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DNA
Protein
Biological Molecules Can Have Complicated Structures
How complicated are living things?
Even a bacterium is made up of at least
10,000 different kinds of molecules.
But these fall into 4 classes of organic
molecules.
4 Kinds of Organic Molecules
Properties of organic molecules:
• Carbon skeletons as backbones
• Side chains bear functional groups that
are chemically active
• polymers: chains of subunits
Organic molecules are built around
carbon skeletons
Functional Groups
chemically active side branches
Organic molecules are polymers
Dehydration (Condensation)
Synthesis - Polymer Elongation
Hydrolysis - Polymer Disassembly
Structures are built of large molecules which
are built of small molecules
Carbohydrates
• carbohydrates are sugar polymers
• used for:
– energy storage
– structural features
Sugars are characterized by size,
the kinds of functional groups and their position
Another example
Linear carbon chains
often become cyclic
Synthesis and breakdown of carbohydrate polymers
Disaccharides
Polysaccharides
Polysaccharides held together by weak bonds are used for energy storage
(e.g., starch), whereas those held together by strong bonds are used or
structural purposes (e.g., cellulose)
Cellulose
Lipids
• One end is hydrophilic, the other hydrophobic
• Often polymers (few large instead of many small subunits,
fatty acid derivatives)
• Used for:
– Energy storage, e.g., fats and oils
– Chemical messengers (hormones) , e.g., steroids
– Chemical defenses , e.g., terpenes
– Membranes , e.g., phospholipids
Fatty Acids
Note: carbon and hydrogen have similar
electronegativities and will form non-polar covalent bonds
A simple lipid - triglyceride
Saturated fat
Unsaturated fat
other lipids:
Terpene
(citronellol)
Prostaglandin
(PGE)
Steroid
(cholesterol)
Phospholipid
Phospholipids function
in membranes
Membranes - more than lipids
Glycoproteins
(proteins with carbohydrate antennae)
Membrane
(lipid bilayer)
lipid monolayer
proteins
membrane systems can be extensive
nuclear envelope
ribosomes
golgi apparatus
rough endoplasmic reticulum
smooth endoplasmic reticulum
Proteins
• Every protein = an unbranched chain of amino acids
• Each kind of protein has a unique amino acid sequence
• Each amino acid sequence confers a specific 3D shape
• Each kind of protein is coded for by a single gene
• Proteins have many functions
Amino acids - 20 kinds
R = functional group
each of the 20
amino acids has a
different kind
R
NH2
C
amino group
COOH
carboxyl group
H
Acidic and basic amino acids
Non-polar amino acids
Polar amino acids
Peptide bond formation
+
-
The peptide
bond is
surrounded
by two
important
charges
A short protein - 4 amino acids
four levels of protein structure
primary
secondary
tertiary
quartenary
Secondary Structure and Hydrogen
Bonds
Quartenary Structure in Hemoglobin
Quartenary structure:
4 proteins (chains)
Hemoglobin and Sickle Cell Anemia:
a single amino acid substitution can make a big difference
under oxygen stress
MUTATION:
valine replaces glutamate
hemoglobin polymerizes,
forming long rods that
distort the cell
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Four levels of protein structure
Proteins differ in their 3D shapes
3D shapes have specific
cavities on their surface
these cavities allow “lock and key”
fits with other molecules with which
the protein interact
Enzymes Control Chemical Activity
Molecules are modified in pathways,
in numerous small controlled steps
Biochemical Pathways
Catalysts Control Chemical Activity
What is the significance of complicated shapes?
Numerous weak bonds among complementary complex
surfaces allow molecular recognition and catalysis.
Nucleic Acids: RNA & DNA
• Nucleic acid molecules consist of polynucleotide strands
• DNA has two complementary strands, RNA has one strand
• Both DNA & RNA can replicate and store information
• Nucleotide sequences code for amino acid sequences
…DNA genes code for RNA and protein structure
• Like proteins, RNA is single stranded and can fold up into
complex 3D shapes ….RNA catalysts are ribozymes
Nucleotides have
three subunits
P
S B
Four kinds of DNA nucleotides
RNA is composed of a single polynucleotide strand
DNA is double stranded
DNA can replicate
•
DNA unzips
•
Single strands act as templates
•
Complementary nucleotides added
to form new complementary
second strands
Replication
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DNA Synthesis - Replication
DNA
DNA
DNA
RNA Synthesis - Transcription
DNA
Gene
RNA
DNA structure is too monotonous to serve catalytic
functions,but single stranded RNA can assume complicated
shapes
DNA is double stranded
cannot be catalytic
RNA is single stranded
can be catalytic (ribozymes)
Protein, RNA and DNA Roles
Heredity
Catalysis
Protein
-
√
RNA
√
√
DNA
√
-
Single
strandedness
can confer
complicated
3D shapes that
permit catalytic
roles
How does DNA store information for
RNA and protein structure?
each kind of molecule is an unbranched sequence of subunits
nucelotide sequences are colinear with the amino acid sequences that they code for
Central Dogma of Biology