1. Cellular Metabolism

2. Introduction Cells require energy and information to build bodies. Cells house the many chemical reactions of metabolism. These reactions break down nutrients to release energy and also build molecules to store energy. Cells carry genetic information that encodes the amino acid sequences of proteins. A special type of protein called an enzyme controls each of the interrelated reactions of metabolism.

3. Metabolic Reactions Anabolism and catabolism are the two major types of metabolic reactions in humans. Anabolism which builds up larger molecules from smaller ones, requires energy. Catabolism which is the breakdown of larger molecules into smaller ones, releases energy.

4. Anabolism Anabolism provides the biochemicals required for cell growth and repair. Dehydration synthesis is an example of anabolism. In dehydration synthesis cells join many simple sugar molecules into a chain of larger molecules of glycogen…a carbohydrate. This process is seen in Figure 4.1 on page 74…when two monosaccharides join, a water molecule is produced, the monosaccharides join, and the chain gets longer.

5. Anabolism Cells also use DS to link glycerol and fatty acid molecules to form fat molecules (triglycerides). In this process seen on page 74, Figure 4.2, a glycerol molecule gives up 3 hydrogen atoms to join with 3 fatty acid molecules. The fatty acid molecules give up an OH group when they join with the glycerol and 3 waters and one triglyceride molecule is formed.

6. Anabolism A third way that cells use DS is when amino acids join together…this is seen on page 75 in Figure 4.3. The OH from one AA, joins with an H from another AA…the C from the first AA joins with the N from the other AA by a peptide bond. When the two AA join up they are referred to as a dipeptide. When many join together, they are called a polypeptide which consists of 100 or more AA and has a specific function and is called a protein. There is no distinct boundary line between a polypeptide and a protein…so we can use them interchangeably for the most part.

7. Anabolism Anabolic steroids are a group of lipids that stimulate anabolism and thus promote the growth of certain tissues. Doctors prescribe steroids to patients to treat various diseases. However, some take steroids to increase their muscle mass, often with the hope of enhancing athletic performance. Using steroids this way can cause adverse changes in liver function, increased risk of heart and blood vessel diseases, upsets in normal hormonal imbalances, infertility and psychological disorders.

8. Catabolism An example of a process that breaks large molecules into smaller ones is called hydrolysis. For example sucrose can be split into glucose and fructose when a water molecule is split. Hydrolysis is the opposite of dehydration synthesis. Hydrolysis, which occurs during digestion, breaks down carbohydrates into monosaccharides, fats into glycerol, proteins into AA and nucleic acids into nucleotides.

9. Control of Metabolic Reactions Specialized cells, like nerve, muscle, or blood cells have distinctive chemical reactions. However, all cells perform certain basic reactions, such as buildup and breakdown of carbohydrates, lipids, proteins and nucleic acids. These reactions include hundreds of specific chemical changes that occur rapidly—yet in a coordinated fashion—thanks to enzymes.

10. Mini Quiz—Review Notes 5 min 1.Is dehydration synthesis known as anabolism or catabolism? Why? 2.Is hydrolysis known as anabolism or catabolism? Why? 3.What results with hydrolysis of a triglyceride? A carbohydrate? A protein? 4.What type of bond connects an amino acid to an amino acid? 5.What type of chemical speeds up reactions of the cells of your body? 6.What class of macromolecules is this chemical from? C, L, P or NA?

11. Enzyme Action Metabolic reactions require energy to proceed, however, the temperature conditions in cells are too low to promote these types of reactions. So, enzymes help make these reactions possible. Enzymes are complex molecules that promote chemical reactions in cells by lowering the mount of initial energy needed to start the reaction. So, enzymes speed the rates of metabolic reactions.

12. Enzyme Action This process is called catalysis and enzymes are called catalysts. Enzymes are needed only in small amounts because they are not used up in a metabolic reaction. Each enzyme only works on a particular chemical which is called its substrate. For example hydrogen peroxide is a toxic by- product of certain metabolic reactions. The enzyme catalase speeds the breakdown of hydrogen peroxide into water and oxygen so that it does not buildup in the body which might cause cell damage.

13. Enzyme Action Specific enzymes catalyze each of the hundreds of different chemical reactions of cellular metabolism. Therefore, each cell contains hundreds of different enzymes and each enzyme must “recognize” its specific substrate. This is possible because of the shapes of the enzymes molecules and their substrates. During the enzyme-catalyzed reaction, part of the enzyme molecule called active sites temporarily combine with parts of the substrate, forming the enzyme-substrate complex.

14. Enzyme Action When the substrate changes it shape due to the interaction, it is more able to react, products are formed and the enzyme is released. The speed of an enzyme controlled reaction depends partly on the number of enzyme and substrate molecules in the cell. The efficiency of different enzymes is different. Some enzymes can catalyze a few substrate molecules per second, while others can catalyze thousands per second.

16. Factors That Alter Enzymes Since almost all enzymes are proteins, they can be denatured by high heat, radiation, electricity, certain chemicals of certain fluids with extreme pH values. For example many enzymes are inactive at 45C and most are denatured at 55C. KCN denatures respiratory enzymes.

