LIFESCI 2N03 Lecture Notes - Very Low-Density Lipoprotein, Cardiac Muscle, Muscle Tissue

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LECTURE 4 LIFESCI 2N03
1
Lecture 4: Bioenergetics
September 30, 2013
Metabolism
Sum of all chemical reactions that occur in the body
Anabolic reactions synthesis of molecules
Catabolic reactions breakdown of molecules
Bioenergetics converting foodstuffs (fats, proteins,
carbohydrates) into energy
Eukaryotic Cells
DNA is kept in a close and distinct compartment
Mitochondrion energy factory; where the cell makes the
money “money” allowing the cell to do certain things
Cellular Membrane major source of cellular electricity
(Na+ and K+ flowing across membrane creating an action
potential) and intra-cellular signaling; selectively keeps
cell in/out of cell;
o Eg/ insulin will signal increase in cellular uptake
of glucose; has to signal to cells on receptors on
cell membrane
Nucleus home of cells genes; making new proteins for
muscle cells to enable it to produce more force
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 ribosomes by tRNA
5. In translation, mRNA is used to determine the arrangement of
amino acids in the polypeptide chain
o Amino acids (dietary) supplies; increase enzymes to increase
cell capability of breaking down sugar or fat as a substrate of
energy; amino acids are the building blocks of enzymes
(proteins)
o Process
Exercise (muscle contract) begins process
Dietary amino acids ingestion of amino acids may be
sufficient to begin synthesis of proteins
Anabolic steroids synthetic drugs that stimulate
process faster (go directly to DNA, increases rate of
synthesis; not allowed in athletics)
Endergonic reactions require energy; endothermic
Exergonic reactions release energy (transfer to mechanical and/or
chemical and thermal); exothermic
Oxidation and reduction are coupled reactions
o Oxidation removing an electron
o Reduction addition of an election
o Often involve transfer of H atom rather than free election
H atom contains one electron
A molecule that loses H also loses an electron; therefore
is oxidized
o NAD oxidizing agent; electron carrier; can readily bind
electrons; becomes reduced
o NADH reducing agent; loses an electron; becomes oxidized
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LECTURE 4 LIFESCI 2N03
2
Enzymes
Enzymes catalysts that regulate the speed of reactions; lower the activation energy
Factors that regulate regular enzyme activity
o Temperature
o pH
Figure: Sucrase binds disaccharide substrate (sucrose) and initiates chemical reaction to
break bond results in two monosaccharide (glucose and fructose); sucrose remains the
same, can go on to next disaccharide
Role in Metabolism speeds up the breakdown of macronutrients that will eventually
make us “money” (ATP, energy)
Effect of Temperature increase temperature = danger of denaturing enzymes
o Exercise requires temperature regulation, or else extensive damage can occur to
structural proteins and enzymes
Effect of pH increase acidity (lower pH) = enzyme activity decreases
Energy
Energy “substrates” – carbohydrates, fats and proteins
o Come from diet and storage (liver, glucose; muscle protein)
o Energy needed to form ATP
Muscle cell
1. Myosin ATPase contractile muscle and enzyme; can bind ATP and harness energy; responsible
for force production
2. SERCA sarco endoplasmic reticulum calcium ATPase; put calcium back after muscle
contraction, or keep muscle rested
3. Na+/K+ ATPase keeps muscles from contracting uncontrollably
ATPase enzyme that can bind to ATP; expend energy
SERCA and Na+/K+ ATPase are responsible for most metabolism during rest
Getting energy from substrates depends on
o Substrate availability diet is a factor
o Enzyme dynamics pH and temperature; exercise; eg/ if you do endurance training, you become better at
endurance activities
o Nervous system demand activate nervous system to activate muscle tissue
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LECTURE 4 LIFESCI 2N03
3
o Metabolic “backup” maximize usage of glucose, then body shifts to other energy substrate
Cellular Energy
o Mechanical events when phosphate is removed harnesses chemical energy to convert to mechanical energy and
thermal energy (60-70%)
Energy for Muscle Activity
o Formation of ATP
Phosphocreatine (PCr) breakdown
Degradation of glucose
Oxidative formation of ATP
o Anaerobic pathways
Do not involve O2
PC breakdown and glycolysis (breakdown of glucose)
Rapid
Enzymes in cytoplasm
o Aerobic pathways
Require O2
Oxidative phosphorylation (glucose, fat and protein)
Enzymes in mitochondria
Creatine
Non-essential dietary element; found in meat and fish
o Cooking meat destroys creatine don’t need to ingest because our body makes it (non-essential)
Greek derivative; kreas = flesh
Found primarily in skeletal muscle, heart, spermatozoa, retinal cells
`
3-5 sec
Exercise
8-12 sec
Time
% contribution to ATP
ATP
PCr
Glycolysis
Oxidative phosphorylation, O2
Use glucose and fat, protein is last resort
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