The structure of DNA and RNA 11/10/2024

Define the following terms:

• Mono
• Pent
• Phosphate group
• Organic group
• Inorganic group
Vocabulary

1. Poly- many

2. Mono- one

3. Pent- five

4. Phosphate – one phosphorus atom bonded to four oxygen atoms.

5. Organic group- contain carbon atoms and are found in living things.
Examples include proteins, carbohydrates, and fats.

6. Inorganic compounds- usually don't contain carbon and are not typically
found in living organisms. Examples include water, salts, and minerals.
 Learning Intentions

The structure of DNA and RNA Describe the basic structure of

mononucleotides
Kent College
Science Department Describe the basic structure of DNA and RNA
as polynucleotides
Key Vocabulary
Tier 2:
Describe complementary base pairing and hydrogen
Tier 3: bonding are involved in the formation of the DNA
Mononucleotides, adenosine triphosphate (ATP) deoxyribonucleic acid (DNA),
ribonucleic acid (RNA), ribose, deoxyribose, purine base, pyrimidine base,
double helix
adenine, guanine, cytosine, thymine, uracil, nucleic acids, polynucleotides,
phosphodiester bonds, complementary base pairs
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Mononucleotides

Both DNA and RNA are polymers that are

made up of many repeating
units called (mono)nucleotides (A, G, C, T/U)

Each nucleotide is formed from:

• A pentose sugar (a sugar with 5
carbon atoms)
• A nitrogen-containing organic base
• A phosphate group
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Mononucleotides
2. The phosphate group PO₄³⁻ means the
1. The two most common types of nucleotides nucleotides are acidic molecules and carry a
have either a purine base or a pyrimidine negative charge.
base.
3. The sugar group contains 5 carbon atoms
Common purines include: (pentose). Which are numbered.
• Adenine (A)
Can you recall how the carbons are
• Guanine (G)
numbered in a ring structure is (topic 1)?
Common pyrimidines include: 4. The sugar, base and phosphate group are
• Cytosine (C) joined together by condensation reactions
• Thymine (T) forming a mononucleotide.
• Uracil (U) This condensation reaction involves the
elimination of 2 water molecules.
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Purine base vs pyrimidine base.

Purines
They have a double ring structure

Pyrimidines
They have a single ring structure
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

DNA nucleotides vs RNA nucleotides

1. Draw the structure of a DNA and RNA

nucleotide.
2. Number the different carbon atoms in your
diagram
3. Describe the differences in their structures
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

DNA nucleotides

The components of a DNA nucleotide are:

• A deoxyribose sugar
with hydrogen at the 2' position
• A phosphate group
• One of four nitrogenous bases -
adenine (A), cytosine(C),
guanine(G) or thymine(T)
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

RNA nucleotides
The components of an RNA nucleotide are:
• A ribose sugar with a hydroxyl (OH) group
at the 2' position
• A phosphate group
• One of four nitrogenous bases - adenine
(A), cytosine(C), guanine(G) or uracil (U)

The presence of the 2' hydroxyl group makes RNA

more susceptible to hydrolysis
• This is why DNA is the storage molecule and
RNA is the transport molecule with a
shorter molecular lifespan.
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

DNA nucleotides vs RNA nucleotides

Key differences

• Ribose and deoxyribose at C2

• DNA has the base T, RNA has the base U

• 2' hydroxyl group makes RNA more susceptible to hydrolysis

• This is why DNA is the storage molecule and RNA is the GO FURTHER
transport molecule with a shorter molecular lifespan. Why does DNA contain the base
thymine whilst RNA contains the
• A short RNA lifespan ensures that the proteins are
base uracil
produced only when needed and in appropriate
amounts
• Prevents the accumulation of unnecessary or potentially
harmful proteins.
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Polynucleotides aka nucleic acids

DNA and RNA are polymers (polynucleotides),

meaning that they are made up of many nucleotides
joined together in long chains.

