Chapter 15: Lipids Flashcards
Describe the various functions of lipids and define their composition.
- Energy storage
- Cell membrane
- Signaling
- Fatty acids(2), Glycerol, (hydrophilic head)
Draw and recognize the common fatty acids from their name.
Myristate 14:0
Palmitate 16:0
Stearate 18:0
Palmitoleate 16:1 Δ9 cis
Oleate 18:1 Δ9 cis
Linoleate 18:2 Δ9,12 cis
A-linolenate 18:3 Δ9,12,15 cis
Arachidonate 20:4 Δ5,8,11,14 cis
Describe the relationship between the chain length and degree of unsaturation on the melting point.
- Longer chain = higher MP
- More double bonds = lower MP
- Cis lower MP than Trans
- Saturated higher MP than unsaturated
Describe the composition of Triacylglycerols (TAG): why are they better storage fuels than glycogen.
- Three fatty acids esterfied to a glycerol
- Oxidation is 6kJ/g compared to 38 kJ/g
- Reduced carbon chains are a better energy source
Explain the specific roles for different types of lipoprotein particles and FA binding proteins in TAG transport from dietary sources, liver, and adipose tissue.
Transporters of TAGs
Chylomicron: largest lowest density
VLDL
LDL
HDL: smallest and most dense lipoprotein
- Albumin will carry FFA
- apolipoproteins embedded in chylomicrons
List the main types of lipids found in the cell membrane and know their structural features.
- Glycerophospholipids
- Sphingolipids
- Cholesterol
Explain the role of lipids in cell signaling, precursors of hormones and functions
Cholesterol:
- Steroid Hormones
- Bile acids
Arachidonate
- Eicosanoids (precursor of immune regulatory molecule)
Explain how NSAIDs inhibit pain and fever: and the reason for side effects
What are the three important roles lipids play in biology?
- Energy storage
- Cell membranes
- Signaling
Describe the structure of lipids. What is a fatty acid?
- Consist of carboxylic acid and hydrocarbon tail (4-36C)
- Most abundant FA are
- Unbranched
- 12-20 C
- Even numbered
- Fatty acids covalently bond to proteins to tether proteins to membranes
What is the difference between a Saturated and Unsaturated fat?
Saturated:
- Contain fully reduced methylene groups
- Free rotation
Unsaturated:
- Contain at least one double bond
- Restricted rotation
What are the differences between Cis and Trans fatty acids?
- Cis is reduced on the same side which causes a bend in the molecule
- Trans is reduced on opposite sides which is more linear
What is the structure for naming standard fatty acids?
C, #double bonds (Δ^# where double bond starts) name
Ex: 18:1(Δ^9) cis-9-octadecenoic acid
What is a PUFA?
Polyunsaturated Fatty Acid
How are omega fatty acids named?
- From the last carbon count forward and the double bond can be either a Omega-3 or Omega-6
- If a double bond is present on both, Omega-3 naming is used
Draw this molecule
How does saturation and length factor into melting point?
- MP increases as chain length increases
- MP decreases as double bonds increase
- Cis has lower MP than Trans
Compare interactions between saturated and unsaturated fatty acids?
- Tightly packed and well ordered means better interactions
- Unsaturated Cis = less tightly packed due to kink means worse interactions
What is the function of Triacylglycerols(TAGs)?
- Energy storage
- Contains 3 fatty acids esterfied to a glycerol
Where are TAGs derived from? Compare glycogen oxidation vs TAG oxidation.
- Dietary sources
- Liver biosynthesis
- Adipocytes
Glycogen = 6kJ/g
TAG = 38 kJ/g
How are TAGs and Cholesteryl esters transported? Why must they be transported like this?
- They are carried in the blood plasma as Lipoprotein particles
- Apolipoproteins are the carrier proteins
- They must be moved from tissue of origin to storage in this way because TAGs and Cholesteryl esters are insoluble in water
What are the four classes of lipoprotein particles?
Chylomicrons (50-200 nm) - Largest and least dense
Very Low-density lipoproteins (VLDL; 28-70 nm)
Low-density lipoproteins (LDL; 20-25 nm)
High-density lipoproteins (HDL; 8-11 nm) Smallest and most dense
What are the functions of the four types of lipoproteins?
*Chylomicrons: Transport TAG and cholesterol from intestine epithelia to tissues
*VLDL: Transport excess TAG and cholesterol from liver to adipose tissue
LDL : Transport cholesterol to non-hepatic tissue
HDL: Transport cholesterol from blood to liver (excretion) and stroidogenic tissue (for hormone synth)
What are some features of Chylomicrons?
