topic 2: cell structure Flashcards
eukaryotic organisms and examples
complex and larger structures e.g. animals, plants and fungi
structure and function of nucleus
STRUCTURE
-NUCLEAR ENVELOPE(double membrane) contain NUCLEAR PORES which allows large molecules like RNA to move between the nucleus and cytoplasm
-CHROMOSOMES (which are made from protein bound linear DNA)
-has one or more NUCLEOLUS
FUNCTION
-the nucleus contains genetic material and CONTROLS CELL ACTIVITIES by controlling the transcription of DNA
- DNA contains genetic code for making proteins
-nucleolus is the site of RNA production and manufactures ribosomes
structure of cell surface (plasma) membrane and function
STRUCTURE
-surrounds animal cells and is inside cell wall of bacteria and plant cells
-contains a phospholipid bilayer (made up of lipids and proteins) with molecules embedded (e.g. proteins, carbohydrates and cholesterol)
FUNCTION
-regulates the movement of substances into and out of the cell
-has receptor molecules which respond to chemicals like hormones + cell recognition
structure of RER (rough endoplasmic reticulum) and function
STRUCTURE
-system of membranes enclosing a fluid filled space
the surface is covered with ribosomes attached to membranes which makes it appear ROUGH
FUNCTION
-PROTEIN SYNTHESIS on ribosomes
-TRANSPORTS processed materials (e.g. proteins made on attached ribosomes)
structure of SER (smooth endoplasmic reticulum) and function
STRUCTURE
-system of membranes enclosing a fluid filled space without ribosomes attached to membranes
FUNCTION
-synthesizes and transports lipids
structure and function of golgi apparatus
STRUCTURE
-a group of fluid filled, membrane-bound flattened sacs, with vesicles at the edges of the sacs
FUNCTION
-modifies and processes proteins that are made in the cell
-packages them into vesicles to be transported out of the cell
-forms lysosomes
structure and function of golgi vesicles
STRUCTURE
-small fluid-filled membrane bound sacs
-found at the edges of golgi apparatus
FUNCTION
-stores lipids and proteins made by the golgi apparatus, and transports them to the cell surface membrane where it fuses with the membrane, which releases contents out of the cell
structure and function of the lysosomes
STRUCTURE
-a round membrane-bound organelle, contains digestive lysosomal enzymes (hydrolytic enzymes)
-type of golgi vesicle
FUNCTION
-digests invading cells and old/worn out organelles in the cell
-break down material - digest large molecules into smaller/ soluble molecules
structure and function of ribosomes
STRUCTURE
-made up of two subunits: RNA and protein
- small organelle
-not surrounded by a membrane
FUNCTION
-site of protein synthesis
-RER transports proteins made on attached ribosomes (to the cell surface membrane and fuses with the membrane, which release contents out of the cell)
structure and function of mitochondria
STRUCTURE
-oval shaped organelle surrounded by a double membrane - the inner membrane folded to form cristae and maximise surface area
-matrix (central part) is inside the inner membrane with enzymes (proteins and lipids) and DNA
FUNCTION
-the site of aerobic respiration, to produce ATP (energy store)
structure and function of chloroplasts (5 structures)
STRUCTURE
-a small, flattened organelle in photosynthesizing cells
-ENVELOPE - surrounded by a double membrane
-contains THYKALOIDS which are flat disks with pigment/chlorophyll in
- GRANA is stacked thylakoids which are linked together by lamellae
-LAMELLAE are flattened membranes which link grana together, to transport chemicals
-STROMA is a fluid which contains enzymes for photosynthesis and stores starch grains#
FUNCTION
-absorbs light energy for photosynthesis
-To produce organic substances eg. carbohydrates / lipids
structure and function of cell wall
STRUCTURE
-a rigid structure that surrounds cells in plants, algae and fungi
-plant and algae - cellulose
-fungi - chitin
FUNCTION
-supports and strengthens cell
-keeps shape of cell and prevents change of shape
structure and function of vacuole
STRUCTURE
-a membrane-bound organelle found in the cytoplasm of plant cells
-contains cell sap (a weak solution of sugars and salts) which gives rigidity
FUNCTION
-maintains pressure inside the cell
-contains cell sap which, keeps cell rigid
-isolation of unwanted chemicals
prokaryotic cells and examples
prokaryotic cells are smaller and simpler e.g. bacteria
prokaryotic and eukaryotic cells differences
-the cytoplasm in P lacks membrane bound organelles
-P has smaller ribosomes (70s)
-P has no nucleus, they have a single circular DNA molecule that is free in the cytoplasm
prokaryotic cells organelles:
-plasmids
-a slime capsule surrounding the cell
-flagella
-cell surface membrane
-cell wall
-cytoplasm
-small ribosomes
-circular DNA
circular/ chromosomal DNA
-free in cytoplasm
-not associated with proteins
flagellum
-a long hair like structure that rotates, which is responsible for the movement of cells
plasmids
-small circular loops of DNA, which passes on genetic information to other bacteria
slime capsule
-the capsule is made up of secreted slime made of protein, which protects the cell from the attack by cells of the immune system (E.g. white blood cells/ phagocytosis)
-protects from pathogens and phagocytosis
small ribosomes
-small ribosomes which are made up of proteins and rRNA, this is the site of protein synthesis
cell wall
-contains murein, a glycoprotein
virus + purpose + structure
-ACELLULAR (not made of cells) and NON LIVING (have no metabolism), which are NOT CELLS
-viruses invade and replicate inside of cells of other organisms, known as host cells and attach to them
