BCH 261 Lecture Notes - Lecture 5: Negative Number, Entropy, Glycolysis
7 Jun 2018
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BCH 261 – 121 – Biochemistry
Professor Gagan Gupta
January 25, 2018
Mastering: Extended deadline date for the first set of assignments. Second set of assignment
deadlines stay as they are. Mastering grades everything they are weighted at the end of the course.
Introduction to Mastering assignment is not graded, it’s just for you to learn.
Lecture: Energy in Biological Systems (Section 2)
A key part of biochemistry is not only learning bonds and chemistry of structures, it’s also
understanding energy of the reactions molecules undergo and how they interact with the energetic
environment as a whole.
This and next lecture will cover everything you need to know about this section. It will introduce
several definitions and there are a couple equations you need to know. This will help you
understand what drives reactions forward or backward or keeps them in equilibrium.
Have to know what a lot of these concepts means a key concepts used to describe phenomena. No
labs associated with this section. We can’t move forward in our course without introducing these
equations and concepts.
Slide: Section 2: Energy in Biological Systems
1. Thermodynamics
2. Coupled reactions
3. Cellular energy sensing systems
Slide: First Law Thermodynamics
In a closed system energy is conserved. Consider the human body is closed, there’s a barrier
between you and the surroundings. In that barrier, there are various energy being produced,
mostly due to what you eat and the oxidation of that. That energy is provided by molecules that
have stored this energy. Energy used up by muscles that then will work.
First law – this energy is not destroyed. It’s converted from one form into another.
You cannot win, you can only break even. This energy came from somewhere, it will be used up
to do something, not destroyed, just converted to a different form. Whatever you put in, you
should get out. The form may change, but the energy currency hasn’t been destroyed.
Slide: Change in Enthalpy a Biochemical Reaction
Complex sugar burned in your body. It’s a solid that will react with oxygen. It will release a lot of
energy and the bi-products are carbon dioxide and water.
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The total energy stored in this system is referred to as the ethyl. Total heat content of the system.
That’s the eternal energy plus the product off the pressure and the volume of all molecules in the
system.
With regards to reactions at constant pressure, can be approximated to internal energy and also by
measuring the temperature change off the reaction.
∆ H…
For this reaction, ∆H is highly negative – a lot of H was given off in this reaction. This reaction is
often referred to as exothermic or exergonic. Two terms are interchangeable.
Slide: How do Restaurants Measure Calories in Food?
Energy food gives off is called calories. By law, restaurants have to post calorie counts on menu
items.
1 calorie of nutrient is 1 Kcal in chemistry which is 5.184 kj in thermochemistry. The text almost
always refers to energy in reactions in joules or kilojoules and not calories. You should be
familiar with switching back and forth between these three terms.
Slide: Measuring Changes in Enthalpy in Biochemical Reaction
Device – blow things up inside a sealed chamber.
Oxygen is fused in, a spark is given so a spark occurs. You combust the…at one bar – during
reaction a lot of heat is given off, the temperature of the water rises. This was a solid reacting
with oxygen to give off another gas, CO2 and water. The volume of the chamber increases
because the pressure is held constant. This volume changes. At the end of the reaction, you’ve
used up all your product and are left with just CO2 and a bit of water.
You can do this for every single food item and this is where you get the calorie value from. It’s
expensive to do this and is one reason food has become more costly over the years.
Slide: Back to Burning Fatty Acids: Where does the Released Energy Go?
In the calorimeter you are releasing heat and that’s how we record the release of energy. But in
biological system you store this energy not as released heat, which will be mostly wasted, but you
store it in a biological batty called ATP.
Slide: Second Law of Thermodynamics
In a closed system, the entropy – figure that measure randomness. If you are really random, you
have high entropy. As humans we are non anthropic entities and that’s probably why we need
2,000 calories per day to survive.
The experiment, you have sucrose in water, imagine you can visualize the molecules, if you
double the water, the sucrose will diffuse out. We intuitively know this happens. Diffusion occurs
for the desire of the universe to be more entropic. In a strict sense, this doesn’t require any extra
energy. These molecules were randomly diffusing to begin with and what you provided when
adding more water, was a bigger playground for them to diffuse in. These molecules were always
Document Summary
Mastering: extended deadline date for the first set of assignments. Second set of assignment deadlines stay as they are. Mastering grades everything they are weighted at the end of the course. Introduction to mastering assignment is not graded, it"s just for you to learn. A key part of biochemistry is not only learning bonds and chemistry of structures, it"s also understanding energy of the reactions molecules undergo and how they interact with the energetic environment as a whole. This and next lecture will cover everything you need to know about this section. It will introduce several definitions and there are a couple equations you need to know. This will help you understand what drives reactions forward or backward or keeps them in equilibrium. Have to know what a lot of these concepts means a key concepts used to describe phenomena. We can"t move forward in our course without introducing these equations and concepts.
