Bài giảng The molecules of cells

g 
model 
Methane 
The 4 single bonds of carbon point to the corners of a tetrahedron. 
LE 3-1b 
Ethane 
Propane 
Carbon skeletons vary in length. 
LE 3-1c 
Butane 
Isobutane 
Skeletons may be unbranched or branched. 
LE 3-1d 
1- Butene 
2- Butene 
Skeletons may have double bonds, which can vary in location. 
LE 3-1e 
Skeletons may be arranged in rings. 
Cyclohexane 
Benzene 
Animation: Carbon Skeletons 
Animation: Isomers 
Animation: L-Dopa 
Hydrocarbons are composed of only hydrogen and carbon 
A series of covalently bonded carbons forms the carbon skeleton of the molecule 
Isomers are molecules with the same molecular formula but different structures and properties 
3.2 Functional groups help determine the properties of organic compounds 
Functional groups are groups of atoms attached to the carbon skeleton of molecules 
Usually participate in chemical reactions 
Give organic molecules their particular properties 
LE 3-2 
Estradiol 
Female lion 
Male lion 
Testosterone 
Five main functional groups are important in the chemistry of life: 
Hydroxyl group 
Carbonyl group 
Carboxyl group 
Amino group 
Phosphate group 
These groups are all polar and make compounds containing them hydrophilic (water-loving) 
3.3 Cells make a huge number of large molecules from a small set of small molecules 
Four main classes of biological macromolecules 
Carbohydrates 
Lipids 
Proteins 
Nucleic acids 
Cells make the most of their large molecules by joining smaller organic monomers into chains called polymers 
Monomers are usually linked by dehydration reactions 
A water molecule is removed 
Animation: Polymers 
LE 3-3a 
Short polymer 
Unlinked monomer 
Dehydration 
reaction 
Longer polymer 
Polymers are broken down to monomers by the reverse process, hydrolysis 
A water molecule is added 
LE 3-3b 
Hydrolysis 
CARBOHYDRATES 
3.4 Monosaccharides are the simplest carbohydrates 
Monosaccharides (single sugars) are carbohydrate monomers 
A monosaccharide has a formula that is a multiple of CH2O 
Contains hydroxyl groups and a carbonyl group 
May be isomers, such as glucose and fructose 
May take chain or ring forms 
LE 3-4b 
Glucose 
Fructose 
LE 3-4c 
Structural 
formula 
Abbreviated 
structure 
Simplified 
structure 
3.5 Cells link two single sugars to form disaccharides 
Two monosaccharides can join to form a disaccharide 
Linked by a dehydration reaction 
Example: two glucose monomers form the disaccharide maltose 
Animation: Disaccharides 
LE 3-5 
Glucose 
Glucose 
Maltose 
CONNECTION 
3.6 How sweet is sweet? 
We perceive a sweet taste when a chemical binds to the sweet receptor on the tongue 
The structure of a compound determines how well it fits into a receptor 
The more strongly the chemical binds to the receptor, the sweeter it is perceived to be 
The chemical can be sugar or another compound, such as aspartame 
3.7 Polysaccharides are long chains of sugar units 
Polysaccharides are polymers of monosaccharides linked together by dehydration reactions 
Some polysaccharides are storage molecules 
Starch in plants 
Glycogen in animals 
Some polysaccharides serve as structural compounds 
Cellulose in plants 
Animation: Polysaccharides 
LE 3-7 
Starch granules in 
potato tuber cells 
Glycogen 
granules in 
muscle 
tissues 
Cellulose fibrils in 
a plant cell wall 
Cellulose 
molecules 
G LYCOGEN 
C ELLULOSE 
S TARCH 
Glucose 
monomer 
LIPIDS 
3.8 Fats are lipids that are mostly energy-storage molecules 
Lipids are diverse compounds consisting mainly of carbon and hydrogen atoms 
Linked by nonpolar covalent bonds 
Hydrophobic (water-fearing) 
Animation: Fats 
Fats, also called triglycerides, are lipids whose main function is energy storage 
Polymers of fatty acids (usually three molecules) and one glycerol molecule 
Formed by dehydration reactions 
Saturated fatty acids 
Contain the maximum number of hydrogens 
Have no double bonds between carbons 
Unsaturated fatty acids 
Contain fewer than the maximum possible hydrogens 
Have double bonds between carbons 
Oils are liquid fats 
3.9 Phospholipids, waxes, and steroids are lipids with a variety of functions 
Phospholipids 
Contain two fatty acid groups and the element phosphorus 
Are a major component of cell membranes 
Waxes 
Consist of a single fatty acid linked to an alcohol 
Form waterproof coatings 
Steroids 
Have backbones bent into rings, as in cholesterol 
Are often hormones or the basis of hormones 
CONNECTION 
3.10 Anabolic steroids pose health risks 
Anabolic steroids are natural and synthetic variants of the male hormone testosterone 
Build up bone and muscle mass 
Can cause serious health problems 
PROTEINS 
3.11 Proteins are essential to the structures and activities of life 
A protein is a polymer constructed from amino acid monomers 
The structure of the protein determines its function 