17. Cofactors and Coenzymes Some enzymes are inactive until they combine with a nonprotein component. These are called cofactors or coenzymes. Cofactors will be ions of elements like copper or iron or zinc and coenzymes will be small organic molecules such as vitamin molecules.

18. Book Quiz 1.What is the difference between the following terms: chromatin, chromosomes, DNA, gene. When a cell is not actively dividing, its nucleus contains chromatin, a tangle of fibers composed of protein and DNA. During cell division chromatin organizes itself into chromosomes. Each chromosome contains a DNA molecule, and each DNA molecule is made up of many genes. Genes are individual segments of DNA that contain the instructions needed to direct the synthesis of a protein with a specific function.

19. Book Quiz 2.What is a nucleoside, nucleotide and a polynucleotide? A nucleoside is a base and a sugar. A nucleotide is a base a sugar and a phosphate group. A polynucleotide is a string of many nucleotides. Base SugarPhosphate

20. Book Quiz 3.There are five Nitrogen bases in nucleic acids. Name them and group them according to their structure. Which of the five bases is found only in RNA and which base does it substitute? Adenine…Thymine Guanine…Cytosine Uracil replaces Thymine in RNA http://www.dnatutorial.com/Nucleosides.sht ml http://www.dnatutorial.com/Nucleosides.sht ml

21. Book Quiz 4.What makes DNA and RNA different? DNA (deoxyribonucleic acid) Sugar is deoxyribose, DNA is a polymer of deoxyribonucleotides, bases are adenine, guanine, cytosine and thymine RNA (ribonucleic acid) Sugar is ribose, RNA is a polymer of ribonucleotides, bases are adenine, guanine, cytosine and uracil (instead of thymine)

22. Book Quiz 5.What sequence of bases of one strand of DNA is complementary to the sequence... T-A-T-G-C-A-G A-T-A-C-G-T-C

23. Quiz 1.Is dehydration synthesis anabolic or catabolic? 2.Is hydrolysis anabolic or catabolic? 3.What type of molecule controls metabolic reactions? 4.How can these molecules be altered in a negative way? 5.Explain with a drawing and words how the enzyme-substrate concept works.

24. 6.What is the difference between the following terms: chromatin, chromosomes, chromatids. 7.What is a nucleoside, nucleotide and a polynucleotide? 8.There are five nitrogenous bases in nucleic acids. Name them and pair them with their buddies. Which of the five bases is found only in RNA and which base does it substitute?

25. 9.What makes DNA and RNA different? 10.What sequence of bases of one strand of DNA is complementary to the sequence...AAA-TCG-CCT… 11.What mRNA molecule will be built from this template strand of DNA?

26. Energy for Metabolic Reactions Energy is the capacity to change or move matter—the ability to do work. So, we recognize energy by what it has done. Common forms of energy are heat, light, sound, electrical energy, mechanical energy and chemical energy. Most metabolic processes use chemical energy.

27. Release of Chemical Energy Chemical energy is held in the bonds between the atoms of molecules and is released when these bonds are broken. These reactions generally start by applying heat to activate the burning process. As the chemical burns, bonds break, and energy escapes as heat and light. Cells “burn” glucose molecules in a process called oxidation. The energy released by the oxidation of glucose powers the reactions of cellular metabolism.

28. Cellular Respiration Glycolysis, the citric acid cycle and the electron transport chain are the three separate steps to cellular respiration. See Figure 4.5 on page 77 for an overview. The products of these reactions include CO 2, H 2 O and energy. Most of the energy is lost as heat to warm the body, however, much is captured in the form of high energy electrons that the cell uses for the synthesis of ATP (adenosine triphosphate).

29. Glycolysis Cellular respiration begins with glycolysis… which means the breaking of glucose. Glycolysis takes place in the cytosol (liquid portion of cytoplasm). It does not require O 2 so it is often referred to as the anaerobic phase of cellular respiration. Glycolysis breaks a glucose molecule into 2 pyruvic acid molecules, 2 ATP molecules and 2 high energy electrons.

30. CA Cycle and e - Transport Chain If oxygen is available the pyruvic acid enters the mitochondria where the citric acid cycle and the electron transport chain take place. The electron transport chain reactions add phosphates to ADP to make ATP. These reactions are also called oxidative phosphorylation. These aerobic reactions yield 36 ATP molecules per glucose molecule + the 2 from glycolysis yields 38 total ATP molecules for each glucose. CO 2 and water are also produced through cellular respiration.

31. Metabolic Pathways Anabolic and catabolic reactions, along with cellular respiration have a number of steps that must occur in a specific sequence. The enzymes that control the rates of these reactions must happen in a specific sequence and they must be positioned correctly inside the cell to do this. A sequence of enzyme controlled reactions is called a metabolic pathway.

32. Metabolic Pathways It is possible to have too many substrates for the enzymes to catalyze. When this happens there is a build up of that particular substrate. If there is 100 enzymes to catalyze 100 different substrates, the one that slows the pathway down is called the rate determining enzyme. It is usually the first enzyme in the series so there is not a build up of any intermediate substrate in the cell.

