Biology- 6A

Explain the 3 types of bacteria

1. Pathogenic : disease causing

2. Saprotrophic: feed on dead organic matter (digestive enzymes)

3. Mutualistic: equally beneficial relationship with another organism

what are the nine structures found in a bacterium

1. cell wall

2. cell surface membrane

3. pilli

4. flagellum

5. plasmids

6. 70s ribosomes

7. capsule

8. cytoplasm

9. nucleoid

what is the roles of cell wall, cell-surface membrane and cytoplasm in a bacterial cell

cell wall: made of peptidoglycan; maintains shape and prevents osmotic bursting

cell-surface membrane: controls movement of substances and site of respiration

cytoplasm: enzymes for metabollic reactions

what is the role of nucleoid, plasmids, capsule, flagellum and pilli in a bacteria cell

Nucleoid: main genetic info, circular DNA

plasmids: small DNA that codes for specific characteristics such as antibiotic resistance

capsule: slime like outer protective layer that covers cell recognition markers and hydrates

flagellum: projection that rotates to allow movement

Pilli: attaches to surfaces and allows DNA tranfers between bacteria

why are virsus’ referred to as “acellular” and “obligate intracellular parasites”

Because they are not made of cells, they have no cytoplasm, ribosomes or organelles

they rely on host cells to reproduce

why can virus’s not reproduce despite hvaing genetic material in the form of DNA or RNA

they do not have the enzymes or ribsomes or energy (ATP) needed for protein synthesis

what are the structures found in most virus’

1. genetic material

2. protein coat - capsid

3. lipid envelope

4. attachement proteins

what is the capsid

protein coat around viral genetic material that protects, gives virsu shape and helps virus to attach to host cell

made of capsomeres (protein subunit repeating that require lil genetic material to make)

what is the lipid envelope

outer covering made of lipids dervied from host as virus exits host cell, contains glycoproteins.

allows membrane to enter host cell

carriers attachment proteins and protects viral components

what are attachment proteins

specifically shaped proteins that determine what host cell a virus can attack

what are features that virus’s have that make them associated. with living and non-living

living: genetic material, can mutate, undergo natural selection

non-living: cannot reproduce independently, no cellular structure and no independent metabolism

what are methods of classifying virus’s

based on their genetic material and how they replicate it

describe DNA viruses

• contain either double or single strand DNA (single needs to be converted into double to make viral mRNA)

• DNA is turned into mRNA in host cell which is used to make viral proteins

describe RNA viruses

• RNA is either single or double stranded

Describe the catergories for single-stranded RNA viruses

1. Positive-sense RNA : can act directly as mRNA

2. Negative-sense RNA: must be converted into positive before functioning as mRNA this is done with enzyme RNA-dependent, RNA polymerase

describe retroviruses and its significance

type of rna virus that contains reverse transcriptase which dna from their rna genome

allows the viral dna to integrate into host chromosomes allowing it to remain for long periods

what are the 4 mechanisms of a virus entering a host

1. direct injection of genetic info

2. receptor-mediated endocytosis

3. membrane fusion

4. vector

what is direct injection and give an example

bacteriophages that infect bacteria

• inject genetic material into host cell w/o entering by attaching to specific receptors using its tail fibres

what is receptor-mediated endocytosis

host membrane folds inwards of virus (with complementary receptors) forming a vesicle. host cell then digests the capsid to release genetic material into cytoplasm

what is membrane fusion

viruses with lipid envelopes can merge membranes (both phosolipid bilayers) allowing contents to enter cytoplasm

What are vectors

used for plant viruses due to very rigid cellulose cell walls that enter the virus through damaged tissue and insects that feed on plant. can then spread through plasmodesmatas

what are the 2 routes a virus follows once entering host cell

1. Lytic pathway

2. Lysogenic pathway

whats the main difference between the lysogenic and lytic pathway

lytic: virus actively reproduces causing the cell to burst

lysogenic: voral dna is integrated into chromosome and lays latent

describe the process of the lytic cycle

1. viral DNA injected into cytoplasm

2. genetic info from virus is used to make protein components which assemble into new viruses

