DNA carries genetic information from one generation to the next and must replicate itself accurately when cells divide. DNA replication occurs via a semi-conservative process where each new DNA strand contains one original strand and one newly synthesized strand. During transcription, mRNA is synthesized from a gene on DNA using one DNA strand as a template. Translation then builds a polypeptide chain from the mRNA codon sequence using tRNA to add amino acids specified by each codon. Molecular recognition allows for specific interactions between proteins and other molecules through complementary binding of receptors, antigens, enzymes and substrates.

1. DNA AND PROTEIN
SYNTHESIS

2. DNA REPLICATION
DNA carries the genetic information from one
generation to the next
When cells divide, each cell must have a copy of
the organisms DNA
When organisms reproduce their genetic
information is passed on to the offspring via the
DNA.
DNA must be able to replicate itself.
When DNA replications occurs, each new strand of
DNA has one of the old strands plus one new
strand.
This process of DNA replication is called:
semi-conservative replication

4. SEMI – CONSERVATIVE REPLICATION
& TRANSCRIPTION
mRNA is synthesized from a gene on the DNA
by “semi-conservative replication”
DNA is a double stranded molecule, one of the
strands act as a template to produce a
molecule of RNA for transcription.
In this process the original DNA double helix
unzips exposing the DNA bases (Helicase
Enzyme).
DNA nucleotides that are floating free within
the nucleus link in a complementary manner
with the help of the enzyme DNA Polymerase.

5. Two new strands are formed, with each strand
having one of the original strands and one
new strand.
When transcription is completed the new
strand is released as a mRNA molecule
moving out of the nucleus through the nuclear
pores into the cytoplasm ready for translation.
The “master” copy of DNA never leaves the
nucleus

6. GENETIC CODE
The functional unit of information on the
chromosome is the gene
A gene consists of a unique sequence of bases
that code for a polypeptide or an RNA molecule.
For the DNA molecule to influence the activities of
a cell, it has to first be translated into proteins.
One gene codes for a polypeptide or an RNA
molecule.
So how can 4 bases be translated into a sequence
of amino acids when there are 20 possible amino
acids to code for?

7. TRIPLETS CODONS
If each base coded for one amino acid only 4 amino
acids could be sequenced.
If we had pairs of bases coding for amino acids, how
many combinations would then be possible?
16 still not enough
The answer is to use 3 bases to code for each amino
acid.
With three bases 64 combinations are possible.
More than enough for the 20 amino acids and start
and stop signals.
This is called the Triplet Code.

8. Experiments have verified that the genetic
code is made up of base triplets.
These base triplets are called codons.
Each triplet codes for an amino acid.
Most amino acids have more than one triplet
codon.
Start (AUG) and Stop (UGA) codons initiate and
terminate polypeptide sequences

9. MRNA CODONS FOR ALL
AMINO ACIDS

10. PROTEIN SYNTHESIS
As we have already learnt:
For the DNA molecule to influence the activities of
a cell, it has to first be translated into proteins.
The flow of information for most organisms is
unidirectional.
It only flows in one direction.
DNA  RNA  Protein
There are two main processes involved in Protein
Synthesis:
Transcription
Translation

11. DNA--> RNA --> PROTEINS
DNA
deoxy ribo
nucleic acid
nitrogen bases
are:
A-T and C- G
RNA
ribo nucleic acid
nitrogen bases
are:
A - U and C
– G
U= uracil
the base which
substitutes for

12. THE FLOW OF INFORMATION
FROM DNA TO PROTEIN IS
UNIDIRECTIONAL
DNA RNA
Protein
(transcription)
(translation)

13. COMMON ABBREVIATIONS
FOR AMINO ACIDS

15. DNA REPLICATION SUMMARY

16. DNA EXTRACTION PRACTICAL

17. TRANSCRIPTION
DNA  RNA
Basically it is a process in which the message written
in DNA code is transcribed into a working copy of
mRNA (messenger RNA).
The process is:
RNA polymerase enzymes separate the two strands
of DNA.
One strand of the DNA is used as a template for
mRNA synthesis
The mRNA molecule forms using Uracil instead of
Thymine
When the mRNA molecule is complete, it breaks away
from the DNA and travels through the nuclear pores
to ribosomes in the cytoplasm

18. TRANSCRIPTIO
N

20. TRANSLATION
A polypeptide chain is built using the codon
sequence on the mRNA molecule.
tRNA transfer free amino acids in the
cytoplasm to the many ribosomes which
synthesize mRNA on the basis of codons on
the m RNA base pairing with the anti-codons
on the tRNA.
Translation is commenced by the start codon
“AUG”
Stop codons are the sequences UAG, UAA and
UGA.

21. RNA  PROTEIN
Basically it is a process in which a polypeptide
chain is built from a codon sequence on the
mRNA molecule.
The process is:
The mRNA molecule attaches to a Ribosome.
tRNA molecules bring specific amino acids to
the ribosome according to the codon on the
mRNA. There is a different tRNA molecule for
each of the 20 amino acids.
Each tRNA molecule is about 80 nucleotides
long and is folded into a clover shape. At one
end there is an exposed triplet of bases called
an anticodon and at the other a specific amino
acid.
The anticodon on the tRNA matches the codon

22. The ribosomes provide the platform
where the tRNA and mRNA are brought
together
As the amino acids are bought
alongside one another they are joined
together by enzymes to form a
polypeptide.
Translation begins with a signal code,
the start codon AUG
AUG codes for the amino acid
Methionine
The ribosome moves along the mRNA
strand one codon at a time.

