Nucleotides
Specification:
• State that deoxyribonucleic acid (DNA) is a
polynucleotide, usually double stranded, made
up of nucleotides containing the bases adenine
(A), thymine (T), cytosine (C) and guanine (G);
• State that ribonucleic acid (RNA) is a
polynucleotide, usually single stranded, made up
of nucleotides containing the bases adenine (A),
uracil (U), cytosine (C) and guanine (G);
Polynucleotides
• Nucelic acids come in two forms: DNA and
RNA
• They hold all the information to make
proteins which is what all living things are
made up of
• Almost all of the DNA in a eukaryotic cell is
found in the nucleus
• RNA is found in 3 different forms
Monomers
• The monomer of all
nucleic acids (DNA and
RNA) is called a
nucleotide
• Each single nucleotide is
made up of; one
phosphate group, one
sugar molecule, one
organic nitrogenous base
• All three sub-units are
joined by covalent bonds
Nucleotides
• There are five different
nucleotides called A, T, C,
G and U
• The phosphate group in
all nucleotides is the
same
• The sugar molecule is a 5
carbon sugar; either
deoxyribose in DNA or
Ribose in RNA
• The 5 possible bases are
adenine; A, Thymine; T,
Guanine; G, Cytosine; C,
and Uracil; U
Joining nucleotides together
• A condensation reaction occurs between the
phosphate group of one nucleotide and the
sugar of another nucleotide
• Repeating the bonding gives a long chain of
nucleotides
• This forms the ‘backbone’ of the molecule
Nucleotides to Nucleic Acids
• Chains of nucleic acids bond together to
make nucleic acids
• Only nucleic acids carrying the same
sugar (ribose or deoxyribose) can be
binded together
• This makes nucleic acids either RNA or
DNA
Too Much Nucleic Acid
• Uric acid is produced when excess purines
(Adenine and Guanine) are broken down
in the liver
• It is excreted in urine
• Some people have too much uric acid in
the blood which is turned into crystals that
are deposited at the joints making them
swollen (this is called gout)
Task
• Using Cambridge Biology
p124- 126, outline the
structure of DNA- you
must include the key
words in bold in the
paragraphs
• When finished, complete
the DNA modelling task
titled ‘Have Your DNA and
Eat It’
• Then complete the
questions on the printed
slide- they will be peer
assessed next lesson!
Questions
1. Outline how DNA replicates
2. Define the term anti-parallel
3. Write down the complimentary strand
sequence for DNA and RNA- ATTAGGCTAT
4. If a DNA is 20% Thymine, what percentage of
each of the other types would it contain?
5. What type of disease can result from DNA
copying going wrong?
Questions
1.
2.
3.
4.
5.
Outline how DNA replicates semiconservatively- the double helix
is untwisted, the hydrogen bonds between the bases are broken
apart and ‘unzip’ to expose the bases, free DNA nucleotides are
hydrogen bonded onto the exposed bases according to the base
pairing rule A-T G-C, covalent bonds are formed between the
phosphate of one nucleotide and the sugar of the next to seal the
backbone
Define the term anti-parallel prallel, but with chains running in
opposite directions
Write down the complimentary strand sequence for DNA and
RNA- ATTAGGCTAT DNA TAATCCGATA RNA UAAUCCGAUA
If a DNA is 20% Thymine, what percentage of each of the other
types would it contain? 20% Adenine, 30% Cytosine, 30%
Guanine
What type of disease can result from DNA copying going wrong?
Cancer may occur if DNA is not copied properly
DNA- Information Storage
• DNA is a long chain polymer of nucleotide
monomers
• The polymer is called a polynucleotide
• A DNA molecule forms when two
polynucleotide molecules come together
forming a ladder like structure
Hydrogen Bonding and Base
Pairing
• The two DNA strands run parallel to each other
• The term anti-parallel is used because the strands run in
opposite directions to one another
• The chains are always the same distance apart because
bases pair up in a specific way.
