lecture 6a introduction to bioenergetics
TRANSCRIPT
Faculdade de Desporto, Universidade do Porto, 1º Ciclo, 1º Ano
2012_2013
BIOQUÍMICA E BIOLOGIA CELULAR
António Ascensão, José Magalhães
IntroducMon to bioenergeMcs
Aims
1. Define the following terms: (1) endergonic reac+ons, (2) exergonic reac+ons, (3) coupled reac+ons, and (4) bioenerge+cs.
2. Describe the role of enzymes as catalysts in cellular chemical reacMons.
3. List and discuss the nutrients that are used as fuels.
4. IdenMfy the high-‐energy phosphates.
Aims
6. Discuss the biochemical pathways involved in anaerobic ATP producMon.
7. Discuss the aerobic producMon of ATP. 8. Describe the general scheme used to regulate
metabolic pathways involved in bioenergeMcs. 9. Discuss the interacMon between aerobic and
anaerobic ATP producMon. 10. IdenMfy the enzymes that are considered rate
limiMng in glycolysis and the Krebs cycle.
Outline
§ Biological Energy Transforma2on Cellular Chemical Reac+ons Oxida+on-‐Reduc+on Reac+ons Enzymes
§ Fuels for Exercise Carbohydrates Fats Proteins
§ High-Energy Phosphates
§ Bioenergetics Anaerobic ATP Production Aerobic ATP production
§ Aerobic ATP § Efficiency of Oxidative
Phosphorylation
§ Control of Bioenergetics
Control of ATP-PC System Control of Glycolysis Control of Krebs Cycle
and Electron Transport Chain
§ Interaction Between Aerobic/Anaerobic ATP Production
General concepts and noMons
• Metabolism – Sum of all chemical reacMons that occur in the body – Anabolic reacMons
• Synthesis of molecules
– Catabolic reacMons • Breakdown of molecules
• BioenergeMcs – ConverMng foodstuffs (fats, proteins, carbohydrates) into energy
General concepts and noMons
• Study of molecular structures and events underlying biological processes – RelaMonship between genes and cellular characterisMcs they control
• Genes code for specific cellular proteins – Process of protein synthesis
• Exercise training results in modificaMons in protein synthesis – Strength training results in increased synthesis of muscle contracMle protein
• Molecular biology provides “tools” for understanding the cellular response to exercise
Steps leading to protein synthesis
1. DNA contains information to produce proteins.
2. Transcription produces mRNA.
3. mRNA leaves nucleus and binds to ribosome.
4. Amino acids are carried to the ribosome by tRNA.
5. In translation, mRNA is used to determine the arrangement of amino acids in the polypeptide chain.
Cellular chemical reacMons
• Endergonic reacMons – Require energy to be added – Endothermic
• Exergonic reacMons – Release energy – Exothermic
• Coupled reacMons – LiberaMon of energy in an exergonic reacMon drives an endergonic reacMon
OxidaMon-‐reducMon reacMons
• OxidaMon – Removing an electron
• ReducMon – AddiMon of an electron
• OxidaMon and reducMon are always coupled reacMons
• Ofen involves the transfer of hydrogen atoms rather than free electrons – Hydrogen atom contains one electron – A molecule that loses a hydrogen also loses an electron and therefore is oxidized
• Importance of NAD and FAD
Enzymes
• Catalysts that regulate the speed of reacMons – Lower the energy of acMvaMon
• Factors that regulate enzyme acMvity – Temperature – pH
• Interact with specific substrates – Lock and key model
The Lock-‐and-‐Key Model of Enzyme AcMon
a) Substrate (sucrose)
approaches the active
site on the enzyme.
b) Substrate fits into the
active site, forming
enzyme-substrate
complex.
c) The enzyme releases
the products (glucose
and fructose).
DiagnosMc Value of Measuring Enzyme AcMvity in the Blood
• Damaged cells release enzymes into the blood – Enzyme levels in blood indicate disease or Mssue damage
• DiagnosMc applicaMon – Elevated lactate dehydogenase or creaMne kinase in the blood may
indicate a myocardial infarcMon
ClassificaMon of Enzymes
• Oxidoreductases – Catalyze oxidaMon-‐reducMon reacMons
• Transferases – Transfer elements of one molecule to another
• Hydrolases – Cleave bonds by adding water
• Lyases – Groups of elements are removed to form a double bond or added to a double bond
• Isomerases – Rearrangement of the structure of molecules
• Ligases – Catalyze bond formaMon between substrate molecules
Factors That Alter Enzyme AcMvity
• Temperature – Small rise in body temperature increases enzyme acMvity
– Exercise results in increased body temperature
• pH – Changes in pH reduces enzyme acMvity – LacMc acid produced during exercise
Macromolecules -‐ Carbohydrates
• Glucose – Blood sugar
• Glycogen – Storage form of glucose in liver and muscle
• Synthesized by enzyme glycogen synthase
– Glycogenolysis • Breakdown of glycogen to glucose
Macromolecules -‐ Fats
• Fajy acids – Primary type of fat used by the muscle – Triglycerides
• Storage form of fat in muscle and adipose Mssue • Breaks down into glycerol and fajy acids
• Phospholipids – Not used as an energy source
• Steroids – Derived from cholesterol – Needed to synthesize sex hormones
Macromolecules -‐ Proteins
• Composed of amino acids • Some can be converted to glucose in the liver
– Gluconeogenesis • Others can be converted to metabolic intermediates – Contribute as a fuel in muscle
• Overall, protein is not a primary energy source during exercise
BioenergeMcs
• FormaMon of ATP – PhosphocreaMne (PC) breakdown – DegradaMon of glucose and glycogen
• Glycolysis – OxidaMve formaMon of ATP
• Anaerobic pathways – Do not involve O2 – PC breakdown and glycolysis
• Aerobic pathways – Require O2 – OxidaMve phosphorylaMon