12.5 Studying Cells Flashcards
what is a cell
the basic unit of life
all cells in multicellular organisms will have the same…
basic structure
in the organism a cell will be related to its…
function
eukaryotic cell definition
- ‘true nucleus’
- DNA of eukaryotes is enclosed by a nuclear membrane
- cells have membrane bound organelles
- linear DNA molecules coiled around histone proteins to form chromatin
all eukaryotic cells
plants, algae, animal, protozoan, fungi
4 eukaryotic kingdoms
1 animalia
2 plantae
3 protoctista (algae, protozoa)
4 fungi (unicellular yeast cells)
plant cells have…
CELLULOSE cell walls
what do algal cells contain
chloroplasts -> photosynthesis
(protoctista)
characteristics of fungi
- multi-cellular fungi have cells joined -> long hyphae
- cell walls made from CHITIN
draw and label an animal cell (eukaryotic)
what’s the difference between a mitochondrion and mitochondria
mitochondrion (singular)
mitochondria (pleural)
draw and label a plant cell (eukaryotic)
draw and label a chloroplast (plants / algae)
5 things in a chloroplast
- granum
- thylakoid membrane
- stroma
- starch grains
- DNA and ribosomes
function of granum
stack of thylakoid membranes
function of thylakoid membrane
contains chlorophyll for photosynthesis & ATP synthase enzyme to produce ATP
function of stroma
fluid filled part, some of the photosynthetic reactions occur here
function of starch grains
the energy storage molecule in plants
function of DNA and ribosomes
contain their own DNA and 70s ribosomes for synthesis of enzymes needed for photosynthesis
draw and label a cellulose cell wall (plants / algae)
3 things in a cellulose cell wall
- many weak H bonds between cellulose fibrils
- micro fibrils arranged in a matrix
- plasmodesmata (gaps in the cell walls that connect cell cytoplasm’s together)
function of many weak H bonds between cellulose fibrils (cellulose cell wall)
very strong -> limits the volume of water that can move into the cell and stops osmotic lysis (bursting)
function of micro fibrils arranged in a matrix (cellulose cell wall)
wall is permeable to most molecules unlike the membrane
function of plasmodesmata (gaps in the cell walls that connect cell cytoplasm’s together) (cellulose cell wall)
allow the easy movement of water-soluble molecules
key differences between plant and animal cells
plant cells
- cellulose cell wall
- chloroplasts present (not in roots)
- large central vacuole
- carbohydrates stored as starch
- has no centrioles
animal cells
- no cell wall
- no chloroplasts
- no large central vacuole
- carbohydrates stored as glycogen
- has centrioles
production, transport and release of proteins from eukaryotic cells
- DNA in nucleus contains genetic code to make proteins
- New protein is synthesised on ribosomes
- Protein is transported though RER
- Vesicles pinched off from the RER (with polypeptide chain inside) are transported to the Golgi apparatus
- Vesicle fuses with Golgi membrane and contents are shed into Golgi sacs
- Proteins are built into more complex molecules such as enzymes or glycoproteins
- Vesicles contain modified proteins (for secretion or cell membrane) bud off at the other end of the Golgi
- Vesicles fuse with cell membrane
- Protein released - leaves cell by exocytosis
- Lysosomes (contain digestive enzymes)
prokaryotic cell definition
- ‘before nucleus’
- do not have nucleus or other membrane bound organelles
- DNA circular, not associated with histone proteins
draw and label a bacterial cell (prokaryotic)
differences between prokaryotic and eukaryotic cells
prokaryotic
- DNA circular, not associated with histone proteins
- no membrane bound organelles (no nucleus, RER, SER, Golgi, Lysosomes)
- no true nucleus (DNA free in cytoplasm)
- smaller ribosomes (70s)
- some have capsule, 1 or more flagella / plasmids
- mesosomes for ATP synthesis
- cell wall (murein / peptidoglycan)
eukaryotic
- DNA linear, associated with histone proteins
- membrane bound organelles (mitochondria, RER, SER, Golgi, Lysosomes)
- nucleus (DNA contained within nuclear membrane)
- larger ribosomes (80s)
- no capsule
- no mesosomes (mitochondria)
- cell wall (plant -> cellulose)
viruses definition
- acellular (not cells), not alive
- very small
- require a living cell to replicate inside
- no cell surface membrane
- no organelles / cytoplasm
- no metabolic reactions
characteristics of viruses
- contain DNA or RNA (can be single or double stranded)
- surrounded by a protein coat (capsid)
- has attachment proteins (enable it to bind to host cells)
- has enzymes (uses to replicate its genetic information and insert it into the host cell DNA)
- liquid envelope
viruses have no organelles so they are unable to do what
- unable to replicate independently
- can’t synthesis protein / DNA to make copies of itself
- USES THE HOST CELL’S ORGANELLES TO DO THIS
is RNA in a:
- prokaryotic cell (bacteria)
- virus
- eukaryotic cell
- YES prokaryotic cell (bacteria)
- YES virus
- YES eukaryotic cell
are ribosomes in a:
- prokaryotic cell (bacteria)
- virus
- eukaryotic cell
- YES prokaryotic cell (bacteria)
- NO virus
- YES eukaryotic cell
is a capsid in a:
- prokaryotic cell (bacteria)
- virus
- eukaryotic cell
