cells Flashcards
what makes a cell eukaryotic?
it has DNA in a nucleus and has membrane bound organelles
examples of eukaryotes:
plants, algae, protozoan, fungi
epithelial cells:
adapted for role in absorption and secretion within digestive system
cell membrane of epithelial cell is folded into structures called microvilli which increases surface area for absorption
nucleus:
- largest organelle in the cell;
contains DNA which codes for protein synthesis; - nuclear membrane (double membrane, two phospholipid bilayers);
- nuclear pores which allow the passage of molecules (mRNA) in and out of nucleus;
- nucleolus - where ribosomal RNA is made and ribosomes;
- ribosomal subunits (proteins) synthesised within nucleus;
- contains chromatin, made from DNA coiled around histone proteins;
how are ribosomes synthesised?
ribosomal proteins and ribosomal RNA are synthesised within nucleus but assembled outside of the nucleus
how does chromatin form chromosomes?
during cell division, chromatin super condenses and forms thread like structures called chromosomes
mitochondrion:
- site of ATP production by aerobic respiration;
- hydrolysis of ATP releases the energy for cellular/metabolic reaction or provides phosphate for phosphorylation of molecules to make substances more reactive or lower Ea;
- double membrane - inner membrane highly folded to form cristae to increase SA for attachment of ATP synthase enzymes;
- within inner membrane is matrix which contains proteins, lipids, mitochondrial DNA and ribosomes;
cells that require a lot of ATP and have lots of mitochondria:
muscle cells for muscle contraction
epithelial cells for active transport of ions
rough endoplasmic reticulum:
- made from highly folded membranes with 80s ribosomes embedded;
- synthesises and transports proteins hroughout the cell;
- joined to nucleus - easier for mRNA to get there to make proteins;
cells which make a lot of proteins have a lot of RER:
secreting extracellular enzymes - enzyme secreting gland cells;
antibodies producing plasma cells
smooth endoplasmic reticulum:
- SER recombines glycerol and fatty acids to make triglycerides;
- SER packages triglycerides into vesicles and transports them to the Golgi apparatus;
ribosomes:
- site of protein synthesis from amino acids;
- eukaryotic cell contains 80s ribosomes;
- two subunits of a ribosome are made of a combination of long strands of rRNA, dotted with ribosomal proteins;
golgi apparatus:
- sorts, modifies and packages proteins and triglycerides into vesicles;
- Golgi vesicles may be used to form lysosomes;
- Golgi apparatus is composed of flattened sacs (cisternae) made of membranes.The sacs are fluid filled and pinch off smaller sacs (called vesicles) at their ends;
- usually only one Golgi body in each cell, is well-developed in secretory cells; as large molecules must be packaged in vesicles to be transported out of the cell;
cells which have an extensive large golgi, packages lots of molecules for export, mostly large amount of proteins:
enzyme secreting gland cells,
antibodies producing plasma cells
lysosomes:
- used to hydrolyse damaged and worn-out organelles;
- bound by a single membrane and have no internal structure;
- contain many hydrolytic enzymes which are lysozymes in an acid solution (low pH), which must be kept separate from rest of cell contents to prevent them from digesting organelles;
cells that contain many lysosomes:
phagocytes (type of white blood cell)
breakdown invading pathogens
cell surface membrane:
- controls the passage of molecules in and out of the cell;
- made of phosopholipids, transport proteins, carbohydrates, glycoprotein (globular protein w/ a polysaccharide chain of sugars attached, made in Golgi body) has a receptor complementary to molecule that binds;
- phospholipid bilayer;
microvilli:
- finger like projections of the cell membrane,
- greatly increase the surface area of the cell membrane,
- this speeds up absorptions of digested food;
- found on epithelial cells in the small intestine
- so there may be more carrier proteins for active transport
eg columnar epithelium lining the small
intestine
centrioles:
- function in mitosis to form a network of spindle fibres across the cell onto which the chromosomes attach;
- fibres pull the chromosomes / chromatids apart during mitosis;
- these organelles are not found in plant cells;
- one centriole = two cylinders at right angles made from microtubules
plant cell structure:
wax cuticle;
upper epidermis;
palisade mesophyll;
spongy meosphyll:
air spaces;
lower epidermis;
stoma;
guard cells with chloroplasts;
waxy cuticle;
animal cell differences to plant cells:
no cell wall
no chloroplasts
no large central vacuole
carbohydrates stored as glycogen
has centrioles
plant cell differences to animal cell:
cellulose cell wall
chloroplasts present
large central vacuole
