Transcript Unit 1 – Chapters 4, 5

UNIT 1 - Chapters 4,5
THE CHEMISTRY OF LIFE
Carbon and its role in life
• Although living cells are made up
of 70% - 90% water, most of the
“meat and potatoes” is made up
of carbon based compounds
• Carbon is a solid in its natural
state
• The study of carbon compounds
is called Organic Chemistry
• Carbon can form 4 covalent
bonds
• The simplest organic molecule is
CH4 or methane
Hydrocarbons
• A carbon backbone surrounded with hydrogen
• Hydrocarbons can exist as straight chains, rings, and
several other structural forms
• A simple chain of carbons with its full complement of
hydrogens (single C-C bonds) is said to be saturated.
These saturated, simple, straight chain hydrocarbons
are known as alkanes.
• Hydrocarbons with double bonds in them are said to
be unsaturated. Their molecules contain at least one
double bond.
• Hydrocarbons containing double C-C covalent bonds
are called alkenes and those with triple bonds are
alkynes
Alkanes
Straight-chain alkanes
Ring-form alkanes
Alkenes
Can you name these alkenes?
Ethene or ethylene
Propene or propylene
Butene or butylene
Alkynes
Ethyne
Propyne
Can you name these alkynes?
Butyne
Isomers
• Sometimes two hydrocarbon molecules
can have the same numbers of the same
atoms but have different arrangements of
these atoms. These are called isomers
• There are 3 major types of isomers:
Structural, Geometric and enantiomers
Structural Isomers
• Have the same molecular
formula, but different
covalent arrangement of
their atoms – so different
chemical properties
Butane vs. isobutane
Geometric Isomers
•Involve molecules with double bonds that prevent free rotation
•The inflexibility of the double bonds allows for different shapes
and hence different properties
cis-2-butene vs. trans-2-butene
cis ethylene dibromide vs. trans ethylene dibromide
Enantiomers
•Different molecular arrangements around an asymmetric Carbon
•An asymmetric carbon is one with 4 different atoms or groups of
atoms around it
•They are mirror images and cannot be superimposed (Chiral)
•They have right-hand (D - for dextrorotatory ) and left-hand (L – for
levorotatory) versions
•There are many enantiomers in a living cell, but usually only one of
the two is active (the cell can distinguish between the two)
Enantiomers, cont’d.
•
•
For example, S-caravone ("left-handed") is the flavor of caraway, while Rcarvone ("right-handed") is the flavor of spearmint.
Spearmint
Caraway
An example of this is thalidomide which is racemic — that is, it contains
both left and right handed isomers in equal amounts. One enantiomer is
effective against morning sickness, and the other is teratogenic. It should
be noted that the enantiomers are converted to each other in vivo. That is,
if a human is given D-thalidomide or L-thalidomide, both isomers can be
found in the serum. Hence, administering only one enantiomer will not
prevent the teratogenic effect in humans.
Functional Groups
• These are the parts of a molecule that give
the molecules its “personality”
• Functional groups are the parts of a
molecule that are most involved in
chemical reactions
• Functional groups have specific behaviors,
regardless of which molecule they are
found in (although the molecules
themselves have unique properties)
Functional
groups
commonly found
in living cells
The Hydroxyl Group
• -OH
• The hydroxyl group is polar because of the
oxygen atom and makes a compound
soluble
• Organic compounds containing OH groups
as the prominent functional group are
called alcohols
• Most alcoholic compounds end with “ol”
as in ethanol, methanol, glycerol, etc.
The Carbonyl Group
• -C=O (Carbon and oxygen sharing a double
covalent bond)
• If the carbonyl group is at the end of a
hydrocarbon chain (terminal), the compound is
considered an aldehyde; these compounds
usually contain an “al” as in Propanal or
Formaldehyde
• If the carbonyl group is not terminal, the
compound is considered a ketone; these
compounds usually contain an “one” as in
Acetone or Propanone
The Carboxyl Group
• Compounds with this functional group are called
carboxylic acids, because they tend to give up the H
from the –OH group (This is because the 2 oxygen
atoms in the carboxyl group pull the shared electrons
away from the H)
• If the –OH was alone or far away from the C=O, the H
would not dissociate as easily

Acetic Acid
+
Acetate Ion
H+
Proton
The Amine Group
• A nitrogen atom bonded to 2 Hydrogens
• Acts as a base, because the –NH2 or NH3
can pick up protons (H+) from their
surroundings; remember nitrogen’s lone pair of electrons
that attract H+ ions?
