Edapt WK 3 Metabolism AND Nutrition PDF

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INTRODUCTION TO NUTRIENTS

In this section you will learn about different chemicals that are consumed for maintenance and growth of cells, called nutrients. Nutrients include macronutrients, vitamins, and minerals; nutrients can be essential, meaning they must be consumed, or non-essential, meaning our bodies have ways of making those components. ESSENTIAL AND NON-ESSE NTIAL NUTRIENTS

You are likely familiar with the term nutrient in terms of diets: it is any material that you ingest and absorb for repair, growth, and maintenance of your cells and tissues. This includes macronutrients which are needed in large amounts and micronutrients needed in small amounts. The macronutrients include the macromolecules as well as water. The macromolecules are a source or energy, whereas water does not provide energy but does help maintain tonicity and fluid/electrolyte balance. Micronutrients, including vitamins and minerals, are needed in small amounts because they play a role as part of enzymes. In this role, they are regenerated several times before being expelled by the body. An essential nutrient is one that must be consumed because our bodies cannot create that nutrient. A nutrient is considered non-essential if the body can produce it if it is not consumed. All minerals are essential because our bodies do not have a way to produce those metal ions independently. Most vitamins are essential but our bodies are capable of producing vitamin D and certain other vitamins. Eight amino acids are essential and only one to three fatty acids are essential. There are no known carbohydrates that are essential. MACRONUTRIENTS

Carbohydrates, fats, and proteins are all required in our diets in large amounts because these biopolymers comprise the majority of the structures of our cells. Additionally, these components can be used as sources of energy and are carefully stored by the human body when in excess. You can consider your body in two main nutritional modes:  

Absorptive state: “feast” mode when nutrients are plentiful, and excess material is stored as polymers Post-absorptive state: “famine” mode when nutrients are not sufficient, and the stored polymers are broken into monomers for use

Carbohydrates, fats, and proteins can all be stored and selectively used when there is need. The majority of the carbohydrates you consume will be used as a fuel source to produce ATP through the oxidation of glucose, though they play an important structural role in ATP, nucleotides, glycoproteins, and glycolipids as well. Your body will store excess carbohydrates as glycogen, a polymer of glucose. When carbohydrate stores are low, most cells can break down glycogen or use fats to ensure the body has a steady supply of energy. However, neurons and erythrocytes are unable to use fats and must be provided with carbohydrates for energy. You might have experienced the acute neurological effects of low blood sugar: sudden dizziness, weakness, and exhaustion. This is one of the reasons that blood sugar is carefully regulated by the protein hormones insulin and glucagon.

The main use of lipids in our bodies is for energy. A small amount of lipids are the structural phospholipids and cholesterol found in the cell membrane, and another small fraction are the steroid hormones. When bound to carbohydrates, the resulting glycolipid can be used for cellular recognition. Fat is a superior molecule to store energy in the body compared to carbohydrates, as it will expel water from its structure due to its hydrophobic nature and thus have less bulk. Carbohydrates are polar and also hydroscopic, and will pull water molecules into their structures. Secondly, the process of generating energy is an oxidative process, so starting with a less oxidized substrate will yield more energy. Because of the reduced hydrophobic tails in lipids, they contain more energy in less space than oxygen-rich carbohydrates. Proteins have more of a structural role in the cell compared to the other macronutrients, though they can also be used for energy if all carbohydrate and lipid sources are depleted. The majority of proteins in your body are used in skeletal muscles. Proteins are additionally used in muscle contraction (actin and myosin), as well as cilia and flagella. Proteins such as keratin are found in hair, skin, and nails and serve a protective role. Globular proteins can be used as enzymes in metabolism and cellular maintenance. Protein hormones such as insulin, glucagon, growth factor, and clotting factor help to regulate body function.

