CHAPTER 5

The Structure and Function of

Macromolecules

KEY CONCEPTS

Focus on how STRUCTURE and biochemical properties relate to FUNCTION

Focus on how building block MONOMERS are bonded together by specific LINKAGES

KEY CONCEPTS

Common SYNTHESIS and

BREAKDOWN reactions

Macromolecules are POLYMERS• MER - units TRI - three• POLY - many DI - two• OLIGO - several MONO - one

POLYMERSmonomer + monomer + monomer +

monomer = a big ‘ol polymer

Unity within diversity the same monomers are common to all

forms of life

How to make a Macromolecule

DEHYDRATION SYNTHESIS - bonding of small subunits to form a larger end product by removing water.

Figure 5.2 The synthesis and breakdown of polymers

How to breakdown a macromolecule…

HYDROLYSIS - digestion or degradation of large polymers by the addition of water

Main Classes Of Macromolecules

CARBOHYDRATES LIPIDS PROTEINS NUCLEIC ACIDS

Carbohydrates Sugars end in -ose aldehydes & ketones Isomer City General formula:

•C H2 O

CARBOHYDRATES MONOSACCHARIDES

examples:•glucose C6 hexose•ribose C5 pentose•glyceraldehyde C3 triose

Identify the carbons

Linear vs. ring structure ?????

DISACCHARIDES

DISACCHARIDES Monosaccharide monomers

Dehydration synthesis

Glycosidic linkages• 1-4 glycosidic linkage (maltose)• 1-2 glycosidic linkage (sucrose)

BIOFUNCTION: transport of fuel

CARBOHYDRATES

POLYSACCHARIDES (100’S --> 1000’S)

StorageSTARCH (plants)

1-4 linkage, unbranched helixGLYCOGEN (animals)

1-6 linkage, branching helix

Figure 5.6 Storage polysaccharides

Molecular Shape

CARBOHYDRATES MORE POLYSACCHARIDES

StructuralCELLULOSE - plant cell walls

– most abundant organic molecule – linear fibrils -> rope --> composite– alpha vs. beta glucose/digestion

CHITIN - exoskeletons & cell walls- tough, insoluble

Figure 5.9 Chitin, a structural polysaccharide: exoskeleton and surgical thread

Figure 5.8 The arrangement of cellulose in plant cell walls

CARBOHYDRATES

Summary of biofunctions

Immediate fuel

Storage & transport of fuel

Structural building material

LipidsA diverse group,

Insoluble in water,hydrophobic,

nonpolar, mostly hydrocarbon chains

technically not polymers??

LIPIDS Fats or Triglycerides

•glycerol + 3 fatty acids

•R -COOH hydrocarbon chain 14-18 carbons + carboxyl group

•ester linkage

LIPIDS

LIPIDSSATURATED

• fully saturated w/ hydrogens• animal fats - solid at room temp.

UNSATURATED • at least one double bond (kink)• plant oils -liquid at room temp.• geometric isomers (cis & trans)

Figure 5.11 Examples of saturated and unsaturated fats and fatty acids 

MORE LIPIDS PHOSPHOLIPIDS

• glycerol + 2 fatty acids + phosphate + charged group

• hydrophilic head• hydrophobic tail

BIOFUNCTION: membranes & micelles

MORE LIPIDS STEROIDS

•4 rings + fat tail •3 cyclohexanes + cyclopentane

+ hydrocarbon chain

MORE LIPIDS STEROIDS

•CHOLESTEROL is modified to form steroid hormones –sex hormones + corticoids

•CHOLESTEROL is also found in cell membranes

CHOLESTEROL

One of the most misunderstood chemicals in the human body

Cho gets a BAD reputation for Atherosclerosis Coronary Heart Disease Heart Attacks Strokes High Blood Pressure

but….

