Transcript The Structure and Function of Macromolecules

Chapter 5
The Structure and Function of
Macromolecules
3 themes are emphasized
Hierarchy of structural levels
Emergent properties
Form fits function
Polymers
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Monomers- units that comprise a
polymer
Polymer- long molecule consisting of
many similar or identical building blocks
linked by covalent bonds
Polymer formation
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Condensation reaction- linking of
monomers through the loss of a water
molecule (dehydration reaction)
Polymer formation
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One molecules provides the hydroxyl
group (-OH) and the other the
hydrogen (-H).
Requires energy and enzymes
Polymer disassembly
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Hydrolysis- dissemble polymers
Water is added to break a bond
Ex: digestion- food polymers broken
down by enzymes
Classes of Polymers
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Carbohydrates
Lipids
Proteins
Nucleic Acids
Other
Carbohydrates
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Monomers called monosaccharides
Cellular use: energy, energy storage,
structure
(C, 2H, O)n
Monosaccharides, disaccharides, and
polysaccharides
Monosaccharides
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Glucose
Aldehydes and ketones
Linear and ring forms
Disaccharides
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2 monosaccharides, sucrose = glucose+fructose
Joined by a condensation synthesis called a
glycosidic linkage.
Polysaccharides
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Several hundred or
more
monosaccharides
Energy storage:
starch and glycogen
Structural: cellulose
and chitin
Starch
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Storage of polysaccaharides in
plants, made up glucose monomers
Provides a way to store surplus
glucose, energy can be withdrawn
by hydrolysis
Humans have enzymes that can
hydrolyze plant starch. High sources
of starch found in potatoes, grains
(wheat, corn, rice).
Glycogen
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Used by animals to store glucose.
More extensively branched than plant
starch.
Stored mainly in liver and muscle
cells. Humans can only store enough
energy for about a day.
Cellulose
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Polysaccharide used by plants from
structure.
Similar to starch except in the location of the
glucose bond:
Starch- alpha linkage, helical shape
Cellulose- beta linkage, straight
shape
Opposing hydroxyl groups bond with
other strands, creating strong fibers.
Why don’t humans eat grass?
Chitin
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structural polysaccharide used by
arthropods (insects, spiders,
crustaceans) to build their
exoskeleton
Also used by fungi rather than
cellulose for their cell walls.
Similar to cellulose except has a
nitrogen appendage to the glucose.
Lipids
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Fats
Not polymers but
Large molecules, composed of
smaller molecules, assembled by
dehydration reactions
Not soluble in water. C-H bonds are non
polar
Triglycerides
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Fat molecule = Triacylglycerol (or triglyceride)
Triacyglycerol= Glycerol + 3 fatty acids
Linked by ester linkage (condensation reaction)
Oils and fats
Animal fat vs. Plant and Fish
fat
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Saturated fat vs
unsaturated fat
Animal fat- usually
saturated- solid at room
temperature
Plant and fish fatusually unsaturatedliquid at room
temperature
Fat- what is it good for?
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Fat- stores energy
1 gram of fat stores 2x energy as starch
Stored in adipose cells
Cushions vital organs
Provide insulation
Phospholipids
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2 fatty acids + phosphate group + glycerol
Phospholipids
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Various molecules attach to the
phosphate group
Tails are hydrophobic
Heads are hydrophilic
What do they do in water?
Phospholipids
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When added to water- they self
assemble so that they shield their
hydrophobic tails
Micelle- phospholipid droplet,
phosphate heads on the outside, tails
are restricted to the water-free
interior
Phospholipid bilayer- major
component of cell membranes
Steroids
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Four interlocking carbon
rings
Regulatory moleculessex hormones
Cholesterol-precursor of
many steroids
Cholesterol is a
component of cell
membranes
Cholesterol can
contribute to
atherosclerosis
Proteins
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Monomers called amino acids
20 different amino acids
Joined by peptide linkage
Chains of amino acids- polypeptide
Function as support, storage, transport,
signaling, defense, movement, and
catalysts
C, H, O, N, S
Make up 50% of cellular DRY weight
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Tens of thousands different types in
humans
Enzymes- regulate metabolism,
accelerate chemical reactions
Amino Acid Structure
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Contains 3
functional groups
Amino, carboxyl
and R groups
Polar, nonpolar,
charged and
uncharged
Amino acid linkage
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Peptide bond- covalent bond catalyzed
by a dehydration reaction
Amino end: N-terminus
Carboxyl end: C-terminus
“Polypeptide” vs “Protein”
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Protein- one or more polypeptides
twisted, folded, and coiled.
Four Levels of Protein
Organization
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Primary- sequence
of amino acids
Sequence determines function
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20 different amino acids
Lysozyme- protein that helps fight
bacteria
129 amino acids long
20129 possible combinations
Sickle cell disease is caused by one
protein substitution in the structure of
hemoglobin.
Four Levels of Protein
Organization
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Primary- sequence
of amino acids
Secondary- coils or
folds
Secondary- coils and folds
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Result from hydrogen bonding on the
backbone of the chain (not the R
groups)
Oxygen and nitrogen are
electronegative with partial negative
charges.
Hydrogen molecules attached to
Nitrogen have partial positive charges.
Secondary coil
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Alpha helixdelicate coil held
together by
hydrogen bonding
between every
fourth amino acid
Secondary Fold
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Beta pleated
sheet- two or
more parallel
chains. Held
together by
hydrogen bonds
of the backbone.
Four Levels of Protein
Organization
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Primary- sequence
of amino acids
Secondary- coils or
folds
Tertiary- R group
interaction
Tertiary structure
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R groups interact
Hydrophobic
interaction
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Hydrophobic (nonpolar)
R groups cluster at the
core
Held together by van
der Waals interactions
Tertiary structure
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Disulfide
bridgesTwo sulfhyryl
groups (-SH) form
covalent bond
Four Levels of Protein
Organization
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Primary- sequence
of amino acids
Secondary- coils or
folds
Tertiary- R group
interaction
Quaternary
Quaternary Structure
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Overall shape of
the proteindetermines its
function.
Denaturationunraveling of a
protein
Reversable?
Protein Research
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100,000 – amino acid sequence is
known
10,000- 3D shape is known
X-Ray crystallography
Chaperonins(chaperone proteins)
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Help proteins fold
correctly
Keeps them away
from bad
influences
Nucleic Acids
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Monomers are nucleotides
Polymers are 2 types: RNA and DNA
Function:
1) control heredity
2) control cell functions
DNA -> RNA -> Protein
Purines and Pyrimidines
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Purines:
1) adenine and
guanine
2) double ring
structure
Pyrimidines:
1) thymine, uracil,
and cytosine
2) single ring
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Deoxyriboselacks an oxygen
atom on its
number 2 carbon
Ribose
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Phosphodiester
linkages- links
between
phosphate of one
nucleotide to the
sugar of the next
DNA and RNA shape
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DNA- double stranded, double
helix
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Shaped discovered by James
Watson and Francis Crick in 1953
RNA- single stranded
Nucleotides
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3 parts: 5-C sugar,
phosphate and
nitrogenous base
2 types of sugars:
ribose and
deoxyribose
2 types of
nitrogenous bases:
purines and
pyrimidines
Evolutionary relationships
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Taxonomy- based on characteristics
DNA sequencing- allows for taxonomy
based on genetic closeness