Molecules and Cells

Question 1

What features distinguish a eukaryotic cell?

Answer 1

Possess internal, membrane-bound components, organelles. The most important of these is the nucleus.

Question 2

What is the basic structure of all membranes and what is it composed of?

Answer 2

Lipid bilayer, composed mainly of phospholipids

Question 3

What are phospholipids?

Answer 3

• amphipathic molecules (hydrophilic polar head and hydrophobic tail of fatty acids)
• tend to bunch up into spheres, micelles, or flatten out, forming a lipid bilayer

Question 4

Nucleus:

What is the nucleus surrounded by?

Answer 4

• nucleus is surrounded by nuclear envelope (double bilayer)
• nuclear envelope are perforated by nuclear pores (channels that allow the movement of certain molecules between the cytoplasm and nucleoplasm)

Question 5

Nucleus:

What does the nucleus store/contain?

Answer 5

Stores genetic information in the form of chromatin (DNA and protein)

Question 6

What does the nucleolus contain and what is it the site of?

Answer 6

• a suborganelle of the nucleus and is a darkly staining spherical region
• contains hundreds of copies of ribosomal RNA (rRNA) genes
• it is the site of synthesis and maturation of rRNA and assembly of ribosomal subunits for export to the cytoplasm for protein synthesis

Question 7

Ribosomes
• free ribosomes
• bound ribosomes

Answer 7

• ribosome subunits are assembled in the nucleolus and move into the cytosol, where they associate with an mRNA molecule, forming a functional ribosome
• free ribosomes - float in the cytosol, mostly making cytosolic proteins
• bound ribosomes - associated with ER, mostly making proteins for membranes, export, and some organelles

Question 8

Where is the endomembrane system and what compartments does it include?

Answer 8

• located between plasma membrane and nuclear envelope
• compartments include:
 - endoplasmic reticulum (ER)
 - Golgi apparatus
 - vesicles
 - lysosomes
 - vacuoles

Question 9

Rough endoplasmic reticulum

Answer 9

• rough ER is continuous with the outer nuclear membrane
• has ribosomes bound to its surface giving it a ‘rough’ appearance
• where proteins are made and modified

Question 10

Smooth endoplasmic reticulum

Answer 10

• no associated ribosomes
• tubular structure
• diverse functions
- lipid synthesis (manufactures nearly all phospholipids and cholesterol needed by cell for membrane repair and synthesis)
- contains enzymes responsible for detoxifying lipid-soluble drugs and harmful metabolic products

Question 11

What is the Golgi apparatus and it’s function?

Answer 11

• layers of flattened membranous sacs (single phospholipid bilayer)
• receives vesicles at its cis face (proteins and glycoproteins enter from rough ER)
• each sac has a different set of enzymes (modifies proteins)
• ships vesicles from its trans face (targets mature products to other organelles or plasma membrane)
• Golgi apparatus is involved in the processing and packaging of glycoproteins and polysaccharides

Question 12

List the ways in which molecules can be transported and get around the endomembrane

Answer 12

Parts of the endomembrane system are connected by:
• physical continuity
• vesicle traffic
 - fusing -> receiving
 - budding -> sending off

Question 13

The function of lysosomes

Answer 13

• membranous sac containing digestive (hydrolytic) enzymes

* involved in breakdown of many types of molecules - hydrolyses macromolecules

Question 14

What are vacuoles?

Answer 14

• very large fluid-filled vesicles (membranous sacs)
• diverse types and functions
- central vacuole
- lytic vacuole (like lysosomes)
- storage vacuole (store proteins, pigments etc)
- contractile vacuole

Question 15

Function of mitochondria

Answer 15

• aerobic cellular respiration

* contain their own DNA and ribosomes

Question 16

Function of chloroplast

Answer 16

• photosynthesis

* contain their own DNA and ribosomes

Question 17

List the three protein-based fibres of the cytoskeleton

Answer 17

• microfilaments (7-8 nm)
• intermediate filaments (8-12 nm)
• microtubules (25 nm)

Question 18

Cytoskeleton - microtubules

What do microtubules comprise of and what are their functions?

Answer 18

• comprised of the protein, tubulin
• diverse functions:
 - tracks for organelle movement
 - whole-cell movement as part of cilia and flagella
 - separating chromosomes during mitosis

Question 19

Cytoskeleton - microfilaments

What do microfilaments comprise of and what are their functions?

Answer 19

• also called actin filaments, form from protein called actin
• functions:
- form network inside plasma membrane to maintain cell shape
- contraction of muscle cells
- cytoplasmic streaming
- animal cell division

Question 20

Cytoskeleton - intermediate filaments

Function and example

Answer 20

• comprised of many different proteins for many different structural functions
• Example:
- Keratin for hair cell
- Lamin for nucleus

Question 21

What are prokaryotes?

Answer 21

• lack membrane-bound organelles
• mostly unicellular
• DNA is a big circle, coiled into the nucleoid region
• diverse cells, metabolism, and habitats

Question 22

Development of eukaryotes

Answer 22

• true nucleus may have developed from infoldings of an ancestral prokaryote’s plasma membrane
• endosymbiosis theory: ancestral prokaryotes living within another cell for the benefit of both
- ancestral aerobic prokaryote becoming mitochondria