Biochem FINAL

What is gluconeogenesis?

A metabolic process that creates glucose from non-carbohydrate sources, such as amino acids, glycerol, and lactate during starvation and vigorous exercise

Why does gluconeogenesis occur?

Tissues require a continuous supply of glucose as a metabolic fuel therefore cells must be able to synthesize it when needed

What organs are gluconeogenesis production exclusive to?

Liver and a little bit of kidneys

What parts of the body only generate ATP from glucose?

Brain, nervous system, and red blood cells

Is gluconeogenesis anabolic or catabolic?

Anabolic because it uses ATP for energy (not phosphorylation)

Where does gluconeogenesis occur in the cell?

Cytosol and mitochondria

Why is gluconeogenesis similar to but not the reverse of glycolysis?

Only 7/11 steps are shared

What are the two precursors of gluconeogenesis in this course?

Glycerol and lactate

In glycerol-dependent gluconeogenesis what part of the molecule is used?

Glycerol backbone (fatty acid tails used for beta-oxidation)

What is glycerol converted to in gluconeogenesis?

Glycerol → glycerol phosphate → DHAP

What happens after glycerol is converted to DHAP in gluconeogenesis?

Essentially glycolysis occurs in reverse

What is the Cori cycle/lactate-dependent gluconeogenesis briefly?

Lactate is released into the blood by exercising skeletal muscle and RBCs into the liver and is converted to glucose which is released back into the blood

Which 3 irreversible steps from glycolysis differ and must be “bypassed” in gluconeogenesis?

Hexokinase, PFK1, PK (2 reactions occur causing gluconeogenesis to be 11 steps)

What is the first goal of lactate-dependent gluconeogenesis?

Make PEP

What is the pathway of lactate-dependent gluconeogenesis (Option L) if an organism does make lactate?

Lactate, cytosol → pyruvate, mitochondria → OAA, matrix → PEP (lactate dehydrogenase, pyruvate carboxylase, mitochondrial PEP carboxykinase)

Why is GTP needed in option L from OAA to PEP?

For phosphorylation because ATP can only be used for energy

In option L what cofactor is needed from pyruvate to OAA?

Biotin with ATP

What is the pathway of lactate-independent gluconeogenesis?

Pyruvate → OAA → malate, cytosol → OAA → PEP (pyruvate carboxylase, mitochondrial malate dehydrogenase, cytosolic malate dehydrogenase, cytosolic PEP carboxykinase)

What does PK do in glycolysis and what enzyme reverses this in gluconeogenesis?

PEP → pyruvate (two reactions therefore two enzymes reverse this: pyruvate carboxylase (pyruvate→OAA) and mitochondrial PEP carboxykinase (OAA→PEP)

What does PFK1 do in glycolysis and what enzyme reverses this in gluconeogenesis?

F6P → F1,6P (FBPase-1 in the cytosol)

What is FBPase-2?

Similar to PFK2 of PK1 it is a regulatory enzyme that converts F2,6 to F6 (opposite of PFK2)

What are 2 allosteric inhibitors of FBPase-1?

>AMP (need ATP therefore glycolysis will occur), >F2,6 (PFK2 rxn pdt that pushes rxn forward)

In terms of regulation of FBPase-1, how does it differ from glycolysis and gluconeogenesis?

An effect on one will have the opposite effect on the other

What does Hexokinase do in glycolysis and what enzyme reverses this in gluconeogenesis?

Glucose → G6P (G6P translocase, transports into lumen of ER and G6P, catalyzes formation of glucose)

Where does the dephosphorylation of G6P occur?

ER

What releases excess P from the dephosphorylation of G6P?

T2 embedded protein removes excess P to the cytosol

What releases glucose from the ER after the dephosphorylation of G6P?

T3-embedded protein transports it out of the liver and to the blood

What regulates gluconeogenesis?

Glucagon is a hormone that is released during the fasting state

In terms of glucose, what do glucagon and insulin do?

Glucagon increases blood glucose levels, insulin decreases blood glucose levels

What is glucagon stimulated by and what is insulin stimulated by?

Low blood sugar, high blood sugar

What is glucagon inhibited by and what is insulin inhibited by?

High blood glucose, low blood glucose

What does glucagon get released and when does insulin get released?

Fasting state, fed state

What is beta-oxidation?

Catabolism of fatty acids (not dietary fats but adipocytes)

What does beta-oxidation produce?

Acetyl-CoA and reducing agents (NADH, FADH2)

Where does beta oxidation take place?

Mitochondria

Why are beta-oxidation and ketones coupled?

Beta-oxidation is required for ketogenesis

What part of the glycerol is used in beta-oxidation?

FA tail of glycerol backbone, each FA is released one at a time

Where does glycerol in beta-oxidation come from?

Triacylglycerols (TAGs) which are energy-rich fuels

How is the degradation also the first stage of beta-oxidation initiated?

Epinephrine and glucagon whichs stimulate lipolysis by initiating cAMP signal which activities PKA and initiates a cascade of enzymes needed to breakdown TAGs (1st messenger=glucagon, 2nd messenger=cyclic AMP)

What are the respective fates of TAGs and its components?

