Download Lecture #6 - Suraj @ LUMS

Functional groups
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Play pivotal role in chemical & physical properties of
organic molecules.
Compounds that are made up solely of carbon and
hydrogen are not very reactive.
Functional groups:
One or more H atoms of the carbon skeleton may be
replaced by a functional group.
Groups of atoms that have unique chemical and
physical properties.
Usually a part of molecule that is chemically active.
Similar activity from one molecule to another.
Together with size and shape, determine unique bonding
and chemical activity of organic molecules.
Structural Polysaccharides:
Used as structural components of cells and tissues.
1. Cellulose: Glucose polymer.
The major component of plant cell walls.
CANNOT be digested by animal enzymes.
Only microbes have enzymes to hydrolyze.
2. Chitin: Polymer of an amino sugar (with NH2 group)
Forms exoskeleton of arthropods (insects)
Found in cell walls of some fungi
Cellulose: Polysaccharide Found in Plant
and Algae Cell Walls
Proteins:
• Large three-dimensional macromolecules
responsible for most cellular functions
Polypeptide chains: Polymers of amino acids linked by
peptide bonds in a SPECIFIC linear sequence
Protein: Macromolecule composed of one or more
polypeptide chains folded into SPECIFIC 3-D
conformations
Polypeptide:
Polymer of amino acids connected in a specific sequence
Amino acid Structure:
Central carbon with:
H atom
Carboxyl group
Amino group
Variable R-group
Amino Acid Structure:
H
|
(Amino Group) NH2---C---COOH (Carboxyl group)
|
R
(Varies for each amino acid)
Amino Acids Have Both -NH2 and -COOH Groups
Proteins have important and varied functions:
1. Enzymes: Catalysis of cellular reactions
2. Structural Proteins: Maintain cell shape
3. Transport: Transport in cells/bodies (e.g. hemoglobin).
Channels and carriers across cell membrane.
4. Communication: Chemical messengers, hormones, and
receptors.
5. Defensive: Antibodies and other molecules that bind to
foreign molecules and help destroy them.
6. Contractile: Muscular movement.
7. Storage: Store amino acids for later use (e.g. egg white).
Protein function is dependent upon its 3-D shape.
Protein Function is dependent upon Protein Structure
(Conformation)
CONFORMATION: The 3-D shape of a protein is determined by its amino
acid sequence.
Four Levels of Protein Structure
1. Primary structure: Linear amino acid sequence, determined by
gene for that protein.
2. Secondary structure: Regular coiling/folding of polypeptide.
Alpha helix or beta sheet.
Caused by H-bonds between amino acids.
3. Tertiary structure: Overall 3-D shape of a polypeptide chain.
4. Quaternary structure: Only in proteins with 2 or more
polypeptides. Overall 3-D shape of all chains.
Example: Hemoglobin (2 alpha and 2 beta polypeptides)
Primary Structure of Protein: Amino Acid
Sequence is Determined by Gene
Secondary Structure of Protein: Regular Folding
Patterns (Alpha Helix or Pleated Sheet)
Protein Shape is determined by bonding between elements
of different amino acids.
There are 4 types of bonds that occur in proteins:
1.
Ionic bond
2.
Disulphide bond
3.
Hydrogen
4.
Hydrophobic interactions
Due to the functional groups attached to amino acids
Tertiary Structure: Overall 3-D Shape of Protein
Tertiary Structure of Lysozyme
Quaternary Structure: Overall 3-D Shape of
Protein with 2 or More Subunits
What determines a protein’s shape?
A. Primary structure: Exact location of each amino
acid along the chain determines the protein’s
folding pattern.
Example: Sickle Cell Hemoglobin protein
Mutation changes amino acid #6 on the alpha chain.
Defective hemoglobin causes red blood cells to assume
sickle shape, which damages tissue and capillaries.
Sickle cell anemia gene is carried in 10% of African
Americans.
What determines a protein’s shape?
B. Chemical & Physical Environment:
Presence of other compounds, pH, temperature, salts.
–
Denaturation: Process which alters native conformation and
therefore biological activity of a protein. Several factors can
denature proteins:
1.
pH and salts: Disrupt hydrogen, ionic bonds.
2.
Temperature: Can disrupt weak interactions.
Example: Function of an enzyme depends on pH,
temperature, and salt concentration.
