TOB S3 - Cell Ultrastructure and Bugs in the System Flashcards
Compare the different types of microscope
See image
How does a transmission electron microscope work?
Has a vacuum. Fire electrons through lenses. They hit a fluorescent screen - fluoresces by different amounts based on how many electrons the specimen has absorbed
Define “limit of resolution”
The minimum distance at which two objects can be distinguished
Explain why electron microscopes are capable of finer resolution than light microscopes
Wavelengths of visible light: violet is 0.4um, deep red is 0.7um. Wavelengths of electrons at 100,000V acceleration is 0.004nm. Theoretical limit of resolution for light microscope is 0.2um, for electron microscope is 0.002nm
Compare the membranes of prokaryotes and eukaryotes
- Prokaryotes have an external membrane but no internal membranes. All the biochemical processes of the cell occur in the same compartment. - Eukaryotic cells are compartmentalised by internal membranes
Outline the contents of a eukaryotic cell
See image
How many different proteins does a typical mammalian cell synthesise?
More than 10,000
Describe the phospholipid bilayer
Phospholipids, which make up cell membranes, are amphipathic. The phospholipid bilayer forms a relatively impermeable barrier to most water-soluble molecules. The protein molecules “dissolved” in the lipid bilayer mediate most of the other functions of the membrane. Membrane proteins can be associated with the lipid bilayer in different ways
What is the glycocalyx?
The cell coat - made up of oligosaccharide and polysaccharide side chains on the outside of the plasma membrane
List the functions of the plasma membrane (plasmalemma)
- Selective permeability - Transport of materials along cell surface - Endocytosis - Exocytosis - Intracellular adhesion - Intracellular recognition - Signal transduction
Describe rough endoplasmic reticulum
Has ribosomes. Proteins made end up in cisternae
Describe smooth endoplasmic reticulum
No ribosomes. Found in liver, mammary gland (lipid biosynthesis), ovary, testis, adrenal gland (steroidogenesis)
Describe endoplasmic reticulum membrane
Continuous and encloses a single lumen
Outline the process of protein synthesis and secretion
PIC
Define “limit of resolution”
The minimum distance at which two objects can be distinguished
Explain why electron microscopes are capable of finer resolution than light microscopes
Wavelengths of visible light: violet is 0.4um, deep red is 0.7um. Wavelengths of electrons at 100,000V acceleration is 0.004nm. Theoretical limit of resolution for light microscope is 0.2um, for electron microscope is 0.002nm
Compare the membranes of prokaryotes and eukaryotes
- Prokaryotes have an external membrane but no internal membranes. All the biochemical processes of the cell occur in the same compartment. - Eukaryotic cells are compartmentalised by internal membranes
Outline the contents of a eukaryotic cell
PIC
How many different proteins does a typical mammalian cell synthesise?
More than 10,000
Describe the phospholipid bilayer
Phospholipids, which make up cell membranes, are amphipathic. The phospholipid bilayer forms a relatively impermeable barrier to most water-soluble molecules. The protein molecules “dissolved” in the lipid bilayer mediate most of the other functions of the membrane. Membrane proteins can be associated with the lipid bilayer in different ways
What is the glycocalyx?
The cell coat - made up of oligosaccharide and polysaccharide side chains on the outside of the plasma membrane
List the functions of the plasma membrane (plasmalemma)
- Selective permeability - Transport of materials along cell surface - Endocytosis - Exocytosis - Intracellular adhesion - Intracellular recognition - Signal transduction
Describe rough endoplasmic reticulum
Has ribosomes. Proteins made end up in cisternae
Describe smooth endoplasmic reticulum
No ribosomes. Found in liver, mammary gland (lipid biosynthesis), ovary, testis, adrenal gland (steroidogenesis)
Describe endoplasmic reticulum membrane
Continuous and encloses a single lumen
Outline the process of protein synthesis and secretion
See image
Describe the Golgi apparatus
Vesicles from RER travel from cis face (receiving face - shorter and more C-shaped) to trans face. Golgi apparatus functions to modify, sort, concentration and package (into secretory vesicles) proteins synthesised on the RER
Describe lysosomes
Generated by the Golgi apparatus and contain many hydrolytic enzymes, which break down anything that is defunct in the cell. Lysosome’s glycocalyx means it itself is not broken down. Lysosome fuses with material requiring digestion
Describe peroxisomes
Present in liver and kidney cells. They detoxify (oxidise) a number of molecules including alcohol, phenols, formic acid and formaldehyde. RH2 + O2 -> R + H2O2. R’H2 + H2O2 -> R’ + 2H2O
What is the primary function of mitochondria?
Generation of potential energy (ATP) by oxidative phosphorylation
Describe the structure of a mitochondrion
- Matrix: hundreds of enzymes and mitochondrial DNA genome - Inner membrane: folded into cristae (in steroidogenic cells cristae are tubular). Enzymes for oxidation reactions of respiratory chains - impermeable to small ions. ATP made. - Outer membrane: permeable by all molecules of
Describe some of the features of mitochondria
- Site of cell’s energy production - More abundant in muscle cells - Contain own genetic information so can divide - Female lineage
What is endosymbiosis theory?
Ribosomes, genetic information and division of mitochondria more closely related to bacteria than humans
Describe actin filaments (microfilaments)
5-9nm diameter, mainly cortical in distribution. Found around edge of epithelial cells. Very often not seen under electron microscope unless specifically stain for it
Describe intermediate filaments
Have a diameter of about 10nm. Several different proteins belong to this family. Common in epithelial cells. Form tough supporting meshwork in cytoplasm. Also found just beneath inner nuclear membrane forming the nuclear lamina
Describe microtubules
Long hollow cylinders made of the protein tubulin. Found at sites where structures are more (i.e. nerve fibres, mitotic spindle, cilia and flagella). Diameter 25nm. Originate from centrosome. “9+2” arrangement in cilium or flagellum. 9 doublets in circle around edge + 2 in centre. Dynein arms reach out. Beats at 12Hz
What is an obligate cell parasite?
Cannot survive without a particular function
Are all agents of infections microbes?
No, vast majority have no symptoms
What is a prion?
Infectious agent, composed entirely of protein, presumed to be cause of TSEs
Give the relative sizes of different infectious agents
Metre -> worms -> mm (10^-3 m) -> Protozoa and yeasts -> um (10^-6 m) -> bacteria -> nm (10^-9 m) -> virus uses -> Å (10^-10 m) -> prions
In tissues, the classic view is that they’re “sterile”, meaning no living microbes are present. Is this the case?
No, there are very low levels but these are dealt with. All epithelial constantly in contact with microbes. Stomach thought it be completely sterile because of acid, but not the case. Preparation and staining method can five misrepresentation
What does haematoxylin do?
Stains acidic components of cells purple/blue e.g. nucleolus (RNA), chromatin (DNA)
What does eosin do?
Stains basic components of cells pink e.g. most cytoplasmic proteins, extracellular fibres
Why don’t we see bacteria at stomach’s epithelial surface in an electron micrograph?
- Stain poorly with H and E - Tissue preparation deliberately removes many of them - Insufficient magnification - Routine histology often ignores or deliberately removes ~10^14 microbial cells normally present on and in human body (~10^12 eukaryotic cells) - These microbial cells comprise our microbiomes and have metabolic power and effects at least equivalent to an organ like the liver - Differences in individuals’ microbiomes are linked to health (tissue differentiation) and diseases such as obesity, diabetes and psoriasis
Describe the special stains and microscopy techniques we need to see microbes
- Gram stain allows us to detect and begin to classify most bacteria - Acid fast stains allow us to detect the bacterial causes of tuberculosis and leprosy - Both these staining methods are applied millions of times every day to help in diagnosis and treatment of infection
Describe the process of the Gram stain
Positively charged Crystal violet binds to negatively charged cell components. Iodine forms large molecular complexes with Crystal violet. Acetone or methanol extract complexes through Gram-negative but not Gram-positive bacterial cell wall. Red dye used to stain unstained Gram-negative cells. Difference in extraction reveals a fundamental and medically important feature in bacteria: the bacterial cell envelope.
Give the results of the Gram stain
- Gram positive = purple -> single membrane surrounded by thick peptidoglycan layer - Gram negative = pink -> thin layer of peptidoglycan between two membranes
Describe bacterial structure
- Shape: cocci, rods/bacilli, coccobacilli - Variations: curved, spiral, filamentous - Internal structures: spores, inclusion granules - External structures: fimbriae/pili, flagellae, capsule - The cell envelope
What are other cell envelope types not visualised with Gram stain?
- Mycobacteria: Acid Fast Stain - Auramine: fluorescent, Ziehl-Neelsen - bright field stains - Mycoplasmas: no peptidoglycan - Too small: treponemes, rickettsia, chlamydia
What are Acid Fast Stains?
Smears for Acid Fast Bacilli (AFB). Rapid but relatively insensitive. Positive AFB smear = infective patient
Why are cell walls of clinical importance?
- Detection and diagnosis via Gram and Acid Fast stains - Endotoxin effects (Gram negative LPS) - Target for antibiotics, as human cells don’t have cell walls: beta-lactams (penicillins and cephalosporins), glycopeptides, Isoniazid (TB)
What is an obligate cell parasite?
Cannot survive without a particular function
Are all agents of infections microbes?
No, vast majority have no symptoms
What is a prion?
Infectious agent, composed entirely of protein, presumed to be cause of TSEs
Give the relative sizes of different infectious agents
Metre -> worms -> mm (10^-3 m) -> Protozoa and yeasts -> um (10^-6 m) -> bacteria -> nm (10^-9 m) -> virus uses -> Å (10^-10 m) -> prions
In tissues, the classic view is that they’re “sterile”, meaning no living microbes are present. Is this the case?
