Topic 25 Topic 25 Topic 25: Biochemistry Table of Contents Topic 25 Topic 25 Basic Concepts...

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Topic 25: Biochemistry

Table of ContentsTable of ContentsTopic 25Topic 25

Basic Concepts

Additional Concepts

• Many of the most important molecules in your body are polymers.

Molecules of Life

Biochemistry: Basic ConceptsBiochemistry: Basic ConceptsBiochemistry: Basic ConceptsBiochemistry: Basic Concepts

• Proteins, carbohydrates, and nucleic acids, all extremely large molecules, are formed from small monomer subunits.

• Although lipids are usually not considered to be polymers, they, too, are formed from smaller molecules that have been linked together.

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• You need relatively large amounts of proteins, carbohydrates, and lipids in your diet.

Molecules of Life


• Complex reactions in your cells use some of these molecules and a few others to make a fourth group of biomolecules, the nucleic acids.

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• The study of the chemistry of living things is called biochemistry.

Biochemistry


• This science explores the substances involved in life processes and the reactions they undergo.

• Other than water, which can account for 80 percent or more of the weight of an organism, most of the molecules of life—the biomolecules—are organic.

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• The elemental composition of living things is different from the relative abundance of elements in Earth’s crust.

Biochemistry


• Oxygen, silicon, aluminum, and iron are the most abundant atoms in Earth’s crust.

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Biochemistry


• All four of these elements can form the strong covalent bonds found in organic molecules.

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• However, more than 95 percent of the atomsin your body are hydrogen, oxygen, carbon, and nitrogen.

Biochemistry

Biochemistry: Basic ConceptsBiochemistry: Basic ConceptsBiochemistry: Basic ConceptsBiochemistry: Basic ConceptsTopic 25Topic 25

• Along with two other elements, sulfur andphosphorus, they are the only elements needed to make most of the proteins, carbohydrates, lipids, and nucleic acids found in every cell.

• A protein is an organic polymer composed of amino acids bonded together in one or more chains.

Proteins


• An amino acid has a central carbon atom, to which are bonded a carboxyl group, an amino group, a hydrogen atom, and a variable side chain designated as R, as shown in the following structural formula.

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Structure of an Amino Acid


• Amino acids bond to each other by forming a peptide bond, an amide group formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another.





• Two amino acids linked by a peptide bond form a dipeptide.

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• A chain of two or more amino acids linked by peptide bonds is called a peptide.



• The term polypeptide is applied to a chain of ten or more amino acids.

• Proteins may have one or several polypeptide chains, and each chain must have an exact sequence of amino acids.

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• Proteins can fold into either round, globular structures or long, fibrous structures.





• The amino acid chains are held in place in three-dimensional structures by attractive forces between the side chains of differentamino acids, which have been brought close together by the bending and folding of the polypeptide chains.

• Many of the proteins in an organism act as enzymes. These proteins catalyze chemical reactions—speeding up reactions or allowing the reactions to take place at a low temperature.

Enzymes


• The reactants in an enzyme-catalyzed process are called substrates. The substrate(s) bind to the enzyme at a location called the enzyme’s active site, forming an enzyme-substrate complex.

Enzymes


• This interaction enables the substrate(s) to react with a much lower activation energy than they would without an enzyme.

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Enzymes


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• Substrates are brought close together in the active sites of an enzyme, which lowers the activation energy of the reaction by facilitating the bonding together of the substrates to form a product.

Enzyme Action


Enzyme Action


• After the substrates have reacted, the product is released.

• The enzyme is then able to bind more substrate molecules and continue catalyzing the reaction.

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• Familiar carbohydrates include sugars, starches, and cellulose.

Carbohydrates


• Simple carbohydrates consist of a chain of carbon atoms having hydroxyl (–OH) groups and a carbonyl group, often in the form of an aldehyde group.

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• The simplest carbohydrates are the simple sugars, or monosaccharides, which commonly have five or six carbon atoms.

Monosaccharides


• Glucose, the main ingredient in corn syrup, is a familiar monosaccharide.

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• Glucose has the molecular formula C6H12O6 and can be represented by the following structures.

Monosaccharides


• The most common simple sugars are glucose, fructose, and ribose.

Monosaccharides


• A polymer of many monosaccharides bonded into a chain is called a polysaccharide.

Polysaccharides


• Starch is a polysaccharide that consists only of glucose units.

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Polysaccharides


• Plants also link glucose units together in a different way to form the polysaccharidecellulose, which forms plant cell walls.

• Animals store glucose as a polysaccharide called glycogen, which is similar to starch.

Polysaccharides


• Lipids are the nonpolar substances—fats, waxes, and oils—produced by living things.

Lipids


• Lipids are not polymers, and their chemical structures vary widely.

