Biochem Chapt 21

Front 1

Catabolism and anabolism of fatty acids via different pathways

Back 1

Catabolism of catty acids:

Produces acetyl-CoA, produces reducing power NADH, FADH, takes place in mitochondria

Anabolism:

Requires acetyl-CoA, requires reducing power NADPH, takes place in cytosol in animals, chloroplast in plants

Front 2

Overview of fatty acids synthesis

Back 2

Builds by processing 2 C at a time to yield malonyl CoA (acetate)

Each pass requires reduction of a carbonyl C to a methylene C

Front 3

Fatty acid synthesis occurs where NADPH is high

Back 3

Cytosol for animals, chloroplast in plants

Source of NADPH: from pentose phosphate pathway

Front 4

Malonyl-CoA is formed from Acetyl CoA and bicarbonate

Back 4

Yields malonyl CoA

Reaction takes acetyl CoA and adds a carboxyl to it by to form actyl-CoA carboxylase (ACC):

Has 3 subunits and a biotin that carries CO2. Bicarbonate (H3O) is source of CO2

This occurs in a 2-step reaction: bicarbonate creates carboxyl group. Transferred to biotin ( ATP). 2. Carboxyl group is carried by bio tin to transcarboxylase

Front 5

2 step reaction of ACC

Back 5

CO2 binds to biotin and is activated with ATP producing carbamoyl

Enzyme undergoes conformational change to carry carbamoyl to transcarboxylase site (are swings around)

CO 2 attached to A-CoA and leaves active site

Front 6

Fatty acid synthase (FAS)

Back 6

Catalyze a repeating 4 step sequence that elongates the fatty chain 2 C at a time

Uses NADPH as an e- donor (reducing agent)

Uses 2 enzyme bound SH groups to activate

Front 7

Fatty acid synthase (FAS) I and II

Back 7

I: single polypeptide chain in vertebrates, single product palmitate formed, C 15 and 16 are from ACoA used to prime

II: made of separate diffusing enzymes in plants and bacteria, makes many branches, lengths

Front 8

Overall FAS type I

Back 8

Goal: attach acetate unit from malonyl-CoA to growing chain and then reduce it

4 enzyme catalyzed steps:

Condensation: of growing chain

Reduction: of carbonyl OH

Dehydration: of alcohol trans alkene

Reduction: of alkene to alkene

Front 9

Acyl carrier protein (ACP)

Back 9

Shuttle acyl group in FAS

Has 4’-phosphopantettheine group (flexible arm carries enzymes from one subunit to another)

Delivers acetate/malonate to FAS

Front 10

Charging ACP malonyl/acetyl-CoA-ACP transferase (MAT)

Back 10

Acetyl group of acetyl-CoA is transferred to KS.

ACP passes this acetate and then ACP-SH is charged wi h malonyl

2 thiols must be charged with the correct acyl groups before condensation can begin

Front 11

Condensation of FAS

Back 11

Attached 2 C from acetyl group to 2 C from malonyl group

Release of CO2 activated malonyl group attachment

Creates beta keto intermediate

Front 12

Step 2 FAS: reduction of carbonyl group

Back 12

First reduction: NADPH reduces the beta keto intermediate (yellow box) to an alcohol

Front 13

Dehydration step 3 FAS

Back 13

OH group from C-2 and H from adjacent CH2 are eliminated and create double bond

Catalyzes to DH

Front 14

Second reduction step 4 FAS: reduction of double bond

Back 14

NADPH reduces double bond made in previous step to yield saturated alkane

Front 15

Final result of FAS

Back 15

4 steps repeat until reaching 16 C where enzyme releases creating palmitate

Front 16

Condensation step 1

Back 16

ACP grabs acetyl COA and attached it to itself

Front 17

step 5 acts as a primer

Back 17

ACP grabs acetyl COA and attached it to itself

Front 18

Step 6

Back 18

ACP finds another malonyl CoA and attached to KS starting fatty acid

Front 19

Condensation step 1

Back 19

Lose the CO2 group by movement of ACP to the KR area

Front 20

Reduction step 2

Back 20

Begins at KR site and move ACP over to DH domain

Front 21

Dehydration step 3

Back 21

At DH starts dehydration moving ACP to ER section

Front 22

Reduce step 4

Back 22

Remove double bond at ER and then moves ACP group back to KS

Front 23

Reduce step 4

Back 23

Remove double bond at ER and then moves ACP group back to KS

Front 24

Moves ACP back to starting position

Back 24

Pic

Front 25

Finally then grabs new malonyl group

Back 25

Pic

Front 26

Acetyl COA is made in mitochondria and needs to be transferred to cytosol

Back 26

Made from pyruvate oxidation and catabolism of carbons from amino acids

This cost 2 ATPs to transfer

FAS cost 3 ATPs per 2 C unit

Front 27

FAS is regulated by acetyl CoA carboxylase (ACC)