Ammonium ion
Amino Acids
• These compounds have both: a carboxyl group as well as an amino group
• Sometimes both the carboxyl end and the amino end are in the ionized state
– these are now called zwitterions
Zwitterion
The Phosphate Group
• PO4
• Derived from phosphoric acid
• The Hydrogens tend to dissociate easily due to the
number and proximity of oxygen atoms
• So phosphoric acid becomes a phosphate ion
• Very important component of the DNA backbone

O
O- P
O
Phosphate ion
O-
The Sulfhydryl Group
• S-H
• Sulfur is under Oxygen in the
periodic table, both can form 2
covalent bonds
• Organic compounds
containing sulfhydryl groups
are called Thiols
• Sulfhydryl groups are found in
certain amino acids like
cysteine and methionine and
are extremely important in the
tertiary structure of proteins
The Structure and Function of
Macromolecules
Polymers
• Large compounds made of
repeating subunits of a
smaller compound called
monomers
• Formed by dehydration
synthesis (Condensation
reaction)
• Dissociated by hydrolysis
Four Biological Macromolecules
• Carbohydrates – Range from simple sugars, to
complex carbs like starch.
• Lipids – Include oils, fats, waxes and steroids.
They are the only macromolecules that are not
considered polymers
• Protein – made up of repeating units of amino
acids
• Nucleic Acids – DNA, tRNA, mRNA, rRNA
CARBOHYDRATES
• The building blocks are simple “single” sugars called
monosaccharides
• Sugars contain a hydrocarbon backbone, with 2
important functional groups:
- multiple hydroxyl groups and a
- carbonyl group
• Monosaccharides can bond to each other and form
disaccharide (2), oligosaccharides (~10) or
polysaccharides (100s or 1000s)
• Sugars are named according to:
- the number of carbons in their backbone
- and the location of the carbonyl group
• Another characteristic of monosaccharides is that they
can act as mild reducing agents. This is because the
aldehyde group (Carbonyl) that is present can be
oxidized to form a carboxylic acid group, or in the
presence of a base, a carboxylate ion group.
Structure of some Monosaccharides
(also known as dextrose)
Sugars end in “ose”
Linear versus Ring forms
Sugars tend to change into ring forms when
placed in an aqueous solution. Here is an
example of straight chain glucose changing
into its ring form. But while in solution, the
molecules can keep changing back-and-forth
from chain to ring, ring to chain.
α and β forms of glucose
OH group on top
OH group on the bottom
When the glucose molecule takes on a ring form, it can form one
of 2 isomers. The tiny difference between these two isomers of
the same molecule means that the polysaccharide that they form
is different. The 2 isomers, α and β forms of glucose is evident
in the diagrams above.
Making Disaccharides
• 2 glucose molecules bond covalently to form maltose
• 1 fructose and 1 glucose bond to form sucrose (table sugar)
• 1 glucose and 1 galactose bond to form lactose (found in milk
and dairy products)
People who are lactose intolerant, do not
make lactase, an intestinal enzyme that
hydrolyzes lactose into its constituent
monosaccharides, glucose and galactose
which can then be easily absorbed into
the blood, across the intestinal lining.
When lactose cannot be broken down, it
ferments in the gut and causes bloating,
diarrhea, flatulence, etc.
70% of the world population is lactose
intolerant. However, only 10% of
Europeans are.
Making Polysaccharides
• Multiple monosaccharides form chains by
forming covalent bonds through
dehydration synthesis. These covalent
bonds are called glycosidic linkages.
• Polysaccharides can be considered either
“storage polysaccharides” or “structural
polysaccharides”, based on their structure
and role in cells.
Storage Polysaccharides
•Plants store their polysaccharides as starch. So starch = stored energy.
•Starch s made up of 2 types of polysaccharides - amylose and amylopectin
•Amylose is α-glucose molecules in 1-4 glycosidic linkages
•Amylopectin is α-glucose molecules in 1-4 as well as 1-6 glycosidic linkages.
This makes amylopectin more highly branched.
•Starch is stored in plant cellular organelles called plastids, including
amyloplasts and chloroplasts.
Storage Polysaccharides, cont’d.
•
•
•
•
Animals store their polysaccharides as glycogen. Glycogen = stored energy
Glycogen is made up of a-glucose molecules in 1-4 as well as 1-6 glycosidic
linkages. It is similar to amylopectin, but more highly branched.
