The structure and function of large biological molecules

The structure and function of large biological molecules

Four classes of biological molecules

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Key concepts

• Macromolecules are polymers built from monomers

• Carbohydrates serve as fuel and building material

• Lipids are a diverse group of hydrophobic molecules

• Proteins have many structures, resulting a wide range of functions

• Nucleic acids store and transmit hereditary information

Macromolecules are polymers, built from monomers

Macromolecules are polymers, built from monomersWhat is a macromolecule?


•Large and complex molecules, often chainlike


•Large and complex molecules, often chainlike•Monomer (simple subunits) building blocks form the chains

Monomer


•Large and complex molecules, often chainlike•Monomer (simple subunits) building blocks form the chains•Chains are called polymers

MonomerPolymer


•Large and complex molecules, often chainlike•Monomer (simple subunits) building blocks form the chains•Chains are called polymers•Monomers are connected via dehydration reactions


•Large and complex molecules, often chainlike•Monomer (simple subunits) building blocks form the chains•Chains are called polymers•Monomers are connected via dehydration reactions

What’s a dehydration reaction?


Dehydration removes a watermolecule, forming a new bond

Short polymer Unlinked monomer

Longer polymer

HO

HO

HO

H2O

H

HH

4321

1 2 3


Dehydration removes a watermolecule, forming a new bond

Short polymer Unlinked monomer

Longer polymer

HO

HO

HO

H2O

H

HH

4321

1 2 3

This process can also be reversed


HO

H2O

H

4321

1 2 3

Hydrolysis adds a watermolecule, breaking a bond

HO

HO HO

H2O

H

H

H321

1 2 3 4

Hydrolysis


H2O

4321

1 2 3• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Which of these is NOT a polymer?


Carbohydrates serve as fuel and building material


What is a carbohydrate?


Carbohydrates include:• Sugars • Polymers of sugars


Carbohydrates include:• Sugars (monosaccharides and disaccharides)



•Molecular formula is generally some multiple of CH2O•Glucose is a common monosaccharide (C6H12O6)•Glucose is a source of cellular energy



•Two monosaccharides joined by a covalent bond (glycosidic linkage)•Examples are sucrose and maltose

Dehydration reaction in the synthesis of maltose



•Two monosaccharides joined by a covalent bond (glycosidic linkage)•Examples are sucrose and maltose•Transport sugars in plants



•Two monosaccharides joined by a covalent bond (glycosidic linkage)•Examples are sucrose and maltose•Transport sugars in plants•Often found in energy supplements


Carbohydrates include:• Sugars (monosaccharides and disaccharides)• Polymers of sugars (polysaccharides)

Polymers of a few hundred to a few thousand monosaccharides joined by glycosidic linkages




•Energy storage polysaccharides •Structural polysaccharides





Different forms in plants and animals


(b) Glycogen: an animal polysaccharide

Starch

GlycogenAmylose

Chloroplast

(a) Starch: a plant polysaccharide

Amylopectin

MitochondriaGlycogen granules

0.5 µm

1 µm

Energy storage polysaccharides (both polymers of glucose)


(b) Glycogen: an animal polysaccharide

Starch

GlycogenAmylose

Chloroplast

(a) Starch: a plant polysaccharide

Amylopectin

MitochondriaGlycogen granules

0.5 µm

1 µm

Energy storage polysaccharides (both polymers of glucose)

How does an organism get energy from these molecules?









i.e. cellulose


Structural polysaccharidesCellulose•The most abundant organic molecule on Earth•Major component of plant cell walls •Made of glucose monomers (Beta linkages)


Structural polysaccharidesi.e. Cellulose•The most abundant organic molecule on Earth•Major component of plant cell walls •Made of glucose monomers (Beta linkages)•Unbranching•Forms microfibrils•Very strong building material

Glucosemonomer

Cellulosemolecules

Microfibril

Cellulosemicrofibrilsin a plantcell wall

0.5 µm

10 µm

Cell walls


Lipids are a diverse group of hydrophobic molecules


This group includes:•Fats•Phospholipids•Steroids

**All are hydrophobic (they do not mix well with water)


Fats•Constructed from glycerol (an alcohol) and fatty acids (long hydrocarbon chains with a carboxyl group)•Form by dehydration reactions

