LIPIDS 1 Flashcards
- is an organic compound found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents.
- Unlike other biomolecules, lipids do not have a common structural features that serves as the basis for defining such compounds.
Lipid
Five categories of lipids
- Energy-storage lipids
- Membrane lipids
- Emulsification lipids
- Chemical messenger lipids
- Protective-coating lipids
o Triacylglycerols
Energy-storage lipids
o Phospholipids
o Sphingoglycolipids
o cholesterol
Membrane lipids
o obile acids
Emulsification lipids
o steroid hormones
o eicosanoids
Chemical messenger lipids
o Biological waxes
Protective-coating lipids
- _________ exhibit structural diversity
- Some are esters, some are amides, and some are alcohols (acyclic and cyclic) and some are polycyclic.
Lipids
Types of fatty acids
Saturated and unsaturated fatty acids
Polyunsaturated fatty acids (pufas)
- Carboxylic acids with linear (unbranched) carbon chain - Fatty acids are naturally occurring monocarboxylic acids
- Even number of Carbon atoms:
o Long chain fatty acids: C12 - C26
o Medium chain fatty acids: C6 – C11
o Short-chain fatty acids: C4 – C5
Saturated and unsaturated fatty acids
- Numbering starts from the end of -COOH group
- See structural notation: it indicates number of C atoms
o Lauric acid has 12 C atoms and no double bonds so it is (12:0)
Saturated fatty acids
- A monounsaturated fatty acid is a fatty acid with a carbon chain in which one carbon–carbon double bond is present.
- Different ways of depicting the structure
Unsaturated fatty acids
- A ________________ is a fatty acid with a carbon chain in which two or more carbon–carbon double bonds are present.
- Up to six double bonds are found in biochemically important PUFAs.
- Two types of unsaturated fatty acids:
o Omega (ω)-3 fatty acids:
o Omega(ω)-6 fatty acid:
Polyunsaturated fatty acids (pufas)
An unsaturated fatty acid with its endmost double bond three carbon atoms away from its methyl end.
o Omega (ω)-3 fatty acids:
is an unsaturated fatty acid with its endmost double bond six carbon atoms away from its methyl end.
o Omega(ω)-6 fatty acid
Selected unsaturated fatty acids of biological importance
* Numbering starts from the other end of COOH
* See structural notation: it indicates number of C atoms
o 18:2 - 18 carbons, 2 double bonds
Selected unsaturated fatty acids of biological importance
* Numbering starts from the other end of COOH
* See structural notation: it indicates number of C atoms
o 18:2 - 18 carbons, 2 double bonds
Essential fatty acids
* Must be part of diet
* Nutritionally important Omega-3 and Omega-6 fatty acids
o Linolenic acid – Omega-3
o Linoleic acid – Omega-6
* Linoleic Acid Deficiency:
o Skin redness - becomes irritated
o Infections and dehydration
o Liver abnormalities
o Children need it the most
o Human milk has more than cow’s milk
American diet
* Sufficient in omega 6 fatty acids
* Deficient in omega 3 fatty acids
o Fish: good source for omega 3 fatty acids
* High rate of heart disease may be due to imbalance in omega 3 and 6 fatty acids
o Ideal ratio – Omega 6 : Omega 3 (4-10 g: 1g)
- Short chain fatty acids have some solubility whereas long chain fatty acids are insoluble
- Short chain fatty acids are sparingly soluble because of carboxylic acid polar group
- Physical properties such as melting point depends on the number of C atoms and degree unsaturation
Water solubility
- Length of carbon chain
- Degree of unsaturation (number of double bonds in a molecule)
The melting point
- The number of bends in a fatty acid chain increase as the number of double bonds increase
o Less packing occurs
o Melting point is lower
o Tend to be liquid at room temperature
Space-filling molecules
- With the notable exception of nerve cells, human cells store small amounts of energy providing materials:
o The most widespread energy storage material - carbohydrate glycogen
o Present in small amounts - Storage material is the triacylglycerols:
o Triacylglycerols are concentrated primarily in special cells (adipocytes)
o Nearly filled with the material.
Energy-storage materials
Two types of triacylglycerols
a. Simple Triacylglycerols
b. Mixed Triacylglycerols
o Three identical fatty acids are esterified
o Naturally occurring simple triacylglycerols are rare
Simple Triacylglycerols
- Chemical Properties due to two functional groups: esters and alkenes
o Hydrolysis: Partial hydrolysis of triacylglycerols
o Breaking of 1-2 ester bonds to give rise to mono - or diacylglycerol and fatty
acid(s)
o Carried out by enzymes produced by the pancreas
Partial hydrolysis
o A triester formed from the esterification of glycerol with more than one kind of fatty acid
o In nature mostly mixed triacylglycerols are found and are different even from the same source depending on the feed
corn
peanut
wheat -fed cows have different triacylglycerols
Mixed Triacylglycerols
- Numerous studies now indicate that eating nuts can have a strong protective effect against coronary heart disease:
o Low amounts of saturated fatty acids
o Nuts also contain valuable antioxidant vitamins, minerals, and plant fiber
protein
Fat and fatty acid composition of nuts
- Addition of hydrogen across double (=) bond - increases degree of saturation
- Many food products are produced by partial hydrogenation of oils and fats
- Peanut oil + H2 Peanut Butter
- Vegetable oil + H2 Margerine
Hydrogenation
- Hydrolysis in basic solution: Produce salt of fatty acid and glycerol
Saponification
- Double bonds in triacylglycerols are subject to oxidation with oxygen in air (an
oxidizing agent) –Leads to C=C breakage - Remember that oxidation of alkenes may result into two short chain molecules –
an aldehydes or a carboxylic acid:
Oxidation
- contains one or more fatty acids, a phosphate group, a platform molecule
(glycerol or sphingosine) to which the fatty acid(s) and the phosphate group are
attached, and an alcohol that is attached to the phosphate group.
Phospolipids
- is a lipid that contains two fatty acids and a phosphate group esterified to a
glycerol molecule and an alcohol esterified to the phosphate group. - All attachments (bonds) between groups in a glycerophospholipid are ester
linkages
Glycerophospholipids
- Structures based on the 18-carbon monounsaturated aminodialcohol sphingosine
- contains one fatty acid and one phosphate group attached to a sphingosine
molecule and an alcohol attached to the phosphate group - Saponifiable lipids
Sphingophospholipids
- are called cerebrosides
- contains a single monosaccharide unit – either glucose or galactose
o they occur primarily in brain (7% of dry mass)
Simple sphingoglycolipids
- Contains both a fatty acid and carbohydrate
sphingoglycolipids
- Complex sphingoglycolipids are called Gangliosides
o contain a branched chain of up to seven monosaccharide residues. - Occur in the gray matter of the brain as well as in the myelin sheath.
Gangliosides
- Lipids: Fused Rings
- Cholesterol: C27 steroid molecule
- A steroid is a lipid whose structure is based on a fused ring system of three 6
carbon rings and one 5 carbon ring. - Important in human cell membranes, nerve tissue and brain tissue
o Important in chemical synthesis: Hormones, vitamins essential for life
Cholesterol: third major type of membrane lipid
- Liver synthesizes cholesterol: ~ 1g everyday; so it is not necessary to consume in the form of diet
- Cholesterol synthesis decrease if it is ingested but reduction is not sufficient:
Leads to cardiovascular disease
o Animal Food: Lot of cholesterol
o Plant Food: No cholesterol
Cholesterol in food
o Separates aqueous interior of a cell from the aqueous environment surrounding the cell
o Up to 80% of plasma membrane is lipid material
o The membranes are lipid bilayer made up of phospholipids
Cells
o Cholesterol helps regulate membrane fluidity – The fused ring system does nor
allow rotation of fatty acid tails in the vicinity
o Fits between fatty acid chains of the lipid bilayer: Make it rigid
o Cholesterol thus acts a membrane plasticizer
Cholestral
o To maintain cellular processes various molecules transported across the cell membranes.
o Three types of transport:
Passive transport
Facilitated transport
Active transport
* ____________ wherein a substance moves across a cell membrane by diffusion from a region of higher concentration to a region of lower concentration.
