Lecture 3:
Biological Macromolecules
Living Organisms Are not in Equilibrium With Their Surroundings
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Chemical reactions run their courses until there is no further change; this is
called equilibrium
In biology: equilibrium = death
Continuous input of energy required to keep processes from going to
equilibrium
To counteract the trend toward equilibrium cells burn fuel molecules (sugar,
fat, amino acids) and use the released energy to make ATP (see below)
Cells use energy for many purposes, including building macromolecules (giant
molecules) from small building blocks
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Without energy input (from ATP) cells break down into small building block
molecules and die (equilibrium state)
Each time a bond is formed to make a macromolecule water is removed
(dehydration)
When macromolecules break down spontaneously they take up water
(hydrolysis)
o This is what happens in digestion
Global picture of energy relationships:
o Cells exist in a stable relationship with the environment called a
steady-state
 Example of steady-state 1: production of fresh water from sea
o
water using energy from sun (non-living steady-state)
 Example of steady-state 2: production of macromolecules from
small molecules using ATP energy (see diagram)
 Example of steady-state 3: photosynthesis- production of
sugars and other carbon compounds from CO2 and water, using
light energy (living steady-state)
In these steady states the system is pushed away from equilibrium by
the continuous inflow of energy from outside
o
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The universe as a whole still running down (that's where the outside
energy comes from); we become more complex at the expense of the
universe
 More than 99% of the energy for life comes from the sun via
photosynthesis
What will happen to a cell with a low supply of energy? Discuss your answer.
AdenosineTriphosphate (ATP) is the Energy Currency of the Cell
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Animal cells cannot directly use most forms of energy
o
o
Most cellular processes require energy stored in the bonds of a
molecule, adenosine triphosphate (ATP)
ATP is referred to as the energy currency of the cell
This is the structure of
ATP. It is a nucleotide,
formed from:
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the
base adenine (the
structure with 2
rings),
the 5
carbon sugar
deoxyribose (one
ring)
3
phosphates
Energy is stored in the
bonds between the
phosphates and is
released when the bonds
are broken
o
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Cells are designed to use chemical energy rather than heat energy
o The cell is not a heat engine- it runs at a constant low temperature
Energy storage:
o Body cannot store much ATP (ATP interferes with many chemical
reactions)
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Most of the body's energy is stored in fats (triglycerides: see below)
and polysaccharides (glycogen: see below)
ATP is generated from the fats & polysaccharides as needed (this is the
o
purpose of glycolysis & the Krebs cycle)
 Cell produces energy by oxidizing ("burning") the stored
energy rich chemicals
 Some of the energy goes off as heat, but most is trapped in the
phosphate bonds of ATP
Some electrical energy is also stored as ion gradients
Cells Contain 4 Major Types of Giant Molecules (Macromolecules or
Polymers)
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Proteins
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Polysaccharides (complex sugars)
Nucleic Acids
Some Lipids (fats)
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Biological Polymers are Made From About 60 Small Building Blocks
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Cells contain thousands of types of giant molecules (macromolecules,
polymers)
Most of the polymers are made from about 60 types of small building block
molecules
Hooking the building blocks together to make polymers requires energy from
ATP
Building
Blocks
Number of
Polymers
Kinds
Amino Acids
20
Proteins
Fatty Acids
10
Storage
Lipids/Membranes
Sugars &
Relatives
10
Polysaccharides/Nucleic
Acids
Nucleotides
5
Nucleic Acids
Others
15
All of Above
Proteins are Made up of Exactly 20 Types of Amino Acids
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Basic amino acid structure: amino (NH2) and carboxyl (COOH) groups
The 20 types have different side groups (designated as R)
In proteins the amino acids are linked head to tail by peptide bonds
Note the amino (NH2),
carboxyl (COOH) and
hydrogen groups (H) which are
found on all amino acids. The
differences in amino acids are
in the 20 different types of R
groups.
Basic Amino Acid Structure
Two amino acids can combine,
with the carboxyl of one
attaching to the amino group of
Formation of a Peptide Bond
the other. Water is removed.
This process also requires
energy in the form of ATP.
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Proteins differ from one another in 2 ways:
o
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Size: number of amino acids
 Typical protein has 200 to 1000 amino acids
o Sequence of amino acids
 Some amino acids are charged or have a polar structure:
hydrophilic (like water)
 Some amino acids are neutral and nonpolar: hydrophobic (hate
water, like to be in lipid)
 Hydrophobic proteins are found in membranes
o Hydrophobicity can be tested by oil/water partition test:
Why do you suppose hydrophobic proteins tend to be found in cell membranes?
Discuss your answer.
