DNA - Unit 3 Slide Presentation

1. UNIT III - DNA
Replication, Transcription, Translation, Biotechnology

2. HISTORICAL EXPERIMENTS

3. Why label with radioactive Phosphate?

4. Why label with radioactive Sulphur?

7. DNA STRUCTURE
• DNA is a double helix in which nucleotide bases are always paired
together (one purine with one pyrimidine)
• Adenine with Thymine
• Cytosine with Guanine
• The base pairing is called complementary base pairing
• The strands run anti-parallel (in opposite directions)

8. DNA REPLICATION
DNA Topoisomerase - Prevents DNA supercoiling
DNA Helicase - Unwinds DNA and breaks hydrogen bonds
DNA Polymerase - Reads DNA to create a copy strand
Okasaki Fragments - Small single stranded DNA segments
DNA Ligase - Joins Okasaki fragments together

9. DNA REPLICATION

10. GENE EXPRESSION
Definition: The conversion of a gene into a protein, tRNA, or
rRNA
A gene is a specific region of DNA nucleotides that encode
information for creating a protein, tRNA or rRNA

11. THE CENTRAL
DOGMA

12. DNA - AMINO ACID LINK
How many nucleotides in DNA?
How many amino acids are there?
How does DNA code for all amino acids?
REDUNDANCY

14. RIBONUCLEIC ACID (RNA)
Definition: Single stranded (typically) nucleic acid containing 4 nucleotide monomers:
Adenine, Cytosine, Guanine, and Uracil
There are 3 main types of RNA:
mRNA – messenger RNA that is used to carry genetic information from the nucleus
to ribosomes
tRNA – transfer RNA that is used to transfer amino acids to the ribosomal units
during protein production
rRNA – ribosomal RNA that is used to produce the ribosomal subunits along with a
number of proteins.

15. TRANSCRIPTION
Definition: The conversion of a DNA template into mRNA
Process
DNA section containing gene unwinds and unzips
DNA is read from 3’ to 5’ starting at the TATA box
RNA polymerase reads DNA and creates an mRNA copy
mRNA is created 5’ to 3’

16. Post-Transcription mRNA Modification
1.5’ Methylated cap is added
2.3’ Poly-A tail is added
3.Introns are removed
4.Exons are spliced together

17. TRANSLATION

18. KEY COMPONENTS OF
TRANSLATION
1. tRNA
2. Mature mRNA
3. Ribosome
4. Amino Acids

20. AUG UCG CCG AAG CGC UUC CCG UAA
START CODON STOP CODON

21. mRNA
A-Site
30S Subunit
50S Subunit
E-Site
P-Site

22. TRANSLATION STEPS
1.Initiation
2.Elongation
3.Termination

23. INITIATION
A specific tRNA (Methionyl) and mRNA bind to the small
subunit of the ribosome
Initiation factors (proteins) recognize the 5’ cap of the mRNA to
also aid in initiation
The Large ribosomal subunit then binds to this complex to form
a functional ribosome.

24. ELONGATION
1. tRNA with specific anticodon enters A-site of ribosome
2. Peptide bond is formed between a.a. in P-site and a.a. in A-site
3. Bond between a.a. and tRNA in P-site broken
4. Ribosome translocates to next codon
5. tRNA moves from P-site to E-site and is released.
6. Process repeats until Termination

26. TERMINATION
1. Elongation is terminated when a stop codon is translocated into
the A site of the ribosome.
2. Release factors recognize the stop codon.
3. The release factor hydrolizes the bond between the tRNA in the
P site and the polypeptide chain.
4. Translation is now complete.
5. The ribosomal subunits dissociate from the mRNA

29. CONTROL OF GENE EXPRESSION
Control of transcription (making mRNA) is the most widely used
system.
Activators: Bind enhancing regions of DNA to aid
transcription
Repressors: Bind silencers regions of DNA to stop
transcription
This control allows for different proteins to be made in different
cells of the body. This makes liver cells different from nerve cells.

30. CONTROL OF GENE EXPRESSION
Post-Transcriptional Control
Examples: mRNA degradation and translational repression
Post-Translational Control
Examples: Protein Cleavage/splicing and Chemical Modification

31. PROKARYOTES
Control of Gene Expression

32. OPERONS
An operon is a group of genes that are transcribed
at the same time.
They usually control an important biochemical process.
They are rarely found in eukaryotes.

33. THE LAC OPERON
The lac operon consists of three genes each involved in
processing the sugar lactose
β-galactosidase - hydrolyses lactose into glucose and
galactose
permease - A protein that allows for quick transport of lactose
into the bacterial cell.
transacetylase - Unknown function

34. WHEN LACTOSE IS ABSENT
Repressor protein is continuously synthesized and
sits on a sequence of DNA just in front of the lac
operon, the Operator site
The repressor protein blocks the Promoter site
where the RNA polymerase settles before it starts
transcribing

35. WHEN LACTOSE IS ABSENT
Repressor
protein
Operator
site
z y a
Regulator
gene lac operon
DNA
I O
RNA polymerase
Blocked

36. WHEN LACTOSE IS PRESENT
When lactose is in the cell it fits onto the repressor
protein at an active site called the allosteric site.
This causes the repressor protein to change its shape
(a conformational change). It can no longer sit on
the operator site. RNA polymerase can now reach its
promoter site

37. WHEN LACTOSE IS PRESENT

38. GENE MUTATIONS
A mutation is defined as a change in the sequence of DNA within
a gene.
There are many types of mutations. Some cause minor to no
changes in the polypeptide chain, while others cause major
changes.

39. SILENT MUTATION

45. A SPECIFIC MISSENSE MUTATION
Sickle Cell Anemia

46. MUTATION CAUSES AND REPAIR
DNA replication errors: DNA polymerase proofreads the
new strand against the old strand, but there are times
when incorrect base pairing will cause mutations.
DNA can repair itself by removing the damaged DNA or
even reversing the affected DNA bases.

47. MUTATION CAUSES AND REPAIR
Free Radicals: Occur in cells due to oxidative metabolism
and cause incorrect base pairing.
Chemical Mutagens
Can act like bases and cause incorrect base pairing
Can change the shape of DNA causing mutation
Radiation
Damages Bases
Breakages of DNA strand(s)

48. TRANSPOSONS: JUMPING GENES
Transposons are specific DNA sequences that move from
place to place within and between chromosomes.
These so-called jumping genes can cause a mutation to occur
by altering gene expression.
It is likely all organisms, including humans, have transposons.

49. CANCER - A FAILURE OF GENETIC
CONTROL
Cancer is a genetic disorder resulting in a tumor, an abnormal mass of cells.
Carcinogenesis, the development of cancer, is a gradual process.
Cancer cells lack differentiation, form tumors, undergo angiogenesis and
metastasize.
Angiogenesis is the formation of new blood vessels to bring additional
nutrients and oxygen to a tumor; cancer cells stimulate and require angiogenesis
to survive.
Metastasis is invasion of other tissues by establishment of tumors at new sites.
Cancer cells fail to undergo apoptosis, or programmed cell death.

51. ORIGIN OF CANCER
Mutations in at least four classes of genes are associated with the development
of cancer.
Oncogenes - Mutation causing a signal to tell the cell to multiply all the time.
Mutations in genes that code for proteins regulating structure of chromatin
can promote cancer.
Tumor-suppressor genes - mutations can prevent normal regulation of
the cell cycle. An example is the p53 gene.
p53 - stops cells with damaged DNA from reproducing and encourages
apoptosis.

53. GENETIC MODIFICATION - PLANTS
1. Ti Plasmid
2. Bacterial Cell
3. Infected plant cell
4. Growth of plant

55. GMO’S IN SOCIETY
WHO: Potato’s, Tobacco plants, and the Ebola vaccine
Golden rice: beta-carotene and vitamin A
Cash crops: Flavr Savr tomato 1994

56. CHAPTER SUMMARY
Since DNA is the genetic material, its structure and functions constitute the molecular basis of
inheritance.
Because the DNA molecule is able to replicate, genetic information can be passed from one cell
generation to the next.
DNA codes for the synthesis of proteins; this process also involves RNA.
In prokaryotes, regulator genes control the activity and expression of other genes.
In eukaryotes, the control of gene expression occurs at all stages, from transcription to
the activity of proteins.
Gene mutations vary; some have little effect but some have a dramatic effect.
Loss of genetic control over genes involved in cell growth and/or cell division cause
cancer.