1. GENETICS OF VIRUSES

2. 1950’S- VIRUSES OBSERVED
THE SMALLEST VIRUSES ARE ONLY 20 nm IN DIAMETER
THE VIRUS PARTICLE, CONSISTS OF NUCLEIC ACID ENCLOSED BY A PROTEIN COAT
MAY BE DOUBLE-STRANDED DNA
SINGLE-STRANDED DNA
DOUBLE-STRANDED RNA
SINGLE-STRANDED RNA

3. COMPARING SIZES

4. CAPSIDS CAPSIDS ARE THE PROTEIN COAT THAT ENCLOSES THE VIRAL GENOME
MAY BE ROD-SHAPED, POLYHEDRAL OR COMPLEX
COMPOSED OF MANY CAPSOMERES, PROTEIN SUBUNITS MADE FROM ONLY ONE OR A FEW TYPES OF PROTEINS

5. ENVELOPE THE ENVELOPE IS THE MEMBRNE THAT COVERS SOME VIRAL CAPSIDS
IT HELPS VIRUSES INFECT THEIR HOST
IT IS DERIVED FROM HOST CELL MEMBRANE

6. VIRAL STRUCTURE

7. VIRAL REPRODUCTION OVERVIEW
VIRUSES CAN ONLY REPRODUCE INSIDE OF A HOST CELL
OBLIGATE INTRACELLULAR PARASITES-CAN EXPRESS THEIR GENES AND REPRODUCE ONLY WITHIN A LIVING CELL
HOST RANGE = LIMITED NUMBER OR RANGE OF HOST CELLS THAT A PARASITE CAN INFECT

8. VIRAL LIFE CYCLES 1) INFECTING HOST CELL WITH VIRAL GENOME
GENERAL PATTERNS:
1) INFECTING HOST CELL WITH VIRAL GENOME
2) CO-OPTING HOST CELL’S RESOURCES TO:
A) REPLICATE THE VIRAL GENOME
B) MANUFACTURE CAPSID PROTEIN
3) ASSEMBLING NEWLY PRODUCES VIRAL NUCLIC ACID AND CAPSOMERES INTO THE NEXT GENERATION OF VIRUSES

9. SIMPLIFIED VIRAL REPRODUCTIVE CYCLE

10. VIDEO: SIMPLIFIED VIRUS LIFE CYCLE

11. BACTERIOPHAGE A PHAGE IS A VIRUS THAT ATTACKS BACTERIA
PHAGES ARE THE BEST UNDERSTOOD OF ALL VIRUSES

12. THE LYTIC CYCLE
VIRULENT BACTERIOPHAGES REPRODUCE ONLY BY A LYTIC REPLICATION CYCLE
VIRULENT PHAGES - PHAGES THAT LYSE THEIR HOST CELLS
LYTIC CYCLE = A VIRAL REPLICATION CYCLE THAT RESULTS IN DEATY (LYSIS) OF THE HOST CELL

13. STEPS OF THE LYTIC CYCLE
1) PHAGE ATTACHES TO CELL SURFACE
2) PHAGE CONTRACTS SHEATH AND INJECTS DNA
3) HYDROLYTIC ENZYMES DESTROY HOST CELL’S DNA
4) PHAGE GENOME DIRECTS HOST CELL TO PRODUCE PHAGE COMPONENTS: DNA AND CAPSID PROTEINS
5) CELL LYSES AND RELEASES PHAGE PARTICLES

14. LYTIC CYCLE OF PHAGE T4

15. LYTIC CYCLE VIDEO

16. BACTERIAL DEFENSES
BACTERIAL MUTATIONS CAN CHANGE RECEPTOR SITES USED BY PHAGES FOR RECOGNITION, AND THUS AVOID INFECTION
BACTERIAL RESTRICTION NUCLEASES RECOGNIZE AND CUT UP FOREIGN DNA, INCLUDING CERTAIN PHAGE DNA. BACTERIAL DNA IS CHEMICALLY ALTERED, SO IT IS NOT DESTROYED BY THE CELL’S OWN RESTRICTION ENZYMES

17. LYSOGENIC CYCLE
SOME VIRUSES CAN COEXIST WITH THEIR HOSTS BY INCORPORATING THEIR GENOME INTO THE HOST’S GENOME
TEMPERATE VIRUSES - VIRUSES THAT CAN INTEGRATE THEIR GENOME INTO A HOST CHROMOSOME AND REMAIN LATENT UNTIL THEY INITIATE A LYTIC CYCLE
THEY HAVE TWO POSSIBLE MODES OF REPRODUCTION, THE LYTIC CYCLE AND THE LYSOGENIC CYCLE

