1. DNA fails to copy accurately
DNA fails to copy accurately. Most of the mutations that we think matter to evolution are “naturally-occurring.” For example, when a cell divides, it makes a copy of its DNA—and sometimes the copy is not quite perfect. That small difference from the original DNA sequence is a mutation.

2. Mutations

3. Mutations Point mutations single base change base-pair substitution
silent mutation
no amino acid change
redundancy in code
missense
change amino acid
nonsense
change to stop codon
When do mutations affect the next generation?

4. Point mutation leads to Sickle cell anemia
What kind of mutation?
Missense!

5. Primarily Africans Sickle cell anemia recessive inheritance pattern
strikes 1 out of 400 African Americans
hydrophilic amino acid
hydrophobic amino acid

6. Mutations Frameshift shift in the reading frame
changes everything “downstream”
insertions
adding base(s)
deletions
losing base(s)
Where would this mutation cause the most change: beginning or end of gene?

7. Cystic fibrosis Primarily whites of European descent
strikes 1 in 2500 births
1 in 25 whites is a carrier (Aa)
normal allele codes for a membrane protein that transports Cl- across cell membrane
defective or absent channels limit transport of Cl- (& H2O) across cell membrane
thicker & stickier mucus coats around cells
mucus build-up in the pancreas, lungs, digestive tract & causes bacterial infections
without treatment children die before 5; with treatment can live past their late 20s
Cystic fibrosis is an inherited disease that is relatively common in the U.S. Cystic fibrosis affects multiple parts of the body including the pancreas, the sweat glands, and the lungs. When someone has cystic fibrosis, they often have lots of lung problems. The cause of their lung problems is directly related to basic problems with diffusion and osmosis in the large airways of the lungs.
People without cystic fibrosis have a small layer of salt water in the large airways of their lungs. This layer of salt water is under the mucus layer which lines the airways. The mucus layer in the airways helps to clear dust and other inhaled particles from the lungs.

8. Effect on Lungs Chloride channel Cl- Cl- bacteria & mucus build up
transports chloride through protein channel out of cell
Osmotic effects: H2O follows Cl-
normal lungs
airway
Cl-
Cl- channel
H2O
cells lining lungs
cystic fibrosis
Cl-
In people without cystic fibrosis, working cystic fibrosis proteins allow salt (chloride) to enter the air space and water follows by osmosis. The mucus layer is dilute and not very sticky.
In people with cystic fibrosis, non-working cystic fibrosis proteins mean no salt (chloride) enters the air space and water doesn't either. The mucus layer is concentrated and very sticky.
People with cystic fibrosis have lung problems because:
Proteins for diffusion of salt into the airways don't work. (less diffusion)
Less salt in the airways means less water in the airways. (less osmosis)
Less water in the airways means mucus layer is very sticky (viscous).
Sticky mucus cannot be easily moved to clear particles from the lungs.
Sticky mucus traps bacteria and causes more lung infections.
Therefore, because of less diffusion of salt and less osmosis of water, people with cystic fibrosis have too much sticky mucus in the airways of their lungs and get lots of lung infections. Thus, they are sick a lot.
H2O
bacteria & mucus build up
thickened mucus hard to secrete
mucus secreting glands

9. Deletion leads to Cystic fibrosis
delta F508
loss of one amino acid

10. What’s the value of mutations?

11. Mutation Worksheet

12. Compare and contrast the lytic to lysogenic cycle in a virus
Open book to pg 324
Compare and contrast the lytic to lysogenic cycle in a virus
You’ll be making a comic on these cycles for your second checklist

13. Recall that bacteria are prokaryotes
With cells much smaller and more simply organized than those of eukaryotes
Viruses
Are smaller and simpler still
Figure 18.2
0.25 m
Virus
Animal cell
Bacterium
Animal cell nucleus

14. (a) Tobacco mosaic virus
Capsids and Envelopes
A capsid
Is the protein shell that encloses the viral genome
Can have various structures
Figure 18.4a, b
18  250 mm
70–90 nm (diameter)
20 nm
50 nm
(a) Tobacco mosaic virus
(b) Adenoviruses
RNA
DNA
Capsomere
Glycoprotein
Capsomere of capsid

