Cell organelle specialization

Question 1

Nucleus

Answer 1

• Usually 1, some cells have multiple or none due to development
  Ex. multiple nucleus= muscle fibres because multiple cells combine together
  Ex. no nucleus- RBC, during development the nucleus is expelled
• Basophilic
• Differing levels of euchromatin (EC) and Heterochromatin (HC).
  EC- appears lighter, less coiled, DNA more exposed because more active nucleus actively replicating whereas HC- appears darker, more coiled, DNA less exposed
• Nucleolus- region where rRNA is made for ribosome synthesis

**Active cells will have more EC and nucleoli

Question 2

Mitochondria

Answer 2

• produce ATP
• Metabolize fatty acids
• Gluconeogenesis
• Calcium buffering- Ca is a signal for many processes, so needs to be regulated
• Regulate apoptosis

Visual appearance gives a clue on cell function
- Energy producing mitochondria form cristae
- Lipid producing mitochondria form tubular projections

Question 3

Ribosomes

Answer 3

Found free in cytoplasm or in the RER.

Makes proteins.

Made up of rRNA and proteins= basophilic

Question 4

Smooth ER

Answer 4

• No ribosomes, continuous with RER
• Synthesizes cholesterol, steroids, carbohydrates, lipids, phospholipids, detoxifies drugs or toxins (in liver), stores Ca (in muscles)
• Abundant in cells that are important for synthesis of lipids and metabolism of drugs and toxins (eg. Hepatocytes) AND cells that produce steroid hormones (eg. Ovarian cells, adrenocortical cells)

Question 5

Golgi apparatus

Answer 5

Function:
- Chemical modification: contains enzymes to chemically modify nascent proteins (eg. Glycosylation, sulfation, phosphorylation, cleavage)
- Packing and storage: initiates packing, concentrations and storage of secretory products, preparing them for transport to specific locations of the cell

Structure:
- Stacked membrane: composed of series of flattened, stacked pouches
- Cis face: the receiving side; closest to the ER. Receives materials from ER for modification
- Trans face: the shipping side; oriented toward the plasma membrane. Sends modified products to their final destinations

**Hard to stain as they are primarily made of lipids.

Question 6

Secretory granules

Answer 6

Made from golgi body.

Can be both basophilic or acidophilic depending on the chemical composition of their contents

Question 7

Lysosomes

Answer 7

Degradation organelle

usually spherical. Appear uniformly granular and electron dense. If less electron dense then degradation is probably underway.

typically acidic due to enzymes

Made in RER, shipped to golgi

Question 8

Function of lysosomes

Answer 8

• Remove obsolete or non-functional proteins, organelles or membranes
  Ex. autophagosomes- lipofuscin
• Store hydrolytic enzymes before they are secreted outside
  Ex. Osteoclasts are bone cells that break down bone tissue. Important for maintenance, repair, and remodeling of bones
• Store hydrolytic enzymes to digest invading pathogens
  Ex. macrophages and neutrophils function to detect, engulf, and destroy invading pathogens

Question 9

Peroxisomes

Answer 9

Degradation organelles

Structure
- Similar to lysosomes
- Abundant in liver and proximal convoluted tubules of the kidney
- Can appear crystalline
- Contains various enzymes that work at neutral pH

Function
- Detoxification
- Beta-oxidation of long fatty acids
- Removes the reactive oxygen species (eg. Catalase, oxidases, peroxidase) to prevent oxidative damage

Question 10

Lipid droplets

Answer 10

Structure:
- Non membrane bound droplets are found in adipocytes, steroid producing cells

Function:
- Lipid storage

Typically dyed orange- typical staining method for lipid droplets