1. Research how polynucleotides are formed.

Key vocabulary to use:

• condensation reactions
• phosphodiester bond
• sugar-phosphate backbone

2. Complete the diagram aside and use it as

an aid to answer question 1 above

A polynucleotide strand: makes basic structure of both DNA and RNA

 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Phosphate One nucleotide

(mononucleotide)

Ester bond
Phosphodiester
Glycosidic
bond formed by Phosphate bond formed by
condensation condensation reaction
reaction Ester bond

Polynucleotide
chain

Sugar-phosphate backbone
Note: backbone excludes
the base
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Polynucleotides aka nucleic acids

DNA and RNA are polymers (polynucleotides), meaning that they are made up of many
nucleotides joined together in long chains.

Separate nucleotides are joined via condensation reactions

• These condensation reactions occur between the phosphate group of one
nucleotide and the pentose sugar of the next nucleotide

A condensation reaction between two nucleotides forms a phosphodiester bond

• It is called a phosphodiester bond because it consists of a phosphate group
and two ester bonds (phosphate with double bond oxygen attached - oxygen -
carbon)
• The phosphodiester bonds link the 5-carbon of one deoxyribose sugar molecule to
the phosphate group from the same nucleotide, which is itself linked by another
phosphodiester bond to the 3-carbon of the deoxyribose sugar molecule of the
next nucleotide in the strand

The chain of alternating phosphate groups and pentose sugars produced as a result of many
phosphodiester bonds is known as the sugar-phosphate backbone (of the DNA or RNA
molecule)
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Polynucleotides: RNA vs DNA

1. Research the structure of the
polynucleotides of RNA and
DNA.

2. Highlight the similarities and

differences in their structures

Refer to ‘Savemyexams’ or ‘Bitesize’

(Edexcel AS version only) or your
textbooks.
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Polynucleotides: DNA
DNA molecules consist of two polynucleotide strands twisted
around each other forming the DNA double helix.

Sugar phosphate groups make the backbone

On the inside bases bond in pairs in a specific way:

• A purine base [Adenine (A), Guanine (G )] always pairs
with a pyrimidine base [Cytosine (C)Thymine (T) Uracil (U
)]
• A pairs with T
• C pairs with G
• Pairs are held together by hydrogen bonds.
• Hydrogen bonds form between the amino and carbonyl
groups of the opposite bases.
• There are 3 hydrogen bonds between C and G and 2
hydrogen bonds between A and T

There are 10 base pairs for each complete twist of the helix.
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Polynucleotides: DNA

See diagram aside:

• Each DNA polynucleotide strand is said to have

a 3’ end and a 5’ end (these numbers relate to
the carbon found on the end of each strand)

• Strand are antiparallel- they run in opposite

directions, one is known as the 5’ to 3’
strand and the other is known as the 3’ to 5’
strand
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Polynucleotides: RNA
RNA molecules forms single polynucleotide strands. Unlike DNA
which is a double strand.
• These strands either fold into complex shapes held in place by
hydrogen bonds or remain as long thread like molecules.

Like DNA, contains the phosphodiester bonds between the sugar

and phosphate groups. Bond is between C5 on one deoxyribose
sugar molecule and C3 on the other

Like DNA, RNA (ribonucleic acid) is a polynucleotide – it is made

up of many nucleotides linked together in a chain.

Like DNA, RNA nucleotides contain the nitrogenous bases

adenine (A), guanine (G) and cytosine (C)
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Polynucleotides: RNA

Unlike DNA, RNA nucleotides never contain the

nitrogenous base thymine (T) – in place of this they
contain the nitrogenous base uracil (U)

Unlike DNA, RNA nucleotides contain the pentose

sugar ribose (instead of deoxyribose)
RNA polynucleotide chains are relatively short compared
to DNA

Example of an RNA molecule include:

• messenger RNA (mRNA), which is the transcript copy
of a gene that encodes a specific polypeptide.
• transfer RNA (tRNA)
• ribosomal RNA (rRNA)
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Consolidate learning
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix
 Describe complementary base pairing and
Describe the basic structure of Describe the basic structure of DNA and
hydrogen bonding are involved in the
mononucleotides RNA as polynucleotides formation of the DNA double helix

Have you met the LI?

Describe the basic structure of mononucleotides

If you didn’t meet (or you are

not confident) about your
Describe the basic structure of DNA and RNA as learning outcomes what are your
polynucleotides next steps? How will you secure
your learning.

Make a learning promise.

Describe complementary base pairing and hydrogen bonding are

involved in the formation of the DNA double helix