Medical Biochemistry w/ Borgon Exam 3 Review

Lipids are organic molecules that have low ________________ in water (hydrophobic).

Solubility

Lipids can be grouped into ____ classes.

8

Note: The eight classes are fatty acids, saccharolipids, prenols, glycerolipids, sterols, glycerophospholipids, polyketides, and sphingolipids.

What are some of the chemical functions of lipids?

Membrane structure, efficient energy storage, cofactors, signaling, antioxidants

What are some of the physical functions of lipids?

Insulation, absorbs heat, absorbs shock, water repellent, protection from water loss, pigments (tomatoes, carrots, pumpkins, some birds), and buoyancy in marine animals

Lipids are classified on their _________________ and function.

Stucture

What are some examples of lipids that do not contain fatty acids?

Cholesterol, terpenes

Lipids that contain fatty acids (complex lipids) are further separated into _____________ lipids and ________________ lipids.

Storage; membrane

Fatty acids are storage lipids. They are ________________ __________ with hydrocarbon chains containing ___-_____ carbons.

Carboxylic acids; 4-36

True or false: Almost all natural fatty acids have an even number of carbons, most unbranched.

True

Match the following types of fatty acids to the correct characteristics:

A. Saturated
B. Monounsaturated
C. Polyunsaturated

1. One double bond between carbons in the alkyl chain
2. No double bonds between carbons in the chain
3. More than one double bond in the alkyl chain

A- 2
B- 1
C- 3

What type of fatty acid is EPA? What type of fatty acid is oleic acid?

Polyunsaturated; monounsaturated

Note: Eicosapentaenoic acid (EPA) is found in fish, while oleic acid is found in olives and avocados.

Solubility _________________ as the chain length increases.

Decreases

Melting point _________________ as the chain length and saturation (__________ bonds) increases.

Increases; single

Saturated chains tend to adopt ________________ conformations.

Extended

What conformation are unsaturated chains with double bonds typically in? Why?

Cis; this kinks the chain and reduces packing

True or false: Sugars carry more energy per carbon than fatty acids.

False;

Fatty acids carry more energy per carbon than sugars because they are more reduced, and they carry less water per gram (saving energy).

Glucose and glycogen are for __________-________ energy needs, and have _________ delivery.

Short-term; quick

Fats are for __________-________ energy needs, good storage, and have _________ delivery.

Long-term; slow

True or false: White fat (adipocytes) are a single lipid droplet.

True

Note: Brown fat is many lipid droplets, with more mitochondria and capillaries, as some are derived from muscle stem cells.

True or false: Children have more brown fat than adults.

True

Note: This is why children don't get cold as easily.

Another note: Brown fat is inverse with weight, is found in hibernating animals, and responsible for nonshivering thermogenesis.

Which is considered the healthier fatty acid: Omega-3 or Omega-6?

Omega-3

Determine whether the following describes omega-3 or omega-6 fatty acids:

A. γ-linolenic acid (GLA)
B. Used to make EPA and DHA
C. Associated with increased risk of cardiovascular disease
D. α-linolenic acid (ALA)
E. Obtsined from a diet of seeds, nuts, and leafy vegetables

A. Omega-6
B. Omega-3
C. Omega-6
D. Omega-3
E. Omega-3

Note: The ratio of omega-6 to omega-3 is recommended to be 1:1 to 4:1. The Mediterranean diet is richer in omega-3s. Lower ratios reduce inflammation in arthritis and asthma, and possibly cancer cell division.

A trans double bond allows a given fatty acid to adopt an extended conformation, which can _______ more regularly and have _________________ melting points than cis form.

Pack; higher

Artificial trans fatty acids are formed by the partial __________________ of unsaturated fatty acids (cis -> trans).

Hydrogenation

Why are artificial trans fatty acids used?

To increase the shelf life or stability at the high temperature of oils used in cooking, deep frying, margarine.

Trans fats may ____________ unsaturated fat metabolism, ________ LDLs, cause atherosclerosis and cardiovascular disease.

Reduce; raise

As the product gets more ____________, trans fat increases.

Solid

Note: Remember that oil is a liquid, but adding hydrogen makes it more solid to stick margarine or shortening.

Triacylglycerols (triglycerides) are _______________ fatty acids that make up the majority of biological systems as body fat. They are _______ soluble in water than fatty acids due to the lack of a charged _______________ group.

Nonpolar; less; carboxylate

Where are triacylglycerols made?

Liver and adipose tissue

For triacylglycerols,

The glycerol comes from _____________________ __________________, which can be made from pyruvate or amino acids via ________________________ if glycolysis is inhibited.

Dihydroxyacetone phosphate (DHAP); glyceroneogenesis

For triacylglycerols,

The lipids are from acyl __________________.

Transferases

How many calories are in a gram of fat?