- NO prokaryotic cell (bacteria)
- YES virus
- NO eukaryotic cell
are membrane bound organelles in a:
- prokaryotic cell (bacteria)
- virus
- eukaryotic cell
- NO prokaryotic cell (bacteria)
- NO virus
- YES eukaryotic cell
3 microscopes
- light microscope
- transmission electron microscope (TEM)
- scanning electron microscope (SEM)
characteristics of light microscopes
- specimens illuminated by light
- focussed using glass lenses
- limited magnification (more lenses -> magnification by larger amount -> loses resolution)
- limited resolution (limited by the wavelength of light)
- 200nm resolution (can see cells but not organelles)
resolution definition
the ability to distinguish 2 objects that are close together
key phrase to remember about the wavelength and resolution of electron microscopes
the shorter the wavelength of the light / electrons, the better / higher the resolution
similarities between TEM and SEM
- both use a beam of electrons to illuminate the specimen
- focused using electromagnets
- detected using a phosphor screen / photographic film (capture image)
- very small wavelength (observes ribosomes - 20nm)
- both produce images with higher resolution
the difference between TEM and SEM
TEM - produces 2D images
SEM - produces 3D images
characteristics of TEM
- electrons pass / fired through specimen
- view organelles / internal structures
- less dense (cytoplasm) absorb less electrons -> appear lighter
- denser areas / structures (nucleolus) absorb more electrons -> appear darker
characteristics of SEM
- electrons bounce off the surface of the specimen
- specimen not sliced
- images always in black and white
- always produce 3D image
ways to remember the electron microscopes
T -> Transmission -> Through
S -> Scanning -> Surface
ILLUMINATION - comparison light and TEM
L -> light
T -> beam of electrons
FOCUSED BY - comparison light and TEM
L -> lens
T -> electromagnets
MAXIMUM MAGNIFICATION - comparison light and TEM
L -> x1500 (individual cells and some large structures - nucleus)
T -> x 500,000 (objects as small as ribosomes
RESOLUTION - comparison light and TEM
L -> 200nm LOWER
T -> 1nm HIGHER
SPECIMEMS - comparison light and TEM
L -> living or dead
T -> dead (they are fixed in resin and sliced very thinly. must be in a vacuum)
STAINING PROCESS - comparison light and TEM
L -> easy (coloured dyes)
T -> complex (using heavy metals, can create artefacts - structures not actually there)
2 pieces of equipment required when using an optical (light) microscope
- eyepiece (lens) graticule
- stage micrometer
what does the eyepiece graticule do
- fits onto the eyepiece lens
- a transport ruler with numbers but has no units
what does the stage micrometer do
- a microscope slide
- has an accurate scale (1mm in 100 divisions so 1 division is 10 μm)
- placed on the stage
- ## used to work out the value of each division on the eyepiece graticule, when using a certain magnification
what is the overall job of the eyepiece (lens) graticule and the stage micrometer
MEASURE THE SIZE OF THE CELLS
(when you take the stage micrometer away and replace it with slides with a tissue specimen -> can measure the size of cells)
why does cell fractionation and differential-centrifugation occur
- to enable scientists to study organelle function
- the organelles must first be separated from the cell in order to be studied
2 stages of cell fractionation and differential-centrifugation
- homogenising
- differential centrifugation
method for separating organelles (step 1)
- tissue is homogenised in blender (liver, heart, leaf etc) to break open the cells releasing the organelles into solution.
what 3 things must the solution be for step 1
ICE COLD
ISOTONIC (same water potential)
BUFFERED
what does the solution being ice cold do
reduce the action of enzymes that would digest organelles
what does the solution being isotonic (same water potential) do
prevents osmosis of water in or out of organelles, so organelles don’t burst (lyse) or shrivel (crenation in animals)
what does the solution being buffered do
to stop pH changes which could denature proteins
method for separating organelles (step 2)
- filter the mixture to remove any large pieces of tissues / cells (cellular debris) producing a solution of suspended organelles (supernatant)
method for separating organelles (step 3)
differential centrifugation of the supernatant by:
- centrifuge at high speed (high g)
- centrifuge at a higher speed / (higher g) for a longer time
why do you first centrifuge at high speed (high g)
the densest organelles (nucleus) are forced to the bottom of the tube into a pellet which is removed. The supernatant can be spun again to obtain the smaller and lighter organelles
why do you then centrifuge at a higher speed / (higher g) for a longer time
the next densest organelles are forced to the bottom of the tube into a pellet. the pellet is removed and can be re-suspended if required.
method for separating organelles (step 4)
this process can be repeated many times, at higher speeds with each step. this separates the organelles (then molecules) according to their relative densities.
anogram for densities
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