Protein Synthesis and Enzyme Activity

Vocabulary practice flashcards covering transcription and essential enzyme concepts, including mechanisms of action, kinetics, environmental factors, inhibition, and cofactors.

Gene

A section of DNA that contains the complete sequence of codons to code for an entire protein.

Transcription

The process by which the base sequence of a gene is copied to produce shorter molecules of RNA that are transported from the nucleus to a ribosome for protein synthesis.

Sense strand

The strand of DNA running from $5'$ to $3'$ that contains the code for the protein to be synthesised.

Antisense strand

The template strand of DNA running from $3'$ to $5'$ that is a complementary copy of the sense strand and is transcribed so the resulting RNA carries the same sequence as the sense strand.

RNA polymerase

The enzyme responsible for forming phosphodiester bonds between RNA nucleotides during transcription.

Enzymes

Globular proteins that act as biological catalysts, interacting with substrate molecules to speed up reactions without requiring harsh environmental conditions.

Anabolic reactions

Chemical reactions required for growth that involve the synthesis and building up of large polymer-based components.

Catabolic reactions

Chemical reactions in metabolic pathways that break down large organic molecules to release energy.

Metabolism

The sum of all the different reactions and reaction pathways happening in a cell or an organism.

$$V_{\max}$$

The maximum initial velocity or rate of an enzyme-catalysed reaction reached when all active sites are saturated with substrate.

Enzyme specificity

The characteristic feature of an enzyme whereby each enzyme catalyses only one specific biochemical reaction.

Activation energy

The initial amount of energy needed to start a chemical reaction, which enzymes lower by helping molecules collide successfully.

Active site

An area within the tertiary structure of an enzyme that has a shape complementary to the shape of a specific substrate molecule.

Lock and key hypothesis

A hypothesis proposing that only a specifically shaped substrate will fit precisely into the complementary active site of an enzyme, much like a key fits into a lock.

Induced-fit hypothesis

A modified enzyme action model where the active site changes shape slightly as the substrate enters, inducing structural changes that strain substrate bonds and lower activation energy.

Intracellular enzymes

Enzymes that act and catalyse reactions within the cells that produced them.

Catalase

An intracellular enzyme found in plant and animal tissues that prevents toxic accumulation by breaking down hydrogen peroxide into oxygen and water.

Extracellular enzymes

Enzymes secreted by cells to work outside the cell that produced them, breaking down large nutrient polymers into smaller absorbable molecules.

Amylase

An extracellular enzyme produced by salivary glands and the pancreas that partially breaks down starch into the disaccharide maltose.

Maltase

An enzyme present in the small intestine that catalyses the breakdown of maltose into the monosaccharide glucose.

Trypsin

A protease produced in the pancreas and secreted into the small intestine that digests proteins into smaller peptides.

Temperature coefficient ($Q_{10}$)

A measure of how much the rate of a reaction increases with a $10\,^\circ\text{C}$ rise in temperature, usually equal to $2$ for enzyme-controlled reactions below the optimum.

Denaturation

The change in an enzyme's precise tertiary structure caused by breaking of internal bonds at high temperatures or extreme pH, causing the active site to lose complementarity to its substrate.

Optimum temperature

The specific temperature at which an enzyme displays its highest rate of activity.

Thermophiles

Organisms adapted to live in very hot environments whose enzymes are more stable due to an increased number of bonds, such as sulfur bridges and hydrogen bonds.

Optimum pH

The hydrogen ion concentration at which an enzyme's active site has the optimal complementary shape to its substrate.

Renaturation

The process by which an enzyme resumes its normal tertiary shape and catalytic activity after the pH returns to the optimum from small deviations.

Serial dilution

A repeated, stepwise dilution of a stock solution, usually done by factors of ten, to produce a range of known or relative concentrations.

Inhibitor

A molecule that prevents enzymes from carrying out their normal function of catalysis or slows down their rate of reaction.

Competitive inhibitor

A molecule with a similar shape to the substrate that binds temporarily to the enzyme's active site, competing with the substrate and blocking its entry.

Non-competitive inhibitor

An inhibitor that binds to an enzyme at an allosteric site, altering the enzyme's tertiary structure and changing the active site shape so the substrate can no longer bind.

Allosteric site

A specific binding site on an enzyme located in an area other than the active site.

End-product inhibition

A negative-feedback control mechanism in which the product of a reaction or pathway acts as an inhibitor to an enzyme that produces it.

Cofactor

A non-protein 'helper' component needed by some enzymes to carry out their catalytic function, which may bind loosely and transfer atoms or form part of the active site.

Coenzyme

An organic cofactor, often derived from dietary vitamins, that assists an enzyme in catalysing biochemical reactions.

Prosthetic group

A non-protein component that is tightly and permanently bound to a protein or enzyme to enable its biological function, such as $\text{Zn}^{2+}$ in carbonic anhydrase.

Apoenzyme

The inactive precursor protein form of an enzyme before its required cofactor is bound.

Holoenzyme

The complete, catalytically active enzyme formed once its cofactor or coenzyme is bound.

Zymogens

Inactive precursor enzymes (also called proenzymes) that are activated by a change in tertiary structure brought about by enzyme cleavage or changes in conditions such as pH.