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Chapter 24

The Chemistry of Life

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Many of the most important molecules in our body are polymers.

Molecules of Life

Proteins (amino acids), polysaccharides– (monosaccharides) and nucleic acids (nucleotides),

lipids are not polymers, no repeating units (monomers)

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In our diet, we need relatively large amts of proteins, carbohydrates, and lipids.

Molecules of Life

• Biomolecules for heredity and protein synthesis.

Nucleic Acids

Organic cpds

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Biochemistry

• study of the chemistry of living things.

Biochemistry

• explores the substances involved in life processes and the rxns they undergo.

• Other than H2O (about 80 % or more of the weight of an organism), most of the molecules of life—the biomolecules—are organic.

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elemental composition of living things

% By mass

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Biochemistry

All 4 of these elements can form the strong covalent bonds found in organic molecules.

more than 95 % of the atoms in our bodies are H, O, C and N.

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Biochemistry

• S and P → proteins

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A protein: an organic polymer composed of amino acids

bonded together in one or more chains. Monomer: amino acids

Proteins

An amino acid has a central C atom, to which are bonded a carboxyl group (-COOH acid),

an amino group (-NH2), a H atom, and a variable side chain designated as R.

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Amino Acids

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Proteins

A protein A peptide with more than about 100 amino

acids.

structural proteins: skin, hair, nails, and muscles

‘Functional’ proteins: enzymes, hormones

needed for almost all chem rxns that take place in the body.

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Proteins

Amino Acids in a Peptide Chain

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Amino Acids

An amino acid cpd that contains an amino group (—NH2) and

a carboxyl group (—COOH) in the same molecule.

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Amino acids bond to each other by forming a peptide bond

Structure of an Amino Acid

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Structure of an Amino Acid

• 2 amino acids linked by a peptide bond form a dipeptide.

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A Peptide: A chain of 2 or more AAs linked by peptide

bonds .

Structure of an Amino Acid

Polypeptide: a chain of 10 or more AAs.

Proteins may have 1 or several polypeptide chains,each chain must have an exact sequence of AAs.

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Protein synthesis

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Enzymes proteins

Enzymes

catalyze biochemical rxns

speeding up rxns

lower Ea

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Substrates The reactants in an enzyme-catalyzed process. bind to the enzyme’s active site, forming an enzyme-substrate complex.

Enzymes

enables the substrate(s) to react with a much lower Ea than …

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The Nature of Enzyme Catalysis

● Enzyme provides a catalytic surface

● This surface stabilizes transition state

● Transformed transition state to product

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BA Catalytic surface

A

Juang RH (2004) BCbasics

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Enzyme Stabilizes Transition State

S

P

ES

EST

EP

ST

Reaction direction

Energy change

Energy required (no catalysis)

Energy decreases (under catalysis)

T = Transition state

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• Familiar carbohydrates include glucose, sucrose, starches, and cellulose.

Carbohydrates

Simple carbohydrates consist of • a chain of C atoms • hydroxyl (–OH) groups and • a carbonyl gp, often in the form of an (alkanal)

aldehyde gp.

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monosaccharides

• The simplest carbohydrates (simple sugars)

Monosaccharides

• e.g. glucose, ribose, fructose, deoxyribose

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Monosaccharides

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Polysaccharide

• A polymer of many monosaccharides bonded into a chain.

Polysaccharides

e.g. Starch consists only of glucose units.

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Polysaccharides

Plants also link glucose units together in a different way to form the polysaccharide cellulose

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Glycogen Animals store glucose as a polysaccharide

Polysaccharides

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Lipids • Fats and oils—produced by living things.

Lipids

• not polymers, • Digestion → fatty acids and glycerol• chem structures vary widely.

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Triglycerides

Lipids: Fats, oils, and other water-insoluble cpds.

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• The most familiar lipids : plant oils and animal fats.

Fatty Acids

These lipids are esters of fatty acids, which are

alkanoic acids with long, straight hydrocarbon chains between 12 and 24 C atoms.

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• The simplest fatty acids are the saturated fatty acids,

• no C ═ C double bonds between C atoms.

Saturated Fatty Acid

• Stearic acid is found in pork and beef tissue.

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• Many other fatty acids have 1 or more double bonds between C atoms → unsaturated fatty acids.

Monounsaturated Fatty Acid

• Oleic acid is a major component of olive oil.

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Triglycerides

Animal fats and plant oils are made up primarily of triglycerides, molecules in which 3 fatty acids are bonded to a glycerol molecule (by ester linkages).

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The Functions of Lipids

• long-term storage of energy is usually in the form of lipids. (more effective than carbohydrates.)

• an important component of our skin and cell membrane.

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DNA and RNA

nucleic acids polymers found primarily in cell nuclei. monomer: nucleotide

2 kinds:

deoxyribonucleic acid (DNA) ribonucleic acid (RNA)

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DNA and RNA

nucleotides. Each consists of aphosphate group, a five-carbon sugar, and a nitrogen base.

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Nucleic Acids

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2 types of nucleic acids

Nucleic Acids

• DNA contains the sugar deoxyribose • RNA contains the sugar ribose.

DNA exists as a pair of polymer chains backbone of each chain consists of alternating

phosphate and deoxyribose units. The bases stick out from the backbone.

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The Structure of DNA

A single DNA molecule contains many thousands of nucleotides.

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• the N bases of 1 chain are H-bonded to the N bases of the other chain.

Base Pairing

• the chains wind into a spiral called a double helix.

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4 different N bases are found in DNA: adenine, guanine, cytosine, and thymine.

Base Pairing

• Adenine— thymine (H-bond)• Guanine— cytosine.

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DNA and RNA

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• The order of these 3 N bases along 1 of the DNA chains provides the informn for the sequences of AAs in proteins.

Base Pairing

• Cell mechanisms “read” the DNA sequence in gps of three bases called triplets.

• Each triplet codes for a specific AA or tells the cell to start or stop making a protein.

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The Genetic Code

A gene

a segment of DNA

carries the instructions for making 1 peptide chain.

The products of genes are the peptides and proteins.

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Question 1

Label the amino group and the carboxyl group of the dipeptide.

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Answer

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Question 2

Draw an arrow pointing to the peptide bond.

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Answer

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Question 3

Draw a square around each variable side chain.

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Answer

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Glucose is a(n)

Question 4

a. polysaccharide.

b. amino acid.

c. part of cellulose.

d. 5-carbon sugar.

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Answer

The answer is C, part of cellulose.

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CST problem 1

Which substance is made up of many monomers joined together in long chains?

A salt

B protein

C ethanol

D propane

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CST problems 2

Some of the molecules found in the human body are NH2CH2COOH (glycine), C6H12O6

(glucose), and CH3(CH2)16COOH (stearic acid). The bonds they form are

A nuclear.

B metallic.

C ionic

D covalent

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CST problem 3

Proteins are large macromolecules composed of thousands of subunits. The structure of the protein depends on the sequence of

A lipids

B monosaccharides

C amino acids

D nucleosides

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The End