Chapter 2
Organic Compounds
II. Lipids
Composition: CHO – lipids have less oxygen atoms in proportion to Carbons and
Hydrogens.
-less soluble in H2O (hydrophobic)
-have greasy or oily consistency
Types of Lipids:
1. Neutral fats and oils
-most abundant lipids
-consists of glycerol joined to one, two, or three fatty acids
-glycerol is a 3 carbon alcohol with 3 –OH groups
-fatty acid is a straight chain of carbon atoms with carboxyl groups
(-COOH) at one end.
-glycerol and fatty acid(s) are joined by an ester bond between the –OH
of glycerol and the –COOH of the fatty acid(s) by way of dehydration.
e.g. glycerol + 1 fatty acid = monoglyceride
glycerol + 2 fatty acids = diglyceride
glycerol + 3 fatty acids = triglyceride
Saturated and Unsaturated fats and oils are triglycerides.
-saturated – contain maximum number of Hydrogen atoms.
(carbons are fully loaded with H)
-tend to be solid at room temperature
-butter, animal fats (lard)
-unsaturated – contains 1 double bond between carbons, therefore, not
fully saturated with Hydrogens.
-polyunsaturated - contain more than one double bond.
-both unsaturated and polyunsaturated are oils and
most are liquid at room temperature.
Note: trans fatty acids are considered unhealthy. They are found in
butter substitutes.
2. Phospholipids
-consists of an organic compound (amino acid), a phosphate group, and a
glycerol molecule attached to two fatty acids.
- the head of the phospholipid are the organic compound, phosphate, and
the glycerol. It is also polar: (+) and (-) and hydrophilic.
-the tail is the fatty acids and hydrophobic
-the term used to describe a molecule that is both hydrophilic and
hydrophobic is amphipathic.
3. Steroids
-carbon atoms arranged in 4 rings: 3 six carbon rings
4 five carbon ring
-steroids are distinguishable by extending side chains.
Types of Steroids:
1. Cholesterol – found only in animal cells and is synthesized in the liver.
- precursor to all steroids
-part of the plasma membrane: 85% synthesized internally
15% dietary
HDL (High Density Lipoproteins) and LDL (Low Density Lipoproteins)
are more than just cholesterol.
-consists of cholesterol, fats, phospholipids and proteins
- name refers to ratio of lipids to proteins
e.g. HDL has lower ratio of lipids to proteins
- may prevent cardiovascular disease
-“Good Cholesterol”
LDL has higher ratio of lipids to proteins
-may cause cardiovascular disease
-“Bad Cholesterol”
2.
3.
4.
5.
6.
Bile salts – emulsify fats in the intestines
Reproductive hormones –estradiol and testosterone
Cortisol – metabolic regulator of blood sugar
Vitamin D – aids in bone metabolism
Eicosanoids – hormone-like chemical signals between cells
Uses for Lipids: energy storage, cellular fuel, structural components of cells, thermal
insulation.
III. Proteins
Composition: CHON and usually S
- large complex molecule formed from amino acids
-central importance in the chemistry of life
-proteins are composed of 20 different amino acids
- amino acids are joined by peptide bond (by way of dehydration)
-2 amino acids = dipeptide
-longer chain= polypeptide (10 – 2000+)
All amino acids consist of: amino group -NH2
carboxyl group -COOH
side chain -R (varies from amino acid to
amino acid)
Some amino acids are polar.
Levels of Structure of Proteins
-polypeptide chains are twisted and folded to form proteins with a 3-D
shape.
-conformation of protein determines functions e.g. unique shape of
enzyme permits it to recognize and act on substrates.
4 Levels of Organization
1° Primary – the sequence of amino acids in a polypeptide chain.
e.g. Met-Val-Leu-Val-Trp-Gly
2° Secondary – polypeptide chain coils into alpha helix and beta pleated
sheet due to H bonding.
3° Tertiary – overall shape assumed by each polypeptide chain-Protein
3-D structure determined by interactions among side chains.
1. H bonding between amino acids
2. Ionic bonding between side chains
3. Hydrophobic interactions by nonpolar side chains
4. Covalent bonding between cysteins (disulfide bonds)
4° Quaternary – 2 or more polypeptide chains or proteins together.
e.g. hemoglobin exists as four tertiary proteins
Prosthetic Group – a non amino acid component of a protein that is
covalently bonded.
-has a specific function
e.g. hemoglobin –has iron ring that binds to
oxygen.
glycoprotein – carbohydrate (sugar) is
prosthetic group.
Enzymes – proteins that function as a catalyst
– permit biochemical reactions to occur rapidly at normal body
temperature.
- they act upon substrates (other substances or molecules)
- suffix –“ase” added to substrate name to distinguish between
enzymes.
e.g. amylase (amyle=starch) or carbohydrease
anhydrease (anhydr – without water) removes water
lipase –enzyme that acts on lipids
3 Characteristics of Enzymes: highly specific to substrates
very efficient – speeds up reactions
under cellular control (genes)
Enzymes have active sites – areas that aid in breaking down or forming
bonds between two or more substrates.
IV. Nucleic Acids
Composition: CHONP
-transmits hereditary information
-determines protein production
-discovered in nuclei of pus cells
Polymers of Nucleotides (monomers): 5 carbon sugar – ribose
phosphate group
nitrogenous bases:
-purine – double ring structure
-pyrimidine –single ring structure
Nucleotides are covalently bonded between phosphate groups and either ribose or
deoxyribose (depending on which nucleic acid) by phosphodiester bond
2 Types of Nucleic Acids
I. RNA (ribonucleic acid)
-functions in protein synthesis
-usually single stranded
-complement to DNA
Bases for RNA: purines- Adenine (A) and Guanine (G)
pyrimidines – Cytosine (C) and Uricil (U)
3 Types of RNA:
1. mRNA (messenger) - transcribes and carries
information for making proteins
out of the nucleus.
2. tRNA (transfer) – links with specific amino acid and
brings it to mRNA.
3. rRNA (ribosmomal) – the site of protein synthesis
-catalyzes reactions; joining of
amino acids into proteins.
-consists of 2 subunits (1 large and
1 small).
2. DNA (deoxyribonucleic acid)
- usually double helix
- has purines: A and G
pyrimidines: T and C
- bases are bonded to a phosphate and sugar backbone
-the sequence of bases makes up genes (hereditary material
of the cell)
- contains instructions for making all proteins.