Chapter 2: Molecules and Cells

Question 1

Describe cell membrane

Answer 1

Forms functional compartments from phospholipid bilayers which are fluid.
-physically compartmentalize systems in functionally essential ways.

Question 2

Describe epithelium

Answer 2

Sheet of cells that covers a body surface or organ, or lines a cavity.

• similar to membranes, but a larger scale.
• compartmentalize body regions by forming boundaries

Question 3

Explain basis and significance of membrane fluidity

Answer 3

Phospholipid bilayer is fluid; heads are hydrophilic and tails are hydrophobic. Phospholipid molecules are not covalently bonded so they move relative to each other and are flexible. Fluidity depends on saturation of hydrocarbon tails.

Question 4

Channel membrane protein

Answer 4

diffusion of solutes through the membrane

Question 5

Transporter proteins

Answer 5

actively binds to molecules and move them across membrane

Question 6

Enzyme proteins

Answer 6

catalyze chemical reactions

Question 7

Receptor protein

Answer 7

binds to molecules and changes membrane permeability

Question 8

structural protein

Answer 8

anchors molecules in membrane; form structural relations

Question 9

tight junctions

Answer 9

(occluding junctions) - place where cell membranes of adjacent cells are tightly joined, no intercellular space.

Question 10

septate junction

Answer 10

(occluding junctions) - instead of tight junctions, invertebrates have these. Look like a double helix.

Question 11

Gap junctions

Answer 11

localized spot where cytoplasm’s of cell communicate through tiny pores

Question 12

Four factors that influence chemical reaction

Answer 12

• number of active enzyme molecules present; they must be able to react with substrate to catalyze reaction
• concentration of substrate molecules; hyperbolic/sigmoid kinetics
• catalytic effectiveness; how fast chemical reaction will occur
• enzyme substrate affinity; how likely enzyme is to stick to substrate

Question 13

relate half-saturation constant to enzyme substrate affinity and reaction velocity

Answer 13

half saturation constant (km) is concentration required to attain half the reaction velocity, which is how fast substrate is converted to product. The enzyme substrate affinity is how likely the enzyme will bind to the substrate.
-lower km mean greater affinity. reaction velocity increases as substrate concentration increases until they reach vmax.

Question 14

Explain how molecular flexibility relates to cooperativity and allosteric modulation

Answer 14

cooperativity is a change in the affinity for one ligand once another has bound, allosteric modulation occurs when a ligand binds and changes catalytic activity or substrate affinity. Molecular flexibility allows these enzymes to function.

Question 15

How is regulation of processes accomplished by enzymes?

Answer 15

• The type and amount of enzyme depends on gene expression and enzyme degradation
• modulation of enzyme molecules permits fast regulation of cell function
• rate limiting reaction set the rate of reaction for entire pathway, branch point reaction effect rapid metabolic regulation
• amplification occurs because each molecules of kinase can catalyze the activation of many molecules of the enzyme following it.

Question 16

Ligand-gated channel

Answer 16

receptor protein that opens to permit ions to pass through when they bind to their ligands. Ions alter the electrical charge across the membrane.
-Hydrophilic inorganic ions are commonly transported

Question 17

G protein-coupled receptor

Answer 17

interacts with two other cell membrane proteins to activate intracellular enzyme catalytic sites. Movement depends on membrane fluidity

Question 18

Enzyme-enzyme linked receptor

Answer 18

interacts directly with other membrane proteins that are enzymes. Binding with the ligand activates a catalytic site on the same molecule, activation causes the production of second messenger cyclic GMP

Question 19

Intracellular receptor

Answer 19

only effective for ligands that can dissolve in and diffuse through the lipid bilayer of the membrane

Question 20

How are membrane protein diverse?

Answer 20

• provide functionality
• primary structure is maintained by covalent bonds
• secondary structure maintained by hydrogen bonds.

Question 21

Apical surface

Answer 21

facing into cavity or open space

Question 22

Basal surface

Answer 22

facing toward the underlying tissue to which the epithelium is attached

Question 23

catabolism

Answer 23

breaking down chemical compounds to release energy

Question 24

anabolism

Answer 24

building up chemical compounds from smaller building blocks, using energy

Question 25

Lactate dehydrogenase

Answer 25

key enzyme in production of ATP.

Question 26

end product inhibition

Answer 26

type of regylation and a form of negative feedback control

-end product is a ligan that binds with ENz to allosterically inhibit it.

Question 27

protein kinases

Answer 27

enzymes that catalyze phosphorylation of other enzymes

Question 28

protein kinase 1

Answer 28

activated by one of various chemical mechanisms, catalyzes phosphorylation of protein kinase 2

Question 29

protein kinase 2

Answer 29

activated by phosphorylation, catalyzes phosphorylation of final target enzyme

Question 30

protein kinase 3

Answer 30

activated by phosphorylation, catalyzes critical metabolic process such as rate limiting or branch point reaction

Question 31

Five secondary messenger systems

Answer 31

• Cyclic AMP, Cyclic GMP, Ca+, DAG, IP3
• all participate in cell signal transduction
• immediate intracellular affect is to activate a protein kinase that is already present in the cell in an inactive form.