Chapter 15 Flashcards
Homeostasis occurs when
concentration of metabolites are kept at a steady state in the body - cannot have equilibrium without steady state
High ______ concentrations inhibit the committed step of glycolysis to prevent excess glucose degradation
ATP
______ inhibits the pentose phosphate pathway from committing substrates to glycolysis
NADPH
________ inhibits most hexokinases
Glucose-6-phosphate
4 ways activity of enzymes can be activated
- the concentration of substrate
- the presence of allosteric effectors
- covalent modifications
- binding of regulatory proteins
Enzymes are commonly regulated at the level of _________ and by both allosteric and covalent mechanisms
regulated at the level of TRANSCRIPTION
3 things that affect the rates of biochemical reactions
- Concentration of reactants
Rate = k[reactants] - activity of the catalyst
the concentration of the enzyme & intrinsic activity of the enzyme - Concentration of effectors
3 ways to speed up reaction rate
catalysts, increased reactants, changing temperature
The initial rate of the reaction is half-max when?
[S]=KM
phosphorylation is catalyzed by….?
protein kinases
Dephosphorylation is catalyzed by….?
protein phosphatases
Typically proteins are phosphorylated on the hydroxyl groups of ______,_____,______
Ser, Thr, Tyr
Metabolic ________ serves to maintain homeostasis at the molecular level
metabolic regulation
Metabolic _______ leads to a change in the output of a metabolic pathway over time
metabolic controls
AMP-activated protein kinase (AMPK) increases what things?
AMPK increases:
- nutrient intake in the brain
- glycolysis and fatty acid oxidation
- glucose uptake
AMPK Inhibits what
AMPK inhibits:
- insulin secretion
-fatty acid synthesis
- glycogen synthesis
Glycogen, a polymeric storage form of glucose in animals, is primarily found in the _____&_____
primarily found in the muscle and liver
What is the synthesis of glycogen?
glycogenesis
What is the breakdown of cellular glycogen to glucose-1-phosphate ?
glycogenolysis
Glucose linkage
alpha 1- 4 linkage
Glucose branches
alpha 1-6 branches every
Glucose 1-phosphate must be isomerized to ______ before being used in further metabolic reactions
Glucose-6-phosphate
What enzyme performs the isomerization of glucose 1-phosphate to glucose-6-phosphate
Phosphaglucomutase
Sources of glucose 6-phosphate
- hexokinase isozymes derive glucose-6-phosphate from glucose
-lactate taken up by liver is converted to glucose-6-phosphate by gluconeogenesis
Glucose-6-phosphate is converted to glucose-1-phosphate by ______ to create UDP-glucose in glycogen synthesis
PHOSPHOGLUCOMUTASE
What substrate serves as the primer for glycogen synthesis
glycogenin
What stimulates the conversion of phosphorylase b into a?
- epinephrine from vigorous muscle activity
- glucagon in the liver
Glycogen is degraded to glucose units for use in _________
energy production
Glycogen can be made from what two things
- excess blood glucose or the recycling of glucogenic metabolites like lactate or certain amino acids
Compounds in which the anomeric carbon of a sugar is activated by attachment to a nucleotide via a phosphate ester linkage
sugar nucleotides
What makes UDP-Glucose suitable for biosynthetic reactions?
- UDP glucose formation is metabolically irreversible
- the nucleotide moiety has many groups that can undergo noncovalent interactions with enzymes
- the nucleotidy group (UDP,ADP) is a good LG
The formation of sugar nucleotides is (endergonic/exergonic)?
exergonic, -delta G
What molecule converts glycogen synthase a to synthase b by adding phosphoryl groups to three serine residues on synthase a
GSK3 (Glycogen synthase kinase 3)
What molecule inactivates glycogen synthase kinase 3 (GSK3)?
Insulin
What form of glycogen synthase is unphosphorylated and catalytically active?
glycogen synthase A
What form of glycogen synthase is phosphorylated and inactive?
glycogen synthase B
Glycogen synthase is regulated by _____?____
phosphorylation
When a muscle returns to rest, what is the role of protein phosphatase 1 (PP1)?
PP1 removes the phosphoryl group from phosphorylase a, converting it to phosphorylase b (less active)
What molecule is activated by insulin and leads to an increase of glycogen synthesis?
PP1 (protein phospatase 1)
What must happen before glycogen synthase kinase 3 (GSK3) can phosphorylate glycogen synthase?
Casein Kinase II (CKII) must first phosphorylate the glycogen synthase on a nearby residue
Why can gluconeogenesis not occur in skeletal muscle?
B/c skeletal muscle lacks the enzymatic machinery for gluconeogenesis
Glycogen synthesis and degradation is regulated by what hormones?
insulin, epinephrine and glucagon
Glycogen breakdown is catalyzed by?
glycogen phosphorylase
Glycogen phosphorylase requires what cofactor in the phosphorolysis reaction?
PYRIDOXAL PHOSPHATE (PLP) which promotes attack by Pi
End product of glycogen phosphorylase reaction?
Glucose 1-phosphate
What must glucose-6-phosphate be hydrolyzed into in order to be released in the blood when blood glucose levels drop
To enter the blood, it gets hydrolyzed into glucose + Pi
What enzyme catalyzes the hydrolysis of glucose-6-phosphate to glucose+Pi?
glucose-6-phosphatASE
Where is the active site for the enzyme glucose-6-phosphatase?
on the lumenal side of the ER
Why might glucose-6-phosphatases active site be located in the lumen?
This allows the cell to separate the rxn from glycolysis (which occurs in the cytosol)
Phosphatases are what kinds of enzymes?
Hydrolytic
How does AMPK respond to a decrease in the ATP/AMP ratio?
by phosphorylating key proteins and regulating their activities
What is AMPK regulated (increased) by?
Sympathetic nervous system (fight or flight)
exercise
hormones (leptin, adiponectin)
Glycogen is stored as cytosolic granules called?
Beta granules. B-granules cluster to form alpha granules
Which type of glycogen storage granule releases glucose faster
The beta granules. Alpha granules are larger and release glucose slower
Biological purpose for having many non-reducing ends?
increasing the number of non-reducing ends increases the number of sites available for glycogen phosphorylase & glycogen synthase
