Download Biological Macromolecules

Lipids
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Hydrophobic molecules

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Carbons bound to hydrogens are not polar
Most often found as fatty-acid
Carboxyl group at one end
 Carbon/hydrogen chain

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Chain may be saturated or unsaturated
Saturated means that each carbon (except the carboxyl carbon) is
bound to the maximum number of hydrogen atoms
Fats
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Used primarily as a long term method of energy
storage
Animal fats tend to contain saturated lipids
Plant fats contain unsaturated fat
Saturated fats are linear molecules and thus able to
pack in more tightly and are solid at room temp
Unsaturated fats have angles and do not pack in
tightly. They are liquid at room temp.

Fats that are liquid at room temp are called oils
Fig. 5-12
Structural
formula of a
saturated fat
molecule
Stearic acid, a
saturated fatty
acid
(a) Saturated fat
Structural formula
of an unsaturated
fat molecule
Oleic acid, an
unsaturated
fatty acid
(b) Unsaturated fat
cis double
bond causes
bending
Structure of fats

Three fatty acid chains
bound to a glycerol
backbone


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Also called
triaclyglycerol
Formed by
dehydration reaction
Fatty acids are bound
to glycerol by ester
linkage
Phospholipids

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Major component of cell membranes
Contain hydrophilic domain that contains
phosphate (and other hydrophilic structure)
Contains hydrophobic domain of lipid chains
Amphipathic Molecules

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Contain both
hydrophobic and
hydrophilic domains
Tend to aggregate with
hydrophobic domains
turned together and
hydrophilic domais
turned outward
Can for bilayers or
micelle structures
 Bilayers are essential
for membrane structure

Fig. 5-14
Hydrophilic
head
Hydrophobic
tail
WATER
WATER
Hormones

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Derived from cholesterol molecules
Used as global regulators in biology



Send signals to distant cells to affect behavior
Are complicated ring structures
Are essential for homeostasis
Lipids Summary


Non-polar molecules that are hydrophobic
Typically found as fatty acids

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


Contain carboxyl group at end of a hydrocarbon
chain
Can be saturated or unsaturated
Are used for long-term energy storage
Phospholipids are amphipathic molecules that
are essential for membrane structure
Are the basis for hormone structure
Protein Functions

Most versatile of the macromolecules
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Structural: collagen, keratin, silk, tubulin
Storage: casein, ovalbumin
Transport: hemoglobin
Hormones: insulin
Receptor: ASGPR
Contractile: actin
Defensive: antibodies
Enzymatic:lysozyme and many others
Amino acids


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Monomeric subunit of polypeptides
Have amino group and carboxyl group
20 natural amino acids
Each has different R group
 Differences in R group makes amino acids react
differently

Functional Groups of Amino
Acids

Based on the chemical properties of the R side
group

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Nonpolar (hydrophobic):glycine, alanine, valine,
leucine, isoleucine, methionine, phenylalanine,
tryptophan and proline
Polar (hydrophilic): serine, threonine, cysteine,
tyrosine, asparagine and glutamine
Electrically charged:
Acidic: aspartic acid, glutamic acid
 Basic: lysine, arginine and histidines

Synthesis of Polypeptides

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Polypeptide is
synthesized by
dehydration reaction
Chain grows from amino
terminus to carboxy
terminus
Chain has a repetitive
backbone with variable
side groups
R groups frequently
interact with others
Fig. 5-18
Peptide
bond
(a)
Side chains
Peptide
bond
Backbone
(b)
Amino end
(N-terminus)
Carboxyl end
(C-terminus)
Four Levels of Protein
Structure

Biological activity of protein is determined by
these levels
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Primary structure is the sequence of amino
acids in a polypeptide (Usually read N-C)
Secondary structures are localized folds or
helices that form within a region of a
polypeptide
Tertiary structures are larger folding events that
are stabilized by interactions between R groups
Quaternary structure is the interaction of
multiple polypeptides within one active proteins
Primary Structure

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Sequence of amino acids within
a single polypeptide
Are often similar among proteins
of similar function
Usually written from amino
terminus to carboxy terminus
Can also provide some insight
into additional structures by the
position of particular groups of
amino acids
Secondary Structure

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Localized within regions
of polypeptide
Stabilized by hydrogen
bonding
a helix-stabilized by
frequent polar groups

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Right handed helices
b-pleated sheets are
formed by consecutive
polar groups on two
regions of polypeptide
Tertiary Structure

Large folding events that are
stabilized by interactions
between amino acids

Hydrophobic interactions


Disulfide bridge


Very stable bond formed
between two distant cysteine
residues
Ionic interactions

-Hydrogen bonds form
between polar groups
Nonpolar regions generally
internalize in structure
Strong bond between
oppositely charged side groups
Quaternary Structure

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Only seen in compound
proteins
Interactions are
maintained between
polypeptide chains by
bonds similar to tertiary
structure
Function is often unique
to quaternary structure

Individual components
are unable to
accomplish task alone
Protein Structure Revisited
Protein Conformation

The 3D structure in which the protein is
biologically active is called the active conformation

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Denatured protein has lost its active conformation
Shape of a protein is consistent under identical
conditions
Proteins will attempt to find the lowest energy form
under conditions
Conditions that affect conformation

Solvent (polar versus non-polar),pH, temperature and
chemical agents (2-mercaptoethanol)
Protein summary

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Very important biological macromolecules that
perform a wide array of functions
Polymers of amino acids
20 natural amino acids that have distinct R side
groups

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The side groups determines the shape and
function of a polypeptide
There are four levels of structural organization
of proteins