Transcript F.1.3 Distinguish between the characteristics of the three domains:

F.1.3 Distinguish between
the characteristics of the
three domains:
Archaea, the first domain,
has no peptidoglycan in
the cells walls, Ether bonds
in the membrane lipids,
70S sized ribosomes, no
introns in its genes, and
only a few species contain
histone proteins.
F.1.3 Distinguish between the
characteristics of the three domains
(continued):
Eubacteria, the second
domain, all the cell walls are
made of peptidoglycan, the
bonds in the membrane
lipids are Ester bonds, they
have size 70S ribosomes, no
genes contain introns, and
none of their species have
histone proteins.
F.1.3 Distinguish between the
characteristics of the three domains
(continued):
Eukaryota, none of the cell
walls are made of
peptidoglycan, they
membrane lipids bond
with Ester bonds, the
ribosomes are size 80S,
the genes do contain
introns, and all species
have histone proteins.
F.1.7 Compare the structure
of the cell walls of Grampositive and Gram-negative
Eubacteria.
• Gram-positive bacteria has a thick
layer of peptidoglycan, a plasma
membrane of phospholipids and
proteins, and appears purple with the
gram-stain.
• Gram-negative bacteria has a thin
layer of peptidoglycan, an outer layer
of lipopolysaccharide and protein, a
plasma membrane of phospholipids
and proteins, and appears red with the
gram-stain
•Gram positive staph infection at the
top, Gram negative Pseudomonas
Aeruginosa infection at the bottom.
F.1.8 Outline the diversity in structure in viruses including: naked capsid versus enveloped
capsid; DNA versus RNA; and single stranded versus double stranded DNA or RNA.
• Viruses probably are diverse in structure because they evolved repeatedly, rather than evolving from a single
ancestral virus.
• There are three key differences in virus structure:
• Capsid envelope: In many viruses, the capsid is naked-- it is the outer layer. In other viruses, there is a lipid bilayer outside
the capsid. These are called enveloped capsids.
F.1.8 Outline the diversity in structure in viruses including: naked capsid
versus enveloped capsid; DNA versus RNA; and single stranded versus
double stranded DNA or RNA. (continued)
Genes of DNA or RNA: The genes in some viruses
are composed of DNA whereas in others they are
RNA.
Single or double-stranded genes: The genes of
viruses can be either single stranded or double
stranded, depending on whether they are
composed of DNA or RNA.
Double
Stranded DNA
Single
Stranded DNA
F.2.5 Explain the
consequences of releasing
raw sewage and nitrate
fertilizer into rivers.
• Nitrate ions are soluble and are
leached from soils very easily if
excessive amounts are applied to
crops. If phosphate and other minerals
also reach a high concentration, the
river becomes eutrophic.
• The eutrophication causes algae to
proliferate. Nitrate from fertilizers
sometimes causes an excessive growth
of algae, called an algal bloom. Some
of the algae are then deprived of light
and die.
• Bacteria decompose the dead algae.
The bacteria create an increased
biochemical oxygen demand and thus
cause deoxygenation of the water.
• Low oxygen levels kill fish and other
aquatic animals.
F.2.8 Explain the principles involved in the generation of methane from
biomass, including the conditions needed, organisms involved and the basic
chemical reactions that occur.
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Methane is sometimes called marsh gas,
because it is naturally produced by microbes in
anaerobic conditions.
These conditions are recreated in bioreactors
used for methane generation. A variety of types
of organic matter can be the feedstock,
including manure from farm animals and
cellulose. The feedstock is loaded into the
bioreactor where anaerobic conditions
encourage the growth of three groups of
naturally occurring bacteria.
The second group convert organic acids and
alcohol into carbon dioxide, hydrogen and and
acetate.
The third group of bacteria are the
methanogenic archaea which produce methane
from carbon dioxide, hydrogen and acetate.
– Methanogenic archaea reactions:
• Carbon dioxide + hydrogen ---->
Methane + water
• Acetate ----> Methane + carbon
dioxide
F.3.2 Explain how reverse
transcriptase is used in
molecular biology.
• Molecular biologists use reverse
transcriptase to make copies of the
genes theta they use in gene transfer.
Cells that are transcribing the required
gene are obtained and mRNA
transcripts are extracted.
• Single stranded DNA copies of the
mRNA are made using reverse
transcriptase. This is called cDNA.
• DNA polymerase is used to convert
the single-stranded DNA into doublestranded DNA, producing genes that
can be transferred into another
organism.
F.3.4 Outline the use of viral vectors in
gene therapy.
Viruses have had millions of years to
evolve efficient mechanisms for
entering mammalian cells and delivering
genes to them. They sometimes also
incorporate these genes into host cell’s
chromosomes. Viruses are therefore obvious
candidates for the gene delivery system, needed
in gene therapy. Modified viruses must be
produced containing the desired gene, which will
infect target cells but not replicate to form more
virus particles. A modified virus that is used in
this way is called a vector. The most widely used
virus vectors are retroviruses. One example of
their use is in the treatment of the SCID, a genetic
disease that is due to the lack of an enzyme
called ADA.
