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BSCI 10001 Study Guide - Fall 2019, Comprehensive Final Exam Notes - Dna, Protein, Gene


Department
Biological Sciences
Course Code
BSCI 10001
Professor
Adam Arthur Leff
Study Guide
Final

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BSCI 10001

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As you well know, water (H20) is a molecule made of two hydrogen atoms plus one oxygen
atom:
Atoms have a nucleus with positively charged protons (plus in all cases except hydrogen, some
neutrons), orbited by negatively charged electrons:
So now let me ask you: Where do all these 112 different kinds of atoms (the elements listed in
the Periodic Table) come from?
They were all made long ago inside stars.
All the different elements that make up the material in the furniture in this room; the room
itself, and all the different kinds of atoms that make up your bodies: all of this was created
billions of years ago in the furnace of stars that existed at an earlier time in our galaxy, long
before our own star (the sun) was formed.
In the center of stars, the huge force of gravity compresses hydrogen nuclei (protons) so tightly
together that they begin to fuse to form helium nuclei. 4 protons fuse to form a helium
nucleus:
Our sun is fusing (“burning”) hydrogen to make helium, and will continue doing so for about
another 5 billion years. Basically, our sun is a long, continuous, sustained hydrogen bomb
explosion!
The energy released in the center of the star by the fusion of hydrogen nuclei to form helium
provides an outward force that counteracts the inward force of contraction due to gravity.
Consequently, once ‘ignition’ has occurred, the star remains at a more or less constant size over
time, as long as it is ‘burning hydrogen.'
As our sun synthesizes helium, this helium accum-ulates in the center of our sun.
Stars bigger than our sun (10x bigger) follow a different fate. After forming carbon, large stars
will successively form neon, then oxygen, silicon, and finally iron:
When all the silicon is depleted, then there is no more fusion-released energy to stave off the
gravitational collapse of the star. The star collapses, and then explodes outwards. This is called
a “Super Nova:
(In the case of stars of size between 10 and 25 times the mass of our sun, the residue left after
a supernova explosion consists of close-packed neutrons; it is called a neutron star; with stars
of mass greater than 25x that of our sun, the neutrons collapse in the face of the huge
gravitational field and a Black Hole forms after the supernova event.)
The huge energies associated with supernova explosions result in the synthesis of all the rest
of the elements in the periodic table.
The cloud of elements blown out into space as “cosmic dust” after a nova event is called a
“nebula”:
The “cosmic dust” from supernovas can then collapse again gravitationally to form new second
generation suns with planetary systems like ours. All the elements like iron, silicon, carbon,
oxygen, silver and gold we find on our planet were made in a sun many billions of years ago.
Our planet, and we ourselves, are literally made of stardust.
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Our sun and planets formed from the nebular remains of earlier supernova explosions in our
galaxy.
(a) Under the influence of gravity, this cosmic dust began to collapse into a rotating, disk-
shaped mass of dust and gas.
(b) The center became super-heated and formed a new star (our sun) (burning hydrogen)
(c) In the rotating disk of dust around the new sun, individual planets began to form, again by
the action of local gravitational attraction. (We now have ways to look for planets around other
suns in our galaxy, and we have found many stars with planets around them.)
(d) By about 5 billion years ago, our solar system was formed
The Big Bang (the birth of our Universe) occurred 13.7 billion years ago. The first stars were
formed from the hydrogen and helium created by the Big Bang within a couple of hundred
million years after the event. Our galaxy, and all the 2 trillion galaxies in the universe, were
formed within the first billion years or so after the Big Bang. Again, our sun is a second
generation star, formed about 5 billion years ago from the supernova dust of a first generation
star that blew up in our galaxy.
More detail on formation of the earth:
Early in the history of the earth, the moon was formed after a glancing collision between the
earth and a Mars-sized object.
This is a picture of the earth and moon, shortly after they had formed and were beginning to
cool off, about 4.5 billion years ago:
The earth still has an iron core. (Solid iron in the center, molten iron above that.)
Above that iron core is hot, molten rock, called the “mantle”.
The heat in the interior of the earth comes mostly from the radioactive decay of uranium,
potassium and thorium isotopes.
The outermost layer of cold, hard rock is called the crust.
Because heat rises, and cool, dense mantle will sink by gravity, the hot, molten mantle moves in
a circular way called “convection”.
The convection of the underlying mantle causes movement of outermost layer of crust.
The surface of the earth consists of moving plates of crust. The movement of these surface
plates is called plate tectonics.
North America, South America, Africa & Europe are all on different moving plates of crust. This
is the way these plates are now:
(But because they move around on the surface of the earth, they used to be in different places.)
This is the way the surface of the earth used to look, long ago:
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