Macronutrient

Function



Structural component of nucleotides, ATP, glycoproteins, glycolipids



Fuel source



Structural component of plasma membrane



Cholesterol in plasma membrane



Lipid hormones



Cell recognition

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Majority of body’s protein is found in skeletal muscles



Muscle contractions



Cilia and flagella



Enzymes



Hair, skin, and nails

Carbohydrates

Fats (lipids)

Proteins

Macronutrient

Function



Protein hormones

VITAMINS

Vitamins, sometimes called coenzymes, are often essential nutrients. Because they contain a carbon backbone, our body can synthesize these from other organic compounds called provitamins. However, many vitamins can be destroyed in the presence of light, oxygen, heat, or acid. Vitamins have two names: letters indicative of their order of discovery, but also a chemical name. For example, Vitamin C is also known as ascorbic acid, and is commonly found in citrus fruits and cabbage. You likely recognize the vitamin letters from common foods, such as Vitamin D added to milk; the name calcitriol indicates that its use is in calcium absorption which is why it is often added to milk. Vitamins can be classified as fat-soluble or water-soluble, depending on their polarity and absorption. Both classes of vitamins are absorbed in the small intestine:  

Water soluble vitamins (B and C) are absorbed with water Fat soluble vitamins (A, D, E and K) are absorbed in conjunction with dietary lipids

Because of their hydrophobic nature, fat-soluble vitamins will be soluble in the stored fat, whereas water soluble vitamins will be quickly flushed out of the body rather than stored. To that end, it is critical to have a diet plentiful with water soluble vitamins and containing a lower amount of fat soluble vitamins, as overdose is more likely with the fat soluble vitamins. Vitamin deficiencies are most commonly caused by the water soluble vitamins; vitamin excess (hypervitaminosis) is most commonly caused by fat soluble vitamins.

Water-soluble vitamin

Major use in the body



Hemoglobin synthesis

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Collagen synthesis



Structure of connective tissues



Antioxidant



Coenzyme required for enzymes in carbohydrate

Ascorbic acid (Vitamin C)

Riboflavin (B2)

Water-soluble vitamin

Major use in the body

metabolism

Folic acid (B9)



Coenzyme required for enzymes in cell division

Cobalamin (B12)

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Coenzyme required for erythropoiesis

Fat-soluble vitamin

Major use in the body



Used in visual pigments



antioxidant

Caclitriol (Vitamin D)



Promotes calcium absorption and bone mineralization

Alpha-tocopherol (Vitamin E)



Antioxidant



Prothrombin synthesis



Blood clotting

Retinol (Vitamin A)

Phylloquinone (Vitamin K)

MAJOR MINERALS

Minerals are inorganic metals that are typically essential nutrients and often function as enzyme cofactors. Unlike vitamins, minerals are not destroyed by heat, oxygen, or acid, and will maintain their chemical identity when combined with other elements. There are two main classes of minerals, based on nutritional need:  

Major minerals are required in large amounts (more than 100 mg/day) Trace minerals are needed in small (trace) amounts (less than 100 mg/day)

As all minerals are ions, they are all water soluble and need to be continually replenished through reabsorption or consumption. In the case of copper and zinc, our bodies are adept at reabsorbing minerals through the small intestines. However, as in the vitamins, too much of a mineral can cause issues such as high blood pressure in the case of table salt (sodium chloride), as higher concentrations of sodium in the blood causes a hypertonic solution and will pull water from the cells.

Major mineral

Role in cell



Essential for structure of bones and teeth



Nerve transmission

Fluoride



Muscle contraction Component of calcified bones and teeth, strengthens enamel on teeth

Calcium



Blood clotting



Blood pressure regulation

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Hormone secretion



Cofactor for enzymes



Structural component of

1. Nucleotides and nucleic acid structures (DNA, RNA) 2. ATP and GTP structure 3. cAMP Phosphorus 4. Phospholipids 5. Creatinine phosphate 6. Inorganic phosphate (Pi)

Sodium

Potassium

Magnesium



Acid-base balance in phosphate buffer system



Fluid and electrolyte balance and component of extracellular fluid



Blood pressure regulation



Muscle and nerve function



Fluid and electrolyte balance and component of intracellular fluid



Blood pressure regulation



Muscle and nerve function

Cofactor that allows metabolism of calcium, sodium, and potassium.

F

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PROTE IN AND NITROGEN BALANCE

Proteins are essential for a variety of cellular structures and processes; keeping material to build proteins is equally critical. Nitrogen is essential for our bodies to build proteins, as it is used in the backbone of amino acids, and the primary source for consuming nitrogen is protein rich foods. Nitrogen balance is the equilibrium state where nitrogen consumed equals nitrogen expelled in urine. Children, pregnant women, and athletes are in states of positive protein balance, where they consume more than they excrete. This excess of protein is used in growth and development in each case. Negative protein balance means that a person is excreting more than they consume, and thus body proteins are being broken down as fuel. It is important to note that protein is used as a fuel source only when carbohydrates and lipids are in short supply. One example of this is muscle atrophy, as muscles are easily broken down as a nitrogen and energy source when need arises.

INTRODUCTION TO METABOLISM

You may be familiar with the term metabolism in terms of fast and slow metabolism: someone with a fast metabolism might eat a lot but burn it off to remain thin. In this section, we will discuss metabolism as a combination of anabolism and catabolism, the roles of cofactors, coenzymes, and enzymes in metabolic processes. METABOLISM = ANABOLISM + CATABO LISM

Metabolism is defined as the sum of all chemical reactions in the body, both the creation of bonds and the breaking of bonds.  

Anabolic reactions create bonds between small molecules to make larger molecules (polymers). Catabolic reactions break bonds in large molecules (polymers) to make small molecules.

Anabolic reactions (synthesis) is the process by which simple, small molecules combine to form larger, more complex molecules known as polymers. Anabolism is considered an endergonic reaction, whereby energy is consumed as the reaction takes place. An example of an anabolic reaction is protein synthesis. Conversely, catabolism is considered an exergonic reaction, whereby energy is released as the reaction takes place. An example of catabolism is the digestion of starch in the GI tract to its glucose monomers. Regardless

of the type of metabolic reaction, some of the energy will be released as heat. The remaining energy is used to convert reactants into products. Rather than thinking of these as opposite processes, consider these two processes as working together for your body to extract nutrients (catabolism) and then building your own cells and tissues (anabolism). This is similar to taking a toy brick castle, then breaking it apart to build a toy brick train.

Metabolic process

Anabolism

Catabolism

Bonds

Bonds are created (synthesis)

Bonds are broken (decomposition)

Energy

Energy is used (endergonic)

Energy is released (exergonic)

Molecules

Small molecules are combined to form polymers (large and more complex molecules)

Polymers are broken into smaller and simpler molecules

ENZYMES PERFO RM CHEMICAL REACTIONS IN CELLS

Although the metabolic chemical reactions that occur in your cells could (and do!) take place outside of cells, they occur much faster inside of cells due to the use of enzymes, chemical catalysts that increase the reaction rate and thus the number of products created per second without being consumed in the reaction. If cells had to wait for these reactions to take place, the cell cycle would not occur in a timeframe conducive for life. For example, the reaction for synthesizing pyrimidine nucleotides uncatalyzed would take 1010 years (100 million millennia) at room temperature; with this enzyme, 20 reactions occur each second. The way that enzymes achieve this enormous rate enhancement is by lowering the activation energy, or the amount of energy required for the reaction to occur. By decreasing this hill, it is easier for more reactions to occur. It should be noted that this does not affect the energy of the substrate or product. Many enzymes involved in metabolism use inorganic cofactors and/or organic coenzymes as part of their structure. When the word enzyme is used, it often implies the protein component (apoenzyme) as well as all coeznymes and cofactors needed for its function. There are some enzymes that are complete without coenzymes or cofactors.     

Holoenzyme – complete and functional enzyme, containing any required cofactors or coenzymes Apoenzyme – the protein portion of a holoenzyme Cofactor – inorganic mineral that can serve as a structural component of a holoenzyme Coenzyme – organic molecule that can serve as a structural component of a holoenzyme Active site – where the substrate is bound and chemistry occurs to create the product

Both cofactors and coenzymes can be structural components that will help the enzyme complete all the steps of its chemical reaction. As discussed in the previous section, many minerals are cofactors and many coenzymes are vitamins. These will need to be regenerated or ‘reset’ to their original states in order for the next reaction to occur in the holoenzyme. Many enzymes have mechanisms to ensure this reset takes place efficiently.

