biochem exam 2 - fatty acid catabolism 7

Question 1

Lipids

Answer 1

Lipids include many types of molecules

• They are not defined by their structure; they are defined by having low solubility in water and high solubility in non-polar solvents
• They are largely hydrophobic
• OR they can be amphipathic (remember?)

Functions:
* Energy Storage
* Fats and oils
* Structural
* (A)glycerophospholipids(B) sphingolipids(C)sterols(membranes)
* Other/Specific Biological Activities
* enzyme co-factors, electron carriers, light-absorbing pigments, hormones, etc.

Question 2

Storage Lipids: Fatty Acids

Answer 2

The simplest lipids are fatty acids which are also constituents of many more
complex lipids

• Their basic structure exemplifies the amphipathic lipid model
• A long hydrocarbon chain (“tail” – hydrophobic)
• A terminal carboxyl group (“head” – hydrophilic)
• Fatty acids are carboxylic acids with highly reduced hydrocarbon chains (4-36 carbons; C4 – C36)
• Most natural fatty acids are unbranched
• Some have double bonds (stay tuned)
• Almost all natural fatty acids have an even number of carbons (12-24)
• Membrane lipids are 16-20 carbons long

Question 3

Saturated and Unsaturated Fatty Acids

Answer 3

Saturated
- * NO DOUBLE BONDS

• Monounsaturated
• ONE DOUBLE BOND
• Polyunsaturated
  MORE THAN ONE
  DOUBLE BOND
• C1 = carboxylic acid

Most double bonds are at C9, C12, C15

Question 4

Saturated and Unsaturated Fatty Acids

Answer 4

Saturated chain adopts extended conformations

• Unsaturated fatty acids are slightly more abundant in nature
• The double bonds in natural unsaturated fatty acids are commonly in cis configuration
• Kinks the chain
• Prevents close packing
  and increases flexibility
• What is the impact of this?

Question 5

Saturated and Unsaturated Fatty Acids: Naming

Answer 5

The first number is how many carbons are present

• The number after the colon is the number of double bonds present
• The number(s) after the delta denote which carbons have the double bonds
• The ω (omega) numbers refer to how many carbons away from the methyl end of the fatty acid chain that the first carbon=carbon double bond appears

Question 6

how do we break down fatty acids?

Answer 6

fatty acid catabolism!

Question 7

Energy Storage Lipids: TriAcylGlycerols (TAGs)

Answer 7

Fatty acids are often incorporated in Triacylglycerols (also called triglycerides, fats, TAGs)

• These are fatty acid esters of glycerol
• Three fatty acids each in ester linkage to 1 glycerol

3 -acyl-glycerols

reduced carbon chains and have a lot energy

lipases
- enzymes that hydrolyze TAGs to yield F.A’s

Question 8

Energy Storage Lipids: TriAcylGlycerols (TAGs)

Answer 8

triacylglycerols as storage fuels: advantages
- high energy density (J/g) has about 2x more energy than carbohydrates
- not water-soluble (compared to carbohydrates)
- do not increase osmotic pressure
- do not bind water (no extra mass)
- chemically inert because they cannot bond to water

the energy is in the fatty acids!

use as fuels: problems
- need to be emulsified to be transported
- need special protein carriers
- “InertAn Aside: TAGs→Fatty Acids: What about the Glycerol?” bonds are hard to break

“Emulsify”
- to force two or more liquids (fat and water) that are normally undissolvable into a mixture. An “emulsifier” stabilizes the emulsion – usually amphipathic.

Question 9

The primary transporters of lipids from the small intestine to other parts of the body are…

A
Acyl transferases

B
Fatty acid transferases

C
Chylomicrons

D
Serum albumins

Answer 9

C
Chylomicrons

D
Serum albumins - go from adipose tissues to the cells

Question 10

Fatty acids are attached to ___ for transport from the cytosol into the mitochondria

A
Coenzyme A

B
Creatine

C
Carnitine

D
Serum albumin

Answer 10

C. Carnitine

Question 11

Which of the following is true of β-oxidation of fatty acids?

A
In a single round, one molecule of FADH2 and one molecule of NADPHare produced.

B
It is the same for both saturated and unsaturated fatty acids.

C
Fatty acids are broken down into two-carbon units

D
It occurs in the intermembrane space of the mitochondria

Answer 11

not D because it is in the matrix

not A because in a single round, we get way more FADH2

Question 12

An Aside: TAGs→Fatty Acids: What about the Glycerol?