Fatty acid(palmitic acid)

Glycerol(a) Dehydration rxn in fat synthesis

Ester linkage

(b) Fat molecule (triacylglycerol)


Fats•Constructed from glycerol (an alcohol) and fatty acids (long hydrocarbon chains with a carboxyl group)•Form by dehydration reactions•Can be saturated or unsaturated

Structuralformula of asaturated fatmolecule

Stearic acid, asaturated fattyacid(a) Saturated fat

Structural formulaof an unsaturatedfat molecule

Oleic acid, anunsaturatedfatty acid

(b) Unsaturated fat

cis doublebond causesbending


Fats•Constructed from glycerol (an alcohol) and fatty acids (long hydrocarbon chains with a carboxyl group)•Form by dehydration reactions•Can be saturated or unsaturated•Their function is energy storage (they store twice as much energy as starch)

Biodiesel


Phospholipids•Major component of cell membranes•Consist of a glycerol with two fatty acids and a phosphate group


Phospholipids•Major component of cell membranes•Consist of a glycerol with two fatty acids and a phosphate group•Polar nature of the molecule causes self-assembling of membranes


Steroids•Lipids with a carbon skeleton that contains four fused rings


Steroids•Lipids with a carbon skeleton that contains four fused rings•Includes hormones-Secreted chemicals that that travel through the body to act on a target


Steroids•Lipids with a carbon skeleton that contains four fused rings•Includes hormones-Secreted chemicals that that travel through the body to act on a target•Also includes cholesterol-common component of animal cell membranes and a precursor from which other steroids are synthesized


Proteins have many structures resulting in a wide range of functions

Proteins have many structures resulting in a wide range of functionsProtein structureProteins are made from

amino acid monomers• All amino acids have a

carboxyl group, an amino group, and an R group (variable)

Proteins have many structures resulting in a wide range of functionsProtein structure

Proteins are made from amino acid monomers

• All amino acids have a carboxyl group, an amino group, and an R group (variable)

• The R group determines the properties of the amino acid

Nonpolar

Glycine(Gly or G)

Alanine(Ala or A)

Valine(Val or V)

Leucine(Leu or L)

Isoleucine(Ile or I)

Methionine(Met or M)

Phenylalanine(Phe or F)

Trypotphan(Trp or W)

Proline(Pro or P)

Polar

Serine(Ser or S)

Threonine(Thr or T)

Cysteine(Cys or C)

Tyrosine(Tyr or Y)

Asparagine(Asn or N)

Glutamine(Gln or Q)

Electricallycharged

Acidic Basic

Aspartic acid(Asp or D)

Glutamic acid(Glu or E)

Lysine(Lys or K)

Arginine(Arg or R)

Histidine(His or H)

Proteins have many structures resulting in a wide range of functionsProtein structureProteins are made from amino

acid monomers• All amino acids have a

carboxyl group, an amino group, and an R group (variable)

• The R group determines the properties of the amino acid

• Polypeptide polymers form when the carboxyl end is adjacent to an amino end (dehydration reaction forms a peptide bond)

Peptidebond

Amino end(N-terminus)

Peptidebond

Side chains

Backbone

Carboxyl end(C-terminus)

(a)

(b)

Proteins have many structures resulting in a wide range of functionsProtein structure• The amino acid sequence represents the proteins

primary structure

Proteins have many structures resulting in a wide range of functionsProtein structure• The amino acid sequence represents the protein’s primary

structure• Secondary structure includes coils (alpha helices) and

pleats (beta pleated sheets). Both result from H-bonds between amino and carbonyl group of nearby amino acids.

pleated sheet

Examples ofamino acidsubunits

helix

Proteins have many structures resulting in a wide range of functionsProtein structure• Tertiary structure results

from interactions between R-groups. Interactions include: hydrophobic interactions (leading to hydrophobic cores), hydrogen and ionic bonds, disulfide bridges

