Biochemical pathways

A biochemical pathway is a series of chemical reactions that occur within a cell, where the product of one reaction becomes the reactant, or substrate, of the next. Each reaction in the pathway is catalysed by a specific enzyme , allowing complex processes to proceed step-by-step in an organised manner.

Think of it like a conveyor belt in a factory: materials move along, and each station on the belt performs a different step until a final product is created.

Use this page to revise the following concepts of biochemical pathways:

Key characteristics

  • Stepwise Reactions: Each step has its own enzyme and produces a specific product.
  • Intermediate Products: Products from one reaction become reactants for the next.
  • Directionality: Pathways often proceed in a single direction, with specific start and end points.
  • Regulation: Cells can regulate pathways by controlling enzyme activity, ensuring efficiency and conserving energy.

A simple biochemical pathway is shown below.

The product of the first reaction is the substrate for the second reaction.

a graphic illustrating a biochemical pathway. At the left-hand side of the image is a square labeled “A” and underneath this square there is a label starting “starting molecule”. To the right of this image is an arrow pointing to the right with the label “enzyme one” above the arrow, and a label “reaction one” below the arrow. This arrow points at a square labeled “B”. To the right of this image is an arrow pointing to the right with the label “enzyme two” above the arrow, and a label “reaction two” below the arrow. This arrow points at a square labeled “C”. To the right of this image is an arrow pointing to the right with the label “enzyme three” above the arrow, and a label “reaction three” below the arrow. This arrow points to a final image of a square, labeled “D” with the text “final product” below the square.

Anabolic reactions

Anabolic reactions are biochemical processes that build complex molecules from simpler ones, requiring energy input. They are crucial for growth, repair, and synthesis of molecules like proteins and nucleic acids in cells.

An image depicting four circles on the left-hand side of the image equally spaced sequentially apart on the same line. To the right of these circles is a plus symbol, and to the right of the plus symbol is a rectangular box labeled “energy”. To the right of this box is an arrow pointing to the right and, to the right of the arrow are four circles in a sequence with their edges touching and no spaces between them.

Examples:

  1. Amino acids are used to build proteins.
  2. Nucleotides are used to build nucleic acids such as DNA and RNA.
  3. Carbon dioxide and water are used to create glucose in photosynthesis.

Catabolic reactions

Catabolic reactions involve the breakdown of complex molecules into simpler ones, releasing energy in the process. This energy is often stored as ATP, which cells use to fuel various functions.

An image depicting, on the left-hand side of the image, four circles in a sequence with their edges touching and no spaces between them. To the right of these circles is an arrow pointing to the right. To the right of the arrow are four circles, sequentially placed and with even spacing between them. To the right of these circles is a “plus” sign and to the right of the plus sign is a rectangular box labeled “energy”.

Examples:

  1. Cellular respiration - the breakdown of glucose to release energy in the form of ATP
  2. Digestion - the breakdown of proteins into amino acids
  3. Digestion - the breakdown of complex carbohydrates to produce glucose.

Factors that affect biochemical pathways

A number of factors can affect biochemical pathways by influencing the enzymes involved or the overall pathway dynamics:

Each of these factors plays a role in maintaining the balance and efficiency of metabolic processes in cells.

In summary

  • Biochemical pathways are ordered series of chemical reactions facilitated by enzymes.
  • They are essential for cellular functions, transforming initial reactants through multiple steps to produce end products that cells need for energy, growth, and repair.