4. Lipids (fats & oils)
- Lipids are biological molecules that are insoluble in water, but
are soluble in non-polar solvents, meaning that they are non-
polar molecules.
- It comprises a group of naturally occurring molecules that
include fats, waxes, sterols, fat-soluble vitamins, such as
vitamins A, D, E, and K, monoglycerides, diglycerides,
triglycerides, phospholipids, and others.
- Some lipids such as steroid hormones serve as chemical
messengers between cells, tissues, and organs, and others
communicate signals between biochemical systems within a
single cell.
5. Lipids (fats & oils)
- Lipids are integral components of cell membrane structure and,
as such, are associated with transportation across cellular
membranes.
- Lipids fall into two categories. One is based on glycerol, and the
other is steroids. Most dietary and storage fats are triglycerides
6. Lipids (fats & oils)
- Lipids are relatively small water-insoluble molecules with
molecular weights of up to 750-1500.
- Because they are defined by their water-insolubility, they are
chemically more diverse than the other classes of biomolecules,
with about half a dozen major types.
- Lipids are used for energy production and storage, hormones,
structural elements of cell membranes, and vitamins.
- Lipids do not polymerize to form macromolecules, but they can
aggregate non-covalently to form very large structures.
7. Lipids (fats & oils)
- Lipids are important constituent of the diet because they are a
source of high energy value.
- Lipids are also important because of the fat-soluble vitamins,
and essential fatty acids found in the fat of the natural food
stuffs.
- Body fat serves as a very good source of energy, it is stored in
adipose tissues. They also act as insulating material in the
subcutaneous tissues and are also seen around certain organs.
- Lipids combined with proteins are important constituents of the
cell membranes and mitochondria of the cell. Lipids are not
generally macromolecules.
8. Lipids (fats & oils)
- Lipids are naturally occurring organic compounds, commonly
known as oils and fats.
- Lipids occur through out the living world in microorganisms,
higher plants and animals and also in all cell types.
- Lipids contribute to cell structure, provide stored fuel and also
take part in many biological processes.
- Lipids are relatively insoluble in water.
- They are soluble in non-polar solvents, like ether, chloroform,
methanol.
- Lipids have high energy content and are metabolized to release
calories
9. Lipids (fats & oils)
- Lipids also act as electrical insulators, they insulate nerve axons.
- Fats contain saturated fatty acids, they are solid at room
temperatures. Example, animal fats.
- Plant fats are unsaturated and are liquid at room temperatures.
- Pure fats are colorless, they have extremely bland taste.
- The fats are sparingly soluble in water and hence are described
are hydrophobic substances.
- They are freely soluble in organic solvents like ether, acetone
and benzene.
10. Lipids (fats & oils)
- The melting point of fats depends on the length of the chain of
the constituent fatty acid and the degree of unsaturation
- Geometric isomerism, the presence of double bond in the
unsaturated fatty acid of the lipid molecule produces geometric
or cis-trans isomerism.
- Fats have insulating capacity, they are bad conductors of heat.
- Emulsification is the process by which a lipid mass is converted
to a number of small lipid droplets. The process of emulsification
happens before the fats can be absorbed by the intestinal walls.
- The fats are hydrolyzed by the enzyme lipases to yield fatty acids
and glycerol.
11. Lipids (fats & oils)
- The hydrolysis of fats by alkali is called saponification. This
reaction results in the formation of glycerol and salts of fatty
acids called soaps.
- Hydrolytic rancidity is caused by the growth of microorganisms
which secrete enzymes like lipases. These split fats into glycerol
and free fatty acids
12.
13. Lipids
- Predominantly Carbon and Hydrogen with some Oxygen
- Non-polar so not very water soluble
- Fats= lipids solid at room temp, most derived from animals are
fats
- Oils= liquid at room temp, most derived from plants are oils
- 3 types of lipid-related molecules Phospholipids, steroids,
eicosanoids
14.
