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biology > 2.2 - Prokaryotic cells > Flashcards

2.2 - Prokaryotic cells Flashcards

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1
Q

what is the function of the bacterial cell wall

A

-the bacterial cell wall is hypertonic (have a greater osmotic pressure) to the medium around them, so water moves into these cells by osmosis
-cell wall prevents the cell from bursting or swelling
-maintains the shape of the bacterium
-gives support and protection to the inside

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2
Q

what is the bacterial cell wall made of

A

a layer of peptidoglycan that has a net-like structure

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3
Q

what is the capsule / slime coat made of and its function

A

-capsule can be formed from starch, gelatin, protein, or glycolipid
-protects the bacterium from phagocytosis by white blood cells
-capsule covers cell markers on the cell membrane that identify the cell, making it easier for a bacterium to be pathogenic
-helps bacteria survive in dry conditions

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4
Q

what are the functions of pili

A

-sexual reproduction
-attachment to a host cell

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5
Q

what disadvantage do pili bring to bacteria and why

A

-pili make viruses more vulnerable to viral infections because a bacteriophage can use pili as an entry point into the cell

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6
Q

what is the function of the flagellum on a bacterium and what is it formed of

A

-movement by rapid rotations
-many helices of flagellin (a protein)

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7
Q

describe the cell surface membrane on bacteria

A

-have similar functions to eukaryotic cell membranes
-as bacteria don’t contain mitochondria, some respiratory enzymes are in the cell membrane
-some bacteria have mesosomes, which are infoldings of the cell membrane

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8
Q

describe plasmids and their function

A

-codes for a specific aspect of the bacterium’s phenotype
E.g. a toxin, resistance to a specific antibiotic
-plasmids can reproduce independently of the nucleoid
-can be transferred from one bacterium to another through the pili during sexual reproduction

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9
Q

describe the nuceoid in a bacterium

A

-the nucleoid (containing DNA) is not contained in a membrane bound nucleus

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10
Q

what are 3 types of prokaryotes

A

bacteria, cyanobacteria, archaebacteria

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11
Q

describe the ribosomes in prokaryotes

A

-only 70s ribosomes
-smaller than 80s ribosomes
-have 2 subunits: the smaller 30s and larger 50s
-where protein synthesis occurs

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12
Q

what is the goal of gram staining and why it is important

A

to determine whether a bacterium is gram negative or gram positive based on their cell wall
useful because the type of cell wall a bacterium has affects its vulnerability to an antibiotic, so different types of bacteria are vulnerable to different types of antibiotics

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13
Q

what 2 stains are used in gram staining

A

Gram stain containing crystal violet
red safranin counterstain

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14
Q

describe the process of gram staining

A

-Gram stain is added which contains crystal violet
-the bacteria is then dehydrated using ethanol
-red safranin counterstain is added

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15
Q

explain what colour gram positive bacteria appear after gram staining

A

-gram-positive bacteria have a thick layer of peptidoglycan which contains teichoic acid
-the thick peptidoglycan layer takes up the crystal violet/iodine solution
-it resists decolouring when ethanol is added (the layer is dehydrated by the ethanol so the crystal violet/ iodine complex is trapped inside the layer)
-the peptidoglycan layer doesn’t pick up the red safranin counterstain leaving the purple/blue colour

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16
Q

describe the structure of a Gram-positive bacterial cell wall

A

-there’s a layer of plasma membrane
-followed by a very thick layer of peptidoglycan
-teichoic acid if around all throughout the peptidoglycan layer

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17
Q

describe the structure of a Gram-negative bacterial cell wall

A

-there’s an inner plasma membrane
-then a very thin layer of peptidoglycan which doesn’t contain any teichoic acid
-then the outermembrane
-liposaccharides are attached to the outer membrane and stick outwards

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18
Q

explain what colour gram negative bacteria appear after gram staining

A

-Gram-negative bacteria have only a thin layer of peptidoglycan in their cell walls with no teichoic acid
-the crystal violet/iodine complex is applied
-the bacteria are dehydrated in ethanol
-the lipopolysaccharide layer dissolves in the ethanol leaving the thin peptidoglycan layer exposed
-the crystal/iodine complex is washed out
-the peptidoglycan takes up the red safranin counterstain so the cells appear red

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19
Q

what do antibiotics generely target to kill bacterial cells

A

antibiotics usually target features on bacterial cells that aren’t present on animal cells
e.g. bacterial cell walls, 70s ribosomes

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20
Q

how does beta-lactam antibiotics (e.g. penicillin) work

A

-inhibit the formation of the peptidoglycan layer in the bacterial cell wall
-so very effective to kill Gram-positive bacteria
-less effective against Gram-negative bacteria as their peptidoglycan layer is protected by the outer membrane, and it’s less vital to the cell wall structure

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21
Q

how do glycopeptide antibiotics work

A

-glycopeptide antibiotics are large polar molecules that cannot penetrate through the outer membrane of Gram-negative bacteria
-but are very effective in killing Gram-positive bacteria

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22
Q

how do polypeptide antibiotics work

A

-they interact with the phospholipids in the outer membrane of Gram-negative bacteria, so are effective against Gram-negative
-do no affect Gram-positive bacteria
-but are rarely used as can cause serious side-effects

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23
Q

what are the 3 ways bacteria can be classified

A

whether they are Gram-positive or Gram-negative
their shape - cocci, bacilli, spirilla, vibrios
their respiratory requirements - obligate aerobes, facultative anaerobes, obligate anaerobes

