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BIOCHEMISTRY TASKSTREAM 208.5.6-01-05

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Sally Sellers

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Transcript of BIOCHEMISTRY TASKSTREAM 208.5.6-01-05

In order to answer the question: "What is the role of fat and why it is important in our diet?" Let us start at the beginning....
Triglyceride...Ester linkage of carbon to oxygen of glycerol and 3 fatty acids
Triglycerides are HUGE energy storage molecules
Cellular respiration burns glucose and lipids by breaking bonds to utilize the energy stored within them. There are 2 types of fats...
saturated & unsaturated.
GRT1 BIOCHEMISTRY

TASKSTREAM 208.5.6-01-05
Sally Sellers MA Ed, RN

LIPIDS....
& the Vital Role FATS
Play in Our Bodies
Presented by:

Sally Sellers MA Ed, RN
Western Governors University
Master of Science, Nursing-Education
To our presentation exploring lipids,the importance of fat in our diet and how a no-fat diet affects the biochemical processes of the body
Welcome
Dietitians
of
Our Local Community Health Center

Unsaturated Fatty Acid 3D Model
Lipids
include fats, waxes, sterols, fat soluble vitamins A,D,E,& K, monoglycerides,
triglycerides,

phosopholipids and more.
Essentially, at room temperature,FATS are solids and OILS are liquids.
Triglycerides: macromolecules that are energy storage molecules.
Triglycerides are made via dehydration synthesis...which is making something new by removing water. Fatty Acids are stored as triglycerides.
Triglycerides are a Glycerol molecule PLUS 3 Fatty Acids
To make a Triglyceride... Start with a Glycerol molecule
The "Backbone" of a Triglyceride.
Saturated Fatty Acid 3D Model
Dehydration Synthesis connects glycerol & fatty acid chains yielding water
Add 3 Fatty Acids each with their own Carboxyl Functional Side Group
Carboxyl group is highlighted in
RED
Ester Linkage
Each OH of Glycerol combines with the HO of the Carboxyl Group on each of 3 Fatty Acids via dehydration synthesis giving off H2O/water linking the
O/oxygen on the glycerol to the
C/carbon on the carboxyl group of each fatty acid forming the new molecule....TRIGLYCERIDE.
Unsaturated Triglyceride with
double carbon bond
resulting in 2 carbons not fully saturated with hydrogen. Note the "Bend" in the molecule at the double carbon bond.
Saturated Triglyceride with all the carbons on fatty acids chains fully saturated by hydrogen.
Lipids are Hydrophobic
Fats and Oils don't mix with water because they are non-polar meaning the carbon chains are fully bonded while water is charged.
Lipids are ENERGY
Now that we have reviewed lipids let us turn our attention to the generation of that basic unit of biological energy... ATP... from fatty acids.
Let's explore HOW ATP is generated from lipid metabolism...
You recall that Triglycerides are composed of a glycerol molecule and 3 Fatty Acids and STORE energy for future use. Energy is locked in the bonds and awaits cellular respiration to break the bonds releasing energy in the form of ATP.
Fatty Acid Metabolism


Fatty acids are a family of molecules classified within the lipid macronutrient class
Moving into the Mighty Mitochondria
To accomplish this CoA is removed and the fatty acid is attached to a molecule of carnitine. The resulting carnitine complex is transported across the inner membrane of the mitochondria.... the fatty acid is then reattached to the coenzyme A in the mitochondrial matrix.



