Lipids Flashcards
What makes something a lipid?
-Insoluble in water (hydrophobic)
-Energy dense
-Structural Diverse
Are some lipids amphipathic? What is an example of one? Why is it important?
-Yes, some have both hydrophilic and hydrophobic parts
-Phospholipids are amphipathic
-Amphipathic is important to digestion
What does it mean when a lipid is energy dense?
-1 gram of fat contains 9.45 kcal while protein and carbohydrate only contain 4.1 kcal/g
-lipids have twice the energy as proteins and carbohydrates
What does it mean by a lipid is structural diverse?
-compared to proteins and carbohydrates, lipids are polymers
What are some functional characteristics of lipids related to digestion?
-Energy dense
-Acids in the solubilizing and absorption of lipid soluble vitamins
-Structural contribution to cells
-Act as messengers
How is a lipid being energy dense relate to nutrition? What are examples of this?
-supplies energy in the diet
-also a storage form of energy in the body
-fatty acids in adipose
-adipose tissue: storage form of fat
How do lipids in the diet aid in vitamin lipid digestion?
-Acids in the solubilizing and absorption of lipid soluble vitamins
How do lipids contribute to the structure of cells? What is an example of something lipid based?
-Phospholipids in membranes
-cortisol and any steroids are lipid base
How do we classify lipids?
-By their diverse structures
What are the 2 varieties of lipid structures?
-glycerol based lipid
-anything else
-basically have a glycerol or not
What are examples of non-glycerol based lipids?
-cholesterol
-fatty acids
-steroids
-prostaglandins
-sphingomyelin/cerebrosides: nervous system lipids
What are examples of glycerol based lipid?
-Triglycerides (triacylglycerols)
-Glycolipids
-Phospholipids
-(lipid and a sugar)
What are the two classifications of glycerol based lipids?
-Simple
-Compound
What is a simple glycerol based lipid?
-triglycerides (glycerol and 3 fatty acids)
What is a compound glycerol based lipid?
-Phospholipids and glycolipids (glycerol and 2 fatty acids)
-Phospholipids: adds a phosphate group and possibly an additional functional group
-Glycolipid: adds a sugar like glucose or galactose
Where are triglycerides found?
-oilseeds like
-soybean
-cotton seed
-sunflower seed
-canola
-peanut
-seeds that can be pressed for oils
What is a glycerol composed of?
-3 carbon molecules and 3 oxygen molecules
What is the storage form of fat in humans and animals?
Triglycerides
Are oils from seeds simple or compound glycerolipids?
Simple
What are examples of compound glycolipid and where are they found?
-Phospholipid: found in cell membrane of animals and plants
-Glycolipid: found in plants, structural lipids of plants
Do phospholipids and glycolipids make up a small or large portion of total mass?
Small
How are fatty acids mostly found?
-fatty acids are most often found esterified meaning attached to something
-Fatty aids rarely found free
What are fatty acids often attached to?
-glycerol backbone like
-a triglyceride
-a phospholipid
-or a glycolipids
What do all triglycerides have?
-a glycerol backbone
Are carbons of glycerol in distinct positions in a triglyceride?
Yes
In a triglyceride how many fatty acids are attached to a glycerol backbone?
-3 fatty acids are attached to glycerol backbone
How do fatty acids vary?
-Chain length
-unsaturation: diverse come from fatty acids
What do fatty acids have?
-an aliphatic chain lacking oxygen and a carboxylic acid group
How does chain length vary in fatty acids?
-from 2 to 20 carbons
-generally even numbers of carbons in plants and animals
What are examples of variations in chain length of fatty acids?
-Two carbon acetic acid C2H4O
-Twenty carbon eicosanoid acid C20H40O2
-In animals even number carbon fatty acids
-Same number of oxygen no matter what 2:1 ratio (H:C)
What does saturation mean?
-saturation is a measure of the number of double bonds in a fatty acid
-no double bonds = saturated fatty acid
-meaning all the bond positions of carbons are occupied by other atoms
What does unsaturated mean?