No, there are very low levels but these are dealt with. All epithelial constantly in contact with microbes. Stomach thought it be completely sterile because of acid, but not the case. Preparation and staining method can five misrepresentation
What does haematoxylin do?
Stains acidic components of cells purple/blue e.g. nucleolus (RNA), chromatin (DNA)
What does eosin do?
Stains basic components of cells pink e.g. most cytoplasmic proteins, extracellular fibres
Why don’t we see bacteria at stomach’s epithelial surface in an electron micrograph?
- Stain poorly with H and E - Tissue preparation deliberately removes many of them - Insufficient magnification - Routine histology often ignores or deliberately removes ~10^14 microbial cells normally present on and in human body (~10^12 eukaryotic cells) - These microbial cells comprise our microbiomes and have metabolic power and effects at least equivalent to an organ like the liver - Differences in individuals’ microbiomes are linked to health (tissue differentiation) and diseases such as obesity, diabetes and psoriasis
Describe the special stains and microscopy techniques we need to see microbes
- Gram stain allows us to detect and begin to classify most bacteria - Acid fast stains allow us to detect the bacterial causes of tuberculosis and leprosy - Both these staining methods are applied millions of times every day to help in diagnosis and treatment of infection
Describe the process of the Gram stain
Positively charged Crystal violet binds to negatively charged cell components. Iodine forms large molecular complexes with Crystal violet. Acetone or methanol extract complexes through Gram-negative but not Gram-positive bacterial cell wall. Red dye used to stain unstained Gram-negative cells. Difference in extraction reveals a fundamental and medically important feature in bacteria: the bacterial cell envelope.
Give the results of the Gram stain
- Gram positive = purple -> single membrane surrounded by thick peptidoglycan layer - Gram negative = pink -> thin layer of peptidoglycan between two membranes
Describe bacterial structure
- Shape: cocci, rods/bacilli, coccobacilli - Variations: curved, spiral, filamentous - Internal structures: spores, inclusion granules - External structures: fimbriae/pili, flagellae, capsule - The cell envelope
What are other cell envelope types not visualised with Gram stain?
- Mycobacteria: Acid Fast Stain - Auramine: fluorescent, Ziehl-Neelsen - bright field stains - Mycoplasmas: no peptidoglycan - Too small: treponemes, rickettsia, chlamydia
What are Acid Fast Stains?
Smears for Acid Fast Bacilli (AFB). Rapid but relatively insensitive. Positive AFB smear = infective patient
Why are cell walls of clinical importance?
- Detection and diagnosis via Gram and Acid Fast stains - Endotoxin effects (Gram negative LPS) - Target for antibiotics, as human cells don’t have cell walls: beta-lactams (penicillins and cephalosporins), glycopeptides, Isoniazid (TB)
What are the different types of bacterial growth?
- Broth turbidity (planktonic) - Colonies ^both above are unrepresentative of bacterial growth in real life) - Biofilms
Describe bacterial growth in broth
Replication by binary fission (double in size and divide in two asexually) giving rise to: Lag, Exponential (log) and Stationary Phases of growth recognised in broth
Describe colonies
Arise from a single cell, grow on agar
Describe Biofilms
Formation - bulk fluid: attachment -> colonisation -> growth. 10^9 bacteria per gram. Responses to antibiotics different to colony or broth growth
What is the clinical importance of bacterial growth?
- Broth turbidity: sensitive detection, fluid-filled cavities - Colonies: easy identification and counting - Biofilms: medical devices (must be removed or get infected) - Speed: rate at which disease develops, time to diagnosis
What are the requirements for bacterial growth?
- Specific energy source 2. Specific building blocks 3. Specific atmosphere (Tells us what might be a source of infection) 1+2+3 = growth environment / habitat / reservoir
What is the growth atmosphere?
- Aerobes - Facultative organisms - Anaerobes (extreme steps to culture)
Give examples of gram positive and negative cocci and bacilli
- Gram positive cocci: Staphylococcus, Streptococcus - Gram negative cocci: Neisseria - Gram positive bacilli: Clostridium*^ - Gram negative bacilli: Escherichia, Salmonella, Heliobacter, Pseudomonas, Legionella, Bacteroides* *= anaerobic ^= spore-forming
Compare prokaryotes and eukaryotes
See image
What is infection?
The establishment of an organism on or in a host associated with its multiplication and damage to or dysfunction of the host specifically related to that organism or its product
What are the causes of infection?
- Pathogenic microbes (Koch’s postulates) - Viruses - Prions - Bacteria - (Archaea) - Protozoa - Fungi - Helminths - (Arthopods? - infestation)
Why do particular individuals get particular infections?
Encounter, virulence vs host resistance, innate and adaptive immunity
What influences the outcome of infection?
Encounter dose and route, virulence vs host resistance, innate and adaptive immunity, timely diagnosis and treatment
What are the limits of resolution of scanning and transmission electron microscopes?
SEM ~ 10nm TEM ~ 2nm