18. STEPS OF LYSOGENIC CYCLE
PHAGE L LIFE CYCLE
1) PHAGE L BINDS TO THE SURFACE OF E.COLI CELL
2) PHAGE L INJECTS ITS DNA INTO THE BACTERIAL HOST CELL
3) L DNA FORMS A CIRCLE AND EITHER BEGINS A LYTIC OR LYSOGENIC CYCLE
4) L DNA INSERTS BY GENETIC RECOMBINATION (CROSSING OVER) INTO A SPECIFIC SITE ON THE BACTERIAL CHROMOSOME

19. REPRODUCTIVE CYCLES OF PHAGE L

20. LYSOGENIC CYCLE VIDEO

21. PROPHAGES
A PHAGE GENOME THAT IS INCORPORATED INTO A SPECIFIC SITE ON THE BACTERIAL CHROMOSOME

22. VIRAL ENVELOPES
SOME ANIMAL VIRUSES ARE SURROUNDED BY A MEMBRANOUS ENVELOPE, WHICH IS UNIQUE TO SEVERAL GROUPS OF ANIMAL VIRUSES. THIS ENVELOPE IS:
OUTSIDE THE CAPSID AND HELPS THE VIRUS ENTER HOST CELLS
A LIPID BILAYER WITH GLYCOPROTEIN SPIKES PROTRUDING FROM THE OUTER SURFACE

23. ENVELOPED VIRUSES LIFE CYCLE
1) ATTACHMENT - GLYCOPROTEIN SPIKES PROTRUDING FROM THE VIRAL ENVELOPE ATTACH TO RECEPTOR SITES ON THE HOST’S PLASMA MEMBRANE
2) ENTRY - AS THE ENVELOPE FUSES WITH THE MEMBRANE, THE ENTIRE VIRUS (CAPSID AND GENOME) IS TRANSPORTED INTO THE CYTOPLASM BY RECEPTOR-MEDIATED ENDOCYTOSIS

24. 3) UNCOATING - CELLULAR ENZYMES UNCOAT THE GENOME BY REMOVING THE PROTEIN CAPSID FROM THE VIRAL RNA
4) VIRAL RNA AND PROTEIN SYNTHESIS-VIRAL ENZYMES ARE REQUIRED TO REPLICATE THE RNA GENOME AND TO TRANSCRIBE mRNA
5) ASSEMBLY AND RELEASE - NEW CAPSIDS SURROUND VIRAL GENOMES. ONCE ASSEMBLED, THE VIRIONS ENVELOP WITH HOST PLASMA MEMBRANE AS THEY BUD OFF FROM THE CELL’S SURFACE

25. REPRODUCTIVE CYCLE OF AN
ENVELOPED VIRUS

26. PROVIRUS
A PROVIRUS IS FORMED WHEN VIRAL DNA INSERTS INTO A HOST CELL CHROMOSOME. (IF IT IS A BACTERIA CELL, IT IS CALLED A PROPHAGE). PROVIRUS’ REMAIN DORMANT UNTIL SOME TRIGGER (USUALLY ENVIRONMENTAL) CAUSES THE VIRUS TO BEGIN THE DESTRUCTIVE LYTIC CYCLE

27. RNA VIRUSES USE RNA TO CARRY GENETIC INFORMATION
THE REPRODUCTIVE CYCLES DEVIATE FROM THE STANDARD LYTIC AND LYSOGENIC CYCLES
IN SOME RNA VIRUSES, THE VIRAL RNA IS USED DIRECTLY AS mRNA

28. RETROVIRUSES RETRO = BACKWARD
RETROVIRUS= RNA VIRUS THAT USES REVERSE TRANSCRIPTASE TO TRANSCRIBE DNA FROM THE VIRAL RNA GENOME
HIV-THE VIRUS THAT CAUSES AIDS IS A RETROVIRUS
RETROVIRUSES HAVE COMPLEX CYCLES BECAUSE THEY MUST FIRST CARRY OUT REVERSE TRANSCRIPTION

29. HIV-THE REPRODUCTIVE CYCLE

30. HIV RETROVIRUS VIDEO

31. VIRUSES AND CANCER SOME TUMOR VIRUSES CAUSE CANCER IN ANIMALS
WHEN ANIMAL CELLS GROWN IN TISSUE CULTURE ARE INFECTED WITH TUMOR VIRUSES, THEY TRANSFORM TO A CANCEROUS STATE
EXAMPLES ARE MEMBERS OF THE RETROVIRUS, PAPOVAVIRUS, ADENOVIRUS, HERPESVIRUS GROUPS
CERTAIN VIRUSES ARE IMPLICATED IN HUMAN CANCERS

