Eukaryotic Cell S&F

Question 1

size of viruses, prokaryotic and eukaryotic cells (diameter)

Answer 1

v: 20-100 nm
prok: 0.2-10 μm
euk: 10-100 μm

Question 2

Key diff.s between prok. and euk. cells (5)

Answer 2

1) Membrane-bound organelles not present in prok. (no endomembrane system)
2) No nucleoli vs nucleoli present
3) Single circular chromosome vs multiple linear chromosomes
4) mode of cell division: binary fission vs mitosis
5) No meiosis in prok.

Question 3

Algae, yeast, amoeba, phytoplankton. What are they?

Answer 3

Unicellular eukaryotic organisms

Question 4

Cell size is kept (___) to maximise (______), thus allowing (__________)

Answer 4

small; SA:V; ↑ chemical exchanges with the extracellular environment and diffusion of materials to occur at a faster rate

Question 5

Lower limit of cell size is determined by

Answer 5

Min. amount of space needed to contain the essential elements of its function

Question 6

Upper limit of cell size is determined by

Answer 6

SA: V needed for exchange of materials between cell and its environment

Question 7

The cytoplasm refers to (______), except (____).

Answer 7

All organelles + cytosol; except nucleus

Question 8

Prok. vs euk. ribosome (size and name)

Answer 8

Euk.: 30nm, 80S
Prok.: slightly smaller, 70S

Question 9

Proteins synthesised by ribosomes on rER are destined for _____ (3)

Answer 9

1) Export out of cell
2) Insertion into membrane (e.g. rER)
3) Transport to membrane-bound organelles (e.g. hydrolytic enzymes in lysosomes)

Question 10

Function of microtubules (3)

Answer 10

1) Structural support
2) Involved in transporting molecules from one site to another
3) Component of spindle fibres

Question 11

Function of MTOCs

Answer 11

Give anchorage and orientation to the microtubule assembly

Question 12

Function of microfilaments (2)

Answer 12

1) involved in cell motility
2) Changes in cell shape

Question 13

Function of intermediate filaments (2)

Answer 13

1) Stabilise organelles like nucleus
2) involved in specialised cell junctions

Question 14

Structure and subunits of microtubules, microfilaments and intermediate filaments

Answer 14

tubulin (helical arrangement), actin (twisted double strand of beads), various proteins (rope-like bundles)

Question 15

Homogenisation [definition]

Answer 15

Disruption of cells and release of the individual cellular components

Question 16

Methods for homogenisation (7)

Answer 16

1) Ultrasound
2) Pressure cell
3) Mortar, Pestle, and abrasive material like sand/silica
4) Osmotic lysis
5) Blender
6) Use of chemicals like detergents to dissolve plasma membrane
7) Electroporation

Question 17

Conditions needed for homogenisation (4)

Answer 17

1) Isotonic medium
2) Buffer solution to maintain suitable pH
3) Temp. of 4℃
4) Temp. > 0℃

Question 18

Purpose of conditions for homogenisation (4)

Answer 18

1) Prevent osmotic damage in organelles
2) constant pH to prevent change in protein structure → membrane stability
3) keep enzymes inactive (to stop cellular processes)
4) above 0℃ to prevent autolysis

Question 19

Differential centrifugation [definition]

Answer 19

Purification of cell components

Question 20

Purpose of centrifugation

Answer 20

To separate organelles

Question 21

Methodology of centrifugation (3)

Answer 21

1) the homogenate is subjected to progressively increasing speeds and duration of centrif. to separate particles in descending size and density.
2) After each speed, the supernatant can be drawn off and re-centrifuged at a higher speed and for a longer duration.
3) A series of pellets containing cell organelles of decreasing size can thus be obtained.

Question 22

Centrifugation is possible because

Answer 22

Most organelles are discrete particles with unique sizes and densities

Question 23

Autoradiography [definition]

Answer 23

Use of X-ray film to visualise molecules or fragments of molecules that have been radioactively labelled

Question 24

Purpose of autoradiography (2)

Answer 24

1) To identify sites of synthesis and cellular distribution of metabolic products
2) used with LM/EM to trace secretion products from their synthesis sites to their eventual destinations

Question 25

Methodology of autoradiography (3)

Answer 25

1) cells/tissue sections as are incubated w radioactive substances
2) Cell/tissue is mounted on glass slides, which is dipped into photographic emulsion
3) The decay of radioactive isotopes create dark spots on the emulsion, allowing for identification of where the radioactive substance is

Question 26

Purpose of homogenisation: to break (_______________) and to release (_____).

Answer 26

Tissues into smaller pieces; organelles

Question 27

Advantages of membranous organelles (2)

Answer 27

1) maintenance of characteristic diff.s between contents of each organelle and cytosol
2) increase efficiency of reactions by increasing membrane surface area

Question 28

Cell theory [definition]

Answer 28

1) All living organisms are composed of one or more cells
2) Cells are the basic units of structure, organisation and function
3) All new cells arise from old/pre-existing cells