The process of fatty acid oxidation is called BETA OXIDATION
These reduction reactions all occur between carbons #2 and #3, with carbon #1 linked to the CoA...resulting in acetyl CoA....ready for the Krebs Cycle in order to synthesize ATP....
We can not synthesize these essential fatty acids so they must be ingested for our health. Deficiencies in these fatty acids lead to a host of symptoms and disorders including abnormalities in the liver and the kidneys, reduced growth rates, decreased immune function, depression, and dryness of the skin.
Lipids are stored in the human body....our "pantry" of energy
Lipids such as triglycerides are stored in your body in specialized fat cells called adipocytes, which make up specialized fatty tissue called adipose tissue.
Krebs Cycle or Citric Acid Cycle
Once the glycerol and fatty acids are broken down into acetyl CoA they are ready to enter the Krebs Cycle in the mitochrondria. The Krebs Cycle is the primary catabolic cyclical pathway in our bodies where oxidation to carbon dioxide occurs for the breakdown of sugars, amino acids and fatty acids which are the cell's major building blocks.
Although adipose tissue has essential functions in your body, excessive lipid storage can compromise cell function.
ATP
Adenosine triphosphate... the energy currency of the cell
Fatty acid metabolism results in energy production in the form of ATP synthesis

When compared to the other macronutrients, carbohydrates and protein,
fatty acids yield the most ATP energy per gram.
Let's take a quick look at ESSENTIAL fats
Essential fats are required by our bodies and we can not synthesize them....

Glycerol component of triglycerides
Interestingly enough....it is only the glycerol component of lipids that can be used to make glucose for cellular energy. Glycerol is easily changed into G3P (glyceraldehyde-3-phosphate) an intermediate in glycolysis.
Before we get to far ahead of ourselves....
We need to know that the breakdown of lipids such as triglycerides takes place inside that specialized fat storage cell known as an ADIPOCYTE...releasing fatty acid and glycerol into the blood stream where it is carried by the serum albumin to cells which need energy. It is inside the cytosol of cells that the glycerol is broken down to make glucose and fatty acid broken down to acetyl CoA, the first steps of ATP production.
So we are on our way to explaining HOW lipids can lead to ATP production!
Now the fatty acid carbon chains are broken down to 2 carbon subunits and then easily converted to acetyl-CoA. To be oxidized, they must be transported through the cytosol of the cell attached to coenzyme A and moved into the mitochrondria.
Saturated Fats occur naturally in many foods...
...mainly from animal sources, including meat and dairy products such as beef, lamb, pork, poultry with skin, beef fat, lard, cream, butter, cheese and other dairy products.
In addition, many baked goods and fried foods can contain high levels of saturated fats. Some plant foods, such as palm oil, palm kernel oil and coconut oil, also contain primarily saturated fats.

Saturated Fats...
Unsaturated Fats...
(ALA) is an essential omega 3 fatty acid and organic compound found in seeds such as flaxseed ,nuts walnuts and vegetable oils.
α-Linolenic acid
(LA) is an unsaturated omega-6 fatty acid found in most vegetable oils and almonds.
Linoleic acid
... include the two heart healthy choices – polyunsaturated and monounsaturated fats. Found primarily in fish, plant oils, seeds and nuts, these “healthy” fats have been shown to lower blood cholesterol levels and lessen your risk of cardiovascular disease.
2 known Essential Fatty Acids are Linoleic acid (LA) and α-Linolenic acid (ALA).
Stored lipids come from dietary sources or from lipids synthesized by the body. Fat storage cells have essentially unlimited storage capacity to store lipids in cell organelles called lipid droplets that can grow to a very large size. Fat is necessary for fuel or energy or ATP, but also it serves as insulation to prevent heat loss and protect vital organs from strain during routine activities. Fat-soluble vitamins A, D, E & K are essential and are stored in our liver and fatty tissues.
Oil & Water Don't Mix
Lipids are determined by their insolubility in water....nonpolar molecules are insoluble in water causing oil to float on top of water and not dissolve in water.
Let's take a look at what a lipid storage molecule is.
The Krebs Cycle
Step #1 acetyl-CoA + oxaloacetate citrate
Traditionally the starting point of Krebs Cycle....but in reality the pathway is cyclic therefore it doesn't have a starting or ending point. The acetyle-CoA resulted from fatty acid oxidation
Step #2 Citrate is isomerized to form isocitrate an unstable molecule
Step #4 a-ketoglutarate to succinyl CoA.. a-ketoglutarate is decarboxylated releasing CO2. NAD+ is reduced forming NADA+ H+