32. VIRUSES AND CANCER RETROVIRUS - LEUKEMIA
HERPESVIRUS - BURKITT’S LYMPHOMA
PAPILOMA VIRUS - CERVICAL CANCER
HEPATITIS B - LIVER CANCER
ONCOGENES - GENES FOUND IN VIRUSES OR AS PART OF THE NORMAL GENOME, THAT TRIGGER TRANSFORMATION OF A CELL TO A CANCEROUS STATE

33. PLANT VIRUSES AS SERIOUS AGRICUTURAL PESTS, MANY OF THE PLANT VIRUSES:
STUNT PLANT GROWTH AND DIMINISH CROP YIELDS
ARE RNA VIRUSES
HAVE ROD-SHAPED CAPSIDS WITH CAPSOMERES ARRANGED IN A SPIRAL
CAPSOMERE - COMPLEX CAPSID SUBUNIT CONSISTING OF SEVERAL IDENTICAL OR DIFFERENT PROTEIN MOLECULES

34. PLANT VIRUSES
PLANT VIRUSES SPREAD FROM PLANT TO PLANT BY TWO MAJOR ROUTES:
1) HORIZONTAL TRANSMISSION - AN ORGANISM RECEIVES THE VIRUS FROM AN EXTERNAL SOURCE SUCH AS INSECTS OR GARDENING TOOLS
2) VERTICAL TRANSMISSION - AN ORGANISM INHERITS A VIRAL INFECTION FROM ITS PARENT

35. VIROIDS
ANOTHER CLASS OF PLANT PATHOGENS, ARE SMALLER AND SIMPLER THAN VIRUSES
THEY ARE SMALL, NAKED, CIRCULAR RNA MOLECULES THAT DO NOT ENCODE PROTEIN, BUT CAN REPLICATE IN HOST PLANT CELLS
THEY DISRUPT NORMAL PLANT METABOLISM, DEVELOPMENT, AND GROWTH BY CAUSING ERRORS IN GENE EXPRESSION
VIROID DISEASES AFFECT MANY COMMERCIALLY IMPORTANT PLANTS SUCH AS COCONUT PALMS, POTATOES, TOMATOES

36. PRIONS
PRIONS ARE PATHOGENS THAT ARE PROTEINS, AND THEY APPEAR TO CAUSE A NUMBER OF DEGENERATIVE BRAIN DISEASES SUCH AS:
SCAPIE IN SHEEP
MAD COW DISEASE
CREUTZFELDT-JAKOB DISEASE IN HUMANS

37. HOW PRIONS MAY PROPAGATE
WHEN A PRION CONTACTS ITS NORMAL “TWIN”, IT
MAY INDUCE THE NORMAL PROTEIN TO ASSUME THE
ABNORMAL SHAPE. THE RESULTING CHAIN REACTION
MAY CONTINUE UNTIL PRIONS ACCUMULATE TO
DANGEROUS LEVELS, CAUSING CELLULAR MALFUNCTION

38. GENETICS OF BACTERIA BACTERIA ARE PROKARYOTES
THEY DO NOT POSSESS ANY OF THE SPECIALIZED ORGANELLES OF EUKARYOTES
HAS A SINGLE, CIRCULAR DNA
REPRODUCES BY BINARY FISSION-THE CHROMOSOME REPLICATES AND THE CELL DIVIDES INTO TWO CELLS

39. BACTERIAL REPLICATION

40. PLASMIDS
BACTERIA ALSO CONTAIN PLASMIDS, SHORT, CIRCULAR DNA MOLECULES OUTSIDE THE CHROMOSOME
PLASMIDS CARRY GENES THAT ARE BENEFICIAL BUT NOT NORMALLY ESSENTIAL TO THE SURVIVAL OF THE BACTERIUM
PLASMIDS REPLICATE INDEPENDENTLY OF THE CHROMOSOME
EPISOMES = PLASMIDS THAT BECOME INCORPORATED INTO THE BACTERIAL CHROMOSOME

41. GENETIC RECOMBINATION IN BACTERIA
THERE ARE 3 NATURAL PROCESSES OF GENETIC RECOMBINATION IN BACTERIA:
TRANSFORMATION
TRANSDUCTION
CONJUGATION

42. TRANSFORMATION
THE PROCESS OF GENE TRANSFER DURING WHICH A BACTERIAL CELL ASSIMILATES FOREIGN DNA FROM THE SURROUNDINGS
ASSIMILATED FOREIGN DNA MAY BE INTEGRATED INTO THE BACTERIAL CHROMOSOME BY RECOMBINATION
PROGENY WILL CARRY A NEW COMBINATION OF GENES

