cell cycle + infectious diseases + cell structure + microscopy

what is a disease?

• illness/sickness that causes reduced effectiveness of functions

• an illness with a set of symptoms that lead to poor physical, mental or social well being

what is an infectious disease?

• disease caused by a pathogen that can cause harm to the health of the host

• can be passed from one organism to another(communicable/transmissable)

what are pathogens?

• disease passing organisms

• prokaryote/eukaryotes

• eg: bacteria, virus, protoctists, fungi

what is the disease transmission cycle?

• pathogens:

1- gain entry to host

2- colonise host tissue(multiply)

3- damage host’s tissues

4- resist host defences

how do we prevent disease from spreading?

break the disease transmission cycle

describe the virus structure

1. non cellular

2. no plasma membrane, cytoplasm or ribosomes

3. ONLY DNA or RNA

4. protein coat=capsid.

   1. it is a protective coat

   2. may have 1 or 2

5. many viruses also have a lipid envelope

6. some proteins may be present

describe bacterial structure

• all bacteria HAVE:

1. plasma membrane

2. cytoplasm

3. peptidoglycan cell wall made of chains cross linked by amino acids

4. 70s ribosomes

5. circular DNA

6. DNA is ‘naked’, not associated with histone proteins

• all bacteria do NOT HAVE:

1. membrane bound organelles

2. nucleus—DNA lies free in cytoplasm in the nucleoid region

how do viruses reproduce?

1. all parasitic

2. can only reproduce by infecting living cells

3. uses protein synthesising machinery of host cell to replicate

what is the causative agent of cholera?

a bacteria called Vibrio Cholerae

what is the causative agent of malaria?

a protoctist called either:

• Plasmodium falciparum

• P. malariae

• P. vivax

• P. ovale

what is the causative agent of HIV/AIDs?

(retro)virus called Human Immunodeficiency Virus

what is the causative agent of tuberculosis?

• a bacteria called Mycobacterium tuberculosis/ M. bovis

• M. tuberculosis—>TB in humans

• M. bovis—> TB in cows + humans

what is the causative agent of smallpox?

a virus called Variola virus

what is an epidemic?

an outbreak of disease that attacks many peoples at about the same time and may spread through one or several countries

what is an endemic?

a disease that exists permanently in a particular region/population(ie malaria)

describe the cholera causative agent

• Vibrio cholerae—a bacterium

• comma shaped, has flagella, motile

explain how cholera is transmitted

• through the ‘fecal-oral’ route:

1. large numbers of Vibrio cholerae found in faeces of infected people

2. infected person’s faeces/sewage contaminates water/food

3. houseflies land on faeces and contaminate food/water

4. uninfected person eats contaminated food/water

describe the mode of action of cholera in the body

1. if bacteria is not killed by stomach acid—>reaches small intestine

2. bacteria secrets choleragen toxin

3. toxin binds to complementary receptor on intestinal epithelial cell—>enters via endocytosis

4. disrupts function of intestine epithelium lining

5. loss of Cl- ions and Na + ions from epithelial cells

6. W.P decreases, water moves out from blood, down W.P gradient by osmosis thru partially permeable membrane

7. causes severe diarrhoea + dehydration

what are the symptoms of cholera?

1. diarrhoea

2. severe dehydration

3. loss of water and salts

4. weakness and fatigue

5. low BP

6. weight loss

7. vomitting

how do we diagnose cholera?

microscopic analysis of faeces

how do we treat cholera?

• oral rehydration therapy:

1. use oral rehydration solution(ORS) that has glucose and salts

2. ensures fluid intake=fluid loss in urine and faeces

3. maintains osmotic balance of blood and tissue fluids

what is the global distribution of cholera?

• endemic in developing countries

• outbreak follows natural disasters/war

• due to absence of proper sanitation—>no treatment of faecal waste—>water supply contaminated

• poor hygiene + poor living conditions

  • lack of education of transmission

what other problems can cholera cause?

1. there are many different strains of cholera—>cannot make a vaccine for it

2. each strain is more virulent than the last

3. adults can be reinfected with cholera

what is malaria caused by in humans?

1. plasmodium falciparum—75%

2. P. malariae, P. ovale, P. vivax—25%

what is a vector?

an organism that carries disease from a person to another

how is malaria transmitted?