3. viral proteins damage cell envelope causing the bacterium to burst and release the new viruses which can infect other cells

what is the significance of the name lytic

lytic means to breakdown or bursting (of a cell)

describe the lysogenic phase

• viral DNA gets incorporated into host nucleic acid, forming provirus, becoming a prophage

• the viral genes are not activated meaning it stays latent and unrecognised for long time (lytic genes suppressed until later)

• it is replicated into daughter cells as the cell divides

• the genetic info can persist across multiple generations

what causes the lysogenic pathway to switch to the lytic pathway

through induction which is where factors such as UV radiation, DNA damage, and certain chemicals or host-cell stress

what are the 4 named viruses

1. Ebola

2. Tobacco mosaic (TMV)

3. Human immunodeficiency (HIV)

4. Lambda bacteriophage

describe the structure of ebola

• single strand negative RNA

• long threadlike

• capsid

• lipid envelope w glycoproteisn attachment

describe the structure of TMV

• single strand positive RNA

• rod

• helical capsid

• no envelope

• infect plants

describe the structure of HIV

• two copies of single strand positive RNA

• cone shape capsid

• envelope with glycoproteins attachment

• it is retrovirus so reverse transcriptase

describe the structure of lambda bacteriophage

• double strand DNA

• capsid with an icosahedral head

• tail (injects)

• no envelope

• can undergo lytic or lysogenic pathways

what is viral latency

similar to lysogenic, where the viral genome is not active in the host cell and can be integrated into the host chromosomes.

why is latent HIV reservoirs significant

they can persist despite antiretroviral treatment as it doesn’t eliminate every cell containing integrated viral DNA

what causes TB and how does it spread

caused by mycobacterium tuberculosis and affects mostly the lungs, is transmitted through the air.

when someone with TB coughs or speaks they release airborne bacteria particles that can be inhaled by other people

what happens when the bacteria enters the lungs?

TB is inhaled into alveoli → macrophages engulf the bacteria by phagocytosis → some bacteria survive → immune responses can produce tubercles

what are tubercle

collection of immune cells that form around an area of TB infection, containing it in a localised area limiting spread

whats the diff between latent and active TB

active is when the bacteria multiply and cause disease and symptoms where it is infectious and can cause damage

why does TB cause breathing issues

when bacteria multiply the immune response can damage lung tissue which affects gas exchange reducing oxygen uptake

in severe cases, lung tissue can breakdown and cavities can develope

what is the treatment for TB

multiple antiobiotics over several months esp for bacteria that may be difficult to reach or slow-growing and to reduce risk of drug resistance

why can TB persist inside macrophages

interferes with normal intracellular killing mechanims

contains a protective waxy coat

what is the distinction between HIV and AIDS

hiv is virus

aids is the most advanced stage of the infection

how is HIV transmitted

when infected bodily fluids enter another persons bloodstreams or contact vulnerable tissue through sexual contact, contamined objects such as needles, transmission from mother to child durinh pregnancy or childbirth or breastfeeding

How does HIV infect T-cells

HIV attachs to receptors on T-helper cells

viral envelope fuses with host cell membrane and content are released, reverse transcriptase converts RNA into DNA which is integrated using integrase into host chromosomes forming provirus. viral proteins produced via host cell

why does HIV weaken the immune system

Tcells important for immune responses by activating macrophages, B-cells that make antibodies and HIV reduces no. of t cells this increases susceptibility of opportunistic infections such as TB which is what eventually leads to death

describe the progression of HIV to AIDS

1. Acute infection (flu-like symptoms or none at all, HIV reproduces rapudly and lot of it in blood)

2. chronic infection (hiv continues to replicated and damage immune system)

3. symptomatic (as t cells no. falls person is more vulnerable to disease and infection so maybe more fevers)

4. AIDs (very weak immune system t cell number very low and serious opportunistic infections may develope)

How is HIV treated

through antiretroviral therapy which uses many medicines that interefere with HIV at diff stages and allows immune system to recover and prevent aids and lifelong treatment to cover integrated HIV as well

describe the 6 different routes of pathogen entry

1. Inhalation- breathing airborne particles (TB)

2. Ingestion- consuming contaminated food or water

3. Direct contact - skin

4. Inoculation- damaged skin, needles or bites

5. Vectors- another organism transmits the pathogen

6. Fomites- inanimate objects transfer pathogens

what are non-specific defences

protection against a wide range of pathogens rather than targeting one particular one

