Module 2 Flashcards
Magnification
- tells you how many times bigger the image produced by the microscope is than the real-life object
Resolution
- the ability to distinguish between objects that are close together
measuring diameter through a light microscope
- use eyepiece graticule
- calibrate graticule using stage micrometer
- calculate length of one epu
- measure diameter of …. in EPU
- take repeat measurements + calculate mean …
- use calibrated EPU to calculate length/diameter of …. in micrometers
Why is using a stain advantageous?
- contrast is higher
- more (internal) structures visible
- some organelles(eg nucleus) more visible because they bind to the stain
- clearer image can be obtained
Optical (light) microscopes
- use light to form an image which limits the resolution of optical microscopes (using light makes it impossible to resolve two objects that are closer than half a wavelength of light)
- Max resolution of 0.2 micrometres (or 200nm)- can see eukaryotic cells and their nuclei but cannot observe smaller organelles eg ribosomes, ER or lysosomes
-max magnification is around x1500
Electron microscopes
-use electrons to form image which greatly increases resolution, giving more detailed image
- beam of electrons has smaller wavelength than light
- max resolution of 0.0002 micrometres (0.2 nm)
- max magnification of x1,500,000
Transmission electron microscopes (TEMs)
- use electromagnets to focus a beam of electrons through a specimen
ADV
-give high resolution images, allowing internal structures within cells to be seen
DISADV
-can only be used on very thin specimens - cannot observe live specimens
-lengthy treatment required to prepare specimens means artefacts can be introduced
-do not produce a colour image
Scanning electron microscopes (SEMs)
- scan a beam of electrons across a specimen
- produce 3 dimensional images that show surface of specimens
ADV
-can be used on thick or 3D specimens
-allow external 3D structure to be observed
DISADV - give lower resolution images than TEMs
- cannot be used to observe live specimens
- do not produce colour image
Laser scanning confocal microscopes
- cells stained with fluorescent dyes
- thick section of tissue or small living organism scanned with laser beam
ADV - can be used on thick/ 3D specimens
- allow external 3D structure to be viewed
- very clear images are produced
DISADV
-slow process - laser can cause photodamage to cells
Cell surface membrane
- controls the exchange of materials between the internal and external cell environment
-partially permeable - formed from a phospholipid bilayer
Cell wall (plant, not animal)
- formed outside cell membrane to offer structural support
- polysaccharide cellulose in plants
- peptidoglycan in bacteria cells
- narrow threads of cytoplasm, called plasmodesmata connect the cytoplasm of neighbouring plant cells
Nucleus
- present in all eukaryotic cells (except RBC)
- double membrane (nuclear envelope) which has many pores
-nuclear pores allow mRNA and ribosomes to travel out of nucleus + allow enzymes and signalling molecules to travel in - contains chromatin, which makes up chromosomes
- nucleolus- sites of ribosome production
Mitochondria
- site of aerobic respiration in all eukaryotic cells
-double-membrane with inner membrane folded to form cristae - matrix formed by cristae contains enzymes for aerobic respiration (eg ATP)
- small circular pieces of DNA and ribosomes also found in matrix (needed for replication)
Chloroplasts
-found in plant cells
-larger than mitochondria, surrounded by double membrane
- membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana
- grana joined by lamellae (thin and flat thylakoid membranes)
- site of photosynthesis
- light-dependent stage in thylakoids
- light- independent stage in stroma
- small circular pieces of DNA and ribosomes to synthesise proteins
Ribosomes
- found in all cells
- freely in cytoplasm of cells as part of rough ER in eukaryotic cells
- each ribosome is a complex of ribosomal RNA (rRNA) and proteins
- 80S ribosomes (in eukaryotes)
- 70S ribosomes (in prokaryotes, mitochondria and chloroplasts)
- site of translation
Endoplasmic reticulum
Rough ER:
- found in animal and plant cells
- surface covered in ribosomes
