Lipid Nomenclature & Metabolism

Question 1

Describe the structure of a fatty acid

Answer 1

a straight chain of an even number of carbon atoms, with hydrogen atoms along the length of the chain and at one end of the chain and a carboxyl group (―COOH) at the other end. It is that carboxyl group that makes it an acid (carboxylic acid)

fatty acids are long chain carboxylic acids

Main purpose is to provide energy, but can also serve as precursors for the synthesis of other molecules.

Question 2

Describe the general structure of a triglyceride

Answer 2

Triglycerides are triesters consisting of a glycerol bound to three fatty acid molecules.

Main purpose is to provide energy, but can also serve as precursors for the synthesis of other molecules.

Question 3

Fatty acid and triglyceride derivates is a large category of molecules that serve what types of roles?

Answer 3

Structural (i.e phospholipids) and signaling

Question 4

True or False

Cholesterol is a category of lipid that has a 6-ring structure and plays a large role in stabilizing the structure of the plasma membrane, as well as having steroid hormones derived from it

Answer 4

False. Cholesterol is a category of lipid that has a 4-ring structure and plays a large role in stabilizing the structure of the plasma membrane, as well as having steroid hormones derived from it

Question 5

Describe the structure of cholesterol

Answer 5

• 4-ring structure
• hyrdoxyl group attached to aromatic ring
• hydrocarbon side chain attached to cyclopentane

Note: Cholesterol derivatives will have 4-ring structure, but the hydroxyl group may be at a different location and they may or may not have a hydrocarbon side chain at all! This is important for mcat

Question 6

____ is the type of lipid that contributes to membrane fluidity in low temperatures and reduces fluidity in high-temperature condirions

Answer 6

cholesterol

Question 7

Name the functional group

Answer 7

An ester

triglycerides contain three ester linkages: one for each fatty acid chain on the molecule

Question 8

A class of molecules derived from 20-carbon (often with 5-carbon rings) polyunsaturated fatty acids, most frequently arachidonic acid

Answer 8

Eicosanoids

Most important category for MCAT: prostoglandins, which have a diverse array of effects i.e modulation of inflammation.
Thromboxanes are involved in clotting

Question 9

What category of lipid are these molecules?

Answer 9

Eicosanoids!

the 20-carbons and 5-carbon rings are giveaways!

Question 10

Isopropene molecules that are lipids because of their solubility in organic solvents and their biosynthetic origin from acetyl- CoA. They consist of repeating isoprene (C5H8) units

Answer 10

Terpenes

One of the most important terpenes to know is a compound called squalene. Squalene is important because it eventually becomes cholesterol, which is a crucial biomolecule in our bodies!

Question 11

For the MCAT, the two main structural lipids that you should know are:

Answer 11

phospholipids and sphingolipids

sphingolipids are enriched in the Central Nervous System (CNS) and display multiple biological functions. They participate in tissue development, cell recognition and adhesion, and act as receptors for toxins

Question 12

Name the lipid

____ are enriched in the Central Nervous System (CNS) and display multiple biological functions. They participate in tissue development, cell recognition and adhesion, and act as receptors for toxins

Answer 12

sphingolipids

have a sphingosine backbone in addition to the typical polar head group and nonpolar fatty acid tail.

Youtube Video

Question 13

These are the most abundant lipids in cell membranes; composed of glycerol, phosphate, two fatty acids, and an amino alcohol

Answer 13

glycerophospholipids

the glycerol, phosphate, and amino alcohol make the polar head, while the fatty acid hydrocarbon tail make the non-polar tails

phospholipids are ampiphatic – they possess both polar and nonpolar properties

Question 14

Identify this structure and its function

Answer 14

micelles

Micelles are spherical amphiphatic structures that have a hydrophobic core and a hydrophilic shell. They form in the lumen of the small intestine and carry lipids to brush border cells for absorption?

Question 15

Identify the structure

Answer 15

bicell

Bicelles are similar to micelles, in that they are lipids arranged in their lowest energy state. However, they are *more disk-shaped *and contain a planar region

Question 16

Compare and contrast flippases and floppases

Answer 16

The goal of both enzymes are to move phospholipids between layers of the cell membrane. Flippases move a phospholipid from an outer leaflet to an inner leaflet. Floppases move a phospholipid from an inner leaflet to an outer leaflet. Since these are energetically demanding processes, ATP is required for both of these enzymes to function.

