Topic 1 - Cell Structure Flashcards
Define Magnfication
Magnification is the number of times larger an image is compared to the actual size of the object.
Define Resolution
Resolution is the ability of a microscope to distinguish between two seperate points (which are close together) on an image. It is the clarity of an image. Higher resolution = clearer/sharper image
How to convert between milimeters, nanometres, and micrometers?
Millimeters–x1000–>Micrometers–x1000–>Nanometers
Nanometers –÷1000–>Micrometers–÷1000–>Millimeters
What are the 4 Main Microscopes?
1) Light Microscope (LM)
2) Laser Scanning Confocal Microscope (LSCM)
3) Transmission Electron Microscope (TEM)
4) Scanning Electron Microscope (SEM)
Radiation Type of LM, LSCM, TEM + SEM?
LM - Light
LSCM - Light (Lasers are intense beams of light)
TEM - Electron Beams (e.g. usually from a hot metal)
SEM - Electron Beams
Magnification of LM, LSCM, TEM + SEM?
LM - x1500
LSCM - x10,000 (greater than LM)
TEM - x2,000,000
SEM - x200,000
Resolution of LM, LSCM, TEM + SEM?
LM - 200nm
LSCM - 50-100nm (greater than LM)
TEM - 0.1nm (0.05nm - 1.0nm)
SEM - (1.0nm-)20nm
Description of the Image viewed from LM, LSCM, TEM + SEM?
LM - Direct view of 2D, Coloured image
LSCM - Indirect view of 3D, Coloured image
TEM - Indirect view of 2D, Black-and-White image
SEM - Indirect view of 3D, Black-and-White image
Living or Dead specimen used for LM, LSCM, TEM + SEM?
LM - Living specimen
LSCM - Living specimen
TEM - Dead specimen
SEM - Dead specimen
Preparation of specimen for TEM + SEM?
For both of them:
- Chemical Fixation: Adding chemicals to maintain the structure of the sample/specimen to prevent electrons from destroying it in contact.
- Dehydration: A vacuum causes liquid water, which is abundant in biological specimens, to ecapourate immediately. If this occurred, the biological sample would vapourise in front of our eyes.
How does the LM work?
Uses light to illuminate the specimen, and glass lenses to magnify and focus on the specimen.
How does the LSCM work?
Uses laser beams to scan across the specimen, which has fluorescent dyes added to it. When the laser hits the specimen, it gives off fluorescent light which focused through a pinhole onto a detector, which generates an image on the computer. The pinhole, blocks out any out-of-focus light, to produce a clearer/sharper image.
How does TEM work?
Uses electron beams to create an image and electromagnets to focus the electrons onto the specimen, whcih is then transmitted through it onto a detector to produce a 2D image. Areas which absorber fewer electrons = forms darker areas of the image.
How does SEM work?
A beam of electrons are scanned across specimen, which kncks of electrons from the specimen. These electrons are then gathered in a cathode ray tube, to produce a 3D image of the specimen surface.
Coating required for LM, LSCM, TEM or SEM?
For SEM + TEM:
Specimen is usually coated in hard metal - the metal ions act to scatter the electrons fired at the sample to give contrast between structures. It also improves imaging on electron microscopes because the metal layer reduces charge building up on specimen that could affect the image and improves electron signal.
Portability of LM, LSCM, TEM + SEM?
LM - Small, easily portable
LSCM - N/A
TEM + SEM - Very large, can take up a full room
Specialist Training required fro LM, LSCM, TEM + SEM?
LM - No (easy to use = lots of applications)
LSCM, TEM + SEM - Yes (TEM + SEM - require great deal of skill)
Specimen held in vaccuum for LM, SEM, TEM or LSCM? If so, why?
LM - No
LSCM - No
TEM + SEM - Yes, because electrons being aimed at the sample would otherwise be knocked off course.
What are LM, LSCM, TEM, SEM, used to view?
LM - Large individual cells and tissue - be able to differentiate between plant and animal cells. Also used to view large organelles such as the nucleus, cytoplasm and cell wall.
LSCM - Used to see smalled organelles + their internal structures, used to look at different depths of thick specimen + used to view specific proteins moving within the cell.
TEM - specimen must be extremely thin Used to view very small organelles and their internal structures very clearly e.g. ribosomes
SEM - Used to see the SURFACE of the specimen (organelles etc)
What is one way in which chemical fixation maintain’s specimen’s structure?
Once a tissue is removed from its natural environments, its (or its organelle’s) appearance may begin to change. E.g. lack of oxygen = mitochondria’s appearance changes. Chemical fixations stops this.