Step #5 Coenzyme A removed from sunccinyl CoA forming succinate and releasing energy
Step #8 Malate to Oxaloacetate which completes the cycle and starts the cycle anew...
Pyruvate enters the mitochondria and is further broken down releasing energy for cellular functions and forming CO2 and H2O
Glycolysis results in 2 pyruvate molecules
...transforming pyruvate to acetyl CoA, allowing aerobic respiration to proceed.
The first step that takes place in the mitochondrion is decarboxylation, the removal of a CO2 molecule...
Side Bar...all roads lead to the Krebs Cycle and electron transport ...
The lipid molecule is broken into glycerol and fatty acids...glycerol enters glycolysis at the intermediate GP3 level and onto pyruvate and acetyl CoA while fatty acids go directly to acetyl-CoA level....both then are readied to enter the mighty mitochrondia's Krebs Cycle on the way to ATP production.
Lipids are the macronutrient that must take 2 roads to ATP...one for the glycerol and one for the fatty acids.
Overview of metabolism to produce energy
Step #3 Isocitrate is decarboxylated releasing CO2 and forming Alpha-ketoglutarate.
Step #6 Succinate to Fumarate...
Step #7 H2O is added to fumarate to form malate
So ATP has been made from the Krebs Cycle....but that's not the whole story
The electron transport chain & oxidative phosphorylation process taking place in the mighty mitochronia yields more ATP!

Big Picture
..Glycolsis through the Krebs Cycle breaking down glucose from the glycerol part of the triglyceride molecule produces ATP and reduced coenzymes...

AND
fatty acids are broken into 2 carbon subunits that each form acetyl-CoA ready to enter the Kreb Cycle to produce ATP.....


Final ENERGY...ATP.. Production occurs in the Electron Transport Chain and Oxidative Phosphorylation
Electrons from the reduced coenzymes coming out of the Krebs Cycle enter the electron transport chain where they are used to create a proton gradient across the inner mitochondial membrane. A protein complex call ATP synthase makes ATP from the movement of protons across the membrane.

Finally....a redux reaction called oxidative phosporylation is responsible for the final ATP production and is driven by oxidation reactions.
ATP END PRODUCTS:

Compared to any other molecule...lipids yield the GREATEST amount of ATP, even if the effort is greater than breaking down a glucose molecule. So lets look at the ATP math:
one stored lipid molecule as triglyceride breaks into a glycerol and 3 fatty acids. Each fatty acid is then broken down into 2 carbon chunks to form an acetyl-CoA that enters the Krebs Cycle and electron transport chain/oxidative phosphorylation redux reactions yielding 12 ATPs per acetyl-CoA molecule. If our triglyceride has eight 2-carbon chunks on each of it's 3 fatty acids that is over 300 ATPs from just the breakdown of the fatty acids! Now throw in the ATPs from the glycerol and you've got one huge energy storage molecule in a lipid!
Here's to FATS! They are truly biology's pride of the pantry!

This concludes PART ONE of our three part series on LIPIDS.
I hope this presentation has been informative and look forward to seeing you in LIPIDS PART TWO as we present the role of fatty acids in the body and the fluid mosaic structure of the cell membrane. Be sure to be on the look out for part three which covers the biochemical affects of no-fat diets on the body.
THANK-YOU!
Part One of a Three Part Presentation on Lipids
http://wgu.thinkwell.com/students/getResources.cfm?levelFourID=5869687&levelThreeID=1820595&levelTwoID=350662&mode=browse
http://wgu.thinkwell.com/students/getResources.cfm?levelFourID=5869687&levelThreeID=1820595&levelTwoID=350662&mode=browse
http://wgu.thinkwell.com/students/getResources.cfm?levelFourID=5869687&levelThreeID=1820595&levelTwoID=350662&mode=browse
http://wgu.thinkwell.com/students/getResources.cfm?levelFourID=5869687&levelThreeID=1820595&levelTwoID=350662&mode=browse
References:
WGU Thinkwell Biology slides found at:
http://wgu.thinkwell.com/students/getResources.cfm?levelFourID=5869687&levelThreeID=1820595&levelTwoID=350662&mode=browse
Full transcript