Sec 4 Molecular Genetics

2. 2
Learning Objectives:
(a) outline the relationship between DNA, genes and
chromosomes.
(b) state the structure of DNA in terms of the bases, sugar and
phosphate groups found in each of their nucleotides.
(c) state the rule of complementary base pairing.
(d) state that DNA is used to carry the genetic code, which is
used to synthesise specific polypeptides.
(e) state that each gene is a sequence of nucleotides, as part of
a DNA molecule.
(f) explain that genes may be transferred between cells

3. 3
Learning Objectives:
(g) briefly explain how a gene that controls the production of
human insulin can be inserted into bacterial DNA to
produce human insulin in medical biotechnology.
(h) outline the process of large-scale production of insulin
using fermenters.
(i) discuss the social and ethical implications of genetic
engineering, with reference to a named example.

4. 4
"Cloning is all very well in theory, but do you have any
proof it can actually work?"

5. 5
1. We inherit traits from aunts, uncles, cousins and siblings
because family members point out the resemblance
between students and their relatives.
2. Some people think that most common traits are “better”.
3. Dominant alleles or traits are always the most common.
4. DNA is a living thing.
5. Only animal contains DNA.
6. Genes from one type organism will not function in a
different type organism.

6. 6
1. Traits can only be inherited from parents, and by
extension, grandparents.
2. No. The traits simply show up more frequently in the
human population.
3. Not necessary.
( A dominant trait may be quite rare, while a recessive trait
may be the most common one observed.)

7. 7
× DNA is a living thing.
× Genes from one type organism will not function in a different type organism.
× Only animal cells contain DNA.
4. DNA is a molecule with instructions for a cell.
5. Plants also contain DNA
6. There is a genetic code common to all living things.

8. 20.1 DNA
20.2 Genes
20.3 Transferring Genes between Organisms
20.4 Effects of Genetic Engineering on Society
Chapter
20
Molecular Genetics

9. Learning Outcomes
After this section, you should be able to:
• describe the basic unit of DNA – the nucleotide;
• state and apply the rule of complementary base
pairing.
20.1 DNA

10. 10
Chromosomes
• Inheritable materials in nucleus of a cell. Numerous genes
are located on it.
• Chromosomes can exist in coiled compact form or uncoiled
extended form.
• Cells undergoing cell division will contain chromosomes in
coiled compact form.

11. 11

12. Function of DNA
• It codes for the synthesis of polypeptides.
• Many polypeptides will join together to form
protein, which is responsible for your traits.
12

13. 13
Structure of DNA
• A molecule that carries genetic information
• The basic unit of DNA is known as nucleotide;

14. 14
adenine
nucleotide
thymine
nucleotide
guanine
nucleotide
cytosine
nucleotide
• Each nucleotide (basic unit) is a complex of three subunits:
a) a sugar (deoxyribose/ribose)
b) a phosphate group
c) a nitrogenous base
• Many nucleotides can be joined together to form
polynucleotides.

15. adenine
nucleotide
thymine
nucleotide
guanine
nucleotide
cytosine
nucleotide
bases
sugar-
phosphate
backbone
polynucleotide

16. “Rule of base pairing”
• Adenine (A) bonds with thymine (T)
• Guanine (G) bonds with cytosine (C)
These pairs of bases are called complementary bases.

17. • The DNA molecule is made of two
anti-parallel polynucleotide
strands. (The two strands run in
opposite directions.)
• The bases on one strand form
bonds with the bases on the other
strand according to the rule of
base pairing.

18. 18

19. Animation: DNA Structure

20. The two anti-parallel strands of the DNA molecule
coil to form a double helix three-dimensional
structure.
bases
sugar-phosphate
backbone
coiling of
DNA
the double helix
3D structure of
DNA

21. Coiling of DNA
Uncoiled DNA
resemble a ladder
(2D structure)
Coiled DNA
resemble a spiral
staircase/
double-helix
(3D structure)

22. Coiling
of DNA

23. 23
Activity: Build Your DNA Model
• Create a DNA model using
materials of their own choice.
• Suggested materials include
straws, pipe cleaners, pasta
• They should include a key that
explains what each item
represents. After you have
completed their models, display
the models to the whole class.