1. vector—>female Anopheles mosquitoes

2. only females take blood meals to supply eggs with nutrients

3. blood transfusions, use of unsterile needles, and can pass across placenta from mother

symptoms of malaria

1. fever

2. anaemia

3. nausea

4. headaches

5. muscle pain

6. shivering

7. enlarged spleen

diagnosis for malaria

• microscopical analysis of blood

• dip stick test for malaria antigens in blood

treatment for malaria

• anti-malarial drugs:

1. quinine, artemisin

2. chloroquine—>inhibits protein synthesis + prevents parasite from spreading in body

3. proguanil—>inhibits sexual reproduction of plasmodium in the mos

• combination therapy—>multiple drugs are used at the same time to prevent drug resistance

how do we prevent malaria?

1. use preventative drugs

2. reduce number of mos

3. prevention of bites

global distribution of malaria

1. endemic in tropical + subtropical areas

2. this is because:

   1. the vector survives and breeds in hot + humid areas

   2. needs still/stagnant water to reproduce

   3. plasmodium reproduces within mos >20 degrees C

what other problems does malaria cause?

1. drug resistant plasmodium

2. insecticide resistant mos

3. global warming resulted in more area for mos to breed

what does HIV have?

1. it is an RNA virus/retrovirus

2. contains single stranded RNA as genetic material

3. has a protein coat/capsid made of capsomeres

4. has outer viral envelope made of a lipid bilayer + proteins mostly derived from host

5. has viral glycoproteins on the outer envelope

6. 2 enzymes:

   1. reverse transcriptase: uses RNA as template to produce DNA in host cell

   2. protease: cleave/process new viral proteins

life cycle of HIV

1. the viral RNA + reverse transcriptase(RT) enters T helper lymphocytes

2. RT converts RNA into DNA

3. the viral DNA is incorporated into the host DNA

4. the cell’s machinery is used to express viral proteins(through transcription + translation)

5. viral proteins are assembled into many new viruses

describe the transmission of HIV

1. direct exchange of bodily fluids

2. virus is unable to survive out of the human body

3. semen, vaginal fluids during sexual intercourse

4. blood transmission via infected blood transfusion/contaminated syringes

5. mother to baby transmission across placenta/breast milk

6. anal intercourse increases risk—>less natural lubrication in the rectum—>rectal lining is easily damaged + virus can pass from semen into blood

symptoms and effects of HIV

1. slow infection—virus can stay dormant for years

2. changes surface proteins to hide from immune system

3. HIV infects T helper cells—>destroyed T helper cells—>numbers decrease—>body unable to defend itself against infection

4. flu like symptoms and then symptomless

5. opportunistic infections can occur as a result of a compromised immune system

6. collection of opportunistic diseases associated with immunodeficiency caused by HIV=AIDs

symptoms and effects of AIDs

• opportunistic infections:

1. oral thrush

2. pneumonia

3. cancers

4. neurogenerative diseases like dementia

5. TB

6. malaria

7. malnutrition+ weight loss + diarrhoea + fever + sweating

how is HIV/AIDs treated?

• no cure for AIDs

• drug therapy for HIV:

  • Zidovudine: similar to Thymine—>binds to viral enzyme reverse transcriptase and inhibits it

  • drugs can target viral protease and inhibit it

  • expensive + many side effects

• combination therapy:

  • strict pattern + timing of medication

  • if not followed properly, patients may develop strains of HIV resistant to drugs

how do we prevent HIV?

• protected sex

• HIV testing

• contact tracing= where the person with HIV traces people he/she has put risk of infection and that person to provided an HIV test

• no needle sharing

• donated blood is screened for HIV + heat-treated to kill viruses

• control mother-to-child transmission using drugs

• HIV+ women of high income countries should use formula

what other problems does HIV/AIDs cause?

• difficult to reach people for widespread testing in rural area

• many symtomless carriers

• drugs are expensive + cause side effects

• pandemic

how is TB transmitted?

• mycobacterium tuberculosis:

  • by aerosol infection

  • pathogen is in airborne droplets

  • infected person coughs/sneezes—>uninfected person breathes it in

• mycobacterium bovis:

  • from infected cows/cattle

  • eat undercooked + contaminated meat

  • drink unpasteurised milk containing bacteria

effects of tuberculosis

1. site of primary infection: lungs

2. secondary infection: lymph nodes + bones + gut

3. slow infection—many infections are controlled by the immune system

4. bacteria may be activated after many years when immune system is weakened by other infections(ie HIV)

5. incubation period is a few weeks-years

symptoms of TB

• central:

  1. appetite loss

  2. fatigue

• lungs:

  1. chest pain

  2. coughing up blood

  3. prolonged cough

• skin:

  1. night sweats

  2. pallor

how do we diagnose TB?

