Biochem exam 3 pt 2

17,18,19

why is glucose important

good fuel, builds carbonskeletons

what can glucose build the carbon skeletons of

amino acids, lipids, nucleotides, cofactors

• the first stage of glucose metabolism

• a sequence of enzyme-catalyzed reaction by which glucose is converted into pyruvate

• In the process, some of the free energy is captured by the synthesis of ATP and NADH

glycolysis

in glycolosis One molecule of glucose is converted to , which gives rise to two molecules of pyruvate

fructose-1,6- bisphosphate

true or false: for all the reactions of glycolysis, there is a requirement for O2!

false

what are the three fates of pyruvate after it is formed

anaerobic glycolysis, aerobic oxidation, anaerobic alcoholic oxidation

what does the presence of o2 determine for pyruvate

wheter it enters the citric acid cycle

list the aerobic conditions

need oxygen, citric acid cycle, over 30 atp per glucose molecule, co2 h2o byprducts, occurs in mitochondria

list the anerobic conditions

oxygen not required, makes lactate (animals) ethanol (yeast), 2 atp per glucose, byproducts lactate (animals) co2 ethanol (yeast), occurs in cytoplasm in cells with low o2

______ respiration dominates during normal activity

aerobic

every glucose yields…

2 atp and 2 pyruvate

for the glycolosis reaction we must supply 2 _____

ATP

what are the 2 phases of glycolosis

priming phase and payoff phase

what happens in the priming phase

2 atp consumed, glucose phosphorylated and makes FBP, fbp split to make 2 g3p

what happens in the payoff phase

2g3p converted to pyruvate, 4 atp and 2 NADH produced

what are the 10 steps of glycolosis (Pretty Iguanas Punch Cats; Intelligent Owls Teach Idiots Difficult Tricks)

phosphorylation, isomerization, phosphorylation, cleavage, isomerization, oxidation, transfer, isomerization, dehydration, transfer

What happens in step 1 of glycolosis (phosphorylation)

phosphorylation of glucose with atp creates glucose-6-phosphate

which hexokinases are invloved in step 1 of glycolosis

I and IV

• found in many tissues (brain, muscle, white blood cells)

• High affinity for glucose (low Km)

• Hill Coefficient = 1

• Regulated by allosteric feedback inhibition of glucose-6-phosphate

hexokinases I, II, III

• Found in the liver and pancreas

• Main function is to regulate blood glucose levels, especially after meals

• Low affinity for glucose (high Km)

• Hill coefficient = 1.5

• No product inhibition

• Glucose is high activity is turned on

• Normal glucose activity is reduced

hexokinase IV or glucokinase

what happend in step 2 of glycolosis (isomerization)

Isomerization of glucose-6-phosphate for fructose-6-phosphate, pyran ring to furan, enzyme Glucosephosphate isomerase

no atoms added or removed; molecular formula remains the same but chemical structure is changed

isomerization

what is step 3 of glycolosis (phosphorylation)

fructose-6-phosphate to fructose-1,6-bisphosphate with atp, enzyme Phosphofructokinase,

what is the rate limiting step in glycolosis

step 3

what happens in step 4 of glycolosis (cleavage)

fructose-1,6,-bisphosphate broken for glyceraldehyde-3-phosphate and dihyroxyacetone

phosphate, enzyme adolase

what happens in step 5 of glycolosis (isomerization)

dihyroxyacetone phosphate makes the 2nd glyceraldehyde-3-phosphate, enzyme triosephosphate, dhap to g3p

what is the energetics for the first 5 steps of glycolosis

2 kj/mol

which steps are irreversible for the priming phase

step 1 and 3

what is step 6 of glycolosis

Glyceraldehyde-3-phosphate is converted to 1,3- bisphosphoglycerate by electron transfer and addition of a phosphate group, enzyme Glyceraldehyde-3-phosphate dehydrogenase

what is the oxdizing agent in step 6 of glycolosis

NAD+

what happens in step 7 of glycolosis (transfer)

1,3-bisphosphoglycerate transfers a phosphate group to ADP forming ATP and 3-phosphoglycerate, enzyme Phosphoglycerate kinase

what happens in step 8 of glycolosis (isomerization)

Isomerization of 3-phosphoglycerate to 2- phosphoglycerate, enzyme Phosphoglycerolmutase

what happens in step 9 of glycolosis (dehydration)

