Cell Metabolism 2023-1 (1).ppsx

Cell Metabolism Chapter 17 Objectives • To understand cell metabolism & be able to describe the two types & list the events that occur in each stage • To understand the role enzymes play in cell metabolism • To discuss briefly the metabolic pathways (carbohydrates, lipids, proteins) • To understan...

Cell Metabolism Chapter 17 Objectives • To understand cell metabolism & be able to describe the two types & list the events that occur in each stage • To understand the role enzymes play in cell metabolism • To discuss briefly the metabolic pathways (carbohydrates, lipids, proteins) • To understand cellular respiration & be able to describe the processes of anaerobic (glycolysis) & aerobic (Kreb’s Cycle, e- transport) respiration • To understand the processes involved in protein catabolism & anabolism Cell Metabolism • Each cell undergoes hundreds of metabolic reactions in its lifetime:      Building molecules Breaking down nutrients Manufacturing Packaging Excreting/Secreting Cell Metabolism • Divided into two categories  Catabolism -> breakdown nutrients & produce energy  Anabolism -> assemble new molecules & build large molecules & use stored energy • Occur simultaneously • Must be in balance with each other in order to maintain adequate levels of energy Catabolic Metabolism • Breakdown of larger molecules into smaller ones (produces energy)  proteins, carbohydrates (CHO) and fats • 3 Stages  Hydrolysis (occurs in lumen of GI tract)  Anaerobic respiration (occurs in cytoplasm of cells)  Aerobic respiration (occurs in mitochondria of cells) Hydrolysis = 1st stage of catabolism • One water molecule is used each time a nutrient molecule is broken down. Hydrolysis • Large sugar molecule can be broken down (hydrolyzed) into two smaller sugar molecules • Disaccharide + Water = 1 Monosaccharide + 1 Monosaccharide • Protein -> amino acids • Nucleic acids -> nucleotides • Fat -> fatty acids & glycerol Hydrolysis The smaller molecules produced by hydrolysis are absorbed through special absorptive cells (enterocytes) that line the small intestines and are then transported to other parts of the body via the circulatory & lymphatic systems See Fig. 17.8, pg 462 Second Stage of Catabolism = Anaerobic Respiration • Occurs intracellularly • Amino acids, glucose, glycerol and fatty acids enter the cell and are further catabolized in the cytoplasm • Process does not use oxygen • Produces acetyl-CoA which is used in the last step of catabolism = aerobic respiration Third Stage of Catabolism = Aerobic Respiration • Acetyl-CoA -> transported to the mitochondria where it is used in aerobic respiration • Requires oxygen • Involves attachment of an inorganic phosphate group (PO4) to adenosine diphosphate (ADP) forming ATP = the energy unit used in the cell to drive its biosynthetic processes Anabolic Metabolism • Cell uses energy in the form of ATP to manufacture substances and to perform many vital functions – Constructive • Biosynthetic process because biochemical substances are produced – – – – – – Proteins for cell membrane growth Cytoskeleton & more organelles Locomotion Production and secretion of hormones Active membrane transport processes Preparation for cell division Dehydration Synthesis • Opposite of hydrolysis – Simple sugars assembled to form chains of polysaccharides – Glycerol and fatty acids are connected to form fat molecules – Chains of amino acids are assembled to form proteins Control of Metabolic Reactions • Living cells are comprised of and contain thousands of molecules • Compartments created within or on the surface of organelles (mitochondria, ER, ribosome) isolate and allow chemical reactions between molecules to take place • Molecular reactions are initiated & controlled by formation & use of specialized proteins = Enzymes Enzymes • Enzymes react with substrates to produce a new molecule called a product • Enzyme reactions are highly specific – One enzyme reacts only w/ one or a combination of substrates • Energy is needed to initiate chemical reactions = energy of activation • Enzymes = catalysts – Substances that speed up reactions by lowering the activation energy Enzymes • Enzymes names end with the suffix -ase • Proteinases break down proteins • Lipases break down lipids • Lactase breaks down lactose, etc. • Synthetases -> synthesize • Transferases -> move parts of molecules Coenzymes and Cofactors • Some enzymes need a little help to complete a reaction. • Cofactors – Iron, zinc, copper, magnesium, calcium, potassium – Needed to complete the shape of a binding site • Nonprotein organic substances can act as cofactors but they are called coenzymes – Often derived from vitamins – Nicotinamide adenine dinucleotide (NAD) Metabolic Pathways – Complex series of biochemical steps that must occur in a particular sequence; each step involves an enzyme specific for that particular step • Carbohydrate Metabolism – Used to provide the energy to fuel metabolic functions such as absorption, secretion, excretion, mechanical work, growth and repair – CHO supplied through the diet (see pg 450-451) or from breakdown of glycogen, glycerol, or, in ruminants, propionate Anaerobic Respiration = Glycolysis • Process by which glucose is converted to G6P (via