Animals store glycogen in muscle and liver cells, in cellular organelles called
mitochondria. Here it is hydrolyzed into glucose molecules, for cellular
respiration.
Animals derive glucose from food – mainly starch from plants, which is
hydrolyzed by the enzyme amylase, into glucose, absorbed into the blood
stream and the excess is converted into glycogen for storage.
Starch - α-glucose molecules
Plant-storage polysaccharide
•α-glucose molecules combine in 1-4 glycosidic linkages to form amylose,
the simplest form of starch. The fact that in α-glucose both hydroxide
groups are on the bottom of the ring means that all of the monosaccharide
rings are in the same plane. This polysaccharide is easily metabolized by
the human digestive system; in fact, it is the principal source of energy for
most people.
•Starch also consists of another more complex form called amylopectin.
The only difference between amylose and amylopectin is that amylopectin
is branched – it has 1-4 as well as 1-6 glycosidic linkages.
Cellulose – β-glucose molecules
Plant structural polysaccharide
β-glucose molecules combine to form
cellulose. Because of the structure of
β-glucose, in cellulose every other
sugar molecule is upside-down to
accommodate 1-4 linkages. Cellulose
is mainly found in plant cell walls.
Cellulose is also known as
dietary fiber. This
polysaccharide cannot be
broken down by the human
digestive system. Instead, it
passes unaffected through
the intestine, with no
nutritional value. Grass-eating
animals cannot break it down
either, but rely on bacteria in
their guts to break it down for
them. Termites do not
produce cellulase, but share
a symbiotic relationship with
protozoans in their gut who do
produce the enzyme.
Chitin – β-glucose molecules
Animal structural polysaccharide
Chitin is almost identical to cellulose, except that its glucose monomers contain
a nitrogen-containing side chain. Chitin is found in the cell walls of fungi and
arthropod exoskeletons (insects, crustaceans, arachnids).
Cellulose, chitin, and starch are
the three most abundant
organic compounds in nature.
Reducing Sugars
• Another characteristic of monosaccharides is that they can act as mild
reducing agents. This is because the aldehyde group that is present can be
oxidized to form a carboxylic acid group, or in the presence of a base, a
carboxylate ion group.
• Fructose can also act as a reducing sugar, even though it has a ketone
group instead of an aldehyde group. Under basic conditions, the fructose
molecules can, essentially, have the location of the carbonyl bond switched
to convert them into a glucose molecule. This occurs in a number of steps
involving removing hydrogens from the #1-C and its oxygen and moving
them to the #2-C and its oxygen.
• In one sense, monosaccharides that are in the ring form are not reducing
sugars because they don't have the aldehyde group that can be oxidized.
However, because they're in equilibrium with the open form, any
monosaccharide molecule that's in a ring form will, within a fraction of a
second, be in the open form and, thus, be able to react with the oxidizing
agent and reduce it.
Laboratory
Detecting reducing sugars in solution
• What is Benedict’s Solution?
It is a deep-blue alkaline solution used to test for the presence of the
aldehyde functional group, -CHO.
The substance to be tested is heated with Benedict's
solution; formation of a brick-red precipitate indicates presence of the
aldehyde group.
Simple sugars (e.g., glucose) give a positive test,
One liter of Benedict's solution contains 173 grams sodium citrate, 100
grams sodium carbonate, and 17.3 grams cupric sulfate pentahydrate.
Benedict's solution contains copper(II) ions complexed with citrate ions in
sodium carbonate solution.
The cupric ion (complexed with citrate ions) is reduced to cuprous ion by the
aldehyde group (which is oxidized), and precipitates as cuprous oxide,
Cu2O, which is a deep brick red.
RCHO + 2 Cu 2+ (in complex) + 5OH-  RCOO- + Cu2O + 3H2O
Benedict’s Test Results
5
0
3
5
2
Detecting starch in solution
Amylose and amylopectin
• When starch is mixed with iodine in water, an intensely
colored starch / iodine complex is formed. Starch
consists of two types of molecules, amylose (normally
20-30%) and amylopectin (normally 70-80%). The
unbranched amylose is a chain of glucose molecules
bounded together. The chain is coiled in the shape of a
helix. The iodine (in the form of KI5) inserts itself into the
helix making it rigid. This changes the color to blue.