Question 17

Describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character

Answer 17

fluid mosaic model

Khan Academy article

Question 18

What role does cholesterol play in the cell membrane?

Answer 18

Cholesterol maintains the cell membrane’s fluidity and stability
↑ temp = ↓ fluidity by limiting phospholipid movement
↓ temp = ↑ fluidity

there is a bidirectional relationship between temperature and fluidi

At high temperatures, cholesterol limits the movement of phospholipids in the bilayer, which prevents the membrane from becoming overly fluid and losing its shape. At low temperatures, the rigid structure of cholesterol serves to disrupt the van der Waals interactions between fatty acid tails. This prevents the membrane from becoming too stiff and prone to breakage.

Question 19

Antigens that characterize blood groups (ABO) are what type of lipid?

Answer 19

sphingolipids

also have different carbohydrate sequences

Question 20

transmembrane proteins tend to have [hydrophobic/hydrophilic] amino acids because….

Answer 20

Transmembrane proteins tend to have hydrophobic amino acids because they need to be in the nonpolar area of the membrane

Transmembrane proteinsoften serve as channels that can facilitate transport or receptors that are involved in signal transduction pathways. G-protein coupled receptors (GPCRs) are just one example of transmembrane proteins you may frequently encounter.

Question 21

What happens to excess water-soluble vitamins in the body? Excess fat-soluble vitamins?

Answer 21

When in excess, water-soluble vitamins will be excreted in the urine, whereas fat-soluble vitamins will be stored in fat tissue

For the MCAT, you should know that vitamins B and C are water-soluble, while vitamins A, D, E, and K are fat-soluble.

Question 22

Unsaturated fatty acids have [cis/trans] bonds

Answer 22

Unsaturated fatty acids have cis bonds, which introduce a kink in their chains

this is especially true for *polyunsaturated *fatty acids

Question 23

Describe how the physical characteristics of cis unsaturated fatty acids affect their chemical characteristics (i.e melting piints, fluidity, electrostatic interactions)

Answer 23

Their cis bonds (causing kinks in their chains) means that they cannot stack on top of one another easily. Thus, they have weaker electrostatic interactions, lower boiling and melting points (they’re liquid at room temp), and make cell membranes more fluid

think of vegetable oils! They’re liquids and healthier for ya

Youtube video

Question 24

True or False

All unsaturated fatty acids have cis bonds

Answer 24

False. Through partial hydrogenation of unsaturated vegetable oils, trans unsaturated fatty acids can be produced

Question 25

When you think of *excess* fat storage in the body, what organ should automatically come to mind?

Answer 25

The liver! ## Footnote In healthy people, about half the fat from a meal is burned for energy, and the rest is shunted to adipose tissue, where it is stored until needed during fasting. **Eating excess calories causes fat to build up in the liver**. When the liver does not process and break down fats as it normally should, too much fat will accumulate. People tend to develop fatty liver if they have certain other conditions, such as obesity, diabetes or high triglycerides.

Question 26

**Chylomicrons** transport dietary triglycerides and cholesterol absorbed by intestinal epithelia to the cells, but some of the triglyceride remnants are sent to the liver. What does the liver produce with these triglycerides?

Answer 26

The liver produces **very-low-density lipoprotein (VLDL)**. After delivering triglycerides to the tissues, VLDL becomes **low-density lipoprotein (LDL)**.

Question 27

A lipoprotein similar to chylomicrons in that it also transports triglycerides to other tissues

Answer 27

**very-low-density lipoprotein (VLDL)** ## Footnote After delivering triglycerides to the tissues, VLDL becomes **low-density lipoprotein (LDL)**

Question 28

Transports cholesterol to the tissues (and blood) that need it after triglycerides are delivered

Answer 28

**low-density lipoprotein (LDL)** ## Footnote you may know this as "bad cholesterol"

Question 29

Transports cholesterol and other lipids away from the blood & tissues, delivering it to the liver for processing and excretion. ## Footnote Cholesterol returened to the liver may be processed into bile

Answer 29

**high-density lipoprotein (HDL)** ## Footnote known as "good" cholesterol

Question 30

In the body, fatty acids are typically stored as what type of cells?

Answer 30

**adipocytes** ## Footnote note: when necessary, fatty acids are mobilized via the action of **hormones**

Question 31

When necessary, fatty acids are mobilized via the action of hormones. What hormones trigger the hydrolysis of triacylglycerols, and what enzyme is used to do this?

