2:1:1 Cell structure Flashcards
What are microscopes
Used to analyse cell components and observe organelles
What are the 3 types of microscope
- Optical/light microscopes
- Electron microscopes
- Laser scanning confocal microscopes
What is magnification
Tells you how many times bigger the image produces is than the real life object
What is resolution
The ability to distinguish between objects that are close together
What are optical/light microscopes
- Use light to form image
- Light causes limited resolution, due to the it being impossible to distinguish between objects closer than half a wavelength of light
- Maximum resolution of 0.2um
- Maximum useful magnification of x1500
- Used to observe eukaryotic cells and certain organelles
What are electron microscopes
- Use electrons to form an image
- This allows for increased resolution and clear images
- Maximum resolution of 0.0002um
- Maximum useful magnification of x1,5000,000
- Used to observe small organelles
What are the 2 types of electron microscopes
- Transmission (TEMs)
- Scanning (SEMs)
What are transmission electron microscopes, as well as their advantages and disadvantages
- Use electromagnets to focus a beam of electrons which is transmitted through the specimen
- Dense areas absorb more electrons so show up as darker
- Advantages: high resolution images, internal structures of organelles shown
- Disadvantages: only used with thin specimens, can’t be used for live specimens, long treatment process for specimens, don’t produce a coloured image
What are scanning electron microscopes, as well as their advantages and disadvantages
- Scan a beam of electrons across specimens
- Beam bounces off the surface, and the electrons are detected and form a 3D image
- Advantages: used of thick specimens, can observe external specimen structure
- Disadvantages: lower resolution than TEMs, can’t use live specimens, don’t produce coloured image
What are laser scanning confocal microscopes, as well as their advantages and disadvantages
- Specimen dyed with fluorescent stains
- Specimens then scanned with a laser beam which is reflected by the dyes
- Advantages: used on thick specimens, show external specimen structure, high resolution images
- Disadvantages: slow process, can cause photo damage to cells
How to prepare a microscope slide with liquid specimen
- Add a drop of sample to the slide with a pipette
- Cover with a coverslip and press to remove air bubbles
- Wear gloves to prevent cross contamination
How to prepare a microscope slide with a solid specimen
- Wear gloves to prevent cross contamination
- Use scissors to cut small sample of specimen
- Use forceps to peel a thin layer of cells from sample
- Apply a stain
- Place coverslip on and press to remove air bubbles
Describe the process of using an optical microscope
- Start with low power objective lens to find what to look for
- Once found increase the power of objective lens
- If the sample dehydrates add a drop of water
- If the image is blurry use the coarse focus and switch to a lower power objective lens
Label a microscope diagram
What is a graticule and what does it help with
- A small disc with an engraved ruler placed into the eyepiece of the microscope
- It must be calibrated by using the scale engraved on the microscope slide (stage micrometer)
- Work out what each graticule unit is worth in um
Why is staining used in light microscopy
- To differentiate between details in cells
- Dyes absorb specific colours of light while reflecting others
- Certain tissues absorb certain dyes, so some specimens are stained with multiple dyes (differential staining)
- Toluidine blue (blue) and phloroglucinol (red/pink) are common stains
Why is staining used in electron microscopy
- TEMs require specimens to be stained to absorb electrons
- The dye shows up in shades of grey
- Heavy metal compounds are used as dyes as they absorb electrons well
- Colours can be added to the image via software
What are the guidelines for microscope drawings
- Drawing must have a title
- Magnification of image must be recorded
- Sharp pencil lines used
- Draw on white paper
- Clear, continuous lines
- No shading
- Should take up more than 50% of the page
- Proper proportions
- Label lines shouldn’t have arrow heads of cross each other, and drawn with a ruler
What is the magnification formula
- Magnification (M)
- Image (I)
- Actual size of specimen (A)
- Every measurement must be in the same unit (magnification had no units)
How to convert from meters to um
What lenses does a optical/light microscope have
- An eyepiece lens (x10)
- 3 objective lenses with increasing magnification
How to calculate total magnification
Total magnification = eyepiece lens magnification x objective lens magnification
How is resolution limited
- By the wavelength of light
- As light passes through a specimen, it’s diffracted, and the longer the wavelength the more it is diffracted
- Light microscopes have long wavelengths so the resolution is worse
What is the cell membrane
- All cells have cell surface membranes
- They control the exchange of of materials between the external and internal cell environment (partially permeable)
