Ultrastructure

Question 1

What is a cell?

Answer 1

The smallest unit of a living organism.

Cells form the basic unit of structure and function.

Question 2

What are the two broad divisions of cells?

Answer 2

• Prokaryotes (primitive)
• Eukaryotes (complex)

Prokaryotes include bacteria and blue-green algae; eukaryotes include animals, plants, and other organisms.

Question 3

What are the three main components of eukaryotic cells?

Answer 3

• Plasma membrane
• Nucleus
• Cytoplasm

The cytoplasm contains fluid, cytoskeleton, and all organelles except the nucleus.

Question 4

What is the function of the plasma membrane?

Answer 4

• Protection
• Communication
• Selectively allow substances in
• Respond to environment
• Recognition

The plasma membrane is flexible and composed of phospholipids, cholesterol, proteins, and carbohydrates.

Question 5

What is the plasma membrane composed of?

Answer 5

• Phospholipids
• Cholesterol
• Proteins
• Carbohydrates

The plasma membrane is a lipid bilayer with hydrophilic heads and hydrophobic tails.

Question 6

What are intrinsic proteins?

Answer 6

Proteins incorporated within the plasma membrane.

Extrinsic or peripheral proteins are attached to the inner or outer surface by weak electrostatic forces.

Question 7

True or False: The plasma membrane is destroyed during apoptosis.

Answer 7

False

In necrosis, the plasma membrane is destroyed, whereas in apoptosis, it remains intact.

Question 8

What is the function of the nucleus?

Answer 8

• Directs activities of the cell
• Stores DNA

The nucleus is the most obvious feature of the cell seen under a light microscope.

Question 9

What structures are encompassed in the nucleus?

Answer 9

• Nuclear membrane
• Nucleoplasm
• Chromosomes
• Nucleolus

Chromosomes are present in the form of chromatin, which consists of DNA and histones.

Question 10

What is the role of ribosomes in protein synthesis?

Answer 10

They align mRNA strands and facilitate the addition of amino acids to the growing polypeptide chain.

Ribosomes are made in the nucleolus and are involved in translation.

Question 11

What is the endoplasmic reticulum (ER)?

Answer 11

The site for synthesis of all transmembrane proteins and lipids for plasma membrane and cellular organelles.

The ER consists of an interconnecting network of membranous tubules, vesicles, and flattened sacs.

Question 12

What is the difference between rough and smooth endoplasmic reticulum?

Answer 12

• Rough ER (rER): Studded with ribosomes, involved in protein production and quality control.
• Smooth ER (sER): Free of ribosomes, involved in lipid synthesis and metabolism of drugs and toxins.

Liver cells, adrenals, and gonads contain a lot of sER.

Question 13

What are lysosomes?

Answer 13

Membrane-bound organelles containing digestive enzymes involved in degradation of particulate material.

They contain more than 40 acid hydrolases.

Question 14

What is the function of peroxisomes?

Answer 14

• Contain oxidases and catalases
• Produce H2O2 for killing microorganisms
• Regulate H2O2 concentration

Peroxisomes have a protective effect by oxidizing toxic substances.

Question 15

What are the three major classes of cytoskeleton proteins?

Answer 15

• Actin
• Intermediate filaments
• Microtubules

The cytoskeleton supports cell shape, maintains polarity, and organizes organelles.

Question 16

What is the function of actin microfilaments?

Answer 16

They are the most abundant cytosolic protein in cells.

Actin plays a role in cell shape and movement.

Question 17

What are intermediate filaments and their significance?

Answer 17

They have tissue-specific patterns and can be used to assign a cell of origin for poorly differentiated tumors.

Examples include vimentin (mesenchymal cells) and neurofilaments (neurons).

Question 18

What role do microtubules play within cells?

Answer 18

They serve as connecting cables for molecular motor proteins that move vesicles and organelles.

Microtubules can form cilia and flagella.