15. Lipids
- Lipids are essential components of all living organisms
- Lipids are water insoluble organic compounds
- They are hydrophobic (nonpolar) or amphipathic (containing
both nonpolar and polar regions)
- 1. Free fatty acids
- 2. Triacylglycerol's
- 3. Phospholipids
- 4. Glycolipids
- 5. Steroids
16. Lipids
- Glycerol = 3 carbon molecule
- Fatty acid = long molecule- long chains of C atoms bound to H
with a carboxyl group at one end (-COOH)
- Saturated = no double bonds between C atoms in chain
- Monounsaturated= 1 double bond in chain
- Polyunsaturated= 2 or more double bonds in the molecule
- More double bonds means less hydrogen
- Shape is more ‘kinked’ with double bonds
17.
18. Lipids
- Glycerol links to 1, 2 or 3 Fatty Acids (FA) to form
mono, di or tri- glycerides
- Triglycerides= triacylglycerol's- most abundant lipid in
body- over 90% =1 glycerol linked to 3 FA
19.
20. Saturated fatty acids
- The saturated fatty acids are derived from both animal fats and
plant oils. Rich sources of dietary saturated fatty acids include
butter fat, meat fat, and tropical oils (palm oil, coconut oil, and
palm kernel oil).
- Saturated fatty acids are straight-chain organic acids with an
even number of carbon atoms. All saturated fatty acids that have
from eight to 16 carbon atoms raise the serum LDL cholesterol
concentration when they are consumed in the diet.
- In the USA and much of Europe, saturated fatty acids make up
12–15% of total nutrient energy intake.
21. Saturated fatty acids
- The predominant saturated fatty acid in most diets is palmitic
acid (C16:0); it is cholesterol-raising when compared with cis-
monounsaturated fatty acids, specifically oleic acid (C18:cis1 n-
9), which is considered to be ‘neutral’ with respect to serum
cholesterol concentrations.
- Another saturated fatty acid, myristic acid (C14:0), apparently
raises LDL cholesterol concentrations somewhat more than does
palmitic acid, whereas other saturates – lauric (C12:0), caproic
(C10:0), and caprylic (C8:0) acids – have a somewhat lesser
cholesterol-raising effect.
22. Saturated fatty acids
- Saturated fat from red and processed meat increases both LDL
(associated with cardiovascular harm) and HDL (associated with
cardiovascular benefits) cholesterol .
- Dietary trans fatty acids also increase LDL cholesterol, but
without increasing HDL cholesterol ; it likely even reduces HDL
23.
24.
25. Saturated fatty acids
- Dietary substitution analyses show that substituting mono- and
poly-unsatured fats for trans and saturated fats reduces LDL
cholesterol without reducing HDL or increasing triglycerides.
- LDL/HDL ratios strongly predict negative cardiovascular
consequences, such as leading to atheromatous plaques, which
reduce blood flow to the heart by narrowing coronary arteries.
- Reduced blood flow from consequences of increased LDL/HDL
ratio can ultimately lead to myocardial infarction
26. Unsaturated Fatty Acids
- Unsaturated fatty acids contain one or more double bonds. A
common method for designating fatty acids gives the carbon
chain length, number of double bonds, and double-bond
positions (in parentheses). Thus, palmitoleic acid is designated
C16:1 and linoleic acid is C18:2
- Unsaturated fatty acids are a component of the phospholipids in
cell membranes and help maintain membrane fluidity.
Phospholipids contain a variety of unsaturated fatty acids, but
not all of these can be synthesized in the body.
27. Unsaturated Fatty Acids
- Unsaturated fatty acids generally predominate over the saturated
ones, particularly in higher plants and in animals occupying
cold environments.
- Adding a double bond to a linear, SFA promotes twisting of the
molecule. Thus, UFAs occupy more space and therefore are less
tightly packed in biologic membranes.
- Their loose structure imparts a lower melting point to
membranes (compared with more tightly packed, linear SFAs).