23. As the tRNA molecule deposits its
amino acid, it is released back to the
cytoplasm to link with another
amino acid.
When a stop codon is reached,
translation ceases and the
polypeptide chain is completed and
released from the ribosome.
The polypeptide folds into its final
protein shape
If the protein is more than one
polypeptide, the chains link and
form their tertiary structure.

24. T RNA WITH ATTACHED AMINO
ACID

25. TRANSLATION

26. PROCESS OF TRANSLATION

27. RELATIONSHIP BETWEEN
TRIPLETS, CODONS, ANTI-
CODONS AND AMINO ACIDS

28. SUMMARY OF PROTEIN SYNTHESIS

29. Note key points
Do focus questions on p15
Protein synthesis simulation

30. MODELLING TRANSCIPTION
1. Organise your own DNA code using the
acetate sugar phosphate backbones and
complementary base. Record the DNA base
sequence in your book
2. Unzip the DNA to expose one strand and
use felt tip pen to record the complementary
base on the tabs of the exposed strand.
Record this exposed strand in black/blue
pen
3. Use the exposed DNA strand as a
template to

31. MODELLING TRANSLATION
3. Use the paper tRNA “molecules’ to
construct the anticodons.
4. Refer to the table of mRNA codons (
pg 8 Key Ideas) choose one coloured ball
to represent each amino acid and
constuct the polypeptide coded for by
your mRNA.
5. Link three different polypeptide
sequences together to form a longer
polypeptide chain.

32. STRUCTURE OF A CELL
MEMBRANE

33. MOLECULAR RECOGNITION
An important aspect of life is the capacity of
cells to exchange materials in and out
through their membranes.
The cell membrane has its own unique
collection of proteins that are embedded in
a phospholipid bi-layer
The human red blood cell membrane has
more than 50
Cell membranes need to select molecules to
pass through and recognise signals from
the environment.

34. PROTEINS IN THE CELL
MEMBRANE
Found on inner and outer surface of cell
membrane.
Many move freely (fluid mosaic model)
while others are fixed.
Act as receptors for chemical messengers
from other cells.
Will display a particular shape to bind to a
specific messenger such as a hormone.
Other proteins act as one-way transport
channels allowing specific molecules
through cell membrane.

35. EXAMPLES OF MOLECULAR
RECOGNITION INCLUDE:
Cell membrane receptor molecules
Transport proteins in the cell
membrane
Hormone receptors in cell
membranes
Antibodies
enzymes

36. CELL MEMBRANE
RECEPTORS
These are protein and glycoprotein molecules
embedded in the cell membrane.
They have distinctive shapes so as to allow
cells to recognise each other.
This is critical when cells are differentiating to
form tissues.

37. COMPLEMENTARY BINDING
TO MEMBRANE CELL
RECEPTOR MOLECULES

38. TRANSPORT PROTEINS
These are transport proteins embedded in
the cell membrane.
They have specific binding sites for the
substance being transported.
They help with:
facilitated diffusion (moving with the
concentration gradient)
Active transport (moving against the
concentration gradient using energy)

39. HORMONES
Hormone receptors can be embedded in cell
membranes or in the cytoplasm of the cell.
Hormones are chemical messengers produced by
specialised cells in one part of the body to act on
target cells in another part.
The receptors are protein molecules:
Cell membrane: Insulin
Induces cell to take in more glucose and convert it
to glycogen
Cytoplasm : Steroids
Lipid soluble and pass through the cell membrane
to bind with receptors in the cytoplasm

40. UPTAKE OF GLUCOSE BY
INSULIN

41. HORMONES
Adrenalin
Binds to protein receptors on the surface
of liver cells and activates the conversion
of glycogen to glucose which is released
into the bloodstream for energy
provision by aerobic respiration – “fight
or light response”

42. ANTIGEN – ANTIBODY
BINDING
Antibodies are part of the immune system.
They are protein molecules
(immunoglobulins) with antigen binding
sites that detect and bind to antigens.
Antigens are foreign substances like
bacteria or viruses.
The binding of the two must be
complementary to inactivate the antigen

43. ANTIBODY STRUCTURE

44. SELF AND NON-SELF
The immune system is able to
distinguish between foreign molecules
and their own body molecules or cells.
They do this using antigen recognition.
Cancer occurs when the body recognises
cancerous cells as normal cells of the
organism.
The immune system will not attach to
them and destroy them because they
think they are normal body cells.

45. ENZYMES
Enzymes are globular protein molecules
with an active site that binds to substrate
molecules to catalyse reactions.
The active site is complementary to the
substrate.
Specific shape of active site
Enzymes are specific to a particular
substrate.
Small changes to the shape of the
enzyme may affect the recognition of

46. ACKNOWLEDGEMENTS
Orange tone tables and images taken from Adelaide
Tuitions Essential textbook for the course.