- formed from continuous folds of membrane continuous with the nuclear envelope
- processes proteins made by ribosomes
Smooth ER:
- found in plant and animal cells
- no ribosomes on surface
- involved in production, processing and storage of lipids, carbs and steroids
Role of membrane in RER
- compartmentalisation/ maintain different conditions from cell cytoplasm
- separating proteins (synthesised) from cell cytoplasm
- hold ribosomes/enzymes in place
Golgi apparatus (golgi complex)
- found in animal and plant cells
- flattened sacs of membrane
- modifies proteins and lipids before packaging them into Golgi vesicles
- vesicles transport proteins and lipids to their required destination
Large permanent vacuoles
- a sac in plant cells surrounded by tonoplast, selectively permeable membrane
- vacuoles in animal cells are not permanent and small
vesicles
- found in animal and plant cells
- a membrane-bound sac for transport and storage
lysosomes
- specialist forms of vesicles which contain hydrolytic enzymes
- break down waste materials such as worn-out organelles
- used extensively by cells of the immune system and in apoptosis (programmed cell death)
Centrioles
-hollow fibres made of microtubules
- two centrioles at right angles to each other form a centrosome , which organises the spindle fibres during cell division
-not found in flowering plants and fungi
Microtubule
- found in all eukaryotic cells
- makes up cytoskeleton of the cell about 25nm in diameter
- made of alpha and beta tubulin combined to form dimers, the dimers are then joined into protofilaments
- the cytoskeleton is used to provide support and movement of the cell
Microvilli
-found in specialised animal cells
- cell membrane projections
-used to increase the surface area of cell surface membrane to increase the rate of exchange of substances
cilia
- hair-like projections made from microtubules
- allows movement of substances over the cell surface
Flagella
- found in specialised cells
- similar in structure to cilia, made of longer microtubules
- contract to provide cell movement (eg in sperm cells)
Protein synthesis process
- nucleolus manufactures ribosomes for protein synthesis in RER
- The nucleus manufactures mRNA (transcription) which is needed by ribosomes to make proteins
- The ribosomes in the RER make proteins (translation)
- The RER processes proteins which are then sent in vesicles to golgi body
- The Golgi body further processes the proteins and sends them in vesicles to the plasma membrane
- The vesicles fuse with the plasma membrane to secrete the finished protein product.
Describe how the molecule is prepared and secreted by cells of the salivary gland after translation has taken place
-transport vesicle from RER
-modification / processing / folding
- in / at, Golgi (body / apparatus)
- (packaged into) secretory vesicle
- vesicles move along the cytoskeleton
-(vesicle) fuses with, cell surface / plasma,
membrane
-(secretion occurs by) exocytosis
Cytoskeleton
-made up of 2 main types of protein fibres: microfilaments and microtubules
- microfilaments: solid strands made up of protein actin. allow cell movements and movement of organelles within cells
- microtubules: tubular (hollow) strands made up of protein tubulin. organelles are moved along these fibres using ATP
- Intermediate filaments also found in cytoskeleton
Importance of cytoskeleton
- Intracellular movement (movement of vesicles and chromosomes)
- cellular movement (via cilia and flagella)
- strengthening and support (mechanical strength)
Suggest two ways t
Tubulin is essential to protein synthesis and protein secretion in
eukaryotic cells
-movement of mRNA from nucleus to ribosome
-movement of polypeptides through the rER
-movement of vesicles from rER to Golgi
-movement of vesicles between cisternae of
Golgi (cis to trans face)
-movement of secretory vesicles from Golgi to
cell surface membrane
Prokaryotic cells vs eukaryotic
Prokaryotic: cytoplasm lacks membrane-bound organelles, smaller ribosomes(70S), no nucleus and a cell wall that contains murein (a glycoprotein). Plasmids (small loops of DNA), capsules, flagellum
-some prokaryotes (eg bacteria) are surrounded by a final outer layer known as a capsule- helps protect bacteria from attack.