- Largest of all lipoprotein particles
- Monolayer of phospholipid membrane containing free cholesterol
- Phospholipid membrane can have up to 6 apolipoproteins
- Inside contains TAGs and Cholesterol esters to be delivered to peripheral tissue
Outline the steps in TAG metabolism.
- Bile acids emulsify TAGs
- Lipase cleavage breaks down TAG into Glycerol and Fatty acid
- Fatty acids resynthesized into TAGs inside cell
- TAGs packed into Chylomicrons
- Chylomicron exported to peripheral tissue
Outline the steps of ApoC-II activating lipoproteins
- ApoC-II binds to lipprotein lipase on endothelial cells which activates lp lipase
- Lipoprotein lipase cleaves acyl ester bond and releases fatty acid and glycerol
- Fatty acids enter endothelial cells
- Fatty acids enter nearby cells
- Formation of albumin-fatty acid complexes
- Transported through microcapillaries to distant cells
What is Albumin?
- Carrier protein for free fatty acids in blood plasma
- Abundant
- Protects cell membranes from detergent effects of free fatty acids
How are TAGs from liver packaged?
- Packaged in VLDL particles
- FAs synth in liver from acetyl-CoA in cytosol are used to generate TAGs in the endomembrane system then packaged into VLDL particles
- Transported to peripheral tissue
How do adipocytes store TAGs?
- Lipid droplets are the storage site for TAGs in adipocytes
How are lipid droplets protected from lipases?
- They are surrounded by phospholipid monolayer with large amounts of perilipin
What does glucagon signaling stimulate?
- Glucagon binding causes cascade = fatty acids into bloodstream
- cAMP activates PKA
- lipases break down TAGs
- Free fatty acids bind to fatty acid binding protein 4 and are exported to circulatory system
- Albumin carries FFA to peripheral tissue
What are three types of membrane lipids?
- Glycerophospholipids
- Sphingolipids
- Cholesterol
What are glycerophospholipids?
- Most abundant in phospholipid membrane
- Substrate for glycerophospholipid synth is phosphatidate
- Phosphatidate is 2 FA and a phosphate group attached to a glycerol
- Phosophatidate + polar head = glycerophospholipid
What are sphingolipids?
- Derived from Ceramide
- Spingosine synth by linking serine to carboxyl group of palmitate
- Sphingosine + Polar head = Sphingolipid
- Sphingoglycolipid is when a glycan group replaces the choline
What is cholesterol?
- Constitutes 25-40% of lipids in plasma memb
- Affects membrane fluidity
- Key metabolic precursor of steroid hormones and bile acid biosynth
- Comes from diet and biosynth
What is a lipid raft?
- Discrete regions that contain high [] of cholesterol and aggregation of transmembrane receptor proteins and glycoproteins involved in cell signaling
- Thicker membrane
What are the two main lipids in Cell signaling?
Cholesterol:
- Steroid homones
- Bile acids
Arachidonate:
- PUFA precursor of immune regulatory molecules called Eicosanoids
How is vitamin D related to cholesterol?
7-Dehydrocholesterol –Ultraviolet on skin—> Vitamin D —>—>1,25 hydroxyvitamin D3
What are the steroid hormones and what are their functions?
Half life: Hours
What is an eicosanoid?
- Signaling molecules derived from PUFAs as arachidonate
- Respond to GPCR by releasing arachidonate from membrane by phosphilases
- Paracrine: half life of minutes
Compare and contrast steroids and eicosanoids.
Stroids: Half life of hours
Eicosanoids: Half life of minutes
Outline the steps in the Eicosanoid pathway.
- GPCR activated
- Phospholipase A2 activation
- Arachadonate and monoacyl phospholipid formed
- Arachidonate broken down by lipoxygenase or forms Prostaglandin H2
- Prostagladin H2 is then transformed into other forms
What are NSAIDs and what do they do?
- They are inhibitors of COX-1 and COX-2 enzymes
- Ibuprofen and Asprin irreversibly bind to both COx enzymes
- Rofecoxib and Celecoxib bind to COX-2
What are the side effects of taking NSAIDs
Non= Asp/Ibu
What does COX-1 inhibition cause?
Stomach bleeding
How is Selective COX-2 different from COX-1 Inhibitors?
What happens if a snake that releases Phospholipase A2 when it bites you?
Cell membranes start to lyse resulting in inflamation
- Preventative measure: Inhibitor for enzyme
