2.2 - Basic components of living systems Flashcards
What is the formula to calculate magnification?
magnification = size of image / actual size of object
Why are cells stained before being viewed with a light microscope
staining increases contrast between different cell components, makes them visible and allows them to be identified
What is an eyepiece graticule?
a glass disc that fits on top of the eyepiece lens that is marked with a fine scale from 1 to 100
What is a stage micrometer?
a microscope slide with a very accurate scale in micrometers engraved on it
What is magnification?
how many time larger an image is than the actual size of the object being viewed
What is resolution?
the ability to see individual objects as separate entities
What is the function of the nucleus?
controls the metabolic activities of the cell as it contains genetic information stored in the form of DNA
What is the nucleolus?
area within the nucleus that is responsible for producing ribosomes
What is the function of mitochondria?
sites of production of ATP in the final stages of cellular respiration
What are vesicles?
membranous sacs that are used to transport materials in the cell
What are lysosomes?
specialised forms of vesicles with hydrolytic enzymes that break down waste materials in cells
What is the role of the cytoskeleton?
controls cell movement, movement of organelles within the cell and provides mechanical strength to the cell
Name three different components of the cytoskeleton
- microfilaments
- microtubules
- intermediate fibres
Give two types of extension that protrude from some cells
- flagella (whip like protrusions)(9+2 microtubule arrangement)
- cilia ( tail like protrusions)
What is the endoplasmic reticulum (ER)?
a network of membranes enclosing flattened sacs called cisternae
What are the functions of the two types of ER?
smooth ER - lipid and carbohydrate synthesis, and storage
rough ER - synthesis and transport of proteins
What is the function of the Golgi apparatus?
plays a part in modifying proteins and packaging them into vesicles
What is cell theory
- both plant and animal tissue are composed of cells
- cells are the basic unit of all life
- cells only develop from existing cells
What are the 4 ways to prepare a sample/slide for light microscopy
Dry mount:
- solid specimens viewed whole or cut into thin slices (sectioning)
- specimen is placed on slide and cover slip is placed on top
Wet mount:
- specimens are suspended in a liquid such as water or an immersion oil
- the cover slip is placed at an angle
Squash slides:
- a wet mount is prepared, then the cover slip is gently pressed down with another slide
Smear slides:
- edge of a slide is used to smear the sample on a slide
- a cover slip is placed over the slide
How does a compound light microscope work?
The objective lens produces a magnified image which is then magnified by the eyepiece lens
What is 1mm in micrometers
1,000 µm
What is 1mm in nanometers
1,000,000 nm
Crystal violet/ methylene blue staining technique
- positively charged dye
- attracted to negatively charged materials in cytoplasm
- stains cell components
Nigrosin/ congo red staining technique
- negatively charged dye
- repelled by negatively charged cytosol
- stays outside of the cell, leaving cells unstained
(negative staining)
Gram staining technique
Used to separate bacteria into gram-positive and gram-negative
- crystal violet dye is applied, then iodine to fix the dye before it is washed off with alcohol
- Gram-positive bacteria retains dye so appears blue or purple
- gram-negative bacteria have thinner cell walls, so loses the dye (counter-stained by safranin so appears red)
- gram-positive bacteria is susceptible to penicillin
Acid-fast staining techique
Used to differentiate species of mycobacterium from other bacteria.
-Lipid solvent is used to carry carbolfuchsin dye into cells
- cells washed with dilute acid-alcohol solution
- mycobacterium retain stain and appear red
- other bacteria lose the stain and appear blue
How to use graticules to calibrate a light microscope
- line up the eyepiece graticule with the stage micrometer
- count the number of eyepiece divisions between the points of coincidence
- calibration factor = number of micrometers / number of eyepiece divisions
How does a transmission electron microscope work
A beam of electrons is transmitted through a specimen and focused to produce an image. Has the best resolution with a resolving power of 0.5nm
How does a scanning electron microscope work
A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected. 3D images of surfaces are produced, with a resolving power of 3-10nm
What are the similarities and differences between scanning electron microscopy and transmission electron microscopy
Both have a magnification of x500,000, produce black and white images and artifacts
SEM:
- electrons sent across surface
- reflected electrons detected
- lower resolution power
- 3D images
- little sample preparation
- samples can be any thickness
TEM:
-electrons transmitted through specimen
- shows internal structure
- higher resolution power
- 2D images
- extensive sample preparation
- thin sample
The creation of artifacts in microscopy
Light microscopy:
- bubbles trapped under the coverslip
Electron microscopy
- loss of continuity of membranes
- distortion of organelles
- empty spaces in the cytoplasm of cells
What are artifacts?
A visible structural detail caused by the processing of the specimen and not a feature. Experience enables scientists to distinguish between an artefact and a true structure
Laser scanning confocal microscopy
A single spot of focused light is moved across a specimen (point illumination). This causes fluorescence from the components labelled with a fluorescent ‘dye’. The emitted light from the specimen is filtered by a pinhole aperture. Only light radiated from very close to the focal plane is detected, because this is the distance that gives the sharpest focus. Very thin sections of specimen are examined and very high resolution images can be obtained.