Answer 12

glycerol + ATP to glycerol-3 phosphate to dihydroxyacetone phosphate that can either go to glycolysis or gluconeogenesis

In Step 5 of glycolysis, Dihydroxyacetone phosphate (DHAP) from Step 4 is converted to Glyceraldehyde-3- phosphate (G-3-P)☺ through triose phosphate isomerase

About 95% of the biologically available energy of TAGs resides in the FAs (the focus of this chapter). 5% comes from the glycerol via glycolysis

Question 13

Outline of Fatty Acid Catabolism

Answer 13

1. digestion and transport of dietary fats
2. mobilization and transport of stored fats
3. fatty acid activation
4. fatty acid transport into the mitochondria
5. beta-oxidation of fatty acids to acetyl-CoA
   - simple case: fully saturated FA with an even number of carbons
   - special case: unsaturated FA (double bonds), odd number of carbons
   - other stuff: ketone bodies
6. remember, acetyl-CoA is oxidized to CO2 in the CAC
7. electrons released from the oxidation in the CAC go to the ETC to ATP

Question 14

How do we get our TAGs?: Diet/Digestion

Answer 14

Fats ingested in diet and go to the gallbladder
- if you do not have a gallbladder, you have to eat low fat diet

1. bile salts emulsify dietary fats in the small intestine, forming mixed micelles
2. intestinal lipases degrade triacylglycerols
3. fatty acids and other breakdown products are taken up by the intestinal mucosa and converted into triacylglycerols
4. triacylglycerols are incorporated with cholesterol and apolipoproteins into chylomicrons
5. lipoprotein lipase activated by apo-C-II in the capillary converts triacylglycerols to fatty acids and glycerols
6. fatty acids are oxidized as fuel reesterified

simplified
- eat fat
- fat goes to the gallbladder
- fats go into chylomicron
- chylomicron releases fat into the blood
- blood takes fat to cells
- cell either stores it or uses it for energy

Question 15

summary of dietary lipids

Answer 15

intestine - emulsification (bile)
hydrolysis (TAG to FA) using lipase

intestinal walls - FA’s to TAGs
incorp. in chylomicrons

transport
- lymph system and blood system

muscle and adipose tissue
- TAG to FA (lipoprotein lipase [LPL])
- FA enters cells
- oxidation or storage (TAG)

Question 16

How do we get our TAGs?: From Storage – Adipose Tissue

Answer 16

low energy, emergency

activate hormones glucagon or epinephrine

TAG hydrolysis (to FA) and transport (carrier serum albumin)

FA catabolism for energy

1. glucagon or epinephrine binds the receptor
2. ATP to cAMP
3. PKA activates hormone-sensitive lipase by adding pi
4. PKA add pi to CGI
5. CGI activates ATGL to turn TAG to DAG to MAG
6. MGL
7. MAG sent out of the cell to the blood
8. MAG binds serum albumin
9. beta oxidiation, CAC, repsirtoy chain break down into energy

Notes:
* 4: Phos. of perilipin causes
* 5: CGI to recruit ATGL (lipase)
* 6:ATGL:TAG→DAG
* 7: Phos. of HSL (hormone-sensitive lipase): DAG → MAG
* 8: MGL (lipase): MAG→ FAs

Question 17

Now that we’ve entered the cell…Fatty Acid Activation?

Answer 17

Catabolism happens in the mitochondrial matrix, but the FA cannot pass through the membranes without first being activated. This step is known as Fatty Acid Activation.

In short, the fatty acid (energy inert) is adenylated (ATP→AMP + PPi + E)
PPi is formed (2 ATP equivalents! which is hydrolyzed → energy)
That released energy allows for the formation of the high energy fatty acyl-CoA (thioester!)

ATP + FA

then CoA-SH attacks the fatty acud adenylate to form fatty acid-CoA

Question 18

Now let’s move the activated FA into the mitochondria!

Answer 18

Activated fatty Acyl-CoA cannot pass through the mitochondrial membranes, so we have to go through the carnitine shuttle

Even though we just activated our FA, because of that CoA bit, it can’t pass through.

• So we do two reactions that switch the CoA for carnitine, and then we switch back.

