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Prokaryotic Cells Flashcards

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1
Q

Draw the structure of a typical bacterium

A

Snap camera roll

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2
Q

What are the features of a bacterial cell wall?

A
  • water generally tends to move into tbe bacterial cell by osmosis and the cell wall prevents the cell swelling and bursting
  • it maintains the shape of the bacterium and gives support and protection to the contents of the cell
  • it consists of a layer of peptidoglycan that is made up of many parallel polysaccharide chains with short peptide cross-linkages forming an enourmous molecule with a net-like structure
  • some bacteria have a slime capsule around their cell walls. This may be formed from starch, gelatin, protein or glycolipid and protects the bacterium from phagocytosis by white blood cells. It also covers the cell markers on the cell membrane that identify the cell. So a capsule can make it easier for a bacterium to be pathogenic as it is less easily recognised by the immune system
  • this is the case for meningitis, tuberculosis and septicaemia
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3
Q

What are pilli?

A
  • thread like protein projections on the surface of some bacteria
  • found on e.coli and salmonella
  • used for attachment to a host cell and for sexual reproduction
  • make bacteria more vulnerable to virus infections, as bacteriophage can use pilli as an entry point to the cell
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4
Q

What are flagella?

A
  • made up of a many stranded helix of the protein flagellin

* the flagella moves the bacterium by rapid rotations - about 100 revolutions per second

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5
Q

Describe the cell surface membrane of bacteria

A
  • similar in both structure and function to the membrane in eukaryotes
  • however bacteria have to mitochondria so it is also the site of some respiratory enzymes
  • some contain infoldings known as mesosomes.
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6
Q

What are plasmids?

A
  • small circles of DNA
  • codes for a particular type of bacterial phenotype in addition to the genetic information in the nucleoid
  • they can reproduce themselves independently of the nucleoid
  • they can be transferred from one bacterium to another in a form of sexual reproduction using the pilli
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7
Q

What is the nucleoid?

A
  • the generic material of prokaryotic cells consists of a single lenth of DNA which is not contained in a membrane bound nucleus
  • however the DNA is folded and coiled to fit into the bacterium. The area where this DNA tangle is found is known as the nucleoid
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8
Q

Where is protein synthesis carried out in bacteria?

A

In 70S ribsomes made up of a 50S large subunit and the 30S small subunit

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9
Q

What are the two main types of cell wall?

A

Gram positive and gram negative

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10
Q

How can the two main types of cell wall be distinguished?

A

By gram staining

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11
Q

What happens when you use gram staining to test for a gram positive bacterial cell wall?

A
  • before staining bacteria are often colourless
  • the cell walls of gram-positive bacteria (e.g. MRSA) have a thick layer of peptidoglycan containing chemicals such as teichoic acid within its net-like structure
  • the crystal violet/ iodine complex in the gram stain is trapped in the thick peptidoglycan layer and resists decolouring when the bacteria are dehydrated using alcohol.
  • as a result it does not pick up the red safranin counterstain leaving the positive purple/ blue colour
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12
Q

What happens when you use gram staining to test for a gram negative bacterial cell wall?

A
  • these cell walls have a thin layer of peltidoglycan with no teichoic acid between the two layers of membrane
  • the outer membrane is made up of lipopolysaccharides
  • after the crystal violet/iodine complex is applied the bacteria are dehydrated in ethanol. The lipopolysaccharide layer dissolves in ethanol leaving the thin peptidoglycan layer exposed.
  • the crystal violet/ iodine complex is washed out and the peptidoglycan takes up the red safranin counterstain, so the cells appear red
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13
Q

What are antibiotics and how do they work?

A
  • they are drugs used against bacterial pathogens
  • they may work by affecting the bacterial cell walls, the cell membranes, the genetic material, the enzymes or the ribosomes
  • antibiotics usually target features of the bacterial cells that differ from those of eukaryotic cells, including the bacterial cell walls and the 70S ribosomes
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14
Q

What do beta-lactam antibiotics do (penicillins ect.)

A
  • inhibit the formation of the peptidoglycan layer of the bacterial cell wall.
  • they are very effective against gram positive bacteria as they have a thick peptidoglycan layer on the surface of the cell
  • less effective against gram-negative bacteria as their peptidoglycan layer is hidden and less vital to the wall structure
  • they do not affect human cells as they do not have a peptidoglycan cell wall at all
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15
Q

What are glycopeptide antibiotics such as vancomycin?

