B2.2

Question 1

Structure and Function of the Nucleus

What is the role of ultracentrifugation in cell fractionation?

Answer 1

• Ultrafugation separates particles by size which enables fractionation to occur (separation of cells into organelles)
• Cells are mized with cold buffer then blended to rupture membranes and release organelles
• Mixture then centrifuged & paused - heavier organelles sink

Question 2

Structure and Function of the Nucleus

What is considered to be an organelle?

Answer 2

• A discreet subunit of a cell adapted to perform one/more vital functions
• NOT organelles: cell wall (extracellular), cytosekelton, cytoplasm.

Question 3

Structure and Function of the Nucleus

What are the benefits of a separate nucleus?

Answer 3

• Protection of DNA from enzymes in cytoplasm
• Translation does not begin until after transcription is completed allowing for mRNA modifications

Question 4

Structure and Function of the Nucleus

What are the benefits of compartmentalisation?

Answer 4

• Enzymes can be concentratoin to areas needed
• Digestive enzymes of the lysosomes are away from rest of cell
• pH levels maintained
• Easy transport of materials
• Increased membrane areas for reactions

Question 5

Structure and Function of the Nucleus

How is compartmentalization a benefit in relation to lysosomes?

Protection during Phagocytosis

Answer 5

• Lysosomes contain hydrolyic enzymes that break things down
• When something needs digesting via phagocytosis, lysosomes merge with the vesicle & release their enzymes to keep hydrolysis safely in one place
• This protects other cellular structures

Question 6

Structure and Function of the Nucleus

What are the benefits of a double membrane?

Answer 6

• Nuclear processes (i.e., replication and transcription of DNA) can occur without being impacted by other cellular processes
• Crucial membrane has pores –> allows exchange of materials between nucleoplasm and cytoplasm (mRNA and ribosome subunits made in nucleus)

Question 7

Structure and Function of the Nucleus

Chromatin and the Nuclear Membrane

Answer 7

• The inner membrane of the double membrane interacts with DNA chromatin
• Helps to keep membrane spread out

Question 8

Structure and Function of the Nucleus

What happens to the Nuclear Membrane during Cell Division?

Both mitosis and meiosis

Answer 8

• Nuclear membrane breaks down to allow for the DNA to spread out so it can align to faciliate the division of the genetic material

Question 9

Structure and Function of the Nucleus

What is the matrix?

Located within the Mitochondria

Answer 9

• Inside the inner membrane is a cytoplasm-like fluid area full of enzymes called the matrix
  Location of Kreb’s cycle for Cellular respiration

Question 10

Structure and Function of the Nucleus

What is the Cristae?

Answer 10

• The tubular regions created by the deep folds of the inner membrane
• Their presence increases the amount of membrane and intermembrane space available for the electron transport chain of aerobic cell resp.

Question 11

Structure and Function of the Nucleus

What are the thylakoids?

Answer 11

• Discs of membrane with a thin thlakoid space inside each one
• They often form stacks called ganum and are connected by lamella

Question 12

Structure and Function of the Nucleus

What is the stroma?

Answer 12

• The aqueous cytoplasm fluid area surrounding the thylakoids
• Contains important enzymes for the Calvin Cycle.

Question 13

Structure and Function of the Nucleus

What is the Cisternae?

Answer 13

• Located in the golgi apparatus, they are stacked flattened sacks of membrane
• Sacks can expand to accept incoming vesicles/bud off to create exporting ones.

Question 14

Structure and Function of the Nucleus

What are clathrins?

Answer 14

• Proteins inside the cell membrane that cell in anchoring specific proteins to certain areas of the membrane.
• Also help anchor receptor proteins important for receptor mediating endocytosis.
• When membranes form vesicles –> clathrins join together to create coated vesicle –> highly specific/efficient well regulated form of endocytosis.

Question 15

Structure and Function of the Nucleus

Outer vs Inner membrane of Mitochondria

Answer 15

• Outer: arisen from an endosymbiotic event. Important for space to help create a proton gradient outside to then faciliate a reaction inside membrane.
• Inner: extensively folded to increase SA of inner membrane, lined with enzymes carrying out aerobic cellular resp.

Question 16

Structure and Function of the Nucleus

What does the final stage of aerobic cellular resp. rely on?

Answer 16

• The Cristae and Small intermembrane space
• Final stage relies on a build up of H+ protons in the intermembrane space
• With a thin intermembrane space, gradient can build up quicker
• Cristate (folds) produces extra intermembrane space, faciliating these reactions.

Question 17

Structure and Function of the Nucleus

What are the benefits of thylakoids with large SA:V ratios?

Answer 17

• Light Dependent reactions of photosynthesis rely on pigments and enzymes in the thylakoid membranes
• Thus, having more thylakoid membranes (stacking very thin membrane discs) means more pigments, more enzymes, more efficient photosynthesis
• Proton gradients can quickly form

Question 18

Structure and Function of the Nucleus

Free vs Attached Ribozomes?

Note that ALL ribozomes produce proteins

Answer 18

• Free: produce proteins used within the cell (i.e., for cytoskeleton, nucleus or mitochondria)
• Attached: create proteins transported via the ER for export outside of cell.

Question 19

Structure and Function of the Nucleus

Cis vs Trans side of the Golgi?

Answer 19

• Cis: side of the golgi apparatus facing the ER, it accepts vesicles produced by it that then merge with the golgi.
• Trans: faces away from ER, vesicles bubble off the golgi to head to the plasma membrane for exocytosis (merge with phospholipid membrane)