• x ray

• microscopical examination of sputum(mucus + pus) for bacteria

how is TB treated?

• long term because bacteria is slow growing + not responsive to drugs

• combination therapy:

  • use multiple antibiotics to prevent drug resistance

• DOTS( direct observation treatment, short course):

  • makes sure patients take medicine regularly and reduce spread of drug resistance

how do we prevent TB?

• BCG(Bacillus Calmette-Guerin) vaccine derived from M. bovis

• isolate patients during infectious stages

• contact tracing

• cattle tested for TB

• pasteurise milk

other problems that emerge from TB

• multiple drug resistant TB

• drugs like isoniazid no longer effective

• not completing course of treatment increases risk of drug resistant TB

describe the global distribution of TB

1. endemic all over the world

2. high rates in cities due to high migration rate

3. overcrowded area

4. areas where HIV/AIDs is prevalent—>TB is an opportunistic infection—>HIV/AIDs causes weakened immune system—>increases risk of TB development + dormant TB more likely to become active in HIV+ person

what are antibiotics?

• drugs used that are derived from microorganisms

• kill/inhibit growth of bacteria without harming infected organism

• bacteriocidal antibiotics—kill bacteria

• bacteriostatic antibiotics—inhibit bacterial growth

• prevent spread of bacteria in body

• have no effect on human cells AND viruses

how do antibiotics work?

1. inhibit bacterial cell wall synthesis

2. inhibit activity of specific membrane protein/glycoprotein—>block binding to cells

3. block specific enzyme action

4. inhibit protein synthesis + nucleic acid synthesis—>target enzymes that bacteria have but humans don’t

what happens to bacteria in the absence of penicillin?

1. bacterial wall is made of peptidoglycan

2. when bacterial cells grow—>secretes autolysins

3. autolysins make tiny holes to allow the cell wall to stretch

4. new peptidoglycan formed

5. peptidase enzyme forms cross links between peptidoglycan chains—>form cell wall

what happens to bacteria in the presence of penicillin?

1. penicillin inhibits peptidase enzyme

2. stops formation of cross links between peptidoglycan polymers in the cell wall

3. autolysins make tiny holes but new peptidoglycans that are formed cannot link up

4. cell wall is weaker

5. cell walls unable to withstand turgor pressure when water moves by osmosis—>bacteria lyses and dies

6. penicillin is only effective when bacteria is growing

what is the spread plate method and what is it used for?

• antibiotic discs are placed in a petri dish with growing bacteria

• the diameter of the zone of inhibition shows how effective the antibiotic is

• method:

  • sample is pipetted onto surface of agar plate

  • sample is spread evenly over surface of agar using sterile glass spreader

  • sample is incubated

  • final results: the one with the bigger inhibition zone=most effective

why are antibiotics not effective against viruses?

1. viruses do not have a peptidoglycan cell wall, have a protein coat

2. viruses do not have their own metabolism, rely on host cells

3. viruses have no cell structure/very few organelles—>very few sites for antibiotics to act on

4. viruses live inside host cells—>out of reach for antibiotics

5. antivirals exist—>target viral glycoproteins on viral envelope—>prevent binding of virus to host cells + inhibit specific viral enzymes

what is antibiotic resistance?

• when antibiotics are no longer effective against bacteria

• can spread from bacteria to bacteria

• many bacteria have penicillinase enzymes which break down penicillin—>resistant to penicillin

what is antibiotic resistance caused by?

1. spontaneous mutation in bacteria

2. mutation causes change in protein/production of new protein that cannot be targeted by antibiotics

3. natural selection enables resistance genes to spread

4. antibiotic is the selection pressure—>antibiotics only kill non resistant bacteria

5. resistant bacteria survive + reproduce—>antibiotic gene is passed to next gen + bacteria

what causes antibiotic resistance?

• patients not completing their course for antibiotics—>some susceptible bacteria survives—>bacteria replicates + have increased chances of mutation/becoming resistant

what are the consequences of antibiotic resistance?

1. bacteria can carry several antibiotic resistant genes—>develop multiple resistance

2. become ‘super bug’

3. wounds do not heal + continuously getting infected with bacteria

4. bacteria cannot be killed by common antibiotics—>need to be controlled by stronger antibiotics—>but we are running out of antibiotics

what is the solution to antibiotic resistance?