Apart from scattering electrons, what is another effect of the metal coating?
Reduces thermal damage from electron beam.
What is a stain?
A stain is a coloured chemical that binds to molecules in or on specimen (to provide contrast).
What is differential staining?
Differential staining is when stains bind to specific cell structures, staining each structure differently (to provide contrast), so that the structures can be identified easily with a single preperation.
More than one stain can be used.
Name the different stains that you need to know.
Acetic Orcein Eosin Sudan red Iodine in Potassium Iodide Methylene blue
What substance + colour does Acetic orcein stain?
Acetic orcein binds to DNA, it stains chromosomes red.
What substance + colour does Eosin stain?
Eosin stains cytoplasm pink
What susbtance + colour does Sudan red stain?
Sudan red stains lipids red
What substance + colour does Iodine in Potassium Iodide stain?
Iodine in Potassium Iodide stains cellulose in cell walls yellow and starch grains, blue/black.
What susbtance + colour does Methylene blue stain?
Methylene blue stains DNA blue.
What are the 2 ways to prepare a slide?
1) Dry Mount
2) Wet Mount
Describe how to prepare a slide (Dry Mount).
1) Using tweezers, place the (thinly cut) specimen in the centre of a clean slide and flatten it out. [Thinly cut, so light can can pass through it + can be seen clearly under microscope].
2) At this point, add a drop of chosen stain on the specimen (to give contrast between cell structures, which absorb the stain varyingly), so that it is clear to see.
3) Slowly lower one side of the cover slip over the stained specimen using a mounted needle, avoding air bubbles.
4) Ready for observation. Once complete place cover slip + slide into disinfectant.
Describe how to prepare a slide (Wet Mount).
1) Begin by placing a small drop of water onto the centre of the slide using a pipette.
2) Place the thinly cut specimen, onto the water droplet.
3) Next, take a cover slip and place it vertically upright beside the specimen, before carefulling tilting it and lowering it so it covers the specimen (once again, avoiding air bubbles).
4) Once the cover slip is placed, place a drop of the stain on one edge of the cover slip and a bit of paper towel at the opposite edge. The stain will get drawn under the slip across the specimen.
How to use a microscope? ( STEPS)
1) Clip the prepared specimen (on slide) onto the microscope stage.
2) Firstly, select the lowest-powered objective lens (lowest magnification)
3) Next, use the course adjustment knob to raise the stage, to just below the objective lens.
4) Look through the eyepiece (containing the ocular lens), and using the coarse adjustment knob to lower the stage, until the image is roughly in focus.
5) Next, adjust the fine adjustment knob, until the the image is clear.
6) If you need to see the slide at a higher magnification, swap to a higher powered objective lens and refocus.
How to calibrate the eyepiece graticule?
1) Start with the lowest powered objective lens.
2) Line up the stage micrometer with the eyepiece graticule (in the eyepiece). The stage micrometer has a 100 divisions, which in total measure 1mm. This means each division on the micrometer is equal to 0.01mm.
3) At the same magnification, 1 division on the stage micrometer, may be equal to 4.5 divisions on the eyepiece graticule. This means one division on the eyepiece graticule is equal to 0.002mm.
4) Now, when measuring an object, which is 20 eypiece divisions long, you know that it measures 0.002mm x 20 = 0.04mm (1sf)
What is the equation to measure magnification?
Magnification = Image size / Actual size
Define eukaryotic cells.
Eukaryotic cells are complex cell containing a nucleus or other membrane-ound organelles
Define prokaryotic cells
Prokaryotic cells are simple cels, that do not contain a ‘true’ nucleus or any membrane-bound organelles.
What organelles do plant cells have that animal cells do not?
- Permanent vacuole
- (Cellulose) Cell wall
- Chloroplasts
What organelles do animal cells have that plant cells do not?
- Centrioles
Define ultrastructure
The structures within a cell which can be seen using an electron microscope.
Structure of the nucleus?
- Largest organelle in a cell.
- Contains the nucleoplasm (a semi-solid fluid which contains the DNA as chromatin) and the nucleolus.
- Surrounded by a nulcear envelope with contains nuclear pores. A double-membrane organelle.
Function of the nucleus?
- Regulates cell activity (e.g. hormones)
- Stores (and transmits) the genetic codes/DNA that control the production of proteins (for growth + repair)
- DNA stored as linear chromatin (diffuse form of chromosomes - spread out and extended - takes this form when the cell is not dividing) wound around histone proteins.
Structure of the nucleolus?
- Made of RNA and proteins
- Not membrane-bound
- Largest sub-structure in the nucleus
Function of the nucleolus?