15. Some viruses have envelopes
Which are membranous coverings derived from the membrane of the host cell
Figure 18.4c
80–200 nm (diameter)
50 nm
(c) Influenza viruses
RNA
Glycoprotein
Membranous envelope
Capsid

16. Bacteriophages, also called phages
Have the most complex capsids found among viruses
Figure 18.4d
80  225 nm
50 nm
(d) Bacteriophage T4
DNA
Head
Tail fiber
Tail sheath

17. General Features of Viral Reproductive Cycles
Viruses are obligate intracellular parasites
They can reproduce only within a host cell
Each virus has a host range
A limited number of host cells that it can infect

18. Viruses use enzymes, ribosomes, and small molecules of host cells
To synthesize progeny viruses
VIRUS
Capsid proteins
mRNA
Viral DNA
HOST CELL
DNA
Capsid
Figure 18.5
Entry into cell and
uncoating of DNA
Transcription
Replication
Self-assembly of new virus particles and their exit from cell

19. Reproductive Cycles of Phages
Are the best understood of all viruses
Go through two alternative reproductive mechanisms: the lytic cycle and the lysogenic cycle

20. The Lytic Cycle The lytic cycle
Is a phage reproductive cycle that culminates in the death of the host
Produces new phages and digests the host’s cell wall, releasing the progeny viruses

21. The lytic cycle of phage T4, a virulent phage
Phage assembly
Head
Tails
Tail fibers
Figure 18.6
Attachment. The T4 phage uses its tail fibers to bind to specific receptor sites on the outer surface of an E. coli cell. 1
Entry of phage DNA and degradation of host DNA. The sheath of the tail contracts, injecting the phage DNA into the cell and leaving an empty capsid outside. The cell’s DNA is hydrolyzed. 2
Release. The phage directs production of an enzyme that damages the bacterial cell wall, allowing fluid to enter. The cell swells and finally bursts, releasing 100 to 200 phage particles. 5
Assembly. Three separate sets of proteins self-assemble to form phage heads, tails, and tail fibers. The phage genome is packaged inside the capsid as the head forms. 4
Synthesis of viral genomes and proteins. The phage DNA directs production of phage proteins and copies of the phage genome by host enzymes, using components within the cell. 3

22. The Lysogenic Cycle The lysogenic cycle Temperate phages
Replicates the phage genome without destroying the host
Temperate phages
Are capable of using both the lytic and lysogenic cycles of reproduction

23. The lytic and lysogenic cycles of phage , a temperate phage
Many cell divisions produce a large population of bacteria infected with the prophage.
The bacterium reproduces
normally, copying the prophage
and transmitting it to daughter cells.
Phage DNA integrates into the bacterial chromosome, becoming a prophage.
New phage DNA and proteins are synthesized and assembled into phages.
Occasionally, a prophage exits the bacterial chromosome,
initiating a lytic cycle.
Certain factors
determine whether
The phage attaches to a
host cell and injects its DNA.
Phage DNA
circularizes
The cell lyses, releasing phages.
Lytic cycle
is induced
Lysogenic cycle
is entered or
Prophage
Bacterial
chromosome
Phage
DNA
Figure 18.7

24. Reproductive Cycles of Animal Viruses
The nature of the genome
Is the basis for the common classification of animal viruses

25. Classes of animal viruses
Table 18.1

26. Viral glycoproteins on the envelope
Viral Envelopes
Many animal viruses
Have a membranous envelope
Viral glycoproteins on the envelope
Bind to specific receptor molecules on the surface of a host cell

27. The reproductive cycle of an enveloped RNA virus
Capsid
Envelope (with
glycoproteins)
HOST CELL
Viral genome (RNA)
Template
proteins
Glyco-
mRNA
Copy of
genome (RNA) ER
Figure 18.8
Glycoproteins on the viral envelope bind to specific receptor molecules (not shown) on the host cell, promoting viral entry into the cell. 1
Capsid and viral genome
enter cell 2
The viral genome (red)
functions as a template for synthesis of complementary
RNA strands (pink) by a viral
enzyme. 3
Complementary RNA
strands also function as mRNA,
which is translated into both
capsid proteins (in the cytosol) and glycoproteins for the viral
envelope (in the ER). 5
New copies of viral
genome RNA are made
using complementary RNA
strands as templates. 4
Vesicles transport
envelope glycoproteins to
the plasma membrane. 6
A capsid assembles
around each viral
genome molecule. 7
New virus 8

