LIPID METABOLISM

physical

major change that TAGs undergo in the stomach is ____ rather than chemical.

chyme

is a thick semi-liquid material made up of partially digested food and gastric secretions (hydrochloric acid and several enzymes).

stomach

lipid digestion begins in

gastric lipase

hydrolysis of TAG occurs by an enzyme called

cholecystokinin

arrival of chyme from the stomach triggers in the small intestine, through the action of the hormone ____, the release of bile stored in the gallbladder.

bile

contains no enzymes acts as an emulsifier

pancreatic lipases

hydrolyze ester linkages between the glycerol and fatty acid units of the TAGs

monoacylglycerol and two free fatty acids

Complete hydrolysis does not usually occur; only two of the three fatty acid units are liberated, producing a

fatty acid micelle

is a micelle in which fatty acids andlor monoacy/glycerols and some bile are present.

chylomicron

is a lipoprotein that transports triacy/glycerols from intestinal cells, via the lymphatic system, to the bloodstream.

lymphatic system

Chylomicrons are too large to pass through capillary walls directly into the bloodstream. Consequently, delivery of the chylomicrons to the bloodstream is accomplished through the body's_____

lipoprotein lipases

TAG release from chylomicrons and their ensuing hydrolysis is mediated by ____. These enzymes are located on the lining of blood vessels in muscle and other tissues that use fatty acids for fuel and in fat synthesis.

acetyl CoA

The fatty acid and glycerol hydrolysis products from TAG hydrolysis are absorbed by the cells of the body and are either broken down to ____ for energy or stored as lipids

churning action

produces small fat droplets (chyme)

gastric lipases

hydrolysis some (10%) TAGs

bile

solubilizes “droplets”

pancreatic lipases

produce monoacylglycerols, which from fatty acid micelles

small intestine

interaction with bile occurs

stomach

chyme is produced

stomach

gastric lipases are active

small intestine

pancreatic lipases are active

small intestine

fatty acid micelles are produced.

intestinal cells

chylomicrons are produced

intestinal cells

monoacylglycerols are converted back to triacylglycerols

adipocyte

is a triacylglycerol-storing cell

adipose tissue

is tissue that contains large numbers of adipocyte cells

adipose tissue

function as a storage location for the chemical energy inherent in TAGs, also serves as an insulator against excessive heat loss to the environment and provides organs with protection against physical shock

adipose cells

among largest cells in the body

epinephrine and glucagon

Use of the TAGs stored in adipose tissue for energy production is triggered by several hormones, including ___

cAMP

Hormonal interaction with adipose cell membrane receptors stimulates production of ____ from ATP inside the adipose cell.

hormone-sensitive lipase (HSL)

the lipase needed for triacylglycerol hydrolysis, a prerequisite for fatty acids to mete the blood stream from an adipose cell

triacyIglycerol mobilization

is the hydrolysis of triacylglycerols stored in adipose tissue, followed by release into the bloodstream of the fatty acids and glycerol so produced

triacylglycerol

reserves would enable the average person to survive starvation for about 30 days, given sufficient water

glycogen

reserves (stored glucose) would be depleted within 1 day.

one

During triacylglycerol mobilization, ____ molecule of glycerol is produced for each triacylglycerol completely hydrolyzed.

liver or kidneys

glycerol travels to the ___, where it is converted, in a two-step process, to dihydroxyacetone phosphate

phosphorylation

first step involves ___ of a primary hydroxyl group of the glycerol.

ketone

In the second step, glycerol's secondary alcohol group (C-2) is oxidized to a___

dihydroxyacetone phosphate

is an intermediate in both glycolysis and gluconeogenesis (It can be converted to pyruvate, then acetyl CoA, and finally carbon dioxide, or it can be used to form glucose.

1. The fatty acid must be activated by bonding to coenzyme A

2. The fatty acid must be transported into the mitochondrial matrix by a shuttle mechanism.

3. The fatty acid must be repeatedly oxidized, cycling through a series of four reactions, to produce acetyl CoA, FADH, and NADH.

There are three parts to the process by which fatty acids are broken down to obtain energy.

fatty acid activation

Here the fatty acid is converted to a high-energy derivative of coenzyme A. Reactants are the fatty acid, coenzyme A, and a molecule of ATP.

fatty acid activation

reaction requires the expenditure of two high-energy phosphate bonds from a single ATP molecule; the ATP is converted to AMP rather than ADP, and the resulting pyrophosphate (PP;) is hydrolyzed to 2Pj•

acyl CoA

The activated fatty acid-CoA molecule is called

acyl

refers to a random-length fatty acid carbon chain that is covalently bonded to coenzyme A

acetyl

refers to a two-carbon chain covalently bonded to coenzyme A

carnitine

A shuttle mechanism involving the molecule ____ affects the entry of acyl CoA into the matrix. The acyl group is transferred to a __ molecule, which carries it through the membrane.

