1. 1

2. Immagini e concetti della biologia Sylvia S. Mader
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

3. B3 - Molecular biology
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

4. DNA and inheritance
Fredrick Griffith’s experiments with Streptococcus pneumoniae (1931) demonstrated that a “transforming substance” was used as replicator.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

5. DNA and inheritance
Alfred Hershey and Martha Chase (1952) used the T2 bacteriophage and Escherichia coli for their experiments.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

6. DNA and inheritance
Hershey and Chase showed that DNA, not proteins, enters bacterial cells and directs the phage reproduction.
Hershey and Chase’s first experiment - virus DNA is labeled.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

7. DNA and inheritance
Hershey and Chase showed that DNA, not proteins, enters bacterial cells and directs the phage reproduction.
Hershey and Chase’s second experiment - virus capsid is labeled.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

8. Nucleic Acids
DNA is a polynucleotides (polymers of nucleotides). Each nucleotide is composed of three parts:
a C5 sugar called deoxyribose;
a phosphate group;
a nitrogen-containing base.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

9. Nucleic Acids
There are four possible nitrogen bases. Adenine (A) and guanine (G) have a double-ring structure and belong to a group called purines. Thymine (T) and cytosine (C) have a single-ring structure and are called pyrimidines.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

10. Nucleic Acids
RNA (ribonucleic acid) contains a C5 sugar called ribose and the bases A,C,G. Uracil (U) replaces T.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

11. DNA DNA is a functional genetic material as it:
varies between species and individuals
can store information
remains constant within a species
replicates
undergoes mutations
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

12. DNA structure
DNA is composed by a double strand of nucleotides where C always pairs with G and T pairs with A.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

13. DNA structure
James Watson and Francis Crick constructed the first model of DNA using Rosalind Franklin and Maurice Wilkins’s X-ray diffraction data.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

14. DNA structure
In Watson and Crick double helix model weak hydrogen bonds between the bases hold the two chains to one another.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

15. DNA is suitable for replication
DNA duplication (or replication) is semiconservative as each new filament contains an old strand and a new strand.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

16. DNA is suitable for replication
DNA duplication involves three steps:
Unrolling and unwinding;
Complementary base paring;
Joining.
DNA polymerase is an enzyme that assists steps 2 and 3.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

17. DNA is suitable for replication
In the C5 deoxyribose, carbons are numbered 1', 2', 3', 4', and 5' to distinguish from the atoms of the nitrogen base ring. The 5' carbon binds to the P-group.
The P-group of a nucleotide is bonded to the 3' C of the adjacent nucleotide.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

18. DNA polymerase
DNA polymerase adds nucleotides to the 3' end of the DNA and needs a primer to start the replication of a strand.
Telomeres are special non-codifying repetitive nucleotide sequences.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

19. DNA replication
The second strand of DNA is duplicated in opposite direction of the replication fork.
Replication is continuous for the leading strand but discontinuous for the lagging strand.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

20. Genes and protein synthesis
Genes are expressed by proteins.
The “one gene one protein” hypothesis is based on the observation that a defective gene causes a defective enzyme.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

21. Protein synthesis The making of a protein requires two steps.
Transcription: DNA is transcribed into mRNA.
Translation: the transcript mRNA directs the amino acid sequence.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

22. Genetic code
The genetic code is the set of information encoded in DNA that is translated into amino acid sequences.
A three-nucleotides codon (i.e. AUC) in a sequence specifies a single amino acid.
With few exceptions, the genetic code is universal.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

23. Transcription
During transcription, complementary base pairing occurs, RNA polymerase joins bases and the coded information passes from the gene to the mRNA.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

24. Transcription
In eukaryotes, exon is a DNA sequence that will be expressed while intron is DNA that has regulatory function but it will not be expressed.
Both introns and exons are transcript to primary mRNA.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

25. Translation
Amino acids are transferred by tRNA (transfer) to the cytoplasm where mRNA is translated into proteins.
tRNA’s anticodon base-pairs with mRNA’s codon.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

26. Ribosomes Translation occurs at ribosomes in the cytoplasm.
A ribosome has a binding site for mRNA and three binding sites for tRNA.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

27. Polypeptide synthesis
Polypeptide synthesis occurs as a ribosome moves down mRNA. A polyribosome is a complex of ribosomes translating the same mRNA.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

28. Polypeptide synthesis: I step
Initiation begins the process of polypeptide synthesis. The starting codon is UAG.
The ribosome tRNA binding sites are: E (exit) site, P (peptide) site and A (amino acid) site.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

29. Polypeptide synthesis: II step
During elongation, a tRNA at the P site passes a peptide to an amino acid-carrying tRNA at the A site.
translocation
elongation
Then translocation occurs: the ribosome moves forward and the peptide bearing tRNA is at the P site.
The used tRNA exits from the E site.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

30. Resume: participants in gene expression
The processes of elongation and translocation occur over and over again. At termination, the ribosome reaches a stop codon and the polypeptide is released.
Transcription and translation make the gene expression possible.
Resume: participants in gene expression
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

31. Mutations
A mutation is a permanent change in the genomic sequence. It affects the gene expression.
Germ line mutations occur in gametes and can be passed on to offsprings.
Somatic mutations involve body cells and are not transmitted to descendants.
Insertions add nucleotides into the DNA, deletions remove one or more nucleotides from the DNA.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

32. Point mutations Point mutations affect only one or a few nucleotides.
Depending on the DNA sequence, those mutations can be harmful or without consequence.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

33. Frameshift mutations
Frameshift mutations involve insertions or deletions of several nucleotides.
Frameshift mutations can lead to the expression of a new non-functional protein and cause genetic disorders as the cystic fibrosis.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

34. Transposons Discovered by Barbara McClintock in 1981.
A transposon (or “jumping gene”) is a sequence of DNA that can change position within the chromosome.
Transposition can block transcription and be a source of translocation, deletions, inversion or duplication.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

35. Genetic mutations and cancer
Apoptosis (programmed cell death) is important in cancer control.
Proto-oncogenes, promote the cell cycle and inhibit apoptosis.
Tumor suppressor genes, protect the cell from the development of the cancer.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

36. Genetic mutations and cancer
Oncogenes and mutated tumor suppressor genes cause excess cyclin which stimulates the cell cycle and makes p53 unavailable so that apoptosis does not occur.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

37. Genetic mutations and cancer
Products of faulty genes interfere with signal transduction when cancer develops.
A stimulatory signal transduction pathway turns on a proto-oncogene whose products stimulates the cell cycle.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

38. Genetic mutations and cancer
When cancer occurs the products of an oncogene leads to overstimulation of the pathway and the cell cycle excellerates.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

39. Genetic mutations and cancer
An inhibitory signal transduction pathway turns on a tumor suppressor gene whose products inhibits the cell cycle.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

40. Genetic mutations and cancer
When cancer occurs, the product of a mutated tumor suppressor gene fails to turn on the pathway and fails to stop the cell cycle.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

41. Cancer development
Carcinogenesis is the development of a malignant tumor due to repeated mutations.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

42. Cancer development
Angiogenesis (formation of new blood vessels) provides nutrients to a growing tumor.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

43. Cancer development
Motile cells invade lymphatic and blood vessels, metastasis occur when new tumors form far from the original site.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

44. Cancer therapy
Cancer diagnosis includes a complete check of patient health, imagine diagnostics, blood and urine analysis, endoscopy.
Surgery of a cancer cell mass is useful only for solid tumors.
Chemotherapy is a cancer treatment that uses drugs to destroy cancer cells.
Radiotherapy uses high energy rays to destroy cancer cells.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018