F.3.5 Discuss the risks of gene therapy.
Most attempts at gene therapy so far
have not been successful and the hopes
of patients and their families have been
raised and then disappointed. There have
also been cases where the treatment has
harmed patients. One example of this is
involved a trial of gene therapy for SCID
using retroviruses, in a group of ten
children in France. Two of the children
developed Leukemia. The viral vector
had
inserted DNA into a cancer-causing gene
and activated it. Adenoviruses are
possible alternative viral vectors, as they
do not insert their genes into host cell
chromosomes, so should not activate the
cancer causing genes.
F.4.4 Outline the symptoms,
method of transmission and
treatment of one named
example of food poisoning.
• Symptoms: if food containing the toxin
is eaten, nausea, vomiting, and diarrhea
develop within a few hours.
• Method of transmission: IF food is
contaminated with pathogenic strains of
S. Aureus during handling and the food is
stored above 4 degrees celsius, the
bacteria multiply and produce harmful
toxins. A wide variety of food can carry
the bacteria and toxins: eggs, poultry,
meat, salads, puddings, sauces and
bakery products containing creams.
• Treatment: the mean aim of treatment
is to replace the substances lost in
diarrhea. Oral dehydration fluids,
including sodium and chloride, together
with a little sugar and some flavoring to
make it palatable. Intravenous fluids are
only given if vomiting prevents
rehydration. Antibiotics are not normally
used as the body clears the infection
without them.
F.6.6 Outline the lytic life cycle of the
influenza virus.
• A life cycle where a virus takes over a host cell and uses it to
reproduce, then bursts open and kills it, is called a lytic life cycle.
• Influenza is caused by an enveloped virus, with single stranded RNA
as its genetic material.
– It binds to glycoproteins on the surface of the cells in these lining of
the upper respiratory tract.
– It is then taken into these cells by endocytosis.
– Once inside the host cells, the viral RNA is replicated and capsid
proteins are synthesized using ribosomes of the host cell.
– New influenza viruses are assembled from the RNA and proteins.
– The host cell is burst open. This is called lysis. The influenza viruses are
released, enveloped in the membrane from the host cell’s plasma.
– The viruses that have been released go on to invade other host cells,
spreading the infection.
F.6.5 Outline the mechanism of the action of antibiotics, including
inhibition of synthesis of cell walls, proteins, and nucleic acids.
• Antibiotics are chemical substances produced by microbes that kill or inhibit the growth of other microbes. Their
discovery and use is one of the triumphs of modern medicine, revolutionizing the treatment of bacterial diseases.
• Antibiotics interfere with some aspect of microbial metabolism. Most of them act against bacteria by one of the
following mechanisms:
• Inhibiting cell wall synthesis: penicillin and some other antibiotics inhibit enzymes that are involved in the
synthesis of the bacterial cell wall
•Inhibiting protein synthesis: erythromycin, streptomycin, and some other antibiotics block one of the stages of
bacterial protein synthesis
•Inhibiting nucleic acids synthesis: rifampin and some other antibiotics block the synthesis of RNA by RNA
polymerase in bacteria.
F.6.10 Discuss the prion hypothesis for the cause of
spongiform encephalopathies.
These are serious, incurable diseases of
mammals. The best known examples are scrapie
in sheep, BSE in cattle, and Creutzfeld-Jacob
disease (CJD) in humans. In each case, the tissues
of the brain are gradually broken down, giving a
spongy appearance and causing premature aging,
dementia and eventually death. Spongiform
encephalopathies are infectious, but the nature
of the infectious agent is puzzling.
• Enzymes that digest DNA and RNA do not
affect it
• It is very heat stable and is not easily
damaged by
ionizing radiation
• It cannot therefore be a living organism
• It is affected by chemical treatments that
denature proteins
F.6.10 Discuss the prion hypothesis for the cause of
spongiform encephalopathies. (continued)
Research has led to a protein of 254 amino acids, now called Prion
Protein or PrP. There are two forms of PrP, the normal PrP^C, which is
found on the surface of neurons and PrP^SC which is found in diseased
brain tissue. According to the prion hypothesis, PrP^C is converted into
PrP^SC by a conformational change and PrP^SC causes this change. So, if
any PrP^SC is present in the brain, it will cause more and more to be
produced by a sort of positive feedback. Brain cells attempt to digest it
using protease, but part of the PrP^SC molecule resists the digestion and
the resulting protein fibrils accumulate in brain cells, presumably causing
symptoms of the disease. Experiments have shown that when
experimental animals are inoculated with PrP^SC spongiform
e n c e p h a l o p a t h i e s d e v e l o p . H o w e v e r, n o t a l l o b s e r va t i o n s c a n b e
accounted for by the prion hypothesis. It does not explain how rapidly
the different forms of the disease progress, including sporadic CJD and
variant CJD in humans. No other hypothesis seems plausible though, so
research is focusing on modifications to the prion hypothesis.