24. 24
Examples:
http://luehy.wikispaces.com/DNA+Pasta

25. Checkpoint 1
1. a) State the bases that are complementary to the bases on
strand shown below:
b) State the ratio of:
(1) adenine : thymine, and
(2) guanine : cytosine
in the DNA of a cell.
Answer:
Answer:
(1)1 : 1
(2)1 : 1

26. • What is the base sequence of the DNA strand that would
be complementary to the following single-stranded DNA
molecule?
GGATCTGATCCAGTCA
A : GGAUCUGAUCCAGUCA
B : CCTAGACTAGGTCAGT
Checkpoint 2

27. • The percent of cytosine in a double-stranded DNA is
21. What is the percent of thymine in that DNA?
A 21%
B 29%
Checkpoint 3

28. • According to base pair rule, the percentage of As, Ts,
Cs, and Gs should add up to 100%, because
A
C
T
G
=
=
Adding all the
bases together
should make
up 100% of the
DNA molecule.

29. • The percent of adenine in a double-stranded DNA is 38.
What is the percent of cytosine in that DNA?
A 12%
B 38%
Checkpoint 4

30. • The percent of guanine in a double-stranded DNA is 14.
What is the percent of adenine in that DNA?
A 14%
B 36%
Checkpoint 5

31. © Boardworks Ltd 2004
What’s the order? Let’s Recap !

32. Let’s Recap !

33. Investigation 13.2 :
DNA Extraction of Onion
33

34. Add 10cm3
detergent
To break nuclear
membrane
Add 10cm3
of ethanol
To separate out the
DNA strand
Add phenol red indicator
Indicate presence of DNA

35. 20.1 DNA
20.2 Genes
20.3 Transferring Genes between Organisms
20.4 Effects of Genetic Engineering on Society
Chapter
20

36. Learning Outcomes
After this section, you should be able to:
• state that DNA molecules contain the genetic
code;
• state what is meant by the genetic code;
• state that a gene is a specific sequence of
nucleotides in a DNA molecule that controls the
production of a polypeptide.
20.2 Genes

37. What is a gene?
• It is a segment of DNA.
• The nucleotide sequence
in the gene determines
the polypeptide formed.
gene
DNA
polypeptide
coded by the
gene
20.2

38. • Three bases, or codon, code for one amino acid.
• A chain of amino acids makes up one polypeptide,
which later can be used to make proteins.
Codon
on DNA
Example of amino acid coded
for
TAC Methionine (M)
TAT Alanine (A)
CAT Lysine (K)
GAG Glutamic acid (E)
ACA Serine (S)

39. “One gene, one polypeptide” theory
• The theory that each gene is responsible for the
synthesis of a single polypeptide

40. What happens when
the nucleotide
sequence in a gene
is altered?
What happens when
the nucleotide
sequence in a gene
is altered?

41. A change in the nucleotide
sequence of a gene is termed as
gene mutation.
A mutation may or may not lead to
a change in the protein product.
A change in the protein product
may or may not lead to an
observable phenotype.
Recall
Two examples of gene
mutation was mentioned
in Chapter 19. Can you
state the two examples?
(1)Albinism
(2)Sickle-cell anaemia

42. Important!
•A cell cannot directly use
the DNA template to make
proteins. It has to go through
the following stages.
How are proteins
made?
How are proteins
made?

43. (a) Transcription:
• Messages in
DNA template is copied into
messenger RNA in the
nucleus.
• (b) Translation :
messenger RNA carries
the message to cytoplasm
and ribosome helps to
convert them into proteins.
44
(a)
Transcription
(b) Translation

44. MicroQuestions
1. Describe the relationship between DNA, genes
and chromosome. [3]
2. Using the idea of molecular structure, describe
the structure of DNA and its function in leading
to a trait. [4]
45

45. 1) (a)
•Gene is a segment of the DNA molecule .
•Chromosomes are made of coiled DNA
molecules.
•DNA carries many genes along its length.