-have multiple double bonds
-one double bond = monounsaturated fatty acid
-two double bonds = polyunsaturated fatty acids
-unsaturated has double bonds btw carbons
What are some common fatty acids?
-16 carbon palmitic acid (saturated)
-18 carbon stearic acid (saturated)
-18 carbon oleic acid (monounsaturated)
-18 carbon linoleic acid (polyunsaturated)
What do double bonds do to a chain of carbons?
-straightens it out
What does cis mean?
-hydrogen on same side of the chain
What does trans mean?
-hydrogens on opposite side of the chain
What does cis geometry implicate about fatty acid shape?
-cis less interaction btw branches
-more space
Is there a higher or lower melting point of a fatty acid has a longer chain length?
-Higher melting point
Is there a higher or lower melting point of a fatty acid if it is more saturated (less unsaturated)?
-means more single bonds
-so lower melting point
What do polyunsaturated fatty acids tend to be at room temperature?
-liquid (oils)
What do longer chains, saturated fatty acids tend to be at room temperature?
-Solid
Do positions of double bonds vary?
-Yes, along the chain
How does double bond position nomenclature work?
-count from the terminal methyl end of the fatty acid
-omega numbers
What does omega w-6 mean? omega-3?
-a double bond is 6 carbons from the methyl end of the fatty acid
-omega 3: 3 carbons in
What are the two essential fatty acids in the diet?
-Linoleic acid
-Linolenic acid
What is linoleic acid?
-18 carbon w-6
-2 double bonds
-omega 6: first double bond at 12th carbon
What is linolenic acid?
-18 carbon w-3
-18 carbons
-3 double bonds
-omega 3: first double bind at 15th carbon
What geometry are linoleic and linolenic acid in?
Cis
Why are linoleic and linolenic acid essential?
-Animals can only add double bonds to fatty acids at position 9 or less along the carbon chain
Where do essential fatty acids have double bonds?
-btw carbon 9 and the methyl end of the fatty acid
Where are essential fatty acids found?
-in cell membranes as fatty acid constituents of phospholipids
What are essential fatty acids used for?
-metabolism: elongated (add more carbons in units of 2) and further desaturated (add more double bonds than in precursor essential fatty acids)
What can linoleic acid (C18:2) become?
-arachidonic acid (C20:4)
What are essential fatty acids precursor to?
-prostaglandins
-thromboxane
-leukotrienes
-short lived local: blood clotting, luteolysis, and immune function
What can linolenic acid (C18:3) become?
-eicosapentaenoic acid (EPA, C20:5)
-docosahexaenoic acid (DHA, C22:6)
~important for nervous system lipids
What omega can fish make?
-omega 3
-they get through diet
Lipid through ruminant?
- Dietary lipids
- Rumen: site of glycolipid hydrolysis and modification of fatty acid profile
- Acid stomach
- Small intestine
Lipid through non-ruminant?
- Dietary lipid
- Acid stomach
- Small intestine: site of glycolipid hydrolysis
How does the rumen modify lipids?
-Microbial lipolysis of glycolipids and biohydrogenation of unsaturated fatty acids
-Emulsification in the small intestine
What do herbivores like ruminants typically consume?
-low lipid diets compared to non-ruminants
Examples of whole plant (forage) lipids?
-glycolipid
-phospholipid
Example of grain (concentrates) lipids?
-triglycerides
Where are glycolipids found?
-structural lipids in plants (hay)
What happens when a ruminant has to much lipids?
-disrupts their digestive
How does rumen microbial lipolysis work?
-bacteria produce lipases capable of hydrolyzing glycolipids
What do phospholipids turn into during rumen microbial lipolysis?
-2 fatty acids
-phosphoglycerol
What do glycolipids turn into during rumen microbial lipolysis?
-2 fatty acids
-glycoglycerol
What do triglycerides turn into during rumen microbial lipolysis?
