If cells are grown in a medium containing radioactive 15N, which of these molecules will be labelled?
both proteins and nucleic acids
10
The basis for diversity, both within a species and among species, is a result of the
arrangement of a few base molecules into many different macromolecular combinations.
11
The following questions are based on the 15 molecules illustrated in the figure below. Each molecule may be used once, more than once, or not at all.
Which of the following molecules consists of a hydrophilic "head" region and a hydrophobic "tail" region?
5
12
Which of the following molecules could be joined together by a phosphodiester type of covalent bond?
11 and 12
13
Which of the following molecules could be joined together by a peptide bond as a result of a dehydration reaction?
7 and 8
14
Which of the following molecules act as building blocks (monomers) of polypeptides?
2,7, and 8
15
Which of the following statements is/are true regarding the chemical reaction illustrated in the figure above?
It results in a peptide bond.
16
Which of the following is an example of hydrolysis?
the reaction of a fat, forming glycerol and fatty acids with the consumption of water
17
Which level of protein structure do the α helix and the β pleated sheet represent?
secondary
18
If cells are grown in a medium containing radioactive 35S, which of these molecules will be labelled?
proteins
19
If a DNA sample were composed of 10% thymine, what would be the percentage of guanine?
40
20
Which of the following are nitrogenous bases of the pyrimidine type?
cytosine and uracil
21
Which bonds are created during the formation of the primary structure of a protein?
peptide bonds
22
At which level of protein structure are interactions between the side chains (R groups) most important?
tertiary
23
Which of the following are nitrogenous bases of the purine type?
guanine and adenine
24
The tertiary structure of a protein is the
unique three-dimensional shape of the fully folded polypeptide.
25
Which of the following is true of cellulose?
It is a major structural component of plant cell walls.
26
Which of these classes of biological molecules consist of both small molecules and macromolecular polymers?
carbohydrates
27
The amino acids of the protein keratin are arranged predominantly in an α helix. This secondary structure is stabilized by
hydrogen bonds.
28
Normal hemoglobin is a tetramer, consisting of two molecules of β hemoglobin and two molecules of α hemoglobin. In sickle-cell disease, as a result of a single amino acid change, the mutant hemoglobin tetramers associate with each other and assemble into large fibres. Based on this information alone, we can conclude that sickle-cell hemoglobin exhibits
altered primary structure and altered quaternary structure; the secondary and tertiary structures may or may not be altered.
29
The enzyme amylase can break glycosidic linkages between glucose monomers only if the monomers are the α form. Which of the following could amylase break down?
The main biological macromolecules found in living cells include nucleic acids, carbohydrates, lipids, and proteins. These molecules form the foundations of all living organisms and make up all the components of the cells.
Examples of nucleic acids include DNA, RNA, and ATP. These molecules all consist of nucleotides that are bonded together. Each nucleotide consists of a sugar molecule, a nitrogen base, and at least one phosphate group.
There are three types of RNA that are found which are all important in the process of protein synthesis in which the DNA code is expressed as protein.
Carbohydrates are a good quick source of energy that can be catabolized in cell respiration. Many carbs also form cell structural components such as cell walls. The lipids include the fats which have many functions from energy storage, to signal molecules, to forming much of the cell membrane.
Proteins also have a range of functions including as cell membrane channels, receptors for ligands and as enzymes that catalyze reactions.
Nucleic acids
The basic unit of a nucleic acid is a nucleotide which consists of a phosphate, a sugar molecule, and a nitrogen base. The nucleic acids include DNA, RNA, and ATP. DNA is deoxyribonucleic acid which is the molecule that contains our genetic code in the form of nitrogen bases.
The bases can be one of four types, namely, adenine, thymine, cytosine or guanine. DNA also contains the sugar deoxyribose which attaches to the nitrogen base.
The DNA usually occurs as a double helix that consists of two strands of polynucleotides that have bonded together at the corresponding bases.
RNA
The ribonucleic acid is RNA, which has a nucleotide that is very similar to that of DNA, but it has ribose sugar present instead of deoxyribose. Another difference is that RNA has the base uracil instead of thymine, and the molecule is never double-stranded or in the form of a helix.
There are actually three types of RNA, messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA). The rRNA is formed in the nucleus and it makes up the ribosomes found in the cytoplasm of the cell.
The mRNA is the type of molecule that is formed during the transcription of the DNA molecule in protein synthesis. The tRNA is involved in the translation stage of the same process and is involved in carrying and arranging the amino acids in the correct sequence.
ATP
Adenosine triphosphate (ATP) is the main energy molecule of living cells. ATP is comprised of an adenine ring, a ribose sugar, and three phosphate groups. The phosphoanyhdride bonds linking the phosphate groups together are the source of energy when the molecule is oxidized.
The ATP can release energy when these bonds are broken. When one bond is broken, energy is released and the ATP is converted into adenosine diphosphate (ADP) which consists of only two phosphate groups.
The ADP can be further oxidized to adenosine monophosphate (AMP) which has only one phosphate group present. ATP is constantly being regenerated in the cell because it is continuously needed for reactions to occur.
ATP is mostly generated during aerobic cellular respiration which occurs in the mitochondrion of eukaryotic cells.
This energy molecule is used to power protein pumps in active transport and is usually also involved in cell signaling processes such as signal transduction pathways.
Carbohydrates
These molecules include the sugars and complex polysaccharides such as cellulose, chitin, glycogen, and starch. All the molecules contain atoms of carbon, hydrogen, and oxygen.
There are many types of carbohydrates that are found, including simple sugars such as glucose and fructose, which often bond together to form larger more complex molecules.
Cellulose and chitin are both important structural molecules that make up the cell walls of the plant and fungal cells, respectively. Starch and glycogen are ways that animal and plant cells are able to store sugars for later use.
Lipids
The basic unit of lipids is fatty acids bonded to a glycerol molecule. Many fats consist of long chains of hydrogen and carbon atoms that are bonded to a carboxyl group.
The bonds between carbons and atoms may be single or double, and because the chains are so long, it means that a great deal of energy is stored in lipids. In fact, lipids store more energy than any other biological macromolecule because of all the bonds.
Phospholipids making up the plasma membrane of living cells are mainly composed of fatty acid tails, which are hydrophobic (repel water).
This hydrophobic component of the membrane is important since this ensures that substances do not easily move into and out of the cell. Another lipid, cholesterol, is important in the cell membrane where it provides fluidity to the membrane of animal cells.
Plant waxes such as the cuticle layer are important in preventing water loss from the plant body.
Proteins
Proteins consist of several amino acids that are linked together to form a polypeptide chain. This is then further folded and more bonding occurs to make a complex three-dimensional structure.
An amino acid has an amino group present along with a side chain (R group) that is attached to a central alpha carbon atom. The R group differs among the different amino acids and is responsible for the properties of the acids.
Proteins act as receptor molecules on cell membranes for signaling pathways and they form channels through the plasma membrane. These channels allow substances to pass through the cell membrane.
Other proteins are enzymes which can speed up biological reactions by lowering the activation energy.