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• The most familiar lipids are the plant oils and animal fats.

Fatty Acids


• These lipids are esters of fatty acids, which are carboxylic acids with long, straight hydrocarbon chains usually having between 12 and 24 carbon atoms.

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• The simplest fatty acids are the saturated fatty acids, which have no double bonds between carbon atoms.

Saturated Fatty Acid


• Stearic acid is found in pork and beef tissue.

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• Many other fatty acids have one or more double bonds between carbon atoms and, as a result, are unsaturated fatty acids.

Monounsaturated Fatty Acid


• Oleic acid is a major component of olive oil.

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• Animal fats and plant oils are made up primarily of triglycerides, molecules in which three fatty acids are bonded to a glycerolmolecule by ester linkages, as shown in the following diagram.

Triglycerides


• Phospholipids are triglycerides in which a polar phosphate group, instead of a third fatty acid, is bonded to the glycerol.

Triglycerides


• Cell membranes consist of a double layer of phospholipid molecules.

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• The membranes of living cells are formed by a double layer of lipids called a bilayer.

Triglycerides


• Another class of lipids, steroids, consists of compounds whose basic structure is very different from those of other lipids, as shown below.

Other Lipids


• Cholesterol, vitamin D, and some hormones are steroids.

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• Lipids have two major biochemical roles in the body.

The Functions of Lipids


• When an organism takes in and processes more food than it needs, excess energy is produced.

• The organism stores this excess energy for future use by using it to bond atoms together in lipid molecules.

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• Later, when energy is needed, enzymes break these same bonds, releasing the energy used to form them.

The Functions of Lipids


• You have learned that carbohydrates also store energy; however, the process is not as efficient as in lipids.

• Therefore, long-term storage of energy is usually in the form of lipids.

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• The sequence of amino acids in a protein is determined by the genetic information coded into long-chain polymers called nucleic acids.

Nucleic Acids


• The monomers that make up nucleic acids are called nucleotides.

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• Each nucleotide is made up of three parts: a phosphate group, a five-carbon sugar, and a nitrogen-containing cyclic compound called a nitrogen base.

Nucleic Acids


• The structure of a nucleotide is shown.

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Nucleic Acids


• The common nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Nucleic Acids


• These names reflect the fact that DNA contains the sugar deoxyribose and RNA contains the sugar ribose.

• DNA exists as a pair of polymer chains in which the backbone of each chain consists of alternating phosphate and deoxyribose units. The bases stick out from the backbone.

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• This model of a portion of a DNA molecule clearly shows its complexity.

The Structure of DNA


• A single DNA molecule contains many thousands of nucleotides.

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• The two chains of DNA are held together because the nitrogen bases of one chain are hydrogen-bonded to the nitrogen bases of the other chain.

Base Pairing


• Because of the change in angle from one nucleotide to the next, the chains wind into a spiral called a double helix.

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• Four different nitrogen bases are found in DNA: adenine, guanine, cytosine, and thymine.

Base Pairing


• Adenine hydrogen bonds to thymine, and guanine hydrogen bonds to cytosine.

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• The order of these four nitrogen bases along one of the DNA chains provides the information for the sequences of amino acids in proteins.

Base Pairing


• Cell mechanisms “read” the DNA sequence in groups of three bases called triplets.

• Each triplet codes for a specific amino acid or tells the cell to start or stop making a protein.

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Basic Assessment QuestionsBasic Assessment Questions

Question 1

Label the amino group and the carboxyl group of the dipeptide.

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AnswerTopic 25Topic 25


Question 2

Draw an arrow pointing to the peptide bond.

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Question 3

Draw a square around each variable side chain.

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Glucose is a(n)

Question 4

a. polysaccharide.

b. amino acid.

c. part of cellulose.

d. 5-carbon sugar.

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Answer

The answer is C, part of cellulose.

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Biochemistry: Additional ConceptsBiochemistry: Additional Concepts Biochemistry: Additional ConceptsBiochemistry: Additional Concepts Topic 25Topic 25

Additional Concepts

Biochemistry: Additional ConceptsBiochemistry: Additional Concepts Biochemistry: Additional ConceptsBiochemistry: Additional Concepts

Anabolism and Catabolism

• The set of reactions carried out by an organism is its metabolism.

• Living organisms must accomplish two major functions in order to survive.

• They have to extract energy from nutrients in forms that they can use immediately as well as store for future use.

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• In addition, they have to use nutrients to make building blocks for synthesizing all of the molecules needed to carry out their life functions.

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Anabolism and Catabolism• A large number of different metabolic

reactions take place in living cells. • Some involve breaking down nutrients to

extract energy; these are catabolic processes.