Answer 31

**Epinephrine** and **glucagon **trigger the hydrolysis of triacylglycerols via **hormone-sensitivity lipase** ## Footnote Remember the important fact that ephinephrine and glucagon modulate glycerol levels !

Question 32

# Name the protein and answer the italicized question This protein helps move many small molecules through the blood, including bilirubin, calcium, progesterone, and medicines. It plays an important role in keeping the fluid in the blood from leaking into the tissues. *What is its role in relationship to fatty acids?*

Answer 32

**Albumin** also transports fatty acids that enter the bloodstream ## Footnote this occurs after triacylglycerols are hydrolyzed via hormone-sensitivity lipase, releasing the free fatty acids into the bloodstream

Question 33

What hormone that we associate with carbohydrate metabolism and blood glucose levels also affects lipid metabolism by *making free fatty acids available to be converted into energy* if necessary?

Answer 33

Glucagon

Question 34

Fatty acids can be broken down into ____, which can be fed into the TCA cycle

Answer 34

Fatty acids can be broken down into **acetyl-CoA** | this occurs in **beta-oxidation** ## Footnote **Beta-oxidation** is the process of catabolism, or breakdown, of fatty acids. [Youtube](https://youtu.be/__jS-pjzb5k) [Youtube video pt. 2](https://youtu.be/ZufZvbhPpws)

Question 35

Why is beta-oxidation called beta-oxidation?

Answer 35

Because the beta-carbon of each fatty acid is oxidized to a carbonyl group (C=O) | beta-oxidation occurs in the **mitochondria** in eukaryotic cells ## Footnote [Youtube](https://youtu.be/__jS-pjzb5k) [Youtube video pt. 2](https://youtu.be/ZufZvbhPpws)

Question 36

What are acetyl-CoA products used for in the body?

Answer 36

acetyl-CoA is either 1. fed into the **citric acid cycle** or 2. used to produce **ketone bodies** in the liver

Question 37

Ketone bodies are formed in the ____ and their function is to....

Answer 37

Ketone bodies are formed in the **liver** and their function is 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 ## Footnote [ketone body synthesis video](https://youtu.be/AK9Q2ClI8y4)

Question 38

Why are fats the most calorie-dense nutrient? (9 kcal/g)

Answer 38

Because fatty acid hydrocarbon charins are highly reduced, so there are a lot of extra electrons that can be pulled away by electron carriers during the oxidation of this molecule

Question 39

What are the three ketone bodies that are produced during ketone synthesis **(ketogenesis)**?

Answer 39

* **beta-hydroxybutarate** (most abundant) * **acetoacetate** * **acetone** ## Footnote [ketone body synthesis video](https://youtu.be/AK9Q2ClI8y4)

Question 40

beta-hydroxybutarate and acetoacetate are both acidic. When they are in the blood at excessively high levels, they can cause blood pH to drop. What condition does this cause?

Answer 40

**ketoacidosis** ## Footnote get it? These *Ketones* make the blood *acidic*

Question 41

Fatty acid synthesis takes place in the ....

Answer 41

Cytosol

Question 42

Summarize fatty acid synthesis using the building block, intermediate, end product, and the location where it takes place

Answer 42

* Creation of fatty acids from **acetyl-CoA** and **NADPH ** * Most important Intermediate: **malonyl-CoA** * End product: **palmitic acid** (saturated fatty acid) * Enzymes used: ** fatty acid synthases**. * Takes place in **cytoplasm ** | FA synthesis is a series of **condensation, reduction, & dehydration** r ## Footnote [Fatty acid synthesis video](https://youtu.be/WuQS_LpNMzo) Note: Fatty acid synthesis requires NADPH, which is generated by the pentose phosphate pathway

Question 43

Fatty acid synthesis requires NADPH, which is generated by which cycle?

Answer 43

The pentose phosphate pathway ## Footnote this pathway is a key linkage between carbohydrate and the lipid world, be sure to understand how they relate to one another wrt metabolism

Question 44

Summarize cholesterol synthesis including where it takes place, its building block, key intermediates

Answer 44

* Building block: **acetyl-CoA** * Key intermediates: **mevalonate** → **isoprenes** → **squalene** → **cholesterol** | mevalonate is the rate-limiting step