The seven major classes of protein are 
Structural: hair, cell cytoskeleton 
Contractile: producers of movement in muscle and other cells 
Storage: sources of amino acids, such as egg white 
Defense: antibodies, membrane proteins 
Transport: carriers of molecules such as hemoglobin, membrane proteins 
Signaling: hormones, membrane proteins 
Enzymes: regulators of the speed biochemical reactions 
Animation: Structural Proteins 
Animation: Storage Proteins 
Animation: Transport Proteins 
Animation: Receptor Proteins 
Animation: Contractile Proteins 
Animation: Defensive Proteins 
Animation: Enzymes 
Animation: Hormonal Proteins 
Animation: Sensory Proteins 
Animation: Gene Regulatory Proteins 
3.12 Proteins are made from amino acids linked by peptide bonds 
Protein diversity is based on different arrangements of a common set of 20 amino acid monomers 
Each amino acid contains 
An amino group 
A carboxyl group 
One of twenty functional ("R") groups 
The three groups and a hydrogen atom are bonded to a central "alpha" carbon 
LE 3-12a 
Carboxyl (acid) 
group 
Amino 
group 
The structure of the R group determines the specific properties of each amino acid 
An amino acid may be hydrophobic or hydrophilic, depending on the characteristics of the R group 
LE 3-12b 
Leucine ( Leu ) 
Serine (Ser) 
Hydrophobic 
Hydrophilic 
Aspartic acid (Asp) 
Cells link amino acids together by dehydration synthesis 
The bonds between amino acid monomers are called peptide bonds 
Dipeptides are two amino acids long; polypeptides are from several to more than a thousand amino acids long 
LE 3-12c 
Amino acid 
Dipeptide 
Amino acid 
Peptide 
bond 
Dehydration 
reaction 
Amino 
group 
Carboxyl 
group 
3.13 A protein's specific shape determines its function 
A protein consists of one or more polypeptide chains spontaneously folded into a unique shape 
LE 3-13 
Groove 
Groove 
The folding of a polypeptide creates grooves that enable other molecules to bind to it 
In denaturation , chemical or physical changes can cause proteins to lose their shape and thus their specific function 
3.14 A protein's shape depends on four levels of structure 
Primary structure: the unique sequence of amino acids forming the polypeptide 
Secondary structure: the coiling or folding of the chain, stabilized by hydrogen bonding 
May be alpha helix or pleated sheet (which dominates the silk protein of a spider's web) 
Tertiary structure: the overall three-dimensional shape of the polypeptide 
Quaternary structure: the association of two or more polypeptide chains (subunits) 
LE 3-14a 
Levels of Protein Structure 
Amino acids 
LE 3-14b 
Levels of Protein Structure 
Amino acids 
Hydrogen 
bond 
Alpha helix 
Pleated sheet 
LE 3-14c 
Levels of Protein Structure 
Amino acids 
Hydrogen 
bond 
Alpha helix 
Pleated sheet 
Polypeptide 
(single subunit 
of transthyretin ) 
LE 3-14d 
Levels of Protein Structure 
Amino acids 
Hydrogen 
bond 
Alpha helix 
Pleated sheet 
Polypeptide 
(single subunit 
of transthyretin ) 
Transthyretin , with 
four identical 
polypeptide subunits 
Animation: Protein Structure Introduction 
Animation: Primary Protein Structure 
Animation: Secondary Protein Structure 
Animation: Tertiary Protein Structure 
Animation: Quarternary Protein Structure 
Collagen is an example of a protein with a quaternary structure 
Three subunits wound into a helix 
Structure provides great strength to long fibers 
TALKING ABOUT SCIENCE 
3.15 Linus Pauling contributed to our understanding of the chemistry of life 
Felt that the study of individual parts must come first, then putting the parts together 
Began his career by studying chemical bonding 
First described the alpha helix and pleated sheet protein structures 
Discovered how abnormal hemoglobin causes sickle cell disease 
Won two Nobel prizes, for chemistry and for peace (for helping produce a nuclear test ban treaty) 
NUCLEIC ACIDS 
3.16 Nucleic acids are information-rich polymers of nucleotides 
There are two types of nucleic acid-DNA and RNA 
Nucleic acids are polymers of nucleotide monomers composed of 
A five-carbon sugar 
A phosphate group 
A nitrogenous base-adenine (A), thymine (T), cytosine ( C), and guanine (G) in DNA; A, G, C, and uracil (U) in RNA 
LE 3-16a 
Nitrogenous 
base (A) 
Sugar 
Phosphate 
group 
Nucleotide monomers are formed into a polynucleotide with a sugar-phosphate backbone and attached nitrogenous bases 
LE 3-16b 
Nucleotide 
Sugar-phosphate 
backbone 
Hydrogen bonding between nitrogenous bases creates the final structure of the nucleic acid 
RNA usually consists of a single polynucleotide strand 
DNA is a double helix 
Two polynucleotides are twisted around each other 
Nitrogenous bases protruding from the backbone pair with each other, A with T and G with C 
LE 3-16c 
Base 
pair 
Specific sequences of DNA make up genes that program the amino acid sequences of proteins