1. Topic : DNA The Code of Life
Grade 12 Life Sciences
Topic : DNA The Code of Life

2. DNA
Structure

3. DNA –Position in the cell
DNA double helix
Nucleus
Chromosomes

4. In each chromosome, the DNA is grouped into
In the nucleus of almost every cell in your body is the collection of DNA needed to make you.
DNA in the nucleus is grouped into 23 sets of chromosomes that are called your "genome."
In each chromosome, the DNA is grouped into
"genes."
Your genome contains about 35,000 genes.

5. Instructions to make your whole body and keep it working is contained in DNA
Instructions is called genetic code
The DNA in your genes tells the cell what
amino acids (protein building blocks) to put
together to make a protein.

6. DNA Structure
DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix.
A molecule of DNA is made up of millions of tiny subunits called Nucleotides.
Each nucleotide consists of:
Phosphate group
Pentose sugar
Nitrogenous base

7. Nucleotides
Phosphate
Nitrogenous
Base
Pentose
Sugar

8. Nucleotides There are four types of nitrogenous bases.
The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.
There are four types of nitrogenous bases.

9. Nucleotides A
Adenine T
Thymine C
Cytosine G
Guanine

10. Remember
DNA
T – A
G - C

11. Nucleotides Each base will only bond with one other specific base.
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Form a base pair.
Form a base pair.

12. DNA Structure
Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

13. A C T G G A T C

14. DNA Structure
To crack the genetic code found in DNA we need to look at the sequence of bases.
The bases are arranged in triplets called codons.
A G G - C T C - A A G - T C C - T A G
T C C - G A G - T T C - A G G - A T C

15. DNA Structure A gene is a section of DNA that codes for a protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the production of a unique protein.
It is these proteins and combination of proteins that give us a unique phenotype.

16. DNA Replication
Unzip into two single strands

17. New bases attached themselves in the correct place of each strand
Free nucleotides in nucleoplasm

18. Two identical strands are formed
Each strand now becomes a double helix.
Strand 1
Strand 2

19. Questions on the DNA Molecule1 G 2 3 T 4 5
Identify the above molecule.
Give labels for parts numbered 1 to 5
3. Describe how the above molecule
replicates itself.
What is the significance of DNA replication?

20. Answers 1.DNA molecule 2. 1. Phosphate 2.Deoxiribose Sugar 3.Adenine
4.Cytosine
5.Weak hydrogen bond

21. 3. DNA Replication 1. The double helix unwinds.
2. Weak hydrogen bonds between nitrogenous bases
break and two DNA strands unzip (separate).
3. Each original DNA strand serves as a
template on which its complement is built.
4. Free nucleotides build a DNA strand onto each of
the original two DNA strands by attaching to their
complementary nitrogenous bases (A to T and C to G)
5. This results in two identical DNA molecules. Each
molecule consists of one original strand and one
new strand .

22. 4.Significance of DNA replication:
Important for growth, reproduction
Mutations can cause variation
The main enzyme that catalyze the process is DNA polymerases
Forms building block for amino acids that forms proteins
Three bases provides more than the 20 combinations needed to code amino acids
The sequence of the three bases is called a codon.

23. Each PERSON’S DNA profile is unique!
DNA Profiling
Each PERSON’S DNA profile is unique!

24. What is DNA Profiling?
A technique used by scientists to distinguish between individuals of the same species using only samples of their DNA

25. Where do we get DNA

26. DNA profiling Technique used to identify sequence of bases
The nucleotides are separated from each other in
the order that they are found in strand of DNA
Nucleotides appear as dark bands
The sequence in this segment
of DNA reads CTT- AGT
Use as DNA fingerprint - Unique for every person

27. DNA PROFILING IS DIFFERENT FROM FINGERPRINTS

28. DNA Profiling can solve crimes
The pattern of the DNA profile is then compared with those of the victim and the suspect.
If the profile matches the suspect it provides strong evidence that the suspect was present at the crime scene (NB: it does not prove they committed the crime).
If the profile doesn’t match the suspect then that suspect may be eliminated from the enquiry.

29. Solving Medical Problems
A child’s paternity (father) and maternity(mother) can be determined.
This information can be used in
-Paternity suits
-Inheritance cases
-Immigration cases

30. DNA Fingerprinting DNA fingerprinting is often used by the police in
identifying the suspect of a crime.
A useful but controversial method
A sample of a suspect’s bodily fluid or tissue is to be
compared with a sample found at the scene of a
crime.
The pattern of lines represents a person’s specific
genetic make-up.
DNA fingerprinting use in 11/9 disaster to identify victims

31. Famous cases
In 2002 Elizabeth Hurley used DNA profiling to prove that Steve Bing was the father
of her child Damien

32. Famous Cases
O.J. Simpson was cleared of a double murder charge in 1994 which relied heavily on DNA evidence.
This case highlighted lab difficulties.

