BIOL 380 Lecture Notes - Lecture 6: Adenosine Triphosphate, Catabolism, Potential Energy
26 May 2018
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BIOL 380 – Lecture 6 – Metabolism
- Metabolism is the sum of all chemical and physical processes by which the
body breaks down and builds up molecules
- the process of making larger, chemically complex molecules from smaller,
more basic ones is called anabolism
o critical for growth, repair, maintenance, and synthesis of chemical
products essential for human functioning
o requires energy
- catabolism is the breakdown or degradation of larger, more complex
molecules to smaller, more basic molecules
o begins with digestion –
chemical reactions break down proteins, lipids,
carbohydrates
o old cells or tissues are broken down for repair
or replacement
o energy is released as a by-product of this
intracellular catabolism
- we never have 100% efficiency yield in terms of
converting all of the energy bonds into ATP
Adenosine Triphosphate (ATP)
- ATP is an organic compound used by cells as a source of energy
o Potential energy is stored in the high-energy phosphate bonds
o When bonds are broken, energy is released
o This energy is used to keep cells functioning
- when ATP is broken, and the
phosphorus group is removed,
the energy from that bond =
phosphorylating other things,
transfers energy to that
molecule
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2
Metabolic reactions
- Condensation is an anabolic process
o Simple units combine to form a larger,
more complex molecule
o Water is released as a by-product
- Hydrolysis is a catabolic process
o A large molecule is broken apart with
the addition of water
- Phosphorylation: addition of a phosphate
group to a compound (done by kinases)
- Dephosphorylation: removal of a phosphate group from a compound (doe by phosphorylases)
- When the high-energy phosphate bonds in ATP are broken
o Energy is released
o Phosphate is transferred to other molecules
Phosphorylated glucose
- Phosphorylated glucose can either be oxidized for energy
or stored as glycogen
- glucose is phosphorylated by hexokinase or glucokinase
(most tissues use hexokinase)
- the liver has different kinetic properties based on what it wants to do (use glucose, or store it)
glucokinase catalyzes the phosphorylation of glucose but found predominantly in the liver
- G6P has 3 different fates
- phosphorylation keeps the glucose in the cell (charged things do not leave the PM of the cell)
oxidation and reduction
- molecule donating an electron is oxidized
- molecule acquiring an electron is reduced
- FADH2 is easily oxidized, losing electrons as
hydrogen, and forming FAD. In contrast, FAD is
easily reduced back to FADH2, by the simple addition of hydrogen
Metabolic enzymes
- Enzymes catalyze chemical reactions (by decreasing the
activation energy)
- Coenzymes are non-protein substances that enhance or
are necessary for enzyme activity
o FAD, FADH2 and vitamins function as coenzymes
- Cofactors are typically minerals required for enzyme
activity
o Iron, magnesium and zinc function as cofactors
o Non-energy containing micronutrients ensure that energy can be extracted from food
* apoenzyme is protein part only
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3
Energy from carbohydrates
- Glucose transported to the liver is;
1. Phosphorylated and metabolized for energy or stored as glycogen
2. Released into circulation for other cells to use as fuel or stored as glycogen (muscle tissue)
3. Converted to fatty acids (if glucose exceeds energy needs) and stored as triglycerides in
adipose tissue
- Fructose and galactose are converted to glucose in the liver and they follow the same process
Glycolysis
- 6 carbon glucose is converted into 2 molecules of 3 carbon pyruvate
- 1st step – phosphorylation of glucose = glucose-6-phosphate and ADP
- Initially the process of glycolysis requires 2 ATP for the phosphorylation of glucose, but
eventually this pathway produces a 4 ATPs, so net of 2 ATP
- Glycolysis = oxidative pathway, because 2 hydrogen atoms are picked up
by the coenzyme NAD, forming NADH, the reduced form of NAD
- 2 ATPs for every glucose molecules
- galactose is v similar to glucose in terms of its structure (steroisomer)
galactose is phosphorylated into galactse-1-phosphate and then it enters
as glucose-6-phosphate
- FRUCTOSE: enters into glycolysis somewhere around 2 G3Pfructose -1-
phosphate, broken down into 2 3 carbon molecules, one is
phosphorylated, one is not, then one gets phosphorylated - so it enters
at 2G3Pfructose-1-phosphate becomes G3P
In the presence of oxygen
- Aerobic conversion of pyruvate to acetyl CoA
- in the absence of oxygen this does not occur
- terminal step in anaerobic conditions
TCA cycle
- continuous circle of 8 metabolic reactions
- first step – entry of acetyl CoA
- the 2 carbon acetyl CoA reacts with 4 carbon oxaloacetate
to form six carbon citrate
- releases CO2, GTP, 8 hydrogen with their electrons are transferred to
2 coenzymes: NAD+ and FAD → producing NADH and FADH2
- acetyl coA now found in mitochondrion
- acetyl CoA (2 carbon molecules) undergo condensation with
oxaloacetate yielding the 6 carbon citrate2 important reduction rxn to
generate NADH
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
We never have 100% efficiency yield in terms of converting all of the energy bonds into atp. Atp is an organic compound used by cells as a source of energy: potential energy is stored in the high-energy phosphate bonds, when bonds are broken, energy is released, this energy is used to keep cells functioning. When atp is broken, and the phosphorus group is removed, the energy from that bond = phosphorylating other things, transfers energy to that molecule. Condensation is an anabolic process: simple units combine to form a larger, more complex molecule, water is released as a by-product. Hydrolysis is a catabolic process: a large molecule is broken apart with the addition of water. Phosphorylation: addition of a phosphate group to a compound (done by kinases) Dephosphorylation: removal of a phosphate group from a compound (doe by phosphorylases) When the high-energy phosphate bonds in atp are broken: energy is released, phosphate is transferred to other molecules.
