Cell Structure Flashcards
2.1.1
What are the uses of stains?
- Coloured chemicals that bind to molecules in a specimen.
- Increases contrast: different components of the cell take up different amount of stains
- Details within the cell can be seen
What are examples of stains?
- Methylene blue: stains living cells blue
- Iodine solution : stains plant cells/ starch grains blue black
- acetic orein : staining nuclei and chromosomes red
- light green : stains plant and cell walls green
What is differential staining?
When you use one or more chemical stains . Different stains bind to
specific structures this can be used to show contrast between organelles, tissues and organelles
What is magnification?
Factor by which the image is larder than the actual specimen
What is resolution?
- The ability to distinguish between two separate point that are very close together
- More can be seen with a higher resoltion
- resoltion gives clarity
What is a laser scanning confocal mircosopes?
- A laser that scans specimen either on or below the surface which are usually tagged with fluoresent dyes and once scanned it gives of fluoresent light
- The light is focused through a pinhole
- Laser scanning microscopes can scan specimens at different depth
- Multiple images produces can be combined by a computer to produces a 3d Image
What are the advantages of a laser scanning confocal microscope?
- Can view live specimen
- high resolution + high contrast 3d image
- view cells as well
- focus on structures at different depths
What are the uses of a laser scanning confocal microscopes?
- Observe fungal filaments within the cornea of a patient with fungal corneal infection
- Used during endoscopy
What is a Scanning electron mircosope ?
- Coated in gold and dried
- The beam moves back and forth across the specimen. Electrons knocked off the specimen is detected which produces a image.
- 3d image
- Useful for the study of sufaces of objects
What is a transmission electron microscope ?
- Sample is thinned thinly
- Coated in hardened resin
- electrons Passed through the specimen where some are obsorbed or passed through to the other side .
- Denser parts absord more electrons
- 2d black and white image
- Internal structure of objects + cells
What is the maximum magnification and resolution of a SEM?
- Magnification: x200,000
- Resolution : 2nm
What is the maximum magnification and resolution of a TEM?
- Magnification: x2,000,000
- Resolution : 0.2nm
What is the maximum magnification and resolution of a Light microscope?
- Magnification: x2000
- Resolution : 200nm
Describe how light mircoscopes work?
- Lenses focus rays of light and magnify the view of a thin slice of specimen
- Different structure absord different amount and wavelenths of light
- Reflected light is transmitted to the observer via the onjective lens and eyepiece
Describe how a TEM works
- Pass a high energy beam of electrons through a thin slice of specimen
- More dense structures appear darker since the absorb electrons
- Focus image onto fluoresent screen or photographic plate using magnetic lenses
Describe how a SEM works
- Focus a beam of electrons onto a specimens surface ising electromagnetic lenses
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate
Describe how a laser scanning confocal mircoscope works
- Focus a laser beam onto a small area on a sample’s surface using objective lenses
- Fluorophores in the sample emit photons
- Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order
How should you recorded a microscope drawing?
- Use a pencil
- Sharp lines
- no shading
- Scale bar
- Label visible structures
Equation for magnification:
Magnification = Image size / actual size
Describe the structure and of the nucleus
- Surronded by a Nuclear envelope - semipermeable double membrane
- Nuclear pores - allow substances to enter and exit the nucleus
- Nucleolus - dense and made of RNA and produces proteins, and assembles ribosomes
What is the function of the nucleus ?
- Contains DNA that codes for proteins
- Contains chromatin which condenses into chromosomes
- The nuclear pores allow the exit mRNA for protein synthesis
- The nuclear envelope keeps reactions separate from the cytoplasm
- The nucleolus manufactures ribosomes
What is the structure and function of the Endoplasmic reticulum?
- Cisternae - network of tubules and flattened sacs extends from the cell membrane and connects to the nuclear envelope and allows transport within cells
- Rough ER - Synthesise and transports proteins ( many ribosomes)
- Smooth ER - Synthesise and transports lipds and steriods
What is the structure and function of the ribosomes?
- Formed of proteins and RNA
- Has a **large subunit and a small subunit **which binds to mRNa with there mRNA binding site
- Protein synthesis
- 22nm / 80s - eukaryotic cells
- 18nm / 70s - prokaryotic cells
What is the structure and function of Golgi apparatus ?
