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Chapter 3: The Molecules of Cells

Objectives:

Categorize organic compounds into the four major groups and list characteristics and functions of each group.

Define isomer and give examples.

Give examples of monosaccharides, disaccharides, and polysaccharides.

Relate the four levels of structure of proteins to the bonding patterns observed at each level.

Compare the structure of DNA to RNA.

I. Building Big Molecules

A .Organic molecules have backbones of covalently bonded ______________ atoms. (Note: not ALL carbon-containing molecule are organic, though; ex. Carbon dioxide.)

B. Organic molecules are the main structural and _______________ molecules of cells. They make up the bodies of all living organisms.

C. There are four main types of organic molecules – carbohydrates, lipids, ________________ , and nucleic acids.

D. Organic molecules show great diversity because carbon atoms form _____ covalent bonds with other atoms. Molecules vary in size, may be straight __________ , branching chains, or rings, and may have single, double, or triple bonds.

E. Compounds and parts of molecules that consist only of carbon and hydrogen are called _____________________ . They have nonpolar covalent bonds and are, thus, hydrophobic.

F. Many organic molecules contain functional groups. This is a chemical group with specific chemical properties.

G. Organic molecules are usually large macromolecules; inorganic molecules tend to be simpler. Organic molecules are often polymers (molecules consisting of repeating identical or similar subunits called ______________________) .

H. All macromolecules are assembled the same way. It is a type of anabolism (metabolism involving synthesis of larger molecules from smaller ones). Done by _____________________ synthesis in which a covalent bond is formed between two subunits by removal of H2O. This process requires energy.

I. The process of breaking down polymers into monomers is essentially the reverse of dehydration synthesis. A molecule of H2O is added to break the covalent bond between the monomers, a type of catabolism called ________________. This process yields energy

· A dehydration reaction is a chemical reaction in which subunits are joined together by the formation of a covalent bond and water is produced during the reaction.

· Used to connect monomers together to make polymers

· Example: formation of starch (polymer) from glucose subunits (monomer)

· A hydrolysis reaction is a chemical reaction in which a water molecule is added to break a covalent bond.

· Used to break down polymers into monomers

· Example: digestion of starch into glucose monomers

II. Proteins make up ~ _________% of the dry weight of cells. Serve diverse functions, such as structure (collagen, keratin), transport (hemoglobin), signals (hormones), movement (actin, myosin), defense (antibodies) and catalysts (enzymes)

A. ______________ acids are the monomers of proteins.

1. Basic structure of an amino acid: α carbon, amino group, carboxyl group, and an R (functional) group

2. There are 20 different amino acids that differ by R group (may be _________ , nonpolar, acidic, basic).

3. Amino acids are combined by dehydration synthesis into chains called polypeptides. The covalent bonds joining them are called ______________ bonds.

B. Protein structure is complex. The order of the amino acids that form the polypeptide affects how the protein folds together. The way that a polypeptide _________ to form the protein determines the protein’s function. Some proteins are comprised of more than one polypeptide.

C. There are ____________ general levels of protein structure: primary structure (1°), secondary structure (2°), tertiary structure (3°) and quaternary structure (4°).

1. Primary structure – the sequence of amino acids in the polypeptide chain. Dictated by a _____________ . This determines all other levels of protein structure.

2. Secondary structure – localized twisting/folding of polypeptide due to ________________ bonding, includes: α-helix and β-pleated sheet. The folded structure may resemble coils, helices, or sheets.

3. Tertiary structure – the final ________ shape of the protein ( functional protein) as a result of interaction among R groups (H bonds, ionic bonds, covalent bonds, hydrophilic/hydrophobic interactions). May be fibrous (collagen, keratin) or globular (like enzymes and hormones).

4. Quaternary structure (not always present) – the interaction of two or more polypeptide chains to form a functional protein. ex. Hemoglobin has ____________ subunits.

D. The function of a protein depends on its shape. Denaturation: Any change in the shape of a protein (tertiary/quaternary structure); alters _______________ . Causes of denaturation: __________, electric current, pH change, addition of salts, and some chemicals.

E. The shape of a protein affects its function. Proteins that serve architectural and structural roles are often long and cable-like. Proteins that act as enzymes are globular, having a special 3-D shape that fits precisely with another chemical; they cause the chemical that they fit with to undergo a reaction.

III. Nucleic Acids

A. Nucleic acids are macromolecules that control _________________ . They are comprised of monomers called nucleotides. Each nucleotide has 3 parts:

1. a five-carbon _____________ (ribose or deoxyribose)

2. a phosphate group

3. an organic nitrogen-containing _____________ (adenine, guanine, cytosine, thymine, uracil)

B. There are two types of nucleic acids: deoxyribonucleic acid (DNA) that _______________ information and ribonucleic acid (RNA) that allows DNA to express itself. RNA is similar to DNA except that it uses uracil instead of thymine, it is comprised of just ________ strand, and it has a ribose sugar instead of deoxyribose.