- Synthesizes ribosomes (ribosome protein sub-units) and ribosomal RNA.
- Seocndary role: immobilises proteins + forms signal recognition particles.
Structure of the nuclear envelope?
- Double membrane phospholipid bilayer (both inner + outer)that contains nuclear pores and surrounds the nucleus.
Function of nuclear envelope?
- Control/Regulate the movmement of substances in and out of the nucleus (between cytoplasm and nucleoplasm) e.g. the movement of steroid hormones into the nucleus, and the movement of mRNA, ribosomes etc out of the nucleus (specify direction in exam)
- Acts as a barrier to seperate the contents of the nucleus from the rest of the cell.
Structure of mitochondria?
- Sausage/rod-shaped
- Double membrane organelle (both of which are phospholipid bilayers)
- The inner membrane is called the cristae and is highly folded.
- The centre of the mitochondria has a region called the mitochondrial matrix.
- It contains its own DNA and ribosomes
- Fluid between its membranes
Function of the mitochondria?
- Site of aerobic respiration/ATP production
- Outer mebrane controls the movement of substances into and out of the cell
- Cristae (Inner membrane) is highly folded, to provide a large surface area for the attachment of proteins (e.g. enzymes) that catalayse the reactions invovled in ATP production (speeds up rate of reaction)
- Can self-replicate, to meet increase energy demands (has its own DNA + ribosomes)
- Matrix contains enzymes, proteins, + DNA requried for respiration.
Structure of Rough Endoplasmic Reticulum (RER)?
- Continuous of the nuclear envelope.
- A network of interconnected membranous sacs + tubules with a fluid filled cavity called the cisternae
- Has ribosomes on the (cytoplasmic side of its) surface.
Function of Rough Endoplasmic Reticulum?
- Intracellular transport system
- Provides a large surface area for the translation of mRNA into a protein on its ribsoomes (protein synthesis)
- Proteins produced by ribosomes, actively pass into the cisternae of the RER to be transported.
- Vesicles containing the protein are pinched off the cisternal membrane to be transported to the Golgi Apparatus.
Structure of Smooth Endoplasmic Reticulum?
- A network of interconnected mebranous sacs + tubules with a fluid filled cavity called the cisternae (more tubular)
- Has no ribosomes on its surface
Function of the Smooth Endoplasmic Reticulum?
- Stores, synthesizes and transports lipids (and carbohydrates)
- Contains enzymes that aid lipid metabolism (the production of steroid hormones + cholestrol)
Structure of Golgi Apparatus?
- A network of interconnected, flattened membranous sacs.
Function of Golgi Apparatus?
- Recieves vesicles from the RER containing proteins (also recieves vesciles containing lipids and carbohydrates), when it fuses with the Golgi body.
- Modifies proteins and re-packages modified proteins into vesicles, for transport within or outside the cell.
- Modifies proteins by combining with sugars to produce glycoproteins, combining with lipids to produce lipoproteins or simply combining polypeptides to form the full functional protein.
- Vesicles that leave the Golgi Apparatus, can fuse with the plasma membrane to secrete its contents via the active process of exocytosis. It can also, be transported to elsewhere in the cell, for e.g. storage. It can also be transported to the plasma membrane to be exported.
Structure of Lysosomes?
- A type of vesicle.
- Vesicles are organelles, with a single phospholipid bilayer membrane enclosing molecules
- The Golgi Apparatus produces lysosomes
- Contains powerful hydrolytic digestive enzymes (e..g lysozymes, proteases etc.)
Function of Lysosomes?
- Abundant in phagocytic cells (which ingest bacteria) and secretory cells (such as pancreatic cells)
- Several roles in cells:
1) Hydrolysis of ingested (foreign) materials by phagocytic cells
2) Digestion of old or damaged organelles to recycle its useful components
3) Complete break down of cells that had died (autolysis)
4) Release of enxymes to digest materials outside of the cell (exocytosis)
Structure of Ribosomes?
- Very small organelles (Eukaryotes - 80S (>20nm [25nm-30nm]) (Prokaryotes - 70S (<20nm [18nm])
- Not membrane-bound
- Consists of two protein sub-units (made of rRNA and proteins)
- Two types: Ribosomes attached to the cytoplasmic side of the RER, Free-floating ribosomes in the cytoplasm.
Function of ribosomes?
- Site of protein synthesis (translation)
- Two types: Ribosomes attached to the cytoplasmic side of the RER code for proteins used outside of the cell. Free-floating ribosomes in the cytoplasm, code for proteins for use inside the cell.
Structure of (cellulose) cell walls?