28. Unsaturated Fatty Acids
- The cis unsaturated fatty acids provide fluidity of triacylglycerol
reserves and phospholipid membranes and many serve as
precursors of eicosanoids (prostaglandins, prostacyclins,
thromboxanes, and leukotrienes).
29. Triacylglycerol
- Triacylglycerol's are synthesized from three fatty acids joined
together by one glycerol molecule. Glycerol by itself is a small
carbohydrate molecule containing three carbons
- Fatty acids are important metabolic fuels (2-3 times the energy
of proteins or carbohydrates)
- Fatty acids are stored as neutral lipids called triacylglycerol's
(TGs)
- Triacylglycerol are composed of 3 fatty acyl residues esterified to
a glycerol (3- carbon sugar alcohol)
- Triacylglycerol are very hydrophobic, and are stored in cells in
an anhydrous form (e.g. in fat droplets)
30. Triacylglycerol
- Triacylglycerol are catabolized by lipases.
- Digestion requires bile salts (solubilize triacylglycerol ).
- Transport of triacylglycerol is accomplished through
lipoproteins.
31.
32. Composed of four interconnected carbon rings with a few polar
hydroxyl groups attached. Cholesterol is source in human body.
33. Phospholipids
- Phospholipids, like triglycerides, have a glycerol backbone; in
phospholipids, this is esterified with two fatty acids and the third
hydroxyl group is linked via a phosphodiester bond to an amino
alcohol such as choline, serine or ethanolamine.
- Phospholipids are therefore amphipathic molecules, with both
hydrophilic (phosphate group) and hydrophobic (fatty acid)
domains. This property is responsible for the capacity of
phospholipids to solubilize other lipids and accounts for their
location on the surfaces of lipoprotein molecules and in the cell
membrane lipid bilayer.
35. Phospholipids
- Phospholipids provide barriers in cellular membranes to protect
the cell, and they make barriers for the organelles within those
cells.
- Phospholipids work to provide pathways for various substances
across membranes. Membrane proteins stud the phospholipid
bilayer; these respond to cell signals or act as enzymes or
transporting mechanisms for the cell membrane.
- The phospholipid bilayer readily allows essential molecules such
as water, oxygen and carbon dioxide to cross the membrane, but
very large molecules cannot enter the cell in this way or may not
be able to at all. With this combination of phospholipids and
proteins, the cell is said to be selectively permeable, allowing
only certain substances in freely and others via more complex
interactions
36. Phospholipids
- Phospholipids provide structure to the cell’s membranes, which
in turn keep organelles organized and divided to work more
efficiently, but this structure also aids in the membranes'
flexibility and fluidity.
- Some phospholipids will induce negative curvature of a
membrane, while others induce a positive curvature, depending
on their makeup.
- Proteins also contribute to the membrane curvature.
- Phospholipids can also translocate across membranes, often by
special proteins such as flippases, floppases and scramblases.
37. Phospholipids
- Phospholipids contribute to the surface charge of membranes as
well. So while phospholipids contribute to stability, their fusion
and their fission, they also aid in transportation of materials and
signals.
- Phospholipids therefore make membranes highly dynamic,
rather than simple bilayer barriers. And while phospholipids
contribute more than originally thought to various processes,
they remain the stabilizers of cellular membranes across species.
38.
39. Lipoproteins
- The lipoproteins are submicroscopic, macromolecular complexes
of lipids (cholesterol, triglycerides, phospholipids) and proteins
(apolipoproteins, enzymes), held by non-covalent forces.
- The basic structure of lipoproteins is a hydrophobic core of
triglycerides and/or cholesteryl esters surrounded by a layer of
amphipathic phospholipids, unesterified cholesterol and
proteins.
- The hydrophilic surface protects the hydrophobic core from the
aqueous environment. Lipoproteins differ in their relative
concentrations of protein to lipid and in their constituent lipids
and protein. The densities of lipoproteins are inversely related to
their size.