Notes:
Outer membrane: Fatty Acyl-CoA + Carnitine → FA-Carnitine + CoA (Transport to Matrix)

Inner Membrane, inside: FA-Carnitine + CoA → Fatty Acyl-CoA + Carnitine (recycles carnitine)

Question 19

Fatty Acyl-CoA is in the Matrix Now!

Answer 19

Time to oxidize!

Oxidation of the FA component of the fatty acyl-CoA is accomplished by an enzyme in the mitochondrial matrix

beta-oxidation of even saturated FA involves a repeated sequence of 4 rxn:

1. oxidation by a dehydrogenase
2. hydration by a hydratase
3. oxidation by a dehydrogenase
4. thiolysis by thiolase

oxidation of unsaturated fatty acids requires additional steps

oxidation of add chain (3,5,7 ect) fatty acids requires additional steps

Question 20

beta oxidation of FA’s

Answer 20

Notes:
* 1: Oxidation of an alkane to an alkene by dehydrogenation (CAC #6)

• 2.Rehydration. The addition of water is always trans (- OH and H added across the double bond). (CAC #7)
• 3. Oxidation again (this time –OH to carbonyl) (CAC #8)
• 4. Cut off acetyl-CoA (2-C molecule) and add CoA (energy) to the remaining hydrocarbon. This reaction energetically drives the previous 3. - thiolysis
• Addendum: the fatty acid is 2 carbons shorter after each round of oxidation.

Question 21

repeated cycles of beta-oxidation of FA’s

Answer 21

for a C-16

7 cycles = 14
1 acetyl coa left

1 acetyl coa (2-C) per cycle

+ 1 NADH + 1 FADH2 per cycle

(carbon #/2) - 1 = # of cycles
- 1 acetyl CoA per cycle + 1 left over is the # of acetyl CoA’s
so basically the# of acetyl-CoA’s = # of carbons/2

Question 22

ENERGY yield from oxidation

Answer 22

n = carbons
n/2 = # of acetyl-CoA
n/2 - 1 = # of FADH2 & NADH

each acetyl-CoA entering the CAC makes:
- 3 NADH, 1 FADH2, 10 ATP’s
so if the # of acetyl-CoA = 7, 7 x 10 = 70 ATP’s from that acetyl CoA

palmitoyl coa - 16 carbons
- 16/2 = 8 acetyl CoA’s
- (16/2) - 1 = 7 NADH & FADH2
- 8 x 10 = 80 ATP’s from acetyl CoA
- 1.5 x 7 = 10.5 ATP’s from NADH
- 2.5 x 7 = 17.5 ATP’s from FADH2
- 10.5 + 17.5 = 28 ATP’s from NADH & FADH2

yield 80 + 28 = 108 ATPs

BUT!
* Fatty acid activation required 2 ATP so
the net yield is: * 108 - 2 = 106 ATPs

Question 23

Special Case: Unsat. FAs (Double Bond!)

Answer 23

• Notes:
  oxidation = lose e- or really lose H’s :)
• Remember the steps of oxidation at saturated FA:
• 1. Remove 2H
• 2. Add H2O
• 3. Remove 2H
• 4. Remove Acetyl-CoA
• Well, at the double bond, Step 1 has already been done (because Step 1 creates a double bond in a Sat. FA)
• So, at the double bond, turn it from cis to trans with isomerase, skip step 1, and continue.

Question 24

Special Case: Polyunsat. FAs (Multiple Double Bonds!)

Answer 24

• Notes:
• With one double bond we just have the isomerase.
• With multiple, we have to add 2,4-dienoyl-CoA reductase
• In combination with isomerase, the cis double bond is removed, and the trans double bond is shifted (position is wrong for the enzyme)
• Multiple double bonds make this FA less energy-rich.

Question 25

Special Case: FA’s with an odd # of Carbons!

Answer 25

Notes:

• Fatty acids with odd
  numbers of carbons are rare in mammals (more common in plants and microbes)
• Oxidation is largely the same until the end, when propionyl-CoA, instead of acetyl-CoA remains
  1.

notes:
* Three enzymes convert propionyl-CoA to succinyl-CoA.