The Facts About Cholesterol

Precursor for steroid hormones Precursor for bile acids Necessary component of cell

membranes

Poor diet and hereditary factors predispose individuals to heart disease

Proteins “first place”

over 50% dry weight of most cells

structure fits function

Proteins Fiberous Enzymes Membrane

Channels Cell

Recognition Hormones

Transport Contraction Defense Osmotic

Homeostasis Gene

Regulators

Check out the animations online

Figure 5.1 Building models to study the structure and function of macromolecules

PROTEINS Building block monomers

are amino acids basic amino acid

structure 20 different R groups

Protein:

High-molecular weight, nitrogen-containing organic compound.

Composed of one or more polypeptides.

Polypeptides are composed of amino acids.

Amino Acid:

Contains the following bonded to a central carbon atom.

Amino groups (NH2)

Carboxyl group (COOH)

Hydrogen atom

R group (different in each amino acid)

Typically charged in the cell (-NH3

+ and COO-)

Fig. 6.1

Fig. 6.2. Acidic and basic amino acids.

Figure 5.15 The 20 amino acids of proteins: nonpolar

Fig. 6.2. Neutral, non-polar (hydrophobic) amino acids.

Fig. 6.2. Neutral, polar (hydrophilic) amino acids.

Amino acids are joined to form unbranched polypeptides by a peptide bond.

Peptide bond = covalent bond between the carboxyl group of one amino acid and amino group of the next amino acid.

N-terminus C-terminus

5’ (DNA) 3’ (DNA)

Fig. 6.3

Amino Acid SummarySide Groups Determine Chemical

Properties

Nonpolar C-H tend to hydrophobic aggregate toward center

Polar O-H, N-H are hydrophilic & tend to be found on the outside

Charged acidic (-COOH) fold to outsidebasic (-NH3) fold to outside

PROTEINS Peptide bond formation

Amino group + carboxylic acid via dehydration synthesis

Residues

N-terminus - polypeptide chain -C-terminus

PRIMARY STRUCTURE • sequence of

AA’s• genetically

determined• involves

peptide bonds

PRIMARY STRUCTURE

Figure 5.20 The secondary structure of a protein

TERTIARY STRUCTURE

• interactions between R groups

• hydrophobic interactions

• ionic bonds

• H-bonds

• disulfide bridges between cysteine

residues

Figure 5.22 Examples of interactions contributing to the tertiary structure of a protein

QUATERNARY STRUCTURE

• two or more polypeptide

chains needed to form one

functional protein

• Insulin - 2 AA chains

• Collagen - 3 AA chains

• Hemoglobin - 4 AA chains

Proteins show four hierarchical levels of structural organization:

1. Primary structure = amino acid sequence

Determined by the genetic code of the mRNA.

2. Secondary structure = folding and twisting of a single polypeptide chain.

Result of weak H-bonds and electrostatic interactions

e.g., -helix (coiled) and -pleated sheet (zig-zag).

• Tertiary structure = three dimensional shape (or conformation) of a polypeptide chain.

Function of R groups contained in the polypeptide.

1. Quaternary structure = association between polypeptides in multi-subunit proteins (e.g., hemoglobin).

Occurs only with two or more polypeptides.

Fig. 6.4

Figure 5.0 Spider’s web made of protein

Figure 5.23 The quaternary structure of proteins

Final Conformation

3-D shape determined by primary sequence ---> interactions -->spontaneous protein folding

Functional domains

Ultimately protein shape is determined by:

Changes in Protein Conformation DENATURE - change in shape

due to change in:

• temperature• pH• salt concentration

WEAK BONDS BROKEN

Changes in Protein Conformation

Nucleic Acids Information

molecules

DNA(ds) & RNA(ss)

Nucleotides monomers• Nitrogen base - 2 kinds

• Pentose sugar - 2 kinds

• Phosphate group bonded to 5’ C

Linkages •Phosphodiester bonds•H-bonds

Biofunction of Nucleic

Acids

Additional Nucleotides

ATP NAD FAD Look up their chemical

structures and explain why they belong in this category