3.1 Cellular Functions

Question 1

The primary structural proteins in the body are?

Answer 1

collagen, elastin, keratin, actin, and tubulin

Question 2

Structural Proteins

Answer 2

• The cytoskeleton
• have highly repetitive secondary structure

Question 3

Motif

Answer 3

• a super-secondary structure—a repetitive organization of secondary structural elements
  together
• gives many structural proteins a fibrous nature

Question 4

Collagen

Answer 4

• trihelical fiber (three left-handed helices woven together to form a secondary right-handed helix) and makes up most of the extracellular matrix of connective tissue.
• makes up most of the extracellular matrix of connective tissue
• provides strength and flexibility
  —forms a unique and specific secondary helical structure based on the abundance of the
  amino acid glycine.

Question 5

Elastin

Answer 5

• important component of the extracellular matrix of connective tissue.
• primary role is to stretch and then recoil like a spring, which restores the original shape of the tissue.

Question 6

Keratins

Answer 6

• intermediate filament proteins found in epithelial cells
• contribute to the mechanical integrity of the cell and also function as regulatory proteins

Question 7

Actin

Answer 7

• makes up microfilaments and the thin filaments in myofibrils
• the most abundant protein in eukaryotic cells
• have a positive side and a negative side; this polarity allows motor proteins to travel unidirectionally along an actin filament, like a one-way street.

Question 8

Tubulin

Answer 8

• makes up microtubules
• Microtubules are important for providing structure, chromosome separation in mitosis and meiosis, and intracellular transport with kinesin and dynein
• Like actin, tubulin has polarity: the negative end of a microtubule is usually located adjacent to the nucleus, whereas the positive end is usually in the periphery of a cell.

Question 9

ATPases

Answer 9

• Enzymatic motor proteins
• power the conformational change necessary for motor function
• have transient interactions with either actin or microtubules
• Myosin is the primary motor protein that interacts with actin

Question 10

Kinesins and dyneins

Answer 10

• motor proteins associated with microtubules
• have two heads, at least one of which remains attached to tubulin at all times.
• Both proteins are important for vesicle transport in the cell, but have opposite polarities

Question 11

Kinesins

Answer 11

• play key roles in aligning chromosomes during metaphase and depolymerizing microtubules during anaphase of mitosis
• kinesins bring vesicles toward the positive end of the microtubule

Question 12

Dyneins

Answer 12

• involved in the sliding movement of cilia and flagella
• dyneins bring vesicles toward the negative end

Question 13

Binding Proteins

Answer 13

• have stabilizing functions in individual cells and the body
• transport or sequester molecules by binding to them
• include hemoglobin, calcium-binding proteins, DNA-binding proteins (often transcription factors), and others.
• the binding protein usually has high affinity for its target across a large range of concentrations so it can keep it bound at nearly 100 percent.
• Transport proteins have varying affinity depending on environment

Question 14

Cell Adhesion Molecules (CAMs)

Answer 14

are proteins found on the surface of most cells and aid in binding the cell to the extracellular matrix or other cells.

Question 15

Cadherins

Answer 15

• a group of glycoproteins that mediate calcium-dependent cell adhesion.
• often hold similar cell types together, such as epithelial cells.
• Different cells usually have type-specific cadherins

Question 16

Integrins

Answer 16

• group of proteins that all have two membrane-spanning chains called α and β.
• chains are very important in binding to and communicating with the extracellular matrix
• play a very important role in cellular signaling and can greatly impact cellular function by promoting cell division, apoptosis, or other processes.

Question 17

Selectins

Answer 17

• unique because they bind to carbohydrate molecules that project from other cell surfaces
• weakest bonds formed by the
  CAMs
• expressed on white blood cells and the endothelial cells that line blood vessels
• play an important role in host defense, including inflammation and white blood cell migration

Question 18

Antibodies (immunoglobulins (Ig)

Answer 18

• proteins produced by B-cells that function to neutralize targets in the body, such as toxins and bacteria, and then recruit other cells to help eliminate the threat
• Disulfide linkages and noncovalent interactions hold the heavy and light chains together

Question 19

Where is the antigen-binding region?

Answer 19

• at the tips of the “Y

Question 20

Constant region

Answer 20

• remaining part of the antibody molecule
• involved in recruitment and binding of other cells of the immune system, such as macrophages

Question 21

What’re the 3 outcomes of antibodies binding to antigens?

Answer 21

• Neutralizing the antigen
• Marking the pathogen for destruction (opsonization)
• Clumping together, to be phagocytized