Lecture 2 - Examining Cells & Tissues

Question 1

What is the largest human cell type that is just visible to the human eye?
What us the smallest human cell type with and without a nucleus?

Answer 1

• The female oocyte
• Platelet (without nucleus)
• Spermatozoa (with nucleus)

Question 2

In histology, what conditions are required for the sample to be analysed?

Answer 2

• Sample needs to be translucent
• Less than 20um (microns) thick
• Need to be fixed (usually with formalin), to prevent t being digested or decayed.

Question 3

What must happen to a specimen after fixation before it can be stained?

Answer 3

• Must be infiltrated with embedding medium that can be thinly sliced when hardened - e.g.: paraffin wax .
• Then mounted on microtome where it is thinly slices (2-10um thick) and placed onto glass slide.

Question 4

What is the most common staining method in histology?

What do the components of this staining method bind to?

Answer 4

• Haematoxylin + Eosin staining (H&E).
• Haematoxylin is a basic dye that binds to acidic structures (e.g.: DNA/RNA)
• Eosin is an acidic dye binds to basic structures, (e.g.: proteins, collagen etc).

Question 5

Which molecules are not detected by H&E staining?

Which method should be used instead?

Answer 5

• Neutral fats & lipids

- Acid-Schiff reagent

Question 6

Describe the basis for immunohistochemistry & immunofluorescence

Answer 6

Use of antibodies labelled with fluorescent dies which bind to specific antibodies in order to visualise the structure directly under a UV light source.

Question 7

Define the “limit of resolution”

Answer 7

Minimum distance at which two objects can be distinguished - therefore proportional to the wavelength of the viewing system.

Question 8

Why do electron microscopes have a finer limit of resolution than light microscopes?

Answer 8

As electron microscopes use electrons, which have a much longer wavelength, and therefore a better limit of resolution than light microscopes which use light.

Question 9

What type of electron microscopy is appropriate for examining the surface of cells and for examining intracellular structures?

Answer 9

Examining surface = T.E.M

Intracellular structures = S.E.M

Question 10

Describe the structure, contents and function of the nucleus, nucleolus and nuclear envelope

Answer 10

• Nucleus = Dark electron dense area on T.E.M containing condensed heterochromatin - not present in terminally differentiated cells.
• Nucleolus = One or more dark electron-dense structures. Sites of rRNA synthesis and ribosome assembly.
• Nuclear envelope = double-membrane which contain pores to allow transport in and out of the nucleus.

Question 11

What is the function of the rough and smooth endoplasmic reticulum?

Answer 11

RER = Attachment of ribosomes to carry out protein synthesis. 
SER = Primarily lipid biosynthesis and intracellular transport.

Question 12

Describe the structure and function of the Golgi apparatus.

Answer 12

• Saucer shaped stacks of cisternae
• Package and modify proteins synthesised by the RER - proteins are packaged and leave via the concave face of the golgi apparatus.

Question 13

What do lysosomes contain and what is their role?

Answer 13

Lysosomes contain hydrolases at pH 5, fuse with endocytosed vesicles (phagosomes, endosomes) and release their contents to digest material.

Question 14

Describe the structure and function of peroxisomes

Answer 14

• Peroxisomes are spherical, containing granular matrix bound by a single membrane.
• Major site of oxygen utilisation and peroxide production. Catalase enzyme utilised this peroxide (H2O2) to oxidise substrates.

Question 15

What is the role of the cytoskeleton?

What are the 3 main types of cytoskeleton?

Answer 15

• Responsible for maintaining and/or changing cell shape, as well as providing structural support and a means of movement for organelles and other structures.
• Microfilaments, intermediate filaments, microtubules.