Biochemistry

Question 1

Most of the world’s population cannot digest milk-based foods.

Answer 1

These people are lactose intolerant, because they lack the enzyme lactase.
This illustrates the importance of biological molecules, such as lactase, in the daily functions of living organisms.

Question 2

Diverse molecules found in cells

Answer 2

are composed of carbon bonded to
other carbons and
atoms of other elements.

Question 3

Carbon-based molecules

Answer 3

are called organic compounds.

Question 4

By sharing electrons

Answer 4

carbon can
bond to four other atoms and
branch in up to four directions.

Question 5

Methane (CH4)

Answer 5

is one of the simplest organic compounds.
Four covalent bonds link four hydrogen atoms to the carbon atom.
Each of the four lines in the formula for methane represents a pair of shared electrons.

Question 6

hydrocarbons

Answer 6

Methane and other compounds composed of only carbon and hydrogen are called hydrocarbons.

Question 7

A carbon skeleton

Answer 7

is a chain of carbon atoms that can be
branched or
unbranched.

Question 8

isomers

Answer 8

Compounds with the same formula but different structural arrangements are call isomers.

Question 9

An organic compound has unique properties

Answer 9

that depend upon the
size and shape of the molecule and
groups of atoms (functional groups) attached to it.

Question 10

A functional group

Answer 10

affects a biological molecule’s function in a characteristic way.

Question 11

hydrophilic

Answer 11

Compounds containing functional groups are hydrophilic (water-loving).

Question 12

The functional groups are

Answer 12

hydroxyl group
carbonyl group
carboxyl group
amino group
phosphate group

Question 13

hydroxyl group

Answer 13

consists of a hydrogen bonded to an oxygen,

Question 14

carbonyl group

Answer 14

a carbon linked by a double bond to an oxygen atom

Question 15

carboxyl group

Answer 15

consists of a carbon double-bonded to both an oxygen and a hydroxyl group

Question 16

amino group

Answer 16

composed of a nitrogen bonded to two hydrogen atoms and the carbon skeleton

Question 17

phosphate group

Answer 17

consists of a phosphorus atom bonded to four oxygen atoms

Question 18

There are four classes of molecules important to organisms:

Answer 18

carbohydrates,
proteins,
lipids, and
nucleic acids.

Question 19

macromolecules

Answer 19

The four classes of biological molecules contain very large molecules.
They are often called macromolecules because of their large size.

Question 20

The four classes of biological molecules

Answer 20

They are also called polymers because they are made from identical building blocks strung together.

Question 21

Monomers

Answer 21

The building blocks of polymers are called monomers.

Question 22

dehydration reactions

Answer 22

Monomers are linked together to form polymers through dehydration reactions, which remove water.

Question 23

hydrolysis

Answer 23

Polymers are broken apart by hydrolysis, the addition of water.

Question 24

enzymes

Answer 24

All biological reactions of this sort are mediated by enzymes, which speed up chemical reactions in cells.

Question 25

A cell makes a large number of polymers from a small group of monomers

Answer 25

For example, proteins are made from only 20 different amino acids and DNA is built from just four kinds of nucleotides. The monomers used to make polymers are universal.

Question 26

Carbohydrates

Answer 26

range from small sugar molecules (monomers) to large polysaccharides.

Question 27

monosaccharides

Answer 27

Sugar monomers are monosaccharides, such as those found in honey, glucose, and fructose. Monosaccharides can be hooked together to form more complex sugars and polysaccharides. The carbon skeletons of monosaccharides vary in length. Glucose and fructose are six carbons long. Others have three to seven carbon atoms. Monosaccharides are the main fuels for cellular work and used as raw materials to manufacture other organic molecules. Many monosaccharides form rings.

Question 28

disaccharide

Answer 28

Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction. The disaccharide sucrose is formed by combining a glucose monomer and a fructose monomer. The disaccharide maltose is formed from two glucose monomers.

Question 29

Polysaccharides

Answer 29

are macromolecules and polymers composed of thousands of monosaccharides. Polysaccharides may function as storage molecules or structural compounds. Polysaccharides are usually hydrophilic (water-loving).

Question 30

Starch

Answer 30

is a polysaccharide composed of glucose monomers and used by plants for energy storage

Question 31

glycogen

Answer 31

is a polysaccharide composed of glucose monomers used by animal cells for energy storage

Question 32

Cellulose

Answer 32

is a polymer of glucose and | forms plant cell walls.

Question 33

Chitin

Answer 33

is a polysaccharide and used by insects and crustaceans to build an exoskeleton.

Question 34

Proteins are

Answer 34

involved in nearly every dynamic function in your body and very diverse, with tens of thousands of different proteins, each with a specific structure and function, in the human body. Proteins are composed of differing arrangements of a common set of just 20 amino acids.

Question 35

Amino acid

Answer 35

have an amino group and a carboxyl group (which makes it an acid). Also bonded to the central carbon is a hydrogen atom and a chemical group symbolized by R, which determines the specific properties of each of the 20 amino acids used to make proteins.

Question 36

peptide bond

Answer 36

Amino acid monomers are linked together in a dehydration reaction, joining carboxyl group of one amino acid to the amino group of the next amino acid, creating a peptide bond. Additional amino acids can be added by the same process to create a chain of amino acids called a polypeptide.

Question 37

enzymes

Answer 37

Probably the most important role for proteins is as enzymes, proteins that serve as metabolic catalysts and regulate the chemical reactions within cells.

Question 38

Structural proteins

Answer 38

provide associations between body parts.

Question 39

Contractile

Answer 39

proteins are found within muscle.

Question 40

Defensive

Answer 40

proteins include antibodies of the immune system.

Question 41

Signal

Answer 41

proteins are best exemplified by hormones and other chemical messengers.

