Enzymes

Phosphorylation of LC20 is required to activate the myosin head, which binds to actin. This myosin–actin interaction forms the basis of the cross-bridge cycle (CBC), which causes muscle contraction, as in skeletal muscle.

Based on the information in the passage, which type of enzyme is most likely to suppress CBC?

A. Phosphorylase

B. Kinase

C. Phosphatase

D. Synthase

C. Phosphatase

kinase →

adds phosphatase

lipase → hydrolyzes triglycerides

Which type of enzyme removes the chemical groups that are added to proteins by kinases?

A. Phosphorylase

B. Cyclase

C. Phosphatase

D. Acetylase

C. Phosphatase

if you see cAMP or IP3/DAG think

G protein coupled receptor

insulin

beta cells, secreted in response to high blood glucose levels, lowers glucose, fed state

glucagon

alpha cells, secreted in response to low blood glucose levels, raises glucose, fasting state

Lactase can be classified as which type of enzyme?

A. Isomerase

B. Hydrolase

C. Transferase

D. Oxidoreductase

B. Hydrolase

Most cytochrome P450 enzymes alter the activity of drugs by:

A. phosphorylating them.

B. dephosphorylating them.

C. oxidizing them.

D. reducing them.

C. oxidizing them.

During phosphorylation of STAT5b proteins, phosphate groups are exchanged for what atoms on tyrosine residues?

A. Hydrogen atoms of hydroxyl groups

B. Hydrogen atoms of methyl groups

C. Oxygen atoms of hydroxyl groups

D. Carbon atoms of methyl groups

A. Hydrogen atoms of hydroxyl groups

Peptidases are enzymes that

digest proteins

Nucleotides are digested by

nucleases

Carbohydrates are digested by

carbohydrases

One such drug is a selective protein kinase C (PKC) inhibitor called Sotrastaurin (STN, Figure 2).

Assuming no mutations to the signaling pathway described in the passage, what event directly activates CARD11?

A. Proteolytic cleavage

B. GTP binding

C. Membrane association

D. Phosphorylation

D. Phosphorylation

Which of the following terms best describes the role of ornithine decarboxylase

A. Catalyst

B. Cofactor

C. Substrate

D. Activator

A. Catalyst

Transfer functional groups from one molecule → another

Examples:

• Kinase

• Methyltransferase

• Transaminase

transferase

Catalyze oxidation/reduction reactions

Examples:

• Dehydrogenase

• Oxidase

• Reductase

oxidoreductase

Break bonds using water

Examples:

• Protease

• Lipase

• Nuclease

• Phosphatase

hydrolases

Break/form bonds WITHOUT water or oxidation

Examples:

• Decarboxylase

• Aldolase

lyases

rearrange molecules

Examples:

• Mutase

• Racemase

Same atoms, different arrangement

isomerase

Join molecules together

Examples:

• Synthetase

ligases

Function: Adds phosphate

Reaction: ATP → ADP

Class: Transferase

Examples:

• Hexokinase

• Protein kinase

kinase

Function: Uses inorganic phosphate (Pi) to break bonds

Class: Transferase

Examples: Glycogen phosphorylase

phosphorylase

Function: Removes phosphate

Class: Hydrolase

phosphatase

Function: Transfers CH3 group

Class: Transferase

Examples: DNA methyltransferase

methyltransferase

Function: Transfers amino groups

Class: Transferase

Examples:

• ALT

• AST

Used in amino acid metabolism

transaminase

Redox reaction involving NAD+/FAD

Class: Oxidoreductase

Examples:

• Lactate dehydrogenase

• Succinate dehydrogenase

dehydrogenase

Function: Uses O₂ as electron acceptor

Class: Oxidoreductase

Examples: Cytochrome oxidase

oxidase

Function: Catalyzes reduction reactions

Class: Oxidoreductase

Examples: Ribonucleotide reductase

reductase

Function: Forms bonds WITHOUT ATP

examples: citrate synthase

synthase

function: Forms bonds USING ATP

Class: Ligase

Examples: Aminoacyl tRNA synthetase

synthetase

function: Joins molecules together; usually uses ATP

Examples:

• DNA ligase

ligase

Breaks/forms double bonds, Without water or oxidation

examples: fumarase

lyase

Function: Removes CO₂

Class: Lyase

Examples:

• Pyruvate decarboxylase

decarboxylase

Splits carbon chains

Class: Lyase

Example:
- Glycolysis:
- Fructose-1,6-bisphosphate → G3P + DHAP

aldolase

function: Breaks fats

Class: Hydrolase

Examples:

• Pancreatic lipase

lipase

function: Breaks proteins

Class: Hydrolase

Examples:

• Trypsin

• Chymotrypsin

• Pepsin

protease

Breaks DNA/RNA

Class: Hydrolase

Examples:

• DNase

• RNase

nuclease

Rearranges molecules

Examples:

• Phosphoglucose isomerase

isomerase

Converts: L ↔ D forms

Class: Isomerase

racemase

Moves functional group to another location

Class: Isomerase

Examples:

• Phosphoglycerate mutase

mutase

Unwinds DNA

helicase

Synthesizes DNA/RNA

Examples:

• DNA polymerase

• RNA polymerase

polymerase

Extends telomeres; Contains RNA template

telomerase

Adds CO₂

Examples:

• Pyruvate carboxylase

carboxylase

Hydrolyzes ATP

ATP → ADP + Pi

Examples:

• Na/K ATPase

ATPase

Forms peptide bonds

Location: Large ribosomal subunit

peptidyl transferase

Cuts DNA at specific sequences

Used in: Molecular biology/genetics

restriction endonuclease

Cuts DNA, relaxes supercoiling; phosphodiester bond

topoisomerase