1. Chapter 4 Cellular Metabolism

2. 4 - 2 u Introduction A living cell is site of enzyme-catalyzed metabolic reactions that maintain life.

3. 4 - 3 Metabolic Processes Metabolic reactions have two types: -Anabolic reactions larger molecules are constructed from smaller ones, a process requiring energy -Catabolic reactions, larger molecules are broken down, releasing energy, reactions of metabolism are reversible

4. 4 - 4 Anabolism -provides substances needed for growth and repair ; reactions occur by dehydration synthesis, removing a molecule of water to join two smaller molecules

5. 4 - 5 Polysaccharides, lipids, and proteins are constructed via dehydration synthesis Form fats, glycerol and fatty acids bond Bond between two amino acids is a peptide bond; two bound amino acids form a dipeptide, while many joined form a polypeptide

6. 4 - 6

7. 4 - 7 Catabolism -breaks apart larger molecules into their building blocks; reactions occur by hydrolysis, a molecule of water is inserted into a polymer which is split into two smaller molecules

8. 4 - 8 Control of Metabolic Reactions Enzymes control rates of cell metabolic reactions They are complex proteins that lower activation energy of a reaction so it proceeds more rapidly. Enzymes are called catalysts. They work in small quantities and are recycled They are specific, acting on only one kind of substrate

9. 4 - 9 Factors that alter enzymes Enzymes (proteins) can be denatured by heat, pH extremes, chemicals, electricity, radiation, and other causes

10. 4 - 10 Energy for Metabolic Reactions Energy is capacity to do work Common forms of energy include heat, light, sound, electrical, mechanical, and chemical energy

11. 4 - 11 Release of Chemical Energy Cellular Respiration Occurs through oxidation of glucose Burning glucose requires energy and end- products of these reactions are heat and stored energy, called ATP, which has a chain of 3 phosphates

12. 4 - 12 ATP Molecules Up to 38 molecules of ATP are produced for each molecule of glucose oxidized Energy is stored while converting ADP to ATP; when energy is released, ATP becomes ADP, ready to be regenerated into ATP

13. 4 - 13 Anaerobic Respiration First part of cellular respiration is splitting of 6-C glucose that occurs through a series enzyme-catalyzed steps called glycolysis The result is two 3-C molecules of pyruvate Glycolysis occurs in cytosol and doesn’t require oxygen (is anaerobic) Energy from ATP is used to start process but there is a net gain of energy as a result

14. 4 - 14 Aerobic Respiration Oxygen is needed for aerobic respiration, which occurs within mitochondria There is a much greater gain of ATP molecules from aerobic respiration The final products of glucose oxidation are carbon dioxide, water, and energy

15. 4 - 15

16. 4 - 16 Metabolic Pathways Enzymes controlling either an anabolic or catabolic sequence of reactions must act in a specific order A sequence of enzyme-controlled reactions is called a metabolic pathway

17. 4 - 17 Regulation of Metabolic Pathways Rate of a metabolic pathway is determined by a regulatory enzyme responsible for one of its steps A rate-limiting enzyme is first step in a series

18. 4 - 18 Nucleic Acids & Protein Synthesis Deoxyribonucleic acid (DNA) contains genetic code needed for synthesis protein (including enzymes) required by cell A gene is a portion of a DNA molecule that contains genetic information for making a single protein

19. 4 - 19 DNA Molecules Nucleotides of DNA form a sugar-phosphate backbone with bases extending into interior of DNA molecule Nucleotides of one DNA strand are compatible to those in other strand (adenine pairs with thymine; cytosine with guanine) and so exhibit complementary base pairing DNA molecule twists to form a double helix and may be millions of base pairs long

20. 4 - 20 Genetic Code Sequence of nucleotides in a DNA molecule gives sequence of amino acids for a given protein Method of storing information for protein synthesis is genetic code RNA molecules copy and transfer this information to cytoplasm where proteins are manufactured

21. 4 - 21 RNA Molecules RNA molecules are single-stranded and contain ribose rather than deoxyribose, and uracil rather than thymine Messenger RNA (mRNA) molecules are synthesized in nucleus in a sequence complementary to DNA template in a process called transcription

22. 4 - 22 Each amino acid corresponds to a triplet of DNA nucleotides; a triplet of nucleotides in messenger RNA is called a codon Messenger RNA can move out of nucleus and associate with ribosomes in cytoplasm where protein will be constructed in a process called translation

23. 4 - 23 Protein Synthesis In cytoplasm, a second kind of RNA, called transfer RNA, has a triplet of nucleotides called anticodon, which is complementary to nucleotides of messenger RNA codon Ribosome holds messenger RNA in position while transfer RNA carries in correct amino acid in sequence, with anticodons matching up to codons Ribosome contains enzymes needed to join amino acids together As amino acids are joined, new protein molecule into its unique shape

24. 4 - 24

25. 4 - 25

26. 4 - 26 DNA Replication Each new cell must be provided with an exact replica of parent cell's DNA DNA replication occurs during interphase -DNA molecule splits -Nucleotides form complementary pairs with original strands Each new DNA molecule consists of one parental strand and one newly-synthesized strand of DNA

27. 4 - 27