UIC BioS 101 Nyberg

Lecture 4 Exam 1

Isotopes, reactions, and measuring energy

Materials and energy acquired from the environment are transformed by reactions which make compounds and provide the energy that powers the cell.

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Reading Assignment

I have asked you to read chapter 2 –for this lecture the part before and after the water section is most relevant.
Isotopes are important in environmental research
Measuring biological energy is important individually and ecologically.

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Isotopes

The number of protons in an atom determines its chemical properties and its element name (=type).
Most elements have more than one isotope (always with different weights)
- Nitrogen has 14N and 15N isotopes.

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Stable versus Radioactive

Isotopes that do not decay spontaneously are referred to as stable.
Isotopes that transform into other elements spontaneously are known as radioactive. Detectable particles are emitted during the radioactive decay event.

Speaker Notes:

Their are 3 kinds of radioactive decay, alpha, beta and gamma.

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Radioactive Decay Rates

The probability that an unstable isotope will break down is independent of the age of the atom.
- ΔN/Δt = -c•N, the change in the number per unit time is proportional to the number.
- Each isotope may be characterized by a time period (called the half life) in which half the original atoms of the isotope undergo decay.
- The half life for 14C is 5600 years.

Speaker Notes:

The amount of isotope left follows an exponential decay pattern.

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Formula relating time and amount remaining

Remaining Amount

= Initial amount • e-(0.693/half life)•t

Application: what percent of 14C will remain after 1000 years?
X% = 100%•e-(.693/5600yrs)•1000yrs
88% = 100% ∙ e-0.124

Speaker Notes:

Go thru some examples in lecture. Emphasize that units must match.

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Ratios of Stable Isotopes

Because isotopes of the same element have the same chemical properties but different weights, all isotopes of an element are found in the same compounds, but heavier isotopes are often slightly enriched or depleted in the products of the reaction.
The slight differences in the proportions of isotopes can tell us about conditions in past.

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Using Stable Isotopes

Stable isotopes can be separated and measured with the mass spectrometer.
Besides nitrogen, stable isotopes of hydrogen (deuterium), carbon and oxygen are widely used in ecological research.

Speaker Notes:

The Messelson-Stahl experiment demonstrating semi-conservative replication of DNA is an example from cell biology.

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Molecules

Atoms are typically linked together by covalent bonds into structures called compounds or molecules.
Molecules can react with other molecules to form new compounds (releasing or absorbing energy).
Many biologically important molecules are built from similar subunits. Most are very large and are called macromolecules.

Speaker Notes:

Start reactions and energy part of lecture.

Energy Accounting

Energy is conserved (potential energy is an accounting device to make this law true).
Energy transformations have a direction –from potential to heat
Spontaneous reactions release heat
- Called exergonic or exothermic

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Reactions create new molecules

Compounds (reactants) interact to produce new compounds (products). This transformation is known as a chemical reaction.
Reactions absorb or release energy. Reactions that release energy can occur spontaneously and are expected to happen.
Reactions go to equilibrium. (At equilibrium the concentrations of reactants and products stay the same, i.e., are constant thru time.)

Speaker Notes:

When input(s) equal output(s) one has an equilibrium.

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Respiration reactions

Reactions that generate energy to run the body involve oxidation.
- Organic compounds are oxidized to Carbon dioxide (CO2) and water.
- CH2O + 02 → CO2 + H20
- CH4 + 2O2 → CO2 + 2H20
The cell uses that energy to build the macromolecules needed to control the flow of materials and energy in the body.

Speaker Notes:

Breaking down and building up.

Source of energy is sun

Photosynthesis involves the capture of energy from the sun and storing it in organic molecules.
All life on earth is dependent on capture of energy from the sun by autotrophs.
Oxygen is a ‘waste’ product of photosynthesis.

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Measures of Energy

A primary measure of heat is the calorie.
In nutrition, the Calorie is 1000 calories, which biologists abbreviate as kcal = kilocalorie.
Energy is a measure of the ability to do work.

Speaker Notes:

SI = Scientific International

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Energy in Food

More reduced organic compounds have more energy per unit weight than less reduced ones.
Lipids and fats have about 9 kcal•g-1 = 9 Cal per gram
2CH2 + 3O2 → 2CO2 +2H2O
The figure of 4 kcal•g-1 is used for protein and carbohydrate (dry weight).

Speaker Notes:

Check some labels on the food you eat.

Functional Groups

Six major functional groups
- Amino
- Carbonyl
- Carboxyl
- Hydroxyl
- Phosphate
- Sulfhydryl

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Problem

Explain why cells can not stay alive long without inputs of energy.
See p 41 in Chapter Review

Speaker Notes:

UIC BioS 101 Nyberg

Lecture 4 Exam 1

Vocabulary

calorie
Kilocalorie = Calorie
Energy
Exergonic
Functional group

Stable isotopes
Exponential decay
Equilibrium
Oxidation
Reaction rate

Speaker Notes: