storage form of glucose
what does branching create
large number of terminal residues
terminal residues are at the sites of action of what 2 enzymes
glycogen phosphorylase
glycogen synthase
what does branching increase the rate of
glycogen synthesis and degradation
where are fatty acids synthesised
cytoplasm
why are fatty acids synthesised in the cytoplasm of a fed state
more carb (hence acetyl CoA) is available than needed for the TCA cycle
what is required to build new fatty acids
ATP
what protein remains bound to the intermediates in fatty acid synthesis
acyl-carrier protein (ACP)
how does the fatty acid chain grow by
sequential addition of 2 carbon units derived from acetyl CoA
what is the activated donor of fatty acid synthesis
malonyl-ACP
what is the transfer driven by and what is released in fatty acid synthesis
a decarboxylation reaction releasing CO2
what are fatty acids stored as
triacylglycerides (TG)
what are the 2 building blocks of fatty acid biosynthesis
and what does it result in
1 acetyl CoA
7 malonyl CoA
= palmitate (C16)
what enzyme catalyses formation of malonyl CoA
acetyl CoA carboxylase
is the formation of malonyl CoA reversible or irreversible
irreversible
committed step
what is the bond that joins the glycerol mol to the fatty acids
ester bond
is triacylglycerol high or low energy
high energy storage biomolecule
how man kJ/g of fat is in a triacylglycerol mol
39
components of a triacylglycerol mol
3 fatty acid groups
glycerol-3 phosphate
3 places that TGs are synthesised
liver
adipose tissue
intestinal tract
how is TG synthesis carried out in the liver
from fatty acids made using glucose (glycolysis) or aa side chains
TG synthesis during transport of dietary fat (what type)
intestines and adipose tissue
can TG cross the cell membrane
no
how does TG get in and out of cells
has to be broken down by lipases
how are TG carried around the body
by lipoproteins in the plasma
how is TG carried from liver to peripheral tissues
very low density lipoprotein
VLDL
how is TG carried from intestine to peripheral tissues
chylomicrons
how is each fatty acid activated
thiol group of CoA forms high energy thioester bond with the carboxylic acid group of the fatty acid
what is the energy source in activation of FA
ATP (2 high energy bonds used)