43. TRANSDUCTION
GENE TRANSFER FROM ONE BACTERIUM TO ANOTHER BY A BACTERIOPHAGE
RANDOM PIECES OF HOST CELL DNA ARE PACKAGED WITHIN A PHAGE CAPSID DURING THE LYTIC CYCLE OF A PHAGE
THIS PROCESS CAN TRANSFER ALMOST ANY HOST GENE AND LITTLE OR NO PHAGE GENES
WHEN THE PHAGE PARTICLE INFECTS A NEW HOST CELL, THE DONOR CELL DNA CAN RECOMBINE WITH THE RECIPIENT CELL DNA

44. TRANSDUCTION

45. CONJUGATION
THE DIRECT TRANSFER OF GENES BETWEEN TWO CELLS THAT ARE TEMPORARILY JOINED
CYCLE: DNA-DONATING CELL EXTENDS EXTERNAL APPENDAGES CALLED SEX PILI
SEX PILI ATTACH TO A DNA-RECEIVING CELL
A CYTOPLASMIC BRIDGE FORMS THROUGH WHICH DNA TRANSFER OCCURS

46. PLASMIDS
PLASMIDS ARE SMALL, CIRCULAR, DOUBLE-STRANDED, SELF-REPLICATING MOLECULAR RINGS OF DNA THAT CARRY EXTRACHROMOSOMAL GENES IN SOME BACTERIA
PLASMIDS CARRY GENES THT ARE BENEFICIAL BUT NOT NORMALLY ESSENTIAL TO SURVIVAL OF THE BACTERIA
PLASMIDS REPLICATE INDEPENDENTLY OF THE CHROMOSOME
EPISOMES = PLASMIDS THAT BECOME INCORPORATED INTO THE BACTERIAL CHROMOSOME

47. F PLASMID
THE F PLASMID (F FOR FERTILITY) HAS ABOUT 25 GENES, MOST OF WHICH ARE INVOLVED IN THE PRODUCTION OF SEX PILI
WHEN A RECIPIENT BACTERIUM RECeiVES THE F PLASMID, IT TOO CAN BECOME A DONOR CELL

48. R PLASMID
R PLASMIDS PROVIDE BACTERIA WITH RESISTANCE AGAINST ANTIBODIES
SOME CARRY UP TO 10 GENES FOR RESISTANCE TO ANTIBODIES
R PLASMIDS CAN TRANSFER RESISTANCE GENES TO BACTERIA OF DIFFERENT SPECIES INCLUDING PATHOGENIC STRAINS. AS A CONSEQUENCE, RESISTANCE STRAINS OF PATHOGENS ARE BECOMING MORE COMMON

49. TRANSPOSONS
TRANSPOSONS ARE PIECES OF DNA, OR TRANSPOSIBLE GENETIC ELEMENTS, WHICH CAN ACTUALLY MOVE FROM ONE LOCATION TO ANOTHER IN A CELL’S GENOME
CONSERVATIVE TRANSPOSITION = MOVEMENT OF PREEXISTING GENES FROM ONE GENOMIC LOCATION TO ANOTHER; THE TRANSPOSON’S GENES ARE NOT REPLICATED BEFORE THE MOVE, SO THE NUMBER OF GENE COPIES IS CONSERVED
REPLICATIVE TRANSPOSITION = MOVEMENT OF GENE COPIES FROM THEIR ORIGINAL SITE OR REPLICATON TO ANOTHER LOCATION; THE TRANSPOSON’S GENES ARE INSERTED AT SOME NEW SITE WITHOUT BEING LOST FROM THE ORIGINAL SITE

50. INSERTION SEQUENCES
THE SIMPLEST TRANSPOSONS, WHICH CONTAIN ONLY THE GENES NECESSARY FOR THE PROCESS OF TRANSPOSITION. INSERTION SEQUENCE DNA INCLUDES TWO ESSENTIAL TYPES OF NUCLEOTIDE SEQUENCES:
1) NUCLEOTIDE SEQUENCE CODING FOR TRANSPOSASE
2) INVERTED REPEATS
TRANSPOSASE = ENZYME THAT CATALYZES INSERTION OF TRANSPOSONS INTO NEW SITES
INVERTED REPEATS (IR) = SHORT NONCODING NUCLEOTIDE SEQUENCES OF DNA THAT ARE REPEATED IN REVERSE ORDER ON OPPOSITE ENDS OF A TRANSPOSON

