Bke2 Biochemistry Lectures

Lecture 10: Introduction to intermediary metabolism
Reading material: Horton, chapter 10.8 - 10.11, 11.1 - 11.4

Abstract:
Metabolism
Living organisms can be divided into two large groups according to the chemical form in which they obtain carbon from the environment. Autotrophs use carbon dioxide from the atmosphere to construct all their carbon-containing biomolecules. Heterotrophs cannot use atmospheric carbon dioxide and must obtain carbon from their environment in the form of relatively complex organic molecules, such as glucose.

The photosynthetic autotrophs obtain their energy from sunlight, whereas heterotrophic cells obtain their energy from the degradation of organic nutrients made by autotrophs.

Autotrophs and heterotophs live together and produce a huge cycling of carbon, oxygen and water in our biosphere with solar energy ultimately providing the driving force for this massive process.

Metabolism is the sum of all of the chemical transformations that occur in a cell or organism. Catabolism is the degrative phase of metabolism, in which organic nutrient molecules are converted to smaller products. In anabolism, also called biosythesis, small molecules are used to make larger and more complex molecules. Anabolic reactions require the input of energy, generally in the form of the free energy of hydrolysis of ATP and the reducing power of NADH and NADPH.

Membrane transport
Ingested nutrients are digested and absorbed in the gastrointestinal tract and transported via the blood system to different organs for use as energy or as precursors for biosynthesis. How is it possible for the molecules to be transported into cells when the lipid bilayer is almost impermeable for most ions and molecules? The answer is that this is accompished by specific membrane proteins often called transporters. Only small uncharged molecules such as water, urea etc. can pass through the lipid bilayer by simple diffusion. Transport of solutes by simple diffusion always occurs from a higher to a lower concentration. Facilitated diffusion is transport of solutes through integral membrane proteins. This transport also occurs from higher to lower concentration without any need for energy input. Active transport is energy dependent and the transport is often connected to the hydrolysis of ATP as an energy source. Input of energy for transportation of solutes makes it possible to transport aqueous solutes against a concentration gradient. Some transporters carry out symport, the simultaneous passage of two species in the same direction; others mediate antiport, in which the two species move in opposite directions, but simultaneously.

Key concepts:

Links:
From the MIT hypertextbook:
Lipids
Introduction to membranes
Membrane structure and composition
Overview of membrane proteins
Membrane transport mechanisms

Lecture index

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]