phosphorylation) then further broken down to form pyruvate (pyruvic acic) – Occurs in the cytosol – Does not require oxygen (anaerobic) – Requires use of 2 ATP molecules & 2 NAD molecules for every molecule of glucose metabolized – 2 molecules pyruvate, 4 of ATP & 2 of NADH are produced (so net energy yield is 2 ATP & 2 NADH) • Pyruvate -> mitochondria where it’s degraded further as part of Cellular Respiration Aerobic Respiration = Cellular Respiration (Oxidation) • Cellular process producing ATP (energy) for the cell from breathed oxygen • Occurs in the mitochondria in two stages: – Kreb’s Cycle (Citric Acid Cycle) – Electron Transport System Cellular Respiration • Pyruvate loses a carbon, becoming a 2 carbon acetyl group, then binds to coenzyme A forming acetyl-CoA • Now acetyl-CoA enters the Kreb’s Cycle, reacts w/ oxaloacetic acid to form citric acid, finally to be converted back to oxaloacetic acid & the whole process begins again • Each turn generates energy in the form of 1 ATP, 1 FADH2 & 3 NADH molecules (x2 per glucose molecule) • CO2 formed as a by product & diffuses out of the cell & into the blood as waste -> lungs & exhaled Cellular Respiration Final stage = Electron Transport System Produces majority of ATP for the cell Occurs in inner mitochondrial membrane FADH2 & NADH, which are at a very high energy level, are carried down the cytochrome chain (cytochromes = electron carrier molecules, each w/ a central core of iron that accepts electrons then releases them at a lower level) • Large amounts of free energy released is captured in the formation of ATP from ADP • Oxygen is the final acceptor of the low energy electrons & joins w/ H+ forming water (H2O) • • • • Review Summary of ATP Synthesis on pg Lipids • Lipids = molecules composed of carbon, hydrogen and oxygen (pg 452454) • Insoluble in water but dissolve easily in other lipids or in organic solvents • Two common types of lipids  Triglycerides – 1 glycerol molecule & 3 fatty acid chains  Phospholipids – phosphorus head & 2 fatty acid chains • Contain more chemical energy than carbohydrates or proteins (have higher # of C-H bonds & energy is stored in bonds between atoms) • Liver is the primary controller of lipid Lipid Metabolism • The liver can remove lipids from the blood & alter their structures  Broken into smaller fragments = lipolysis  Hydrolysis of triglycerides w/ subsequent fragmentation of fatty acid chains into multiple 2 carbon fragments (= betaoxidation), then conversion to acetyl-CoA or to ketone bodies • Energy gains from oxidation of fatty acid chain is about 4x more than that generated from catabolism of 1 molecule of glucose • Fat serves as energy reserve rather than a source to meet immediate energy Proteins • There are many different kinds of proteins each with a unique function and structure to fit its function      Structural (microtubules, hair, collagen) Regulatory (insulin, other hormones) Contractile (actin & myosin) Transport (hemoglobin, myoglobin) Storage, protective, membrane & osmoregulatory proteins also • Proteins = chains of amino acids (aa) linked by peptide bonds • Difference lies in type, # & sequence of aa • Several hundred aa used to form a protein Protein Metabolism • Proteins from food are hydrolyzed into aa by enzymes, proteases and peptidases, in the GI tract -> liver via hepatic portal system; liver controls subsequent release & use in nonhepatic tissues • 22 different aa; Some aa are not formed in the body and must be supplied in the diet = Essential amino acids • Most species require 10 • Felines require 11 (taurine) • Protein Catabolism • Occurs in most tissues but especially important in intestine, kidney, liver, brain & skeletal muscle • Occurs in mitochondria & require pyridoxine • 2 Processes: Deamination – amine group removed & becomes ammonia in liver -> converted to urea -> excreted in urine (See Clinical Application pg 475) Remaining carbon chain enters Kreb’s cycle to produce energy or be converted to glucose or fat Transamination - amine group transferred to another carbon chain forming another aa -> diffuses across mitochondrial Protein Anabolism (Chapter 4) • Types of proteins made depends on function of the cell • Protein synthesis begins in nucleus -> instructions in DNA transferred to mRNA (Transcription) using RNA polymerase & carried to cytoplasm where aa are assembled into proteins (Translation) on ribosomes (which are composed of protein & ribosomal RNA (rRNA)) w/ help of transfer RNA (tRNA) See Summary of Protein Synthesis Box 4.1, pg 102 Nucleic Acids (pg 42) • DNA & RNA • Made up of chains of nucleotides, each composed of:  Nitrogenous base  5-carbon sugar  Phosphate group • DNA molecules are divided into subunits called genes and the sequence of the nitrogenous bases makes up the genetic code • DNA replication occurs during interphase of mitosis & requires DNA polymerase (Read about Genetic Mutations on pg 98- Review • Two types of cell metabolism & the differences between the two • Hydrolysis and dehydration synthesis • Composition of carbohydrates, proteins, fat • Metabolism of each (briefly) • Enzymes and their role in cell metabolism • Cellular Respiration • Where protein catabolism & anabolism occur & the processes & molecules involved