carbohydrates stored as starch
has no centrioles
chloroplasts (found in plants and algae)
function:
- absorbs light energy and converts it to chemical energy;
- chemical energy used to make carbohydrates from CO2 and H2O;
- these then used for respiration to make other organic molecules in cell, which enables plant to grow;
chloroplasts structure:
- double membrane
- granum = stack of thylakoid membranes;
- thylakoid membrane = contains chlorophyll for photosynthesis & ATP synthase enzymes to produce ATP;
- stroma = fluid filled part, some of the photosynthetic reactions occur here, colourless;
- starch grains = energy storage molecules in plants;
- DNA and ribosomes = chloroplasts have their own DNA and 70S ribosomes to make enzymes needed for photosynthesis;
cellulose cell wall (in plants and algae):
- very strong (many WEAK hydrogen bonds between cellulose fibrils), limits the volume of water that can move into the cell and stops osmotic lysis;
- wall is permeable to most molecules, unlike the membrane (micro fibrils arranged in a matrix);
- cell walls of adjacent cells separated by middle lamella (thin layer), acts to stick the walls together with pectin;
- plasmodesmata = gaps in the cell walls that connect cell cytoplasm’s together, to allow the easy movement of water-soluble molecules;
bacterial cell (prokaryotic cell):
- prokaryotes do not have nuclei or other membrane bound organelles.
- circular DNA, found free the cytoplasm, and it is not associated with histones.
- cell membrane, cell wall, plasmid, 70s ribosomes, flagellum, capsule
prokaryotic cells:
- circular DNA, not associated with histones;
- contains no membrane blund organelles;
- smaller ribosomes 70s;
- mesosomes for ATP synthesis;
- murein or peptidoglycsn cell wall;
eukaryotic cells:
- linear DNA;
- contains membrane bound organelles (mitochondria, RER, SER, Golgi body, lysosomes);
- larger ribosomes 80s
- no capsule
- plant cells have cell wall made of cellulose
viruses:
- not cells, not alive
- small
- require a living cell to replicate inside
- contains DNA or RNA, which can be single or double standed
- protein coat = capsid
- attachment proteins enable it to bind to host cells
- enzymes used to replicate genetic information and insert into host cell DNA
- no organelles
fungi cell walls are made out of
chitin
light microscopes:
- specimens illuminated with light
- focussed using glass lens;
- specimens can be dead or living;
- organelles need to be stained with colours dye to make them visible;
- dye binds to a specific protein due to charge/bond;
- magnification is limited;
- low resolution, longer wavelength of light
how to use eyepiece graticule:
measure each stomata using an eyepiece graticule
calibrate the eyepiece graticule against a state micrometer
take at least 5 measurements and calculate a mean = more acc, more rep
eyepiece graticule and state micrometer:
eyepiece graticule fits into eyepiece lens, transparent rule with numbers but no units
stage micrometer is a microscope slide, acc scale, placed on stage, used to work out value of each division on eyepiece graticule when using a certain magnification
allows you to take stage micrometerr away and replace it with slides with a tissue specimen to measure size of cells
transmission electron microscope:
- produces 2D images;
- higher resolution, electrons have smaller wavelength;
- focussed using electromagnets;
- electrons pass through specimen;
allows you to view internal structures/organelles; - specimens fixed in resin and sliced extremely thin = must be dead;
- stained using heavy metals = complex, lengthy process and can create artefacts
- electrons fired through specimen,
- less dense (cytoplasm) absorb less electrons so appear lighter
- denser areas (nucleolus) absorb more electrons and so appear darker,
- specimens must be in a vaccum so specimen must be dead
scanning electron microscope:
- produces 3D images;
- higher resolution, electrons have smaller wavelength;
- focussed using electromagnets;
- specimens are not sliced, and the electrons bounce off the surface of the specimen;
magnification equation:
Image size / actual size
cell fractionation and differential centrifugation:
- tissue is homogenised in blender, in ice cold, isotonic, pH buffered solution to break open the cells releasing the organelles
- mixture is then filtered to remove any large pieces of tissues/ cells (cellular debris)
- differential centrifugation at high speeds, densest organalles go to bottom as a pellet
- pellet is removed and supernatant is spun again at higher speeds for the next dense organelle
ice cold, isotonic, pH buffered solution:
ice cold: reduce the action of enzymes that would digest organelles
isotonic: prevents osmosis of water in or out of organelles so organelles don’t burst or shrivel
pH buffered: to stop pH changes which could denature proteins
