Biochemistry Chapter 9: Lipid Metabolism Flashcards
Glycerol ( 1,2,3 propanetriol )
arachidonic acid is important as a precursor for the biosynthesis of
eicosanoid signaling molecules
types of eicosanoids
prostaglandins, thromboxanes, and leukotrienes.
What are fatty acids?
long-chain carboxylic acids
What are triglycerides/ triacylglycerols?
formed by 3 FAs esterified to a 3-carbon glycerol backbone. Main role is to provide energy.
What are phospholipids/fatty acid derivatives?
Large category including phospholipids and sphingolipids; play structural/signaling roles.
What is Cholesterol and its derivatives:
Four-ring structure. Cholesterol contributes to fluidity of plasma membrane; steroid hormones are derived from cholesterol
What are Eicosanoids?
Eicosanoids are not hormones in the classical sense (like insulin or cortisol), but they act as local signaling molecules with hormone-like functions.
Derived from arachidonic acid; have 20 carbons and a 5-carbon ring
prostaglandins
Eicosanoid that modulate inflammation
Thromboxanes
Eicosanoids involved in clotting
More double bonds in fatty acids means what for melting/boiling pts?
More unsaturated and lower melting/boiling point = greater contribution to fluidity of membrane.
Beta oxidation
Fatty acid broken down into acetyl-CoA (2-carbon) units in the mitochondria
What are the fate of acteyl-CoA products from beta-oxidation?
are fed into the citric acid cycle or used to produce ketone bodies in the liver. Ketone bodies are formed in the liver and sent to provide energy to other cells, where they are broken back down into acetyl-CoA (think of ketone bodies as an acetyl-CoA delivery service
Carnitine shuttle moves activated FAs
into the mitochondria
Four major steps in beta oxidation
A C=C double bond is formed between C2 and C3, and FAD → FADH₂.
An OH group is added to C3.
C–OH → C=O at C3, coupled with NAD⁺ → NADH.
Molecule is broken up, generating acetyl-CoA and a shorter acyl-CoA.
Ketone body formation upregulated in starvation and untreated diabetes
What is the building block of fatty acid synthesis?
Acetyl-CoA is the ultimate building block, but malonyl-CoA (a three-carbon compound generated by carboxylating acetyl-CoA) is the intermediate that transfers two-carbon units to an extending chain.
Fatty Acid synthesis takes place in the
cytosol
What is the cholesterol synthesis pathway?
Built from mevalonate → repeating isoprene units → squalene → cholesterol; mevalonate is limiting step
What are chlyomicrons?
Least density; first transporters of triacylglycerols to tissue.
Very-low-density lipoprotein (VLDL)
Transport triacylglycerols from liver to tissue.
Low-density lipoprotein (LDL)
Transport cholesterol to tissue; high levels associated with risk of cardiovascular disease
High-density lipoprotein (HDL)
Transport cholesterol from tissue to liver; high levels are cardioprotective
Goal of Fatty Acid Synthesis
To create fatty acids, which are stored as triglycerides for energy reserves or used in membrane formation
To produce phospholipids and cholesterol for cellular structures and signaling molecules
Location of Fatty Acid Synthesis
Cytoplasm:
Fatty acid synthesis primarily occurs in the cytoplasm of cells, particularly in the liver and adipose tissue.
Smooth Endoplasmic Reticulum:
Final steps of triglyceride synthesis, phospholipid synthesis, and cholesterol synthesis occur here
Inputs/Outputs for Fatty Acid Synthesis
Inputs
CO₂ (Carbon Dioxide) – Released during the formation of malonyl-CoA from acetyl-CoA.
CoA (Coenzyme A) – Released when acetyl-CoA and malonyl-CoA are incorporated into the growing fatty acid chain.
NADP⁺ (Nicotinamide Adenine Dinucleotide Phosphate, oxidized form) – Generated from the oxidation of NADPH used in the reduction steps.
H₂O (Water) – Released during the dehydration step of the elongation cycle.
Outputs
Fatty Acids:
1) Synthesized as long-chain fatty acids like palmitic acid (16:0).
2) Triglycerides (Triacylglycerols):
Fatty acids combined with glycerol to form energy-storage molecules.
3) Phospholipids:
Essential for membranes and signaling.
