Download Week 3

Biology 160 Week 3 class notes
Monday: Poster project work: topics found and approved by instructor; discussion on finding good
scientific information sources and how to present a scientific topic using a poster
Tuesday: Continued review of Chemisry of life (Chapters 2-3).
Carbon as the backbone, long strings of carbon-carbon bonds make up the structure of the four major
categories of “Large biological molecules”: Carbohydrates, Proteins, Nucleic Acids, and Lipids (fats).
Carbohydrates: simple sugars and polymers of simple sugars. Polymers made via hydration reaction,
chains broken by dehydration reaction. Simple sugar examples: glucose, fructose, sucrose, lactose,
maltose…; complex carbohydrate examples: starch, glycogen (both store energy) and cellulose which
makes up cell walls in plants and becomes the fiber of wood.
Proteins: made up of amino acids: Each amino acid has a central carbon, a carboxyl (aka acid) group on
one side, and amine group (containing nitrogen) on another side, a hydrogen in the third bonding
position, and finally a variable “side group” which is the only thing that varies from one amino acid to
another.
Amino acids are strung together into chains via “peptide bonds”. The order of amino acids in the
chain define the “primary structure”. Depending on the primary structure the chain will fold and spiral
on itself giving a “secondary structure”. The shape that the whole chain of amino acids (the peptide)
makes is called the “tertiary structure”. And when multiple chains get together to form a polypeptide
this overall shape is the “quaternary structure.”
Nucleic Acids: DNA and RNA. DNA forms double strands that are exact complements of each other (like
an imprint, or a negative copy). RNA is single stranded. Both are made up of “bases” or “nucleitides”
Adenine and Thymine (which complement each other) and Cytosine and Guanine (which complement
each other) making up a 4 letter alphabet which encodes all the genetic information in all known forms
of life. In RNA, Thymine doesn’t exist but is replaced by Uracil which is very similar in structure and also
complements Adenine.*we discussed that copying DNA and making and RNA molecule from a DNA
strand is called “transcription” (i.e. copying) whereas the process by which RNA is used to form proteins
is calles “translation” because proteins are a whole other language (made up a sequence of amino acids,
see above).
Lipids: Different somewhat from the other “large biological molecules” because it doesn’t form
polymers. Each lipid molecule is made up of a glycerol molecule bonded to three fatty acid molecules.
Lipids are highly non-polar, so they don’t mix well with polar solvents like water (i.e. oil and water don’t
mix). As you’ll remember from the cell membrane, it is this lipid layer in the middle of the cell
membrane that creates a barrier for the cell to use (phospholipid bilayer). Lipids are often referred to as
“saturated” or “unsaturated” fats, the difference being the bonds contained in the fatty acid tails of the
lipid molecules. Saturated fats contain fatty acids with only single bonds between carbon atoms, which
leads to a uniform shape and in turn leads to higher melting temperatures (which is why saturated fats
like lard or butter are solid at room temperature). Unsaturated fats have one (mono-unsaturated) or
more (poly-unsaturated) double bonds between carbon which puts a kink in the fatty acid tail of the
lipid molecule. These kinks keeps unsaturated lipid molecules from forming solids as easily, and hence
they stay liquid even at relatively colder temps.
Thursday:
pH: Hydrogen can form an ion (it has only one electron in its outer shell after all), and when it does, it
tends to be very reactive and can break apart other molecules (corrosion of metals for instance) and
that is acidity. The pH scale measures acidity by measuring the concentration of Hydrogen ions in a
water-based (aqueous) solution. It is a “logarithmic” scale which means that small changes in pH can
mean big changes in acidity (pH 4 is 10 times more acidic than pH 5). The pH scale is also a negative
scale for acidity, low numbers mean more acidic, high numbers mean less acidic (or more basic).
We reviewed the organelles: learn them all and their functions. Learn which are and aren’t found in
specific types of organisms (i.e. prokaryotes vs. eukaryotes, plants vs. animals).