Molecular basis of heredity. Realization of hereditary information.

1. Molecular basis of heredity. Realization of hereditary information. Lecturer: ass. prof. Rybitska L.N.

2. Lecture questions • Proteins are the main living things. • Types of proteins . • Lipoproteins and Glycoproteins. • Nucleotides and Nucleic Acids. • Protein synthesis. • - Transcription • - Translation

3. Protein functions • enzymes are only one class of proteins. • proteins also form the scaffolding, or structure, of a good deal of tissue; • active in transporting molecules from one site to another; • they allow muscles to contract and cells to move; • some hormones are made from them

4. Proteins are prime examples of the building-block type of molecule. • The monomers in this case are called amino acids. • String an arbitrary number of them together in a chain—and you have a polypeptide; • when the polypeptide folds up in a specific three-dimensional manner, you have a protein. • As a practical matter, proteins are likely to be made of hundreds of amino acids strung together and folded up

6. Shape is critical to functioning of all proteins

7. Types of proteins • Enzymes-Quicken chemical reactions (surcease brocks sugar to glucose and fructose) • Hormones- chemical messengers (growth hormone) • Transport–move other molecules (hemoglobin) • Contractive –movement (myosin and actin -allow muscles to contract) • Protective- healing, defense against invader (fibrinogen: stops bleeding antibodies: kill bacterial invaders) • Structural –mechanical support (keratin: hair collagen: cartiilage) • Storage - stores nutrients (ovalbumin: egg white: used as nutrient for embryos) • Toxins - defense, predations (bacterial diphteria toxin) • Communication – cell signaling (glicoprotein: receptors on cell surface)

8. Simple proteins Consist from only polypeptide chains

9. Large proteins Consist from polypeptide chains and nonprotein components Lipoproteins -are a combination of lipids and proteins; they are active in transporting fat molecules throughout the body via the bloodstream. They amount to a capsule of protein surrounding a globule of fat.

10. Large proteins • Glycoproteinsare combinations of proteins and carbohydrates. • Most receptors are usually glycoproteins, meaning mostly protein with a side-chain made of carbohydrate.

11. Large proteins • Chromosomes- combination of nucleic acids and proteins

12. Fibrous (insoluble in water) – structural: hair, cartilage

13. Globular (soluble in water) –chemical: enzymes, antibodies, receptors.

14. Nucleic acids • there are 2 types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). • DNA Provides Information for the Structure of Proteins

15. DNA Basics: • Located in nucleus, packaged into chromosomes • Organelles (mitochondria, chloroplasts) have their own chromosomes • DNA is double stranded, present in the form of a double helix 3. Bases make up complementary base pairs

16. Nucleic acids • The nucleic acids are polymers of smaller units called nucleotides. • A nucleotide consist of: • 1) five-carbon sugar (deoxyribose in DNA and ribose in RNA); • 2) a phosphate group (PO4); • 3) one of five types nitrogen-containing compounds called nitrogenous bases.

17. Nucleic acids • The nitrogenous bases are: • Purines, which are larger – Adenine (A), Guanine (G); • Pyramidines, which are smaller – Thymine (T), Cytosine (C), Uracil (U).

18. Nucleic acids • The sugar and phosphate components of the nucleotides link up to form the outer "rails" of the DNA molecule, while the bases point toward the molecule's interior. • Two chains of nucleotides are linked, via hydrogen bonds, to form DNA's double helix. • Two of these chains then link together—as if a ladder, split down the middle, were coming together—forming the most famous molecule in all of biology, the DNA double helix.

19. Nucleic acids • A gene is generally a collection of DNA nucleotides that contains the instructions for an individual protein. • A player in this series of steps protein synthesis is another nucleic acid, ribonucleic acid or RNA, which is involved in ferrying the DNA-encoded instructions to the sites in the cell where proteins are put together.

20. RNA –a polymer of ribose-containing nucleotides, with forms single-strand. • Messenger RNA carries the genetic code to the cytoplasm to direct protein synthesis. • 1. This single-stranded molecule (hundreds to thousands of nucleotides). • 2. mRNA contains codons that are complementary to the DNA codons from which it was transcribed • Transfer RNA is folded into a cloverleaf shape and contains about 80 nucleo­tides. • 1. Each tRNA combines with a specific amino acid that has been activated by an enzyme. • 2. One end of the tRNA molecule possesses an anticodon, a triplet of nucleotides that recognizes the complementary codon in mRNA. • Ribosomal RNA associates with many different proteins (including enzymes) to form ribosomes. • 1. rRNA associates with mRNA and tRNA during protein synthesis. • 2. rRNA synthesis takes place in the nucleolus and is catalyzed by RNA polymerase.

21. Most Genes encode proteins • DNA  mRNA  protein • DNA is copied into RNA via transcription • The Genetic Code is universal

22. DNA replication • 1. DNA helicase (enzyme) unwinds the DNA. The junction between the unwound part and the open part is called a replication fork. • 2. DNA polymerase adds the complementary nucleotides and binds the sugars and phosphates. DNA polymerase travels from the 3' to the 5' end.

