Lecture Notes - Chapter 3
Homework - Review questions 1-7
Macromolecules consist of thousands of atoms assembled by linking hundreds of
smaller molecules into long chains. There are 4 types of macromolecules that make up
the basic chemical building blocks from which all organisms are assembled. These are
carbohydrates, lipids, proteins, and nucleic acids.
I.
II.
The Building Blocks of Organisms
A.
The Chemistry of Carbon
- Organic molecules contain carbon.
- Attached to the carbon backbones are groups of atoms referred to as
functional groups.
B.
Building Macromolecules
- Most macromolecules are polymers –
- Dehydration reaction - removing an -OH group from one subunit and a
hydrogen atom from another, forming a covalent bond between the two
subunits, and resulting in the formation of a molecule of water (anabolic
reaction; requires energy).
- Hydrolysis reaction - macromolecules are disassembled into subunits by
the addition of water (catabolic reaction; energy is released).
Proteins
Enzymes - catalysts that facilitates special chemical reactions (globular proteins).
Fibrous proteins play structural roles, and include keratin, actin, myosin, and
collagen.
Peptides are short proteins that are used as intercellular messengers.
A. Amino Acids are the Building Blocks of Proteins
- An amino acid is a molecule containing an amino group (-NH2), a
carboxyl group (-COOH), and a hydrogen atom, all bonded to a central
carbon atom.
- Only 20 amino acids are commonly used in proteins, the identities and
chemical properties of which are determined by the nature of the side
group (R).
-
Amino acids can be divided into five chemical classes based on the side
groups:
1) nonpolar amino acids - e.g. leucine - R groups contain -CH2 and CH3;
2) polar uncharged amino acids - e.g. threonine - R groups contain
oxygen or only -H;
3) ionizable amino acids - e.g. glutamic acid - R groups contain acids or
bases;
4) aromatic amino acids - e.g. phenylalanine - R groups contain an
organic ring with alternating single and double bonds;
5) special-function amino acids - properties unique to each amino acid methionine initiates chains of amino acids, proline causes kinks in
chains, cysteine links chains together.
B. Proteins are Chains of Amino Acids
- composed of one of more long chains of amino acids, called a polypeptide.
C. The Shape of Globular Proteins - these are
- proteins composed of long amino acid chains folded into complex shapes
- all the internal amino acids are nonpolar due to hydrophobic interactions.
- There are four levels of structure to globular proteins: primary, secondary,
tertiary, and quaternary.
1) Primary structure - the specific amino acid sequence of the protein.
Determined by the nucleotide sequence of the gene that encodes the
protein.
2) Secondary structure - hydrogen bonding links an amino acid to another
further down the chain (-helix configuration), or between amino acids
of two separate chains (-pleated sheets).
3) Tertiary structure - the final folded shape of a protein. Most often the
result of a protein’s interaction with water, which drives the nonpolar
amino acid side groups into the interior.
4) Quaternary structure - two or more polypeptide chains (in their tertiary
structures) associate to form a functional protein.
D. Denaturation
- process by which a protein changes its shape or unfolds in response to a
change in its environment,
- change in the pH, temperature, or ionic concentration of solutes.
III. Lipids
A. Fats
- long-term storage of energy (glucose) due to more C-H bonds.
- composed of two subunits - glycerol backbone (3-carbon alcohol - each
carbon bears a hydroxyl group) and three long fatty acid chains (long
hydrocarbon chains ending in a carboxyl group). Triglyceride.
- The three fatty acid chains may be present in one of two forms:
1) Saturated - contains the maximum number of hydrogen atoms and no
double bonds.
2) Unsaturated - contains one (mono) or more (poly) double bonds
between successive carbon atoms.
-
Fats store more than twice the amount of chemical energy than
carbohydrates. Fats = 9 kcal/g, carbohydrates = 4 kcal/g.
IV. Carbohydrates
A. Sugars are Simple Carbohydrates
- function as energy-storage molecules as well as structural elements.
- contain carbon, hydrogen, and oxygen in the ratio of 1:2:1 (empirical
formula is (CH20)n.
- contain many carbon-hydrogen bonds, which release energy when broken,
so they are well-suited for energy storage.
- The carbohydrates you eat or produce will be used in one of three ways:
1) some is maintained as glucose and is available for immediate energy;
2) is converted into transport disaccharides and carried to other parts of
the organism;
3) some is converted into storage forms, such as fats, and reserved for
future use.
V. Nucleic Acids
These macromolecules are the information storage centers of the cells.
Two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic
acid).
Long polymers of repeating subunits called nucleotides - these consist of a fivecarbon ribose or deoxyribose sugar, a phosphate group, and an organic, nitrogencontaining base.
Five nucleotide bases present in DNA or RNA, divided into 2 groups based on
their ring structure:
1) Purines - large, double-ring molecules - present in both DNA and RNA,
and include adenine (A) and guanine (G);
2) Pyrimidines - smaller, single-ring molecules, and include cytosine (C) in
DNA and RNA, thymine (T) in DNA, and uracil (U) in RNA.
Nucleic acid polymers are formed when the phosphate group of one nucleotide
binds to the hydroxyl group of another, releasing water and forming a phosphodiester
bond.
A. DNA
- exists as double chains wound around each other like a circular staircase
(double helix).
- each step of the staircase is composed of a nucleotide base-pair held
together by hydrogen bonds.
- adenine pairs with thymine (DNA) or uracil (RNA); cytosine pairs with
guanine. These pairs are complements to each other.
B. RNA
- single-stranded formation
- complement of a DNA template
- similar to DNA, but the ribose sugar has a hydroxyl group where DNA has
a hydrogen, and utilizes uracil instead of thymine.
- RNA directs the synthesis of a protein whose amino acid sequence
corresponds to the nucleotide sequence of the DNA from which the RNA
was copied.