Name: fatty acids: energy, membranes, and cholesterol
Uploaded: 2023-04-30T10:06:24.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.3

Overview of Fatty Acid Metabolism

Fatty acid metabolism includes the synthesis of fatty acids in the cytoplasm and their breakdown in the mitochondria and peroxisomes. Both of these processes are tightly regulated depending on nutrient availability.
For example, consider the breakdown of an eight-carbon fatty acid molecule. It is first esterified to produce fatty acyl-CoA in the cytoplasm and subsequently transported into mitochondria for beta-oxidation.
Here, the fatty acyl-CoA molecule loses two carbon atoms to produce a six carbon fatty acid chain along with a molecule of acetyl coenzyme A, NADH, and FADH2. This process is repeated until the fatty acid is completely converted into acetyl CoA, which then enters the citric acid cycle producing more NADH and FADH2.
These reduced coenzymes donate their electrons to the electron transport chain to produce ATP.
During fatty acid synthesis, malonyl-CoA, a three-carbon molecule, donates two carbons to an acetyl group forming a four-carbon fatty acid molecule, while the third carbon is released as carbon dioxide. This process repeats until the desired eight-carbon fatty acid is formed.

overview of fatty acid metabolism

Lipids also are sources of energy that power cellular processes. Like carbohydrates, lipids are composed of carbon, hydrogen, and oxygen, but these atoms are arranged differently. Most lipids are nonpolar and hydrophobic. Major types include fats and oils, waxes, phospholipids, and steroids.
Fatty acids are catabolized in a process called beta-oxidation, which takes place in the matrix of the mitochondria and converts their fatty acid chains into two-carbon units of acetyl groups. The acetyl groups are picked up by CoA to form acetyl CoA that proceeds into the citric acid cycle. Excess fats are stored in adipocytes as triacylglycerides and can be used as energy reserves.
Trans Fats
The food industry artificially hydrogenates oils to make them semi-solid and of a consistency desirable for many processed food products. Hydrogen gas is bubbled through oils to solidify them. During this hydrogenation process, double bonds of the cis- conformation in the hydrocarbon chain may convert to double bonds in the trans- conformation.
Recent studies have shown that an increase in trans fats in the human diet may lead to higher levels of low-density lipoproteins (LDL), or &#34;bad&#34; cholesterol, which in turn may lead to plaque deposition in the arteries, resulting in heart disease. Many fast food restaurants have recently banned using trans fats, and food labels are required to display the trans fat content.
Omega Fatty Acids
Essential fatty acids are those that the human body requires but does not synthesize. Consequently, they must be supplemented through ingestion via the diet. Omega-3 fatty acids&#160; and omega-6 fatty acids are the only two that humans require. These Polyunsaturated fatty acids are termed omega-3 because a double bond connects the third carbon from the hydrocarbon chain&#39;s end to its neighboring carbon, while in omega-6 the double bond is present on the sixth carbon.
Phospholipids
Phospholipids are major plasma membrane constituents that comprise cells&#39; outermost layer. Like fats, they are fatty acid chains attached to a glycerol or sphingosine backbone. However, instead of three fatty acids attached as in triglycerides, there are two fatty acids forming diacylglycerol, and a modified phosphate group occupies the glycerol backbone&#39;s third carbon. A phosphate group alone attached to a diacylglycerol does not qualify as a phospholipid. It is phosphatidate (diacylglycerol 3-phosphate), the precursor of phospholipids. An alcohol modifies the phosphate group. Phosphatidylcholine and phosphatidylserine are two important phospholipids that are in plasma membranes.
Steroids
Cholesterol is the most common steroid. Cholesterol is mainly synthesized in the liver and is the precursor to many steroid hormones such as testosterone and estradiol, which are secreted by the gonads and endocrine glands. It is also the precursor to Vitamin D. Cholesterol is also the precursor of bile salts, which help in the emulsification of fats and their subsequent absorption by cells.
This text is adapted from <a href="https://openstax.org/books/biology-ap-courses/pages/3-3-lipids">Openstax, Biology for AP Courses, Section 3.3: </a><a href="https://openstax.org/books/biology-ap-courses/pages/3-3-lipids">Lipids</a>

Lipids also are sources of energy that power cellular processes. Like carbohydrates, lipids are composed of carbon, hydrogen, and oxygen, but these atoms ...

Education

JoVE Core

Cell Biology

Unit 1

Introduction to Metabolism

KEY TERMS AND CONCEPTS

fatty acids: energy, membranes, and cholesterol

Fatty acids help cells store and use energy, and they also support important cell structures. Lipids are nonpolar and hydrophobic, so they do not mix well with water. Major lipid types include fats and oils, waxes, phospholipids, and steroids.

Cells break down fatty acids by beta-oxidation. This process happens in the matrix of the mitochondria and cuts fatty acid chains into two-carbon acetyl groups. CoA picks up these groups to form acetyl CoA, which then enters the citric acid cycle. Extra fats are stored in adipocytes as triacylglycerides and can serve as energy reserves.

Some processed foods contain trans fats. Food makers can artificially hydrogenate oils to make them semi-solid, which gives products a desired texture. During this process, double bonds in the cis form may change to the trans form. Higher trans fat intake may raise LDL, or “bad” cholesterol, which can contribute to plaque in arteries and heart disease. Many fast food restaurants now avoid trans fats, and food labels must show trans fat content.

The body also needs essential fatty acids from the diet. Humans require omega-3 fatty acids and omega-6 fatty acids, but do not make them on their own. These polyunsaturated fatty acids are named by the position of the first double bond. In omega-3, the double bond is at the third carbon from the end of the hydrocarbon chain. In omega-6, it is at the sixth carbon.

Phospholipids are key parts of the plasma membrane, which is the cell’s outer layer. Like fats, they have fatty acid chains attached to a glycerol or sphingosine backbone. Triglycerides have three fatty acids, but phospholipids have two fatty acids and a modified phosphate group on the third carbon of the glycerol backbone. A phosphate group by itself does not make a phospholipid. It is phosphatidate, also called diacylglycerol 3-phosphate, and an alcohol must modify the phosphate group. Phosphatidylcholine and phosphatidylserine are two important membrane phospholipids.

Steroids are another major lipid group. Cholesterol is the most common steroid and is mainly made in the liver. It is a precursor to steroid hormones such as testosterone and estradiol, which are secreted by the gonads and endocrine glands. Cholesterol is also needed to make vitamin D and bile salts. Bile salts help emulsify fats so cells can absorb them.

Fatty Acids: Energy, Membranes, and Cholesterol

fatty-acids-energy-membranes-and-cholesterol

overview of metabolism

Metabolism in Plants, Animals, and Microbes

Metabolism is the set of chemical reactions that keep living cells working. These reactions are linked through many pathways. Together, they support the normal function of cells in plants, animals, and microbes. In plants, sunlight is the main energy source. Chlorophyll pigments in the leaves absorb this light. The plant then uses that energy for photosynthesis. During photosynthesis, water is oxidized to oxygen and carbon dioxide is reduced to glucose. Glucose then serves as a starting...

carbohydrate metabolism

Carbohydrates, Digestion, and Blood Sugar

Carbohydrates are an important source of energy and a key part of human nutrition. They are made of carbon, hydrogen, and oxygen. One gram of carbohydrate provides four kilo-calories of energy, so carbohydrates are the body’s most efficient instant fuel. Starch makes up about 60% of the carbohydrates people eat. It is broken down by amylase enzymes, but amylase cannot work in the stomach’s acidic environment. That is why starch digestion happens in the mouth and the small intestine. Simple...

glycolysis: preparatory phase

Glycolysis: Energy Investment Steps

Glycolysis begins with energy investment steps in the cytoplasm of both prokaryotic and eukaryotic cells. It is the first step in cellular metabolism, which is the complete breakdown of glucose to extract energy. In heterotrophic cells, glucose enters by secondary active transport or through GLUT proteins, which are glucose transporter proteins that help glucose diffuse into the cell. The pathway starts with one six-carbon, ring-shaped glucose molecule and ends with two three-carbon molecules...

glycolysis: pay-off phase

Glycolysis: ATP and NADH Output

The pay-off phase of glycolysis turns the two three-carbon sugar molecules into ATP, NADH, and pyruvate. By this stage, the cell has already spent two ATP molecules. The remaining reactions recover that investment and add two more ATP molecules and two high-energy NADH molecules. The sixth step oxidizes glyceraldehyde 3-phosphate, a three-carbon sugar made earlier in glycolysis. High-energy electrons are transferred to NAD+, which becomes NADH. A second phosphate group is then added to form...

fates of pyruvate

Pyruvate Pathways in Fermentation

Pyruvate is a key product of glycolysis and can follow different pathways depending on oxygen availability. During glycolysis, glucose is oxidized to pyruvate, NAD+ is reduced to NADH, and two ATP are made by substrate-level phosphorylation. In aerobic organisms, pyruvate then enters the citric acid cycle, which helps produce the reduced coenzymes NADH and FADH2. These coenzymes are later oxidized in the electron transport chain to make ATP and regenerate NAD+ and FAD. When oxygen is absent,...