-3 fatty acids
-glycerol
Where is glycerol process mostly done in ruminants?
-in the rumen (hydrolyzed)
How do ruminants modify unsaturated fatty acids?
-rumen microbes hydrogenate unsaturated fatty acids
-biohydrogenation
How does biohydrogenation work?
-hydrogenation by rumen microbes as opposed to industrial hydrogenation that produces margarine
-done by living things
-reduces the number of double bonds
-reduces unsaturation
-increased the saturation of dietary fatty acids
Are essential fatty acids saturated or unsaturated?
Unsaturated
What does biohydrogenation do to dietary fatty acids?
-reduces the dietary content of essential fatty acids
Do ruminants become essential fatty acid deficient? How do they cope?
-No, ruminants have evolved to conserve (robust) essential fatty acids to live on low EFA
~Conversation of the absorbed EFA
-Hydrogenation reduces number of double bond
What is the rumen outflow of dietary lipids?
- Dietary lipids enter esterified as glycolipids
- Lipids leave the rumen as free fatty acids
- Unsaturated fatty acids enter with feeds
- much of entering unsaturated fatty acids leave saturated and only some of the entering unsaturated fatty acids leave the rumen intact (60-90% of unsaturated fatty acids entering the rumen are hydrogenated)
What is the difference btw free and volatile fatty acids?
-Volatile: 4 carbons or less and leave through wall of rumen
-Free: exit rumen and go to small intestine
How do non-ruminant digest lipids?
-Hydrolysis of glycolipids
-Emulsification
How does lipase work?
-Lipase enzymes hydrolyze glycolipids in the lumen of the small intestine
-released by the pancreas
-go to lumen
What does phospholipase hydrolyzes?
- phospholipids
-products: 1 fatty acid and 1 lysophospholipid
What does pancreatic lipase hydrolyzes?
-triglycerides
-products: 2 fatty acids and a monoglyceride
Why is emulsification important?
-Lipids are hydrophobic and digesta is aqueous
~mixing is an issue
What is emulsification?
-solubilizes lipids into droplets within the digesta
How does emulsification work?
-relies on amphipathic molecules: those that can interact with hydrophobic and hydrophilic aspects of the lipids and aqueous digesta
-droplets containing different molecules with the effect of stabilizing lipids in the lumen of the small intestine for absorption
What is the structure when emulsification happens?
-2 monoglycerides
-phospholipids
-bile salts
What does emulsification produce?
-mixed micelles
What do mix micelles interact with?
-interact with enterocytes
How does the absorption of lipids work?
- the enterocyte plasma membrane consists of lipid (phospholipids)
- Fatty acids, 2 monoglycerides, and phospholipid digestion products are capable of crossing-flipping- the apical plasma membrane of the enterocyte
- Mostly, fatty acids in mixed micelles are absorbed across the plasma membrane
What type of transports do some types of lipids use?
-cholesterol bc very long chain saturated fatty acid
How does re-esterification work?
-absorb fatty acids and 2 monoglycerides are re-esterified to triglycerides for export from the enterocyte
How is this different from amino acid and glucose
-Amino acid and glucose are released into the blood in the form they are absorbed
-While lipids are re-esterified and reassembled
What do enterocyte produce?
-triglycerides using the products of glycolipid digestion: reassembly of glycolipids
What does the production of chylomicrons serve?
-packing absorbed lipids for circulation
What are chylomicrons?
-lipid-rich particles assembled from triglycerides, cholesterol, phospholipids and some protein in the enterocyte
Where are chylomicrons released?
-NOT in the blood
-Released into the lymphatic vessels of the small intestine called lacteals
-Chylomicrons enter blood at the thoracic duct where lymph joins venous blood
What do chylomicrons do?
-allow lipids to float through blood
What is on the outside of a chylomicron?
-phospholipids allows enter to aqueous solution
If chylomicrons are released into the lymph and not blood, when does the liver get access to the absorbed dietary lipids?
