Cell Ultrastructure

Question 1

State 3 details about the nucleus.

Answer 1

• Brain of the cell.
• Double nuclear membrane.
• Houses DNA (in the form of chromatin) within the nucleolus (site of ribosomal RNA formation i.e. DNA transcription).

Question 2

What is the mitochondria responsible for?

Answer 2

The site of oxidative phosphorylation.

Question 3

What does the mitochondria consist of?

Answer 3

Matrix and double membrane where the inner membrane is highly folded (and there is an intramembranous space).

Question 4

What occurs in the matrix of the mitochondria?

Answer 4

Tricarboxylic acid (Kreb’s) Cycle.

Question 5

What occurs in the outer membrane of the mitochondria?

Answer 5

Lipid synthesis and fatty acid metabolism.

Question 6

What occurs in the inner membrane of the mitochondria?

Answer 6

Respiratory chain/electron transport ATP production.

Question 7

What occurs in the intramembranous space of the mitochondria?

Answer 7

Nucleotide phosphorylation from ADP to ATP.

Question 8

Why is the rough endoplasmic reticulum rough?

Answer 8

Due to the numerous ribosomes on the surface.

Question 9

What is the rough endoplasmic reticulum?

Answer 9

Highly folded flattened membrane sheets and the site of protein synthesis.

Question 10

What is the smooth endoplasmic reticulum?

Answer 10

Highly folded flattened membrane sheets- the site of lipid synthesis and processes and stores synthesised proteins (check notes- is it meant to be lipids).

Question 11

What is the golgi apparatus?

Answer 11

Parallel stacks of membrane- processes and modifies macromolecules synthesised in the ER.

• Located close to the cell nucleus.
• N.B. In most cells the golgi apparatus cannot be seen, however, it can be seen clearly in plasma cells.

Question 12

What is the cis (first) golgi?

Answer 12

Nuclear facing, receives the (smooth) ER vesicles and protein phosphorylation occurs here.

Question 13

What is the medial golgi?

Answer 13

The middle/central part, modifies (lipid and protein) products by adding sugars to form complex oligosaccharides.

Question 14

What is the trans golgi?

Answer 14

The last part (this transfers)- the proteolysis of peptides into active forms and the sorting of molecules into vesicles (which bud from the surface).

Question 15

What are vesicles?

Answer 15

Very small, spherical membrane-bound organelles.

Question 16

What is the purpose of vesicles?

Answer 16

Transport & store material and exchange cell membrane between compartments

Question 17

Name 5 types of vesicles.

Answer 17

1. Cell-surface derived (pinocytotic and phagocytotic vesicles).
2. Golgi- derived transport vesicles.
3. ER - derived transport vesicles.
4. Lysosomes.
5. Peroxisomes.

Question 18

What are lysosomes responsible for?

Answer 18

• Waste disposal system and is the site of breakdown for most molecules, derived from golgi.
• They also breakdown debris from dead cells & bacteria and damaged cell organelles.

Question 19

How do lysosomes function?

Answer 19

• Contains digestive enzymes.
• H+ - ATPase on the membrane pumps H+ ions into the cell, creating a low pH (pH5) to enable acid hydrolases to function.

Question 20

What are peroxisomes responsible for?

Answer 20

• Small, membrane-bound organelles containing enzymes which oxidase long-chain fatty acids (long chain FAD-amino oxidase, catalase and urate oxidase - INVOLVED IN THE PROCESS BY WHICH FATTY ACIDS ARE BROKEN DOWN INTO TWO-CARBON FRAGMENTS WHICH THE CELL CAN USE AS A SOURCE FOR GENERATING ATP) - BETA OXIDATION.
• They also produce hydrogen peroxide (by-product of the breakdown of fatty acids) which can be used to destroy pathogens etc.
  N.B. Hydrogen peroxide is toxic to cells, but peroxisomes can destroy hydrogen peroxide thereby preventing its toxic effects and protecting the body etc.

Question 21

What is the cytoskeleton?

Answer 21

• Filamentous proteins which brace the internal structure of the cell.
• Not visible in light microscopy.

Question 22

What is the purpose of the cytoskeleton?

Answer 22

• Helps cells maintain their shape and internal organisation.

Question 23

What are microfilaments?

Answer 23

• (5nm).

- ACTIN forms a bracing mesh (cell cortex) on the inner surface of the cell membrane.

Question 24

What are intermediate filaments?

Answer 24

• (10nm + 6 types of protein).

- Anchored transmembrane proteins which can spread tensile force through tissues.

Question 25

What are the 6 proteins intermediate filaments?

Answer 25

1. Cytokeratins - epithelial cells (found in many different cells).
2. Desmin - myocytes.
3. Glial fibrillary acidic protein (supports neurones in the brain) - astrocytic glial cells.
4. Neurofilament protein - neurons.
5. Nuclear laminin - nuclei of all cells.
6. Vimentin - mesodermal cells.

Question 26

What are microtubules?

Answer 26

• (25nm).
• TUBULIN ( alpha and beta, which arrange in groups of 13 to form hollow tubes).
• Arise from centrosome (comprises of 2 centrioles).
• Found in all cells except for erythrocytes (red blood cells).

Question 27

Why are microtubules not present in erythrocytes?

Answer 27

Erythrocytes have no nuclei thus no microtubules required since no cell division occurs thus no cell structure is really required.

Question 28

What is lipofuscin?

Answer 28

• Membrane-bound orange-brown pigment.
• Peroxidations of lipids (degradation of lipids) in older cells.
• Common in heart and liver, found in older people - sign of wear and tear.

Question 29

Where is lipofuscin found?

Answer 29

• Common in heart and liver, found in older people - sign of wear and tear.

Question 30

How are lipids found in the cell?

Answer 30

• Non-membrane-bound vacuoles.
• Appears as empty space in histology since washed /dissolved in processing.
• Stored in adipocytes and the liver.

Question 31

Where is lipid found?

Answer 31

Stored in adipocytes and the liver.

Question 32

What is glycogen?

Answer 32

• CHO polymer in cytoplasm.
• Normally only seen on electron microscopy.
• May accumulate in some cells and in some diseases.