Helix amylose possesses a relatively hydrophobic inner
surface that holds a spiral of water molecules. It is
responsible for the characteristic binding of amylose to
chains of charged iodine moleclues (polyiodides formed
from neutral iodine molecules in aqueous solution). The
blue color is due to donor acceptor interactions between
water and the electron deficient polyiodides. When heat
is applied, the complex is destroyed. When the solution
has cooled the 'blue' of the amylose/iodine combination
appears.
• Starch from different sources contains different
proportions of amylose and amylopectin. Waxy rice
consists of 100% amylopectin and no amylose.
Amylopectin having a branching structure does not form
a helix. It reacts with iodine to form red-brown color.
Iodine Test Results
0
2
0
1
Lipids
• Lipids are the only major biological
macromolecules that are not polymers (no
repeating units)
• The lipid family consists of fats, oils,
waxes, phospholipids and steroids.
• All lipids are hydrophobic (completely or
partially)
Fats - Triglycerides
•Fats or triglycerides are composed of 3 fatty acids and one glycerol
molecule.
•Fatty acids are long hydrocarbon chains with a terminal carboxyl group
•The “tail” of a fatty acid is a long hydrocarbon chain, making it
hydrophobic. The “head” of the molecule is a carboxyl group which is
hydrophilic.
•They have varying lengths and may contain double or triple bonds
• If they contain only single
bonds, they are considered
saturated (carrying their full
complement of Hydrogen
atoms.
• If they contain double or triple
bonds, they are considered
either mono or poly
unsaturated
Fats – Triglycerides, cont’d.
• Fats and oils are made from
two kinds of molecules:
glycerol (a type of alcohol with
a hydroxyl group on each of its
three carbons) and three fatty
acids joined by dehydration
synthesis. Since there are three
fatty acids attached, these are
known as triglycerides.
• Although fatty acids are part
hydrophilic, when the head end
is attached to glycerol to form a
fat, the whole fat molecule is
hydrophobic.
Is this a saturated or unsaturated fat?
Fat = 1 glycerol + 3 fatty acids
3 ester linkages (OH + COOH) are formed through dehydration synthesis,
releasing 3 water molecules.
Fats vs. Oils
• Saturated fats tend to have a high melting
point, because their fatty acid chains are
straight and the fat molecules can pack
closely together making them solid at room
temperature. Saturated fats are found in
animals (lard) and are to blame for
clogging arteries!
• Unsaturated fats have kinks in their tails, so
they cannot pack closely. This gives them a
low melting point and the tendency to be
liquid at room temperature and are called
oils. Oils are found in plants and fish. Much
better for your arteries!
What are Hydrogenated Fats?
• Oils tend to have a shorter shelf life
because they become rancid – oxidized
through exposure to air and light
• Oils are therefore often “artificially
saturated” or hydrogenated, so they
become solid at room temperature and
more stable
Trans-Fatty acids
• The body utilizes the curved structure of
unsaturated fats to
a) form pathways in and out of cells,
b) to transmit electric impulses.
Double bonds (cis) have a slight charge
where single bonds and straightened
(trans) double bonds do not. This makes
the passage of cis-fatty acids across
membranes easier.
Omega-3 oils, which are healthy unsaturated
oils, are simply oils that contain a double
bond after the 3rd carbon atom. Omega-6 oils
contain a double bond after the 6th carbon
atom. A healthy diet should contain a balance
of both omega-3 and omega-6 oils.
Wax
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•
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Wax has traditionally referred to a substance that is secreted by bees
(beeswax) and used by them in constructing their honeycombs.
In modern terms, wax is an imprecisely defined term generally
understood to be a substance with properties similar to beeswax,
namely
plastic (malleable) at normal ambient temperatures
a melting point above approximately 45 °C (which differentiates
waxes from fats and oils)
a relatively low viscosity when melted (unlike many plastics)
insoluble in water
hydrophobic
Waxes may be natural or artificial. In addition to beeswax, carnauba (a
vegetable wax) and paraffin (a mineral wax) are commonly
encountered waxes which occur naturally. Ear wax is a sticky
substance found in the human ear. Some artificial materials that
exhibit similar properties are also described as wax or waxy.
Chemically, a wax may be an ester of ethylene glycol (ethan-1,2-diol)
and two fatty acids, as opposed to a fat which is an ester of glycerin
(propan-1,2,3-triol) and three fatty acids. It is a type of lipid.
Eeeeewww! Ear Wax!