Atomic force microscopy
- gathers information about a specimen by ‘feeling’ its surface with a mechanical probe
- create 3D images of surfaces
- very high resolution (0.1nm) so atomic level information is gained
- living systems can be examined
- when the probe is brought close to surfaces, forces between the specimen and the probe causes deflections, detected by a laser beam
- fixation and staining not required
- used by pharmaceutical companies
Fluorescent tags in microscopy
Using antibodies with fluorescent ‘tags’, specific features can be targeted and then studied by confocal microscopy. Green fluorescent protein (GFP) = produced by jellyfish emits green light. Can be used to study the production and distribution of proteins in cells and organisms. The gene for this protein has to be isolated and then attached through genetic engineering to the genes coding for the proteins
Super resolved fluorescent microscopy
Combining many very small images or superimposing many images with a normal resolution to create a very high resolution image. A way of viewing living cells with a very high resolution as electron microscopes cannot be used to examine living cells
Sample preparation for electron microscopes
The inside of an electron microscope is a vacuum (so electron beams move in straight lines) so samples have to be prepared in specific ways:
- fixation using chemicals or freezing prevents decomposition
- staining with heavy metals creates contrast
- dehydration with solvents prevents vapourisation of the water in the vacuum
What is the function of ribosomes
made of rRna molecules and either free floating or attached to the rough ER
site of protein synthesis
What are microfilaments
- flexible contractile fibres formed from the protein actin
- responsible for cell movement and contraction (e.g. in cytokinesis)
What are microtubules
- formed from globular tubulin
- rigid
- forms a scaffold-like structure and tracks for the movement of organelles
- determines cell shape
- makes up spindle fibres
Intermediate fibres
- formed from intermediate filament proteins
- maintains cell integrity and provides mechanical strength
How do cells move using the cytoskeleton
(treadmilling)
Actin filaments change lengths with the addition and removal of monomer subunits. Subunits are added at a faster rate at the plus end, so the filaments therefore increase in length faster in one particular direction
cell surface membrane
selectively permeable plasma membrane, controls which substances enter and exit the cell
Centrioles
- Component of the cytoskeleton
- Made up of microtubules
- Forms centrosomes which control spindle fibres
- Plays a role in positioning flagella and cilia
Cytoskeleton
Network of fibres that gives shape and stability to cells. Holds organelles in place, controls cell movement and movement within the cell
Cytoplasm
Internal fluid of cells. Composed of cytosol (water, salts and organic molecules), organelles and cytoskeleton
What happens to proteins after synthesis?
- proteins are synthesised on the ribosomes bound to the rough ER
- proteins pass into the cisternae and are packaged into transport vesicles
- vesicles are moved by the cytoskeleton into the Golgi apparatus
- vesicles fuse with the cis face of the apparatus and proteins enter
- the proteins are structurally modified before leaving the apparatus in vesicles from the trans face
- secretory vesicles carrying the proteins move towards and fuse with the plasma membrane, releasing them by exocytosis
Differences between plant and animal cells
Plant:
- cell wall
- regular shape
- chloroplasts
- permanent vacuole
- larger
Animal:
- no cell wall
- irregular shape
- flagella and centrioles
- smaller
- not permanent smaller vacuoles
Vacuoles
(large, permanent)
Membrane lined sacs in the cytoplasm containing cell sap.
Importance in the maintenance of turgor
Membrane is called tonoplast
Selectively permeable, used for storage
Cellulose cell wall
- made from cellulose, a complex carbohydrate
- freely permeable
- gives the plant cell shape
- contents of cell push against wall, making it rigid, supporting the cell and plant as a whole
- acts as a defense mechanism, protecting the cell against invading pathogens
Structure and function of chloroplasts
Responsible for photosynthesis. Found in green parts of plants e.g. leaf.
- double membrane structure
- fluid enclosed called stroma, contains enzymes, DNA, ribosomes and starch granules
- internal network of membranes form flattened sacs called thylakoids, stacked into grana
- grana joined by lamellae
- chlorophyll pigments, large surface area
Prokaryotes
Unicellular cells with no membrane bound organelles. Can be classed into two evolutionary domains; Archaea and Bacteria
Prokaryotic DNA
The structure is fundamentally the same as eukaryotes, but it is packaged differently. Generally they only have one molecule/chromosome of DNA, supercoiled to make it compact and free floating.
- genes are grouped into operons, meaning a number of genes can be switched on or off
Prokaryotic ribosomes
Smaller than those in eukaryotic cells
(relative size is determined by the rate at which they settle in solution)
- prokaryotic ribosomes are 70S, eukaryotic are 80S (associated with forming more complex proteins)
Prokaryotic cell wall
Made from peptidoglycan, a complex polymer formed from amino acids and sugars
Differences in prokaryotic flagella
- thinner than eukaryotic flagella
- do not have 9+2 arrangement
- the energy needed to rotate the filament that forms the flagellum is provided by chemiosmosis, not ATP
- attached to the cell membrane by a basal body and rotated by a molecular motor
Differences between eukaryotic and prokaryotic cells
Prokaryotic:
- bacteria, archaea
- smaller (0.1-10µm)
- no nucleus, circular DNA
- reproduce through binary fission
- unicellular
Eukaryotic:
- plants, animals, fungi
- larger (10-100)µm
- nucleus, linear DNA
- multiple chromosomes wrap round histones to form chromatin
- asexual or sexual reproduction
- unicellular and multicellular
What is calibration and why is it needed
An eyepiece graticule and stage micrometer are used to measure the size of the object when viewed under a microscope
The type of microscope and magnification used can vary significantly so the eyepiece graticule needs to be calibrated each time when measuring objects