Question 42

Receptor

Answer 42

proteins transmit signals into cells.

Question 43

Transport

Answer 43

proteins carry oxygen.

Question 44

Storage

Answer 44

proteins serve as a source of amino acids for developing embryos.

Question 45

A polypeptide

Answer 45

A polypeptide contains hundreds or thousands of amino acids linked by peptide bonds. The amino acid sequence causes the polypeptide to assume a particular shape. The shape of a protein determines its specific function. If a protein’s shape is altered, it can no longer function.

Question 46

denaturation

Answer 46

In the process of denaturation, a polypeptide chain unravels, loses its shape, and loses its function. Proteins can be denatured by changes in salt concentration, pH, or by high heat.

Question 47

A protein can have four levels of structure

Answer 47

primary structure secondary structure tertiary structure quaternary structure

Question 48

The primary structure of a protein

Answer 48

The primary structure of a protein is its unique amino acid sequence. The correct amino acid sequence is determined by the cell’s genetic information. The slightest change in this sequence may affect the protein’s ability to function.

Question 49

Protein secondary structure

Answer 49

results from coiling or folding of the polypeptide. Coiling results in a helical structure called an alpha helix. A certain kind of folding leads to a structure called a pleated sheet, which dominates some fibrous proteins such as those used in spider webs. Coiling and folding are maintained by regularly spaced hydrogen bonds between hydrogen atoms and oxygen atoms along the backbone of the polypeptide chain

Question 50

tertiary structure

Answer 50

hydrogen atoms and oxygen atoms along the backbone of the polypeptide chain. The overall three-dimensional shape of a polypeptide is called its tertiary structure. Tertiary structure generally results from interactions between the R groups of the various amino acids. Disulfide bridges may further strengthen the protein’s shape.

Question 51

quaternary structure

Answer 51

Two or more polypeptide chains (subunits) associate providing quaternary structure. Collagen is an example of a protein with quaternary structure. Collagen’s triple helix gives great strength to connective tissue, bone, tendons, and ligaments.

Question 52

gene

Answer 52

The amino acid sequence of a polypeptide is programmed by a discrete unit of inheritance known as a gene.

Question 53

DNA

Answer 53

Genes consist of DNA(deoxyribonucleic acid), a type of nucleic acid. DNA is inherited from an organism’s parents. DNA provides directions for its own replication. DNA programs a cell’s activities by directing the synthesis of proteins. DNA does not build proteins directly. DNA works through an intermediary, ribonucleic acid (RNA). DNA is transcribed into RNA. RNA is translated into proteins.

Question 54

nucleotides

Answer 54

``` DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides. Nucleotides have three parts: a five-carbon sugar called ribose in RNA and deoxyribose in DNA, a phosphate group, and a nitrogenous base. DNA nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G). RNA also has A, C, and G, but instead of T, it has uracil (U). ```

Question 55

polynucleotide

Answer 55

A nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers, when the phosphate of one nucleotide bonds to the sugar of the next nucleotide, by dehydration reactions, and by producing a repeating sugar-phosphate backbone with protruding nitrogenous bases.

Question 56

double helix

Answer 56

Two polynucleotide strands wrap around each other to form a DNA double helix. The two strands are associated because particular bases always hydrogen bond to one another. A pairs with T, and C pairs with G, producing base pairs. RNA is usually a single polynucleotide strand.

Question 57

Lipids

Answer 57

are water insoluble (hydrophobic, or water-fearing) compounds, are important in long-term energy storage, contain twice as much energy as a polysaccharide, and consist mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds. Lipids differ from carbohydrates, proteins, and nucleic acids in that they are not huge molecules and not built from monomers. Lipids vary a great deal in structure and function.

Question 58

three types of lipids

Answer 58

simple lipids (fats and oils), phospholipids, and steroids.

Question 59

A simple lipid

Answer 59

A simple lipid (fat or oil) is a large lipid made from two kinds of smaller molecules, glycerol and fatty acids. A fatty acid can link to glycerol by a dehydration reaction. A fat contains one glycerol linked to three fatty acids. Fats are often called triglycerides because of their structure.

Question 60

unsaturated fatty acids

Answer 60

Some fatty acids contain one or more double bonds, forming unsaturated fatty acids that have one fewer hydrogen atom on each carbon of the double bond, cause kinks or bends in the carbon chain, and prevent them from packing together tightly and solidifying at room temperature.

Question 61

saturated fatty acids

Answer 61

Fats with the maximum number of hydrogens are called saturated fatty acids. Unsaturated fats include corn and olive oils. Most animal fats are saturated fats.

Question 62

trans fats

Answer 62

Hydrogenated vegetable oils are unsaturated fats that have been converted to saturated fats by adding hydrogen. This hydrogenation creates trans fats associated with health risks.

Question 63

Phospholipids

Answer 63

Phospholipids are structurally similar to fats and the major component of all cells. Phospholipids are structurally similar to fats. Fats contain three fatty acids attached to glycerol. Phospholipids contain two fatty acids attached to glycerol. Phospholipids cluster into a bilayer of phospholipids. The hydrophilic heads are in contact with the water of the environment and the internal part of the cell. The hydrophobic tails band in the center of the bilayer.

Question 64

Steroids

Answer 64

are lipids in which the carbon skeleton contains four fused rings.

Question 65

Cholesterol

Answer 65

is a common component in animal cell membranes and starting material for making steroids, including sex hormones.

Question 66

Anabolic steroids

Answer 66

are synthetic variants of testosterone, can cause a buildup of muscle and bone mass, and are often prescribed to treat general anemia and some diseases that destroy body muscle. Anabolic steroids are abused by some athletes with serious consequences, including violent mood swings, depression, liver damage, cancer, high cholesterol, and high blood pressure.