Disulfide bridge

Ionic bond

Hydrogenbond

Proteins have many structures resulting in a wide range of functionsProtein structure• Quaternary structure results from aggregation of

multiple polypeptide subunits

Proteins have many structures resulting in a wide range of functionsProtein function•Proteins serve many important functions. Act as enzymes, cell signaling, movement, immune functions, etc.•Protein structure is often critical to their function (it often depends on the ability to recognize or bind other molecules)

Antibody protein Protein from flu virus

Proteins have many structures resulting in a wide range of functionsProtein function•Proteins serve many important functions. Act as enzymes, cell signaling, movement, immune functions, etc.•Protein structure is often critical to their function (it often depends on the ability to recognize or bind other molecules)•Environmental conditions can lead to protein denaturation (hence protein dysfunction)

Proteins have many structures resulting in a wide range of functionsProtein function•Proteins serve many important functions. Act as enzymes, cell signaling, movement, immune functions, etc.•Protein structure is often critical to their function (it often depends on the ability to recognize or bind other molecules)•Environmental conditions can lead to protein denaturation (hence protein dysfunction)

Proteins have many structures resulting in a wide range of functions

Nucleic acids store and transmit hereditary information


The role of nucleic acids• RNA and DNA are nucleic acids• DNA is the genetic material inherited from

parents• DNA contains the information that programs

all of life’s activities (RNA helps relay the information)

• DNA to RNA to proteins


The structure of nucleic acids• Nucleotide monomers link to

form polynucleotides (or nucleic acids)

5' end

5'C

3'C

5'C

3'C

3' end

Nitrogenousbase

3'C

5'C

Phosphategroup

Sugar


The structure of nucleic acids• Nucleotide monomers link to

form polynucleotides (or nucleic acids)

• Nucleotides contain three parts:– Nitrogenous base

• Purines (Adenine and Guanine)• Pyrimidines (Cytosine, Thymine,

Uracil)– 5-C sugar (Deoxyribose in DNA,

Ribose in RNA)– Phosphate group

5' end

5'C

3'C

5'C

3'C

3' end

Nitrogenousbase

3'C

5'C

Phosphategroup

Sugar


The structure of nucleic acids• Nucleotide monomers link to form

polynucleotides (or nucleic acids) • Nucleotides contain three parts:

– Nitrogenous base • Purines (Adenine and Guanine)• Pyrimidines (Cytosine, Thymine, Uracil)

– 5-C sugar (Deoxyribise in DNA, Ribose in RNA)

– Phosphate group

• Adjacent nucleotides are joined by a phosphodiester linkage (phosphate group that links the sugars of two nucleotides)

5' end

5'C

3'C

5'C

3'C

3' end

Nitrogenousbase

3'C

5'C

Phosphategroup

Sugar


The structure of nucleic acids• Nucleotide monomers link to form

polynucleotides (or nucleic acids) • Nucleotides contain three parts:

– Nitrogenous base • Purines (Adenine and Guanine)• Pyrimidines (Cytosine, Thymine, Uracil)

– 5-C sugar (Deoxyribise in DNA, Ribose in RNA)

– Phosphate group

• Adjacent nucleotides are joined by a phosphodiester linkage (phosphate group that links the sugars of two nucleotides)

5' end

5'C

3'C

5'C

3'C

3' end

Nitrogenousbase

3'C

5'C

Phosphategroup

Sugar

Notice the distinct 5’ and 3’ ends


The DNA double helix• Unlike RNA, DNA consists of

two polynucleotides that form a double helix

5' end

5' end

3' end

3' end




• The two polynucleotides run in opposite 5 → 3 directions (antiparallel)

5' end

5' end

3' end

3' end




• The two polynucelotides run in opposite 5 → 3 directions (antiparallel)

• The nitrogenous bases pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C)

5' end

5' end

3' end

3' end






• The strands are complimentary!

5' end

5' end

3' end

3' end






• The strands are complimentary!

5' end

5' end

3' end

3' end

How would an RNA molecule look different?


Key concepts

• Macromolecules are polymers built from monomers

• Carbohydrates serve as fuel and building material

• Lipids are a diverse group of hydrophobic molecules

• Proteins have many structures, resulting a wide range of functions

• Nucleic acids store and transmit hereditary information

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The structure and function of large biological molecules