A
  • large polar molecules that cannot penetrate the outer membrane layer of gram negative bacteria
  • very effecitve against gram positive bacteria, even ones that have developed resistance to many other antibiotics
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16
Q

What are polypeptide antibiotics?

A
  • rarely used as they have very serious side effects
  • very effective against gram-negative bacteria because they interact with the phospholipids of the outer membrane
  • do not affect gram positive bacteria
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17
Q

What do anitbiotics that effect both gram positive and gram negative bacteria do?

A

Target common processes such as protein synthesis by the ribosomes. But they only target prokaryotic ribosomes

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18
Q

What are the different shapea you can identify bacteria by

A
  • spherical (cocci)
  • rod shaped (bacilli)
  • twisted (spirilla)
  • comma-shapes (vibrios)
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19
Q

What are the different respiratory requirements that you can group bacteria into?

A
  • obligate aerobes: need oxygen for respiration
  • facultative anaerobes: use oxygen if available but can manage without
  • obligate anaerobes: can only respire in the abscence of oxygen. Oxygen will kill them
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20
Q

what are viruses?

A
  • obligate intracellular parasites - they can only exist and reproduce as parasites in the cells of other living organisms
  • because they invade and take over living cells to reproduce they usually cause damage and disease of some sort
  • they can withstand drying and long periods of storage whilst maintaining their ability to infect cells
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21
Q

What is the structure of a virus?

A
  • they usually have geometric shapes and similar basic structures
  • there is variation in the structure of their protein coat (capsid)
  • they may or may not have an envelope
  • the protein coat (capsid) is made up of simple repeating protein units known as capsomeres arenaged in different ways. Using repeated units minimises the amount of genetic material needed to code for coat production. It so makes sure that assembling the protein coat in the host cell is as simple as possible
  • in some viruses the genetic material and protein coat is covered by a lipid envelope produced from the host cell. The presence of the envelope makes it easier for the viruses to pass from cell to cell but it makes them vulnerable to substances that will dissolve the lipid membrane
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22
Q

How do viruses attach to their host cells?

A

By means of specific proteins known as virus attachment particles (VAPs) that target proteins in the host cell surface membrane. They respond to particular molecules of the host cell surface so are usually quite specific in the tissue they attack

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23
Q

How are viruses classified?

A

By their genome and mode of replication

Viral genetic material can be DNA or RNA. The nucleic acid is sometimes double stranded and sometimes single

24
Q

What are DNA viruses?

A
  • the genetic material is DNA
  • the viral DNA acts directly as a template for new viral DNA and for the mRNA’s needed to induce synthesis of viral proteins
  • examples include the smallpox virus, adenoviruses (colds) and some bacgeriophages (viruses which infecr bacteria) such as the lambda phage
25
Q

What are RNA viruses

A
  • viruses that have RNA as their genetic material. Makes up 70% of viruses
  • much more likely to mutate than DNA viruses
  • do not produce DNA as part of their life cycle
  • most of them contain a single strand of RNA and are known as ssRNA viruses
  • positive ssRNA viruses have RNA that can act directly as mRNA and be translated at the ribosomes.
  • examples of plant and animal diseases caused by positive ssRNA viruses include tobacco mosaic viruses, SARS, polio and hepatitis C
  • negative ssRNA viruses cannot be directly translated. The RNA must be transcribed before it is translated at the ribosomes
  • exampels of diseases cause by negative ssRNA viruses include measles, influenza and ebola
26
Q

What are RNA retroviruses?

A
  • retroviruses are a special type of RNA virus. They have a protein capsid and a lipid envelope
  • the single strand of viral RNA directs the synthesis of a special enzyme called reverse transcriptase
  • this goes on to make DNA molecules corresponding to the viral genome
  • the DNA is then incorporated into the host cell DNA and used as a template for new viral proteins and ultimately a new viral RNA genome.
  • HIV is a retrovirus and some forms of leukaemia are too
27
Q

How do bacteriophages attack their hosr cells?

A

They inject their genome into the host cell but the bulk of viral material remains outisde the bacterium. The viral DNA forms a plasmid within the bacterium

28
Q

How do viruses infect animal cells?

A
  • some types are taken into the cell by endocytosis- either with or without the envelope. The host cell then digests the capsid, releasing the viral genetic material.
  • more often the viral envelope fuses with the host cell surface, releasing the rest of the virus into the cell membrane
29
Q

How do plant viruses usually get into the plant cell?