23. DNA replication • 3. DNA polymerase adds complementary nucleotides on the other side of the ladder. Traveling in the opposite direction. • 4. One side is the leading strand - it follows the helicase as it unwinds. • 5. The other side is the lagging strand - its moving away from the helicase

24. DNA replication • Problem: it reaches the replication fork, but the helicase is moving in the opposite direction. It stops, and another polymerase binds farther down the chain. • This process creates several fragments, called Okazaki Fragments, that are bound together by DNA ligase.

25. DNA replication • 6. During replication, there are many points along the DNA that are synthesized at the same time (multiple replication forks). It would take forever to go from one end to the other, it is more efficient to open up several points at one time.

26. All organisms use the same genetic codeEach set of three nucleotides codes for an amino acid = “The Genetic Code”

27. The genetic code • consists of 64 triplet codons (A, G, C, U) 43 = 64 • all codons are used in protein synthesis • 20 amino acids • 3 termination (stop) codons: UAA, UAG, UGA • AUG (methionine) is the start codon (also used internally) • multiple codons for a single amino acid = degeneracy • Genetic code is unambiguous. Each triplet codon has only one meaning • 5 amino acids are specified by the first two nucleotides only • 3 additional amino acids (Arg, Leu, and Ser) are specified by six different codons

28. Accuracy of Replication • The mismatched nucleotide causes a pause in replication, and the mismatched nucleotide is excised from the daughter strand. • The errors that slip through nucleotide selection and proofreading cause a gene mutation to occur. • Actually it is of benefit for mutations to occur occasionally because variation is the raw material for the evolutionary process.

29. Point Mutations • Point mutations involve a change in a single nucleotide and therefore a change in a specific codon. • When one base is substituted for another, the results can be variable. For example, if UAC is changed to UAU, there is no noticeable effect, because both of these codons code for tyrosine. Therefore, this is called a silent mutation.

30. Point Mutations • If UAC is changed to UAG(stop codon. • If this substitution occurs early in the gene, the resulting protein may be too short and may be unable to function. Such an effect is called a nonsense mutation.

31. Point Mutations • Finally, if UAC is changed to CAC, then histidine is incorporated into the protein instead of tyrosine. This is a missense mutation.

32. Point Mutations • The term reading frame applies to the sequence of codons because they are read from some specific starting point as is this sentence: • THE CAT ATE THE RAT. If the latter C is deleted from this sentence and the reading frame is shifted, • THE ATA TET HER AT –something that doesn't make sence. • That call frameshift mutations.

33. Gene Expression • The process by which a gene produces a product, usually a protein, is calledgene expression. • DNA not only serves as a template for its own replication, it is also a template for RNA formation. • Gene Expression in prokaryotes: • transcription, translation. • Gene Expression in eukaryotic cells: • transcription, processing, translation.

34. Transcription • The process by which a mRNA copy is made of a portion of DNA is called transcription • It is the first step required for gene expression. • During transcription, a mRNA molecule is formed that has a sequence of bases complementary to a portion of one DNA strand; • A, T, G, or С is present in the DNA template, • U, A, C, or G is incorporated into the mRNA molecule

35. Transcription • Transcription begins at a region of DNA called a promoter. • A promoter is a special sequence of DNA bases where RNA polymerase attaches and the transcribing process begins. A promoter is at the start end of the gene to be transcribed. • Elongation of the mRNA molecule occurs as long as transcription proceeds. Finally, RNA polymerase comes to a terminator sequence at the other end of the gene being transcribed. • The terminator causes RNA polymerase to stop transcribing the DNA and to release the mRNA molecule, now called a RNA transcript

36. RNA Processing • Special molecular splicing complexes cut out sections of introns. Then the remaining portions of the mRNA tape are spliced together. • exons: portions of the mRNA transcript that code for amino acids. • From this, it follows that introns are noncoding portions of the original mRNA tape; they do not contain information for the sequencing of amino acids in a protein.

37. Translation • During translation, the sequence of codons in mRNA directs the sequence of amino acids in a protein. • Two other types of RNA are needed for protein synthesis. • rRNA is contained in the ribosomes, where the codons of mRNA are read • tRNA carries amino acids to the ribosomes so that protein synthesis сan occur.

38. The steps of translation. • mRNA Binds to Ribosome; • Polypeptide Chain Is Elongated • Termination of the Growing Chain

39. The steps in translation are: • The ribosome binds to mRNA at a specific area. • The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.

40. Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain.

41. The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA.

42. The polypeptide forms into its native shape and starts acting as a functional protein in the cell

43. Regulation of Gene expression • lac operon in E. Coli • Function - to produce enzymes which break down lactose(milk sugar) • when lactose is present, they turn on and produce enzymes • Two components - repressor genes and functional genes • Promoter (P) - aids in RNA polymerase binding • Operator (O) - "on/off" switch - binding site for the repressor protein • Repressor (lacI) gene • Repressor gene (lacI) - produces repressor protein w/ two binding sites, one for the operator and one for lactose • The repressor protein is under allosteric control - when not bound to lactose, the repressor protein can bind to the operator • When lactose is present, an isomer of lactose, allolactose, will also be present in small amounts.  Allolactose binds to the allosteric site and changes the conformation of the repressor protein so that it is no longer capable of binding to the operator

44. Operation - If lactose is not present:the repressor gene produces repressor, which binds to the operator. This blocks the action of RNA polymerase, thereby preventing transcription

45. Thank You for attention! Do you have any questions ?