▪ Illustrate the structure of RNA and DNA using simple labelled
diagrams;
▪ Draw a nucleotide using shapes; recognise (not draw) the structural
formulae of nucleotides, ribose, deoxyribose, pyrimidines, purines;
nature of hydrogen bonds.
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▪ What are nucleic acids?
▪ What does DNA stand for?
▪ What does RNA stand for?
▪ What are nucleic acids made up of?
▪ Using a diagram, describe the structure of nucleotides.
▪ How are dinucleotides and polynucleotides formed?
▪ Name the five nitrogenous bases. Which are purines and pyrimidines?
▪ How does the structure of purines differ to those of pyrimidines?
▪ Which nitrogenous base is not found in RNA?
▪ Which nitrogenous base is not found in DNA?
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▪ Nucleic acids are perhaps the most
important molecules in biology. They
contain the genetic material (instructions) of
every single living organism on the planet,
even the simplest virus.
NUCLEIC ACIDS
▪ DNA and RNA are nucleic acids. DNA
stands for deoxyribonucleic acid and RNA
for ribonucleic acid. They are
polynucleotides: polymers made from
monomers called nucleotides.
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Nucleotides have three parts to them:
▪ A phosphate group, which is
negatively charged.
▪ A pentose sugar, which has 5 carbon
atoms in it. In RNA the sugar is ribose.
In DNA the sugar is deoxyribose.
▪ A nitrogenous base. There are five
different bases. Adenine (A), Guanine
(G), Thymine (T), Cytosine (C), and
Uracil (U). The base thymine is found
in DNA only and the base uracil is
found in RNA only.
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▪ Nucleotides polymerise by
forming phosphodiester bonds between
the 3’ carbon of the pentose sugar of one
nucleotide and an oxygen atom of the
phosphate group of another nucleotide via a
condensation reaction.
NUCLEOTIDE
POLYMERISATION
▪ The bases do not take part in the
polymerisation, so the chain is held together
by a sugar-phosphate backbone with the
bases extending off it. This means that the
nucleotides can join together in any order
along the chain. Many (up to several million)
nucleotides form a polynucleotide.
▪ A polynucleotide has a free phosphate
group at one end and a free OH group at the
other end.
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▪ What are nucleic acids?
▪ What does DNA stand for?
▪ What does RNA stand for?
▪ What are nucleic acids made up of?
▪ Using a diagram, describe the structure of nucleotides.
▪ How are dinucleotides and polynucleotides formed?
▪ Name the five nitrogenous bases. Which are purines and pyrimidines?
▪ How does the structure of purines differ to those of pyrimidines?
▪ Which nitrogenous base is not found in RNA?
▪ Which nitrogenous base is not found in DNA?
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▪ What are the main features of the 3-dimensional structure of DNA?
▪ What type of bonds are formed between the bases in DNA?
▪ How many hydrogen bonds are formed between AT, AU and GC?
▪ How many base pairs are there in on complete turn on the DNA spiral?
▪ What is the distance between each base pair sequence along the spiral in DNA?
▪ How is RNA different to DNA?
▪ What are the different types of RNA?
▪ What are the functions of DNA?
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The main features of the 3-dimensional structure of DNA are:
▪ DNA is double-stranded, so there are two polynucleotide strands (chains)
alongside each other.
▪ The polynucleotide chains run in opposite directions to each other and are
therefore antiparallel
▪ Each of the two strands form a right-handed helical spiral and are wound
around each other to form a double helix.
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▪ The two strands are joined together by hydrogen bonds between the bases.
The bases therefore form base pairs, which are like rungs of a ladder.
▪ The base pairs are specific. A only binds to T (and T with A), and C only
binds to G (and G with C). These are called complementary base pairs.
This means that whatever the sequence of bases along one strand, the
sequence of bases on the other strand must be complementary to it.
▪ The base pairs can occur in any other, i.e. there is no restriction to their
sequence
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▪ The width between the two sugar-phosphate backbones is constant and to the
width of a base pair.
▪ Along the chain, base pairs are 0.34 nm apart.
▪ A complete turn of the double helix is 3.4 nm and consists of 10 base pairs.
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▪ …… (hydrogen bond)
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RNA is different to DNA in that:
THE STRUCTURE
OF RNA
▪ RNA has the sugar ribose instead of deoxyribose
▪ RNA has the base uracil instead of thymine
▪ RNA is usually single stranded
▪ RNA is usually shorter than DNA
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Messenger RNA (mRNA)
▪ Formed in the nucleus
▪ Has a single chain twisted into a helix whose length and
base sequence vary
▪ Has a short life
▪ Is involved in protein synthesis
▪ An mRNA molecule carries a portion of the DNA code to
other parts of the cell for processing
▪ mRNA is created during transcription.
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Transfer RNA (tRNA)
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•
•
•
tRNA matches amino acids to their codon
tRNA is only about 80 nucleotides long, and
it folds up by complementary base pairing
to form a clover-leaf structure.
At one end of the molecule there is an
amino acid binding site
On the middle loop there is a triplet
nucleotide sequence called the anticodon.
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▪ Ribosomal RNA (rRNA)
▪ Made in the nucleolus and
forms over half the mass of
ribosomes
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▪ DNA is the genetic material, and genes are made of DNA. DNA therefore has two
essential functions: replication and expression.
▪ Replication means that the DNA, with all its genes, must be copied every time a cell
divides.
▪ Expression means that the genes on DNA must control characteristics. A gene is a
section of DNA that codes for a particular protein. Characteristics are controlled
by genes through the proteins they code for, like this:
Sequences
of bases in
DNA
Shape &
determines Sequence of
determines
determines
function
of
amino acids in
protein
polypeptides
(eg. enzme)
Characteristics
of cell
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▪ Expression can be split into 2 parts
▪ Transcription:
▪ Making RNA
▪ Translation
▪ Making proteins
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▪ The sum total of all the genes in an organism is called the genome
▪ Genes only seem to comprise about 2% of the DNA in a cell
▪ The majority of the DNA does not form genes
▪ Some of this ‘junk DNA’ is used to produce non-coding RNA components
▪ The rest doesn’t seem to do anything…(or so we think)
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▪ Codon
▪ a sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA
molecule
▪ Anticodon
▪ a sequence of three nucleotides forming a unit of genetic code in a transfer RNA
molecule, corresponding to a complementary codon in messenger RNA
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▪ If a sample of DNA had 18% of guanine nucleotides, what percentage of its
nucleotides would be thymine?
▪ List 2 similarities between DNA and RNA.
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▪ What are the main features of the 3-dimensional structure of DNA?
▪ What type of bonds are formed between the bases in DNA?
▪ How many hydrogen bonds are formed between AT, AU and GC?
▪ How many base pairs are there in on complete turn on the DNA spiral?
▪ What is the distance between each base pair sequence along the spiral in DNA?
▪ How is RNA different to DNA?
▪ What are the different types of RNA?
▪ What are the functions of DNA?
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