Download Two types of nucleic acids

Nucleic acids
Objectives
• State that DNA is a polynucleotide
usually double stranded, made up of
nucleotides
• State that RNA is a polynucleotide
usually single stranded, made up of
nucleotides
Two types of nucleic acids
• DNA (deoxyribonucleic acid)
• RNA (ribonucleic acid)
polymers
• DNA and RNA are polynucleotides
• They are made up of many monomers
called nucleotides
Nucleotide structure
A phosphate group
B sugar molecule (specify)
C organic nitrogenous base (not just base)
Nucleotides
Phosphate
Base
Sugar
A Nucleoside = sugar + base
The sugar component
• In DNA
– Deoxyribose
• In RNA
– Ribose
The phosphate component is always
the same in DNA and RNA
But there are 5 possible different
organic nitrogenous bases
The organic nitrogenous bases
Purines
Purines have
2 rings
A
adenine
G
guanine
Pyrimidines
C
cytosine
T
thymine
U
uracil
Formation of nucleotides
Each component of a
nucleotide is joined
together by a covalent bond
•Each polymer strand is
a polynucleotide
•Nucleotides are joined
by phospho diester
bonds to form a ‘sugarphosphate backbone’
•Chains of nucleotides
joined together form
nucleic acids
•only nucleotides
containing the same
sugar can join together
Homework
• Find out how nucleotides may be
involved in Gout
• Interactive ICT DNA code activity on
Finding the structure: pieces of the
puzzle – Finding the structure only. This
will be needed as background for the
starter in the next lesson.
THE DOUBLE HELIX
Objectives
• Describe how a DNA molecule
is formed by H bonds between
complementary base pairs
forming 2 antiparallel DNA
strands
• Explain how DNA twists to
form a double helix
DNA
is a
double
helix
DNA is double stranded
A DNA molecule forms when 2 polynucleotide
chains bond together
Q. What do you notice about the two
polynucleotide strands?
A. They run in opposite directions (antiparallel)
Anti-parallel strands
Base-pairing
The two strands of DNA are held together
by the base pairs.
Q. What type of bond holds them
together?
A. Hydrogen bonds
Q. Why do the bases always pair; A to T
and C to G?
A. Complementary shape, a pyrimidine will
always pair with a purine
Adenine and Thymine;
Guanine and Cytosine
have a ratio of 1 to 1.
Answer….
• 24% is Adenine
• Thymine must also be 24%
• Total 48%
Answer….
• 52% left for the other two bases
• 26% each
So how do they join?
‘A Tea for 2’
Adenine joins with Thymine by 2
hydrogen bonds
…and the other base pair
Cytosine joins with Guanine by 3
hydrogen bonds
Which are weak or strong
bonds?
• What
is the
significance of
the weak bonds?