- Main organic component in plant cell walls are cellulose (a polysaccharide)
- Main organic component in fungal cell walls is chitin (another polysaccharide
- Many cellulose molecules join together to form bundles of cellulose fibres
- External to the plasma membrane
- Many cellulose cell walls contain plasmodesmata
Function of cell walls?
- Provides mechanical strength to prevent the cell from bursting by withstanding the turgid pressure.
- Maintains cell shape
- Provides strength and stability for the whole plant
- Plasmodesmata allow the movement of substances between adjacent cells.
- Cellulose cell walls are fully permeable for so water and mineral ions can reach the plasma membrane, as well as being abel to cross multiple cell walls.
Structure of Chloroplasts?
- 2-10µm long
- Double membrane organelle both of which are phospholipid bilayers.
- Grana (singular = granum) are stacks of flattened discs.
- Each disk is called a thylakoid and the thylakoid contains the photosynthetic pigment, chlorophyll.
- Grana are connected to each other by intergranal lamellae.
- Surrounding the thylakoid membrane (the network of grana) is a fluid called the stroma. This contains, proteins enzymes, starch grains and the chloroplast’s own DNA + ribosomes. All enclosed in the inner membrane.
- The space inside the thylakoid is called the thylakoid lumen
Function of Chloroplasts?
- Chloroplasts are the site of photosynthesis
- 1st stage of photosynthesis takes place in the grana.
- 2nd stage of photosynthesis takes place in the stroma.
- The enzymes, DNA, protein and ribosomes in the stroma allow the chlotoplast to quickly and easily manufacture the proteins for photosynthesis.
Structure of Permanent Vacuole?
- Fluid-filled sac containing different dissolved solutes
- Surrounded by a single membrane called the tonoplast (phospholipid bilayer)
- Permanent (large) vacuole are not found in animal cells.
Function of Permanent Vacuole?
- Maintains the structure of plant cells because when they become full, it pushes against the cell wall, making it turgid.
- Contains sugars and other molecules that may act as a temporary enrgy store for the plant
Structure of Cytoplasm?
- Jelly-like substance that surround the organelles of a cell
Function of Cytoplasm?
- An aqueous solution with dissolved solutes used in metabolic reactions (site of chemical reactions)
Structure of Plasma membrane?
- Phospholipid bilayer that surrounds the cell
- Contains receptors and antigens
Function of Plasma membrane?
- Controls the movement of substances in and out of the cell.
- Acts as a barrier, seperating the contents of the cell from the external environment.
- Receptors and antigens for cell recognsition and cell communication/signalling.
- May release chemicals
Structure of centrioles?
- Small, hollow cylinders of microtubules
- Found in pairs at right angles to each other. Found in isolation at basal regions of cilia and flagella
- Not membrane bound
- Made of tubulin sub-units
Function of centrioles?
- Involved in the formation of undulipodia and cilia
- Involved in the seperation of chromosomes in cell division, as the spindle fibres are formed from centrioles.
Structure of Cilia/Undulipodia?
- Mainly used to describe eukaryotic cells.
- Protrusions above cell surface covered by the extension of the plasma membrane
- Formed from centrioles
- Has a central region, called the axoneme: PC - 9+0, MC - 9+2.
- Undulipodia have same arrangment as motile cilia, however they are longer and found in fewer numbers.
- Sperm cells have a tail made from a cluster of undulipodia.
Function of Cilia/Undulipodia?
- Carries out a synchronised beat/waft-like motion to move substances (e.g. mucus) across the surface.
- All cell types have one cilia which acts as an antenna (contians receptors) to detect signals about its immediate environment.
Structure of Flagella?
- Same structure as cilia (9+2 arrangement of microtubules) but longer
- mainly used to describe prokaryotic cell but still used for eukaryotic cells (in undulipodium)
Function of Flagella?
The microtubules contract to make the flagella move and thus the cell to move.
What is the cytoskeleton?
A network of protein structures found in the cytoplasm of cells.
In eukaryotic cells, how are the protein threads arranged?
Arranged as:
1) Microfilaments (Very thin strand - 7nm)
2) Microtubules (Thin, protein cylinders - 18nm-30nm)
3) Intermediate filaments (10nm)
What is the structure of microfilaments?
Microfilaments are a polymer made of repeating actin protein sub-units.
What is the structure of Microtubules?
Microtubules are a polymer Meade from repeating tubulin protein sub-units.
Function of the Cytoskeleton?
1) Whole cell-support + stability, maintains shape.
2) Movement of cilia, undulipodia and flagella,
3) Moves certain organelles around or holds certain organelles in position.