46. 1) (b)
Function:
DNA codes for the synthesis of polypeptide.
Polypeptides are used to make proteins , which are
responsible for many traits.
Structure of DNA:
• Basic unit made of nucleotide
• Nucleotide is made a phosphate group, a sugar and a
base.
• The 2 strands of polynucleotide joined together by the
‘complementary base pairing rule’ (A & T , G & C)
• 2 strands are twisted to form a double helix 3D structure

48. DNA
template
transcription
mRNA
- RNA contains
uracil (U) instead of
thymine (T)
polypeptide
translation
Pure Biology

49. It is a temporary molecule that
is made when needed.
It is a permanent molecule in the
nucleus.
It is a small soluble molecule.It is a large insoluble molecule.
No fixed ratio between A and U
and between G and C.
Ratio of A:T and G:C is 1:1.
Nitrogen-containing bases are
adenine (A), uracil (U), guanine
(G) and cytosine (C).
Nitrogen-containing bases are
adenine (A), thymine (T),
guanine (G) and cytosine (C).
Sugar unit is ribose.Sugar unit is deoxyribose.
RNADNA (double helix)
DNA vs. RNA
Pure Biology

50. Transcription and translation
1
2
template strand gene unzips
transcription
ribosome
mRNA
mRNA
molecule
3 attachment to ribosome
Pure Biology

51. The biological molecules involved are:
(1) Amino acids
- There are a total of 20 different
amino acids.
(2) Transfer RNA (tRNA) molecules
- Each tRNA molecule has an amino
acid attached.
- The amino acid attached depends
on the tRNA’s anticodon.
(3) Ribosomes
- Ribosomes help make polypeptides
from mRNA molecules.
(4) mRNA molecules
Translation
anticodon
Pure Biology

52. Translation
peptide bond
amino acids
attached to tRNA
ribosome
codon
first tRNA
is released
a new tRNA
fits into the
ribosome
ribosome moves along
the mRNA strand
1
2
Pure Biology

53. 3
polypeptide formed
stop
codon
Amino acids are
continually attached until
the ribosome reaches the
stop codon on the mRNA.
Upon encountering the
stop codon, the ribosome
leaves the mRNA.
The complete polypeptide
is produced.
URL
Pure Biology

54. 20.1 DNA
20.2 Genes
20.3 Transferring Genes between Organisms
20.4 Effects of Genetic Engineering on Society
Chapter
20
Pure Biology

55. Learning Outcomes
After this section, you should be able to:
• define genetic engineering;
• describe human insulin production as an example
of an application of genetic engineering;
• differentiate between selective breeding and
genetic engineering.
20.3
Pure Biology

56. 57
“Pigs that glow in the dark””
• The scientists will use
the transgenic pigs to
study human disease.
• Because the pig's
genetic material
encodes a protein that
shows up as green, it
is easy to spot.
http://science.howstuffworks.com/framed.htm?parent=question388.htm&url=http://news.bb

57. • Genetic engineering refers to the manipulation of an
organism’s genetic material.
• It involves the transfer of genes from one organism to
another.
• This is done by the use of a vector.
• A vector molecule is DNA molecule that is used to
carry the gene or genes to be transferred.
• Plasmids (circular DNA) from bacteria are commonly
used as vectors.
Genetic engineering

58. The process
Isolate the desired gene
- Cut the gene using restriction enzymes.
Insert the gene into the vector DNA
- Restriction enzymes that were used to cut the
desired gene are used to cut the vector DNA.
- Both the cut vector DNA and gene are mixed
together with DNA ligase, an enzyme that will help
join the two molecules together.
Insert the recombinant plasmids into bacteria
- Mix recombinant plasmids with bacteria and heat- or electric-shock
the cells.
1
2
3
20.3

59. • Mass production of human insulin for type 1 diabetes
patients was made possible through the use of genetic
engineering.
• The human insulin gene is transferred to bacterial cells
that are able to express the gene. The product (insulin)
can then be harvested.
Producing human insulin
Background:
Type 1 diabetes is caused by the inability of the islets
of Langerhans to produce sufficient insulin.

