Chapter 20 - Biochemistry

Biochemistry

Chapter 20

Outline

I. Carbohydrates II. Lipids

III. Proteins

3

Carbohydrates

Carbohydrates are

• a major source of energy from our diet

• composed of the elements C, H, and O

• also called saccharides, which means “sugars”

Types of Carbohydrates

The types of carbohydrates are

• monosaccharides, the simplest carbohydrates

• disaccharides, which consist of two

monosaccharides

• polysaccharides, which contain many

What do monosaccharaides look like?

CH₂OH O H OH H HO H OH OH H H C C C C C

CH2OH

O H OH H HO H OH HO H H C C C C C

CH₂OH O H OH H HO H HO H OH H C O CH₂OH

C C C

CH₂OH OH OH

HO H

H H

Some Important Monosaccharides

Glucose (C₆H₁₂O₆) is

• an aldohexose • found in fruits,

vegetables, corn syrup, and honey

• found in disaccharides • the monosaccharide in

polymers of starch,

7

Some Important Monosaccharides

Fructose is

• a ketohexose with the

formula C₆H₁₂O₆

• the sweetest

monosaccharide

• found in fruit juices and

honey

• converted to glucose in the

Cyclic Structures

Cyclic structures

• _{are the prevalent form of monosaccharides with}

five to six carbon atoms.

• _{form when the hydroxyl on C5 reacts with the}

aldehyde or ketone group

9

Important Disaccharides

A disaccharide

• _{consists of two monosaccharides} • _{is linked by a glycosidic bond}

H+

Maltose + H₂O Glucose + glucose H+

Lactose + H₂O Glucose + galactose H+

Polysaccharides

Polysaccharides include

• _{all polymers of glucose}

• _{amylose and amylopectin,}

starches that store -glucose

• _{glycogen (animal starch in}

muscle), which is made of -glucose

• _{cellulose (plant and wood),}

How does the structure of polysaccharides differ

from monosaccharide and disaccharides?

starch

Lipids

Lipids are

• biomolecules that contain fatty acids or a steroid nucleus

• soluble in organic solvents, but not in water

Lipid Function

•

Energy Storage

–

2 X the calories of carbohydrates per gram

•

Important components of brain and nerve

tissue

•

They store and provide fat soluble

vitamins

–

(Vitamins A, D, E, and K)

•

They serve as protective padding and

insulation for vital organs.

•

They are a major constituent of cell

Types of Lipids

The lipids that contain fatty acids are

• waxes

• _{fats and oils (triacylglycerols)} • glycerophospholipids

• prostaglandins

The types of lipids that do not contain fatty acids are

15

Fatty Acid Formulas

• _{are long-chain carboxylic acids}

• _{typically contain12 to18 carbon atoms} • _{are insoluble in water}

Saturated Fatty Acids

Saturated fatty acids

• _{contain only single C–C}

bonds

• _{have molecules that fit}

closely together

• _{have higher melting points}

than unsaturated fatty acids

17

Unsaturated Fatty Acids

Unsaturated fatty acids

• _{contain one or more double}

C=C bonds

• _{have chains with “kinks” that}

do not allow molecules to pack closely

• _{have lower melting points}

than saturated fatty acids

• _{are liquids at room}

temperature

Cis and Trans Structures of an

Unsaturated Fatty Acid

The double bond in unsaturated fats

19

Triacylglycerols

A triacylglycerol

• is a triester of glycerol and three fatty acids

• that is solid at room temperature is a fat

prevalent in meats, whole milk, butter, and cheese

• that is liquid at room temperature is an oil

Formation of Triacylglycerols

Triacylglycerols are

• produced by esterification

• formed when the hydroxyl groups of glycerol react

with the carboxyl groups of three fatty acids

How are unsaturated triacylglycerols

converted to saturated triacylglycerols?

23

Steroid Nucleus

A steroid nucleus

• has three cyclohexane rings

• has one cyclopentane ring

Cholesterol

Cholesterol, the most abundant steroid in the body, which is not found in plants, has

• two methyl CH₃- groups • _{one alkyl chain}

• _{one double bond}

Amino Acids

Amino acids

• _{are the building blocks of proteins}

• _{contain carboxylate groups and ammonium}

groups on the alpha () carbon

• _{are ionized in biological systems}

27

Types of Amino Acids

Amino acids are classified as

• nonpolar with hydrocarbon

sides chains (hydrophobic)

• polar with polar side chains

(hydrophilic)

• acidic with carboxylate side

chains (hydrophilic)

• basic with ammonium side

chains (hydrophilic)

[[page 625 from Table 18.4]]

Nonpolar Polar (neutral)

Dipeptide

A dipeptide

• _{forms when a peptide bond links the COO}− of one

amino acid with the NH₃+ of the next amino acid

• _{is named with a yl ending for the N-terminal amino}

29

Example of a Peptide Bond

Write the formation of the dipeptide serylthreonine. OH CH₃

| |

CH₂ O HCOH O

₊ | ║ ₊ | ║

H₃N─CH─C─O – + H

3N─CH─C─O–

Ser Thr

OH CH₃ | |

CH₂ O H HCOH O

+ | ║ | | ║

NH₃─CH ─C─N─CH ─ C─O– _{+ H} 2O

Primary structure

•

_{refers to the number and sequence of}

amino acids in a peptide chain

•

_{the unique sequences of each of the}

Secondary structure

•

_{Refers to the ordered arrangement of the}

polypeptide backbone.

Tertiary structure

•

_{Refers to the unique}

3-D shape that results

from the unique

folding of the

35

Quaternary Structure

Quaternary structure

• _{occurs when two or more}

protein units combine

• _{of hemoglobin consists of}

four polypeptide chains as subunits

• _{is stabilized by the same}

37

Enzymes

Enzymes

• _{are catalysts for}

biological reactions

• _{are mostly protein} • _{increase the rate of}

reaction

• _{lower the activation}

Active Site

The active site

• is a region within an enzyme that fits the shape of the reacting molecule, called a substrate

Nucleotide

•

_A

_nucleotide

_{in DNA consists of}

one of the 4 bases linked to a

deoxyribose sugar which is

linked to a phosphate:

Bases in DNA and RNA

The bases in DNA and RNA are pyrimidines

• Cytosine (C)

• Thymine (T)

• Uracil (U)

And the purines

• Adenosine (A)

43

Ribose and Deoxyribose Sugars

The pentose (five-carbon) sugar

• in RNA is ribose

• in DNA is deoxyribose, with no O atom on carbon 2′

Structure of RNA

The structure of RNA

• _{consists of the}

nucleotides A, C, G, and U

• _{is a single strand of}

45

Complementary Base Pairs:

A and T

Complementary Base Pairs:

G and C

DNA contains complementary base pairs G-C in which guanine is always linked by three hydrogen bonds to cytosine (G−C).

[[page 636 Figure 18.21 bottom

47

Double Helix of DNA

The DNA structure is a double helix that

• consists of two strands of nucleotides that form a

double helix structure like a spiral stair- case

• has hydrogen bonds

between the bases A–T and G–C

RNA

•

_RNA

_{is a single stranded polymer of}

nucleotides that contains ribose rather than

deoxyribose and the base uracil rather than

thymine.

•

_{The main function of RNA is to direct the}

synthesis of proteins in the ribosomes of the

cell.

•

Transcription

is the process by which DNA

Copyright 2011 John Wiley & Sons, Inc