Topic 3 - Cell Structure

Question 1

What is the equation for magnification?

Answer 1

size of image / actual size

Question 2

In cell fractionation, why must the tissue be placed in a cold, isotonic, buffered solution?

Answer 2

Cold = reduce enzyme activity
Same WP as tissue = prevent organelles bursting or shrinking from osmosis.
Buffered = so pH does not fluctuate which could alter the organelles structure.

Question 3

How a cells homogenised?

Answer 3

Large pieces of cells and debris are removed in a homogeniser.

Question 4

What is ultracentrifugation?

Answer 4

1) Cellular fragments placed in a centrifuge.
2) Spun at a low speed - heaviest organelles forced to the bottom, forming a thin sediment/pellet.
3) Supernatant is removed.
4) Supernatant transferred to another tube and spun faster than before so next heaviest organelles are forced to bottom.
5) Process is repeated, increasing the speed each time.

Question 5

What is a Transmission Electron Microscope (TEM)?

Answer 5

• Uses a beam of electrons.
• Can magnify objects up to 500,000x
• Good resolving power (0.1nm)

Question 6

How does a TEM work?

Answer 6

1) Electrons ‘fired’ from electron gun, pass through section of the specimen.
2) Electron beam is focused using electromagnets and denser parts of specimen absorb more electrons.
3) Image produced on a fluorescent or photographic plate.

Question 7

What are the limitations of a TEM?

Answer 7

• Cannot be used on living specimens.
• Must be extremely thin.
• Can result in artefacts.
• Only 2D images are captured.
• Black and white image.

Question 8

What is a Scanning Electron Microscope (SEM)? How does it work?

Answer 8

1) Electrons are passed across surface of specimen.
2) Scattered electrons form image on screen.
3) Depressions appear darker and extensions appear lighter.
4) Image is 3D

Question 9

What are the limitations (and advantages!) of a SEM?

Answer 9

+ Specimens don’t need to be thin.
+ Preparation technique is less complex than TEM (less chance of artefact).

• No 2D images.
• Resolving power is lower than TEM.

Question 10

Nucleus:
Nucleolus
Nuclear pores
Chromatin
Nuclear Membrane

Answer 10

• Site of ribosome synthesis.
• Allows diffusion of large molecules out nucleus.
• Diffuse form of a chromosome.
• Outer part continuous with RER.

Question 11

Mitochondria:
Outer Membrane
Cristae
Inner Membrane

Answer 11

• Increase surface area for attachment of proteins involved in respiration.
• Contains proteins, lipids, ribosomes, and DNA.
• Controls entry and exit of materials.

Question 12

Ribosomes

Answer 12

• Tiny granules made from 2 subunits - small and large.
• Site of polypeptide synthesis.

Question 13

Rough Endoplasmic Reticulum (RER)

Answer 13

• Enclose a network of cisternae.
• Site of protein synthesis.
• Provides pathway for transport of materials.

Question 14

Smooth Endoplasmic Reticulum (SER)

Answer 14

• Enclose a network of cisternae.
• No ribosomes.
• Site of lipid and carbohydrates synthesis, store and transport.

Question 15

Golgi Apparatus

Answer 15

• Combines carbohydrates and proteins = glycoproteins.
• Processes enzymes
• Secrete carbohydrates.
• Transport, modify, and store lipids.
• Form Golgi vesicles.

Question 16

Lysosomes.

Answer 16

• Produced by Golgi apparatus.
• Contain lysozymes which digest unwanted material in the cell.
• Digest pathogens, worn out organelles, and cells after they die.

Question 17

Prokaryotic cell:
Slime capsule
Cell wall
DNA
Cytoplasm
Flagellum
Plasmid
Ribosome

Answer 17

• Stores waste, protects against drying out.
• Made of murein, protects cell.
• Carries genes for the proteins the cell needs.
• House and maintains optimal environment for protein synthesis.
• For locomotion.
• Carries genes.
• Protein synthesis.

Question 18

What is cell differentiation?

Answer 18

Structure of each cells that make up a specialised cell is adapted to carry out specific functions.

Question 19

What are some specialised cells?

Answer 19

Sperm cells
Dendritic cells
Lymphocyte cells