Chapter 3 Questions: MasteringBiology

carboxylic acid [carboxyl group]

-C(2x)O-OH; acts as an acid

aldehyde [carbonyl group]

-C(2x)O; may be a structural isomer of a ketone

amine (amino group)

-NH2; acts as a base

The molecule shown here contains four functional groups.

-OH, _SH, -NH2, -OPO2-;3

alcohol

-OH; is highly polar and may act as a weak acid

organic phosphate (phosphate group)

-OP(2x)O-32-; contributes negative charge

thiol [sulfhydryl group]

-SH; forms disulfide bonds

How many hydrogen atoms can be attached to carbon B?

1 (already as 1C and 2C)

How many amino acids differ between the gibbon and the human sequences?`

2

How many hydrogen atoms can be attached to carbon A?

3 (already has 1 C)

Write the complementary sequence for the following DNA sequence, in order from 3' to 5': 5′−CGATATTGAGCTAAGCTT−3′

3′− GCTATAACTCGATTCGAA −5′

Which molecules show an appropriate number of bonds around each carbon atom?

4 bonds per carbon

DNA and polypeptide sequences from closely related species are more similar to each other than sequences from more distantly related species. In this exercise, you will look at amino acid sequence data for the β polypeptide chain of hemoglobin, often called β-globin. You will then interpret the data to hypothesize whether the monkey or the gibbon is more closely related to humans. In the alignment shown here, the letters give the sequences of the 146 amino acids in β-globin from humans, rhesus monkeys, and gibbons. Because a complete sequence would not fit on one line, the sequences are broken into segments. The sequences for the three different species are aligned so that you can compare them easily. For example, you can see that, for all three species, the first amino acid is "V" (valine) and the 146th amino acid is "H" (histidine). Click on the alignment to view it at a larger size. Scan along the aligned sequences, letter by letter, noting any positions where the amino acids in the monkey or gibbon sequences do not match the human sequence. How many amino acids differ between the monkey and the human sequences?

8

What percent of monkey β-globin amino acids are identical to the human sequence? (This is called the percent identity between the monkey and human β-globin sequences.)

94.5%

What percent of gibbon β-globin amino acids are identical to the human sequence? (This is called the percent identity between the gibbon and human β-globin sequences.)

98.6%

Select the statement that is incorrect. Complex sugars are carbohydrates. All carbohydrates have the general formula Cn(H2O)n. Simple sugars are carbohydrates. Simple sugars contain only carbon, oxygen, and hydrogen atoms.

All carbohydrates have the general formula Cn(H2O)n.

Based on the β-globin alignment, identify the best hypothesis about how humans are related to monkeys and gibbons.

Gibbons are more closely related to humans than monkeys are because the gibbon β-globin sequence is a closer match with the human sequence.

Complete the following sentences about carbohydrates.

Lactose, the sugar in milk, is a disaccharide, because it can be split into two monosaccharides. A simple sugar is composed of equal parts carbon and water, which gave rise to the general name of any sugar as a carbohydrate . A carbohydrate that yields many monosaccharides when hydrolyzed is a polysaccharide . A monosaccharide cannot be hydrolyzed any further.

How do these hydrocarbons differ?

One of these hydrocarbons has a double bond.

How do these hydrocarbons differ?

One of these hydrocarbons has a ring structure.

How do these hydrocarbons differ?

One of these hydrocarbons is branched.

How do these hydrocarbons differ?

One of these hydrocarbons is longer than the other.

Complete the following vocabulary exercise relating to the level of structure in proteins.

Primary structure is the sequence of amino acids in a protein. Secondary structure describes the alpha-helices and beta-sheets that are formed by hydrogen bonding between backbone atoms located near each other in the polypeptide chain. Tertiary structure is achieved when a protein folds into a compact, three-dimensional shape stabilized by interactions between side-chain R groups of amino acids. Quaternary structure is the result of two or more protein subunits assembling to form a larger, biologically active protein complex.

Rank the following base pairs according to their stability.

The base pair adenine-cytosine occurs very rarely in nature. It only happens during a mutation event. When the DNA is replicated, one of the two daughters will contain a guanine-cytosine base pair in the location of the mutation, and the other daughter will contain an adenine-thymine base pair.

Amino acids are the building blocks of proteins. There are 20 amino acids that most commonly occur in proteins. Based on the functional group making up their side chain, or R group, amino acids are classified as acidic, basic, or neutral. The physical and chemical properties of the R group determine the unique characteristics of each amino acid. Acidic amino acids have acidic R groups. Their electrically charged R groups make these molecules highly soluble in water. Basic amino acids have basic R groups. Their electrically charged R groups make these molecules highly soluble in water. Neutral (neither acidic nor basic) amino acids can be further classified as nonpolar or polar. The neutral nonpolar amino acids have R groups that contain no charged atoms; most of these amino acids are not water soluble. The neutral polar amino acids have R groups that have a dipole moment. The partial charges in their R groups make these molecules generally water soluble.

acidic - NONE basic - arginine neutral polar - glutamine, asparagine neutral nonpolar - alanine

Classify these amino acids as acidic, basic, neutral polar, or neutral nonpolar.

acidic: NONE basic: lysine neutral polar: serine neutral nonpolar: phenylalanine, proline, methionine

Classify these amino acids as acidic, basic, neutral polar, or neutral nonpolar.

acidic: glutamic acid basic: NONE neutral polar: threonine, tyrosine neutral nonpolar: valine, tryptophan

Both DNA and RNA

adenine, guanine, cytosine, phosphate

The large diversity of shapes of biological molecules is possible because of the extensive presence of _____ in the molecules.

carbon

Identify three possible components of a DNA nucleotide.

deoxyribose, phosphate group, thymine

Exclusively DNA

deoxyribose, thymine

Exclusively RNA

ribose, uracil

What other evidence could you use to analyze evolutionary relatedness among gibbons, monkeys, and humans?

the amino acid sequences of other proteins from gibbons, monkeys, and humans