• Cerumen is produced in the outer third of the
cartilaginous portion of the human ear canal. It is a
mixture of viscous secretions from sebaceous glands
and less-viscous ones from modified apocrine sweat
glands (Alvord & Farmer, 1997). Cerumen is genetically
determined – Asians and Native Americans are more
likely to have the dry type of cerumen (grey and flaky),
whereas Caucasians and Africans are more likely to
have the wet type (honey-brown to dark-brown and
moist; Overfield, 1985). In fact, cerumen type has been
used by anthropologists to track human migratory
patterns, such as those of the Inuit (Bass & Jackson,
1977).
Phospholipids
• Phospholipids are diglycerides that are covalently
bonded to a phosphate group by an ester linkage
• In many cells the phospholipids are further modified by
the covalent bonding of additional compounds the
phosphate.
Phospholipids, cont’d.
• Phospholipids are amphipathic
• When phospholipids are
suspended in water they can
form a variety of structures. In all
cases the hydrophilic phosphate
region interacts with water and
the hydrophobic fatty acid
regions are excluded from water
and form hydrophobic
interactions.
How do detergents work?
1. Made up of phospholipids
2. The hydrophobic tails surround greasy dirt
particles
3. Hydrophilic heads face water and lift the grease
to the surface
4. Water washes off trapped grease particle
Phospholipid Bilayers
• One structure that can result when phospholipids are suspended in
water is shown below. A bilayer of phospholipids forms a sphere in
which water is trapped inside. The hydrophilic phosphate regions
interact with the water inside and outside of the sphere. The fatty
acids of the phospholipids interact and form a hydrophobic center of
the bilayer.
PL bilayers form plasma (cell) membranes
Steroids
• Another major class of lipids is
steroids, which have structures
totally different from the other
classes of lipids. The main
feature of steroids is the ring
system of three cyclohexanes
and one cyclopentane in a
fused ring system as shown
below. There are a variety of
functional groups that may be
attached. The main feature, as
in all lipids, is the large number
of carbon-hydrogens which
make steroids non-polar.
• Steroids include such well
known compounds as
cholesterol, sex hormones,
birth control pills, cortisone,
and anabolic steroids.
Proteins
• Proteins can be categorized into several
different families, depending on their role
in a living organism
• Amino acids are the building blocks of
proteins
• There are over 100 amino acids, only 20
of which are used in protein building, by all
organisms
Collagen
DNA Polymerase
Catalase, Amylase
An amino acid
2 is in the Zwitterion state – when a compound can exist as an
anion and a cation at the same time
The 20
Amino
acids used
for protein
synthesis
These amino
acids have been
separated
according to the
chemical
properties of their
side chains
Source of amino acids
• Unlike by plants, most amino acids cannot be synthesized by
animals. Those that cannot be synthesized are called essential
amino acids (EAA) and animals have to rely on obtaining them
through their diet (either from plants or from other animals which
already contain them) or on their synthesis by gut bacteria.
The Essential Amino Acids
Histidine
Isoleucine
Leucine
Lysine
Methionine (and/or cysteine)
Phenylalanine (and/or
tyrosine)
Threonine
Tryptophan
Valine
Dipeptides, Polypeptides
• Amino acids are joined end – to –end by
enzymes through dehydration synthesis, to
form polypeptides (releasing a water
molecules as a by product)
• The covalent bond that forms between the
carbon of one amino acids and the nitrogen
of another is called a peptide bond.
Polypeptides
• All polypeptides have a carboxyl end (Cterminus) and an amino end (N-terminus)
N-terminus
C-terminus
Protein structure
• Once a polypeptide forms, it tends to fold
into several possible structures
• These structures form due to various types
of bonding and chemical interactions
between the amino acids in the chain
Primary Structure
• The first level of structure is called primary
structure. The primary structure of a peptide or
protein is simply the sequence of amino acids.
The sequence of amino acids determines the
structural and functional characteristics of the
protein. Proteins with very different sequences of
amino acids (different primary structures) will
have very different properties.
• The primary structure is held together by peptide
(covalent) bonds
Secondary Protein Structure
-Helix and -pleated sheets
•Depending on the sequence of amino acids, a
polypeptide chain can fold in a number of ways. This
folding will be driven in part by the tendency of
hydrophobic side chains to minimize their contact with
water and hydrophilic side chains to maximize their
contact with water.
