Functions and structures of DNA and nucleotide
2. Functions and structures of DNA and nucleotide
3. Learning objectives• 184.108.40.206 establish a link between DNA structure
and its function
• 220.127.116.11 describe the chemical structure of the
nucleotides and explain their connection and
location in the DNA molecule
4. success criteriaDNA:
1. Knows the structure of DNA.
2. Describes the functions of DNA.
3. Establish a link between DNA structure to its function.
1. Knows the chemical structure of a nucleotide.
2. Describes their connection.
3. Explain how the nucleotides are located in the DNA.
5. Terminology• DNA/ nucleotide
• Adenine/guanine/ cytosine/ thymine
• Phosphate group/pentose sugar/ deoxyribose/ nitrogenous-bases
• H-bond/ covalent bond/ ester bond/ glycoside bond
6. DNADNA stands for deoxyribonucleic acid. DNA is
also polymer, made up of many similar,
smaller molecules joined into a long chain.
The smaller molecules from which DNA
molecules are made are nucleotides. DNA is
therefore polynucleotides. They are often
referred to simply as nucleic acids.
7. DNA structure• The 3’ -5’ linkage
• Antiparallel stands
• The bases and hydrogen
8. The 3’ -5’ linkageThe carbons in the sugar are numbered from 1 to 5 in a clockwise direction starting
after the oxygen at the apex.
The base is attached to carbons 1.
Carbon 2 has just a hydrogen attached instead of an OH group. (called - deoxyribose)
Carbon 3 is where te next nucleotide attaches in one direction.
Carbon 5 has a phosphate group attached to it.
This means that each nucleotide is linked to those on
either side of it through carbons 3 and 5.
9. Antiparallel standsDNA molecules are made
of two polynucleotide
strands lying side by side,
running in opposite
directions. The strands are
said to be antiparallel.
10. The bases and hydrogen bondingThe two strands are held together
by hydrogen bonds between the
The bases can be purines or
pyrimidines. From Figure, you will
see that the two purine bases,
adenine and guanine, are larger
molecules than the two
pyrimidines, cytosine and
11. Hydrogen bondsDNA molecules are made of
two polynucleotide strands
lying side by side, running in
opposite directions. The
strands are said to be
antiparallel. The two strands
are held together by hydrogen
bonds between the bases.
12. Covalent bondsEach nucleotide is linked to
the next by covalent bonds
between the phosphates and
13. NucleosomesA eukaryotic chromosome is composed
of a double stand of DNA, combined
with proteins. This proteins called –
histones, combine together in groups of
either to form a bead – like structure.
It is held in place on the bead by a ninth
The groupe of nine histone with the DNA is
called a nucleosome.
The function of nucleosome: help to supercoil the chromosomes during mitosis, meiosis and help regulate transcription.
14. Coding strand and non coding strand
16. NucleotideNucleotides are made up of three
smaller components. These are:
• a nitrogen-containing base
• a pentose sugar
• a phosphate group.
17. Nitrogen-basesThere are just five different nitrogen-containing bases found in DNA and RNA.
In a DNA molecule, there are four: adenine, thymine, guanine and cytosine.
These bases are often referred to by their first letters: A, T, C, G and U.
This complementary base pairing is a very important feature of polynucleotides,
as you will see later.
18. Complementary baseTwo polynucleotides, running in
opposite directions, are held
together by hydrogen bonds
between the bases.
• A links with T by two hydrogen
• C links with G by three
This is complementary base
19. Pentose sugar• The pentose (5-carbon) sugar can be either ribose (in RNA) or
deoxyribose (in DNA). As their names suggest, deoxyribose is almost
the same as ribose, except that it has one fewer oxygen atoms in its
21. Role of Phosphodiester linkage
23. The components of nucleotides
25. Type of bonds (types of links)
type of links.
In DNA it is formed
of alternating sugars and
phosphates linked together,
the bases projecting
The covalent sugar–
bonds) link the 5-carbon of
one sugar molecule and the
3-carbon of the next.
29. Home task• Read the text about the structure of DNA.
• Pages: 111 – 112 “Nucleotides” and 113 “Polynucleotides”.