- Planar stack of membrane- bound , flattened sacs, cis face aligns with rough ER. Molecules are processed in cisternae . Vesicles bud off trans face via exocytosis
- It modifies and packages proteins for export
- Synthesises glycoproteins
- secretory vesicles which are produced my the Golgi apparatus will fuse with the cell surface membrane to release hormones or enzymes from the cell
What is the structure and function of Lysosomes?
- Vesicles which containa hydrolytic enzymes enclosed in a membrane
- Isolates potentially harmful enzymes from the cell
- Breaks down matertial ingested by phagocytes
- Breaks down old organelles
- Breaks down cells when the die
What is the structure of mitochondrion?
- Surronded by a double membrane
- Folded inner membrane which forms cristae - site of electron transport chain
* Fluid matrix - contains mitochondrial DNA , enzymes, lipids and proteins - a lipid
What is the structure of a chloroplast?
- Double mebrane - isolates photosynthesis
- Thylakoids - flattened discs stack to form grana ( increase SA for photosynthesis with chlorophyll)
- Stroma - Fluid filled stacks
- Strach grains - carbohydrate store
- Small ribosomes - protein synthesis
- DNA - codes for proteins
- Lipids droplets - for membranes
What is the function of mitochandria and chloroplasts?
Mitochondria: site of aerobic respiration to produce ATP
Chloroplasts: site of photosyntheis to convery solar energy to chemical energy
What is the structure and function of centrioles?
- Composed of 9 set of 3 mircotubles
- 2 in animal cells , right angles to each other and adjacent to the nucleus
- Migrate to opposite poles of a cell during prophase and form spindle fibres during nuclear division to control the separation of chromatids and chromosomes
What is the structure of a cytoskeleton?
- Microtubles - fine hollow tubes
- Microfilaments - small solid protein strands
- intermediate filaments - more stable protein strands
What is the function of the cytoskeleton?
- Support cell organelles postion
- Enable movement of organelles, vesicles and proteins
- Strengthen cell and maintain shape
- Allows cell movement
What is the structure and function of cilia + flagella
2 central mircotubles surronded by 9 pairs
Cilia -
* Hairlike/ threadlike projections on eukaryotic cells
* Moves back and forth to remove foreign substances ( bronchi and trachea waft mucus towards the throat
Flagella
* Longer whip-like projections
* Flagella and undulipodia are mainly used for movement
What is the structure and function of the vacuole ?
- Cell sap contained with the tonoplast
- Maintains turgor for support
- Storage for dissolved minerals, sugars, pigments etc
what is the structure of the Plant cell wall?
- Made of cellulose secreted by the living cell
- Rigid and permeable
- Plasmodestmata - form apart of apoplast pathwat to allow molecules to pass between cells
- Middle lamella seprates adjacent cell walls
similarites between a eukaryotic cell and prokaryotic cell
- cell membrane
- cytoplasm
- ribosomes
What is present in a prokaryotic
cell?
Always present:
* ribosomes
* cell wall
* cytoplasm
* Nucleoid area
* circular DNA
* Plasma membrane
Not always present
* Piii - attachment to other cells
* Plasmids - circular DNA
* Capsule - extra protection
* Mesosome - aerobic respiration and formation cell walls
* Infoldig of plasma membrane -
* flagella ( flagellum )- movement
The differences between a eukaryotic cell and a prokaryotic cell
Prokaryotic cell:
* small (0.1-0.5 um) + unicellular
* cirular DNA not associated to proteins
* No membrane bound organelles
* no nucleus
* cell wall (Made of murein or peptidoglycan)
* Small ribosomes - 70s
* Capsule , sometimes plasmids and cytoskeleton
Eukaryotic cell:
* Larger ( 10 - 100um) + often multicellular
* nucleus + organelles
* chromosomes with histone proteins
* Ribosomes (80s)
* no cell wall (only in plant cells )
* no capusle + plasmids
* always cytoskeleton
What is division of labour?
- Proteins are synthesised on the ribosomes bound to the endoplasmic reticulum
- They then pas into the cisternae and are packaged into transport vesicles
- Vesicles containing the newly synthesised proteins more towards the Golgi apparatus via transport function of the cytoskeleton
- The vesicles fuse with the cisface of the Golgi apparatus and the proteins enter. The proteins are structurally modified before leaving the Golgi apparatus in the vesicles from its transface.
- Secretory vesicles carry proteins that are to be released from the cell. The vesicles move towards and fuse with the cell surface membrane , releasing their contents by exocytosis . Some vesicles form lysosomes these contain enzymes for use in the cell