B-oxidation pathway

is a repetitive series of four biochemical reactions that degrades acyl CoA to acetyl Co A by removing two carbon atoms at a time, with FADH, and NADH also being produced.

saturated fatty acid

For a ____, the B-oxidation pathway involves the following functional group changes at the & carbon and the following reaction types.

parallel

The reaction sequence dehydrogenation-hydration-dehydrogenation in the B-oxidation pathway has a ___ in Steps 6-8 of the citric acid cycle

step 1; first dehydrogenation

carbon -carbon single bond is converted to a carbon carbon double bond.

step 2; hydration

a hydration reaction occurs

trans

enzyme involved is stereospecific in that only ___ double bonds are produced.

step 2; hydration

enzyme involved in this hydration will also hydrate a cis double bond, but the product then is the D isomer.

step 3; dehydrogenation

Removal of two hydrogen atoms converts the B-hydroxy group to a keto group, with NAD* serving as the oxidizing agent.

step 4; thiolysis

The fatty acid carbon chain is broken between the a and B carbons by reaction with a coenzyme A molecule. The result is an acetyl CoA molecule and a new acyl CoA molecule that is shorter by two carbon atoms than its predecessor.

step 1, 3

loss of hydrogen atoms (oxidation) occurs

thiolysis

The chain cleavage reaction that occurs in Step 4 is called _____ by analogy with the process of hydrolysis, which also involves breaking a molecule into two parts.

even number

fatty acids normally found in Triacylglycerols in an

trans- Enoyl CoA

step 1; dehydrogenation

L-B- Hydroxyacyl CoA

step2; hydration

B- Ketoacyl CoA

step 3; dehydrogenation

acetyl CoA, New acyl CoA

step; 4 thiolysis

equal

B-oxidation pathway is ___ to half the number of carbon atoms in the fatty acid.

C18 fatty acid

9 acetyl CoA ( 8 repetitive sequences)

C14 fatty acid

7 acetyl CoA (6 repetitive sequences)

step 3

NAD+ is reduced to NAD

step 4

acetyl CoA molecule is produced

step 2

carbon carbon double bond is converted to a carbon carbon single bond

step 1

FAD is reduced to FADH2

step 3

secondary alcohol group is oxidized to a ketone group

step 4

coenzyme A molecule is needed as a reactant.

thiolysis

enzyme needed is thiolated

first dehydrogenation

enzyme needed is acyl CoA dehydrogenase

thiolysis

The substance B-ketoacyl CoA is a reactant.

hydration

enzyme enoyl CoA hydratase is needed

first dehydrogenation

A stereospecific enzyme that produces trans-carbon carbon double bonds is needed

first dehydrogenation

The substance acyl CoA is a reactant.

thiolysis

The substance acyl CoA is a product.

unsaturated fatty acids

are common components of dietary triacylglycerols. Their oxidation through the B-oxidation pathway requires two additional enzymes besides those needed for oxidation of saturated fatty acids.

epimerase that can change a D configuration to an L configuration and a cis-trans isomerase-are needed for two reasons.

B-oxidation pathway requires two additional enzymes besides those needed for oxidation of saturated fatty acids

s cis double bonds

First, the double bonds in naturally occurring unsaturated fatty acids are nearly alway___, which yield on hydration a D-hydroxy product rather than the L-hydroxy product needed for Step 3 of the pathway.

epimerase

enzyme effects a configuration change from the D form to the L form.

trans-(2,3) double bond

Second, the double bonds in naturally occurring unsaturated fatty acids often occupy odd-numbered positions. The hydratase in Step 2 of the pathway can effect hydration of only an even-numbered double bond. The cis-trans isomerase produces a___from a cis-(3,4) double bond.

two acetyl CoA

in the final four reaction sequence, ___are produced in addition to the FADH2 and NADH

eight repetitions

of the B-oxidation pathway are required for the oxidation of stearic acid, an 18-carbon acid.

9 acetyl CoA molecules, 8 FADH, molecules, and 8 NADH molecules

These eight repetitions of the pathway produce

106 atp

What is the net ATP production for the complete oxidation of palmitic acid, the C16 saturated fatty acid, to CO2 and H20?

do 2.5% times as much damage

The fact that fatty acids (stearic acid) yield 2.5 times as much energy per gram

4 kcal

1 gram of carbohydrate equals

9 kcals

1 gram of fat equals

fatty acids uses

1. Skeletal muscle uses glucose (from glycogen) when in an active state. In a resting state, it uses fatty acids.

2. Cardiac muscle depends first on fatty acids and secondarily on ketone bodies (Section 25.6), glucose, and lactate.

3. The liver uses fatty acids as the preferred fuel.

4. Brain function is maintained by glucose and ketone bodies (Section 25.6).
   Fatty acids cannot cross the blood-brain barrier and thus are unavailable.

oxaloacetate and acetyl CoA.

first step of the citric acid cycle involves the reaction between

Oxaloacetate concentration depends on pyruvate produced from glycolysis (Section 24.2); pyruvate can be converted to oxaloacetate by pyruvate carboxylase

pyruvate carboxylase

Oxaloacetate concentration depends on pyruvate produced from glycolysis (Section 24.2); pyruvate can be converted to oxaloacetate by

(1) dietary intake high in fat and low in carbohydrates

(2) diabetic conditions in which the body cannot adequately process glucose even though it is present and

(3) prolonged fasting conditions, including starvation, where glycogen supplies are exhausted.

Certain body conditions upset the lipid-carbohydrate balance required for acetyl CoA generated by fatty acids to be processed by the citric acid cycle These conditions include

RER

is the ratio of carbon dioxide to oxygen inhaled divided by the ratio of carbon dioxide to oxygen exhaled.

0.7 L

It takes _____ of oxygen to burn 1 gram of carbohydrate and 1.0 L of oxygen to burn 1 gram of fat.

The excess acetyl CoA is diverted to the formation of ketone bodies

What happens when oxaloacetate supplies are too low for all acetyl CoA present to be processed through the citric acid cycle?

ketone body

is one of three substances (acetoacetate, B-hydroxybutyrate, and acetone) produced from acetyl CoA when an excess of acetyl Co A from fatty acid degradation accumulates because of triacyglycerol-carbohydrate metabolic imbalances.

Acetoacetate and b-hydroxybutyrate.

It is a C4 molecule

acetoacetate

it is a ketoacid