4) Cholesterol:
Used for steroid hormones, bile acids, and membrane fluidity.
Beta Oxidation Goals
To break down fatty acids into acetyl-CoA, which can enter the Krebs cycle for ATP production.
To produce ketone bodies during fasting or starvation for use as an alternative energy source.
Location of Beta Oxidation
Mitochondria:
Beta-oxidation occurs in the mitochondrial matrix.
Liver:
Produces ketone bodies during prolonged fasting.
Adipose Tissue:
Releases free fatty acids into the blood when triglycerides are broken down.
starvation and untreated diabetes mellitus can lead to the overproduction of
ketone bodies
Ketoacidosis
High levels of ketone bodies D-β-hydroxybutyrate and acetoacetate (acidic) in the blood, leading to a drop in blood pH known as diabetic ketoacidosis.
can detect on patient’s breath because acetone accumulates to a noticable level
True or false: Lipids can absorb visible light
False
they lack conjugated double bonds or other chromophores that interact with photons in the visible spectrum (wavelengths ~400–700 nm)
Chylomicrons
lipoprotein particles that transport dietary lipids (mostly triglycerides) from the intestine to other parts of the body via the lymphatic and circulatory systems.
lipoprotein density compares what to what
Lipid to protein. therefore the LEAST dense has the highest ratio of lipids to proteins
Order of density from least to greatest lipoproteins
VLDL < IDL < LDL < HDL
VLDL journey
VLDL starts off with high fat ratio, unloads fat content as it continues and eventually becomes LDL which can exist easier in the blood stream
LDL contains more ________ than triglycerides
cholesterol
Job of LDL
Deliver cholesterol to tissues that need it
HDL job
Pick up stray cholesterol and taking it back to the liver
Fatty acid catabolism consists of what 2 steps
lipolysis (fatty acid molecule mobilized from storage) and beta oxidation
True or false: even number FA chain beta oxidation is easier than odd number
true
Acyl CoA vs acteyl CoA
Acyl-CoA is a broader term referring to any molecule where a fatty acid chain (the “acyl group”) is attached to coenzyme A (CoA), while acetyl-CoA is a specific type of acyl-CoA where the acyl group is a two-carbon acetic acid
Major steps of beta oxidation
1) Oxidation
2) Hydration
3) Oxidation
4) Thiolysis
Inputs and outputs of beta oxidation
Inputs
-
Fatty Acids:
- Released from triglycerides stored in adipose tissue.
- NAD⁺: Electron carrier for oxidation reactions.
- FAD: Electron carrier for dehydrogenation steps.
- ATP: Required to activate fatty acids for transport into mitochondria. (needed to activate the fatty acid, before beta oxidation)
Outputs
-
Acetyl-CoA:
- Fed into the Krebs cycle for ATP production or used to generate ketone bodies.
-
NADH and FADH₂:
- High-energy electron carriers for the electron transport chain.
-
Ketone Bodies (during fasting):
- Acetoacetate, β-hydroxybutyrate, and acetone (used by tissues like the brain and muscles).
enzyme that hydrolyzes stored triglycerides in adipose tissue into free fatty acids and glycerol, regulated by hormones like epinephrine and insulin to control fat mobilization.
hormone sensitive lipase
Fats produce approx how much ATP per carbon?
About 7n ATP, where n = number of carbons
Why are fats high energy?
Because they are highly reduced
Most abundant fatty acid in the body
palmitic acid (C16:0)
Fatty acid synthesis is accomplished by fatty acid synthase, a large enzymatic complex with multiple active sites and a long acyl carrier arm that moves the growing fatty acid between these active sites. This type of synthetic mechanism increases catalytic efficiency how?
increases catalytic efficiency by limiting substrate diffusion.
Fatty acid synthase has which has highly specific substrates. By preventing intermediates from diffusing away and having to diffuse back into the next active site, fatty acid synthase is able to more efficiently conduct the sequential reactions necessary to form a complete fatty acid.
Malonyl-CoA
is a key intermediate in fatty acid synthesis and an inhibitor of β-oxidation, formed from acetyl-CoA by acetyl-CoA carboxylase (ACC). 🚀
Steps of fatty acid synthesis
1) Transacylation
2) Condensation
3) Reduction
4) Dehydration
5) Reduction