A

By using a vector to pierce the cell wall

30
Q

What is the lysogenic pathway of virus replication?

A
  • many DNA viruses are non-virulent when they first get into the host cell
  • they insert their DNA into the host DNA so it is replicated every time the host cell divides
  • this DNA inserted into the host is called a provirus
  • Messenger RNA is not produced from the viral DNA because one of the viral genes causes the production of a repressor protein that makes it impossible to translate the rest of the viral genetic material
  • the virus does not affect the host cell kr make the host organism ill at this stage in the life cyle
  • during this period of lysogeny the virus is said to be latent
31
Q

What is the lytic pathway?

A
  • the viral genetic material is replicated independently of the host DNA straight after entering the host
  • mature viruses are made and eventually the host cell bursts, releasing large numbers of new virus particles to invade other cells
  • the virus is said to be virulent (disease causing)
  • the process of replicating and killing cells is known as the lytic pathway
  • under certain conditions viruses in the lysogenuc state are activated. The amount of repressor protein decreases and the viruses enter the lytic pathway
32
Q

What is lysis?

A

Where the bacterial cell bursrs releasing lots of phages

33
Q

How do positive ssRNA viruses replicate?

A
  • they contain a single strand of DNA that is a sense strand
  • it is used directly as mRNA for translation into proteins at rhe ribosomes
  • the proteins made include viral structural proteins and an RNA polymerase which is used to replicate the viral RNA
34
Q

How do negative ssRNA viruses replicate?

A
  • the single strand in these is an antisense strand
  • it first must be transcribed onto a sense strand
  • the virus imports RNA replicase which uses free bases in the host cell to transcribe the antisense RNA strand and produce a sense strand that can be translated at the ribosomes
  • once the RNA strand has been transcribed it acts as mRNA at the ribosomes and codes for viral proteins including RNA replicase
  • these viral proteins combine with replicated viral RNA to form new viral particles
35
Q

How do negative ssRNA viruses replicate?

A
  • the single strand in these is an antisense strand
  • it first must be transcribed onto a sense strand
  • the virus imports RNA replicase which uses free bases in the host cell to transcribe the antisense RNA strand and produce a sense strand that can be translated at the ribosomes
  • once the RNA strand has been transcribed it acts as mRNA at the ribosomes and codes for viral proteins including RNA replicase
  • these viral proteins combine with replicated viral RNA to form new viral particles
36
Q

How do RNA retroviruses replicate?

A
  • they have viral RNA as their genetic material. It cannot be used by mRNA but is translated into DNA by the viral enzyme reverse transcriptase in the cytoplasm of the cell
  • this viral DNA passes into the nucleus of the host cell where it is inserted into the host DNA
  • host transcriptase enzymes then make viral mRNA and new viral genome RNA
  • New viral material is synthesised and the new viral particles leave the cell by exocytosis
  • the host cell continues to function as a virus making factory while the new viruses move on to infect other cells
37
Q

How can viruses cause the symptom of disease?

A
  • by the lysis of the host enzymes
  • by causing the host cells to release their own lysosomes and digest themselves from the inside
  • by the production of toxins that inhibit cell metabolism
38
Q

Why are viral infections often specific to particular tissues?

A
  • due to the presence or absence of cell markers on the surface of host cells
  • each type of cell has its own recognition markers and different types of virus can only bind to particular markers
  • the presence or absence of these markers can even affect whether a group of living organisms is vulnerable to attack by viruses at all
39
Q

How can viral diseases be spread?

A

Through infected mucus, droplets of saliva, infected blood or faeces or simple contact between infected organims

40
Q

How is foot and mouth disease spread?

A
  • through bodily secretions such as milk and semen
  • transmitted in the breath and faeces of infected animals
  • healthy animals can pick up the virus from contaminated pens, food, water, contact with diseased animals and from infected meat and animal products if they are eaten
41
Q

How can ebola be spread?

A
  • it’s an animal disease that spreads to humans through faeces, urine, blood and meat of infected animals
  • it then spreads from person to person by the direct contact of the skin or mucous membranes of a healthy person with blood, faeces and other bodily fluids of an infected person. Even with bedding and surfaces contaminated with fluids from an infected person
42
Q

What do antiviral treatments target?

A

Virus replication

43
Q

What are the different ways that antiviral treatments work?

A

They can:
• target the receptors by which viruses recognise their host cell
• target the enzymes that help to translate or replicate the viral DNA or RNA
• inhibit the protease enzymes that enable new virus particles to bud from host membranes

44
Q

Scientists cannot cure viral infections but what can they do?