33. Metabolic Pathways We only looked briefly at glucose coming into cellular respiration through glycolysis, but proteins and fats can also come into cellular respiration to release ATP (energy). The most common point of entry is in the CA cycle as acetyl coenzyme A or acetyl CoA.

34. Nucleic Acids Because enzymes control the metabolic processes that enable cells to survive, cells must have instructions for producing these specialized proteins, as well as, many other types of proteins. DNA molecules hold such information in the form of a genetic code. The code “instructs” cells how to synthesize enzymes and other specific protein molecules.

35. Genetic Information Genetic information in the form of DNA passes from parents to child. The portions of DNA molecules that contain the genetic information for making particular proteins are called genes. So, the inherited traits are determined by the genes contained in the parents’ sex cells (egg/sperm), which fuse to form the first cell of an offspring’s body.

36. Genetic Information As an offspring develops, mitosis passes the information from cell to cell. Genetic information “tells” the cell of the developing body how to construct specific protein molecules, which in turn function as structural materials, enzymes, or other vital biochemicals. In other words, genes instruct cells to synthesize the enzymes that control metabolic pathways.

37. DNA Molecules The building blocks of nucleic acids are nucleotides joined so that the sugar and phosphate portions alternate. They form a long backbone to the polynucleotide chain. In a DNA molecule, the organic bases project from this backbone and bind weakly to the bases of the second strand resembling a ladder. The organic base of a DNA nucleotide can be one of four types: adenine, thymine, cytosine or guanine.

39. DNA Molecules Both strands of a DNA molecule consist of nucleotides in a particular sequence. The bonding between organic bases is set as A to T and C to G called complementary base pairing. A DNA strand with base sequence of G, A, C, T joins to a second strand with the sequence C, T, G, A. The sequence of base pairs along a DNA molecule encodes the genetic information that specifies a particular protein’s AA sequence. A DNA molecule twists to form a double helix.

40. DNA Molecules The building blocks of nucleic acids are nucleotides joined so that the sugar and phosphate portions alternate. They form a long backbone to the polynucleotide chain. In a DNA molecule, the organic bases project from this backbone and bind weakly to the bases of the second strand resembling a ladder. The organic base of a DNA nucleotide can be one of four types: adenine, thymine, cytosine or guanine.

41. DNA Molecules Proteins, carbohydrates, lipids and nucleic acids all depend on the instructions written on the genes. This is true because proteins function as enzymes which are necessary for the chemical reactions in the cell. And since proteins are involved in so many aspects of cell function, genes provide the instructions that are necessary for cell survival.

42. Protein Making Instructions Genetic information contains the instructions for making proteins. Because proteins consist of 20 types of AA joined in specific sequences, the genetic information must tell how to position the AA correctly in a polypeptide chain. Each of the 20 AA types is represented in a DNA molecule by a particular sequence of 3 nucleotides. So, GGT represents one AA, while GCA represents another and TTA represents a third.

43. Protein Making Instructions This method of storing information for protein synthesis is the genetic code. Other nucleotide sequences represent the instructions for beginning or ending the synthesis of a protein molecule. These are called start or stop codes for protein synthesis.

44. Transcription Remember that DNA molecules are in the nucleus and that protein synthesis happens in the cytoplasm. So, DNA information must be carried from the nucleus to the cytoplasm by molecules of messenger RNA or mRNA in a process called transcription. RNA is like DNA except RNA is single stranded, ribose is the sugar and thymine is replaced by uracil nucleotides.

45. Transcription mRNA is synthesized by the enzyme RNA polymerase according to the rules of complementary base pairing. The DNA double strand unzips and the RNA polymerase reads the strand of DNA with the information and makes the needed mRNA strand. So, if the sequence of DNA is ATGCG, the mRNA made will be UACGC.

46. Transcription Somehow the enzyme knows which strand to read, which direction to follow and when to start and stop. Once this process is complete, the mRNA is made, the DNA zips back up and transcription is now complete. Next comes translation…

47. Translation The mRNA leaves the nucleus and work together with a ribosome. Recall that each AA in a protein was originally represented by a series of 3 bases in DNA. Those AA, in proper order, are represented by a series of 3 bases sequences called codons in mRNA. In the ribosome, the series of codons on mRNA will be converted from the language of nucleic acids to the language of AA.

48. Translation Another type of RNA called transfer RNA, tRNA, is responsible for seeing the next codon in line on the mRNA in the ribosome and gather the appropriate AA to add to the growing protein chain. Since there are about 20 different AA, there are about 20 different tRNA molecules responsible for attaching their particular AA to the chain. Table 4.1 on page 82 shows the AA/codon pairs. Figure 4.13 on page 83 shows a good picture of how translation occurs.

49. Replication When a cell divides, each newly formed cell requires a copy of the parent cell’s genetic information. To accomplish this, DNA molecules must be duplicated or replicated. As replication begins, hydrogen bonds between complementary base pairs of the double strands break. Then the double helix unwinds.

50. Replication New DNA nucleotides form complementary pairs with the exposed bases and enzymes knit the two new strands to the original strands. These two new DNA molecules become incorporated into replicate copies of a chromosome and separate during mitosis so that one passes to each of the newly forming cells.