What are the forms of protection the skin provides

1. Physical- thick outer epidermis, which makes penetration difficult

2. chemical- sebum and sweat inhibit growth of microorganisms

3. biological - normal skin miccroorganisms compete with potential pathogens for space and nutirents

What are the forms of protection the respiratory tract provides

mucus- traps microorganisms and particles entering airways

cilia- hairlike structures that move mucus away

how are lysozymes protective

enxyme found in tears, salive and mucus which break bonds in peptigoglycan bacterial walls which weakens them and potentailly casues cells to undergo lysis

how is stomach acid and normal flora protective

s: HCl creates acidic that inhibits microorganisms

n: microorganisms that naturally inhabit parts of body which creates competition for nutrients, attachment sites and some can produce inhibitory substances

what does culturing mean and explain the conditions needed

• growing under controlled conditions

conditions:

• nurtients- energy for growth

• water - metabolic reactions

• temp + ph- metabolic reactions (enzymes)

• oxygen in aerobic-respiration

what are the two types of culture mediums

1. solid agar - show colony growth

2. liquid nutrient broth - gets cloudy

what is a pure culture

contains only one species or strain

what are aseptic techniques and examples

prevents unwanted contaminting from environment

• sterilise equipment, disinfect surfaces, inoculating loops, open containers when necessary, wash hands, bunsen burner (kills airborne), lid upside down to prevent condensation

what is a colony and the name used for colony counting methods

• visible mass arising from viable cells or small groups of cells

• colony-forming units (CFU)

what are selective and differential mediums

s: isolates certain microorganisms my inhibiting others

d: allows microorganisms to be distinguished by observable changes such as colour

describe the four methods of measuring microbial growth and disadvantages

1. Direct counting - Haemocytometer + stains that distinguish between viability

2. Turbidity (measuring cloudiness) - using colourimeter but can’t est. viability

3. Dilution plating- est. viable cells by serial dilutions and incubating on agar, highest colony count is used to est. original sample (CFU) - but not every viable cell forms a colony

4. Measuring dry mass- seperates microbrial cells, drys them and determines dry biomass but doesn’t est. viability and small amounts difficult to measure accurately

describe the four phases of bacterial growth

1. lag- bacteria still adapting, prepping for reproduction so lil to no increase in population

2. exponential growth - favourable conditions, bacteria reprouces exponentrially

3. stationary phase- rate of cell division equal to death rate due to depleeting resources, waste accumulates

4. death phase- death > growth

why is the colorimeter calibrated

to adjust it to the light absorbtion to only the broth itself so the reading only varies for microorganism growth

what are the control, independent and dependent varibles in measuring microorganism growth

c: glucose conc, temp, pH, yeast conc

i: time

d: absorbance/transmission

why does a turbidity graph not show a death phase

because dead cells can still scatter light and change readings on colorimeter

what are reliability and validity limitations with measuring microorganism growth

• un-uniform mixture

• fingerprints of cuvette

• variable temp

• only one culture

• repeat!!!

• using the same cuvette

What enters the host cell when HIV attached to T-cells

• enzymes (reverse trasncriptase + integrase)

• nucleic acids

how does HIV exit host cell

through exocytosis

does HIV undergo lysogenic

no because once encorporated into cell DNA it starts reproducing using cell machinery

What are endotoxins and how do they cause disease?

Lipopolysaccharides in Gram-negative bacterial outer membranes; they can trigger inflammation, fever and septic shock.

What are exotoxins and how do they cause disease

Protein toxins produced by bacteria that act on specific host-cell targets, causing cell damage or disrupting functions.

what do you need to remember when using a haemocytometer

• vol of one square = 0.1 mm³

• convert to mL is x10⁴

• only count two consistent sides

• Avg cell viable cells per mL = avg x dilution factor x 10⁴

quality checklist before using a haemocytometer:

• no air bubbles

• grid fully and evenly covered

• cell dispersed not clumped