C. The structure of DNA is a double ________________.There are only two base pairs possible: 1) Adenine (A) pairs with thymine (T) and 2) Cytosine (C) pairs with Guanine (G). The bonds holding together a base pair are _______________ bonds. A sugar-phosphate backbone comprised of covalent phosphodiester bonds gives support. The structure of DNA helps it to function:

1. The _______________ bonds of the base pairs can be broken to unzip the DNA so that information can be copied.

2. Each strand of DNA is a mirror image so the DNA contains two copies of the information. Having two copies means that the information can be accurately copied and passed to the next generation.

D. ATP is a modified nucleotide.

IV. Carbohydrates are used for __________ or sometimes as structural molecules.

A. A carbohydrate is any molecule that contains the elements C, H, and O in a 1:2:1 ratio.

B. Include: ____________ carbohydrates – made up of one or two monomers and complex carbohydrates – long polymers.

1. Monosaccharides are simple sugars. They are composed of three to seven carbon atoms: ex. Trioses, pentoses, hexoses. They have many polar hydroxyl groups that are ____________________ (water-loving). They may exist as straight chains or closed rings. Glucose (C6H12O6)is the most common one. Functions: 1) _________ source (produced by photosynthesis, used in respiration)and 2) used as a monomer to build larger carbohydrates.

2. Disaccharides ( ________________ sugars) consist of two monosaccharides bonded together by dehydration synthesis (anabolism) and broken down by hydrolysis (catabolism). Examples:

glucose + fructose = ______________ (table sugar)

Glucose + glucose = maltose (malt sugar)

Glucose + galactose = lactose (milk sugar)

3. Complex carbohydrates are long polymer chains called polysaccharides. These polymers consist of monosaccharides bonded together by dehydration synthesis and broken down by hydrolysis. May be straight or branching __________ . Two functions in cells (energy storage and structural). Plants and animals store energy in polysaccharide chains formed from glucose. Plants form _________________ , and animals store glycogen. Some polysaccharides serve structural functions and are resistant to digestion by enzymes: 1.) ______________ is found in the cell walls of plants, 2) chitin is found in the exoskeletons of many invertebrates and in the cell walls of fungi, and 3) Peptidoglycan is in the bacterial cell wall.

V. Lipids are both structurally and functionally a diverse group of macromolecules with one thing in common: they are ________________ , not soluble in water

Lipids include triglycerides (fats), oils, phospholipids, steroids, rubber, waxes, and some pigments. Types of lipids:

A. Fats (triglycerides) are used for long-term ________________ storage. They have two subunits. 1) 3 fatty acids (chains of C and H atoms) and 2) Glycerol (a three C alcohol that serves as a backbone of the molecule). They are formed by dehydration synthesis and broken down by hydrolysis.

1. Fatty acids have different chemical properties due to the number of hydrogens that are attached to chain of carbons. If the maximum number of hydrogens are attached, then the fat is called ___________________ , and if there are fewer than the maximum attached, then the fat is called ________________.

2. Functions of triglycerides (fats): 1) energy storage in animals (>2.5X the energy of the same volume of carbohydrates), 2) padding, 3) ________________ , and floatation (sharks, diatoms)

3. Trans-Fats and Cardiovascular Health

a. Trans-fats (a type of fat, or lipid)

b. Are made by adding hydrogen to unsaturated fats, a process called hydrogenation.

c. Are used to increase food shelf life and flavor/texture.

d. May cause worse health effects than saturated fat in an individual’s diet.

e. FDA now requires trans-fat labeling on foods and in restaurants.

B. Biological ____________ involve lipids. Phospholipids make up the two layers of the _________________________. Cholesterol (a steroid) is embedded within the membrane. Cholesterol is the precursor molecule for several other steroids. Cholesterol (LDL, VLDL) can also contribute to circulatory disorders.

C. Steroids are composed of _____ fused rings with various functional groups attached to the carbon skeleton. Functions: component of animal cell membrane, regulation. Examples: cholesterol, testosterone, estrogen. Testosterone and estrogen are sex hormones differing only in the functional groups attached to the carbon skeleton. Cholesterol is the precursor for several other steroids. Cholesterol (LDL and VLDL) can contribute to circulatory disorders.

D. _________________ consist of long-chain fatty acids connected to carbon chains containing alcohol functional groups. They are solid at room temperature, waterproof, resistant to degradation. Function: protection. Examples: earwax (contains cerumen), plant cuticle, beeswax.

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