Proteins Do Most of the Work of the Cell
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Every cell has thousands of different types of proteins, each specialized to do a
certain job
Some proteins are structural: control shape of cells and bind cells together
o Example: collagen- binds all of the cells of the body together
Chemical reactions of the cell are controlled by protein enzymes
Protein pumps move things across the cell membrane
Proteins give mobility:
o Muscles
o Flagella & cilia
o "Molecular motors": Click to see some current research on molecular
motors at the University of York
Defend the body against foreign invaders: antibodies
Receptors: required for signaling in endocrine and nervous systems
Nucleic Acids are the Molecules of Heredity
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Two major types: DNA & RNA
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Both types have code which specifies the sequence of amino acids in
proteins
DNA = archival copy of genetic code, kept in nucleus, protected
RNA = working copy of code, used to translate a specific gene into a
protein, goes into cytoplasm & to ribosomes, rapidly broken down
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Nucleic acids are made of 5 nucleotide bases, sugars and phosphate groups
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This is the purine
base, adenine (A)
This 5 carbon
sugar is
deoxyribose. It is
found in DNA,
but not RNA.
Phosphate is an inorganic
anion (negative charrge)
o
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This is the pyrimidine
base, thymine (T).
Found in DNA but
not RNA
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This is the RNA 5
carbon sugar,
ribose. Found in
RNA, but not
DNA.
o
More
information on
nucleotide bases.
DNA
structure and
function
Hydrogen
bonds
Summary of the differences between DNA and RNA:
5 Carbon
Nucleotide Sugar
Strands Code
Bases
(a pentose
Phosphate
sugar)
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DNA
2
Archive A, C, G, T Deoxyribose Yes
RNA
1
Working
A, C, G, U Ribose
copy
Yes
The bases make up the genetic code ; the phosphate and sugar make up the
backbone
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RNA is a molecule with a single strand
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DNA is a double strand (a double helix) held together by hydrogen bonds
between the bases
o A = T; C= G because:
 A must always hydrogen bond to T
 C must always hydrogen bond to G
Lipids Form Cell Membranes and Energy Storage Depots
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Lipids are a group of unrelated molecules with these properties:
o
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Insoluble in water
High oil/water partition coefficients
Oil/water partition illustrated with colored dyes:
TThe oil/water partition coefficient = amt. of substance in oil/amt of
substance in water
 Hydrophobic substances have high oil/water partition
coefficients
 In the body, hydrophobic molecules tend to accumulate in fat
tissue
 Hydrophobic drugs cross cell membranes faster than water
soluble drugs
Triglycerides: storage fat
o Composed of 3 fatty acids & glycerol
This is an
example of a
triglyceride.
To the right
is a 3 carbon
glycerol
molecule.
Attached to
it are 3 fatty
acids with
long chains.
Triglycerides
are the main
storage form
of energy in
the body.
You can
store 9
Calories per
gram as
triglycerides.
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Phospholipids: form cell membranes
o Composed of 2 fatty acids, glycerol, phosphate and polar groups
o Like triglycerides, but one of the 3 fatty acids is replaced by polar
groups
Steroids: have 4 rings- cholesterol, some hormones, found in membranes
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This steroid is cholesterol
Cholesterol is
required to produce
stable cell
membranes.
It is also a
precursor for several
hormones produced in
the testes, ovaries and
adrenal glands.
Too much cholesterol will
promote atherosclerosis.
o
Sex hormones, cortisone and aldosterone are steroids
Polysaccharides are Used for Structure and Energy Storage
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Polysaccharides are polymers made of sugar molecules linked together
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Glycogen: energy storage in animals (4 Calories/gram): made of
glucose
Starch: energy storage in plants: also made of glucose
Glucose is most important sugar (6 carbons = a hexose sugar)
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This is
the 6 carbon sugar,
glucose
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Major energy
source for the body.
Glucose is
burned in glycolysis
& the Krebs cycle to
make ATP
Regulation of
blood glucose by
hormones.
o
Major source of cell energy
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The brain is very sensitive to the blood glucose concentration because
it cannot use fats for an energy supply
Some sugars are attached to membrane proteins (example: ABO blood groups)
Summary of Biological Macromolecules
Macromolecule
Building
Blocks
Functions
Polysaccharides
Sugars
Energy storage (4
Cal/gm)
Structure (cell walls,
exoskeletons)
Lipids:
triglycerides
Fatty acids, Energy storage (9
glycerol
Cal/gm)
Lipids:
phospholipids
Fatty acids,
glycerol,
Cell membranes
phosphate,
polar groups
Cell structure
Amino
Proteins
Nucleic Acids:
DNA
(forms a double
helix)
acids: 20
types
C, G, T
Storage of hereditary
Deoxyribose information (genetic
sugar,
code)
phosphate
Protein synthesis:
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RNA
3 types:
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channels
Hormones &
receptors
Immune system:
antibodies
4 Bases: A,
Nucleic Acids:
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Enzymes
Molecular motors
(muscle, etc)
Membrane pumps &
m-RNA
t-RNA
r-RNA
(usually a single
working copy
of genetic
4 Bases: A,
C, G, U
Ribose
sugar,
phosphate
m-RNA:
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code for a
gene
(transcription)
t-RNA &
r-RNA:
translation of
the code
strand)
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More information on energy storage in the body is given in the exercise
lecture.
Click to see a more complete review of the biological building blocks.
Click to go to a set of building block pictures that you can print out to study.
Suppose that a man has 15 lbs of stored fat. How many Calories does he have
stored in the fat? How far could he walk using this stored energy? A pound is
454 grams and a 70 kg person (154 lbs) requires 55 Calories to walk a mile.