33. Three types of RNA and their functions
1. Messenger RNA (mRNA)
2. Transfer RNA (tRNA)
3. Ribosomal RNA (rRNA)

34. 1. Messenger RNA (mRNA) Acts as a template for protein synthesis
Has the same sequence of bases as the DNA strand that has the gene sequence.

35. 2. Transfer RNA (tRNA)
One for each triplet codon that codes for a specific amino-acid (the building blocks of proteins).
tRNA molecules are covalently attached to the corresponding amino-acid at one end
At the other end they have a triplet sequence (called the anti-codon) that is complementary to the triplet codon on the mRNA.

36. 3. Ribosomal RNA (rRNA)
Make up an integral part of the ribosome, the protein synthesis machinery in the cell.

37. COMPARE & CONTRAST DNA & RNA

38. Differences between DNA and RNA
Double strand
Single strand
Deoxyribose sugar
Ribose sugar
Thymine and Adenine
Thymine and Uracil
Guanine and Cytosine

39. PROTEIN SYNTHESIS

40. IMPORTANCE OF PROTEINS
Play essential roles in the cells of all living creatures.
They serve as building blocks of cells, control chemical reactions, and transport materials to and from cells.
Composed of long chains of amino acids.
The specific sequence of amino acids in a chain determines the exact function of the protein.

41. DNA MUST REPLICATE 1 2 3
In preparation for the manufacture of mRNA, a DNA molecule in the nucleus separates into two strands in the region of a gene carrying instructions for a specific protein. Each sequence of three bases in a DNA strand is called a triplet, which is a code for one of 20 amino acids, the building blocks of protein.

42. IN NUCLEUS IN CYTOPLASM
TRANSLATION
TRANSCRIPTION
mRNA moves to ribosome r RNA
tRNA carries amino acid to ribosome
Amino acids linked up to form protein molecule
DNA unzip to expose a gene
mRNA copies the gene

43. DNA RNA T – A U – A G – C G - C TRANSCRIPTION TO RNA
One DNA strand acts as the template, or pattern, for the construction of mRNA in the nucleus.
In this process, called transcription, free-floating RNA nucleotides travelling in the cell nucleus pair with complementary bases on the DNA template strand.
RNA nucleotides use the base uracil (U) instead of thymine (T).
Transported out from the DNA of nucleus into the cytoplasm
DNA RNA
T – A U – A
G – C G - C

44. mRNA ATTACHED TO THE RIBOSOME
Once mRNA is completely formed, the mRNA strand leaves the cell nucleus to enter the cytoplasm, where it attaches to a cellular organelle called a ribosome. Protein synthesis occurs in the ribosomes

45. tRNA bind to amino acids
The single-stranded chain is folded in a 'clover-leaf’
Scattered throughout the cytoplasm are different types of transfer RNA (tRNA), each capable of attaching to one of the 20 different amino acids that are used to build a protein.
One end of a tRNA molecule attaches to a specific amino acid as determined by the anticodon at the other end of the tRNA.
An anticodon is a three-base sequence that recognizes a particular mRNA codon
Anticodon
C C G
tRNA

46. Protein synthesis in the cell
Free amino acids
tRNA brings amino acid to ribosome
Ribosome incorporating amino acid in protein chain
mRNA being translated

47. Practical Activity
P. 12 training manual

48. Question 2.1
2.1 During their work to establish the structure of DNA, Watson and Crick were interested in the proportion of nitrogenous bases in the DNA of skin cells from a particular organism. They considered results from three different samples done in the same laboratory, as shown in the table below.

49. ANSWERS

50. ANSWER 2.1.4

51. QUESTION 2.2

52. ANSWERS

53. QUESTIONS ON PROTEIN SYNTHESIS

54. ANSWER 1.4
Translation
mRNA strand from nucleus becomes attached to a ribosome with its codons exposed
Each RNA molecule carrying a specific amino acid according to its anticodon matches up
with/compliments the codon on the mRNA
So that the amino acids are placed in the correct sequence
Adjacent amino acids are linked to form a protein (8)

55. QUESTIONS ON PROTEIN SYNTHESIS

56. ANSWER 1.5.1

57. QUESTION ON PROTEIN SYNTHESIS

58. ANSWERS