Biochemistry Chapter 3: Nonenzymatic Protein Function and Protein Analysis

Question 1

What are structural proteins?

Answer 1

Compose the cytoskeleton, anchoring proteins and much of the extracellular matrix.

Question 2

What is collagen?

Answer 2

STRUCTURAL - makes up most of the extracellular matrix of connective tissue - found throughout the body and is important in providing strength and flexibility

Question 3

What is elastin?

Answer 3

STRUCTURAL - extracellular matrix, stretches and then recoils like a spring, restoring the original shape of the tissue

Question 4

What are keratins?

Answer 4

STRUCTURAL - intermediate filament proteins in epithelial cells. Makes up hair and nails. Makes up the mechanical integrity and functions as a regulatory protein.

Question 5

What is actin?

Answer 5

STRUCTURAL - microfilaments and thin filaments in myofibrils. have a + and - side, allowing them to slide along actin filament

Question 6

What is tubulin?

Answer 6

STRUCTURAL - makes up microtubules. polarity. Aids in structure, chromosome separation, and intracellular transport

Question 7

What is myosin?

Answer 7

MOTOR - interacts with actin in myofibril, can also be involved in cellular transport

Question 8

What are Kinesins and Dyenins?

Answer 8

MOTOR - associated with microtubules

Question 9

What are characteristics of motor proteins?

Answer 9

• Catalytic activity, acting as ATPases

- Have 1+ heads capable of force generation

Question 10

What are binding proteins?

Answer 10

Bind a specific substrate, either to sequester it in the body or hold its concentration at steady state.

Question 11

What are Cell adhesion molecules?

Answer 11

Allow cells to bind to other cells or surfaces

Question 12

What are 3 types of Cell Adhesion Molecules?

Answer 12

• Cadherins
• Integrins
• Selectins

Question 13

What are cadherins?

Answer 13

Calcium-dependent glycoproteins that hold similar cells together.

Question 14

What are integrins?

Answer 14

permit cells to adhere to proteins in the extracellular matrix

Question 15

What are selectins?

Answer 15

allow cells to adhere to carbohydrates on the surfaces of other cells and are most commonly used in the immune system.

Question 16

What are antibodies used for?

Answer 16

used by the immune system to target a specific antigen, which may be a protein on the surface of a pathogen or a toxin

Question 17

What do immunoglobins contain?

Answer 17

They contain a constant region and a variable region; the variable region is responsible for antigen binding.

Question 18

What are antibodies formed from?

Answer 18

2 identical heavy chains and 2 identical light chains form an antibody. they are held together by disulfide linkages and noncovalent interactions.

Question 19

What are three types of ion-channels?

Answer 19

Ungated: always open
Voltage-gated: open in a certain range of membrane potential
Ligand-gated: open in the presence of a specific ligand

Question 20

What are enzyme-linked receptors?

Answer 20

Participate in cell signaling through extracellular ligand binding and initiation of second messenger cascades

Question 21

What are G protein-coupled receptors?

Answer 21

have a membrane-bound protein associated with a trimetric G protein. They also initiate second messenger systems.

Question 22

What is the G protein-coupled receptor pathway?

Answer 22

1. Ligand binding engages G protein
2. GDP is replaced with GTP; the alpha subunit dissociates from the beta and gamma subunits
3. The activated alpha subunit alters the activity of adenylate cyclase or phospholipase C
4. GTP is dephosphorylated to GDP; the alpha subunit rebinds to the beta and the gamma subunits.

Question 23

What is electrophoresis?

Answer 23

uses a gel matrix to observe the migration of proteins in response to an electric field.

Question 24

What is Native PAGE?

Answer 24

Maintains protein’s shape, but results are difficult to compare because the mass-to-charge ratio differs for each protein.

Question 25

What is SDS-PAGE?

Answer 25

Denatures the protein and masks the native charge so that comparison of size is more accurate, but the functional protein cannot be recaptured from the gel.

Question 26

What is isoelectric focusing?

Answer 26

Separates proteins by their isoelectric point; the protein migrates toward an electrode until it reaches a region of the gel where pH = pI of the protein.

Question 27

What is chromatography?

Answer 27

separates protein mixtures on the basis of their affinity for a stationary phase or a mobile phase.

Question 28

What is column chromatography?

Answer 28

uses beads of a polar compound, like silica or alumina, with a nonpolar solvent

Question 29

What is Ion-exchange chromatography?

Answer 29

Uses a charged column and a variable saline eluent.

Question 30

What is size-exclusion chromatography?

Answer 30

Relies on pourous beads. Larger molecules elute first because they are not trapped in the small pores.

Question 31

How is protein structure primarily determined?

Answer 31

through X-ray crystallography, NMR can also be used

Question 32

How can amino acid composition be determined? sequencing?

Answer 32

Comp = simple hydrolysis
Seq = Edman degradation

Question 33

How can activity levels of protein be determined?

Answer 33

• Watch for color change

- BCA assay, lowry reagent assay and Bradford protein assay (most common)