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CHAPTER 4: CELLULAR METABOLISM METABOLIC REACTIONS • 2 major types: Anabolism & Catabolism • Anabolism • Provides biochemicals required for cell growth & repair • Ex. Cells join many monosaccharides into a chain to form larger molecules of glycogen using an anabolic process called dehydration synthesis • Ex. Links glycerol & fatty acid molecules in fat (adipose) cells to form triglycerides • Ex. Join amino acid molecules to build protein molecules; water molecule forms & a peptide bond joins the two amino acid molecules together • Two bound amino acids form a dipeptide & many joined in a chain form a polypeptide • Polypeptides with specific functions consisting of ~ 100 or more amino acid molecules is called a protein CATABOLISM • Physiological processes that break larger molecules into smaller ones • Hydrolysis is an example • Decomposes carbohydrates, lipids, and proteins & splits a water molecule in the process • Hydrolysis of a disaccharide like sucrose yields two monosaccharides glucose & fructose • Hydrolysis occurs during digestion • Breaks down carbohydrates into monosaccharides • Fats into glycerol & fatty acids • Proteins into amino acids • Nucleic acids into nucleotides CONTROL OF METABOLIC REACTIONS • Metabolic reactions require energy to happen • The temperature in cells is usually too mild to promote the reactions required to support life enzymes make these reactions possible • Enzymes are almost always proteins & promote chemical reactions within cells by lowering the amount of energy required to start these reactions • Enzymes speed the rates of metabolic reactions (catalysis) • Enzymes are required in small quantities because if they are not completely consumed they can be recycled • Each enzyme only acts on a particular chemical (substrate) • Ex. Catalase’s substrate is hydrogen peroxide • During an enzyme –controlled reaction, parts of the enzyme molecule combine with portions of the substrate • Forms an enzyme-substrate complex • The interaction between the molecules distorts or strains the chemical bonds within the substrate this increases the likelihood that the reaction will occur • Many enzymatic reactions are reversible FACTORS THAT ALTER ENZYMES • Almost all enzymes are proteins so they can be denatured by exposure to heat, radiation, electricity, certain chemicals or fluids with extreme pH values • Temperature also affects enzymes • Many become inactive at 45 oC and nearly all are denatured at 55 oC • Poisons can denature enzymes • Cyanides interfere with respiratory enzymes, this impairs a cell’s ability to release energy from nutrient molecules ENERGY FOR METABOLIC REACTIONS • Energy is the capacity to change or move matter; the ability to do work • Common forms of energy are heat, light, sound, electrical energy, mechanical energy & chemical energy RELEASE OF CHEMICAL ENERGY • Most metabolic processes use chemical energy • It is held in the bonds between atoms and is released when the bond breaks • Oxidation • Cells burn glucose molecules • This powers the reactions of cellular metabolism • Oxidation inside cells differs from the burning of substances outside cells • ‘Burning’ requires a large amount of energy to begin; most of the energy released escapes as heat or light • Enzymes reduce the amount of energy required for oxidation in cells GLYCOLYSIS • Enzymes break down glucose in the cytosol into 2 three-carbon pyruvic acid molecules • Does not require O 2 so it is the anaerobic phase of cellular respiration • Requires some energy more is released than consumed • This excess energy is used to synthesize ATP AEROBIC RESPIRATION • Second phase following glycolysis • Oxygen must be present for this phase to happen • Happens inside the mitochondria & transfers considerably more energy to ATP molecules • When glucose breakdown is complete, CO 2 & H2 remains • CO2 diffuses out of the cell as waste • H2 combine with O 2 to form water ATP MOLECULES • For each glucose molecule that is decomposed completely, 38 molecules of ATP can be produced • 2 from glycolysis, the rest from aerobic respiration • ATP molecules break apart to release energy for a variety of functions • Muscle contraction, active transport, synthesis of various compounds • ATP molecules that are broken apart becomes an ADP molecule • ADP can convert back into ATP by capturing energy & a phosphate 1. Describe the metabolic pathways of carbohydrates, lipids, & proteins. 2. What are the products fro each of the metabolic pathways above? 3. Explain how DNA & RNA store and carry genetic information. 4. Explain how genetic information controls cellular processes. 5. How do DNA molecules replicate? RNA MOLECULES • Messenger RNA (mRNA) – carries the information in a gene’s nucleotide sequence from the nucleus to the cytoplasm • Synthesis of mRNA begins when the enzyme RNA polymerase associates w/ the DNA base sequence at the beginning of a gene • Other enzymes begin to unwind and pull apart the double stranded DNA molecule • This exposes the first portion of a gene • RNA polymerase then moves along this strand • Exposes other portions of the gene & stringing together mRNA from nucleotides • Complimentary to those along the unwound DNA strand RNA MOLECULE • EX) If the DNA bases sequence is: A T G C G T A A C A • The complimentary bases in the mRNA molecule will be: U A C G C A U U G U • RNA polymerase somehow knows which of the two DNA strands contains this information • It also knows the correct direction to read DNA • (Just like reading a sentence in a book) RNA MOLECULE • RNA polymerase continues to move along the DNA strand exposing the gene until it gets to a specific DNA base sequence that represents the end of a gene • Called the termination signal • The mRNA molecule is released by RNA polymerase & leaves the DNA • Transcription: process of copying DNA information into the structure of mRNA RNA MOLECULE • Because an amino acid is encoded by a particular sequence of 3 nucleotides in a DNA molecule, the transcribed mRNA represents the complementary set of 3 nucleotides of the amino acid • Codon: a triplet of nucleotides in mRNA that specifies a particular amino acid • Translation: when mRNA molecules associate with ribosomes & act as patterns or templates for the synthesis of protein molecules