2.1 Cell structure Flashcards
What is a microscope?
Instrument that allows an object to be magnified
When was the first light microscope developed?
16th to 17th century
When was the first cell observed, by who?
1665, Robert Hooke
When was the first living cell observed?
1674
When was the first nucleus observed, by who?
1833, Robert Brown
When was the universal cell theory made, what is it?
1873, “all living things are composed of cells and cell products”
How does a light microscope work?
Two lenses, objective and eyepiece. Light passes through the specimen
What is magnification?
How much bigger the image is than the actual object
What is resolution?
The ability to distinguish between two objects
What is magnification and resolution of a light microscope?
Magnification up to 2000
Resolution of 200nm
What is the equation for magnification?
M = Image size / Actual size
What is the difference between dry and wet mounts, examples?
Dry mount - thin small samples are placed on the slide with a coverslip on top. Eg hair/pollen
Wet mount - Specimens are suspended in liquid, coverslip is placed at an angle. Eg aquatic samples
What is a squash slide, example?
Wet mount, a soft sample is squashed between two slides, creating a thin layer of cells. Eg Root tips
What is a smear slide, example?
A wet mount, the edge of a different slide is used to smear a sample, creating a thin, even layer of cells. Eg blood
Why is it important to stain light microscope samples?
Increase contrast between organelles, by being absorbed more or less by different components
How to stain a slide?
Sample is allowed to air dry, then passed through a flame, the specimen is now adhered to the slide, and will take up the stain
What are crystal violet and methylene blue attracted to?
Negatively charged materials in cytoplasm
What are Congo red and Nigrosin attracted to?
Repelled by negatively charged cytosol, so dye stains outside of cells
What does differential staining do?
Distinguishes between two types of organisms that would otherwise be harder to identify
What is the risks of staining?
Many stains are an irritant
How should scientific drawing be drawn?
Title, magnification, sharp pencil, white unlined paper, big drawing, smooth continuous lines, no shading, clearly defined structures, proportions are correct, label lines do not cross and do not have arrow heads and are parallel to the top of a page, with a ruler
What is an eyepiece graticule?
Glass disk with a scale of 1 to 100, which has no units. The relative size of the divisions increase in magnification, but it remains unchanged
What is a stage micrometer?
Microscope slide with a scale in micrometers
How does a transmission electron microscope work?
A beam of electrons passed through the specimen
What is the magnification/resolution of a TEM?
x500,000, 0.5nm
How does a scanning electron microscope work?
A beam of electrons is sent across the surface of a specimen
What is the magnification/resolution of a SEM?
x500,000, 3-10nm
Compare light microscopes and electron microscopes.
Light
Small/portable
Simple sample prep
Up to x2000, 200nm
Specimens are living or dead
Electron
Expensive
Large
Complex sample prep, distorts material
Vacuum needed
Black and white images
x500,000,
Specimens are dead
How does a laser scanning confocal microscope work?
Moves a spot of focused light over a specimen, fluorescence from dyed areas, which are filtered through a pinhole aperture. Only light from close is sharp, from far away it is blurry, but these both have the same focal plane, so it is not blurry
What is the advantage of laser scanning?
Non invasive, used in development of new drugs
What is a fluorescent tag? What is an advantage?
Glowing under UV light. Allows for more precision
What is a cell?
Basic unit of all life
What is the difference between prokaryotic and eukaryotic?
Prokaryotic - single celled organisms with no membrane bound organelle
Eukaryotic - multicellular organisms with membrane bound organelle
Describe the structure of the nucleus.
● Surrounded by a nuclear envelope
● Nuclear pores allow substances to enter/exit.
● Dense nucleolus
Describe the function of the nucleus.
● Contains DNA in the form of chromosomes.
● Controls cellular processes
Describe the function of the nucleolus.
Producing ribosomes, composed of proteins and RNA, which is used to make rRNA and combined with proteins to make ribosomes
Describe the structure and function of the endoplasmic reticulum (ER).
● Cisternae: network of tubules & flattened sacs extends from cell membrane & connects to nuclear envelope:
● Rough ER: many ribosomes attached for protein synthesis & transport.
● Smooth ER: lipid synthesis.
Describe the structure and function of the Golgi apparatus.
● Modifies & packages proteins for export.
● Synthesises glycoproteins.
Describe the structure and function of ribosomes.
Formed of protein & rRNA.
Have large subunit which joins amino acids & small subunit with mRNA binding site.