-As blood reaches the liver
What can be done to essential fatty acids?
-Elongation and desaturation to longer chain polyunsaturated fatty acids
What type of fatty acids can plants produce?
-fatty acids with double bonds beyond carbon 9 (counting from the carboxyl carbon)
Where does linoleic acid have double bonds at?
Has double bonds at carbon 9 and 12
Where does linoleic acid have double bonds at?
Has double bonds at carbons 9, 12, and 15
What characteristics do fatty acids derived from EFA that are functional in animals have?
-longer chains
-more double bonds
Where can animals add double bonds?
carbons 5 and 6
What is elongation?
-addition of 2 carbon units
What is desaturation?
addition of more double bonds
What is arachidonic acid an important precursor to?
for other regulatory lipid molecules like prostaglandins
What is the process of desaturation of linoleic acid?
-add double bond at carbon 6
-add two carbons; double bonds now at 8, 11, and 14
-add double bond at 5
What is lipogenesis?
-fatty acid synthesis from precursors
Are lipogenesis and fatty acid synthesis the same thing?
Yes
Where can fatty acids be produced?
-in the liver
-or adipose tissue
-depending on the species
Where are fatty acids produced in humans and avian species?
Liver
Where are fatty acids produced in pigs, ruminants, and horses?
Adipose tissue
Where can rodents produce fatty acids?
Both the liver and adipose tissue
What is the substrate for lipogenesis?
-Acetate in the form of acetyl-CoA is used to make fatty acid synthesis in the body
What is the major source of acetyl-CoA in non-ruminants for fatty acid synthesis?
-Glucose
-(glycolysis)
What is the major source of acetyl-CoA in ruminants for fatty acid synthesis?
-acetate is produced in the rumen from fermentation of carbohydrates
What is citrate and intermediate of? and what can it be cleaved to release?
-Kerb’s cycle
-acetyl-CoA
Where does lipogenesis occur?
Cytoplasma
What is the process of lipogenesis?
-starts with carboxylation of acetyl-CoA by acetyl-CoA carboxylase
-Acetyl-CoA + CO2 + ATP -> Malonyl-CoA +ADP + Pi
What are the 4 steps carried out by fatty acid synthetase in fatty acid synthesis?
-Condensation: lose CO2
-Reduction
-Dehydration
-Reduction
~These steps are repeated over and over until desired chain length: often 16 carbons
What are the two enzymes in fatty acid synthesis?
-Acetyl-CoA carboxylase
-Fatty acid synthetase
What does Acetyl-CoA carboxylase do?
adds CO2 to acetyl-CoA to produce malonyl-CoA
What does Fatty acid synthetase do?
-carries out all other reactions of fatty acid synthesis
-adds acetyl-CoA units to the elongation chain producing even number carbon fatty acids
-requires 2 NADPH2 to complete the 2 carbon elongation of the fatty acid
Do hydrogens close bonds off?
Yes
Components of fatty acid storage
-adipose tissue
-esterification to triglycerides
-lipolysis
-circulation
What is a compact way to store energy?
fatty acids
How are fatty acids stored?
As triglycerides in adipocytes of adipose tissue
Where can triglycerides be present?
-in other cells as lipid droplets
-liver hepatocytes or skeletal muscle cells (small droplets)
Are adipocytes almost entirely triglycerides?
Yes
How do fatty acids from diet or synthesized get packed?
-into a condensed form
-efficient cells, push cytoplasm against cell wall, and store triglycerides
What are the substrates of fatty acid storage?
-dietary fatty acids
-fatty acids synthesized by lipogenesis in the body
How are fatty acids synthesized in the body?
-synthesized in the adipose tissue then incorporated into triglycerides
Where is fatty acid synthesized? and released as what? and where?
-synthesized in liver
-released as triglycerides into the blood, hydrolyzed to release glycerol and fatty acids to be uptake by cells of tissues including adipose tissue
What happens to fatty acids from the diet after absorption?