• discover more antibiotics by slightly modifying preexisting ones but discovery takes time

• prevention:

  • only use antibiotics when prescribed

  • always finish course

  • never use left over antibiotics

  • do not share antibiotics

  • good hygiene

What are the two types of microscopes?

light and electron

light microscope

An optical instrument with lenses that refract (bend) visible light to magnify images of specimens.

electron microscope

a microscope that focuses a beam of electrons to magnify objects

what do light microscopes use as their source of light radiation?

visible light

What is the typical magnification of a light microscope?

10x

How many lenses are typically below the eyepiece in a light microscope?

three to four lenses, known as an objective lens

what is the function of an objective lens?

helps to magnify the object of interest

How do you work out magnification using the magnification of the eye piece and the objective lens?

eye piece M x objective lens M

ie: 10x 10= 100

What can light microscopes be used for?

- Light microscopes & stains can be used to visualise cells

- The light from the microscope shines through the specimen, allowing it to be visualised

- Watch cell division take place

what do electron microscopes depend on?

Rely on the specimens to be stained with heavy metal elements and placed in a vacuum, hence, only non-living organisms can be viewed with it

What type of specimens do electron microscopes show?

-biological specimens

-inorganic specimens

what biological specimens does the electron microscope show?

-microorganisms

-cells and tissues

what is magnification?

The ratio of an object's image size to its real size

What is resolution?

The ability to clearly distinguish the individual parts of an object, the higher the resolution, the closer the two objects are to each other, meaning

What is resolution determined by?

The wavelength of light used and the numerical aperture of the lens

What is aperture?

The size of the opening of the lens

what is the general rule of resolution to visible light?

The longer the wavelength, the lower the resolution

what is the wavelength of visible light?

400-700nm

What is the resolution of visible light?

200nm, meaning objects closer together than 200nm cannot be seen as two distinct object points

electron microscope vs light microscope

How do you prepare a microscope slide using a liquid specimen?

- Add a few drops of the liquid sample to a clean slide using a pipette

- Lower a coverslip over the specimen and gently press down to remove air bubbles

How do you prepare a microscope slide using a solid specimen?

- Use scissors or a scalpel to cut a small sample of the tissue, and peel away or cut very thin layers of cells

- Place the sample onto a slide and add a drop of water

- Apply iodine stain

- Lower a coverslip over the specimen and press down to remove air bubbles

Why do we prepare small samples in a solid slide prep?

to allow light to pass through

how do you prepare a slide using human cells?

1- Brush teeth thoroughly to remove any bacteria, so as not to obstruct the view of the cheek cells

2- Take a sterile cotton swab and gently scrape the inside cheek surface of the mouth for -10 seconds

3- smear the cotton swab on the centre of the microscope

4- Add a drop of methylene drop solution

5- This causes the nucleus and mitochondria to appear darker than their surroundings

6- Place a coverslip on top

7- Lay the coverslip down at one edge from a 45-degree angle and then gently lower the other edge until it is flat to remove gas bubbles

why do we use methylene blue drop solution when preparing a slide using human cells?

Methylene blue stains charged molecules in the cell, including DNA and RNA

why do we use coverslips?

to protect the microscope lens from liquids and help prevent drying out

what are permanent slides?

microscope slides that have a specimen preserved and mounted in a solid mounting medium, making them suitable for long-term storage and observation

What is staining?

colouring microorganisms with a dye that emphasises certain structures

common microscope stains and uses

what is the function of a biological drawing?

to record the observations seen under a microscope

what are biological drawings?

Biological drawings are line pictures which show specific features that have been observed when the specimen was viewed.

What are the rules when drawing a biological drawing?

1- title

2- The magnifications under which the observations shown by the drawings are made and recorded

3- no shading or no a lack of clear lines

4- Well-defined structures should be shown

5- Drawing takes up most of the page and is made with proper proportions

6- clearly labelled without arrows and connected directly to the labelled part

when are drawings with higher magnification made?

when visualising cells at a higher magnification power

when are drawings with lowermagnification made?

tissues viewed under lower magnifications

plant cell biological drawing

bacterial cell biological drawing general

animal cell drawing

how do you calculate magnification?

magnification = image size/actual size

How many micrometres are in a millimetre?

1000 µm = 1 mm

How many nanometers are in a micrometer?

1000 nanometers

converting units