Essential BiochemistryThe Significance of Biochemistry “A thorough understanding of each moleculeʼs physical structure and chemical reactivity helps to lead to an understanding

Lecture Notes for

Chapter 1 The Chemical Basis of Life

Essential Biochemistry Third Edition

Charlotte W. Pratt | Kathleen Cornely

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Biochemistry involves the study of 4 types of molecules.

Biochemistry The scientific discipline

that seeks to explain life at the molecular

level Carbohydrates

Nucleic Acids Proteins

Lipids

© 2014 John Wiley & Sons, Inc. All rights reserved.

Central Questions in Biochemistry

•  What are living organisms made of?

•  How do organisms acquire and use energy?

•  How does an organism maintain its identity across generations?


The Significance of Biochemistry

“A thorough understanding of each

molecule’s physical structure and

chemical reactivity helps to lead to an

understanding of how molecules cooperate

and combine to form large functional units

and, ultimately, the intact organism.”


KEY CONCEPTS: Section 1-2

•  Biological molecules are composed of a subset of all possible elements and functional groups.

•  Cells contain four major types of biological molecules and three major types of polymers.


Elements Found in Biological Systems •  Biological molecules are mainly composed

of H, C, N, and O. •  Other elements are also necessary for life.

Abundant Trace Moderately Abundant


Cells contain four major types of biological molecules.

•  Amino acids •  Carbohydrates

(also called monosaccharides or sugars) •  Nucleotides •  Lipids


Amino acids are a major type of biological molecule.

•  Amino acids contain: – An amino group

– A carboxylic acid

group

– A side chain Alanine

an amino acid with a methyl group as its side chain


Carbohydrates are a major type of biological molecule.

•  Carbohydrates are monosaccharides or sugars.

•  General chemical formula: (CH2O)n where n ≥ 3

Sugars can be drawn as a

Fischer projection.

Sugars can be drawn as a

cyclical Haworth

representation.


Nucleotides are a major type of biological molecule.

•  Nucleotides are the building blocks of nucleic acids.


Lipids are a major type of biological molecule.

•  Lipids (fats) have a variety of structures.

•  One of the most important lipids in human health is cholesterol.


Monomers link sequentially to form polymers.


There are three major kinds of biological polymers.

•  Polypeptides and proteins •  Nucleic acid •  Polysaccharides


Amino acids link to form polypeptides and proteins.

•  Amino acid residues are connected via peptide bonds.

•  Polypeptide sequences are always read from the N terminus to the C terminus.


Nucleotide residues link via phosphodiester

bonds.

Polymers of nucleotides yield

nucleic acids. © 2014 John Wiley & Sons, Inc. All rights reserved.

Polymers of sugars are polysaccharides.

Glycosidic Bond



•  The free energy of a system is determined by its enthalpy and entropy.

•  Living organisms obey the laws of

thermodynamics.


Thermodynamic Terms •  Enthalpy, H

– The heat content of a system – Units = J • mol-1

•  Entropy, S – A measure of the system’s disorder or

randomness – Units = J • K-1mol-1

•  Gibbs free energy, G – A measure of the free energy of a system based

on H and S – Units = J • mol


Basics of Thermodynamics

•  It is easier to measure thermodynamic changes than discrete values.

•  ΔG = ΔH – TΔS

– ΔG = Gibbs free energy change – ΔH = Enthalpy change – ΔS = Entropy change


The sign of ΔG is meaningful.

•  When ΔG <0, the reaction is spontaneous or exergonic.

•  When ΔG >0, the reaction is nonspontaneous or endergonic.


Coupled Chemical Reaction ΔG is positive for the

AàB transition. Nonspontaneous reactions

do not generally occur.

ΔG is negative for the BàC transition.

Spontaneous reactions can be coupled with

nonspontaneous reactions so that the net reaction occurs spontaneously.


Energy from photosynthesis involves a coupled chemical reaction.

Reduction = gain of electrons Oxidation = loss of electrons


Carbon has different oxidation states.



•  Modern prokaryotic and eukaryotic cells apparently evolved from simpler nonliving systems.

•  The three domains of life are bacteria, archaea, and eukarya.


Prokaryotes and eukaryotes are the predominant life forms.


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Essential BiochemistryThe Significance of Biochemistry “A thorough understanding of each moleculeʼs physical structure and chemical reactivity helps to lead to an understanding