28. RNA as Viral Genetic Material
The broadest variety of RNA genomes
Is found among the viruses that infect animals

29. Retroviruses, such as HIV, use the enzyme reverse transcriptase
To copy their RNA genome into DNA, which can then be integrated into the host genome as a provirus
Figure 18.9
Reverse transcriptase
Viral envelope
Capsid
Glycoprotein
RNA (two identical strands)

30. The reproductive cycle of HIV, a retrovirus
Figure 18.10
mRNA
RNA genome for the next viral generation
Viral RNA
RNA-DNA hybrid
DNA
Chromosomal DNA
NUCLEUS
Provirus
HOST CELL
Reverse transcriptase
New HIV leaving a cell
HIV entering a cell
0.25 µm
HIV
Membrane of white blood cell
The virus fuses with the
cell’s plasma membrane.
The capsid proteins are
removed, releasing the viral proteins and RNA. 1
Reverse transcriptase
catalyzes the synthesis of a
DNA strand complementary
to the viral RNA. 2
catalyzes the synthesis of a second DNA strand
complementary to the first. 3
The double-stranded DNA is incorporated
as a provirus into the cell’s DNA. 4
Proviral genes are transcribed into RNA molecules, which serve as genomes for the next viral generation and as mRNAs for translation into viral proteins. 5
The viral proteins include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER). 6
Vesicles transport the
glycoproteins from the ER to
the cell’s plasma membrane. 7
Capsids are
assembled around
viral genomes and
reverse transcriptase
molecules. 8
New viruses bud
off from the host cell. 9

31. Viruses do not really fit our definition of living organisms
Evolution of Viruses
Viruses do not really fit our definition of living organisms
Since viruses can reproduce only within cells
They probably evolved after the first cells appeared, perhaps packaged as fragments of cellular nucleic acid

32. Diseases caused by viral infections
Concept 18.2: Viruses, viroids, and prions are formidable pathogens in animals and plants
Diseases caused by viral infections
Affect humans, agricultural crops, and livestock worldwide

33. Viral Diseases in Animals
Viruses may damage or kill cells
By causing the release of hydrolytic enzymes from lysosomes
Some viruses cause infected cells
To produce toxins that lead to disease symptoms

34. Vaccines
Are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen
Can prevent certain viral illnesses

35. Emerging Viruses Emerging viruses
Are those that appear suddenly or suddenly come to the attention of medical scientists

36. Severe acute respiratory syndrome (SARS)
Recently appeared in China
Figure A, B
(a) Young ballet students in Hong Kong wear face masks to protect themselves from the virus causing SARS.
(b) The SARS-causing agent is a coronavirus like this one (colorized TEM), so named for the “corona” of glycoprotein spikes protruding from the envelope.

37. Outbreaks of “new” viral diseases in humans
Are usually caused by existing viruses that expand their host territory

38. Viral Diseases in Plants
More than 2,000 types of viral diseases of plants are known
Common symptoms of viral infection include
Spots on leaves and fruits, stunted growth, and damaged flowers or roots
Figure 18.12

39. Bacterial cells divide by binary fission
Which is preceded by replication of the bacterial chromosome
Replication fork
Origin of replication
Termination of replication
Figure 18.14

40. Mutation and Genetic Recombination as Sources of Genetic Variation
Since bacteria can reproduce rapidly
New mutations can quickly increase a population’s genetic diversity

41. Further genetic diversity
Can arise by recombination of the DNA from two different bacterial cells
EXPERIMENT
Figure 18.15
Only the samples from the mixed culture, contained cells that gave rise to colonies on minimal medium, which lacks amino acids.
RESULTS
Researchers had two mutant strains, one that could make arginine but not tryptophan (arg+ trp–) and one that could make tryptophan but not arginine (arg trp+). Each mutant strain and a mixture of both strains were grown in a liquid medium containing all the required amino acids. Samples from each liquid culture were spread on plates containing a solution of glucose and inorganic salts (minimal medium), solidified with agar.
Mutant strain arg+ trp–
Mixture
Mutant strain arg trp+