Enzymes and Cofactors in Metabolic Processes

COE NZYMES: NAD, FAD, AND COEZNYME A

There are three important coenzymes in metabolism: NAD, FAD, and Coenzyme A. When oxygen is present, all three of these cofactors are used to generate additional ATP in the mitochondrion. 





NAD becomes reduced to high energy NADH as sugars are oxidized o Generated in glycolysis and Krebs cycle o Donates electrons to electron transport chain to generate additional ATP FAD becomes reduced to high energy FADH2 as sugars are oxidized o Generated in Krebs cycle o Donates electrons to electron transport chain to generate additional ATP COENZYME A prepares polar pyruvate to enter the mitochondrion o Three carbon pyruvate attaches to Coenzyme A o Pyruvate-CoenzymeA is oxidized while NAD is reduced to NADH o One carbon is from pyruvate is lost as CO2, and two carbons remain attached to Coenzyme A, called Acetyl CoA

As discussed in A&P 1, NAD+ and FAD+ are used as electron carrier molecules used in aerobic cellular respiration. These molecules become reduced as glucose is oxidized in the different phases of cellular respiration, producing NADH and FADH2. You can note that the addition of H (an electron attached to a proton) to these molecules shows reduction. Pyruvic acid is a polar molecule and because of its charge is unable to penetrate through the hydrophobic outer membrane of the mitochondria. To bypass this membrane, each pyruvate will be added to a Coenzyme A molecule. As this occurs, the carboxylic acid functional group (-COO-) will be stripped from the molecule, giving off carbon dioxide and a two carbon Acetyl-CoA. The Acetyl-CoA enters the mitochondrion, and the CO2 is expelled from the cell. See this Reductions Reactions video to learn more https://cdnapisec.kaltura.com/index.php/extwidget/preview/partner_id/2363221/uiconf_id/43522921/entry_id/1 _nqlm62fp/embed/dynamic Cells obtain energy during cellular respiration by oxidizing food molecules such as glucose. The energy derived from these oxidation reactions is used to form ATP. Oxidation can be defined as the removal of hydrogens from a molecule. Since a hydrogen consists of a proton and an electron, a proton and an electron I removed during oxidation. Whenever a molecule is oxidized, hydrogens removed, another molecule must be reduced. Hydrogens added to it during an oxidation reduction reaction in the cell. And enzyme is involved in transferring the hydrogen, proton plus electron to a coenzyme called NAD plus. This enzyme has a binding site for both the substrate and NAD plus. Once the substrate and NAD plus are bound with the enzyme, the hydrogen is transferred from the substrate to the NAD plus. In other words, the substrate is oxidized, loses the hydrogen and the NAD plus is reduced to NADH. As with all enzyme mediated reactions. Once the reaction is complete, the product separate from the enzyme and the enzyme can be used again. Nadh, a high-energy electron carrier, diffuses away and is available to donate the hydrogen to other molecules.

REACTIONS IN METABOLISM

The chemical reactions that occur throughout metabolism can be grouped into different categories: 









Oxidation and Reduction: simultaneous movement of electrons between two molecules o Oxidation – loss of electrons on a molecule o Reduction – gain of electrons on a molecule o Requires NAD(H) or FAD(H) cofactors to occur o Catalyzed by dehydrogenase enzymes o Example: Alcohol dehydrogenase uses acetaldehyde and NADH to produce ethanol Decarboxylation: removal of a carboxylic acid group as CO2 from a molecule o Catalyzed by decarboxylase enzymes o Example: Pyruvate decarboxylase enzyme catalyzes the removal of CO2 to produce an acetaldehyde Deamination: removal of an amine (-NH2) with addition of H2O o Catalyzed by deaminase enzymes o Example: Cytidine deaminase removes an amine from the nucleotide base Cytidine to create Uridine Dephosphorylation: removal of a phosphate group from a molecule o Catalyzed by phosphatase enzymes o Example: Protein phosphatase removes a phosphate from a protein Phosphoryl...