-the structure of a virus particle consist of nucleic acid (DNA & RNA), capsid and attachment protein
virus structure
-nucleic acid/ genetic material
-attachment protein
-capsid
-genetic material/ nucleic acid: consists of nucleic acids (either DNA or RNA), surrounded by a capsid (protein coat)
-capsid: a protective protein coat which encloses the virus
-attachment proteins: sticks out from the edge of the capsid, allows the virus to attach to a specific host cell
cell fractionation
used to separate and isolate the different organelles, so they can be studied easily under an electron microscope
3 steps of cell fractionation
- homogenisation: breaking up the cell
- filtration: getting rid of large cell debris
- ultracentrifugation: separating the organelles
homogenisation
-this breaks up cells by vibrating the cells or grinding the cells up in a blender
-this breaks up the plasma membrane and releases the organelles into the solution
3 characteristics the solution must have
-ice cold: to reduce enzyme activity so organelles are not digested and damaged
-isotonic: so water doesnt move in and out of organelles by osmosis, so they dont burst
-buffered: to maintain the pH, so enzymes dont denature
- filtration
the homogenised (broken up) solution if filtered through a gauze to remove any large cell debris, the organelles are small and will pass through the gauze
- ultracentrifugation
-the solution is poured into a test tube, then put into a centrifuge (a machine that seperates material by spinning) and is spun at a low speed
-the heaviest organelles (e.g. nuclei) go to the bottom of the tube by the centrifuge and form a pellet (thick sediment at the bottom)
- the rest of the lighter organelles stay suspended (split) in the fluid above the sediment - the supernatant
-the supernatant is drained and poured into another test tube, and respun in the centrifuge at a higher speed, with the next heaviest organelles (e.g. mitochondria) forming a pellet at the bottom of the tube
-the process is repeated at higher and higher speeds, until all the organelles are separated out
-each time, the pellet at the bottom of the tube is made up of lighter and lighter organelles
organelles are separated in order of mass
-nucleus, chloroplasts, mitochondria, lysosomes, ER (endoplasmic reticulum), ribosomes
magnification
-how much bigger the image is than the specimen (actual size)
resolution
(how detailed the image is)
-the able to distinguish between 2 points that are close together on an image
2 types of microscopes
-optical (light) microscope
-electron microscopes (2 types: SEM (Scanning electronic microscope) and TEM (transmission electron microscopes))
how does a optical microscope work?
-uses light to form an image by illuminating the specimen
-specimens must be thin enough to transmit the light
-light passes through specimen, different structures absorb different amounts and wavelength
Why is the resolution of an optical microscope low?
Light has a relatively long wavelength, so the resolution is low
advantage of optical light microscope
-colour image
-can view living organisms
-cheap and easy to use
disadvantages of optical microscope
-can only be used on thin specimens
-low resolution due to long wavelength of light
-cant see internal structure or organelles or ribosomes
-low magnification
-2D image of a cross section
how does a scanning electron microscope work?
-electrons focused using electromagnets
-scans a beam of electrons across the specimen, knocks electrons off the specimen and gathered in a cathode ray tube to form an image
-can only view dead organelles
advantages of scanning electronic microscope
-3D images
-shows the surface of the specimen
-specimens doesnt need to be thin
disadvantages of scanning electron microscope
-lower resolution image than TEM
-can only view dead specimens
-can’t see internal structures
-black and white image
-complex preparation
how does a transmission electron microscope work?
-electrons focused using electromagnets
-the beam of electrons are transmitted through the specimen - denser parts absorb more, so look darker
-can only view dead organelles
advantages of transmission electron microscope
-highest magnification and resolution than SEM
-can see internal structures of organelles and ribosomes
-very high resolution due to short wavelength of electrons
disadvantages of transmission electron microscope
-used only on thin specimens
-black and white image
-2D
-can only view dead specimens
-complex preparation
How can an eyepiece graticule be used to measure magnification?
The eyepiece graticule is CALIBRATED against a STAGE MICROMETER SCALE (known length) - works out the length that each eyepiece graticule division represents
describe how the size of an object is viewed with an optical microscope can be measured
- LINE UP the scale of eyepiece with scsale of stage micrometre
- CALIBRATE eyepiece graticule- use stage micrometre to calculate size of divisions on eyepiece graticule
- Take micrometre away and use graticule to measure howmanydivisions make up the object
- Calculate size of object by multiplying number of divisions by size of division
- Recalibrate eyepiece graticule at different magnifications
artefact
-Something that results from the way a specimen is prepared
-Artefacts are anything seen in the image that are not part of the specimen
suggest how the scientific community distinguished between artefacts (e.g. dust, air bubbles occuring during preparation) and cell organelles
-scientists prepared specimens in different ways
-if an object was seen with one technique but not another, it was more likely to be an artefact than an organelle
