topic 2 Flashcards
Prokaryote and
animal cell
comparison
- Bacterial cell is much smaller than a human cell;
- Bacterial cell has a cell wall but human cell does not;
- Bacterial cell lacks a nucleus but human cell has a nucleus;
- Bacterial cell lacks membrane-bound organelles but human cell has membrane-bound organelles;
- Bacterial ribosomes smaller than human ribosomes / bacteria have
70S ribosomes whereas humans have 80S ribosomes; - Bacterial DNA is circular but human DNA is linear;
- Bacterial DNA is ‘naked’ whereas human DNA is bound to histones / proteins
Phospholipid arrangement in a
membrane
- Bilayer OR Water is present inside and outside a cell;
- Hydrophobic (fatty acid) tails point away/are repelled from water
OR
Hydrophilic (phosphate) heads point to/are in/are attracted to water;
Hydrophobic
substances moving
across membranes
- Lipid soluble;
- (Diffuse through) phospholipid (bilayer);
Role of organelles and
proteins
- DNA in nucleus is code (for protein);
- Ribosomes/rough endoplasmic reticulum produce (protein);
Accept rER for ‘rough endoplasmic reticulum’ - Mitochondria produce ATP (for protein synthesis);
- Golgi apparatus package/modify;
OR
Carbohydrate added/glycoprotein produced by Golgi apparatus;
Accept body for ‘apparatus’ - Vesicles transport
OR
Rough endoplasmic reticulum transports; - (Vesicles) fuse with cell(-surface) membrane;
Describe how you
would use cell
fractionation
techniques to obtain a
sample of
mitochondria from
leaf tissue.
- Macerate / homogenise / blend / break tissues / cells (in solution);
- Centrifuge the supernatent;
- At different / increasing speeds until mitochondria fraction obtained/until 3 rd pellet is obtained;
Explain the conditions
that would be
necessary for cell
fractionation.
- Ice-cold - Slows / stops enzyme activity to prevent digestion of
organelles / mitochondria; - Buffer - Maintains pH so that enzymes / proteins are not denatured;
Reject reference to cells - Same water potential - Prevents osmosis so no lysis / shrinkage of organelles / mitochondria;
Explain how
ultracentrifugation
separates different
molecules.
- Spin (liquid / supernatant) at (very) high speed / high g;
Need context of high, not just ‘faster’, ‘higher’ in context of use of bench centrifuge - Molecules separate depending on (molecular) mass / size / density;
Why is a detergent
used to lyse (breaking
open) cells and
organelles.
- Cell membranes made from phospholipid;
- (Detergent) dissolves membranes / phospholipid (bilayer);
Ignore breaks down
Reject hydrolysis
TEM compared to
optical microscope
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller organelles / named cell structure can be
observed
OR
greater detail in organelles / named cell structure can be observed; - TEM view only dead / dehydrated specimens and optical (can) view
live specimens; - TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming preparation;
- TEM focuses using magnets and optical uses (glass) lenses
TEM compared to
SEM
Higher resolution OR View internal structures
Why must a sample
for a microscope be
thin?
- Need a single layer of cells / only a few cells thick / not too many layers / detail obscured by cells underneath;
- Light must be able to pass through;
Making a temporary
mount (microscope
slide)
- Add drop of water to (glass) slide;
- Obtain thin section (of plant tissue) and place on slide / float on drop of water;
- Stain if necessary;
- Lower cover slip using mounted needle.
Measuring dry mass
- Heat at 100°C / heat to temp to evaporate water;
Value which would not burn material - Weigh and heat until no further change in mass;
Mitosis
(During prophase)
1. Chromosomes coil / condense / shorten / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the centromere;
(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;
(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles /
ends of the cell / separate;
(During telophase)
8. Chromatids / chromosomes uncoil / unwind / become longer
Mitosis - root tip
experiment
Why the tip?
Pressed down firmly
on the cover slip?
Ensuring accuracy
Where dividing cells are found / mitosis occurs
Single / thin layer of cells / spread out cells so light passes through
1. Examine large number of fields of view / many cells;
2. To ensure representative sample;
OR
3. Repeat count;
4. To ensure figures are correct;
OR
5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting