The following four slides relate to Chapter 4 and will be discussed in that context

Chemical modifcations of bases in DNA can lead to permanent changes in the sequence of bases due to mispairing

The events that may take place after base mispairing. Any permanent change in a base sequence is called a mutation

A+A+ B-B- A-A- B+B+ A+A+ B+B+ A-A- B-B- Homologous recombination The information in very similar (homologous) DNA molecules can be exchanged by homologous recombination systems. Non-homologous recombination systems also exist. Recombination takes place in all organisms.

A more detailed view of the mechanism of homologous recombination by ”strand invasion”

Slides on metabolism starts her

Glycolysis is a wide-spread pathway for utilization of glucose. It generates chemical energy in the form of ATP and NADH. It ends with pyruvate, which can be degraded further to CO 2 in the citric acid cycle (Krebs cycle)

To enter the Krebs cycle pyruvate is first converted to acetyl CoA

Molecular formulas of some important compounds coupled to metabolism

Some enzymes require additional factors to function. Coenzymes are examples of such factors, and refer to complex organic or metalloorganic compounds that act as transient carriers of specific functional groups. So coezymes are NOT enzymes! Simple factors such as metal ions are called cofactors.

Oxidation-reduction reactions with FAD

How NAD is converted from oxidized (NAD + ) to reduced form (NADH)

The Krebs cycle is a circular process involving many enzymes

A simplified view of the energy-generating steps of the Krebs cycle

Overview of glycolysis plus the citric acid cycle plus transfer of energy from reduced carriers (NADH, FADH2) to ATP via the electron transport system, which involves a series of proteins that can carry out the energy transfer reactions. Note the role of atmospheric oxygen in this!

A summary of the total energy gains from conversion of glucose to ATP

The citric acid cycle is coupled to amino acid synthesis, and the amino acids are required for protein synthesis. There are numerous other such connections inside living cells (see fatty acids on the figure), and together they form very complex metabolic networks

This overview of the metabolic networks show why we now need computers, particulary if we want to predict cell behaviour! In recent years these needs have led to the development of ”Systems Biology”, which involves mathematical analysis and modelling of living cells. Hint: think about this figure by considering our previous discussions about Km and Vmax values of enzymes,and membranes and uptake systems