3: Cell Structure

Question 1

magnification equation

Answer 1

image = actual size x magnification

Question 2

What is resolution

Answer 2

minimum distance apart two objects can be in order to be distinguished

Question 3

cell fractionation importance

Answer 3

to obtain large number of isolated organelles for studying structure and function of cells

Question 4

Why put cell tissue into a cold buffered solution of the same water potential?

Answer 4

cold: to reduce enzyme activity that might break down organelles
buffered: so pH doesn’t fluctuate and alter organelle structure
same water pot: to prevent organelles bursting or shrinking as result of osmotic water loss/gain

Question 5

Homogenation

Answer 5

cells broken up in homogeniser to release organelles from cells, filtered to remove complete cells and large debris

Question 6

ultracentrifugation

Answer 6

cell fragments of homogenate seperated in a centrifuge. spins at high speed to produce centrifugal force, heaviest organelles forced to bottom of test tube, form pellet. Process repeated with leftover supernant at higher speeds.

Question 7

Transmission Electron Microscope (TEM)

Answer 7

Electron beam onto thin specimen, absorbed or pass through, produce photomicrograph, 0.1nm resolution.

Question 8

TEM limitations

Answer 8

• vacuum so not living specimen
• complex staining process and image not in colour
• extremely thin specimen
• image may be obstructed by artefacts

Question 9

Scanning Electron Microscope

Answer 9

same as TEM, but specimens do not need to be extremely thin. electron beam passed back and forth in regular pattern, building up 3D image.

Question 10

Calibrating eye piece graticule

Answer 10

line up graticule and stage micrometer scale.
Calculate length of divisions on graticule and therefore ratio

Question 11

Eukaryotic cell structures

Answer 11

Nucleus
Mitochondria
Chloroplasts
Endoplasmic reticulum
Golgi apparatus
Lysosomes
80S Ribosomes
Cell wall
Vacuoles

Question 12

functions of the nucleus

Answer 12

acts as control centre through manufacture of mRNA tRNA and therefore protein synthesis

retains genetic material of cell in form of DNA and chromosomes

manufactures rRNA and ribosomes

Question 13

Mitochondria structure

Answer 13

double membrane, controls entry/exit
cristae, extension of inner memb, attachment of resp enzymes and proteins
matrix, contains proteins, lipids, ribosomes, DNA that control own protein production. contains most resp enzymes.

Question 14

Mitochondria function

Answer 14

Site of aerobic resp (krebs and oxidative phosphorylation)
produce ATP

Question 15

Chloroplast structure

Answer 15

Envelope- double plasma membrane
grana- light absorption stage, large surface area
thylakoids (chlorophyll)
stroma- 2nd stage of photosynthesis, contains starch grains, enzymes
contains DNA, ribosomes to manufacture proteins for PS

Question 16

Rough endoplasmic reticulum

Answer 16

ribosomes on surface, provides large SA for protein/glycoprotein synthesis
path for transport of materials throughout cell (e.g proteins)

Question 17

Smooth endoplasmic reticulum

Answer 17

tubular appearance, synthesise, store, transport lipids and carbs

Question 18

Golgi apparatus structure & function

Answer 18

formed of stacks of cisternae & vesicles. transports, stores, modifies proteins and lipids (e.g adds carb to form glycoprotein, produces secretory enzymes, forms lysosomes)

Question 19

Lysosomes function

Answer 19

hydrolyse material in phagocytic cells
release enzymes out cell by exocytosis
digest worn out organelles to be reused
break down dead cells, AUTOLYSIS

Question 20

Ribosomes

Answer 20

80S eukaryotic
70S prokaryotic
site of protein synthesis
2 subunits rRNA and protein

Question 21

Cell wall

Answer 21

microfibrils of cellulose, provides mechanical strength so cells don’t burst from pressure of osmosis, and to plant as a whole, allows water to pass along

Question 22

Vacuole

Answer 22

single membrane, tonoplast. Keeps cell turgid. contains minerals, salts & AAs (temp food store), waste, pigment