9

Note: A 150 lb human has 33 lbs of fat (could last 12 weeks), but only 12 hours of glycogen.

How many calories are a gram of sugar or protein?

4

Triacylglycerol formation is activated by _______________.

Insulin

True or false: Glucagon and epinephrine activate triacylglycerol breakdown in liver (not adipocytes).

False;

Glucagon and epinephrine activate triacylglycerol breakdown in the adipocytes (not liver).

Triacylglycerol is broken down and sent into the blood when needed. 75% are converted back to TAGs, even during starvation (can be affected by drugs like thiazolidinedione for diabetes, which promote insulin sensitivity). This ___________ ________ may provide an energy reserve in the blood for the fight or flight response or generate heat.

Futile cycle

Waxes are esters of long-chain saturated and unsaturated fatty acids with long-chain _______________. They are _____________ with __________ melting points.

Alcohols; insoluble; high

What is the role of waxes?

Storage of fuel (plankton)
Protection for hair and skin (sebum, earwax)
Waterproofing in birds
Protection from evaporation in plants
Polishes, lotions, shampoos

Note: Human skin oil (sebum) is 41% triglycerides, 26% wax, 12% squalene, 16% free fatty acids

Another note: Earwax (cerumen) is 60% keratin, the rest is free fatty acids, alcohols, squalene, and cholesterol

Structural lipids are typically found in the _________________, and are ____________-based phospholipids or sphingolipids.

Membrane; glycerol

True or false: Structural lipids contain nonpolar head groups and polar tails.

False;

Structural lipids contain polar head groups and nonpolar tails.

How can structural lipids be diversified?

Modifying the head groups, changing the fatty acids, or modifying the backbone.

True or false: The properties of head groups determine the surface properties of membranes.

True

Glycerophospholipids (phosphoglycerides) are the primary constituents of cell ________________. They are made in the _____________ ______, converted, and sent to _________ ___________ to be sent to the _______________ (too nonpolar to diffuse).

Membrane; smooth ER; Golgi vesicles; membrane

True or false: In a glycerophospholipid, two fatty acids form ester linkages with a glycerol.

True

In a glycerophsopholipid, the ______ ________ is charged at a physiological pH, and may be further modified.

Head group

True or false: Plasmalogen and platelet-activating factor are examples of ether lipids.

True

Note: Plasmalogen- high levels in nervous, cardiovascular, and immune tissue
Platelet-activating factor- signaling, stimulates aggregation of blood platelets, inflammation

Sphingolipids are phospholipids with an ___________ linkage, a _______ head group, and _________________ (an amino alcohol).

Amide; polar; sphingosine

True or false: The sugar-containing glycosphingolipids are found largely in the inner face of plasma membranes.

False;

The sugar-containing glycosphingolipids are found largely in the outer face of plasma membranes.

What is the role of sphingolipids?

Signaling, cell recognition, and surrounding myelin sheath

The bloog groups are determined in part by the time of sugars located on the head groups in _______________________.

Glycosphingolipids

The structure of sugar is determined by an expression of specific _________________.

Glycosyltransferases

Match these antigens to their correct transferase:

A. A antigen
B. B antigen
C. O antigen

1. No group transfer
2. Galactose group transfer
3. N-acetylgalactosamine group transfer

A- 3
B- 2
C- 1

The polar lipids of membranes undergo constant metabolic _______________, the rate of their synthesis normally __________________ by the rate of breakdown.

Turnover; counterbalanced

The breakdown of lipids is promoted by hydrolytic enzymes in ______________, each enzyme capable of hydrolyzing a specific bond.

Lysosomes

True or false: Defects in membrane turnover lead to disease.

True

___________________ __________ lipids play vital roles as signaling molecules, at lower concentrations than other lipids.

Biologically active

What are some examples of biologically active lipids?

Cholesterols, hormones, lipid-soluble vitamins (A, D, E, and K), and redox cofactors

True or false: Plants use isoprene to make thousands of volatiles.

True

Vitamin ____ (from plants) and ___ (animal sources) regulates calcium uptake.

D2; D3

Which vitamin from diet is important in vision?

A

Sterols are ________ fused rings, nearly __________, with a __________ head (hydroxyl) and various ________________ sidechains.

Four; planar; polar; nonpolar

Cholesterol and related sterols are present in the membrane of most eukaryotic cells, and ______________ the plasma membrane to reduce membrane ______________.

Thicken; fluidity

Mammals obtain cholesterol from _____ or synthesize it in the ______, and it is transported to other tissues.

Food; liver

Steroids are ____________ derivatives of sterols, and have the sterol nucleus but lack the _________ sidechain found in cholesterol, so are __________ polar than cholesterol.

Oxidized; alkyl; more

Steroid hormones are synthesized from cholesterol in the ______________ and ____________ ___________, and are carried through the bloodstream on ______________ ______________.