Protein synthesis.
Describe the relationship between the organelles involved in the production and synthesis of proteins.
The ribosomes that synthesise proteins are attached to the rER. Vesicles transport proteins to the cis side of the Golgi apparatus, which modifies proteins for secretion via (secretory) vesicles.
Describe the structure of a mitochondrion.
● Surrounded by double membrane.
● Folded inner membrane forms cristae
● Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins.
Describe the structure of a chloroplast.
● Double membrane.
● Thylakoids: flattened discs stack to form grana, containing chlorophyll
● Lamellae: tubes attach thylakoids in adjacent grana.
● Stroma: fluid-filled matrix.
State the function of mitochondria and chloroplasts.
● Mitochondria: site of aerobic respiration to produce ATP.
● Chloroplasts: site of photosynthesis to convert solar energy to chemical energy.
Describe the structure and function of a lysosome.
Hydrolytic enzyme removes waste products.
Describe the structure and function of a plant cell wall.
● Made of cellulose (support plant)
● Plasmodesmata form pathway to allow molecules to pass between cells.
● Middle lamella separates adjacent cell walls.
Describe the function and structure of a permanent vacuole
Selectively permeable membrane called tonoplast, cell sap contained inside
Maintains turgor and rigid shape of cell
What are bacterial and fungal cell walls made of?
Bacteria: peptidoglycan (murein)
Fungi: chitin
Describe the structure and function of centrioles.
● Spherical group of 9 microtubules arranged in a 9+2 arrangement
● Located in centrosomes.
● Migrate to opposite poles of cell during prophase & spindle fibres form between them.
Describe the structure and function of flagella.
● Made of the protein flagellin.
● Rotates to move (unicellular) organism.
Describe the structure and function of pili.
● Protrusions on eukaryotic cells.
● Move back and forth rhythmically to sweep foreign substances / movement.
Why is the cytoskeleton important?
● Provides mechanical strength.
● Aids transport within cells.
● Enables cell movement.
Compare eukaryotic and prokaryotic cells.
Both have:
● Cell membrane
● Cytoplasm
● Ribosomes
Contrast eukaryotic and prokaryotic cells.
Prokaryotic:
0.5-5µm
DNA is circular with no proteins, in the cytoplasm
Cell division occurs by binary fission - no spindle involved
70s ribosomes
No membrane bound organelles
Cell wall is made from peptidoglycan and murein
Eukaryotic:
100µm
DNA is associated with proteins, and formed into proteins (linear)
Cell division occurs by mitosis or meiosis involves spindle fibres (Separate chromosomes)
80s ribosomes
Membrane bound organelles, and not membrane bound organelles
Cell wall is present in plants (cellulose), fungi (chitin)
Describe the structure and function of the cell-surface plasma membrane.
‘Fluid mosaic’ phospholipid bilayer with extrinsic & intrinsic proteins embedded.
● Acts as a barrier
● Semi permeable
● Involved in cell signalling / cell recognition.
Explain the role of cholesterol, glycoproteins & glycolipids in the cell-surface membrane.
● Cholesterol: steroid molecule connects phospholipids & reduces fluidity.
● Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together.
● Glycolipids: cell signalling & cell recognition.
2.1.1
How to prepare a stained temporary mount of onion epidermis
Use the forceps to peel of a thin layer of onion epidermis
Place onto the centre of the microscope slide, not folded over
Add two drops of iodine solution to cover
Use a mounted needle to lower coverslip at 45 degrees
2.1.1
How to prepare a stained temporary mount of cheek cells
Use a marker to put a small dot in the middle of the bottom of the slide
Use a cotton bud to remove cells from the inside of the cheek
Rub the cotton bud on the centre of the slide
Dispose of cotton bud in beaker of disinfectant
Add two drops of methylene blue, use a mounted needle to lower a coverslip at 45 degrees
2.1.1
How to calibrate arbitrary eyepiece graticule measurement with a stage micrometer
Lowest power objective lens
Clip stage micrometre onto stage
Focus, move so that eyepiece graticule and stage micrometre are lined up
Record how many eyepiece graticule units (EPGUs) correspond to 1000 micrometres (micrometers/EPGUs)
Repeat for other magnifications
2.1.1
Calculating specimens size from EPGU
Replace stage micrometer with specimen
line up a suitable cell with eyepiece graticule scale
Count how many EPGUs fit into the cell
Convert using conversion number
