University:
Amherst College
Course:
BIOL 191 | Molecules, Genes and Cells
Academic year:

2011
Views:

425

Pages:

18
Author:

orisontpjb

Biological Building Blocks I What are we made of? • Chemical Bonds – Covalent and Ionic • Important Biological Molecules – Carbohydrates – Fats and Membranes • Energy storage and compartmentalizaIon – Amino Acids • Building blocks of proteins/enzymes – Nucleic Acids • Building blocks of DNA and RNA ObservaIon Solid to SoluIon • Both sugar and salt “go into soluIon” – Solvent being water – Solute being sugar or salt • But what really happens to them then? • If you could observe with your eyes: – Na+ and Cl-‐ molecules surrounded by water – C12H22O11 surrounded by water Why does salt “dissociate” and sugar stay together? • All about the types of bonds molecules form – Ionic Bonds: Very strong electrostaIc aSracIon • Although very strong, water can break them apart – Covalent Bonds: Sharing of electrons between atoms • • • • weaker than ionic, but can not be broken by water (example sugar) only outermost electrons (valence) interact Single bonds: weaker bonds, longer, and atoms can rotate Double bonds and Triple bonds: stronger, shorter bonds: atoms can not rotate (bond is more rigid) Why does salt “dissociate” and sugar stay together? • All about the types of bonds molecules form It all comes back to the periodic table Rows go horizontally: 1st row, H, He; 2nd row, Li, Be, B, C, N, O, F, Ne; 3rd row.. Columns go verIcally and have same number of electrons in their valence shells Figure 2-8a Essential Cell Biology Figure 2-7 Covalent bonds and number of electrons Valence Number: 1. Valence number of an element is the typical number of bonds it makes with other atoms. 2. Each element is diﬀerent in the number of bonds it prefers to make. Why? 3. Each single bond is made of two shared electrons. Valence Electrons: 1. How do you determine the number of valence electrons owned by each element? 2. When bonds are made, each atom tries to ﬁll up its outer shell. 3. The number of electrons needed to ﬁll up the outer shell is two (1st Row), eight (2nd Row), or sixteen (3rd row) To understand Biological Molecules, we need to understand bonding • To understand bonding, we need to understand electrons: 1. For a neutral atom, the number of electrons equals the number of protons 2. For a neutral atom, the total number of electrons is the same as the atomic number 3. Inner shell electrons are buried and don’t interact with the environment 4. Outershell (valence) electrons can be shared in bonds or unshared in lone pairs 5. The number of outershell electrons is the same for each of the elements in a column in the periodic table How is Bonding related to Valence? Example Molecules Look for number of bonds: Hydrogen Oxygen Carbon Nitrogen Sugars we know • Table sugar (cane or beet sugar) – Crystallin Sucrose, a disaccharide of glucose and fructose • High Fructose Corn Syrup – Mostly a mix of fructose and glucose in water Some sweet basics • All sugars have the suﬃx: -‐ose • Are carbohydrates (means carbon plus water) • Two classes of simple sugars Keto Aldo • Simple sugars can contain 5 or 6 carbons – Hexose or pentose Some Hexose and Pentose sugars • Carbohydrates – CH2O • Sugars like to cyclize – Straight Chain – Ring form Glucose Sugars get complex • “Complex Carbohydrates” – Disaccharides and Oligosaccarides Biology can link diﬀerent simple sugars together to make new molecules for diﬀerent tasks. Two Complex Uses of Sugars • Glycogen – Easily accessed source of glucose – Controlled storage and release • Amount of glucose in blood • Insulin, used to trigger glucose storage • Blood Type Glycogen • Primary polysaccharide used to store energy – Primarily stored in the liver and muscles – Polymer of thousands of glucose molecules • Reservoir of stored energy – About enough to last one day Figure 13-21 Essential Cell Biology ABO Blood types deﬁned by sugars • Blood sugar groups are assembled by enzymes that catalyze speciﬁc reacIons • Sugar groups are transferred to outer membrane of RBC • Our DNA determines which enzymes we have, therefore what sugars get added. • Sugars recognized by anIbodies N-acetylgalactosamine N-Acetylglucosamine Galactose Fucose The ABO blood group diﬀer in the kind of sugars on the red blood cell • The funcIons of many of the blood group anIgens are not known, and if they are missing from the red blood cell membrane, there is no ill eﬀect. • This suggests that if the blood group anIgens used to have a funcIon, e.g., one parIcular blood group anIgen made red blood cells more resistant to invasion from a parasite, it is no longer relevant today.

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