8.1
Nucleotides
Starter
What is DNA ?
Where will you find DNA in a cell?
Draw the basic structure of a pentose sugar
8.1
Nucleotides
Aims:
•What are the components of DNA?
•How are these components arranged
within the DNA double helix?
•What is the function of DNA?
Phosphate group
Nucleotide structure
(monomer)
Organic
nitrogenous base
Pentose sugar
What type of reaction is involved when the
phosphate group and base are joined to the sugar?
What type of bonds are formed?
DNA (and RNA) is a nucleic acid
It is made from lots of nucleotide
monomers joined together by condensation
reactions to form a poly nucleotide
DNA - deoxyribonucleic acid
The pentose sugar
in DNA is deoxyribose
Spot the difference
RNA - ribonucleic acid
The pentose sugar
in RNA is ribose
Nitrogenous bases
Double ring
Single ring
Adenine &
Guanine
Cytosine &
Thymine
Polynucleotide
Draw the structure of a nucleotide
Which nitrogenous bases will you find in
DNA?
Which of these are purines? pyrimidines?
Nucleotide structure
(monomer)
Phosphate group
Organic
nitrogenous base
Pentose sugar
DNA is usually double
stranded
There are two
antiparallel DNA
strands held
together by hydrogen
bonding between
complementary bases
The two strands are
twisted into a double
helix
Label the nitrogenous bases & show the
hydrogen bonds between complementary
base pairs
thymine
adenine
guanine
cytosine
10 bases for each
complete turn (3.4nm)
What is the relationship
between the quantities adenine
and thymine in DNA?
What is the relationship
between the quantities of
guanine and cytosine in DNA?
What about the ratio in
different species?
Understanding checkpoint!
Using the sweets can you explain:
•What are the components of DNA?
•How are these components arranged
within the DNA double helix?
10 bases for each
complete turn (3.4nm)
What do you think
is the function of
DNA?
How is the DNA
adapted for its
function?
Plenary
Construct a table to show the function and
adaptations of DNA.
Function
Adaptation
Passing on genetic material
Very stable and therefore can pass
from generation to generation
without change
Plenary
Construct a table to show the function and
adaptations of DNA.
Function
Adaptation
Passing on genetic material
Very stable and therefore can pass
from generation to generation
without change
2 separate strands only joined by
H bonds allows them to be
separated easily during DNA
replication
Large number of bases (3.2 billion
for variation)
Large molecule can carry lots of
genetic information
Depends on sequence of bases
By having base pairs within the
helix protects them from being
corrupted
8.1
Nucleotides
Aims:
•What are the components of DNA?
•How are these components arranged
within the DNA double helix?
•What is the function of DNA?
2.1 – 16
DNA
Starter
What do you know about the structure of DNA?
Teaching objectives
The structure of DNA
Replication of DNA
Learning outcomes
Draw an outline structure of DNA
Describe the semi-conservative replication
of DNA
Before a cell divides the DNA must be
replicated.
This happens during interphase of the cell
cycle
DNA replication
Controlled by a group of enzymes called DNA
polymerase
The double helix unwinds
Hydrogen bonds between the complementary
bases are broken to ‘unzip’ the DNA
Free nucleotides (from the nucleoplasm) pair up
with complementary bases and hydrogen bonds
form between them
Condensation reactions occur between the
phosphate & pentose sugar of neighbouring
nucleotides to form the sugar phosphate
backbone
The process of DNA replication occurs all
the way along the DNA strand resulting in
an exact replica of the DNA molecule.
DNA replication is described as ‘semi
conservative’ because each of the
resulting DNA molecules has one strand of
the original DNA and 1 newly synthesised
strand
Plenary
A DNA molecule is 23% guanine.
What percentage of each of the
other bases would it contain?
G = 23%
C + G = 46%
C = 23%
So A + T = 54%
A = 27%
(to make a total of 100%)
T = 27%
2.1 – 17
The roles of DNA & RNA
Starter
What is the function of DNA?
Teaching objectives
The structure of RNA
The role of DNA & RNA in the cells of
living organisms
Learning outcomes
State what a gene is
Describe the 3 different types of RNA
Outline the concept of protein synthesis
RNA
What type of molecule is RNA?
What are the monomers of this molecule?
What type of bond joins these monomers
together?
In what way is the pentose sugar found in
RNA, different from the pentose sugar
found in DNA?
In what way are the bases found in RNA
different to the bases found in DNA?
There are 3 different types of RNA
•
Messenger RNA (mRNA)
•
Ribosomal RNA (rRNA)
•
Transfer RNA (tRNA)
Describe the structure of mRNA
Describe the
structure of tRNA
There are 2 different units of rRNA – a
large subunit and a small subunit which,
together with proteins form ribosomes
A gene is a section of DNA nucleotides
that codes for the sequence of amino acids
that make up a particular polypeptide.
Different genes are switched on and off in
different cells.
When a gene is activated that section of
the DNA is copied into a complementary
strand of mRNA
The mRNA then leaves the nucleus through
a nuclear pore and attaches to a ribosome
(made of rRNA and protein).
As the mRNA passes through a groove in the
ribosome, tRNA brings specific amino acids
into position.
The sequence of amino acids is joined by
peptide bonds to form the primary structure
of the polypeptide.
Depending on the specific groups in each
amino acid the polypeptide chain then forms
secondary & tertiary structures
Outline the role of DNA and RNA in living cells
DNA – genetic code – contains genes with
instructions for making specific polypeptides
RNA – responsible for reading the instructions
on the DNA and translating them into amino
acids to form polypeptides