•In an  - helix, hydrogen bonding between every fourth
amino acid maintains the structure
•In -pleated sheets, the hydrogen bonding is between
adjacent amino acids
Secondary Protein Structure
-Helix and -pleated sheets
•Depending on the sequence of amino acids, a polypeptide chain can fold in a number of
ways. This folding will be driven in part by the tendency of hydrophobic side chains to
minimize their contact with water and hydrophilic side chains to maximize their contact with
water.
•In an  - helix, hydrogen bonding between every fourth amino acid maintains the structure
•In -pleated sheets, the hydrogen bonding is between adjacent amino acids
Tertiary Structure
• This occurs when the protein folds into a
complex 3-dimensional shape
• It involves many different kinds of bonds and
interactions between amino acids side chains
such as: Hydrogen bonds, Hydrophobic
interactions, Van der Waals forces, disulfide
bridges and ionic bonds.
• These proteins are usually called globular and
are soluble in water
• Enzymes are examples of globular proteins
Tertiary Structure
Quaternary Structure
• When multiple tertiary
structures interact to
form a more complex
globular protein, it is
called a quaternary
structure
• Hemoglobin is a protein
made up of 4 tertiary
protein chains
• The quaternary structure
is usually held together
by hydrogen bonds
between the chains
Protein Structure Summary, cont’d.
Protein Denaturation
• When a protein loses its tertiary
or secondary structure, it also
loses its function – it is
denatured
• A change in pH (treatment with
an acid or base), or
temperature (freezing or boiling)
can cause a protein to denature
• Occasionally, if the denatured
protein remains dissolved, it
can return to its original
conformation when the
denaturing agent is removed.
Protein Manufacture
• Polypeptides are assembled at the
ribosomes
• They are then folded into their native
configuration either in the endoplasmic
reticulum, or in the cell cytoplasm
• This folding is “supervised” by many
proteins called Chaperone proteins.
Biuret Reagent for protein detection
Nucleic Acids
• Category consists of DNA and RNA
• DNA = Deoxyribonucleic Acid, RNA = Ribonucleic Acid
• DNA is double stranded, contains the sugar deoxyribose and
the nitrogenous bases Thymine, Adenine, Guanine and
Cytosine
• RNA is single stranded (usually), contains the sugar ribose and
the nitrogenous bases Uracil, Adenine, Guanine and Cytosine
Nucleotide triphosphates
• A nucleotide is the building block of DNA or RNA
• It consists of a 5-Carbon sugar (either ribose or deoxyribose), 1
Phosphate groups and a Nitrogenous base
• A nucleotide that has not been incorporated into DNA starts out with 3
phosphates instead of 1
• 2 of the 3 phosphates are hydrolyzed by enzymes. This gives the
enzyme energy to incorporated the nucleotide into the DNA
Enzymatic hydrolysis of high
Energy bond between 2nd and 3rd
Phosphates
Pyrophosphate released
( Inorganic phosphate (PPi)
Deoxyribonucleotide triphosphate (dNTP)
)
Deoxyribonucleotide monophosphate (dNMP)
Incorporation of Nucleotides into DNA
The Nitrogenous Bases
• They are Nitrogen-containing
compounds that are basic in
nature – but overall, DNA is
mildly acidic
• Divided into Purines and
Pyrimidines
• Purines are larger in structure
than pyrimidines
• Adenine and Guanine are
purines
• Cytosine, Thymine and Uracil
are pyrimidines
• A and T or A and U can form 2
Hydrogen bonds
• G and C form 3 Hydrogen bonds
(a stronger alliance than A-T)
Guanine and Cytosine
Adenine and Thymine
3’ to 5’ direction
Sugar-phosphate backbone
5’ to 3’ direction
Sugar-phosphate backbone
DNA is antiparallel.
One strand runs 5’ to
3’ and the other 3’ to
5’. This is the only
configuration that will
allow proper H bond
formation and
distances between
the bases.
Minor groove
• 2 antiparallel strands
• Sugar-Phosphate backbone held together
by phosphodiester bonds
• Right-handed
• One full turn every 3.4 nm or 10 base pairs
• Sugar phosphate backbones on the
outside
• Bases stacked on the inside
• Purine-pyrimidine pairing, stabilized by H
bonds (G=C) and (A=T)
• B-DNA form is most common in organisms
• Major groove and minor groove – major
groove is where enzymes that replicate
DNA bind to the molecule
Major groove
DNA in a nutshell
DNA - View from the top
DNA gets packaged into
a chromosome
Types of RNA