Back 27

ACC is feedback inhibited by palmitoyl but activated by citrate (made in mitochondria and signals extra energy so store fat)

ACC is inhibited when energy is needed by glucagon and epinephrine

Front 28

Other modes of regulation in FAS

Back 28

Changes in gene expression

If extra malonyl CoA, it will inhibit transfer to mitochondria

Front 29

Palmitate can be lengthened to longer chain fatty acids

Back 29

Occurs in ER and mitochondria

Adds 2-C

Stearate (18:0) is the most common product

Front 30

Palmitate can be lengthened to longer chain fatty acids

Back 30

Occurs in smooth ER and mitochondria

Adds 2-C at a time

Stearate (18:0) is the most common product but could be further with additional acetyl groups

Front 31

Can desaturate

Back 31

Enzyme desaturase can do this for both palmitate and stearate at position 9 (btw C9 and C10)

Also requires cofactors NADPH

4 e- are added: 2 to O and 2 to CH2 bind forming a double bond

Front 32

Plants and humans desaturate

Back 32

Humans can’t go past 9 but plants can to 12 and 15

This is why we have to get from our diet. Important for membrane fluidity

Front 33

Plants desaturate by

Back 33

Do not oxidize free fatty acids

Oxidize fatty acids attached to glycerol

Can then be hydrolyzed from glycerol backbone

Front 34

Synthesis of TAGs: Synthesis of backbone of TAGs and phospholipids, then makes phosphadtidic acid (first stage)

Back 34

Siphones off dihydroxyacetone phosphate (DHAP) from glycolysis via glycerol 3 dehydrogenase

Happens when we have lots energy

Front 35

Synthesis of phosphophatidic acid

Back 35

Happens before TAGs

Phosphatidic acid is precursor which can be made into either TAGS or glycerophospholipids

For TAGS pathway, phosphatidic acid is hydrolyzed by phosphatidic acid phosphatase (lipin) to diacylglycerol

Diacylglycerol is then converted to TAGs

2 fatty acids are attached by acyl transferases

Releases CoA

Front 36

To form phospholipid and TAGs

Back 36

Phosphatidic acid phosphatase (lipin) removes 3-phosphate from acid

Then third carbon removed to form Triacylglycerol

Front 37

Regulation of Triacyglycerol

Back 37

Insulin results in stimulation of triacylglycerol synthesis

Lack of insulin results in failure to synthesize fatty acids from carbs or glucose (can lead to increase ketone body formation)

lipolysis ( TAG breakdown)

Front 38

Triacylglycerol breakdown and resynthesis (lipolysis)

Back 38

75% of free fatty acids get recycled (reesterified) rather than used for fuel

During starvation

Front 39

Biosynthesis of membrane phospholipids

Back 39

1. Synthesis of backbone (glycerol or sphingosine), 2. Attachment of fatty acids 3. Addition of hydrophilic head to backbone (through pho Forster linkage) 4. Alteration or exchange of the head group or fatty acids to yield the final phospholipid product

Begins with phosphatidic acid or diacylglycerol

Attach head gro to C-3 OH group

Acid condenses with 2 alcohols and eliminates H2O

Front 40

Activation is required for attaching phospholipid head (2 strategies)

Back 40

Needed molecule-Cytidine diphosphate (CDP): contributes the phosphate to connect the head group

Strategy 1: CDP is attached to diacylglycerol forming activated phosphatidic acid.

