Please enable JavaScript.
Coggle requires JavaScript to display documents.
Lipid Metabolism - Coggle Diagram
Lipid Metabolism
Fats and oils
storage forms of reduced carbon
found in soybeans, sunflowers, peanuts, cotton, rape (canola), olives, avocados, etc
store energy efficiently
fat/oil: 40 kJ g-1
starch: 15.9 kJ g-1
Major types of Lipids:
Triacylgylcerides: fats and oils stored in seeds
main form of storage lipid
stored in oleosome (aka lipid body)
oleosins
proteins in membrane
keep oleosomes from fusing
recruit lipases for breakdown
oleosomes synthesized in ER
deposited between lipid layers in membrane
oleosome buds off
Triacylglyceride Degradation
degradatin of triacylglycerides occurs for germinating seeds to obtain sugars and ATP for growth and development of embryo and seedling
cell compartments in triacylglyceride degradation
oleosome
Triacylglyceride hydrolysis
occurs at surface of oleosome
lipases recruited by oleosins in oleosome membrane
lipase cleaves FA from glycerol backbone
FAs move to glyoxysome
Glycerol moves to cytoplasm
saturated FAs go to glyoxysome
glycerol goes to cytoplasm
glyoxysome
b-Oxidation degrades lipids to acetyl-CoA
pathway only oxidizes saturated FAs, not unsaturated
input into beta-oxidation pathway
FAs released by lipase in oleosome
FAs enter glyoxysome
FAs are substrate for beta-oxidation
outputs from beta-oxidation pathway
acetyl-CoA produced and utilized by glyoxylate cycle
Process:
FADH produced and oxidized in glyoxysome
produces 1 FADH per cycle
oxidation produces peroxide
catalase detoxifies peroxide
NADH contributes to energy metabolism
produces 1 NADH per cycle
NADH oxidized in mitochondria (ATP synthesis via MET and chemiosmosis)
Glyoxylate Cycle converts acetyl-CoA to succinate
after lipids are depleted, glyoxysome reverts to peroxisome
inputs into glyoxylate cycle:
acetyl-CoA from beta-oxidation cycle input at two sites
output from glyoxylate cycle:
succinate, which is then utilized in mitochondria
NADH contributes to energy metabolism
produces 1 NADH per cycle
NADH oxidized in mitochondria (ATP synthesis via MET and chemiosmosis)
Suc moves to mitochondria
mitochondria
Reduce succinate to OAA
malate/OAA moved to cytoplasm
produces 1 FADH
may produce 1 NADH
Cytoplasm
produces 1-2 NADH
consumes 2ATP
PEP carboxykinase
gluconeogenesis
carbohydrate metabolism
sucrose translocation
Polar glycerolipids: membrane lipids
unit membrane structure:
cell/organelles bounded by membranes
restrict movement of molecules
basic unit structure:
lipid bilayer
membrane proteins
unique properties of each membrane:
lipid composition
protein composition
Membrane lipid composition in cellular membranes:
each membrane has specific composition
lipid composition determines membrane properties
acyl chain length affects melting temp, with shorter chain = lower melting temp
desaturation lowers melting temperature
basis for membrane fluidity concept during chilling
responses to chilling at 5-15 C
maintain membrane fluidity at decreased temp
desaturation influences ability to tolerate decreased temp
freezing at less than 0 C
water forms crystals
membrane physically punctured by water cystrals
there is a shift toward unsaturated FAs in chilling-resistant species
C=C add kinks to lipid structure
permits less dense packing
liquid crystalline v gel state
interactions with specific proteins
Polyunsaturated lipids for chloroplast development
mutant fails autotrophically, but grows on sucrose
required for signaling
1 more item...
Main structural lipids of membranes
C16 and C18 FAs attached to glycerol
head group varies
class defined by head group
glyglyceroplipids: sugar head group; found in chloroplast membrane
glycerophospholipids: phosphate head group; found in most membranes
Non energy related lipids such as:
waxes
isoprenoids
terpenoids
sterols
carotenoids
Lipid structure:
glycerol backbone
fatty acid (FA) side chain
common FAs:
range from 12-24 C
always have an even number of C (bc of addition of acetyl-CoA)
saturated FAs have no C=C; include lauric, myristic, palmitic, and stearic acid
Unsaturated FAs have C=C, include oleic, linoleic, and linolenic acids
FA composition varies among species, and specific composition gives oils unique properties such as:
melting temperature
heat capacity
flavors/aromas
FA Biosynthesis
fatty acid synthase complex
Plant fatty acid synthase complex
type II: 6 dissociable subunits
condensing enzymes
b-Ketoacyl-ACP synthase III
b-Ketoacyl ACP-synthase II
b-Ketoacyl-ACP synthase I
b-Ketoacyl-ACP reductase
b-Ketoacyl-ACP dehydratase
b-Ketoacyl reductase
reflects prokaryotic origin
ACP
tethers nascent FA chain to complex
rotates nascent FA chain into position for each enzyme in sequence
occurs mainly in plastids of plants
stages:
Charging
charging of malonyl-ACP
Acetyl-CoA carboxylase
dicots:
composed of four subunits, each with a single catalytic domain
resembles enzyme in prokaryotes
monocots:
single polypeptide (22o-240 kD) with 3-4 catalytic domains
resembles protein in other eukaryotes
rate-limiting reaction for FA biosynthesis
Initiation
initiation of acyl chain
condensation of malonyl-ACP and acetyl-CoA
catalyzed by b-Ketoacyl-ACP synthase III/Condensing Enzyme III
reaction only occurs once per fatty acid synthesized
Reduction
reduction of keto-acyl chain
set of reactions that reduces keto-acyl chain to acyl chain
functions during each cycle of fatty acid synthesis
after initiation reaction
after each elongation reaction
Elongation
elongation of acyl chain
condense acyl-ACP with malonyl-CoA
b-Ketoacyl-ACP synthase II elongates chains >16C
b-Ketoactyl-ACP synthase I elongates chains <16C
spatial difference in active sites of the 2 condensing enzymes
desaturation simultaneous for most 18:0 elongations forming 18:1 FA
Release
fatty acids released from ACP
16:0, 18:0, or 18:1 FAs usually released
substrate for triacylgylceride and phospholipid synthesis
Energy requirements:
for 16:0 saturated fatty acid:
8 ATP
16 NADPH
for 18:0 saturated fatty acid:
9 ATP
18 NADPH
Incorporation of FAs into lipids
chloroplast/prokaryotic pathway:
occurs in envelope
addition of acyl unit to phosphatidic acid
desaturation reactions
sequential desaturation at specific positions
Release to thylakoids
May import 18:2 lipid from ER and process
ER/eukaryotic pathway:
FAs leave chloroplast as thioester
phosphatidic acid is starting point
addition of acyl tails to oil bodies
sequential desaturation reactions
to oil bodies
to membrane lipids
to chloroplast
Glyoxysomes
specialized peroxisome in oil-containing seeds
breakdown fatty acids to succinate
b-oxidation
glyoxylate cycle
reverts to peroxisome when lipids depleted
polar head group