Internal Organisation Of The Cell

Question 0

What is endocytosis?

Answer 0

Invagination of the plasma membrane that forms a membrane bound vehicle containing material that was extracellular.

However, may be specially targeted.

Question 1

Two alternatives for the last stage of secretory pathway?

Answer 1

Constitutive secretion - this is the default pathway and occurs in all cells. It involves vesicles undergoing exocytosis as soon as reaching plasma membrane.

Regulated secretion - this is signal dependant and only fuses with membrane when a specific signal triggers exocytosis.

Question 2

Pinocytosis?

Answer 2

When material brought into a cell by endocytosis is mainly liquid. This is how a cell “drinks” and brings water and electrolytes into the cell

Not targeted

Question 3

Phagocytosis?

Answer 3

Ingestion of particular matter or cell debris, or preying on smaller cell by engulfing it.

This is targeted

Question 4

Two phagocytosis situations?

Answer 4

1) predatory unicellular protests devour their prey by phagocytosis. Eg: amoeba
2) white blood cells move around and defend against infection by getting rid of debris and micro organisms

Question 5

Types of endocytosis?

Answer 5

Pinocytosis
Phagocytosis
Receptor mediated endocytosis

Question 6

What is an endosome?

Answer 6

A vehicle containing material newly ingested from the extracellular space by endocytosis

Question 7

Enzymes in lysosomes?

Answer 7

Acid hydrolases

Work best in low pH conditions

Question 8

What are the many functions of a vacuole?

Answer 8

• DIGESTION of waste macromolecules
• STORAGE of nutrients and waste products etc
• WATER BALANCE
• CELL SIZE adjustments by uptake of water. Turgor pressure leads to increase in cell size.
• MAINTENANCE OF pH by acting as a buffer. Increase in H+ in cytosol leads to h+ uptake into vacuole

Question 9

How do vacuoles adjust water content in plants?

Answer 9

They either break down polymers or re synthesise monomers into polymers
Polymers have a week osmotic effect, monomers have a strong effect.

Alternatively, the rate of transport metabolites across the vacuolar or plasma membrane is altered. Leading to changes in osmolarity of the cytosol or vacuole

Question 10

The two topologically Inequivalent organelles?

Answer 10

Nucleus and mitochondria

Question 11

Two types of chromatin?

Answer 11

Euchromatin - loosely packed

Heterochromatin - tightly packed

Question 12

What are nucleosomes?

Answer 12

146 base pairs of DNA around a group of 8 proteins
Packed to form a 300nm fibre

Beads on a string

Question 13

What is the NPC?

Answer 13

Nuclear Pore Complex

Gates, pores in nuclear membrane with specialised intricate structure made from multiple proteins. This allows for LARGE molecules like RNA and protein to pass through

Question 14

Where can translation occur?

Answer 14

In the cytosol by free ribosomes, or in the rER surface

Question 15

In which direction are proteins synthesised?

Answer 15

5’ to 3’

Question 16

What is a polyribosome?

Answer 16

When multiple ribosomes bind to a mRNA and simultaneously synthesise protein.

They all start at the 5’ end and move at the same rate

Question 17

What is translocation?

Answer 17

The passage of proteins to the ER.

Ribosomes bind to the ER after beginning translation, directed by a signal sequence on the protein.

Protein translation stops until bound to receptor/protein complex on ER membrane (translocator)

Protein is either released into the lumen of ER or becomes a transmembrane protein

Ribosomal subunits dissociate into cytosol

Question 18

Post translational modifications in ER?

Answer 18

• assisted folding (secondary and tertiary structure)
• recognition of faulty or mis folded proteins (removal from pathway or degradation)
• structural changes
• glycosylation

Question 19

Role of sER?

Answer 19

Lacks ribosomes

• major site of lipid synthesis
• calcium storage compartment
• enzyme driven metabolic processes
• steroid hormone synthesis

Question 20

What is the vesicular pathway called?

Answer 20

Biosynthetic-secretory pathway

Question 21

Advantages of vesicles?

Answer 21

• Topology – The lumens of the donor organelle, the vesicle and the target organelle are topologically equivalent to each other. This means that fusion of the vesicle with the target organelle will automatically transfer the contents of the vesicle into the lumen of the target organelle. Nothing else has to be done to effect this transfer.
• Membrane proteins – Orientation is correctly maintained. The cytosolic side of a transmembrane protein remains cytosolic, even with multiple transfers. This is clearly shown in both of the figures here.
• Versatile – It is a widely applicable solution. It works in principle with any protein (so long as the appropriate protein is packaged into the vesicle) and with any organelles that share the same topology.
• Efficient bulk transfer – a bunch of proteins are transported in one go. Transport to different destinations is simply a matter of sending several vesicles.
• Low maintenance – because phospholipid bilayers immediately self-repair after each budding event.

Question 22

What is exocytosis?

Answer 22

Vesicle fusing with plasma membrane so that its contents are released to the exterior

Question 23

Trans and cis face of Golgi?

Answer 23

Cis - vesicle received

Transport - departing vesicle

Question 24

What happens in the Golgi apparatus?

Answer 24

Proteins may be modified (glycosylation)

Proteins are sorted into appropriate vesicles to locations appropriate to their function.