Strategy 2 (mammals): CDP is attached to the hydroxyl of the head group

Front 41

Phosphaticdycholine

Back 41

Essential in membranes

Also called lecithin

Derived from phosphatudylethanolamine

Front 42

Phohatidylserine and phosphatidyltic pathways to regulate (NOT ON EXAM)

Back 42

Regulation of the two so we don’t have too much through a backward exchange of head groups

Savage the choline

Front 43

Synthesis of sphingolipids use similar pathways

Back 43

4 stages:

1. synthesis of sphinganine (from palmitoyl and serine)

2. Attachment of fatty acid in amide linkage

3. Desaturation of sphinganine moiety to form N-acylsphingosine (ceramide)

4. Attachment of head group to produce cerebroside or sphingomyelin

Front 44

Cholesterol is built on 5-C unit

Back 44

Isoprene

Front 45

Cholesterol synthesis overview

Back 45

3 acetates condense to form mevalonate

Mevalonate makes activated isoprene

6 isoprenes polymerize to form a 30-C squalene

Squalene forms the 4 rings to produce cholesterol

Front 46

Step 1 forming mevalonate from acetate

Back 46

2 acetyl-CoAs condense to acetoacetyl-CoA which then condenses with another ACoA to form beta-hydroxy -beta methylglitaryl-CoA (HMG-CoA)—-> catalyzed by acetyl CoA transfer ace and HMG CoA synthase

HMG-CoA is a rate limiting step

Acetate goes to HMG which is reduced to mevalonate (HMG-CoA reductase)

Front 47

Step 2: conversion os mevalonate to activated isoprenes

Back 47

3 phosphates transferred from ATP to mevalonate

Decarboxylation and hydrolysis create isoprene

Phosphate activated isoprene group

Front 48

Step 3: activated isoprene condensed to form squalene

Back 48

Add on isoprenes in steps until get to 30

Front 49

Step 4: conversion of squalene to 4 ring steroid

Back 49

Adds O to end of squalene chain

This is where plants and animals are different: product for animals is Lanosterol and for plants is eegosterol

Front 50

Lipoprotein particles

Back 50

Carry lipids, spherical

Surface is made of protein (apolipoprotein) and a Single layer of phospholipids

Interior: cholesterol, TAGs, cholesterol esters. All nonpolar so want to keep away from blood

Front 51

4 major classes of Lipoprotein

Back 51

Determined by density in centrifuges

Chylomicrons

VLDL

LDL

HDL

Front 52

Chylomicrons

Back 52

Least dense, very large

Contain variety of proteins and TAG

Free fatty acid to release fuel in fat, heart, and skeletal muscle

When depleted for back to liver via endocytosis by apoE mediated (linked to Alzheimer’s)

Front 53

VertLDL

Back 53

Contains TAG and cholesterol ethers in high concentrations

Frees fatty acids at adipocytes to recovery them to TAG for storage in lipid droplets

Muscle uses TAG for E

Front 54

LDL

Back 54

Produced by removal of TAG from VLDL, enriched in cholesterol and ch. ethers

Bind to receptors on muscle and adipose tissue

Myocytes bad adipocytes take up cholesterol via receptor mediated ebdocytosis

Front 55

HDL

Back 55

High density

Can convert left over from LDL to esthers for stating other products (bike salts)

Pick up cholesterol from cells and return to live to be metabolized (bile salts)

Front 56

Receptor mediated endocytosis

Back 56

See pic

Front 57

Lecithin cholesterol Acyl Transferase (LCAT) enzyme

Back 57

Present on surface of HDL

Allows to recognize cholesterol from LDL and VLDL to combine it with a side chain to convert to cholesterol ethers (starting for bile salts)

Front 58

5 modes of regulation of cholesterol synthesis and transport: first 3 HMG-CoA reductase when dephosphorylated

Back 58

Short term regulations

AMP dependent prorate in kinase decreases, decrease pathway

Glucagon and Epi. Increase down regulate

Insulin increase, pathway increases

Front 59

Transcriptional HMG-CoA )longer term)

Back 59

Insulin induced gene protein (Insig) senses cholesterol levels

When levels of sterols are high, keeps sterol binding element binding protein (SREBPs) in ER and tags HMG-CoA reductase for degradation with ubiquiton

When levels are low, SREBP is cleaved and moved to nucleus for transcription

Front 60

Second regulatory system by LXR mediated transcription

Back 60

In liver: liver x receptor

Front 61

Cardiovascular disease causes

Back 61

High LDL: inability to clear and begin to build up. Send monocytes which became macrophages and then foam cells which can explode

Low HDL cholesterol: picks up cholesterol and carry back to liver so need higher level of these