42. Mechanisms of Gene Transfer and Genetic Recombination in Bacteria
Three processes bring bacterial DNA from different individuals together
Transformation
Transduction
Conjugation

43. Transformation Transformation
Is the alteration of a bacterial cell’s genotype and phenotype by the uptake of naked, foreign DNA from the surrounding environment

44. Phage infects bacterial cell that has alleles A+ and B+
Transduction
In the process known as transduction
Phages carry bacterial genes from one host cell to another 1
Figure 18.16
Donor cell
Recipient cell A+ B+ B– A–
Recombinant cell
Crossing over
Phage infects bacterial cell that has alleles A+ and B+
Host DNA (brown) is fragmented, and phage DNA and proteins are made. This is the donor cell.
A bacterial DNA fragment (in this case a fragment with the A+ allele) may be packaged in a phage capsid.
Phage with the A+ allele from the donor cell infects
a recipient A–B– cell, and crossing over (recombination)
between donor DNA (brown) and recipient DNA
(green) occurs at two places (dotted lines).
The genotype of the resulting recombinant cell (A+B–) differs from the genotypes of both the donor (A+B+) and the recipient (A–B–). 2 3 4 5
Phage DNA

45. Conjugation and Plasmids
Is the direct transfer of genetic material between bacterial cells that are temporarily joined
Figure 18.17
Sex pilus
1 m

46. The F Plasmid and Conjugation
Cells containing the F plasmid, designated F+ cells
Function as DNA donors during conjugation
Transfer plasmid DNA to an F recipient cell

47. Conjugation and transfer of an F plasmid from an F+ donor to an F recipient
Figure 18.18a
A cell carrying an F plasmid (an F+ cell) can form a mating bridge with an F– cell and transfer its F plasmid.
A single strand of the F plasmid breaks at a specific point (tip of blue arrowhead) and begins to move into the recipient cell. As transfer continues, the donor plasmid rotates (red arrow). 2
DNA replication occurs in both donor and recipient cells, using the single parental strands of the F plasmid as templates to synthesize complementary strands. 3
The plasmid in the recipient cell circularizes. Transfer and replication result in a compete F plasmid in each cell. Thus, both cells are now F+. 4
F Plasmid
Bacterial chromosome
Bacterial chromosome
F+ cell
Mating bridge 1
Conjugation and transfer of an F plasmid from an F+ donor to an F– recipient
(a)
F– cell

48. Chromosomal genes can be transferred during conjugation
When the donor cell’s F factor is integrated into the chromosome
A cell with the F factor built into its chromosome
Is called an Hfr cell
The F factor of an Hfr cell
Brings some chromosomal DNA along with it when it is transferred to an F– cell

49. Conjugation and transfer of part of the bacterial chromosome from an Hfr donor to an F– recipient, resulting in recombination
F+ cell
Hfr cell
F factor
The circular F plasmid in an F+ cell can be integrated into the circular chromosome by a single crossover event (dotted line). 1
The resulting cell is called an Hfr cell
(for High frequency of recombination). 2
Since an Hfr cell has all the F-factor genes, it can form a mating bridge with an F– cell and transfer DNA. 3
A single strand of the F factor breaks and begins to move through the bridge. DNA replication occurs in both donor and recipient cells, resulting in double-stranded DNA 4
The location and orientation of the F factor in the donor chromosome determine the sequence of gene transfer during conjugation. In this example, the transfer sequence for four genes is A-B-C-D. 5
The mating bridge usually breaks well before the entire chromosome and the rest of the F factor are transferred. 6
Two crossovers can result in the exchange of similar (homologous) genes between the transferred chromosome fragment (brown) and the recipient cell’s chromosome (green). 7
The piece of DNA ending up outside the bacterial chromosome will eventually be degraded by the cell’s enzymes. The recipient cell now contains a new combination of genes but no F factor; it is a recombinant F– cell. 8
Temporary
partial
diploid
Recombinant F–
bacterium A+ B+ C+ D+
F– cell A– B– C– D–
Conjugation and transfer of part of the bacterial chromosome from an Hfr donor to an F– recipient, resulting in recombination
(b)
Figure 18.18b

50. Virus Comic