24
Q

what are cocci

A

spherical bacteria

25
Q

what are bacilli

A

rod-shaped bacteria

26
Q

what are spirilla

A

bacteria with a twisted or spiral shape

27
Q

what are vibrio

A

comma-shaped bacteria

28
Q

what are obligate aerobes

A

require oxygen for respiration

29
Q

what are facultative anaerobes

A

use oxygen for respiration if it is available, but can also respire without it

30
Q

what are obligate anaerobes

A

can only respire in the absence of oxygen
oxygen will kill them

31
Q

do all viruses cause harm to host cells

A

viruses invade and take over the living cell to reproduce, so mostly cause damage or disease

32
Q

what is the capsid on a viruses made from

A

-capsomerers, which are repeating protein units
-using repeating protein uses minimises the amount of genetic material the virus needs

33
Q

describe the envelope on a virus

A

-is some viruses the genetic information and capsid are covered in a lipid envelope made by the host cell
-making it easier for viruses to pass between cells

34
Q

how do viruses attach to host cells

A

-by virus attachment particles (antigens)
-these attach to molecules on the host cell’s cell surface membrane

35
Q

what 2 things are used to classify viruses

A

genome
mode of replication

36
Q

describe DNA viruses

A

-the genetic material is DNA
-the viral DNA acts as a template for DNA replication and protein synthesis

37
Q

what are the 3 types of viruses

A

DNA viruses, RNA viruses, RNA retroviruses

38
Q

describe RNA viruses

A

-the genetic material is RNA (much more likely to mutate that DNA)
-do not produce DNA as part of their life cycle
-there are 2 types of RNA viruses: positive ssRNA viruses and negative ssRNA viruses
-all types of ssRNA viruses conatin only 1 strand of RNA
-positive ssRNA viruses have RNA that can act directly as mRNA and be translated in ribosomes
-for negative ssRNA viruses, their RNA has to be transcribed before it can be translated

39
Q

describe RNA retroviruses

A

-the genetic information is a single strand of RNA
-the viral RNA codes for the synthesis of reverse transcriptase (enzyme)
-this makes DNA molecules corresponding to the viral genome
-these DNA molecules are incorporated into the host cell’s DNA and used as a template for new viral proteins and viral genome

40
Q

give an example of a DNA virus

A

λ (lambda) phage

41
Q

give an example of an RNA retrovirus

A

human immunodeficiency virus (HIV)

42
Q

give an example of an RNA virus

A

tobacco mosaic virus
ebola virus

43
Q

What are the 3 ways viruses cause disease in animals

A

-causing the host cell to release its own lysosomes and digest the cell from inside
-causing host cell to lysis
-by producing toxins that inhibit cell metabolism

44
Q

Why are viruses specific in which cells they infect

A

-each cell has its own recognition markers
-different types of viruses can only bind to certain cell markers

45
Q

how do antiviral treatments work

A

-antiviral treatments target viral reproduction, because viruses don’t have a metabolism it is hard to create treatments which affect the virus particles themselves
-antiviral treatments work in different ways, they can:
-target receptors which viruses use to enter host cells
-target the enzymes that help to translate or replicate the viral DNA or RNA
-inhibit the protease enzymes that enable new virus particles

46
Q

why are viruses classified as non-living

A

-they cannot self replicate
-have no metabolism

47
Q

what is an epidemic

A

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

48
Q

What is the main goal of disease control for viral infections and how is it achieved

A

preventing spread of viruses, by identifying the pathogen early and putting transmission control measures in place as soon as possible

49
Q

what are some ways of controlling the spread of viral diseases

A

-rapid identification of of disease
-preventing transmission from one person to another. Through simple measures such as regular hand washing and health care workers washing hands before and after contact with each patient, careful disposal of infected bodily fluids, frequent disinfecting of surfaces.
-sterilising medical equipment and bedding after use
-wearing protective clothing by health care workers. Like facemasks, gloves, goggles.
-identifying people who have been in contact with infected people so they can be isolated/treated
-nursing in isolation units(only used for serious infections like Ebola)

50
Q

what are some reasons against using untested drugs

A

-unexpected side effects
-severely ill patients cannot give informed consent
-difficulty to decide which individuals get the drugs first. E.g. during Ebola local people may feel like they are used as guinea pigs if given the drugs first, but may feel resentful if only health care workers are treated

51
Q

what factors should be taken into account when considering if a drug should be fast-tracked for use during a pandemic

A

-severity of the disease
-availability of other treatments
-effectiveness of standard disease control measures
-how to achieve informed consent when giving the drug to individuals

52
Q

what is a pandemic

A

an epidemic that takes place in several countries at once

53
Q

describe Ebola
causes and effects

A

-Ebola is a viral disease caused by the Ebola virus
-often fatal, especially is symptoms are left untreated
-transmitted between people through bodily fluids (blood, urine, faeces)

54
Q

outline what happened during the 2014 Ebola pandemic

A

-Ebola virus spread rapidly through West Africa due to lack of hygiene
-high mortality rate
-no vaccine or drugs, so disease control was used to reduce spread

55
Q

describe the disease control measures that contributed to the 2014 Ebola epidemic

A

-it took a long time to identify Ebola in West Africa, so disease control measures were put in place when a large number of people were already infected
-people needed to be nursed in isolation becuase the Ebola virus can be transmitted easily, however there was a lack of sealed isolation units
-lack of sterilising medical equipment, at the beginning of the Ebola epidemic the main cause of transmission was use of unsterilised needles
-simple measures weren’t taken to prevent transmission of Ebola (disinfecting surfaces, carefully disposing of infected bodily fluids)

biology (4 decks)

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