51. INSERTION SEQUENCES, THE SIMPLEST TRANSPOSONS

52. INSERTION OF A TRANSPOSON AND CREATION OF
DIRECT REPEATS

53. OPERONS: THE BASIC CONCEPT
OPERON = A REGULATED CLUSTER OF ADJACENT STRUCTURAL GENES WITH RELATED FUNCTIONS
COMMON IN BACTERIA AND PHAGES
HAS A SINGLE PROMOTER REGION, SO AN RNA POLYMERASE WILL TRANSCRIBE ALL STRUCTURAL GENES ON AN ALL OR NONE BASIS

54. OPERONS THERE ARE 4 MAJOR COMPONENTS OF AN OPERON:
1) A REGULATORY GENE PRODUCES A REPRESSOR PROTEIN, A SUBSTANCE THAT CAN PREVENT GENE EXPRESSION BY BLOCKING THE ACTION OF RNA POLYMERASE
2) THE PROMOTER REGION IS A SEQUENCE OF DNA TO WHICH THE RNA POLYMERASE ATTACHES TO BEGIN TRANSCRIPTION

55. 3) THE OPERATOR REGION CAN BLOCK THE ACTION OF THE RNA POLYMERASE IF THE REGION IS OCCUPIED BY A REPRESSOR PROTEIN
4) THE STRUCTURAL GENES CONTAIN DNA SEQUENCES THAT CODE FOR SEVERAL RELATED ENZYMES THAT DIRECT THE PRODUCTION OF SOME PARTICULAR END PRODUCT

56. REGULATION OF A METABOLIC PATHWAY

57. Trp OPERON
AN OPERON IN E.COLI, TRP OPERON PRODUCES ENZYMES FOR THE SYNTHESIS OF THE AMINO ACID TRYPTOPHAN. THE REGULATORY GENE PRODUCES AN INACTIVE REPRESSOR THAT DOES NOT BIND TO THE OPERATOR. AS A RESULT, THE RNA POLYMERASE PROCEEDS TO TRANSCRIBE THE STRUCTURAL GENES NECESSARY TO PRODUCE ENZYMES THAT SYNTHESIZE TRPTOPHAN

58. WHEN TRYPTOPHAN IS AVAILABLE TO E
WHEN TRYPTOPHAN IS AVAILABLE TO E.COLI FROM THE SURROUNDING ENVIRONMENT, THE BACTERIUM NO LONGER NEEDS TO MAKE ITS OWN TRYPTOPHAN. IN THIS CASE, RISING LEVELS OF TRPTOPHAN INDUCE SOME TRYPTOPHAN TO REACT WITH THE INACTIVE REPRESSOR AND MAKE IT ACTIVE. HERE TRPTOPHAN IS ACTING AS A COREPRESSOR. THE ACTIVE REPRESSOR NOW BINDS TO THE OPERATOR REGION, WHICH, IN TURN, PREVENTS THE TRANSCRIPTION OF THE STRUCTURAL GENES. SINCE THESE STRUCTURAL GENES STOP PRODUCING ENZYMES ONLY IN THE PRESENCE OF AN ACTIVE REPRESSOR, THEY ARE CALLED REPRESSIBLE ENZYMES

59. THE TRP OPERON

60. LAC OPERON
THE LAC OPERON IN E.COLI CONTROLS THE BREAKDOWN OF LACTOSE. THE REGULATORY GENE IN THE LAC OPERON PRODUCES AN ACTIVE REPRESSOR THAT BINDS TO THE OPERATOR REGION. WHEN THE OPERATOR REGION IS OCCUPIED BY THE REPROSSOR, RNA POLYMERASE IS UNABLE TO TRANSCRIBE SEVERAL STRUCTURAL GENES THAT CODE FOR ENZYMES THAT CONTROL THE UPTAKE AND SUBSEQUENT BREAKDOWN OF LACTOSE.

61. WHEN LACTOSE IS AVAILABLE, SOME OF THE LACTOSE (IN A CONVERTED FORM) COMBINES WITH THE REPRESSOR TO MAKE IT INACTIVE. WHEN THE REPRESSOR IS INACTIVATED, RNA POLYMERSE IS ABLE TO TRANSCRIBE THE GENES THAT CODE FOR THE ENZYMES THAT BREAK DOWN LACTOSE. SINCE A SUBSTRATE (LACTOSE) IS REQUIRED TO INDUCE (TURN ON) THE OPERON, THE ENZYMES THE OPERON PRODUCES ARE SAID TO BE INDUCIBLE ENZYMES.

62. LAC OPERON