4) Changes shape when necessary e.g. phagocytosis in neutrophils
5) Movement/Transport of materials inside the cell:
- Movement of chromatin/chromosomes/mRNA + formation of spindle fibres from centrioles
- Movement of vesicles
Name the cytoskeletal motor proteins.
1) Dyneins
2) Kinesins
3) Myosins
Function of Motor proteins?
Drag substances along the protein fibres that make up the cytoskeleton.
• E.g. mediating intercellular transport, has an ATP binding site, and hydrolyses this ATP, to provide itself energy (acts as an enzyme here)
What can affect the function of the cytoskeleton?
The assembly of microtubules and microfilaments and the movement of materials along them, requires energy from respiration. As a result their functioning can be reduced by respiratory inhibitors.
Outline the interrelationship between organelles involved in the production and secretion of proteins?
1) The gene coding for protein X, housed on a chromatin is transcribed into mRNA in the nucleus.
2) The mRNA then leaves the nucleus through a nuclear pore in the nuclear envelope and travels to a ribosome on the RER.
3) Here, the ribosome translates the mRNA by assembling protein X molecules, which then actively pass into the cisternae of the RER.
4) Vesicles containing the molecules of protein X are then pinched of the cisternal membrane and are transported to the Golgi apparatus via motor proteins across the cytoskeleton.
5) The vesicle then fused with the Golgi apparatus releasing its contents (molecules of protein X) into the Golgi body.
6) The Golgi Apparatus modifies these proteins and repackages they into vesicles.
7) These vesicles then travel towards the plasma membrane and fuse with it to release protein X to the outside of the cell - through an active process known as exocytosis.
Similarities between Prokaryotic and Eukaryotic Cells?
They both contain cytoplasm, RNA and DNA, plasma membrane and ribosomes for assembling proteins.
Difference between Prokaryotic and Eukaryotic Cells?
1) P - Extremely small cells [diameter: < 2μm], E- Larger cells [diameter: 10-100μm]
2) P - DNA is circular + naked, E - DNA is linear + not naked (wound around histone proteins)
3) P - No nucleus - DNA floats freely in the cytoplasm, E - Nucleus present, DNA is inside the nucleus
4) P - Cell wall (of bacteria)made of peptidoglycan (a polysaccharide), not cellulose or chitin, E - Cellulose (plants) or chitin (fungi) cell wall, animal cells do not have cell walls.
5) P - Few organelles (does not contain membrane-bound organelles), E - Many organelles (contains membrane-bound organelles)
6) P- Small ribosome - 18nm/70s (<20nm), E - Large ribosome - 80S (>20nm, between 25-30nm)
7) P - Does not contain centrioles, E - Contains centrioles (plant cells do not)
8) P - Much less well-developed cytoskeleton, E - Well-developed cytoskeleton
9) P - Flagella (when present), made of protein flagellin, arranged in a helix, E - Flagella (when present) made of Microtubules arranges in a ‘9+2’ arrangement
When DNA is linear, what does it mean?
When DNA is linear, it has two distinct ends. Circular DNA on the other hand, does not.
What organelles do prokaryotic cells always have?
- Cytoplasm
- Cell wall (peptidoglycan)
- Ribosomes
- Plasma membrane
- (Cytoskeleton)
{Look at table, in notes, in file}
What organelles do prokaryotic cells never have?
- They do not have membrane-bound organelles: ER, Nucleus, Golgi Apparatus, Lysosomes, Chloroplasts, Mitochondria.
- They also don’t contain centrioles.
What do prokaryotic cells SOMETIMES have?
- Flagellum
- Capsule
- Pilli
- Plasmid
What is the nucleoid?
The nucleoid is a region of the cytoplasm where the main DNA molecule is found.
Describe the prokaryotic DNA
Circular, large, loop of DNA which is naked (not associated with any proteins)
What other form of genetic materials may prokaryotic cells sometimes contain?
Plasmids - smaller loops of naked circular DNA, not part of the main loop of DNA.
Some benefits of ‘plasmids’
- They can be replicated + passed on in cell division
- They can also be transferred between prokaryotic cells to transfer useful genes e.g. antibiotic resistance.
What is a capsule?
This is a protective waxy outer layer surrounding the cell wall that prevents detection by other cells and allows individual bacteria to stick together.
What is a pilli?
A long hair-like projection made of protein that extend out of the bacteria enabling them to adhere to host cells or to each other
Function of peptidoglycan?
Same as cellulose
Provides mechanical strength, preventing cell from bursting due to turgid pressure and maintain cells shape.
Why do light microscopes have a low resolution?
Light microscopes have a low resolution because the wavelength of light are too long.
