Types of Microscopes
Magnification- the degree to which the size of the image is larger than the object itself Resolution- the degree to which it is possible to disinguish between two objects that are very close together (the higher the resolution the greater detail you can see).
- Uses number of lenses for diffferent magnifications, x4, x10, x40, x100.
- The maximun magnification is x1500 and the maximum resolution is 200nm.
- Widely used in education, laboratory analysis and research
- Cannot give detailed information about internal cell structure (due to low max resolution)
- Specimens are stained so they can be seen and put in wax to be cut without distortion.
- Resolution 0.2nm so can produce detailed images of cell structures.
- TEM electrons passed through sample, maximum magnification x500,000
- SEM electrons bounce off sample, produces 3D images, maximum magnification x100,000
- Samples have to be placed in a vacuum.
- They are very expensive and require a lot of training to use them.
Cells and Living Processes Part 1
Movement Respiration Sensitivity Nutrition Excretion Reproduction and Growth
- Fibres made of protein which keep the cell's shape stable (internal framework)
- Filaments (like in muscle tissue) move some of the organelles around inside the cell.
- Microtubules,25nm in diameter, move microorganism through liquid or waft liquid past cell.
- Microtubule motors (proteins) move organelles and cell content along microtubule fibres.
- This is how chromosomes are moved during mitosis and vesicles move from ER to Golgi apparatus (ATP drives these movements).
Flagella and Cilia
- In eukaryotes the fagella (undulipodia) and cilia are the same structurally, made up of a cylinder with nine microtubules arranged in a circle. Also two microtubules in a central bundle.
- Undulipodia are longer than cilia.
- Some bacteria have flagella but with different structure to those in eukaryotes, made of spiral of protein attached to a protein disc, using ATP energy the disc rotates spinning the flagellum.
Cells and Living Processes Part 2
Vesicles and Vacuoles
- Vesicles are membrane bound sacs used to carry many substances around cells.
- In plant cells, the large vacuole maintains cell stability. It is filled with water and solutes and pushes the cytoplasm against the cell wall. making the cell turgid to support the plant.
Plant cell walls
- On the outside of the plasma membranes
- Made out of cellulose
- Cellulose forms a sieve-like network of strands that makes the wall strong.
- Because it is held rigid by the pressure inside the turgid cell, it supports the cell and therefore the whole plant.
NUCLEUS- MEMBRANE BOUND
- Largest organelle.
- Surrounded by a nuclear envelope, a structure made of two membranes with fluid between them.
- Nuclear pores go throught the envelope and these pores are large enough for relatively large molecules to pass through.
- There is a dense spherical structure called the nucleolus inside the nucleus.
- Houses nearly all of the cells genetic material.
- Chromatin consists of DNA and proteins and has the instructions for making proteins.
- Some of these proteins regulate the cell activity.
- When cells divide chromatin condenses into visible chromosomes.
- The nucleolus makes RNA and ribsomes
- Ribosomes pass into the cytoplasm and proteins are assembled at them.
Organelles- Endoplasmic Reticulum
ENDOPLASMIC RETICULUM- MEMBRANE BOUND
- Consists of a series of flattened, membrane bound sacs called cisternae
- Continuous with outer nuclear membrane.
- Rough ER is studded with ribosomes
- Smooth ER has no ribosomes.
- Rough ER transports proteins made on the attached ribosomes.
- Some of the proteins made may be secreted by the cell while some will be place on the cell surface membrane
- Smooth ER is involved in making the lipids that the cell needs.
Organelles- Golgi Apparatus
GOLGI APPARATUS- MEMBRANE BOUND
- A stack of membrane bound, flattened sacs.
- Receives proteins from the ER and modifies them (maybe by adding sugar molecules)
- Packages the modified proteins into vesicles to be transported.
- Some modified proteins may go to the surface of the cell to be secreted.
MITOCHONDRIA- MEMBRANE BOUND
- Can be spherical or sausage shaped.
- They have two membranes separated by a fluid filled space.
- The inner membrane is highly folded to form cristae.
- The central part is calld the matrix
- Produce most of the ATP during respiration.
- ATP is the energy behind almost all activities that happen in the cell.
CHLOROPLAST- MEMBRANE BOUND
- Found only in plant cells and cells of some protoctists.
- Have two membranes separated by a fluid filled space.
- Inner membrane is continuous, with a network of flattened membrane sacs (thylakoids).
