CH1: Cellular Proteins

Question 1

What are the two roles of cellular proteins?

Answer 1

Receptors
- Modify cell’s response to the environment (why we feel cold/hot, hungry)
Enzymes
- catalysts for biochemical reactions within cells (most metabolic pathways are catalyzed by enzymes

Question 2

What are receptors and where are they located?

Answer 2

Highly specific proteins located in the plasma membrane and facing the exterior of the cell
They act as attachment sites for specific external stimuli such as hormones, growth factors, antibodies, lipoproteins and certain nutrients

Question 3

What are the external stimuli that bind to receptors called?

Answer 3

Ligands

Question 4

What are the three types of receptors?

Answer 4

Those that generate internal chemical signals
Those that function as ion channels
Those that internalize stimuli

Question 5

What is the most common receptor

Answer 5

G-receptors

Question 6

Analyze this graph of g-receptors

Answer 6

Question 7

Is the enzymes active site specific?

Answer 7

Yes it is highly specific
Its functionality depends on protein and prosthetic group or coenzyme

Question 7

What are catalytic proteins (enzymes) and where are they found?

Answer 7

Found in all cellular compartments
They are catalysts that take part in a reaction but are not part of the final product of that reaction
Some function externally, others are components of the cellular membranes and associated with organelle membranes or in the inner membrane surfaces

Question 8

Are enzymes reversible?

Answer 8

Most of them are
Meaning that most enzymes can catalyze reactions in both directions

Question 9

What are the ways in which enzymes are regulated?

Answer 9

Covalent modification of enzymes
Modulation of allosteric enzymes
Increase in enzyme production by induction
- synthesis of more enzyme

Question 10

What are examples of catalytic proteins? (6)

Answer 10

Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases

Question 11

What is the function of oxidoreductases?

Answer 11

Reactions in which one compound is oxidized, another is reduced

Question 12

What is the function of transferases?

Answer 12

Functional group is transferred from one substrate to another

Question 13

What is the function of hydrolases?

Answer 13

Hydrolysis of carbon bonds

Question 14

What is the function of lyases?

Answer 14

Cleavage of C-C, C-S. and C-N bonds (no hydrolysis/O-R)
* utilized more in the keto diet

Question 15

What is the function of isomerases?

Answer 15

Interconversion of optical or geometric isomers
They are only found in the liver

Question 16

What is the function of ligases?

Answer 16

Catalyze formation of C and other bonds (O, S, N, others)

Question 17

What is Vmax?

Answer 17

The maximum rate that can be observed in the reaction
- if the substrate is present in excess, this is the max rate that the enzyme can work at
- enzyme can be saturated (all active sites are occupied by substrate molecules) (zero order reaction)

Question 18

What is Km?

Answer 18

The concentration of the substrate which permits the enzyme to achieve half Vmax

Question 19

Does an enzyme with low Km have a higher or lower catalyzing capability?

Answer 19

Lower Km -> easier to reach highest reaction rate -> higher catalyzing capability

Question 20

What are examples of clinical applications of cellular enzymes?

Answer 20

Tumor markers
- Oncogenes: mutated genes that encode abnormal, mitosis-signaling proteins that promoted unregulated cell division
Conditions for diagnostic suitability
- enzyme must have sufficiently high of organ or tissue specificity
- steep concentration gradient of enzyme activity between cell and surroundings
- Enzyme must function in cytosol
- Enzyme must be stable

Question 21

What is activation energy?

Answer 21

The minimum amount of energy that must be imposed on the system to raise the reactants to their transition state or start a reaction