Ch5.3

Question 1

What does EGF stand for, and what is its primary function?

Answer 1

EGF stands for epidermal growth factor, and its primary function is to stimulate cell growth and division.

Question 2

Wat type of protein does EGF bind to in order to trigger its effects?

Answer 2

EGF binds to the EGF receptor (EGF-R) on the surface of cells.

Question 3

How was the EGF-R protein isolated for study?

Answer 3

The EGF-R protein was isolated from a human tumor cell line that expresses the receptor at elevated levels, specifically an epidermoid carcinoma of the uterus.

Question 3

How does the activated EGF receptor promote cell proliferation?

Answer 3

Once activated, the Src-like kinase in the cytoplasmic domain phosphorylates tyrosines on cytoplasmic proteins, leading to cell growth and division.

Question 4

What is the primary structural feature of the EGF receptor’s ectodomain?

Answer 4

The ectodomain of the EGF receptor is a large N-terminal domain comprised of 621 amino acid residues that protrudes into the extracellular space and is involved in recognizing and binding EGF.

Question 4

Describe the cytoplasmic domain of the EGF receptor.

Answer 4

The cytoplasmic domain of the EGF receptor extends into the cytoplasm and contains a sequence similar to that of the Src protein, which plays a role in signal transduction.

Question 4

What happens to the EGF receptor upon EGF binding?

Answer 4

Upon EGF binding, the ectodomain of the EGF receptor transmits a signal through the plasma membrane, activating its cytoplasmic domain.

Question 4

What is the length of the transmembrane domain of the EGF receptor, and what is its role?

Answer 4

The transmembrane domain of the EGF receptor is 23 amino acid residues long and threads through the lipid bilayer of the plasma membrane.

Question 5

EGF

Answer 5

Epidermal Growth Factor, a protein that stimulates cell growth and division by binding to the EGF receptor.

Question 5

What role does phosphorylation play in the function of the EGF receptor?

Answer 5

Phosphorylation of tyrosines on certain proteins acts as a signal that induces cellular responses, including proliferation and changes in cell behavior.

Question 5

What evolutionary significance do the receptors and ligands in cell signaling have?

Answer 5

These receptors and their ligands are relatively recent evolutionary inventions and have been retained in modern metazoa, suggesting a vital role in multicellular life.

Question 6

receptor (EGF-R)

Answer 6

A cell surface protein that specifically recognizes and binds EGF, transmitting signals into the cell to induce growth and division.

Question 6

Tyrosine kinase

Answer 6

An enzyme that phosphorylates tyrosine residues on proteins, playing a critical role in cell signaling and regulation of growth.

Question 7

Ligand

Answer 7

A molecule that binds to a specific receptor to initiate a physiological response; in this context, EGF serves as the ligand for the EGF receptor.

Question 8

Ectodomain

Answer 8

The extracellular portion of a membrane protein, in this case, the EGF receptor’s large N-terminal domain that binds EGF.

Question 9

Transmembrane domain

Answer 9

A segment of a membrane protein that spans the lipid bilayer, facilitating communication between the extracellular environment and the cytoplasm.

Question 10

Cytoplasmic domain

Answer 10

The intracellular portion of a receptor that transmits signals inside the cell after ligand binding, often containing kinase activity.

Question 10

Src protein

Answer 10

A well-known kinase involved in signaling pathways, which exhibits structural similarities to the cytoplasmic domain of the EGF receptor.

Question 11

Metazoan

Answer 11

Multicellular organisms that evolved from single-celled ancestors, possessing complex cellular communication systems.

Question 11

How do different growth factor-receptor pairs vary in functions?

Answer 11

Different growth factor-receptor pairs can trigger multiple biological responses besides growth and division, including changes in cell shape, survival, and motility.

Question 11

Phosphorylation

Answer 11

The addition of a phosphate group to a molecule, often used to activate or deactivate enzymes and receptors in cell signaling.

Question 12

What historical significance does EGF have in growth factor research?

Answer 12

EGF was the first growth factor discovered, leading to significant advancements in understanding cell signaling and proliferation.

Question 12

Why was the isolation of the EGF receptor protein challenging?

Answer 12

It was challenging because the EGF receptor is usually expressed at low levels in cells, making it difficult to obtain adequately.

Question 12

What discovery was made regarding the evolution of tyrosine kinase receptors?

Answer 12

Research discovered a tyrosine kinase receptor gene in a single-cell eukaryote, suggesting a link to the common ancestor of all metazoans.

Question 13

What insight did the sequencing of EGF-R protein provide?

Answer 13

Sequencing revealed structural features that enable the EGF receptor to function effectively in cell signaling and proliferation.