Gonads; adrenal glands; carrier proteins

True or false: Many of the steroid hormones are male and female sex hormones.

True

Eicosanoids are signaling lipids in the ________________ acid pathway.

Arachidonic

Match the following:

A. Prostaglandins
B. Thromboxanes
C. Leukotrienes

1. Inflammation and fever
2. Formation of blood clots
3. Smooth muscle contraction in lungs

A- 1
B- 2
C- 3

The various lipids used for energy storage, membrane structure, coenzymes, signaling molecules, etc. must be synthesized or derived from ______________.

Precursors

Anabolism of fatty acids occurs in the ________________, catabolism in the _____________.

Cytosol; mitochondria

Fatty acid biosynthesis occurs in the cytosol of _________________, _________________, and mammary glands.

Adipocytes; hepatocytes

Fatty acids are built in several passes, processing _____ acetate unit at a time.

One

________________ (from glycolysis) + bicarbonate is converted to _________________ to begin the process (high-energy thioester).

Acetyl-CoA; Malonyl-CoA

Fatty acid synthesis is catalyzed by _________________ _____________________.

Acetyl-CoA carboxylase

Fatty acid synthase catalyzes a repeating four-step sequence that elongates the fatty acyl chain by ____ carbons.

2

For fatty acid synthase,

_____________ is used as the electron donor, and two enzyme-bound -SH as ________________ groups.

NADPH; activating

FAS I in vertebrates and fungi is single polypeptide chain, produces _______________.

Palmitate (16C)

True or false: FAS II in plants and bacteria is made of separate, diffusible enzymes, which makes many products.

True

Fatty acid synthase's acyl carrier protein (ACP) domain uses coenzyme A as a 2 nm _______________ ___________.

Biological tether

CoA delivers _____________ (in the first step) or ______________(in all the next steps) to the fatty acid synthase, and shuttles intermediates from one domain to the next.

Acetate; malonate

Humans obtain CoA via Vitamin ____, an obligate cofactor in 4% of all enzymes.

B5

Coenzyme A attaches to acyl carrier protein (ACP) via __________ (phospodiester bond). CoA is bound to the growing fatty acid.

Ser-41

The 2C acetate unit from ________________ is added to the growing chain and ________________. The growing chain is initially attached to the enzyme via a __________________ linkage.

Malonyl-CoA; reduced; thioester

Four-step enzyme-catalyzed reaction: Condensation with an acetate, ________________ to a hydroxyl, _____________ to an alkene, reduction to an alkene, repeat.

Reduction; dehydration

What is used to cleave the growing chain to generate palmitate?

Thioesterase

True or false: In fatty acid synthesis, each cycle adds one carbon to the growing fatty acid.

False;

Each cycle adds two carbons to the growing fatty acid.

Fatty acid biosynthesis involves _____________ cycles of condensation, reduction, dehydration and reduction using NADPH.

Seven

What is the equation for fatty acid biosynthesis?

7 acetyl-CoA + 7 CO2 + 7 ATP -> 7 malonyl-CoA + 7 ADP + 7 Pi

Acetyl-CoA + 7 malonyl-CoA + 14 NADPH + 14H+ -> Palmitate + 7 CO2 + 8 CoA + 14 NADP+ + 6H2O

Fatty acid synthesis occurs when energy is _________, and β-oxidation when energy is ________.

High; low

Wha is acetyl-CoA carboxylase (ACC) activated by?

Citrate (precursor for acetyl-CoA)
High levels of ATP
Insuln, which leads to dephosphorylation

What is ACC inhibited by?

Palmitoyl-CoA
Glucagon and epinephrine, which lead to phosphorylation and inactive filaments

True or false: Palmitate can be lengthened and desaturated for use in many other fats.

True

Where does elongation of palmitate occur?

Endoplasmic reticulum and mitochondria

As in palmitate synthesis, each step adds units of 2C, with ____________ (18:0) being most common. Chains can then be further ________________.

Stearate; desaturated

Note: Palmitate (16:0) -> palmitoleate (16:1, Δ9)
Stearate (18:0) -> Oleate (18:1, Δ9)

Another note: Δ indicates where the double bond is.

What is the enzyme that converts stearate to oleate?

ACP desaturase

Humans cannot desaturate beyond _______.

Δ9

True or false: Plants can produce linoleate 18:2 (Δ9, 12) and α-linoleate 18:3 (Δ9, 12, 15), which are essential to humans.

True

Why is fatty acid desaturation important?

It helps control membrane fluidity and are precursors to eicosanoids.

True or false: Oxidases incorporate oxygen into the product.

False;

Oxidases do not incorporate oxygen into the product (oxygen atoms end up in H2O2), such as desaturases. Oxygenases incorporate oxygen into the product.

Stearoyl-ACP desaturase produces _____________, and is upregulated by saturated fats and linked to _______________.

Oleate; diabetes