• When a purine appears on one side, a pyrimidine
appears on the other
• Adenine always pairs with thymine, and guanine always
pairs with cytosine
• As the strands come together, hydrogen bonds form
between the bases
• The base pairing is described as complimentary
Double Helix
• In a complete DNA molecule, the anti-parallel
chains twist, like twisting a rope ladder, to
form the final structure known as a double
helix
Making Copies
• DNA replication takes place during
interphase of the cell cycle
• It is the process that creates identical
sister chromatids
Making Copies
• In order to make a new copy of
a DNA molecule:
• The double helix is untwisted
• Hydrogen bonds between the
bases are broken apart to
‘unzip’ the DNA and expose
the bases
• Free DNA nucleotides are
hydrogen bonded onto the
exposed bases according to
the base pairing rules (A-T and
C-G)
• Covalent bonds are formed
between the phosphate of one
nucleotide and the sugar of the
next to seal the backbone.
Making Copies
• This continues all the way
along the molecule until two
new DNA molecules (double
helices) are formed, each is an
exact replica of the original
DNA molecule because of the
base pairing rules.
• This process is known as
semi-conservative replication.
• Each new DNA molecule
consists of one conserved
strand plus one newly built
strand
How is the Structure of DNA related
to its function?
• The sequence of bases acts as
information storage in the form
of codes to build proteins
• The molecules are long to
store more information
• The base pairing means that
complementary strands of
information can be replicated
• The double helix gives the
molecule stability
• Hydrogen bonds allow for easy
unzipping for copying and
reading information
Reading the Instructions
• RNA
• Contains the sugar
ribose
• Has uracil instead of
thymine
• Usually single
stranded
• Exists in 3 forms
Base Pairing of RNA
• Contains the purines
adenine and guanin
and the pyrimidines
cytosine and uracil
• Base pairing of A-U
and G-C occur
Three forms of RNA
• mRNA: messenger RNA is made as a strand that is
complimentary to one strand of the DNA molecule (the
template strand) it is therefore a copy of the other DNA
strand as it contains the opposite bases plus Uracil
• rRNA: is ribosomal RNA and is found in ribosomes- it
decodes mRNA into amino acids
• tRNA: transfer RNA carries amino acids to the ribosomes
where they are bonded together to form polypeptides
Task: Now complete the Protein Synthesis sentence sort
Sentence Sort: What are the
instructions for?
• The sequence of bases on DNA make up codes for particular
proteins- they code for the sequence of amino acids
• The sequence coding for a particular protein (a gene) can be
exposed by splitting the hydrogen bonds in the particular area of the
DNA molecule
• RNA nucleotides from a complementary strand (mRNA) which is a
copy of the DNA coding strand (or gene)
• The mRNA peels away from the DNA and leaves the nucleus
through a nuclear pore
• The mRNA attaches to a ribosome
• The tRNA molecules bring amino acids to the ribosome in the
correct order, according to the base sequence of the mRNA
• The amino acids are joined by peptide bonds to give a protein with a
specific primary structure which can then give rise to the secondary
and tertiary shape of the protein
Task
• Complete a windows
movie explaining the
steps involved in protein
synthesis
• Success Criteria:
• No more than one minute
• Include scientific
information and diagrams
• Explain simply the terms
transcription and
translation
Questions
1. Explain why the MRNA strand produced in the
nucleus is complementary to the template
strand, and a copy of the coding strand
2. If a DNA template strand code reads
ATTCGCGTTAAT, what would the
complementary MRNA strand read?
3. Suggest why MRNA is less stable than DNA,
and explain why this is a necessary feature of
MRNA
4. Make a table to compare and contrast the
structure of DNA with that of RNA
Questions
1.
2.
3.
4.
Explain why the MRNA strand produced in the nucleus is complementary
to the template strand, and a copy of the coding strand complementary
RNA nucleotides are lined up against each base on the template strand,
producing a complementary strand. As base pairing rules apply, this
lining up will be the same as it appears on the coding strand- apart from
U in RNA replacing T in DNA
If a DNA template strand code reads ATTCGCGTTAAT, what would the
complementary MRNA strand read? UAAGCGCAAUUA
Suggest why MRNA is less stable than DNA, and explain why this is a
necessary feature of MRNA RNA is single stranded and so less stable, as
nucleotide bases are exposed and not paired. It also contains uracil
instead of thymine, which may contribute to the lower stability of the
molecule. mRNA results in the production of proteins. If the cell is to
control protein production, the disintegration of mRNA stops too much of
a certain protein being made, and so allows for regulation of the protein
levels in a cell
Make a table to compare and contrast the structure of DNA with that of
RNA