MCAT Molecular Bio

The biological process by which genetic information produces a functional protein.

Gene Expression

The first step of gene expression.

Transcription

The second step of gene expression.

Translation

The process by which cells become specialized.

Cell Differentiation

The ability of cells to alter gene expression in response to environmental signals.

Gene Regulation

A protein that binds DNA to regulate transcription.

Transcription Factor

DNA sequence where RNA polymerase binds to initiate transcription.

Promoter

DNA sequence that increases transcription when activators bind.

Enhancer

DNA sequence that decreases transcription when repressors bind.

Silencer

The DNA sequence where a repressor protein binds.

Operator

Genes expressed continuously regardless of environmental conditions.

Constitutive Genes

Genes expressed only under certain conditions.

Regulated Genes

Proteins that increase transcription by helping RNA polymerase bind DNA.

Activators

Proteins that decrease transcription by blocking RNA polymerase.

Repressors

The process of turning genes on or off.

Gene Regulation

A protein's function depends primarily on this level of structure.

Tertiary Structure

The sequence of amino acids in a protein.

Primary Structure

The alpha helix and beta pleated sheet are examples of this protein structure.

Secondary Structure

Three

dimensional folding of a single polypeptide chain.

Association of multiple polypeptide chains into one functional protein.

Quaternary Structure

Proteins that assist in proper protein folding.

Chaperone Proteins

Loss of normal protein structure due to heat or pH changes.

Denaturation

Protein returning to its native conformation after denaturation.

Renaturation

Weak interactions responsible for stabilizing protein structure.

Hydrogen Bonds

Attraction between nonpolar amino acids that stabilizes protein folding.

Hydrophobic Interactions

Covalent bond formed between two cysteine residues.

Disulfide Bond

Proteins destined for secretion are synthesized on this organelle.

Rough Endoplasmic Reticulum

Organelle responsible for modifying and packaging proteins.

Golgi Apparatus

Small molecules added to proteins after translation.

Post

Common post

translational modification involving addition of phosphate groups.

Enzymes responsible for phosphorylation.

Kinases

Enzymes responsible for removing phosphate groups.

Phosphatases

Addition of carbohydrate groups to proteins.

Glycosylation

Small protein attached to proteins destined for degradation.

Ubiquitin

Large protein complex responsible for degrading ubiquitinated proteins.

Proteasome

The process of breaking down damaged proteins.

Proteolysis

Small signaling protein released by cells to communicate with neighboring cells.

Cytokine

A signaling molecule that binds a receptor on the same cell that secreted it.

Autocrine Signal

A signaling molecule affecting nearby cells.

Paracrine Signal

A signaling molecule traveling through the bloodstream to distant cells.

Endocrine Signal

The molecule that binds to a receptor to initiate signaling.

Ligand

Protein embedded in the plasma membrane that binds signaling molecules.

Receptor

Receptors located inside the cell commonly bind this type of molecule.

Lipid

Second messenger commonly produced after GPCR activation.

cAMP

Enzyme that converts ATP into cAMP.

Adenylate Cyclase

Enzyme activated by cAMP to phosphorylate target proteins.

Protein Kinase A

Second messenger released from the endoplasmic reticulum during signaling.

Calcium Ion (Ca²⁺)

Membrane lipid cleaved into DAG and IP3 during signal transduction.

PIP2

Second messenger that opens calcium channels in the endoplasmic reticulum.

IP3

Second messenger that activates Protein Kinase C.

DAG

Family of membrane receptors coupled to G proteins.

G Protein

Proteins that relay signals from GPCRs to intracellular targets.

G Proteins

A biological catalyst that lowers activation energy without being consumed.

Enzyme

The molecule upon which an enzyme acts.

Substrate

The region of an enzyme where the substrate binds.

Active Site

A molecule that decreases enzyme activity.

Inhibitor

An inhibitor that competes with the substrate for the active site.

Competitive Inhibitor

An inhibitor that binds an allosteric site and decreases Vmax without changing Km.

Noncompetitive Inhibitor

An inhibitor that binds only the enzyme

substrate complex and decreases both Km and Vmax.

An inhibitor that can bind either the enzyme or enzyme

substrate complex with different affinities.

A molecule that binds somewhere other than the active site to alter enzyme activity.

Allosteric Regulator

Binding of a molecule that increases enzyme activity at an allosteric site.

Allosteric Activation

Binding of a molecule that decreases enzyme activity at an allosteric site.

Allosteric Inhibition

Maximum reaction rate achieved when all enzyme active sites are occupied.

Vmax

The substrate concentration at which the reaction rate equals one

half of Vmax.

A low Km indicates this property of an enzyme.

High Substrate Affinity

A high Km indicates this property of an enzyme.

Low Substrate Affinity

The relationship describing enzyme velocity as substrate concentration increases.

Michaelis

A graph used to determine Km and Vmax by plotting reciprocal values.

Lineweaver

Enzymes that display sigmoidal kinetics rather than Michaelis

Menten kinetics.

The increased affinity of an enzyme after one substrate molecule binds.

Cooperativity

The classic protein that displays positive cooperativity.

Hemoglobin

The regulation of an enzyme by the final product of a metabolic pathway.

Feedback Inhibition

The process by which inactive enzymes become active after cleavage.

Proteolytic Activation

Inactive enzyme precursor requiring activation.

Zymogen

Pancreatic proteases are secreted in this form to prevent autodigestion.

Zymogens

The movement of information from a receptor to intracellular targets.

Signal Transduction

Protein family commonly involved in cell surface signaling.

G Protein

The receptor family that activates G proteins after ligand binding.

G Protein

Protein that exchanges GDP for GTP during GPCR activation.

G Protein Alpha Subunit

Enzyme activated by G proteins that produces cAMP.

Adenylate Cyclase

Second messenger produced from ATP by adenylate cyclase.

cAMP

Enzyme activated by cAMP.

Protein Kinase A

Enzyme responsible for adding phosphate groups to proteins.

Kinase

Enzyme responsible for removing phosphate groups from proteins.

Phosphatase

Receptor family possessing intrinsic tyrosine kinase activity.

Receptor Tyrosine Kinase (RTK)

Cell signaling pathway commonly activated by growth factors.

MAPK Pathway

Second messenger released from the endoplasmic reticulum after IP3 signaling.

Calcium Ion (Ca²⁺)

Second messenger that activates Protein Kinase C.

DAG

Second messenger that opens calcium channels in the endoplasmic reticulum.

IP3

Membrane phospholipid cleaved into DAG and IP3.

PIP2

Enzyme responsible for cleaving PIP2.

Phospholipase C

Small GTP

binding protein frequently mutated in cancer.

The process by which normal cells become cancerous.

Carcinogenesis

Genes that normally stimulate cell growth but can cause cancer when mutated.

Proto

Mutated proto

oncogenes that promote uncontrolled cell division.

Genes that normally prevent uncontrolled cell division.

Tumor Suppressor Genes

Tumor suppressor known as the "guardian of the genome."

p53

Tumor suppressor that regulates the G1/S checkpoint by binding E2F.

Rb Protein

The process of programmed cell death.

Apoptosis