-re-esterified to triglycerides and
-released as chylomicrons
Where are triglycerides released and what happens to them?
-released into blood
-hydrolyzed to release glucose and fatty acids to be uptake by cells of tissues including adipose tissue
What is the esterification pathway for fatty acids?
In adipose tissue, fatty acids are esterified to glycerol through glycerol-3-phosphate pathway
How does triglyceride synthesis start? and the end?
-starts with glycerol-3-phosphate and
-through the sequential addition of 3 fatty acids becomes a triglyceride
What is the process of triglyceride synthesis?
-sequence of 3 fatty acids
-use fatty acid with acetyl-CoA
1. fatty acid CoA interacts with glyercol-3-phosphate
2. Acyl-CoA added
3. phosphate removed
4. Another CoA
What are the three fatty acids involved with triglyceride synthesis?
-Lysophosphatidic acid
-Phosphatidic acid
-diacylglycerol (DAG)
When does stored energy get taken out of storage?and what happens?
-when there is an energy deficit
-fatty acids are mobilized/liberated from triglyceride storage in adipocytes for energy in other tissues
~Only fatty acids are released from adipose tissue not triglycerides
What happens to triglycerides in lipolysis?
-triglycerides are hydrolyzed and the products are released into the blood in small concentration
What products are released when triglycerides are hydrolyzed in lipolysis?
-glycerol
-3 free (non-esterified) fatty acids
Where can free fatty acids circulate?
-in the blood to tissues and cells that need substrates for energy
What carries out lipolysis in adipocytes?
hormone-sensitive lipase
What is the process of lipolysis?
-Adipose tissue
-Adipocytes
-liquid droplet
-triacylglycerol
-glycerol and 3 fatty acids
-glycerol goes into gluconeogenesis
-Fatty acids go into the TCA cycle
-Both produce energy
What does adipose tissue store?
-triglycerides in large liquid droplets for energy reserve
What regulates lipolysis?
-stimulated by epinephrine, glucagon, and norepinephrine
-Inhibited by insulin
Why is lipolysis stimulated by epinephrine, glucagon, and norepinephrine? and inhibited by insulin?
-stimulation hormone sensitive
-fight or flight epi glucagon low glucose get from adipose
-insulin inhibits bc insulin storage
What does fatty acid beta oxidation do?
-get energy back out of fatty acids
Where do free fatty aids enter once they have been absorbed by a tissue?
Into the mitochondria to be oxidized
Where does oxidation (kerb’s cycle) occur?
Mitochondria (liver, skeletal, and cardiac muscle)
Where does total energy from oxidizing come from?
- beta-oxidation
-acetyl-CoA
in the kerb’s cycle
Major steps of beta oxidation?
-free fatty acids enter the mitochondria
-get oxidized (oxygen added)
-broken down into acetyl-CoA
-feed acetyl-CoA into kerb’s cycle (get energy from this)
-liver socks up energy
Detailed steps of beta oxidation
- CoA is added to a fatty acid to produce fatty acid acyl-CoA which enters B-oxidation and through sequential steps produces FADH2 and NADH2 that can be used through oxidative phosphorylation to produce ATP
-Acetyl-CoA is also produced and enters the kerb’s cyle to produce more ATP, FADH2 and NADH2
What type of fatty acid structure does beta oxidation use?
16 carbon fatty acid
How many cycles of beta oxidation does a 16 carbon fatty acid go through?
8 cycles
What is the yield of beta oxidation?
-7NADH2 for 21 ATP
-7 FADH2 for 14 ATP
-8 Acetyl-Coa
What is the yield of the kerb’s cycle?
-24 NADH2 for 72 ATP
-8 FADH2 for 16 ATP
-8 GTP to ATP
What is the total ATP yield from beta oxidation and the kerb’s cycle?
-129 ATP
-Not 131 bc 2 ATP used when a fatty acid is activated with CoA
