In unit 2 you studied the catabolism of biomolecules. In this unit you will learn about their synthesis.
After a brief look at carbohydrates and lipids, proteins will be examined.
You will learn about the genetic code and protein synthesis. You may want to review information about
DNA on page 34. Protein synthesis involves two key processes transcription and translation. Transcription
occurs in the nucleus. During transcription, genetic information is transferred from DNA to mRNA. Translation,
on the other hand, occurs in the cytoplasm. During translation, the coded information in mRNA is used to
assemble a protein. The protein is not finished yet. The protein may undergo further modification and must reach
its intended destination. You will see that some of the proteins that are synthesized by the cell remain in the cell,
whereas other proteins are "packaged" for export.
The metabolic pathways introduced in Unit 2 function in the synthesis of biomolecules, as well as in
their breakdown. Reversible reactions allow the pathways to "run in reverse". Figure 422 depicts the reverse of
glycolysis gluconeogenesis. Amino acids, lactate, pyruvate and glycerol can enter this pathway and produce
glucose. Note that glucose cannot be created from fatty acids. The glycolysis pathway can be used to create
triglyceride as shown in figure 423.
Glycogenolysis • The breakdown of glycogen into glycolysis intermediates
o Glycogen + P i▯G6P ▯Glycolysis
o Glycogen + H O ▯Glucose + ATP ▯G6P ▯Glycolysis
• 90% of the time converted to G6P, saving the cell 1 ATP molecule
Glycogenesis • The synthesis of glycogen from glucose
• The reverse process of glycogen breakdown
o Glucose linked together into glycogen
o G6P synthesized into glycogen by the removal of a Pgroup
Gluconeogenesis • The production of glucose from nonglucose precursors such as proteins or glycerol
portions of lipids
• Similar to reverse glycolysis but with different enzymes/precursors
o AA/Lactate/Glycerol ▯Pyruvate ▯Gluconeogenesis ▯G6P ▯Glucose
Lipid Synthesis • The production of lipids by combining glycerol + FA in the SER
• Difficult to generalize synthesis because lipids are so diverse
• 1 Glycerol + 3 FA ▯Triglyceride
o Glycerol made from glucose via glycolysis
o 2C acyl units from acetyl CoA linked by fatty acid synthetase to form FA
1 Module II
Proteins are extremely important and diverse. You should know the sequence of events, and where they
occur, during transcription and translation. Figure 428 is a good summary. Proteins have to be guided to their
intended destination and may need further processing. Figure 429 depicts the pathway for proteins that are to
be secreted from the cell.
Gene A region of DNA that contains all the information needed to make a functional piece of
DNA Deoxyribonucleic acid; a nucleotide that stores genetic information in the nucleus.
RNA Ribonucleic acid; a nucleotide that interprets the genetic information stored in DNA &
uses it to direct protein synthesis.
Chromosome A threadlike strand of DNA and protein in the cell nucleus that carries the genes in a linear
Genome The full DNA sequence of an organism.
Transcription Once a gene is activated, transcription converts its DNA base sequence into a functional
piece of RNA (mRNA).