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• Others involve using energy to build large biological molecules; these reactions are anabolic processes.

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Anabolism and Catabolism• The term catabolism refers to the metabolic

reactions that break down complex biological molecules such as proteins, polysaccharides, triglycerides, and nucleic acids for the purposes of forming smaller building blocks and extracting energy.

• The term anabolism refers to the metabolic reactions that use energy and small building blocks to synthesize the complex molecules needed by an organism.

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ATP

• Catabolism and anabolism are linked by common building blocks that catabolic reactions produce and anabolic reactions use.

• A common form of potential chemical energy also links the two processes.

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ATP

• ATP (adenosine triphosphate) is a nucleotide that functions as the universal energy-storage molecule in living cells.

• During catabolic reactions, cells harness the chemical energy of foods and store it in the bonds of ATP.

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Photosynthesis

• What is the source of the energy that fuels metabolism? For most living things, certain wavelengths of sunlight provide all of this energy.

• Some bacteria and the cells of all plants and algae, including the brown algae, are able to capture light energy and convert some of it to chemical energy.

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Photosynthesis

• Animals can’t capture light energy, so they get energy by eating plants or by eating other animals that eat plants.

• The process that converts energy from sunlight to chemical energy in the bonds of carbohydrates is called photosynthesis.

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Photosynthesis• ATP is a nucleotide that contains an

adenine nitrogen base, a ribose sugar, and three phosphate groups.

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Photosynthesis

• When the final phosphate group is removed from ATP, as modeled by the red dotted line, ADP is formed and energy is released.

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Photosynthesis• During the complex process of

photosynthesis, carbon dioxide and water provide the carbon, hydrogen, and oxygen atoms that make up carbohydrates and oxygen gas, which also is formed.

• The following net reaction takes place during photosynthesis.

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Photosynthesis

• Photosynthesis results in the reduction of the carbon atoms in carbon dioxide as glucose is formed.

• During this redox process, oxygen atoms in water are oxidized to oxygen gas.

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Cellular Respiration• Most organisms need oxygen to live. Oxygen

that is produced during photosynthesis is used by living things during cellular respiration, the process in which glucose is broken down to form carbon dioxide, water, and large amounts of energy.

• Cellular respiration is a redox process; the carbon atoms in glucose are oxidized while oxygen atoms in oxygen gas are reduced to the oxygen in water.

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Cellular Respiration• The net reaction that takes place during

cellular respiration is

• Note that the net equation for cellular respiration is the reverse of the net equation for photosynthesis.

• These two processes complement each other in nature.

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Fermentation

• During cellular respiration, glucose is completely oxidized, and oxygen gas is required to act as the oxidizing agent.

• Can cells extract energy from glucose in the absence of oxygen?

• Yes, but not nearly as efficiently. Without oxygen, only a fraction of the chemical energy of glucose can be released.

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Fermentation

• Whereas cellular respiration produces 38 moles of ATP for every mole of glucose catabolized in the presence of oxygen, only two moles of ATP are produced per mole of glucose that is catabolized in the absence of oxygen.

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Fermentation

• This provides enough energy for oxygen-deprived cells so that they don’t die.

• The process in which glucose is broken down in the absence of oxygen is known as fermentation.

• There are two common kinds of fermentation. In one, ethanol and carbon dioxide are produced.

• In the other, lactic acid is produced.

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Alcoholic fermentation

• Yeast and some bacteria can ferment glucose to produce the alcohol ethanol.

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Alcoholic fermentation

• Alcoholic fermentation is needed to make bread dough rise, form tofu from soybeans, and produce the ethanol in alcoholic beverages.

• Another use of the ethanol that is produced by yeast is as an additive to gasoline, called gasohol.

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Lactic acid fermentation

• During strenuous activity, muscle cells often use oxygen faster than it can be supplied by the blood.

• When the supply of oxygen is depleted, cellular respiration stops.

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• Although animal cells can’t undergo alcoholic fermentation, they can produce lactic acid and a small amount of energy from glucose through lactic acid fermentation.

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Lactic acid fermentation Topic 25Topic 25



• The lactic acid that is produced is moved from the muscles through the blood to the liver.

• There, it is converted back into glucose that can be used in catabolic processes to yield more energy once oxygen becomes available.

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• However, if lactic acid builds up in muscle cells at a faster rate than the blood can remove it, muscle fatigue results.

• Buildup of lactic acid is what causes a burning pain in the muscle during strenuous exercise.

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Additional Assessment QuestionsAdditional Assessment Questions

What effect do enzymes have on the chemical reactions that take place in living things?

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speed reactions by lowering activation energy



Your cells carry out cellular respiration. What is the function of this process?



releases energy for life processes



What process is the reverse of cellular respiration?



photosynthesis


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