• Succinyl-CoA → CAC step 4!
• 1. Use biotin to add CO2 → D-methylmalonyl-CoA. Similar to Bypass #1 in Gluconeogenesis.
• 2. Epimerase–switching stuff around a chiral carbon (Epimers – Ch 7). Moving the thioester once.
• 3. Moving the thioester again. Vitamin B12 involved (1 of 2 in humans that require it)

Question 26

More about Vitamin B12

Answer 26

made only by microorganisms (in the digestive tract, meats, food contaminants)

required in minute amounts (about 3ug/day)

deficiency may result from a lack of intrinsic factor, which is required for intestinal absorption of vitamin B12, this is referred to as pernicious anemia

to get around absorption problems, B12 is available as cyanocobalamin (IMM injection nasal spray or orally)

deficiency may also result from a strict vegetarian diet but this is rare because the liver can store a 3-6 year supply. This is the only B vitamin that is stored in our bodies in any significant amount

Question 27

omega oxidation of FA’s

Answer 27

notes

omega is the carbon farthest from the carboxyl group

minor cellular process

after step 3 either end of the fatty acid can attach to the coA

the molecule then enters beta-oxidation

succinate one of the products can enter the CAC

takes place in the endoplasmic reticulum of liver and kidney cells

Question 27

Regulation of FA Catabolism

Answer 27

We have to be careful. FAs are valuable energy sources for the cell, so they should be degraded only if needed.

Otherwise, they should be stored or used as needed in the cells.

primary regulation is at the entry of the FA’s into the mitochondria (an exergonic an drate limiting step) because once the FA’s are inside the mitochondria generally move ahead full speed

if FA’s are prevented from entering the mitochondria, they are converted to TAG’s or phospholipids

Question 28

Regulation of FA Catabolism – The Fasting State

Answer 28

FA’s ate not simultaneously synthesize and degraded

Question 29

Regulation of FA Catabolism – The Fasting State

Answer 29

Adipose tissue is very important in the fasting state

• Lipolysis is greatly activated due to low blood sugar
• The blood level of fatty acids is increased, which are used in preference to glucose (more ATP) by many tissues
• In this case, fatty acids are oxidized rather than glucose. Lipolysis also provides the ATP necessary for gluconeogenesis.

Question 30

Regulation of FA Catabolism – The Fed State

Answer 30

If the liver is full of glycogen, and supplied with glucose: glucose → fatty acid synthesis (Ch. 21)

The first intermediate in this process is malonyl-CoA which inhibits FAs → mitochondria through the
inhibition of carnitine acyltransferase I

The FAs are then stored as TAGs or phospholipids

• Carbs→fat

Question 31

other FA oxidation regulation (allosteric)

Answer 31

rxn 3 is inhibited nay high [NADH & NAD+]

rxn #4 is inhibited by acetyl-CoA, its product

Question 32

genetci defects affecting FA catabolism

Answer 32

most common in the US is in medium-chain acyl-CoA dehydrogenase (MCAD) gene

results in the inability to oxidize certain FA’s

fat accumulates in the liver - hypoglycemia

major health problem for those affected (25-60% mortality among the 1 in 10,000 affected)

Question 33

an alternative fate of acetyl-CoA - ketone bodies

Answer 33

Notes:

• Under normal conditions, most of the acetyl-CoA is produced during FA oxidation → CAC.
• Only small amounts of excess acetyl-CoA are produced.
• Ketone bodies are soluble, so none of these chylomicrons/micelle stuff

if abundant acetyl-COA is available and if the CAC intermediates are depleted instead of entering the CAC the acetyl-CoA may be metabolized in the liver to produce ketone bodies

not all KD’s are ketones and not all ketones are KBs

the acetone produced is toxic and volatile so you can smell it on their breathe

Question 34

what can leader to KB formation

Answer 34

poorly controlled diabetes
- poor glucose intake so little glc to cells
- cell synthesize glc (gluconeogenesis)
- FA’s are catabolized to acetyl-CoA
- acetyl CoA cannot enter the CAC (low supply of intermediate - gluconeogenesis - use oxaloacetate
- severe starvation (or very low-carb diets induces gluconeogenesis

Question 35

do ketone bodies do any good

Answer 35

they are alternative sources of fuel (energy) for various organs

cardiac and muscle tissue will primarily consume ketone bodies to save glucose for the brain

but ketone bodies can cross the BBB and the brain can use it as fuel

so ketogenic diet for the treatment of drug-resistant epilepsy

Question 37

what if there is XS KD formation

Answer 37

increased blood levels of acetoacetate and hydroxybutyrate lower the pH: acidosis. Extreme acidosis leads to coma and death

KB in the blood and urine of untreated diabetes can reach extremely high levels: ketosis

the combo is ketoacidosis