Animal Cells (Part One)

Question 1

Phospholipids are amphiphatic.

What does this mean?

Answer 1

A molecule that possesses both a hydrophilic and hydrophobic region.

Question 2

Describe how cholesterol influences membrane fluidity.

Answer 2

• Reduces membrane fluidity at moderate temperature

- Avoids solidification at low temperatures

Question 3

Cholesterol is the source of two sex hormones.

Name these hormones.

Answer 3

• Estradiol

- Testosterone

Question 4

What are lipid rafts?

Answer 4

Membrane regions that assemble specialised lipids and proteins to perform a certain task

Question 5

Name the protein responsible for the closing over of a bleached area during FRAP.

Answer 5

Sso1

Question 6

Give 6 potential roles of a protein embedded in the plasma membrane of a cell.

Answer 6

• Transporters
• Enzymes
• Receptors
• Cell-cell recognition
• Intracellular joining
• Attachment to extracellular matrix and intracellular cytoskeleton

Question 7

Name the four kinds of gated channels.

Answer 7

• voltage gated
• mechanically gated
• temperature gated
• ligand-gated (chemical)

Question 8

What is the function of a Tight Junction?

Answer 8

• Acts as a diffusion barrier

- Holds cells together

Question 9

What do Tight Junctions consist of?

Answer 9

Plasma-membrane proteins, claudin and occuldin, that interact

Question 10

Name the two proteins that compose an Adherens Junction.

What is the role of each protein?

Answer 10

• Cadherins; bridge between the cells.

- Catenins; link to the actin cytoskeleton.

Question 11

What is the function of an Adherens Junction?

Answer 11

Involved in controlling actin organisation in epithelial cells.

Question 12

What are the connecting channels of a Gap Junction made of?

Answer 12

Connexins

Question 13

What is the function of a Gap Junction?

Answer 13

• Allows passage of ions and small molecules (1-2nm in diameter)
• Supports exchange between cytoplasm of adjacent cells.

Question 14

Name the proteins found in Desmosomes.

What is the role of this protein?

Answer 14

Catherin proteins; interact with each other and intermediate filaments.

Question 15

What is the function of a Desmosome?

Answer 15

Resists shear force in the epithelia and in muscle.

Question 16

Name the main protein found in a Hemidesmosome, and state its function.

Answer 16

Integrins; interacts with the extracellular matrix.

Question 17

Where in the body are Hemidesmosomes found?

Answer 17

In skin epithelial cells

Question 18

What is the function of the Hemidesmosome?

Answer 18

• Anchors the epithelia to the basal lamina

- Signalling

Question 19

Name the 5 cell-cell contacts.

Answer 19

• Gap Junctions
• Tight Junctions
• Adherens Junctions
• Desmosomes
• Hemidesmosomes

Question 20

Name the three secreted proteins in the extracellular matrix.

Answer 20

• Collagen
• Matrix proteins
• Glycoproteins

Question 21

What are the roles of the extracellular matrix?

Answer 21

• holds tissue together
• provides strength
• directs cell migration

Question 22

Name the two major intracellular signalling mechanisms.

Answer 22

• Phosphorylation of proteins

- Signalling by GTP-binding proteins

Question 23

What are G-proteins?

Answer 23

Molecular switches

Question 24

What are G-proteins

a) activated by?
b) deactivated by?

Answer 24

a) G-proteins are activated by a Guanine nucleotide exchange factor (GEF)
b) G-proteins are deactivated by a GTPase-activaitng protein

Question 25

What is the role of small-monomeric G-proteins?

Answer 25

To receive signals from many receptors.

Question 26

What is the role of large trimeric G-proteins?

Answer 26

To interact with G-protein-coupled receptors.

Question 27

Fill in the blank:

Phosphorylated _________ can control the activity of effector proteins.

Answer 27

Kinases or phosphatases

Question 28

What is a kinase?

Answer 28

An enzyme that carries out phosphorylation.

Question 29

What is a phosphatase?

Answer 29

An enzyme that removes a phosphate group from a protein, a process called dephosphorylation.

Question 30

What percentage of human proteins carry a phosphate group.

Answer 30

30%

Question 31

How many kinases in the human genome?

Answer 31

520

Question 32

How many phosphatases in the human genome?

Answer 32

150

Question 33

What is the role of Cdk kinase?

Answer 33

Control of cell cycle progression

Question 34

What is the role of Src-type kinase?

Answer 34

Control and regulation of various biological functions.