Water is eliminated from 2-phosphoglycerate to form phosphenolpyruvate (PEP), better phosphoryl donor made, increased double bonds more unstable more phosphate release,

what happens in step 10 of glycolosis (transfer)

Phosphoenolpyruvate transfers a phosphate group to ADP forming ATP and pyruvate, enzyme Pyruvate kinase, inhibited by excess atp

glycolosis is ______ and releases _____ kj/mol

exergonic, 73.3 kj/mol

what are the three control points in glycolosis that undergo decreases in free energy and the enzymes are under allosteric control

step 1 hexokinsae inhibited by g6p, step 3 phosphofrcuctoskinase inhibited by ATP, step 10 pyruvate kinase inhibited by atp

NAD+ is requierd for ______ of glyolosis and is then recycled back into NADH

step 6

If O2 is available (aerobic), NADH is re-oxidized by the ___________ during oxidative

phosphorylation

electron transport chain

If O2 is unavailable (anaerobic), NADH is re-oxidized by the __________ to either lactate or ethanol

reduction of pyruvate

under anaerobic conditions what is the most important process for the regenration of NAD+ and what enzyme helps

pyruvate to lactate, Lactate dehydrogenase

• skeletal muscle, supports anaerobic, favor pyruvate to lactate to regenerate NAD+

• lactate dehydrogenase subunit

LDH5 (M4)

• heart muscle, supports aerobic, More likely to convert lactate back to pyruvate to favor TCA cycle

• lactate dehydrogenase subunit

LDH1 (H4)

lactate builds up in the muscle, leading to fatigue as it creates an acidic environment that inhibits

________________

muscle contraction

After exercise (O2 available),lactate is transported to liver and converted back to _______ and then ______

pyruvate, glucose

what are the steps of NADH being reoxidized to NAD+ for anaerobic alcohol fermentation (yeast)

decarboxylation of pyruvate, reduction of acetaldehyde accepts 2 electrons 1 proton and regenerates NAD+ to make ethanol

glucose units (a1-4) are attached by

linear glycosidic bonds

glucose units (a1-6) are attached by

branching glycosidic bonds

what is the role of glycogen

store glucose or supply glucose to glycolosis pathway

Glycogen synthesis or _______– process where glycogen is formed from glucose molecules

glycogenesis

________ is a highly branched polymer of glucose

glycogen

what are the 5 steps of glyogen synthesis (Ugly Iguanas Fight Enormous Bears)

glucose uptake phosphorylation, isomerization to glucose1phosphate, formation udp glucose, chain elongation, branching enzyme

what happens in step 1 of glycogen synthesis (uptake)

glucose transporters take glucose from blood and bring to cytosol, phosphorylated to glucose 6 phosphate

what enzymes are used in step 1 of glycogen synthesis

Glucokinase in liver, Hexokinase in muscle

• Found in the liver, pancreas, and kidneys

• glucose transporter

GLUT2

• muscle and adipose tissue-Higher affinity for glucose

• glucose transporter

GLUT4

what happens in step 2 of glycogen synthesis (isomerization)

Isomerization of glucose-6-phosphate to glucose-1-phosphate, enzyme Phosphoglucomutase

Glucose-1-phosphate + UTP=

UDP glucose +2Pi

why is udp glucose created in the 3rd step of glycogen synthesis

substrate and energy for enzyme glycogen synthase that will link glucose units

is the formation of UDP glycogen endergonic or exergonic

exergonic

What is UDP glycogen made up of

Uracil base + pentose sugar + 2 Phosphates

what happens in the first part of step 3 in glycogen synthesis

transfer UMP to g1P releases PPi, enzyme UDP-glucose pyrophosphorylase

what happens in the second part of step 3 in glycogen synthesis

PPi hysrolosis into PO4 3-, enzyme inorganic Pyrophosphatase

what happens in step 4 of glycogen synthesis (elongation)

Transfer of glucose from UDP- glucose to Tyr-194 of glycogenin, repeat until 8 glucose and glycogen synthase takes over, uses UDP glucose to add the glucose unit to non reducing end of existing glycogen chain makes a(1,4) glycosidic bond