40. Lipoproteins
- The lipoproteins can be classified on the basis of their size,
density or protein composition.
The nomenclature of the lipoproteins is based on their density:
- Chylomicrons (< 0.95 g/mL)
- VLDL (0.95–1.006 g/mL)
- Intermediate density lipoproteins (IDL) (1.006–1.019 g/mL)
- Low density lipoproteins (LDL) (1.019–1.063 g/mL)
- High density lipoproteins (HDL) (1.063–1.210 g/Ml
- The classes are not homogeneous; each represents a continuum
of particles of differing size, density and fate and, in the case of
VLDL, also of origin
41. The effects of lipoproteins on β-cell function and survival
42. Steroids
- Steroids and their metabolites often function as signaling
molecules (the most notable examples are steroid hormones),
and steroids and phospholipids are components of cell
membranes.
- Steroids such as cholesterol decrease membrane fluidity. Similar
to lipids, steroids are highly concentrated energy stores
- Steroid hormones: produced in the adrenal cortex, testis, ovary,
and some peripheral tissues (adipose tissue, the brain!)
- All steroid hormones share a typical (but not identical) ring
structure.
43. Types of steroid hormones
- Glucocorticoids; cortisol is the major representative in most
mammals
- Mineralocorticoids; aldosterone being most prominent
- Androgens such as testosterone
- Estrogens, including estradiol and estrone
- Progestogens (also known a progestins) such as progesterone
44. Steroid hormones
- Are not packaged, but synthesized and immediately released
- Are all derived from the same parent compound: Cholesterol
- Enzymes which produce steroid hormones from cholesterol are
located in mitochondria and smooth ER
- Steroids are lipid soluble and thus are freely permeable to
membranes so are not stored in cells
45. Steroid hormones
- Steroid hormones are not water soluble so have to be carried in
the blood complexed to specific binding globulins.
- Corticosteroid binding globulin carries cortisol
- Sex steroid binding globulin carries testosterone and estradiol
- In some cases a steroid is secreted by one cell and is converted to
the active steroid by the target cell: an example is androgen
which secreted by the gonad and converted into estrogen in the
brain
46. Steroid hormone synthesis
- All steroid hormones are derived from cholesterol.
- A series of enzymatic steps in the mitochondria and ER of
steroidogenic tissues convert cholesterol into all of the other
steroid hormones and intermediates.
- The rate-limiting step in this process is the transport of free
cholesterol from the cytoplasm into mitochondria. This step is
carried out by the Steroidogenic Acute Regulatory Protein
(StAR)
47. Steroids
- Steroids and their metabolites often function as signaling
molecules (the most notable examples are steroid hormones),
and steroids and phospholipids are components of cell
membranes.
- Steroids such as cholesterol decrease membrane fluidity. Similar
to lipids, steroids are highly concentrated energy stores
48. Functions of Hormones Derived from Cholesterol Product
- Progesterone prepares uterus lining for implantation of ovum
- Glucocorticoids (cortisol) (produced in adrenal cortex)
(catabolic steroid) promote gluconeogenesis; favor breakdown of
fat and protein (fuel mobilization); anti-inflammatory
- Mineralocorticoids (aldosterone) (produced in adrenal glands)
maintains blood volume and blood pressure by increasing
sodium reabsorption by kidney
49. Functions of Hormones Derived from Cholesterol
- Androgens (strongest = testosterone) (produced in testes
primarily but weak androgens in adrenal cortex) (anabolic
steroid) development of male secondary sex characteristics;
prevents bone resorption
- Estrogen (produced in ovaries primarily but also in adipose cells
of males and females) development of female secondary sex
characteristics
- Prevents bone resorption Vitamin D (not a steroid hormone)
(produced in the skin in response to UV light and processed to
active form in kidney)
- Intestinal calcium absorption; promotes bone formation;
prevents phosphate loss by kidneys