Nucleic acids
Store and transmit hereditary information for all living
things
There are two types of nucleic acids in living things:
A. Deoxyribonucleic Acid (DNA)
Contains genetic information of all living organisms.
Has segments called genes which provide information to
make each and every protein in a cell
Double-stranded molecule which replicates each time a
cell
divides.
B. Ribonucleic Acid (RNA)
Three main types called mRNA, tRNA, rRNA
RNA molecules are copied from DNA and used to make
gene products (proteins).
DNA and RNA
are polymers of nucleotides that determine the
primary structure of proteins
Nucleotide: Subunits of DNA or RNA.
Nucleotides have three components:
1. Pentose sugar (ribose or deoxyribose)
2. Phosphate group to link nucleotides (-PO4)
3. Nitrogenous base (A,G,C,T or U)
Purines: Have 2 rings.
Adenine (A) and guanine (G)
Pyrimidines: Have one ring.
Cytosine (C), thymine (T) in DNA or uracil (U) in
RNA.
James Watson and Francis Crick Determined the 3D Shape of DNA in 1953
Double helix: The DNA molecule is a double helix.
Antiparallel: The two DNA strands run in opposite
directions.
Strand 1: 5’ to 3’ direction (------------>)
Strand 2: 3’ to 5’ direction (<------------)
Complementary Base Pairing: A & T (U) and G & C.
A on one strand hydrogen bonds to T (or U in RNA).
G on one strand hydrogen bonds to C.
Replication: The double-stranded DNA molecule can
easily replicate based on A=T and G=C
--- pairing.
SEQUENCE of nucleotides in a DNA molecule dictate
the amino acid SEQUENCE of polypeptides
DNA: Double Helix of Two Complementary
Strands Held Together by H-Bonds
A Gene
• A specific segment of a DNA molecule with information for
cell to make one polypeptide.
DNA
(transcribed into single stranded RNA “copy”)
mRNA
(single stranded “copy” of the gene)
Polypeptide (mRNA message translated into polypeptide)
Genetic Information Flow: DNA to RNA to Protein
Lipids:
Fats, phospholipids, and steroids
Diverse groups of compounds.
Composition of Lipids:
C, H, and small amounts of O.
Functions of Lipids:
Biological fuels
Energy storage
Insulation
Structural components of cell membranes
Hormones
Lipids:
Fats, phospholipids, and steroids
1. Simple Lipids: Contain C, H, and O only.
A. Fats (Triglycerides).
Glycerol : Three carbon molecule with three hydroxyls.
Fatty Acids: Carboxyl group and long hydrocarbon
chains.
Characteristics of fats:
Most abundant lipids in living organisms.
Hydrophobic (insoluble in water) because nonpolar.
Economical form of energy storage (provide 2X the
energy/weight than carbohydrates).
Greasy or oily appearance.
Fats (Triglycerides):
Glycerol + 3 Fatty Acids
Lipids:
Fats, phospholipids, and steroids
Types of Fats
Saturated fats: Hydrocarbons saturated with H.
Lack -C=C- double bonds.
Solid at room temp (butter, animal fat, lard)
Unsaturated fats: Contain -C=C- double bonds.
Usually liquid at room temp (corn, peanut, olive oils)
Saturated Fats Contain Saturated Fatty Acids
Complex Lipids:
Phospholipids
In addition to C, H, and O, also contain other elements, such
as phosphorus, nitrogen, and sulfur.
A. Phospholipids: Are composed of:
Glycerol
2 fatty acid
Phosphate group
Amphipathic Molecule
Hydrophobic fatty acid “tails”.
Hydrophilic phosphate “head”.
Function: Primary component of the plasma
membrane of cells
Phospholipids: Amphipathic Molecules
In Water Phospholipids Spontaneously
Assemble into Organized Structures
Steroids:
Lipids with four fused carbon rings
1.
Includes cholesterol, bile salts, reproductive, and adrenal
hormones.
Cholesterol: The basic steroid found in animals
• Common component of animal cell membranes.
• Precursor to make sex hormones (estrogen,
testosterone)
• Generally only soluble in other fats (not in water)
• Too much increases chance of atherosclerosis.
Waxes: One fatty acid linked to an alcohol.
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Very hydrophobic.
Found in cell walls of certain bacteria, plant and insect coats.
Help prevent water loss.