60. insulin gene
cut using restriction
enzyme
sticky end
DNA fragment that contains
the insulin gene
Isolating the human insulin gene
1

61. Inserting the gene into the vector2
cut by same
restriction enzyme
sticky ends
insulin gene inserted
into plasmid
insulin gene
bacterial plasmid

62. Inserting the recombinant
plasmids into bacteria
3
recombinant plasmid
(bacterial plasmid with
human insulin gene
inserted)
bacterial DNA
recombinant
plasmid
transgenic bacterium

63. • The transgenic bacteria need to be burst open in
order to extract the human insulin that is produced in
the bacteria.
• In order to obtain large amounts of human insulin,
large amounts of transgenic bacteria need to be
cultured.
• This is done through the use of large sterile
containers called fermenters.
Large-scale production of human insulin

64. 66
Mass production
of insulin in a
fermenter
Pure

65. • Creation of transgenic plants that are resistant to
herbicides.
• Creation of transgenic plants that are pest-resistant.
• Gene therapy – healthy genes can be transferred from
one person to the cells of another person with
defective genes.
Other applications of genetic engineering
20.3

66. • Genes can be transferred between organisms of
different species (as shown in the production of
insulin) and between organisms of the same species.
• An example of gene transfer between organisms of
the same species is the transfer of a pest-resistant
gene from wild wheat plants to common wheat plants
that are grown as crop.
Note that:
20.3

67. Selective breeding vs. genetic engineering
More efficient as transgenic
organisms grow faster and may
require less food
Less efficient as organisms grow
more slowly and may require more
food
A process which uses individual
cells that reproduce rapidly in a
small container in a laboratory.
Slow process that involves several
generations.
Selection of genes before transfer
eliminates the risk of transferring a
defective gene.
There is a possibility that defective
genes will be transmitted to the
offspring.
Genes from an organism can be
inserted into non-related species or
different species.
Organisms involved in selective
breeding must be closely related or
of the same species.
Genetic engineeringSelective breeding

68. 20.1 DNA
20.2 Genes
20.3 Transferring Genes between Organisms
20.4 Effects of Genetic Engineering on
Society
Chapter
20
Molecular Genetics

69. Learning Outcomes
After this section, you should be able to:
• discuss the advantages and disadvantages of
genetic engineering;
• state the social and ethical implications of this
technology.

70. Advantages of genetic engineering
Nutritional quality of foods are
improved.
Development of foods
designed to meet specific
nutritional goals
The use of costly pesticides that may
damage the environment is reduced.
Development of pesticide-
resistant crops
Farmers are able to grow crops in
environmental conditions that are not
favorable for cultivating most crops.
Production of crops that
grow in extreme conditions
Drugs like human insulin become
more affordable.
Low cost production of
medicines
Benefits to societyApplications of genetic
engineering

71. Disadvantages of genetic engineering
Environmental hazards
• Genetically-modified (GM) crop plants that produce insect
toxins may result in the deaths of insects that feed on
them and may result in loss of biodiversity.
Economic hazards
• If the prices of the seeds of modified crop plants are not
regulated, poorer farmers may not have the financial
capacity to benefit from this technology while richer
farmers continue to get richer through the technology.

72. Disadvantages of genetic engineering
Social and ethical hazards
• Genetic engineering may lead to class distinctions.
• Some religions do not approve of genetic engineering as
it may not be appropriate to alter the natural genetic
make-up of organisms.
Health hazards
• Genes that code for antibiotic resistance may be
accidentally incorporated into bacteria that cause human
diseases.