A

Reduce the time a person is sick and delay the development of symptoms after infection

45
Q

What is the average mortity rate for ebola and what does it depend on?

A
  • 50 %
  • depends on the stain of the virus, the health of the infected person and the speed with which they get support and healthcare
46
Q

What does disease control focus on with viral infections?

A

Vaccination and reducing the spread of viruses

47
Q

What happens when an epidemic breaks out in terms of vaccination?

A

There is a big rush to deliver vaccines to everyone not vaccinated. Usually healthcare workers the very young and the elderly are vaccinated first

48
Q

What viral infections do we not have vaccines against?

A

HIV/ AIDS and ebola

49
Q

What is an epidemic?

A

When the levels of people with a particular disease are much higher than expected over a given period of time

50
Q

What are the different ways of contolling the spread of a disease?

A
  • rapid identification of the disease
  • nursing in isolation: this is for serious infections only. It is readily available in countries like the UK but sealed isolation units are rarely available in developing countries. Simple units nursing all infected patients together can help
  • preventing transmission from one individual to another: simple measure such as regular handwashing, handwashing before and after every contact with patients by healthcare workers and families, care in handling bodily fluids and wastes, careful disposal of infected bodily wastes and frequent disinfecting of surfaces and people
  • sterilising or disposing equipment and bedding after use
  • the wearing of protective clothing by healthcare workers. When dealing with highly infectious diseases healthcare workers should wear facemasks, gowns, gloves, and goggles. The gloves should be washed and disinfected before removal and the hands washed too
  • identifying contacts. People who have been in contact with the infected person need to be monitored
51
Q

What happens in the development of new medicines?

A
  • initial ideas for potential drugs come from a wide range of sources including genome analysis of pathogens, computer modelling, clinical compound banks and medicinal plants
  • these chemicals have to go through thorough research and testing on cell tissue cultures, safety analyses and molecular modifications
  • this is followed by animal testing to ensure the compound works in a whole organism and is safe
  • this is then followed by three phases of human testing to further ensure safety and that the drug works well
  • this goes along with complex regulation and licensing procedures until finally, a new drug may reach the doctors surgery
  • the process takes up to 10, involves many different scientists and doctors and costs millions of pounds
52
Q

What happens when an epidemic develops in terms of developments of new medicines?

A

The testing of a new medicine or vaccine may be sped up to try and save lives and prevent the spread of a deadly disease

53
Q

What did potential fast tracked drugs for ebola include and in what developmental stage were they in?

A
  • they has passed many if the developmental stages but had not completed human trials
  • ZMapp tm was an experimental drug produced after long term studies of people who had survived ebola in previous less widespread outbreaks. Scientists had genetically modified tobacco plants to produce three antibodies thag seemed to be associated with surving the disease. In trials it was effective in treating mokeys but had not been tried on people. Tiny amounts of the drug were available and used to treat 7 people including African, American, Spanish and British health workers who developed ebola
  • vaccines: several companies had vaccines in trials that are being fast- tracked for use against Ebola. They are making many doses of the vaccine so that if they are safe to use in humans many healthworkers and people living in epidemic areas could be vaccinated
54
Q

What are the factors that have to be evaluated when considering whether a drug should be fast tracked for use in an epidemic?

A
  • the severity of the disease
  • the availabily of any other treatments for the disease
  • the effectiveness of standard disease contol measures in halting the spread of the disease
  • transparency about the process and informed consent of those given the treatment
  • freedom of choice over participation
  • involvement of the affected community - community consent
  • collection of clear clinical data from the use of new medicines in this situation so an on-going assesment of the safety and efficacy of the drug or vaccine can be made
55
Q

What are reasons against using an untested (fast-trackes) drug?

A
  • some people simply feel that it is not ethical under any circumstances to use drugs that have not completed full human trials
  • if an untesred drug produces unexpected side effects it can make the situation worse
  • deciding who get the drug can be difficult e.g. in a situation such as the ebola epidemic, local people might feel they were being used as Guinea pigs for western medicine if they are given the medicine but might feel resentful if only healthworkers are treated
  • informed consent is an issue as it depends on a level of education to understand the drug and how it works and also clarity of thought. People who are dying may grasp at straws but their relatives may then blame the treatment for an inevitable death
  • issues of trust between individuals or communities and healthworkers, especially if supplies of a new drug are limited

Biology (15 decks)

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