Topic in Biochemistry

1. Lipids and Related
Systems
GROUP 2

2. What are lipids?
● A heterogeneous class of naturally occurring organic compounds classified
together on the basis of common solubility properties
● An organic compound found in living organisms that is insoluble (or only
sparingly soluble) in water but soluble in non-polar organic solvents
● Amphipathic in nature
● Fatty compounds that perform a variety of functions in your body.
○ Storing Energy
○ Regulating and Signaling
○ Insulating and Protecting
○ Aiding Digestion and Increasing Bioavailability

3. Structure of Lipids

4. Classification based on Biochemical
Function
Lipids are divided into five categories based on their biochemical function:
● Energy-storage lipids (triacylglycerols)
● Membrane lipids (phospholipids, sphingoglycolipids, and cholesterol)
● Emulsification lipids (bile acids)
● Messenger lipids (steroid hormones and eicosanoids)
● Protective-coating lipids (biological waxes)

5. Classification based on Saponification
Saponification reaction - Hydrolysis reaction that occurs in a basic solution
Based on saponification reactions, lipids are
divided into two categories:
● Saponifiable lipids (triacylglycerols, phospholipids, sphingoglycolipids,
cholesterol, and biological waxes)
● Nonsaponifiable lipids (bile acids, steroid hormones, and eicosanoids)

6. Biosynthesis: What is Biosynthesis?
Biosynthesis is the process by which living things use chemical reactions to
create products useful for cellular metabolism. Biosynthesis reactions are
also known as anabolic reactions because the final products are large,
complex structures called macromolecules.

7. Biosynthesis: Importance
Biosynthesis in living organisms is a process in which substrates are
converted to more complex products. The products which are produced as a
result of biosynthesis are necessary for cellular and metabolic processes
deemed essential for survival. Biosynthesis is often referred to as the
anabolism branch of metabolism that results in complex proteins such as
vitamins.

8. Biosynthesis: Lipids

9. Lipid Transport, Storage, and
Utilization
Lipoproteins are transport vehicles for moving water-insoluble lipids around
the body. Different types of lipoproteins do different jobs. However, all are
made up of the same four basic components: cholesterol, triglycerides,
phospholipids, and proteins.
The interior of a lipoprotein—called the lipid core—carries the triglycerides
and cholesterol esters, both of which are insoluble in water. Cholesterol
esters are cholesterol molecules with fatty acids attached.
The exterior of lipoproteins—called the surface coat—is made up of
components that are at least partially soluble in water: proteins (called
apolipoproteins), phospholipids, and unesterified cholesterol.

10. Lipid Transport, Storage, and
Utilization
The phospholipids are oriented so that their water-soluble heads are pointed
to the exterior, and their fat-soluble tails are pointed toward the interior of the
lipoprotein.
Apolipoproteins are similarly amphipathic (soluble in both fat and water),
a property that makes them convenient for aiding in the transport of lipids in
the blood.

11. Lipid Transport, Storage, and
Utilization
While all lipoproteins have the same basic structure and contain the same
four components, different types of lipoproteins vary in the relative amounts
of the four components, their overall size, and their functions. These are
summarized in the graph and table below, and the following sections give
more details on the role of each type of lipoprotein.

12. Lipid Transport, Storage, and
Utilization

13. Lipid Transport, Storage, and
Utilization
Except for chylomicrons, the names of the lipoproteins refer to their
density. Of the four components of lipoproteins, protein is the densest, and
triglyceride is the least dense. (This is why one pound of muscle is much
more compact than one pound of adipose or fat tissue.) High-density
lipoproteins are the densest lipoproteins because they contain more protein
and less triglyceride. Chylomicrons are the least dense because they contain
so much triglyceride and relatively little protein.

14. Chylomicrons Deliver Lipids to Cells for
Utilization and Storage
Chylomicrons are formed in the cells of the small intestine, absorbed into the
lymph vessels, and then eventually delivered into the bloodstream. The job of
chylomicrons is to deliver triglycerides (originating from digested food) to the
cells of the body, where they can be used as an energy source or stored in adipose
tissue for future use.
How do the triglycerides get from the chylomicrons into cells? An enzyme
called lipoprotein lipase sits on the surface of cells that line the blood vessels. It
breaks down triglycerides into fatty acids and glycerol, which can then enter
nearby cells. If those cells need energy right away, they’ll oxidize the fatty acids to
generate ATP. If they don’t need energy right away, they’ll reassemble the fatty
acids and glycerol into triglycerides and store them for later use.

15. Chylomicrons Deliver Lipids to Cells for
Utilization and Storage
As triglycerides are removed
from the chylomicrons, they
become smaller. These
chylomicron remnants travel to the
liver, where they’re disassembled.

16. Lipid Transport from the Liver
The contents of chylomicron remnants, as well as other lipids in the liver, are
incorporated into another type of lipoprotein called very low-density lipoprotein
(VLDL). Similar to chylomicrons, the main job of VLDL is delivering triglycerides to
the body’s cells, and lipoprotein lipase again helps to break down the triglycerides
so that they can enter cells.
As triglycerides are removed from VLDL, they get smaller and more dense,
because they now contain relatively more protein compared to triglycerides. They
become intermediate-density lipoproteins (IDL) and eventually low-density
lipoproteins (LDL). The main job of LDL is to deliver cholesterol to the body’s cells.
Cholesterol has many roles around the body, so this is an important job. However,
too much LDL can increase a person’s risk of cardiovascular disease.

17. Lipid Transport from the Liver
High-density
lipoproteins (HDL) are
made in the liver and
gastrointestinal tract.
They’re mostly made up of
protein, so they’re very
dense. Their job is to pick
up cholesterol from the
body’s cells and return it to
the liver for disposal.

18. Fluid mosaic model
● The fluid mosaic model explains various observations regarding the structure of
functional cell membranes. According to this biological model, there is a lipid bilayer
(two molecules thick layer consisting primarily of amphipathic phospholipids) in which
protein molecules are embedded.
● The biological model, which was devised by Seymour Jonathan Singer and Garth L.
Nicolson in 1972, describes the cell membrane as a two-dimensional liquid that restricts
the lateral diffusion of membrane components.

19. ● The current model describes important features relevant to many cellular processes,
including: cell-cell signaling, apoptosis, cell division, membrane budding, and cell fusion.
● The fluid mosaic model is the most acceptable model of the plasma membrane. Its main
function is to separate the contents of the cell from the exterior.

21. PHYSIOLOGIC SIGNIFICANCE
OF LIPIDS
● Major source of energy for the body
● Important dietary constituent
● Fat is stored in adipose tissue
● Serve as thermal insulator
● Act as electrical insulator
● Combination of lipid and protein (LP) serves as the means of
transporting lipid in blood.

22. PHYSIOLOGIC SIGNIFICANCE
OF LIPIDS
● Provide hydrophobic barrier that permits partitioning of the aqueous
contents of cells and subcutaneous structures.
● Some fat soluble vitamins have regulatory or coenzyme function
● Prostaglandins and steroid hormones play a major role in the control
of the body’s homeostasis.
● Have essential role in nutrition and health
● Imbalance of lipid metabolism may lead to some major clinical
problems:
○ Atherosclerosis
○ Obesity
○ Diabetes mellitus

23. CLINICAL IMPLICATIONS
Following diseases are associated with abnormal chemistry
or metabolism of lipids
● Obesity
● Atherosclerosis
● Diabetes mellitus
● Hyperlipoproteinemia
● Fatty liver
● Lipid storage diseases