Prokaryotes
SIZE: 0.5-5 micrometres diameter
GENOME: DNA circular with no proteins, in the cytoplasm
CELL DIVISION: occurs by binary fission, no spindle involved
RIBOSOMES: 70S
ORGANELLES: very few, no membrane-bound organelles
CELL WALL: made of peptidoglycan (polysaccharide and amino acids) and meurin
Eukaryotes
SIZE: up to 100 micrometres diameter
GENOME: DNA is associated with histones (proteins) formed into chromosomes
CELL DIVISION: occurs by mitosis or meiosis and involves a spindle to separate chromosomes
RIBOSOMES: 80S
ORGANELLES: numerous types of organelles membrane-bound
single membranes: lysosomes, golgi complex, vacuoles
double membranes: Nucleus, mitochondria, chloroplast
no membrane: ribosomes, centrioles, microtubules
CELL WALL: present in plants (cellulose or lignin) and fungi (chitin, similar to cellulose but contains nitrogen)
Properties of water
-hydrogen bonds :
- solvent (allows chemical reactions to occur, transport medium due to polarity of water)
- high specific heat capacity (allows water to be a suitable habitat, optimal temperature maintained within cells and bodies due to presence of many H bonds)
- high latent heat of vaporisation (coolant due to presence of many H bonds)
- water is less dense when it freezes
-water has a high surface tension and cohesion
-It acts as a reagent
-Cohesion and Adhesion (enables movement of water, eg up the xylem) due to H bonds
specific heat capacity
energy needed to raise the temperature of 1 gram of substance by 1C. H bonds between water molecules mean it can absorb a lot of energy and doesn’t experience rapid temp changes
high latent heat of evaporation
-takes a lot of energy to break H bonds
- so water has high latent heat of evaporation- lots of energy used up when heat evaporates
Cohesion
-due to polarity, very cohesive
- helps water flow
- good for transporting substances, eg up the stem in transpiration stream
good solvent
-ions get totally surrounded by water molecules (dissolve)
-useful solvent in living organisms eg. important ions dissolve in water in the blood for transport
Less dense when solid
- water freezes at low temps
-H20 held further apart in ice than water, 4 H bonds creates lattice
-makes ice less dense than water so it floats - ice forms insulating layer for organisms like fish, so they don’t die and freeze
Monomers
smaller units from which larger molecules are made
Polymers
molecules made from a large number of monomers joined together in a chain
- made by process of polymerisation
Macromolecules
very large molecules
high molecular mass
Condensation reactions
occurs when monomers combine together by covalent bonds to form polymers(polymerisation) or macromolecules (lipids) and water is removes
Hydrolysis reactions
hydrolysis means to break with water
in the hydrolysis of polymers, covalent bonds are broken when water is added
Types of covalent bonds
Carbohydrates-=glycosidic- C-O-C
Proteins= peptide O=C-N-H
Lipids= ester C-O-C=O
Nucleic acids= phosphodiester
Carbohydrate
- most are polymers
- monomers that make up carbs are monosaccharides
-eg glucose
Monosaccharide
simple sugar monomer, all are reducing sugars
eg; glyceraldehyde, ribose, glucose
function: source of energy in respiration, building blocks for polymers
ribose
-monosaccharide with 5C atoms therefore pentose monosaccharide
C5H10O4
Disaccharide
a sugar formed from two monosaccharides joined by a glycosidic bond in a condensation reaction
eg; maltose (glucose+glucose), sucrose (glucose+ fructose), lactose (glucose+ galactose)
function: sugar found in germinating seeds [maltose], mammal milk sugar [lactose], sugar stored in sugar cane [ sucrose]
Polysaccharide
a polymer formed by many monosaccharides joined by glycosidic bonds in a condensation reaction
eg; cellulose (B glucose) , starch , glycogen (a glucose)
Proteins
C,H,O,N (sometimes S)
required for cell growth and repair
structurally important e.g in muscles, collagen and elastin in the skin
Proteins can also act as carrier molecules in cell membranes, antibodies, enzymes or hormones
Nucleic acids
C,H,O,N ( in their bases) ,P (in form phosphate groups)
-carry genetic code in all living organisms
- essential in the control of all cellular processes including protein synthesis
Reducing sugars
-can donate electrons (carbonyl group becomes oxidised), the sugars become the reducing agent
- detected using Benedict’s test as they reduce soluble copper sulphate to insoluble brick-red copper oxide
eg. glucose, fructose and galactose
Non- reducing sugars
- cannot donate electrons, therefore cannot be oxidised
- to detect, they must be hydrolysed (neutralise solution by adding sodium hydrogencarbonate) to break the disaccharide into its two monosaccharides before a Benedict’s test can be carried out
E.g Sucrose
Glucose
C6H12O6
-hexose monosaccharide
-main function is as an energy source
-main substrate used in respiration, releasing energy for the production of ATP
- soluble
-isomer
- Alpha glucose (OH below the ring)
-Beta glucose (OH above the ring)
The glycosidic bond
Two hydroxyl (-OH) groups on different saccharides interact to form a strong covalent bond called the glycosidic bond, forming disaccharides and polysaccharides.
-condensation reaction
Breaking glycosidic bond
- broken through hydrolysis
- catalysed by enzymes
Common disaccharides
- maltose (glucose+glucose)
- sucrose (glucose+fructose)
- lactose (glucose+galactose)
all have formula C12H22O11
polysaccharides
-starch, glycogen and cellulose
- macromolecules that are formed by many monosaccharides joined by glycosidic bonds in condensation reaction to form chains.
Starch
2 different polysaccharides
-amylose
-amylopectin
Main energy storage material in plants
-Insoluble, therefore good storage molecule as no water enters by osmosis
amylopectin
amylopectin- 1,4 glycosidic bonds + 1,6 glycosidic bonds between a glucose mols.
-long branched chain
-side branches allow enzymes that break down the molecule to attack bonds easily
-glucose can be released quickly
amylose
amylose- 1,4 glycosidic bonds between a glucose molecules
- long unbranched chain. angles of glycosidic bonds make it have coiled structure, makes it compact so good for storage
Glycogen
- main energy storage in animals
- polysaccharide
- made up of alpha glucose molecules
- there are 1,4 + 1,6 glycosidic bonds between glucose molecules creating a branched molecule
Cellulose
- polysaccharide found cell wall in plants
- consists of long unbranched chains of B glucose joined by 1,4 glycosidic bonds
to form 1,4 glycosidic bonds consecutive B glucose mol must be rotated 180 ° to each other - due to inversion, many H bonds form, giving cellulose its strength, forming strong fibres called microfibrils
-structural support for cells
polysaccharides- storage molecules
starch + glycogen due to being compact and insoluble (no osmotic effect unlike glucose which lowers water potential)
Starch- storage in plants. Stored as granules in plastids such as amyloplasts and chloroplasts
Glycogen- storage in animals and fungi, highly branched and not coiled
Iodine test for starch
-add a few drops of orange/brown iodine in potassium iodide solution to the sample
-if starch is present, iodide ions interact w centre of starch molecule
- turns blue-black colour
Colorimetry
The use of a spectrophotometer to determine the absorption of various wavelengths of visible light by a given solution
Lipids
- macromolecules containing C,H and O
- non polar and hydrophobic (insoluble in water)
- triglycerides (main component of fats and oils) and phospholipids
- important role in energy yield, energy storage, insulation and hormonal communication
Triglycerides
formed from glycerol + 3 fatty acids
glycerol- an alcohol
fatty acids- methyl group at one end of an R group and carboxyl group at other end RCOOH = may be saturated or unsaturated
Phospholipids
- only 2 fatty acids bonded to a glycerol molecule in a phospholipid as one has been replaced by a phosphate ion (PO43-)
- HEAD as the phosphate is polar it is soluble in water (hydrophilic)
- TAIL fatty acid ‘tails’ are non-polar and therefore insoluble in water (hydrophobic)
- form monolayers or bilayers in water
Ester bond
- triglycerides are formed by esterification
-forms when hydroxyl (-OH) group from glycerol bonds with the carboxyl (-COOH) group of the fatty acid - formation of ester bond is condensation reaction (H from glycerol combines with OH from fatty acid)
- 1 triglyceride= 3 water mols released
saturated
containing the greatest possible number of hydrogen atoms , without carbon-carbon double or triple bonds
Unsaturated
Having carbon=carbon double or triple bonds and therefore not containing the greatest number possible of hydrogen atoms
Surfactants
Compounds that lower the surface tension of water
Sterols
Type of liquid; carbons arranged in rings; Cholesterol is most well known
Emulsion test