role of reduced coenzymes nadh and fadh&#8322;

Electron Carriers in Cellular Energy

Electron carriers help store and move energy during nutrient breakdown. Cells can save released energy by reducing these carriers or by making ATP, the cell’s main energy molecule. These mobile electron carriers bind high-energy electrons and shuttle them between compounds in metabolic pathways. The main carriers discussed here come from the B vitamin group and are nucleotide derivatives. They include nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and flavin...

overview of nitrogen metabolism

Nitrogen Cycle in Soil and Plants

Nitrogen moves through soil, plants, animals, and microbes in a cycle that keeps this macronutrient available for life. It is a major part of proteins and nucleic acids, so cells need it to build both amino acids and nucleotides. In nature, nitrogen is recycled from organic compounds and stored in several forms, including ammonia, ammonium ions, nitrate, nitrite, and nitrogen gas. Many of the key steps in this cycle are carried out only by prokaryotes. The largest nitrogen pool in terrestrial...

Fatty acids help cells store and use energy, and they also support important cell structures. Lipids are nonpolar and hydrophobic, so they do not mix well with water. Major lipid types include fats and oils, waxes, phospholipids, and steroids. Cells break down fatty acids by beta-oxidation. This process happens in the matrix of the mitochondria and cuts fatty acid chains into two-carbon acetyl groups. CoA picks up these groups to form acetyl CoA, which then enters the citric acid cycle. Extra...

sugars as energy storage molecules

Glucose Storage in Plants and Animals

Glucose storage in plants and animals helps cells manage energy for metabolism. Sugar is a simple carbohydrate, and cells use it because a lot of energy is stored in its bonds. Consumed carbohydrates often come from photosynthesizing organisms, especially plants. Plants make glucose during photosynthesis by using sunlight to convert carbon dioxide into sugar molecules. Because this builds a larger, energy-storing molecule, the process needs an energy input. Glucose can then be stored for later...

fats as energy storage molecules

How Triglycerides Fuel ATP Production

Triglycerides store long-term energy in fats. A triglyceride is built from glycerol and three fatty acids. When the body needs energy, these molecules are broken down first. This breakdown is called lipolysis, and it happens in the cytoplasm by hydrolysis. Lipolysis splits triglycerides into fatty acids and glycerol. The glycerol then enters glycolysis as DHAP, which connects fat breakdown to the cell’s main energy pathway. The fatty acids are then oxidized by beta-oxidation into acetyl-CoA.

regulation of metabolism

How Cells Control Metabolic Enzymes

Cells control metabolic enzymes to match changing needs and conditions. Different cells use different enzymes and energy levels, and those needs can also change within the same cell over time. Stomach cells, fat storage cells, skin cells, blood cells, and nerve cells do not all need the same metabolic activity. A digestive cell also works harder soon after a meal than it does many hours later. As cell needs change, the amount and activity of enzymes change too. Enzymes lower activation energy,...

positive and negative feedback loops

Homeostasis and Body Feedback Control

Homeostasis keeps body conditions in a steady range through feedback control. Animal organs and organ systems constantly adjust to internal and external changes. This balance is called a dynamic equilibrium because the body keeps adapting while still staying within specific ranges. The goal of homeostasis is to stay near a set point, which is the value the body tries to maintain. A change in the internal or external environment is a stimulus. A receptor detects that change and sends a signal...

key terms and concepts

Learn how fatty acids fuel cells, how trans fats affect health, and how phospholipids and cholesterol support membranes, hormones, and digestion.

Fatty Acids: Energy, Membranes, and Cholesterol | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

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SC.912.L.18.1

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SC.912.L.18.2

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SC.912.L.18.4

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The ADP/ATP Carrier Protein

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SC.912.L.18.5

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SC.912.L.18.6

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SC.912.L.18.7

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SC.912.L.18.8

A. All living things are composed of four basic categories of macromolecules and share the same basic needs for life.

B. Living organisms acquire the energy they need for life processes through various metabolic pathways (primarily photosynthesis and cellular respiration).

C. Chemical reactions in living things follow basic rules of chemistry and are usually regulated by enzymes.

D. The unique chemical properties of carbon and water make life on Earth possible.

Fatty Acids: Energy, Membranes, and Cholesterol

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