Glycerol→liver (gluconeogenesis), Fatty acids→albumin→muscle→mitochondria (beta-oxidation)

How are FAs activated in the cytoplasm of the cell?

Using enzyme FA thiokinase which adds CoA creating Fatty acyl CoA

How is Fatty acyl CoA transported from the cytoplasm to the mitochondria?

CPT1 (embedded transport molecule) that removes CoA and attaches carnitine creating acylcarnitine

How is acylcarnitine transported into the mitochondrial matrix?

Carnitine-acylcarnitine translocase

How is Fatty Acyl CoA regenerated in the matrix? How is carnitine-acylcarnitine translocase used again here?

CPT2 removes carnitine from acylcarnitine and adds CoA, to remove carnitine out of matrix

What are the 4 steps of beta-oxidation?

1) Oxidation, +FADH2 (ETC), 2) Hydration, 3) 2nd Oxidation, +NADH (ETC), 4) Thiolysis, +Acetyl-CoA (TCA)

How is a fatty acid tail broken down in beta-oxidation?

2 C at a time (even with odd-numbered tails)

How much ATP is produced from beta-oxidation resulting in 8 acetyl-CoA, 7 NADH, 7 FADH2?

131 ATP (net=129 ATP)

Will the body prioritize beta-oxidation to obtain energy?

No, glucose is always broken down first

When does ketogenesis occur?

When the body lacks sufficient carbohydrates to burn for energy and uses the Acetyl-CoA from beta-oxidation to make ketones

Where is ketogenesis restricted to?

Liver, unlike beta-oxidation which can occur in any cell

What are the 3 ketone bodies produced?

acetoacetate, 3-hydroxybutyrate (beta-hydroxybutyrate), and acetone (exhaled product)

Where are ketone bodies used?

muscle and brain primarily

How does ketogenesis begin?

Combining 2 acetyl-CoA molecules

What determines if 3-hydroxybutyrate (beta-hydroxybutyrate) is produced instead of acetoacetate?

Whether NADH is reduced or not

Where are the ketone bodies used?

Muscle, anywhere not the liver

How is 3-hydroxybutyrate used by tissues?

Oxidized to yield acetoacetate and NADH

How is acetoacetate used by tissues?

Converted to acetoacetyl CoA (from Succinyl CoA) and cleaved to produce 2 Acetyl CoA

What cycle uses the products of both ketogenesis and gluconeogenesis to create energy?

TCA

What is glycogen and where is it stored?

Branched polymer of glucose, largest stores of glycogen are in liver and skeletal muscles

What are the two types of bonds that connect glycogen?

Straight bonds held by alpha 1,4 branch bonds held by alpha 1,6

What are the 3 steps of glycogen synthesis?

1) glycogenin creates the glycogenic core 2) glycogen synthase extends the core using alpha 1,4 bonds into a straight line 3) glycogen branching enzyme creates branches using alpha 1,6 bonds

What form of glucose must be used in glycogen?

Activated form of glucose called UDP-glucose formed by the reaction of UTP and glucose 1-phosphate

What is UDP-glucose’s role in glycogen production?

Glucose donor

Why is glycogen an efficient storage form for glucose?

It only takes 1 ATP to make and release 31 ATP when broken down

What are the 3 steps of glycogen breakdown?

1) release of glucose 1-phosphate from glycogen [glycogen phosphorylase] 2) remodeling of glycogen to allow continued degradation [transferase+debranching enzyme/alpha 1-6 glucosidase] 3) conversion of glucose 1-6 phosphate into glucose 6-phosphate [phosphoglucomutase]

How is glucose 6-phosphate utilized?

1) glycolysis 2) gluconeogenesis 3) pentose phosphate pathway

What enzyme converts glucose 1-phosphate to glucose 6-phosphate?

phosphoglucomutase

Why does glycogen phosphorylase leave one glycosidic bond?

It leaves the alpha 1,6 linkage because it can only break alpha 1,4 bonds

What enzyme removes the lonely glucose molecule left behind by the glycogen phosphorylase?

alpha 1,6 glucosidase

Glycine

nonpolar

Alanine

nonpolar

Valine

nonpolar

Leucine

nonpolar

Isoleucine

nonpolar

Phenylalanine

nonpolar

Tryptophan

nonpolar

Methionine

nonpolar

Proline

nonpolar

Serine

polar

Threonine

polar

Tyrosine

polar

Asparagine

polar

Glutamine

polar

Cysteine

polar

Histidine

basic

Lysine

basic

Arginine

basic

Aspartic acid

acidic

Glutamic acid

acidic

Acidic side chains…

Donate protons

Basic side chains…

Accept protons

Acidic side chains…

Donate protons

Basic side chains…

Accept protons

What is physiologic pH?

7.4

What is the pH of an amino group?

About 9.6

What is the pH of a carboxy group?

About 2

At physiologic pH how does an amino acid look?

carboxyl deprotonated (COO-), amino protonated (-NH3+)

At what pH are both amino and carboxyl groups ionized?

7.4, physiologic

What is physiologic pH?

7.4

What is the pH of an amino group?

About 9.6