• primer protein initiates the first few glucose units called glycogen primer

• glycogen synthesis elongation

Glycogenin

true or false: glycogen chain detaches from glycogenin protein in elongation

false

what does glycogen synthase require

growing glucose chain with free hydroxl at C4 on terminal glucose and UDP glucose

what is step 5 of glycogen synthesis

glycogen branching enzyme transfers 7 glucose units to site to produce a(1-6) glycosidic bond (branch point)

what are the rules for step 5 of glycogen synthesis

7 glucose residues is taken from chain of at least 11, branch point must be at least 4 residues away from other branch point

Glycogen breakdown or ________– process where glycogen is released back into glucose units and energy

glycogenolysis

what are the steps for glycogen breakdown (really interesting racoons)

release glucose1phosphate, isomerization g1p to g6p, remodeling glycogen

what is step 1 of glycogen breakdown

Glucose is cleaved from glycogen and reacts with Pi to make glucose-1- phosphate, enzyme glycogen phosphorylase

uses phosphate instead of water to cleave the glycosidic bond

phosphorolysis

what enzyme is used for the isomerization of g1p to g6p

phosphoglucomutase

why is aa remodeling step needed for glycogen breakdown

glycogen phosphorlyase cant break 1,6 branch points a debranching enzyme is needed

what 2 reactions are catalyzed in glycogen breakdown

transferase activity - shift block of three glucose connects from one branch to another, a16 glucosidase activity- hydrolsis of a16 glycosidic bond releases glucose

glycogen Phosphorylase ___ - phosphorylated, active, phosphorylation control

a

glycogen Phosphorylase ____ - dephosphorylated, less active, phosphorylation control

b

how does an organism control the glycogen synthesis and breakdown pathway

dual regulation-covalent modification (phosphorylation) allosteric control

glycogen ___ form - tense, less active, allosteric control conformation

t

glycogen ___-form - relaxed, more active, allosteric control conformation

r

why in phosphorylase A (phosphorylated), glucose favors the transition to the T-form (less active)

high glucose decreases need for cell to break down glycogen

explain what the t form does

exposes serine 14 (phosphorylation site) and permits dephosphorylation by phosphoprotein phosphatase

In phosphorylase B (dephosphorylated) ATP and/or Glucose-6-phosphate favor the T-form because…

ATP or G6P decreases need for cell to breakdown glycogen into glucose

in phosphorylase b why does amp favor the r form

high levels of amp indicate low energy status

what are the enzymes that can phosphorylate glycogen synthase

glycogen synthase kinase 3 (GSK3), protein kinase (PKA), and AMP-activated protein kinase (AMPK)

Glycogen synthase can be dephosphorylated by enzyme

protein phosphatase I

the body controls two opposite processes in opposite directions so they don't happen at the same time

reciprocal regulation

Pathway by which glucose is synthesized from pyruvate or other non-carbohydrate precursors during times of fasting, prolonged exercise, or low carbohydrate intake

gluconeogenesis

why is gluconeogenesis not a simple reversal of glycolosis

because of the three irreversible steps

what is the reverse of step 10 glycolosis

pyruvate+ATP→ oxaloacetate + GEP → PEP, Enzymes Pyruvate Carboxylase and PEP Carboxykinase, occurs in mitochondria| and mito cytoplasm, requires biotin atp acetyl coa activator, and |GTP

what is the reverse of step 3 glycolosis

F-1,6-BP → F-6-P enzyme Fructose- 1,6-Bisphosphatase

what is the reverse of step 1 glycolosis

G-6-P → Glucose enzyme Glucose-6-phosphatase

how does oxaloacetate get to the cytoplasm in the reversal of step 10 glycolosis

turns into malate and then converted back

Effectors (substrates, products, or coenzymes) of a pathway inhibit or activate an enzyme. (Responds rapidly to external stimuli.)

allosteric

Inhibition or activation of an enzyme depends on formation or breaking of a bond, frequently by phosphorylation or dephosphorylation. (Responds rapidly to external stimuli.)

covalent modification

Two opposing reactions, such as formation and breakdown of a given substance, are catalyzed by different enzymes, which can be activated or inhibited separately. (Responds rapidly to external stimuli.)

substrate cycles

as a regulator of metabolism high atp

inhibits glycolosis

the reversal of glycolosis is…

endergonic

gluconeogensis is…

exergonic

as a regulator of metabolism high amp

accelerates glycolysis, inhibits gluconeogenesis