o Only a few types of molecules, including
o O2, N2, H2O, urea, and ethanol, can cross membranes by passive transport
Passive transport
o Responsible for moving substance such as nutrients and electrolytes across
the membrane
o Receptors for hormones and neurotransmitters
o Act as markers: process by which different cells recognize each other
Proteins
- a substance moves across a cell membrane with the aid of a membrane protein from a region of higher concentration to a region of lower concentration.
o The specific protein carriers or transporters are involved in the process
Facilitated transport
- a substance moves across a cell membrane, with the aid of membrane proteins, against a concentration gradient with the expenditure of cellular energy.
o Proteins involved in active transport are called “pumps.” The needed energy is
supplied by molecules such as ATP.
Active transport
- An __________ is a substance that can disperse and stabilize water-insoluble substances as colloidal particles in an aqueous solution.
emulsifier
- ___________ are tri- or dihydroxy cholesterol derivatives
- The carbon 17 side chain of cholesterol has been oxidized to a carboxylic acid
- The oxidized acid side chain is bonded to an amino acid (either glycine or taurine)
through an amide linkage - Bile is a fluid containing emulsifying agents (Bile acids) secreted by the liver,
stored in the gallbladder, and released into the small intestine during digestion
Bile acids
- A ___________is a biochemical substance produced by a ductless gland that has a
messenger function. - ____________ serve as a means of communication between various tissues.
o Some hormones are lipids.
Hormones
: derivatives of cholesterol
Steroid hormones
: derivatives of arachidonic acid
Eicosanoids
: control reproduction and secondary sex characteristics
Sex hormones
: control numerous biochemical processes in the body
Adrenocorticoid hormones
- Classified into three major groups:
o Estrogens
o Androgens
o Progestins
Sex hormones
the female sex hormones
Estrogens
the male sex hormones
Androgens
the pregnancy hormones
Progestins
- Produced by the adrenal glands - small organs located on top of each kidney
- 28 Different hormones have been isolated from the adrenal cortex
- Two types of adrenocorticoid hormones:
o Mineralocorticoids
o Glucocorticoids
Adrenocorticoid hormones
control glucose metabolism and counteract inflammation
Glucocorticoids
control the balance of Na and K ions in cells
Mineralocorticoids
o Have profound physiological effects at extremely low concentrations.
o Eicosanoids are hormone-like molecules
o Exert their effects in the tissues where they are synthesized.
o Eicosanoids usually have a very short “life.”
- Eicosanoids Arachidonic acid
- C20-fatty-acid derivative containing cyclopentane ring and oxygen-containing functional groups
o Involved in raising body temperature,
o Inhibiting the secretion of gastric juices,
o Increasing the secretion of a protective mucus layer into the stomach,
o Relaxing and contracting smooth muscle, directing water and electrolyte
balance, intensifying pain, and enhancing inflammation responses.
Prostaglandins
o Inflammatory response
o Production of pain and fever
o Regulation of blood pressure
o Induction of blood clotting
o Control of reproductive functions, such as induction of labor
o Regulation of the sleep/wake cycle
- Physiological effects of eicosanoids:
- C20-fatty-acid derivative containing a cyclic ether ring and oxygen-containing functional groups
o Promote platelet aggregation
Thromboxanes
- C20-fatty-acid derivative containing three conjugated double bonds and hydroxy groups
o Promote inflammatory and hypersensitivity (allergy) responses
Leukotrienes
: a monoester of a long-chain fatty acid and a long-chain alcohol.
biological wax
Water-insoluble and water-repellent because of
long nonpolar hydrocarbon chains.
Properties of Biological waxes
Cholesterol derivatives that functions as emulsifying agents that make
dietary lipids soluble in aqueous environment of the digestive tract:
o Approximately one third of cholesterol produced by liver is converted to bile
acids.
o Action similar to soap in washing
Bile Acids
Monounsaturated Fats
Omega 3 and 6
Good Fats
saturated fat
Trans-monounsaturated fats
Bad Fats
Predominantly Saturated
Solids or semisolids at room temperature
Animal source and tasteless
Fats
Predominantly unsaturated
Liquids at room temperature
Plants and fish oil
Oils