- Formed from a phospholipid bilayer
What is the cell wall
- Only in plant cells
- Provide structural support due to cellulose (plants) and peptidoglycan (bacteria)
- Freely permeable
- Pores connecting adjacent cells (plasmodesmata)
What is the nucleus
- Present in all eukaryotic cells
- Double membrane (nuclear envelope)
- Nuclear pores allow molecules (e.g. mRNA) in and out of
- Contains chromatin
- Has a nucleolus as the site of ribosome production
What is mitochondria
- Site of aerobic respiration
- Surrounded by double membrane
- Inner membrane folds to form cristae
- Matrix contains enzymes
- MitochondrialDNA found in the matrix
What are chloroplasts
- Only in plant cells
- Surrounded by double membrane
- Thylakoids stack to form grana which are joined by lamellae
- Site of photosynthesis
- Contain chloroplast DNA
What are ribosomes
- Found in the cytoplasm of rough ER of all cells
- Complex of ribosomal RNA and proteins
- 80S ribosomes are composed of 60S and 40S subunits and are found in eukaryotic cells
- 70S ribosomes are composed of 50S and 30S subunits and are found in prokaryotes
- Site of protein synthesis
What is the smooth endoplasmic reticulum
- No ribosomes on the surface
- Involved in the production, processing and storage of lipids, carbohydrates and steroids
What is the rough endoplasmic reticulum
- Surface covered in ribosomes
- Formed from continuous folds of nuclear envelope membrane
- Processes protein made by ribosomes
What is the golgi apparatus
- Flattened sacs of membrane similar to the SER
- Modifies proteins and lipids before packaging them in golgi vesicles
- Vesicles then transport to required destination
What is the large permanent vacuole
- Only in plant cells
- Surrounded by selectively permeable membrane (tonoplast)
- Filled with cell sap
What are vesicles
- Membrane bound sacs for transport and storage
What are lysosomes
- Specialised vesicles containing hydrolytic enzymes
- Break down waste
- Used by immune system and in apoptosis
Label a plant cell diagram
Label an animal cell diagram
What are the roles of the cytoskeleton
- Strength and support
- Intracellular movement
- Extracellular movement
What are microtubules
- Found in all eukaryotic cells
- Makes up the cell cytoskeleton
- Made of alpha and beta tubulin which combine to form dimers
- Dimers join to form protofilaments
- Protofilaments in a hollow cylinder make a microtubule
- Used for support and intracellular movement
What are microtubules
- Hollow tubes of protofilaments which are made of alpha and beta tubulin
- Makes up the cytoskeleton of eukaryotic cells
- Provide support and intracellular transport
- 25nm diameter
What are microvilli
- Cell membrane projection found on specialised animal cells
- Increase cell surface area
What are cilia
- Hair like projections made of microtubules
- Allow the movement of substances over the cell surface
What are flagella
- Found in specialised cells
- Made of long microtubules
- Provide cell movement (e.g. sperm cells)
What are microfilaments
- Made of the protein actin which forms solid strands
- Breaks down and builds up easily so helps with cell shape and movement
What structures are unique to animal cells
- Centrioles
- Microvilli
What structures are unique to plant cells
- Cell wall
- Large permenant vacuole
- Chloroplasts
- Plasmodesmata
- More regular shape
What would an image of a cell under a light microscope look like
What would a cell look like under a transmission electron microscope
What would a cell look like under a scanning electron microscope
What would a cell look like under a laser scanning confocal microscope
What are organelles
Specialised parts of a cell that carry out a particular function (e.g. production and secretion of proteins)
What are centrioles
- Hollow fibres made of microtubules
- Centrioles form centrosomes which organise into spindle fibres during cell division
Describe the roles of organelles in the production and secretion of proteins
- DNA from the nucleus is copied into a molecule of mRNA
- mRNA leaves through the nuclear pore and attaches to a ribosome on the RER
- The ribosome synthesises a protein from the mRNA
- Protein passes into the lumen of the RER to be processed
- Processed proteins are transported in vesicles to the Golgi apparatus, and fuse with it to release the proteins
- Golgi apparatus modifies the proteins in preparation for secretion
- Modified proteins leave the Golgi apparatus in Golgi vesicles
- The vesicles fuse with the cell surface membrane and proteins are released via exocytosis
Label a cytoskeleton diagram
What are eukaryotic cells
- Animal and plant cells
- Have membrane bound nucleus and chromosomes
- Contain membrane bound organelles
What are plasmids
Small loops of DNA in prokaryotic cells that contain genes that can be passed between cells
What are (slime) capsules
Outer layer that helps protect prokaryotic cells from drying out and from attack by cells of the host cells immune system
Label a prokaryote cell diagram with features that are always and sometimes there
Comparisons or prokaryotic and eukaryotic cells (size, genome, cell division, ribosomes, organelles, cell wall)
