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Summary Learning objectives Molecular Biology
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Summary of unit 8, the ecology of life - Biology, a global approach, 12th edition
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Samenvatting Biology chapter 19, 20, 21, 22, 23
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Samenvatting Biology chapter 13, 14, 15, 16
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Chapter 21. Describe the build of atoms and name concepts like atoms, mass and atom number
- Atoms
o Protons (positive charge) Mass of 1 Dalton (Da)
o Neutrons (neutral charge) Mass of 1 Da
o Electrons (negative charge) Mass is negligible
o Protons and neutrons in the atom nucleus
o Electrons in a cloud around the nucleus
o Mass number: protons + neutrons Upper left corner of the element ( 12C)
o Atomic number: number of protons Bottom left corner of the element (6C)
Atoms with the same atom number have the same chemical characteristics
and are the same element
Determines which the kind of element
o Example: an element with atom number 19 and mass number 39 has 19 protons, 19
electrons and 20 neutrons
2. Know the difference between two isotopes of an element
- Isotopes and radioactive decay
o Isotopes are atoms with the same number of protons but a different number of
neutrons
Different mass number but same atomic number
Example: there are three types of carbon:
Carbon-12 has 6 protons and 6 neutrons
Carbon-13 has 6 protons and 7 neutrons
Carbon-14 has 6 protons and 8 neutrons
o Radioactive isotopes unstable isotopes
Carbon-14 decays into nitrong-14
Carbon-14 (β-decay) nitrogen-14 + electron + antineutrino
Decay rate expressed in half-life Varies per isotope
Applications
Radioactive tracers
Radiometric dating
3. Determine which type of binding is plausible from the distribution of electrons in shells.
And divide the electrons in shell 1 and 2 over different orbitals
- Electron distribution
o Chemical characteristics of an atom is determined by the distribution of electrons
Elements with the same distribution means same characteristics
o Valence electrons electrons in the outermost shell (valence shell)
o Atoms try to fill up their outermost shell
Making them inert (less reactive)
o Orbitals (cloud of electrons)
Every shell contains a specific number of orbitals
Every orbital contains two electrons
o Shell 1 1 orbital (1s) 2 electrons
o Shell 2 4 orbitals (2s and three 2p; 2px, 2py, 2pz) 8 electrons
,4. Distinguish between the different types of binding (covalent and noncovalent) and
determine the type of binding, polar or nonpolar, by using the concept of electron-
negativity
- Bonds
o Covalent: electron pair sharing
Interaction between atoms
, Hydrogen has a valence of 1 two hydrogen atoms can share their
electrons making H2
Oxygen has a valence of 2 two hydrogen atoms and one oxygen
atom can share their electrons making H 2O
Single covalent bond sharing one electron pair
Double covalent bond sharing two electron pairs
Triple covalent bond sharing three electron pairs
Display of molecules
Molecular formulas (H2)
Lewis Dot structure (H:H)
Structure formulas (H – H, single bond) (O=O, double bond)
Space-Filling model (represent the actual shape of the molecule)
Not always an equal distribution
Electron negativity of the atom
o Depends on the number of protons and the distance from
the shell to the nucleus
o Determines the type of bond
Nonpolar covalent bond (H2)
Electrons distributed equally
Electron negativity difference of less than 0,5
Polar covalent bond
Electrons are closer to one of the atoms
Electron negativity difference of 0,5 to 1,6
Causes partial charge of the molecule
For example, H2O has hydrogen and oxygen share a polar covalent
bond because oxygen is one of the most electronegative elements
o The oxygen atom has a partial negative charge δ-
o The hydrogen atom has a partial positive charge δ+
o Ion: electron transmission
Atoms take over the electrons of their binding partner atom
Both atoms are charged after transmission
o Charged atom/molecule = ion
Cation is positive
Anion is negative
o NaCl Na+ + Cl-
Chemical ion bond salts
Create crystal structure
5. Distinguish between the strength of different kinds of binding
- Weak chemical interactions
o Hydrogen bonds
Hydrogen atom
Covalently linked to a strong electronegative atom
Attracted to other electronegative atoms
o Van der Waals forces
Coincidental unequal distribution of electrons over a molecule
Attraction between molecules that are in close proximity
o Cause big biological molecules to stay intact
o Interaction is reversible
, Chapter 3
6. Explain the four important characteristics of water
- Polarity of water
o Polar covalent bond
o Water is a polar molecule
Charges are unequally distributed
o Water molecules form hydrogen bonds
Weak
Short lived
Changing contacts
- Cohesion characteristics
o Hydrogen bonds keep water molecules together cohesion
o Attraction between different compounds (water and glass) adhesion
o The surface tension of water is very high by cohesion of water molecules
- Temperature and thermal energy
o Thermal energy is kinetic energy of the molecules
Random movements of molecules and atoms
o When two objects come into contact
Thermal energy of warm objects to colder objects
o Water can absorb high amounts of energy
High specific warmth
1 calory = energy needed to warm one gram of water
Water works as a buffer in the world sea
Heat absorption H-bond breaks
Heat release H-bond forms
High heat of evaporation
Energy needed to evaporate one gram liquid to gas
Evaporation = when some molecules move fast enough to leave the
liquid
Evaporation also takes place at lower temperatures but faster at
higher temperatures
Evaporative cooling liquids evaporate, remaining liquid cools down
o sweat
- Expansion by freezing
o In ice water forms a crystal structure
Hydrogen bonds are not broken anymore
Water molecules are further apart
o The density of ice is lower than water
Making ice float above the water
- Solvent
o A solution is a liquid with a homogeneous mix of compounds
Solvent and solute
o Water is an excellent solvent
o Hydrophilic high affinity for water
o Hydrophobic low to no affinity for water
Oil, most nonpolar covalent bindings
Membranes consist partly of hydrophobic molecules
Micelles
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