- Stack of thylakoids is a granum.
- Chlorophyll molecules present on the thylakoid membrane and in interganal membranes.
- Chloroplasts are the site of photosynthesis in plant cells.
- Light energy used to drive reactions of photosynthesis.
LYSOSOMES- MEMBRANE BOUND
- Spherical sacs
- Surrounded by single membrane
- Contain powerful digestive enzymes.
- Enzymes break down material (for example invading orgainisms in white blood cells).
- The specialised lysosome in sperm helps penetrate the egg by breaking down the material surrounding the egg.
RIBOSOMES- NOT MEMBRANE BOUND
- Small size
- Some are free in the cytoplasm.
- Some are bound to the endoplasmic reticulum.
- Each ribosome consists of two subunits.
- Site of protein synthesis (making new proteins).
- Where coded info (mRNA) from nucleus is used to assemble proteins from amino acids.
CENTRIOLES- NOT MEMBRANE BOUND
- Small tubes of protein fibres (microtubules).
- Pair of them next to the nucleus in animal cells and cells of some protoctists.
- Play a part in cell division.
- Form fibres, known as the spindle, which move chromosomes during nuclear division.
Organelles at Work
Note: The instructions to make hormones are in the DNA in the nucleus, a specific instruction to make a hormone is called a gene, genes are found on chromosomes.
Divison of Labour
- Nucleus copies DNA instructions into a molecule called mRNA.
- mRNA molecule leaves the nucleus through the nuclear pore and attaches to a ribsome.
- Ribosome may or may not be attached to the rough endoplasmic reticulum.
- Ribsome reads the instructions and uses the codes to assemble the hormone (protein).
- Protein is 'pinched off' in a vesicle and transported to the Golgi apparatus.
- Golgi apparatus packages the protein and may also modify it so it is ready for release.
- Protein is then packaged into a vesicle and moved to the cell surface membrane.
- Vesicle fuses with the cell surface membrane and the protein is then released/secreted.
Eukaryotes and Prokaryotes
- Have a nucleus
- Contain organelles, some of which are bound by membranes.
- Complicated internal structure.
- Each organelle performs specific role.
- All cells apart from prokaryotics have this structure.
- Are bacteria cells and are 1-5um (smaller than eukaryotes).
- Only one membrane (cell surface membrane) and no membrane bound organelles.
- Surrounded by cell wall usually made of peptidoglycan not cellulose.
- Outside the wall is usually a slippery protective layer called the capsule.
- Contain ribosomes that are smaller than the ones in eukaryotes.
- Single loop of DNA in cytoplasm, many also contain small loops of DNA called plasmids.
- DNA not surrounded by membrane, area where DNA is found is called the nucleoid.
- ATP produced in specialised interfolded areas of surface membrane called mesosomes.
- Some have flagella (like undulipodia but different structure) many have pilus.
Prokaryotes and Disease
- Some strains of bacteria are resistant to antibiotics.
- MRSA (methicillin-resistant Staphylococcus aureus) is one such strain.
- Resistance is coded on plasmid DNA.
- Bacteria can share plasmids with each other, so can pass resistance btween cells.
- Can also pass on resistance to daughter cells during binary fission.
Some prokaryotes help...
- Food industry uses bacterial species for making cheese and yoghurt.
- In mammalian intestines, bacterial cells help with vitamin K production and digestion.
- Skin covered in 'normal flora' of bacteria, prevent harmful microorganisms entering body.
- Sewage treatment and natural recycling, digesting and respiring dead/waste material.
Biological Membranes- Fluid Boundaries Part 1
Roles of membranes
- Separating cell contents from the outside environment.
- Separating cell components from cytoplasm.
- Cell recognition and signalling.
- Holding components of some metabolic pathways in place.
- Regulating transport of materials into or out of cells.
Nature of Phospholipids
- Phosphate 'head' is hydrophilic.
- Two lipid (fatty acid) 'tails' are hydrophobic.
- These properties come from the way the charges are distributed across molecule.
- If phospholipid molecules are mixed with water, they form a layer at the water surface with the phosphate head sticking into the water and the lipid tail sticking out.
If surrounded by water a bilayer will form, phosphate heads on each side will stick into the water and the tails will point towards each other, effectively held away from the water molecules. The hydrophilic heads cannot easily pass through the hydrophobic region in the middle which gives the bilayer some stability even though the molecules are not bonded together.